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G EOTECH N ICAL DESIGN REPORT
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DONNER CREEK (MOUSEHOLE)_PEDESTRIAN UNDERPASS AND
---------------
MULTI-USE PATHWAY ON STATE HIGHWAY 89, PLACER AND
NEVADA COUNTIES IN AND NEAR TRUCKEE, CALIFORNIA
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Prepared for: Prepared by:
lih �C�'►' ?l =111 SHANNON 6WILSON, INC.
GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS
�1 GEOTECHNICAL AND EN IAL CONSULTANTS
SHANNON 6WILSON, ING
GEOTECHNICAL DESIGN REPORT
DONNER CREEK(MOUSEHOLE) PEDESTRIAN UNDERPASS AND
MULTI-USE PATHWAY ON STATE HIGHWAY 89,
IN PLACER AND NEVADA COUNTIES IN AND NEAR TRUCKEE
FROM 0.8 MILE SOUTH TO 0.1 MILE SOUTH OF ROUTE 80/89 SEPARATION
Caltrans District 3, Placer and Nevada Counties, State Highway 89,
Mile Posts 0.0/0.4 and 21.4/21.7
Caltrans Project Identification No. 03 0000 0231
Bridge No. 17-0106
Contract No. 03-1C0804
Prepared for:
HDR Engineering, Inc.
2121 North California Boulevard, Suite 475
Walnut Creek, CA 94596-7334
S&W Project No. 21-1-21072-002
February 1, 2013
1722 THIRD STREET, SUITE 100
SACRAMENTO,CALIFORNIA 95811-6208
916-438-2300 FAX: 916-438-2395
TDD 1-800-833-6388
www.shannonwilson.com
SHANNON 6WILSON, INC. CALIFORNIAALASKA
GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS COLORADO
FLORIDA
MINNESOTA
MISSOURI
OREGON
WASHINGTON
February 1, 2013
Mr. Patrick Casey
HDR Engineering, Inc.
2121 North California Boulevard, Suite 475
Walnut Creek, CA 94596-7334
RE: GEOTECHNICAL DESIGN REPORT,DONNER CREEK(MOUSEHOLE)
PEDESTRIAN UNDERPASS AND MULTI-USE PATH ON STATE HIGHWAY
89,IN PLACER AND NEVADA COUNTIES IN AND NEAR TRUCKEE FROM
0.8 MILE SOUTH TO 0.1 MILE SOUTH OF ROUTE 80/89 SEPARATION
Dear Mr. Casey:
As authorized, we have completed our geotechnical investigation for the proposed Mousehole
pedestrian undercrossing and multi-use pathway to be constructed on the east side of State
Highway 89, between West River Street and Deerfield Drive in Truckee, California. Our work
has been completed in general accordance with the general accordance with the HDR
Engineering, Inc. Subcontract Agreement, dated April 8, 2011, and the Subcontract Amendment,
dated August 22, 2011.
This report defines the geotechnical conditions as evaluated from field and laboratory test data
and used in the development of geotechnical design. It provides recommendations and
specifications for project design and construction.
1722 THIRD STREET, SUITE 100
SACRAMENTO,CALIFORNIA 95811-6208
916-438-2300 FAX: 916-438-2395
TDD 1-800-833-6388
www.shannonwilson.com 21-1-21072-002
Mr. Patrick Casey 6WILSON,INC.
HDR Engineering, Inc.
February 1, 2013
Page 2 of 2
We appreciate the opportunity to provide you with our geotechnical consulting services for this
project. If you have any questions regarding this report, please contact me at (916) 438-2304.
Sincerely,
SHANNON & WILSON, INC.
0 F S
ichael M. Watari o
u No. 2675 z
c(- Exp. 12/31/2013
il GEOTECHNICAL
QF` CAL I�' l I�191 t3
Michael M. Watari, P.E., G.E.
Senior Principal Geotechnical Engineer
N42
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Ro ert A. (Red) Robinson
Senior Vice President
MMW:RAR/mmw
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SHANNON 6WILSON,INC.
TABLE OF CONTENTS
Page
1.0 INTRODUCTION..................................................................................................................1
2.0 PROPOSED IMPROVEMENTS...........................................................................................1
3.0 EXISTING SITE CONDITIONS...........................................................................................2
4.0 FILES REVIEWED ...............................................................................................................3
5.0 PHYSICAL SETTING...........................................................................................................4
5.1 Climate.......................................................................................................................4
5.2 Topography and Drainage..........................................................................................4
5.3 Man-made Features of Engineering and Construction Significance..........................5
5.4 Regional Geology.......................................................................................................5
5.5 Seismic Setting--------------------------------------------------------------- .....6
6.0 FIELD EXPLORATION........................................................................................................8
6.1 Field Explorations and Sampling...............................................................................8
6.1.1 General.........................................................................................................8
6.1.2 Soil Borings .................................................................................................9
6.1.3 Test Pits........................................................................................................9
6.1.4 Utility Potholing.........................................................................................10
6.2 Geophysical Study....................................................................................................1 l
7.0 GEOTECHNICAL TESTING .............................................................................................11
7.1 In Situ Testing..........................................................................................................11
7.2 Laboratory Testing...................................................................................................12
7.2.1 General.......................................................................................................12
7.2.2 Soil Corrosion Potential.............................................................................12
8.0 ENVIRONMENTAL SAMPLING AND TESTING...........................................................14
9.0 GEOTECHNICAL CONDITIONS......................................................................................15
9.1 Site Geology.............................................................................................................15
9.2 Soil Conditions.........................................................................................................16
9.2.1 Embankment Conditions............................................................................16
9.2.2 Alluvium Conditions..................................................................................17
9.3 Groundwater Conditions ..........................................................................................17
9.4 Surface Water...........................................................................................................18
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TABLE OF CONTENTS (cont.) SHANNON 6WILSON,INC.
Page
9.4.1 Scour..........................................................................................................18
9.4.2 Erosion.......................................................................................................18
9.4.3 Flooding.....................................................................................................18
10.0 PROJECT SITE SEISMICITY............................................................................................19
10.1 Ground Motions .......................................................................................................19
10.2 Surface Fault Rupture...............................................................................................19
10.3 Liquefaction and Seismically Induced Settlement...................................................19
11.0 GEOTECHNICAL ANALYSIS AND DESIGN.................................................................20
11.1 Dynamic Analysis ....................................................................................................20
11.2 Cuts and Excavations ...............................................................................................20
11.2.1 Stability......................................................................................................20
11.2.2 Rippability..................................................................................................21
11.2.3 Grading Factors..........................................................................................22
11.3 Embankment Stability..............................................................................................22
11.4 Tunnel Design and Construction..............................................................................23
11.4.1 General.......................................................................................................23
11.4.2 Embankment Stabilization by Ground Freezing........................................24
11.4.3 Box-Jacking...............................................................................................25
11.4.4 Jacking Loads.............................................................................................26
11.4.5 Lateral Earth Pressures on Tunnel Walls...................................................27
11.4.6 Tunnel Surcharge Loads ............................................................................27
11.5 Retaining Walls........................................................................................................27
11.5.1 Shallow Foundations..................................................................................27
11.5.1.1 Bearing Resistance....................................................................27
11.5.1.2 Shallow Foundation Lateral Resistance....................................28
11.5.2 Wall Drainage............................................................................................28
11.5.3 Lateral Earth Pressures for Portal Headwall and Retaining Walls ............29
11.5.4 Global Stability..........................................................................................30
11.6 Box-Jacking Tunnel Foundation..............................................................................30
11.6.1 Drilled, Cast-in-place Piers........................................................................30
11.6.1.1 Axial Resistance........................................................................31
11.6.1.2 Lateral Resistance .....................................................................31
12.0 MATERIAL SOURCES ......................................................................................................32
13.0 MATERIAL DISPOSAL.....................................................................................................32
14.0 CONSTRUCTION CONSIDERATIONS ...........................................................................33
14.1 Construction Advisories...........................................................................................33
14.2 Construction Considerations that Influence Design.................................................34
14.3 Construction Monitoring and Instrumentation.........................................................35
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TABLE OF CONTENTS (cont.) SHANNON 6WILSON,INC.
Page
14.3.1 Preconstruction Survey..............................................................................36
14.3.2 Geotechnical Instruments...........................................................................36
14.3.2.1 Deformation Monitoring Points (DMPs)..................................36
14.3.2.2 Inclinometers.............................................................................3 8
14.3.2.3 Crack Monitors (CMs)..............................................................38
14.3.2.4 Optical Survey...........................................................................38
14.3.2.5 Monitoring Frequency...............................................................38
14.3.2.6 Response Values .......................................................................39
14.3.2.7 Data Reduction and Review......................................................40
14.4 Hazardous Waste Considerations.............................................................................40
14.5 Differing Site Conditions .........................................................................................41
15.0 EARTHWORK RECOMMENDATIONS...........................................................................41
15.1 Site Clearing and Grubbing......................................................................................41
15.2 Engineered Fill Construction ...................................................................................42
15.3 Structural Backfill ....................................................................................................42
15.4 Drainage Layer.........................................................................................................44
15.5 Wet Weather Earthwork...........................................................................................45
16.0 LIMITATIONS....................................................................................................................46
17.0 REFERENCES.....................................................................................................................48
TABLES
1 Climate Data for Truckee Ranger Station (No. 049043).........................................4
2 Active Faults Within 62 Miles (100 Kilometers) of Project Site.............................7
3 Summary of Vacuum Pothole Findings.................................................................10
4 Summary of Corrosion Test Results......................................................................13
5 Generalized Soil/Rock Engineering Parameters....................................................17
6 California Building Code 2010 Seismic Parameters for New Structures (Site
ClassC)..................................................................................................................20
7 L-Pile Input Parameters .........................................................................................31
8 Summary Of Project Response Values For Construction......................................39
9 Minimum Gradation Requirements for Structural Fill Materials ..........................42
10 Recommended Minimum Degrees of Structural Fill Compaction........................43
11 Class 2 Aggregate Base Grading Requirements....................................................44
12 Minimum Class 2 Aggregate Base Quality ...........................................................44
13 Class 2 Permeable Aggregate Base Grading Requirements..................................45
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TABLE OF CONTENTS (cont.) SHANNON 6WILSON,INC.
Page
FIGURES
1 Vicinity Map
2 Exploration and Site Plan
3 Topographic Map of Proposed MUP Site
4 Geologic Map of Truckee
5 Faults Mapped in Vicinity of Truckee
6 BV-1 and BV-2 Cross Section
7 BH-1 and BV-3 Cross Section
8 BH-2 Cross Section
9 BH-3 Cross Section
10 BH-4 Cross Section
11 Floodplain Mapping
12 Acceleration Response Spectra
13 Caltrans Deterministic Peak Ground Acceleration Map
14 Configuration of Freeze Zone Around Jacked Tunnel
PHOTOGRAPHS
1 Southerly view of the SR-89 Mousehole Tunnel.....................................................3
2 Inclined-face digger shield equipped with sand decks and augmented
withbreast doors....................................................................................................24
APPENDICES
A Subsurface Exploration
B Log of Test Boring Sheets
C Ground Penetrating Radar Report by GeoRecon International
D Geotechnical Laboratory Testing Procedures and Results
E Environmental Analytical Results
F Global Stability Analysis
G Foundation Design Recommendations
H Important Information About Your Geotechnical/Environmental Report
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SHANNON 6WILSON,INC.
GEOTECHNICAL DESIGN REPORT
DONNER PASS (MOUSEHOLE) PEDESTRIAN UNDERPASS AND
MULTI-USE PATHWAY ON STATE ROUTE 89
IN PLACER AND NEVADA COUNTIES IN AND NEAR TRUCKEE
FROM 0.8 MILE SOUTH TO 0.1 MILE SOUTH OF ROUTE 80/89 SEPARATION
1.0 INTRODUCTION
This report presents the results of our geotechnical investigation for the proposed pedestrian
underpass (or tunnel) and multi-use pathway (MUP)to be constructed on the east side of State
Route 89 (SR-89) adjacent to the existing Mousehole Tunnel in Truckee, California(see
Figure 1). The proposed improvements are located between West River Street and Deerfield
Drive. Our work has been accomplished in general accordance with the HDR Engineering, Inc.
(HDR) Subcontract Agreement, dated April 8, 2011, and the Subcontract Amendment, dated
August 22, 2011.
The purpose of this report is to document subsurface soil,rock, and groundwater conditions
along the project alignment, provide analyses of anticipated site conditions as they pertain to the
project described herein, and to provide recommendations regarding the design and construction
of the planned improvements. This report was prepared for the exclusive use of HDR, Town of
Truckee, California Department of Transportation (Caltrans), and other members of the design
team for specific application to this project. This report has been prepared in general accordance
with the guidelines for preparing Geotechnical Design Reports (Caltrans, 2006).
2.0 PROPOSED IMPROVEMENTS
The project includes construction of a pedestrian underpass and path as well as other associated
improvements, including a bus turnout area and retaining walls. The project will improve non-
motorized access to SR-89 and alleviate"bottleneck" traffic conditions as pedestrian/bicyclists
attempt to pass through the existing tunnel. The project also will significantly improve highway
usage by providing a separate, safe means for pedestrian and bicycle travel beneath the mainline
tracks of the Union Pacific Railroad (UPRR) at Milepost 204.54 of the Roseville subdivision.
The project site coordinates are approximately 39.3178 degrees north latitude and approximately
-120.2057 degrees west longitude (Google Earth, 2011).
Currently, pedestrian and bicycle traffic share the paved, two-lane roadway, without benefit of
walkways or shoulders, with traffic in the existing Donner Creek Underpass (Bridge No. 17-
0016), known as the Mousehole Tunnel,passes under the 32- to 34-foot-high embankment that
supports the UPRR mainline tracks. The proposed pedestrian tunnel will have inside dimensions
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of about 12 feet wide by 121/z feet high and will be about 110 feet long. Design indicates the
tunnel will be a rectangular-shaped, concrete box hydraulically jacked through the railroad
embankment. The embankment height above the concrete box will be on the order of 18 feet.
To maintain the stability of the UPRR embankment materials, ground freezing technology will
be used. Portal walls up to 16 feet tall will be constructed at each end of the tunnel. In addition
to the portal walls, a new MUP will be constructed on each end of the tunnel.
The proposed MUP will be about 10 feet wide and paved with concrete. The total length of the
MUP will be about 1,400 lineal feet. The proposed paved section for the MUP is 4 inches of
Portland cement concrete over about 14 inches of Class 2 aggregate base. Associated
development will include construction of three, cast-in-place,reinforced, concrete, cantilever
retaining walls (Types 1 and 5 per Caltrans classifications) supported on shallow foundations.
The retaining walls are identified as Retaining Walls 1 through 3, progressing from south to
north as shown on Figure 2.
Retaining Wall 1 (Type 5)will be about 377 feet long and located on the south side of the
proposed pedestrian tunnel. Specifically, this retaining wall will be constructed between West
River Street and the Donner Creek Mobile Home Park driveway. The proposed wall will range
from about 4 to 10 feet tall, constructed with a level backfill. The wall will be supported on a
shallow foundation.
Retaining Wall 2 (Type 1)will be about 554 feet long located to the north of the new pedestrian
tunnel. Wall 2 will vary in height from 6 to 16 feet with a level backfill. The wall will be
supported on shallow, conventional spread foundations.
Retaining Wall 3 (Type 5)will be an extension to an existing 6-foot-high retaining wall near the
intersection of Deerfield Street and SR-89. The wall will extend about 264 lineal feet. The wall
will be supported on shallow spread foundations similar to Retaining Wall 2. Rock slope
protection will be provided at the base of the retaining wall.
3.0 EXISTING SITE CONDITIONS
The "Mousehole"two-lane highway tunnel (Photograph 1) is located on SR-89 as it passes
beneath the UPRR double mainline tracks. The top of the embankment at SR-89 is at about
elevation+5,929 feet relative to mean sea level (MSL). The 25-foot-wide, 22-foot-high by
70-foot-long tunnel was built in 1929 and replaced a wooden trestle that crossed over Donner
Creek on the west side of the Town of Truckee. The highway pavement in the tunnel is at about
elevation+5,895 feet MSL.
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SHANNON&WILSON,INC.
Photograph 1—Southerly view of the SR-89 Mousehole Tunnel.
Donner Creek passes beneath the embankment via a 20-foot-wide by 200-foot-long culvert
located about 150 feet east of the Mousehole Tunnel. It is likely that the creek has historically
meandered from side to side in the valley. Groundwater levels are below the base of the
embankment, at about the same level as the creek(about elevation+5,850 feet MSL).
We reviewed historical information from the Town of Truckee. Our review suggests that when
the embankment was constructed in 1928, the wooden trestle supporting the railroad tracks was
left in place. The coarse, granular fill was placed around the trestle and around the cast-in-place
concrete Mousehole Tunnel to construct the present 32-to 34-foot-high embankment.
4.0 FILES REVIEWED
Supplemental information used in the preparation of this report included review of the following
reports prepared by our firm and others:
■ Shannon&Wilson, Inc., 2009, Geotechnical report—preliminary assessment of State
Route 89 Mousehole Tunnel: Report prepared by Shannon& Wilson, Inc., Seattle,
Wash.,job no. 21-1-21072-001, for HDR Engineering Inc.,Walnut Creek, CA, June,
23 p.
■ Geocon Consultants, Inc. (Geocon), 2009, Site investigation report of UPRR
Embankment,Nevada County, CA: Report prepared by Geocon Consultants, Inc.,
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SHANNON 6WILSON,INC.
Rancho Cordova, CA,job no. S9300-06-82, for Caltrans, Marysville, CA, December,
10 P.
■ HDR Engineering, Inc. (HDR), 2011, SR89 Multi-use pathway Underpass Type
Selection Report, July, 12 p.
5.0 PHYSICAL SETTING
5.1 Climate
Review of climate data available from 1904 through 2011 indicates the average minimum
temperature measured at the Truckee Ranger Station No. 049043 in Truckee, California, ranges
from 14.6 degrees Fahrenheit (°F) in January to 41.7°F in July (Western Regional Climate
Center, 2012). The average maximum temperature ranges from 39.2°F in January to 82.3°F in
July. More than 80 percent of the average yearly precipitation occurs between the months of
November and April (National Oceanic and Atmospheric Administration [NOAA], 2002). A
summary of the climatic data is provided in Table 1.
TABLE 1
CLIMATE DATA FOR TRUCKEE RANGER STATION (NO. 049043)
Month Jan I Feb Mar Apr May Jun I Jul I Aug I Sep I Oct Nov Dec Annual
Average
Max. 39.2 41.9 46.7 53.7 63.0 72.9 82.3 81.2 74.4 63.4 49.5 40.8 59.1
Temperature
(°F)
Average
Min. 14.6 16.7 21.0 26.2 32.3 37.4 41.7 40.3 35.8 29.0 22.3 16.1 27.8
Temperature
(°F)
Average
Total 5.79 5.02 4.28 1.96 1.31 0.59 0.35 0.35 0.63 1.52 3.25 5.11 30.15
Precipitation
(inches)
Average
Total 48.3 41.9 37.4 15.3 4.1 0.4 0.0 0.0 0.4 2.8 16.2 34.9 201.8
Snowfall
(inches)
Note:
of=degrees Fahrenheit
5.2 Topography and Drainage
The topography along SR-89 in the vicinity of the Mousehole Tunnel forms a low pass or
"saddle"with surface elevations of about+5,870 feet MSL near each end of the alignment to
about+5,895 feet MSL near the existing tunnel. Embankment fills above the tunnel are at an
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elevation of about+5,930 feet MSL. Side slopes along SR-89 drain towards the sides of the
roadway and into drain culverts and nearby Donner Creek. A topographic map of the project
area is included in Figure 3.
5.3 Man-made Features of Engineering and Construction Significance
The project alignment is located in an area that contains numerous man-made features such as:
■ Embankment fills supporting UPRR railroad mainline tracks and Caltrans right-of-
way pavements;
■ Buried abandoned wooden railroad trestle and other UPRR structures;
■ Tunnel walls and foundations;
■ Drain culverts;
■ Underground utilities including high-pressure gas mains, natural gas mains, electrical,
fiber optics, etc.; and
■ Overhead utilities.
These man-made features will have a significant impact on the proposed construction and should
be considered in the design and construction of the planned improvements. To help identify the
location of these utilities, 22 vacuum excavated potholes were performed at various locations
along the alignment as shown in the Exploration and Site Plan (Figure 2). Vacuum pothole G-17
was not performed due to the depth of the utility and the limitations of the vacuum truck.
Additional information regarding the vacuum potholing can be found in Section 6.1.4 Utility
Potholing in this report.
5.4 Regional Geology
The project is located in a geologic feature called the Tahoe Graben, which separates the
easternmost Sierra Nevada from the westernmost range of the Basin and Range physiographic
province. The Tahoe Graben consists of a series of west-tilted blocks bounded by east-dipping
faults that produce the north-south-trending basin that Lake Tahoe now occupies. Lake Tahoe
was formed by a combination of block faulting and damming of the outlet at the north end of the
basin by repeated episodes of volcanic activity and glacial advances. The geology in the project
vicinity is dominated by these three geologic features: east-dipping faulting, large accumulations
of generally andesitic to basaltic flows of Miocene to Pleistocene age, and several Pleistocene
glacial episodes.
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In the vicinity of the site, Pleistocene glaciation sculpted the landscape observed today and
deposited the surficial soils. The valley floor and the hillsides surrounding the Donner Lake
valley are mapped as being underlain by deposits from two Pleistocene glacial episodes
(Saucedo, 2005), the Tioga (approximate age of 10,000 to 25,500 years before present) and the
Tahoe glacial episodes (approximate age of 56,000 to 118,000 years before present) as shown in
Figure 4. Along the Truckee River, outwash deposits include large volcanic and granitic
boulders attributed to catastrophic glacial outburst floods during the Tahoe Glaciation.
5.5 Seismic Setting
The project site is located in a deep alluvium filled valley along Donner Creek, with the nearest
mapped active faults being the North Tahoe Fault located approximately 13 miles to the south
and the Mohawk Valley Fault located approximately 20 miles to the northwest.
Earthquake-related damage to surface structures is normally related to shaking, liquefaction,
slope movements, and offsets along faults. However, tunnels tend to resist damage from
earthquake-related ground movements, as indicated by the numerous tunnels around the
San Francisco Bay area that were reviewed by Shannon&Wilson staff after the magnitude 6.9
Loma Prieta earthquake in 1989. Only minor cracks or sloughing were noted in the concrete and
brick-lined railroad tunnels as a result of the earthquake. Similarly, the only damage observed in
transit tunnels in Seattle after the magnitude 6.8 Nisqually earthquake in 2001 were damaged
utility pipes anchored to the tunnel walls. Only a few instances of serious structural damage to
tunnels due to earthquakes have been reported and all are directly related to offsets along faults,
as occurred in the 1999 Taiwan earthquake, or to offsets due to seismically induced slope
movements.
To evaluate the potential seismic risks to the project,we reviewed"active" faults within a radius
of 62 miles (or 100 kilometers) from the site. Faults defined by California Geological Survey
(CGS) to be active near the site are summarized in Table 2. A map of the known "active" faults
near the site is shown in Figure 5. However, we are aware of a recently discovered fault,
recognized in the CGS database in 2012 and identified as the Polaris Fault located near the
Martis Creek Dam located approximately 4.6 miles east of the project site(CGS, 2012). The
Polaris Fault is considered to be active within the last 30,000 years based on recent fault
delineation work(Brown, 2009). The Polaris Fault is capable of triggering a 6.4 to 6.9-
magnitude earthquake (Hunter and others, 2011).
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TABLE 2
ACTIVE FAULTS WITHIN 62 MILES (100 KILOMETERS) OF PROJECT SITE
Deterministic
Approx. Magnitude
Distance (Moment
from Site Magnitude Fault Dip Angle Dips Site Slip Rate
Fault Source Miles(km) Scale) Mechanism (degrees) To Lies (mm/yr)
West Tahoe 4(6) 7.1 Normal 50 E NW Unknown
North Tahoe 8(13) 6.7 Normal 50 E W 0.2-1
Little Valley Fault 11 (18) 6.54 Normal 40-60 E W 0.2-1
Mount Rose Fault 12(19) 6.89 Normal 40-60 E W 1-5
Zone
Kings Canyon 14(23) 6.52 Normal 40-60 SE NW 0.2-1
Fault Zone
Carson Range Fault 14(23) 7.08 Normal 40-60 E NW 1-5
Peavine Peak Fault 15(24) 6.36 Normal 40-60 NE SW Less than
Zone 0.2
Carson City Fault 16(26) 6.48 Normal 40-60 SE NW Less than
0.2
Petersen Mountain 17(27) 6.72 Normal 40-60 E SW Less than
Fault 0.2
Indian Hills Fault 17(27) 6.13 Normal 40-60 SE NW Less than
0.2
Freds Mountain 18(28) 6.78 Normal 40-60 E SW Less than
Fault 0.2
Spanish Springs 19(30) 6.62 Normal 40-60 E SW Less than
Valley Fault 0.2
Spanish Springs 21 (34) 5.88 Strike Slip 90 --- SW Less than
Peak Fault 0.2
Smith Valley Fault 26(42) 7.37 Normal 40-60 E W 0.2-1
Antelope Valley 28(45) 6.95 Normal 40-60 E NW 0.2-1
Warm Springs 29(46) 6.92 Strike Slip 90 --- SW Less than
Valley Fault Zone 0.2
Honey Lake 30(48) 7 Strike Slip 90 --- S 1-5
Eastern Pyramid 31 (49) 6.99 Normal 40-60 W SW Less than
Lake Fault 0.2
Pyramid Lake Fault 34(54) 7.27 Strike Slip 90 --- SW 1-5
Zone
Singatse Range 35(56) 6.85 Normal 40-60 E W Less than
Fault Zone 0.2
Nightingale 37(60) 6.88 Normal 40-60 W SW Less than
Mountains Fault 0.2
Notes:
E=east;N=north;W=west;S=south
km=kilometer
mm/yr=millimeters per year
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6.0 FIELD EXPLORATION
6.1 Field Explorations and Sampling
6.1.1 General
Our field investigation for the project occurred in two phases with the initial investigation
occurring in October and November of 2008. During this period, four horizontal borings (BH-1
through BH-4), three vertical borings (BV-1 through BV-3), four test pits (TP-1 through TP-4),
and a ground penetrating radar (GPR) survey were performed at the locations shown in the
Exploration and Site Plan (Figure 2). These explorations were selected and located to assess
ground conditions along several tunnel alignments, including two highway replacement tunnels
and a pedestrian tunnel.
The second phase of the investigation occurred in May 2011. Six additional vertical soil
borings (BV-4 through BV-9)were drilled and sampled, seven test pits (TP-5 through TP- 11)
were excavated and 17 holes were vacuum "potholed" at suspected utility locations, as shown in
Figure 2, to further assess ground conditions in the vicinity of the MUP. The explorations were
also used to assess ground conditions along various retaining walls and to log the soil cover and
depth for various subsurface utilities that were located within close proximity of the MUP.
A field representative from our firm was present during the field exploration activities to
perform a visual reconnaissance of the site,verify the boring and test pit locations, observe the
drilling and excavation activities, assist in obtaining soil samples, and prepare field logs of the
borings, test pits and utility potholes. The logging procedures were performed in general
accordance with Caltrans requirements (Caltrans, 2010a).
A Standard Penetration Test (SPT) sampler was used in the borings at selected depths.
The SPT sampler consists of a 24-inch-long, split-barrel measuring 1.5-inch, inside-diameter and
2-inch, outside-diameter. The tests were performed in general accordance with ASTM
International (ASTM) Designation: D 1586, Standard Method for Penetration Testing and Split-
barrel Sampling of Soils (ASTM, 2011). The sampler was driven a distance of 18 inches into the
bottom of the borehole with an automatic 140-pound hammer falling 30 inches. The number of
blows required for the last 12 inches of penetration is termed the Standard Penetration Resistance
(N-value). The N-value is an empirical parameter that provides a means for evaluating the
relative density, or compactness, of granular soils and the consistency, or stiffiiess, of cohesive
soils. The N-values are plotted on the boring logs and Log of Test Boring (LOTB) sheets
presented in Appendices A and B, and prepared in general accordance with Caltrans
requirements.
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The samples were field classified and recorded on the logs by our field representative.
The SPT samples were collected in plastic jars and immediately sealed to preserve the moisture
in the sample. All soil samples were returned to our office and a laboratory testing program was
developed.
After completion of the drilling activities,the borings were backfilled with a slurry of
neat-cement,bentonite, and water. Borings drilled within paved surfaces were backfilled with
hot asphalt concrete in accordance with Caltrans requirements.
6.1.2 Soil Borings
The subsurface conditions at the site were explored with 9 vertical soil borings,
designated BV-1 through BV-9, and 4 horizontal soil borings, BH-1 through BH-4, were drilled
through the existing UPRR embankment and adjacent valley fill, at locations shown in Figure 2.
The borings were drilled in two groups based on the project design requirements that included an
initial design concept to explore the Mousehole Tunnel with twin highway tunnels (2008) and a
subsequent concept to construct a multi-use pathway. The boring groups are:
■ Four horizontal borings, BH-1 to BH-4, in October and November 2008;
■ Three vertical borings, BV-1 to BV-3, in November 2008; and
■ Six vertical borings, BV-4 to BV-9, in May 2011.
The borings were drilled by PC Exploration of Lincoln, California. The horizontal
borings (BH-1 to BH-4) through the UPRR embankment were drilled using a track-mounted
Puntel MX 600 drill rig with a Centrix cased drill bit and air circulation. In addition, the Puntel
drill rig was utilized to drill three vertical borings (BV-1 to BV-3) at the locations shown in
Figure 2. In May 2011, PC Exploration drilled an additional six vertical borings (BV-4 through
BV-9)by utilizing an Ingersoll-Rand A-400 truck-mounted drill rig equipped for ODEX air
rotary drilling. General descriptions of the soil borings and the boring logs are presented in
Appendix A, Subsurface Exploration.
6.1.3 Test Pits
We observed excavation of 11 test pits along the project alignment. These test pits,
designated TP-1 to TP-11, were located at various intervals along the project alignment, as
shown in Figure 2. Test pits TP-1 through TP-4 excavated on November 6, 2008,were
performed by Jim Dobbas, Inc. of Newcastle, California, and, the remaining test pits (TP-5
through TP-11)were excavated on May 24, 2011, by Ron Tilford Backhoe of Orangevale,
California. The test pits excavated for this effort extended to a maximum depth of 8 feet below
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existing site grades by utilizing a rubber-tired backhoe. A description of the field methods and
procedures and logs of the test pits are presented in Appendix A.
6.1.4 Utility Potholing
We observed the excavation of 22 vacuum potholes located at various locations along
several mapped existing utility line alignments. The vacuum potholes extended to depths
ranging from about 3 to 7 feet below existing grades. The vacuum potholes were excavated
using a Vactor HXX hydro-excavator provided by Hydro X Services of Woodbridge, California.
At the completion of vacuum potholing, the holes were initially backfilled with sand to cover the
existing utility pipe, and then filled with two-sack sand-cement slurry, containing two 90-1b
sacks of cement per cubic yard of sand, to about 6 inches of final grade. Vacuum potholes
located within the highway right-of-way were restored to grade with hot asphalt concrete as
required by Caltrans. A summary of the field observations made during the vacuum potholing is
provided in Table 3.
TABLE 3
SUMMARY OF VACUUM POTHOLE FINDINGS
Horizontal Distance
Horizontal Distance from from Edge of
Location Marker to Pothole Marker Description Pavement De) to Pi)e
W-1 7 feet 4 inches(west) White rooster tail nail 1 foot 8 inches(east) 4 feet 0 inch
W-2* 8 feet 4 inches(west) White rooster tail nail 8 feet 0 inch(west) 5 feet 0 inch
W-3 4 feet 8 inches(west) White rooster tail nail 2 feet 4 inches(east) 3 feet 2 inches
W-4 --- --- 1 foot 6 inches(east) Not located
W-5 3 feet 9 inches(east) White rooster tail nail 2 feet 10 inches(west) Not located
G-1** 4 feet 2 inches(north) White rooster tail nail 1 foot 6 inches(east) 6 feet 4 inches
G-2 2 feet 0 inch(west) White rooster tail nail 0 foot 6 inches(west) 6 feet 8 inches
G-3 2 feet 0 inch(west) White rooster tail nail 1 foot 8 inches(west) 4 feet 11 inches
G-4 2 feet 0 inch(west) White rooster tail nail 1 foot 9 inches(west) 5 feet 0 inch
G-5 1 feet 10 inches(west) White rooster tail nail 1 foot 5 inches(west) 5 feet 0 inch
G-6 2 feet 5 inches(west) White rooster tail nail 2 feet 1 inch(west) 5 feet 0 inch
G-7 4 feet 3 inches(west) White rooster tail nail 4 feet 0 inch(west) 5 feet 2 inches
G-8 6 feet 6 inches(west) White rooster tail nail 6 feet 2 inches(west) 4 feet 10 inches
G-9 10 feet 0 inch(west) White rooster tail nail 9 feet 1 inch(west) 4 feet 7 inches
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Horizontal Distance
Horizontal Distance from from Edge of
Location Marker to Pothole Marker Description Pavement De th to Pi e
G-10 9 feet 4 inches(west) White rooster tail nail 8 feet 3 inches(west) 5 feet 1 inch
G-11 17 feet 5 inches(west) White rooster tail nail 16 feet 6 inches(west) 5 feet 0 inch
G-12 4 feet 8 inches(west) White rooster tail nail 2 feet 3 inches(east) 5 feet 0 inch
G-13 3 feet 1 inch(west) White rooster tail nail 9 feet 10 inches(east) 3 feet 10 inches
G-14 5 feet 0 inch(west) White rooster tail nail 16 feet 6 inches(east) 4 feet 1 inch
G-15 3 feet 3 inches(west) White rooster tail nail 23 feet 1 inch(east) 3 feet 0 inch
G-16 4 feet 4 inches(west) White rooster tail nail 22 feet 4 inches(east) 6 feet 0 inch
G-18** 3 feet 4 inches(south) Yellow rooster tail nail 1 3 feet 9 inches(west) 1 3 feet 0 inch
Notes:
* The pipe located at location W-2 appeared to be a gas line,not a water line.
** Pothole location is in line with rooster tail,i.e.,distance from offset marker measured parallel to road centerline.
6.2 Geophysical Study
In November 2008, a portable GPR unit was used by GeoRecon International along three 300-
foot-long lines on the crest of the embankment adjacent to the twin UPRR tracks and along the
centerline of the embankment to look for and interpret anomalies within the embankment. The
GPR used a 200-megahertz antennae and a GSSI SIR 3000 portable GPR unit. A survey wheel
was used to position and determine the location of the antennae. The GPR is capable of locating
large anomalies within the embankment and allows extrapolation between borings to a maximum
depth of about 30 feet below grade. To some degree, the application of this geophysical
technique was experimental in attempting to locate boulders; however, it did identify and locate
what is likely to be an abandoned wood railroad trestle that extends east and west from the crown
of the Mousehole Tunnel, and with the top of the trestle at a depth of about 15 feet below the top
of the embankment. A report from GeoRecon International on the GPR survey along the top of
the UPRR embankment above the Mousehole Tunnel is included in Appendix C.
7.0 GEOTECHNICAL TESTING
A variety of field and laboratory tests were conducted to characterize the site soils and rock.
7.1 In Situ Testing
Field tests included SPT values in the vertical borings, GPR measurements along the top of the
embankment, and Schmidt Hammer tests of cobbles and boulder fragments. Schmidt Hammer
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Index testing of the volcanic and granitic cobbles and boulders within the fill were used to assess
rock strength. The Schmidt Hammer tests resulted in rebound numbers ranging from 35 to 48.
Assuming a unit weight for igneous rock of 150 to 165 pounds per cubic foot (pcf), these
Schmidt Hammer index numbers reflect an approximate unconfined compressive strength
ranging between 8,000 to 20,000 pounds per square inch (psi). This range in unconfined
compressive strength compares well with the range of 9,000 to 24,000 psi reported for basalt
bedrock in the area by Gates (1994). For design and construction purposes, we recommend that
the granular soils be considered to be abrasive and that the cobbles and boulders be considered to
have an upper bound strength of 25,000 psi.
7.2 Laboratory Testing
7.2.1 General
Samples recovered from borings and test pits were tested to evaluate the basic index and
engineering properties of the subsurface soils. Geotechnical laboratory testing of recovered soils
included visual classifications,water content determinations, grain size analyses, and corrosion.
All laboratory tests were performed in general accordance with ASTM standard test procedures.
The geotechnical laboratory testing was conducted at several different offices including our
office in Los Angeles; Wallace Kuhl &Associates of West Sacramento, California; and Sunland
Analytical of Rancho Cordova, California. The geotechnical laboratory tests performed for the
project included:
■ Natural Moisture Content(ASTM D 2216);
■ Grain Size Distribution (ASTM D 422); and
■ Atterberg Limits (ASTM D 4318).
Results of the laboratory tests are presented in Appendix D and are also shown in the
boring logs and on the Log of Test Boring sheets in the project drawings, at the corresponding
sample depths.
7.2.2 Soil Corrosion Potential
Representative soil samples of near-surface soils were collected from the test pits and
submitted to Sunland Analytical. The samples were tested for a variety of corrosion parameters,
including pH, resistivity, and chloride and sulfate concentrations. Soil measurements were
determined by the Caltrans-approved test methods. The following parameters were tested:
■ Sulfate and Chloride Concentration: Sulfate is an ion that can lead to damage to
metallic and concrete structures. Chloride is an ion that converts to hydrochloric acid,
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which can cause corrosion of metals. Also, its presence tends to decrease the soil
resistivity.
■ Resistivity: Soil resistivity is a measure of the tendency for electrical currents produced
during the corrosion process to flow freely through the electrolyte. A decrease in
resistivity relates to an increase in potential corrosion activity. In general, for gravelly
soils with little fine matrix, typical resistivity values range from about 50,000 to 100,000
ohm centimeters (0-cm). For soils that are silty or clayey, the resistivity decreases to
range from about 1,000 to 20,000 f2-cm.
■ pH: Soil pH is an indication of the acidity or alkalinity of soil and is measured in pH
units. Soil pH is defined as the negative logarithm of the hydrogen ion concentration.
The pH scale goes from 0 to 14 with a pH of 7 as the neutral point. As the amount of
hydrogen ions in the soil increases, the soil pH decreases, thus becoming more acidic.
From a pH of 7 to 0, the soil is increasingly acidic; from a pH of 7 to 14, the soil is
increasingly alkaline or basic. Soils commonly have a pH range of about 5 to 8.
Results of the soil corrosion testing are summarized in Table 4.
TABLE 4
SUMMARY OF CORROSION TEST RESULTS
Sample Identification
Analyte Test Method TP5 at 3 Feet TP8 at 4 Feet TP10 at 7 Feet
Soil pH CA DOT 643 6.19 6.43 5.95
Minimum CA DOT 643 4,020 Q-cm 2,950 Q-cm 750 Q-cm
Resistivity
Chloride CA DOT 422 28.2 ppm 50.2 ppm 481.5 ppm
Sulfate CA DOT 417 10.0 ppm 5.9 ppm 47.2 ppm
Notes:
CA DOT=California Department of Transportation
Q-cm=ohm centimeters
ppm=parts per million
A "corrosive area" is defined by the California Department of Transportation Standard
Specifications (Caltrans, 2012) as an area where the soil and/or water contains a chloride
concentration of more than 500 ppm, sulfate concentration more than 2,000 ppm, or has a pH of
less than 5.5. The corrosivity test results suggest that the site soils are not highly corrosive to
exposed buried metal or reinforced concrete. Test results also suggest that the sulfate exposure is
"negligible"based on Section 1904A.5 of the California Building Code(CBC, 20 10) and Table
4.3.1 of Section 4.3 of the American Concrete Institute (ACI) 318-08 (ACI, 2008). Ordinary
Type I-II Portland cement is considered suitable for use on this project, assuming that a
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minimum concrete cover is maintained over the reinforcement. For specific corrosion protection
methods, a qualified corrosion engineer should be consulted.
8.0 ENVIRONMENTAL SAMPLING AND TESTING
To support in situ soil characterization of material that will be generated during site
development, 18 soil samples were collected from the borings and submitted under chain-of-
custody documentation to Kiff Analytical, LLC of Davis, California. Samples were analyzed for
the following constituents:
■ Gasoline-range hydrocarbons (TPH-G)by the U.S. Environmental Protection
Agency (EPA)Method M8015G;
■ Diesel-range and lubricating oil-range hydrocarbons (TPH-D and TPH-O)by EPA
Method M8015D;
■ Polycyclic aromatic hydrocarbons (PAHs)by EPA Method 8270C; and
■ CAM Title 22 metals (antimony, arsenic, barium, beryllium, cadmium, chromium,
cobalt, copper, lead, mercury, molybdenum, nickel, selenium, silver, thallium,
vanadium, and zinc)by Method 6010B/7471A.
Analytical results for the 18 soil samples are presented in Table E-1 of Appendix E; copies of the
analytical laboratory reports also are contained within Appendix E. PAH and TPH analysis were
conducted to indicate the potential presence of contamination. Presently, the State of California
does not have any specific disposal classification criteria for these analytes. The analytical
results for metals were screened against Title 26 California Code of Regulations Soluble
Threshold Limit Concentration hazardous waste (California hazardous waste) classification
criteria and the Resource Conservation Recovery Act (RCRA) Toxicity Characteristic Leaching
Procedure hazardous waste (RCRA hazardous waste) classification criteria to assess potential
disposal requirements. A brief summary of the data is provided below:
■ PAHs were not detected in the samples analyzed from the borings;
■ Copper, lead and zinc were detected in one boring (BV-2) at total concentrations
above the soluble total limit concentration (STLC) established by the State of
California. The remaining samples analyzed did not reveal elevated concentrations of
metals.
■ TPH-G was not detected in the samples analyzed from the borings.
■ TPH-D and TPH-O were detected at all sampled locations. TPH-D concentrations
ranged from 25 to 530 milligrams per kilogram (mg/kg),while TPH-O concentrations
ranged from 130 to 2,900 mg/kg.
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Arsenic was detected in various samples collected from the borings. Arsenic is naturally present
in the minerals and volcanic rocks in the Truckee area. In the Tahoe-Martis area, trace elements
including arsenic were present at high concentrations in about 19 percent of the primary aquifers
(USGS, 2012). Therefore, arsenic concentrations are not anticipated to adversely impact the
proj ect.
In 2009, Geocon Consultants (Geocon)performed an environmental assessment of the UPRR
embankment soils. Geocon advanced one horizontal borehole approximately 80 feet into the
embankment. Soil samples were collected and analyzed for various constituents. Results of
Geocon's environmental testing suggested that higher concentrations of petroleum hydrocarbons
were encountered in the outer portions of the embankment. For specific information regarding
the environmental testing of the UPRR embankment soils,please refer to the Site Investigation
Report, dated December 2009, prepared by Geocon (Geocon, 2009).
Naturally occurring asbestos in the form of chrysotile is commonly found in some serpentine
rock in the foothills of the Sierra Nevada (Casella, 2006). However, asbestos is not found in all
serpentine rock, but when it does occur, it can be present in amounts ranging from less than
1 percent up to 25 percent. Asbestos is released when serpentine rock is broken or crushed.
Review of the Naturally Occurring Asbestos Hazard in Placer County prepared by the CGS
(2008) indicates that the project site is in an area least likely to contain naturally occurring
asbestos. In addition, no detectable concentrations of asbestos were detected in soil samples
collected from the UPRR embankment(Geocon, 2009). Therefore, it is our opinion that
naturally occurring asbestos should not be a significant factor in design and construction of the
planned improvements.
9.0 GEOTECHNICAL CONDITIONS
9.1 Site Geology
The exploration program encountered alluvium deposits that filled the Truckee River Valley to
depths in excess of the boring depths of 40 to 65 feet. None of the borings were thought to have
penetrated bedrock, although at least two of the borings encountered large boulders, in excess of
3 to 5 feet in diameter. As noted above and observed in the general vicinity, bedrock is likely to
consist of various volcanic and igneous rock types.
Geologic maps indicate that the entire project alignment is underlain by alluvium,which in turn
is underlain by till of the Tioga glaciations,which is described as unconsolidated boulder-laden
till characterized by large, unweathered, granitic boulders. At or just beyond the northern and
southern limits of the project, deposits of Tioga glacial outwash are mapped, consisting of
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unconsolidated boulder and cobble gravel with sand and silt. The outwash may be underlain by
Tioga till. The outwash is likely to have fewer fines in the matrix and better drainage properties.
Along the Truckee River, glacial outwash deposits include large volcanic and granitic boulders,
as much as 10 feet in diameter, attributed to catastrophic glacial outburst floods during the Tahoe
Glaciation. Such deposits could extend into the southern portion of the alignment.
Recent alluvium, comprising unconsolidated gravel, sand, and silt, is also mapped just beyond
the northern end of the alignment adjacent to Donner Creek. Although not mapped, alluvium is
likely present adjacent to Donner Creek along the portions that flow through the project corridor.
As the recent alluvium largely comprises reworked glacial outwash and till deposits,
compositions are likely to be similar, and may be difficult to distinguish in the project
explorations,particularly in the borings.
Although not observed in the borings, the glacial deposits are underlain at various depths by
volcanic bedrock comprising basalt and latite flows associated with Pliocene and Pleistocene
volcanic eruptions. Volcanic bedrock is mapped on the hillside traversed by the UPRR tracks,
just east of the tunnel, and in scattered locations farther from the project.
In addition to natural deposits, human-placed fill material is present along the project corridor.
Fill is likely present beneath and adjacent to SR-89 and was placed during roadway construction.
Fill depth is likely to be greatest along the eastern edge of the roadway where it was placed to
create a level bench for the roadway. Fill was also placed to form the embankment used to
support the UPRR tracks across the topographic low traversed by SR-89 and Donner Creek.
Much of the fill is likely derived from local sources and is likely to be similar in composition to
the native deposits of gravel and sand with scattered to abundant cobbles and boulders. Fill
within the UPRR embankment may also contain trestle timbers,used to support the track prior to
construction of the existing embankment, or other wood debris such as timber ties. Field
observations made during our investigations indicate that the road embankment slopes and
UPRR embankment slopes appeared stable with no obvious signs of instability or sloughing.
9.2 Soil Conditions
9.2.1 Embankment Conditions
The exploration program indicates that the embankment is constructed with granular fill,
consisting of clean to slightly clayey, silty sand; gravel; abundant cobbles; and up to 30 percent
granite and basalt boulders up to 5 feet in diameter. The boulders appear to occur in zones or
lenses 15 to 25 feet thick. Near the middle of the embankment 53 to 60 feet from the south toe,
horizontal boring BH-1 encountered several zones of wood fragments,probably portions of the
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abandoned timber trestle that may have been left in place and filled around. Samples tested from
the embankment borings were generally classified as slightly silty to silty, gravelly sand to sandy
gravel with 5 to 20 percent silt. During drilling and sampling,we did not observe evidence of
contamination, such as odor or visual staining. Cross sections through the embankment area are
shown in Figures 6 through 10.
9.2.2 Alluvium Conditions
The embankment fill overlies alluvium deposited by various periods of heavy flow to
torrential floods in Donner Creek and possibly the Truckee River. The alluvium appears to
consist of alternating irregular layers of dense sand and gravel and layers of flood deposits
consisting of up to 30 percent 2- to 10-foot-diameter basalt and granite boulders in a matrix of
predominately silty, gravelly sand to gravelly, silty sand with trace amounts of clay. Grain size
analyses indicated that the alluvium contains 18 to 50 percent silt. The generalized soil
engineering parameters used in our study are provided in Table 5. During drilling and sampling,
we did not observe evidence of contamination, such as odor or visual staining.
TABLE 5
GENERALIZED SOIL/ROCK ENGINEERING PARAMETERS
Average Blow
Counts per foot Total Unit Weight Cohesion Friction Angle
Soil Tvpe (N-values) ( cf) ( sf) (de rees)
UPRR Embankment 20 130 400 34
Fills
New Structural Fills --- 120 0 34
Silty Sand w/Gravels 30 140 0 35
Silty Gravelly Sand w/ 30 140 100 35
trace Clay
Gravelly Sand with 35 145 0 40
cobbles and boulders
Notes:
pcf=pounds per cubic foot,psf=pounds per square foot
9.3 Groundwater Conditions
The exploration program revealed that the UPRR embankment did not contain perched water or
seasonal water. However, groundwater was encountered during our recent borings drilled on
May 24 and 25, 2011, in the underlying alluvium at depths ranging from 12 to 26 feet below
existing highway grades (approximate elevations +5,865 to +5,867 feet MSL). In addition,
groundwater was observed in test pit TP-11 at a depth of approximately 61/2 feet below existing
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grades on May 24, 2011. Please note that the borings and test pit may not have been left open
long enough for water levels to reach static equilibrium. Groundwater conditions in the area are
anticipated to fluctuate due to subsurface soil conditions, seasonal variations and the water levels
of Donner Creek. However, it seems unlikely that groundwater levels would approach the
elevation of the roadway and current tunnel invert at elevation+5,894 feet MSL.
9.4 Surface Water
9.4.1 Scour
It is our understanding that scour analysis of the pedestrian tunnel and MUP retaining
walls is not required due to the proposed elevation of these structures.
9.4.2 Erosion
The subsurface conditions along the project alignment generally consist of silty sands
with gravels. In our opinion, the undisturbed soils and fills along the alignment will be
susceptible to erosion by surface runoff that occurs during the winter and spring months or
periods of intense rainfall. As a minimum, erosion control measures should consist of straw bale
sediment barriers or silt filter fences in areas where surface runoff may be concentrated. Rock
slope protection for the retaining wall foundations should be provided in general accordance with
Caltrans requirements. A site-specific erosion and sediment control plan should be developed by
the project civil engineer based on their site grading and drainage plans and the anticipated
construction schedule. The plan should be developed in general accordance with state and local
guidelines.
9.4.3 Flooding
We have reviewed the Flood Insurance Rate Map (FIRM) for Nevada, County to evaluate
the potential hazard from flooding at a given location. The FIRM was published by the Federal
Emergency Management Agency's National Flood Insurance Program. Our review of the FIRM
indicates that the major portion of the project alignment including SR-89 is located outside the
0.2 percent annual chance floodplain boundary. However, portions of the alignment that are
within close proximity of Donner Creek between Stations 309+00 to 314+00, are immediately
adjacent to areas that possess a 0.2 percent annual chance of flood. A plot showing the
floodplain mapping for the area is provided as Figure 11.
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10.0 PROJECT SITE SEISMICITY
10.1 Ground Motions
Considering the site is located within relatively close proximity to active faults capable of
producing earthquakes with a maximum moment magnitude of 6.0 or more, the project area has
a high potential for experiencing relatively strong ground motion. To determine the design
acceleration response spectra(ARS) for the project site,we utilized the ARS online tool
(Version 2.1.05)provided by Caltrans (2009a) and the guidelines to determine seismic design
criteria(Caltrans, 2010b). The design ARS curve developed for the site is presented as Figure
12. The design ARS curve represents an equally probable response spectrum in horizontal
directions with no vertical contributions and applies to both the deterministic and probabilistic
spectra. Review of the Caltrans Deterministic peak ground acceleration (PGA)map (Caltrans,
2007), indicates the project site is mapped near the 0.4g peak bedrock acceleration contour
(Figure 13). Based on the above, it is our opinion that the PGA of 0.475g is appropriate for the
site.
10.2 Surface Fault Rupture
Surface fault rupture is generally caused by relative displacement across a fault during an
earthquake. The site is not located within an Alquist-Priolo Earthquake Fault Zone and is not
underlain by known active faults. The Alquist-Priolo Earthquake Fault Zoning Act produced
1:2,000 scale maps of active faults as determined by the State Geologist for the CGS. Since
there are no recognized active faults at the project site,the potential for fault surface rupture at
the site is considered to be low.
10.3 Liquefaction and Seismically Induced Settlement
The explored ground conditions around the Mousehole Tunnel do not support the potential for
significant earthquake-related damage. The boulder-laden, relatively dense, granular alluvium
appears to be at least 50 feet deep with a 25- to 45-foot-deep groundwater table (below tunnel
invert elevation),based on the borings to date. The SPT blow counts indicate dense, granular
soils that are not prone to liquefaction during a major earthquake. No known active faults cross
the project limits, which could potentially result in rupture and offset of the tunnel and MUP
retaining walls. Lastly, the Mousehole Tunnel and the pedestrian tunnel are located in a valley,
so earthquake-induced slope movements would not impact tunnel operation.
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11.0 GEOTECHNICAL ANALYSIS AND DESIGN
11.1 Dynamic Analysis
Table 6 summarizes the 2010 CBC seismic design parameters considered applicable for
the project. Seismic design of structures using this code requires mapped short-period and 1-
second-period spectral accelerations, SS and Si,respectively. Ss and Si are for a risk-targeted
maximum considered earthquake,which corresponds to ground motions with a 2 percent
probability of exceedance in 50 years or about a 2,500-year return period (with a deterministic
maximum cap in some regions). The Probabilistic Seismic Hazard Analysis (PSHA) ground
motion results were obtained from the USGS website (USGS, 2012a). The results of the updated
USGS PSHA were referenced to determine SS and S1 for this site.
TABLE 6
CALIFORNIA BUILDING CODE 2010
SEISMIC PARAMETERS FOR NEW STRUCTURES (SITE CLASS Q
Spectral Response Acceleration(SRA)
and Site Coefficients Short Period 1-Second Period
Mapped SRA S,= 1.25g S,=0.42g
Site Coefficients Fa= 1.0 F,=1.39
Maximum Considered Earthquake SRA SMS= 1.25g SM,=0.58g
Design SRA SDS=0.83g SDI=0.38g
11.2 Cuts and Excavations
11.2.1 Stability
Consistent with conventional construction practice, temporary excavation slopes should
be made the responsibility of the Contractor. The Contractor is continually at the site and is able
to observe the nature and conditions of the subsurface materials encountered, including
groundwater, and has responsibility for the methods, sequence, and schedule of construction. If
instability is detected, slopes should be flattened or shored. Regardless of the construction
method used, all excavation work should be accomplished in compliance with applicable local,
state, and federal safety codes.
Unsupported, temporary excavation slopes may be used where planned excavation limits
will not:
■ Undermine existing roadways, structures, utilities, or other facilities;
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■ Interfere with other construction; or
■ Extend beyond construction limits.
Where there is not enough area for sloped excavations, temporary shoring should be
provided. If shallow temporary shoring is required,we recommend that it be designed to
withstand the lateral earth pressures provided as Figure G-1 in Appendix G.
Stability of excavated slopes will depend on the following factors: (a) the presence of
groundwater; (b) the type and density of the soils; (c) the depth of excavation; (d) surcharge
loading adjacent to the excavation such as that from excavated material, existing facilities, or
construction equipment; and (e) the time of construction. For planning purposes, we recommend
that temporary slopes be excavated at no steeper a slope than 1.5 horizontal to 1 vertical
(1.5H:IV) in loose to medium dense, near-surface, native soils or fills up to 20 feet in height.
Steeper slopes may be achievable depending on site conditions and construction time.
Flatter slopes or slope protection could be required where seepage is present or during wet
weather conditions. Plastic sheeting could be necessary to protect the slopes from erosion and
raveling in wet weather. It should be expected that the cut face could experience some sloughing
and raveling. Fill should be carefully compacted on the slope face in a series of horizontal
benches, or the fill embankment could be overbuilt and cut back to a 2H:IV configuration.
Except as otherwise designed and/or specifically covered in the contract, the Contractor
should be made responsible for control of all surface and groundwater encountered during
construction. In this regard, sloping, slope protection, ditching, sumps, trench drains,
dewatering, and other measures should be employed as necessary to permit proper completion of
work. Evidence of a regional groundwater table was detected during drilling of vertical
boreholes along the alignment at depths in excess of 40 feet. Consequently, we do not anticipate
that major groundwater seepage will be encountered for the project provided that excavations
due not exceed 40 feet in depth. However, localized perched groundwater zones are likely to
occur due to presence of layers with increased clay or silt content. If seepage is encountered, the
Contractor should be prepared to provide trenches and sump pumps to control groundwater
during excavation activities.
11.2.2 Rippability
The on-site soils and igneous rock boulders at the site are anticipated to be excavatable
within the limits of the proposed alignment. Isolated boulders or areas of less weathered rock
that may be more difficult to excavate than the rock encountered at our boring and test pit
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locations, could exist in areas not explored during our fieldwork. Based on the Caterpillar
Performance Handbook Edition 41 (Caterpillar, Inc., 2011), the on-site soils are considered
rippable with heavy, track-mounted dozers equipped with a single-tooth ripper. The larger
boulders may have to be broken up with a hoe-ram or light blasting, if permissible.
11.2.3 Grading Factors
Grading factors for on-site materials by laboratory testing is not possible due to the nature
of the rocky materials (gravel, cobbles and boulders). Based on our previous experience, grading
factors for the on-site soils mixed with cobbles and boulders could increase in volume by 5 to 10
percent depending on the Contractor's ability to break large rocky materials into pieces suitable
for use as fill. Soils with little or no cobbles and boulders may decrease in volume when the
material is excavated and placed as engineered fill. An approximate 10 percent decrease in
volume may be expected for soil with few or no cobbles or boulders. The actual percent of
shrinkage will be dependent on the degree of compaction used when placing the fills. Soils
compacted to 95 percent relative compaction will have a higher percent volume shrinkage than
soils compacted to 90 percent relative compaction. It is our opinion that an accurate prediction
of overall grading factors for the project is not possible. Therefore,we recommend that the
grading plans provide for either changes in grade or spoils and borrow areas to accommodate
some shortage or excess of materials.
11.3 Embankment Stability
For fill embankments constructed using the requirements for structural fill placement and
compaction outlined in Section 15.3, permanent fill slopes should be constructed no steeper than
2H:IV for stability and maintenance considerations. If wetted by surface water, the slopes may
be subject to erosion. Slope protection, including use of a plastic covering weighted down with
sand bags, should be employed, as appropriate, to reduce erosion.
We evaluated global stability of existing UPRR embankment for both static and seismic loading
conditions by using the computer program SLOPE/W Version 7.18 (Geo-Slope International,
2007). Our evaluation used the General Limit Equilibrium method of analysis. For seismic
analysis,we applied a horizontal acceleration (kh) of 0.16g, equal to one-third of the PGA
(Caltrans, 2009b). The post-seismic (liquefied) condition was not analyzed because the
groundwater table is well below the base of the embankment and therefore soil liquefaction is
not an issue at the site.
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The results of these analyses indicate that the existing UPRR embankment slopes are stable with
a minimum calculated factor of safety of 1.3 for static conditions and 1.1 for seismic conditions.
Complete results of our analyses are presented in Appendix F. In our opinion, the existing and
proposed slopes at the project site will be stable for both static and seismic conditions.
11.4 Tunnel Design and Construction
11.4.1 General
We understand the preferred tunnel construction method will involve pipe jacking a
precast, reinforced concrete tunnel through the UPRR embankment. Pipe jacking is a trenchless
construction technique, in which the tunnel will be shoved through the embankment by hydraulic
jacks that rely on the stability of a reaction block located at one side of the crossing. For the
purposes of this report,we have presumed that the jacking system will be constructed on the
south side of the UPRR embankment. The reaction system anticipated to be used for this project
would include the installation of large-diameter drilled piers. Alternative reaction systems, such
as a large soil embankment, driven piles, etc., are considered suitable for the project; however,
due to the limited available room for constructing the large embankment, the close proximity to
the nearby mobile home park, and the presence of numerous boulders within the alluvium soil,
we anticipate that these systems may not be feasible.
As the tunnel is jacked through the ground, a variety of excavation procedures may be
used, such as building up a plug in the tunnel box to minimize ground loss and surface settlement
or excavating at the face to relieve face pressure and reduce jacking pressures. For large-
diameter pipe jacking such as this project, a tunneling shield or tunneling machine is typically
attached to the leading edge of the precast box structure to cut through the embankment materials
and provide support for soils at the face of the excavation. Shields are configured to address a
wide variety of ground conditions and, consequently, should be carefully designed or selected.
Proper design and use of the shield can facilitate rapid excavation and advance, while controlling
ground loss, settlement, and alignment of the tunnel. The tunneling shield is typically only about
1 to 1.5 inches larger in diameter than the tunnel itself, allowing a tight fit and reducing the
potential for ground loss and excessive skin friction as the tunnel is advanced. The annular gap
produced by this overcut should be filled with bentonite mud, as discussed later, to lubricate the
outside of the tunnel box, and to reduce ground loss. The use of an inclined face shield equipped
with sand decks and augmented with breast doors or breasting bulkheads can prevent significant
ground loss and protect the tunnel crown area, thereby reducing the potential for settlement
above the jacked tunnel. The excavation methods and ability to work at the tunnel face are also
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controlled by the shield design. A critical issue for this project is the presence of large-diameter
boulders and the possibility of an old wood trestle that may necessitate excavation immediately
in front of the leading edge of the shield. Photograph 2 presents a typical inclined face shield
with sand decks and doors.
jr -
F.
Photograph 2—Inclined-face digger shield equipped
with sand decks and augmented with breast doors.
11.4.2 Embankment Stabilization by Ground Freezing
The results of our field investigation revealed highly variable materials within the UPRR
embankment consisting of silty sands with cobbles,boulders, and possible remnants of a timber
railroad trestle. The embankment soils are considered to be cohesionless and would require
stabilization to mitigate ground loss or chimneying that could threaten the UPRR track subgrade.
The risk of running ground and raveling of the face is exacerbated by the vibrations from
overhead train passage and by possible boulders located around the perimeter of the shield, and
that may require over-excavation for removal. Hence,preventing ground loss above the tunnel is
a critical design and construction challenge to avoid settlement or other adverse impacts to the
UPRR track subgrade. Two methods of stabilizing the embankment soils were considered for
the project: 1) ground freezing and 2) a pipe arch canopy in the shape of a half-moon or
horseshoe over the tunnel. Ground freezing has the ability to solidify the soil, boulders, and
timber into a solid mass, and will extend 2 to 3 feet radially around each freeze pipe. Due to the
high percentage of silt in the embankment, grout penetration outward from the perforated pipes
of a pipe arch canopy is uncertain. Therefore, ground freezing is considered to be the preferred
stabilization method for this project.
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Ground freezing involves the installation of freeze pipes drilled every 3 to 4 feet,
typically with two overlapping rows of 3-inch brine circulation pipes around the top half to two-
thirds of the planned tunnel perimeter. An approximate 3- to 6-foot-thick, horseshoe-shaped
canopy of frozen ground would then be created for pre-support of the soil down to the tunnel
mid-height as shown in Figure 14. The freeze pipes should, in our opinion, extend portal to
portal. Daylighting the pipes at both ends would allow verification of each pipe's location,
which is critical to ascertain that the pipes are not within the shield horizon and are appropriately
spaced to get a continuous arch of frozen ground. Access to both ends of each pipe would allow
for easier repair or maintenance in the event of pipe rupture and disruption of the freezing
operation. Due to the relatively dry condition of the embankment fill, small amounts of water
would have to be injected into the embankment soils through drilled in perforated pipes to enable
the fill soils to be frozen. Due to the depth of overburden above the tunnel crest,we do not
anticipate track heave to occur due to freezing or pipe jacking, and as discussed later, a
monitoring program should be implemented observe any settlement or heave and to allow
corrective action to be taken by the contractor.
The area around the tunnel must be uniformly saturated so that unfrozen zones of
embankment fill materials do not occur that could run into the shield face during tunneling.
Careful alignment of the freeze pipes will be essential so they are located at least 2 to 3 feet
outside the shield perimeter in order to minimize potential bending damage to the pipes or the
possibility of encountering and breaking a freeze pipe and releasing brine into the ground, which
would inhibit further freezing efforts. A non-freezing lubricant or heating coils may be needed
along the outside of the shield and rectangular pipe to prevent it from being frozen in place
during a prolonged stoppage. The freeze system needs to be established at least a month before
construction and must be diligently maintained and operated until the tunnel is fully in place,
which may require additional on-site personnel to operate and maintain the freeze system. A
backup power supply would also be required because power supply failure could result in
thawing and ground loss.
11.4.3 Box-Jacking
Bentonite or foam-lubricating slurry should be pumped during box jacking through
regularly spaced grout ports through the perimeter of the tunnel to fill the annular space,which
reduces friction between the soil and the tunnel and fills the void to reduce settlement. When the
tunnel is in place, grout should be pumped through the ports to displace or consolidate the slurry
and permanently fill any voids between the soil and the tunnel, providing positive long-term
settlement control.
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To create an unobstructed pathway for the box jacking, any large-diameter boulders
encountered by the cutting edge of the shield would have to be mechanically broken up to allow
removal and permit forward advance of the tunnel. The shield should be jacked forward so as to
"cookie-cut"its way through the fill materials. During mechanical excavation with a backhoe
blade or vibrating hydraulic rock hammer, the undercut sandy fill materials could tend to ravel
inward, unless is it grouted or frozen. Also, a combination of sand decks and mechanically
closeable"breasting" doors should be required and used to limit over excavation or ground loss
ahead of and potentially above the shield.
In general, the specifications should allow the Contractor to select the type of box jacking
shield to install and alternatives to stabilize running soil. Any over-break around the top of the
shield and below the frozen ground should be filled with a low strength grout. The grout might
consist of a very lightly cemented bentonite mix or similar that is essentially incompressible, but
will not bond to the exterior of the shield or jacked steel pipe.
11.4.4 Jacking Loads
Jacking loads for advancing the box tunnel through the ground are primarily a function of
the friction between the soil and rectangular box along its path, the face pressure needed to retain
stability of the soil, and the thrust along the cutting edge of the shield needed to penetrate the
ground. As previously mentioned, injecting bentonite slurry and/or synthetic polymers through
grout ports regularly spaced at the quarter to third points around the box will help to fill voids as
well as to reduce the skin friction.
For this project, a challenging aspect will be the excavation of boulders and a buried and
abandoned wooden trestle during advance of the tunnel. It is our opinion that excessive jacking
against large-diameter boulders will likely result in damage to the jacked pipe. Consequently,
the Contractor who is awarded the work should anticipate excavating numerous high strength
granite and basalt boulders up to 10 feet in diameter, as well as abundant cobbles, as the shield
and box are advanced. Additionally, the boulders and embankment fill material remaining below
the tunnel invert will add a significant component to the friction along the bottom and increase
the resulting required jacking loads. The Contractor should be required to inject bentonite or
other lubricant through the shield and box invert, sidewalls, and crown to reduce this frictional
resistance. The Contractor should determine the anticipated jacking loads and provide sufficient
jacking capacity, including capacity to provide for a margin of safety. We estimate friction and
adhesion between the box exterior and the embankment soils to range from 100 to 400 psf and
consequently for jack loads to be on the order of 700 to 1,400 tons, depending on shield size,
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thickness of the cutting edge,roughness of the exterior of the jacked pipe, boulders and other
debris trapped in front of the cutting edge, completeness of lubrication, adhesion of ice and
frozen soil, and straightness of the alignment.
11.4.5 Lateral Earth Pressures on Tunnel Walls
Based on laboratory testing and engineering analysis, the tunnel walls should be capable
of resisting an "at-rest" lateral earth pressure equal to an equivalent fluid pressure of 61 pounds
per square foot (psf)per foot.
11.4.6 Tunnel Surcharge Loads
The train live load surcharge (equivalent to two simultaneous Cooper E-80 axle loads)
should be considered to be a 2,400 psf uniform surcharge on the embankment,with 20 feet of
soil cover top of the tunnel. This load should be applied over a width equal to the outer width of
the railroad ties (typically 8.5 feet) for both sets of tracks plus the overburden load caused by the
depth of embankment over the top of the tunnel. The dead load should be calculated using the
soil unit weight of 130 pcf for the embankment soil and 140 pcf for frozen ground.
11.5 Retaining Walls
Retaining walls will be constructed on both sides of the pedestrian underpass and MUP. The
proposed portal headwalls and retaining walls may be supported on shallow spread foundations
or drilled cast-in-place piers (or shafts). For the purposes of this report, we have assumed the
retaining walls will be supported on shallow conventional spread foundations.
11.5.1 Shallow Foundations
Shallow foundations distribute continuous wall loads to the underlying soil at a nominal bearing
pressure. The subsurface conditions encountered in the borings and test pits performed along the
alignments indicate that wall foundations will mostly bear on dense, gravelly sands; engineered
fill; or a combination of these materials.
11.5.1.1 Bearing Resistance
Shallow foundation load capacity is governed by the strength and settlement
characteristics of the underlying soil strata. In the load and resistance factor design (LRFD), the
bearing resistances for strength and extreme event limit states are obtained by selecting
appropriate soil strength parameters and computing a nominal bearing pressure at which shear
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failure of the bearing soil would likely occur. For our analyses,we assumed the portal
headwalls and MUP retaining walls would be supported on spread footings bearing at least 2 feet
below lowest adjacent soil grade. The nominal bearing resistance, when multiplied by the
appropriate resistance factor, gives the factored bearing resistance. The service limit for bearing
resistance is controlled by settlement. Bearing resistance analyses were performed using an in-
house spreadsheet for the anticipated bearing soil for various footing widths. Our analyses
results are presented as Figure G-3 in Appendix G.
Based on the anticipated wall heights of less than 16 feet, the recommended
allowable bearing pressure, and our experience with similar structures, we estimate total
settlements for the reinforced concrete retaining walls to be on the order of 1/z inch. Differential
settlements would be about one-half of the total settlements over a distance of approximately
30 feet along the wall alignment. Because of the anticipated granular nature of the foundation
soils,we anticipate that the majority of the estimated settlements would occur as the loads are
applied during construction.
11.5.1.2 Shallow Foundation Lateral Resistance
Resistance to lateral forces caused by wind, seismicity, unbalanced earth
pressures, and/or other forces can be provided by both passive earth pressures acting against the
embedded portion of foundations and frictional resistance against the base of foundations. We
recommend an allowable coefficient of friction of 0.45 be used between cast-in-place concrete
and subgrade soil for calculating the resistance to sliding at the base of the footings. Additional
lateral resistance may be assumed to develop against the vertical face of the foundations and may
be computed using an allowable passive lateral earth pressure equal to an equivalent fluid
pressure of 300 psf per foot of depth. These two modes of resistance should not be added unless
the frictional component is reduced by 50 percent since full mobilization of the passive
resistance requires some horizontal movement, which significantly diminishes the frictional
resistance. Additionally, the passive resistance value is based on the assumption that the footings
extend at least 2 feet below lowest adjacent grade and that a minimum of 5 feet exists between
the bottom of the foundation and nearest slope.
11.5.2 Wall Drainage
Even though the site is 30 to 40 feet above the measured groundwater table, a suitable
drainage system should be installed to prevent the inadvertent buildup of groundwater pressures
behind the portal and retaining walls during heavy rains, spring thaw and flooding. A 1-foot-wide
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drainage blanket consisting of Class 2 permeable materials (Caltrans Specification Section 68-
2.02F) should be constructed between the base of the wall extending to within 1 foot of the top
of the wall or proprietary geocomposite drainage board. The top foot of the drainage layer
should consist of compacted on-site materials,unless covered by a concrete slab or pavement.
Weep holes or perforated rigid pipe should be provided at the base of the wall to collected
accumulated water that could develop due to rapid snow melt or possible flooding. Drain pipes,
if used, should slope to discharge at not less than 1 percent fall to suitable drainage facilities.
Open-graded, '/z- to 3/4-inch clean crushed rock may be used in lieu of Class 2 permeable
materials if the crushed rock and drain pipes are completely enveloped in an approved non-
woven geotextile filter fabric.
Structural backfill materials for the retaining wall, other than the drainage layer, should
consist of on-site or imported granular soils as described in Section 15.3. The drainage layer
should consist of Class 2 permeable materials as described in Section 15.4.
11.5.3 Lateral Earth Pressures for Portal Headwall and Retaining Walls
We developed lateral earth pressure recommendations for the portal headwall and
retaining walls in general accordance with the American Association of State Highway and
Transportation Officials (AASHTO) LRFD Bridge Design Specifications (2010) and Caltrans
(2004). Earth pressures were calculated using the Rankine theory. The type of earth pressure
used for design depends on the ability of the wall to yield in response to the earth loads. For
walls that are free to slightly rotate about their base (i.e., flexible walls and walls on spread
footings that are able to move horizontally a small amount), active pressures should be used.
Flexible walls are further defined as being able to displace laterally at least 0.001H, where H is
the height of the wall. Non-yielding walls should be analyzed using the at-rest lateral earth
pressures. Non-yielding walls include abutment walls tied into the tunnel, wall corners, and
braced walls (i.e., walls that are cross-braced to another wall or structure).
Lateral earth pressures to be used for design of the proposed walls for fully drained
conditions are detailed as Figures G-1 and G-2 in Appendix G. Abutment and portal walls
adjacent to the tunnel will potentially be in the at-rest state, as they may be restrained from
movement. Consequently, we considered active,passive, and at-rest pressures for the abutment
walls. We recommend the backslope behind the walls be no steeper than 2H:IV. Lateral earth
pressure diagrams include surcharge and seismic loads.
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Seismic lateral earth pressures against the walls were calculated using one-half times the
PGA and the Mononobe-Okabe procedures (Mononobe and Matsuo, 1929; Okabe, 1926), which
is based on a pseudo-static model. This approach assumes the wall backfill is completely
drained (i.e.,not susceptible to liquefaction) and cohesionless. Current practice indicates the
seismic lateral earth pressure is a rectangular-shaped distribution with depth and the resultant
dynamic force should be applied at one-half times the height of the retaining wall (AASHTO,
2010).
11.5.4 Global Stability
We performed global stability analyses for selected cross sections and subsurface
conditions for the proposed MUP retaining walls by using SLOPE/W as described above. The
walls were evaluated under static and seismic loading conditions. For seismic analysis,we
applied a horizontal acceleration (kh) of 0.16g equal to one-third of the PGA (Caltrans, 2009b).
The post-seismic (liquefied) condition was not analyzed because soil liquefaction is not
anticipated at the site.
We assumed the walls were internally stable and, if required,modeled the wall as a very
stiff soil element with high cohesion to force the failure surface around/beneath the wall. We
assumed a minimum embedment of 2 feet for the retaining wall foundations.
Results of our global stability analyses indicate the proposed walls would be stable with
factors of safety ranging from 1.9 to 2.8 for static conditions and about 1.4 to 2.0 for seismic
conditions. These calculated factors of safety exceed the minimum recommended factors of
safety of 1.3 for static conditions and 1.1 for seismic conditions. Complete results of our
analyses are presented in Appendix F.
11.6 Box-Jacking Tunnel Foundation
11.6.1 Drilled, Cast-in-place Piers
We considered 4-foot-diameter drilled piers for the reaction pile system for the tunnel
jacking. The following sections provide our recommendations for axial and lateral resistance of
the drilled piers. Construction considerations for the drilled piers are provided in Section 14.2 of
this report.
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11.6.1.1 Axial Resistance
Axial resistance analyses were performed in general accordance with AASHTO
LRFD Bridge Design Specifications (AASHTO, 2010).
We evaluated axial resistance drilled piers for service, strength, and extreme limit
states. The analyses were based on the subsurface conditions encountered in the project borings
and our experience with similar soil and project conditions. Subsurface conditions anticipated to
be encountered during the drilled shaft construction include silty, gravelly sands with boulders
and cobbles. We estimated unit side and tip resistance values based on the average SPT values
(N-values) and laboratory test results.
Results of our axial resistance analyses for the 4-foot-diameter drilled piers are
presented as Figure G-4 in Appendix G. These results are presented as plots of nominal and
factored axial resistance versus depth for service, strength, and extreme event limit states.
Recommended resistance factors for each limit state are provided beneath each plot. To evaluate
the factored uplift resistance,we recommend using the nominal side resistances shown on axial
resistance plots with a resistance factor of 0.55 for the on-site soils. Recommended resistance
factor values could be increased if a test program is implemented for the project.
11.6.1.2 Lateral Resistance
To evaluate the lateral resistance of the drilled piers, we have developed soil
parameters that may be used with the LPILEPi'us (Ensoft, Inc., 20 10) computer program Version
5.0.46 and are summarized in Table 7. Soil liquefaction is not anticipated for this project,
therefore,we recommend using the static LPILEPLus parameters for seismic loading conditions.
TABLE 7
L-PILE INPUT PARAMETERS
Effective Unit Friction
p-y Curve Top Layer Bottom Layer Weight Angle (gyp) p-y Modulus
Model (feet) (feet) ( ci) (degrees) ( ci)
Sand (Reese) 0 8 0.069 30 90
Sand (Reese) 8 50 0.078 32 225
Note:
pci=pounds per cubic inch
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12.0 MATERIAL SOURCES
The native soil along the project alignment is considered suitable for use as fill materials if free
from rubbish, rubble, organic concentration, or deleterious debris. However, boulders will be
encountered in some areas that will be difficult to break down to a size suitable for use as
engineered fill. The boulders may breakdown by using pneumatic jackhammers mounted on
large excavators. Contractors should be aware that oversized material must be crushed to less
than 12-inch-diameter particles and thoroughly mixed with soil to produce a well-graded
material with no gap grading.
Rock exceeding 12 inches up to a maximum diameter of 24 inches may be allowed in deeper
fills. If used in deeper fills, the oversized rock should be spread and thoroughly mixed with soil
to avoid excessive concentrations or nesting. Boulders should not be placed in contact with each
other to reduce the chances of voids being created within the fill. The use of large rocks also
should be minimized in areas where later excavation is likely, such as for underground utility
lines.
13.0 MATERIAL DISPOSAL
Typically, during construction the excavated materials are stockpiled, testing is performed, and
the materials are classified as non-hazardous waste, California hazardous waste, or RCRA
hazardous waste prior to offsite disposal. Alternatively, if excavation limits are well-defined
prior to construction and the excavation sequencing can be closely controlled during
construction, additional preconstruction characterization could be performed. This alternative
requires additional preconstruction and construction oversight effort, but streamlines the
construction process by minimizing stockpiling requirements and eliminating waiting for test
results.
The nearest disposal site that accepts non-hazardous materials and/or construction debris is the
Lockwood Landfill in Sparks,Nevada. Additional effort may be worthwhile to identify other
potential off-site disposal facilities and their requirements for disposing of the excavated material
that will be generated during construction. In addition to disposal rates, facility-specific
information of interest would include transportation modes and distances, materials handling
facilities and capacities, and physical and chemical characterization testing requirements.
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14.0 CONSTRUCTION CONSIDERATIONS
14.1 Construction Advisories
Prior to site grading, construction areas should be cleared of all surface and subsurface structures
associated with current development of the site including all foundations, concrete pavements
and asphalt concrete,utility poles, fence poles, underground utilities, undocumented fills, and
other deleterious debris. Trees or shrubs designated to be removed should include the entire
rootball and all roots larger than 1/z-inch-diameter. This may require that laborers handpick roots
from the subsurface soils prior to compaction.
Difficulty in achieving subgrade compaction or unusual soil instability may be indications of
loose fill associated with past subsurface items such as unknown utility lines or previous test pits.
Should these conditions exist, the unsuitable materials should be excavated to check for
subsurface structures and the excavations backfilled with structural fill placed and compacted in
accordance with Section 15.3 of this report.
Numerous underground utilities are crossed by or run parallel to SR-89 and the proposed
improvements. Affected utilities could include several or all of the following:
■ Storm drains ■ Fiber-optic cables
■ Sanitary sewers ■ Telephone/cable lines
■ Natural and high-pressure gas lines ■ Traffic signal conduits
■ Water mains ■ Electrical conduits
These utilities could require abandonment, relocation, or replacement prior to construction.
Existing utilities that are not relocated could require additional protection against heavy surface
loads caused by fills, tracks,pavements, or other structures. The following sections present our
recommendations for design and construction planning of new underground utilities and
considerations for existing utilities.
Types of excavations included in this project could consist of: (a)trench excavations for new
pipes, (b) excavations for manholes or vaults, or(c) excavations to replace existing utilities. The
type of excavation support system selected for construction of proposed utilities would depend
on the proposed depth of excavation, the proximity to existing structures, and the depth to
groundwater. Since the project is located in a largely undeveloped area outside of the existing
yard, it is anticipated that most of the trench excavations greater than 4 feet deep could be
sloped.
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The Contractor should select the best excavation method, and must consider worker safety and
the potential impacts of ground movements on adjacent facilities (particularly in the existing
yard). In addition, the excavation must conform to all federal, state, and local safety regulations.
The Contractor should be held solely responsible for all damages related to ground movements
resulting from trench excavations.
Utility trench bedding and backfill for new or relocated underground utilities should conform to
pipe manufacturer's recommendations and local agency requirements. Trench backfill should be
composed of structural fill as described in Section 15.3, moisture-conditioned to within±2
percent of the optimum moisture content and uniformly compacted to at least 90 percent of the
maximum dry density (MDD)per ASTM D 1557.
Existing and proposed utilities could be located in areas where increased surface loads due to
construction equipment, soil stockpiles, etc. could be imposed. In areas where existing utilities
are under railroad tracks or roadways,the utilities could require protection against the heavy
surface loads, depending on the pipe type, load combination, and soil conditions. Existing
utilities could require protection using surface slabs or steel plates for load distribution, casing of
existing pipes, abandonment, or replacement of the existing pipe sections.
14.2 Construction Considerations that Influence Design
Horizontal borings through the UPRR embankment revealed a mixture of silty, gravelly sand
with intermittent boulders up to 5 feet in diameter. Additionally, horizontal boring BH-1
encountered remnants of the former wood trestle on the side of the proposed pedestrian
underpass. Due to the presence of boulders and the wooden trestle within the UPRR
embankment, specific recommendations to jack the precast tunnel have been provided in
Section 11.4.
Construction of drilled shafts for the tunnel jacking reaction system will require the boring of
holes of a specified diameter and depth, then backfilling the hole with reinforced concrete. The
selection of equipment and procedures for constructing drilled piers is a function of the shaft
dimensions, the subsurface conditions, and the groundwater characteristics. Consequently, the
design and performance of drilled piers can be significantly influenced by the equipment and
procedures used for construction and also by the method of placement and properties of the
concrete. Therefore, construction procedures and methods are of paramount importance to the
success of the drilled pier installation at this project site.
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Drilled pier contractors who participate in this project should be required to demonstrate that
they have suitable equipment and adequate experience in the construction of drilled piers using
generally accepted methods including the dry method, the casing method, and the wet method.
Based on the subsurface conditions encountered in our borings, in our opinion, drilled pier
installation for this project should proceed using the dry method.
14.3 Construction Monitoring and Instrumentation
We recommend that a geotechnical instrumentation program be developed to assist with
documenting and monitoring the Contractor's performance during construction of the project.
Specifically, the geotechnical instrumentation would be used to document and monitor work
performed near the deformation sensitive Mousehole tunnel and portals, utilities, railroad tracks,
and other improvements. The primary objectives of the geotechnical instrumentation program
are to:
■ Indicate whether or not the construction procedures used are generating surface and
subsurface ground movements within specified limits.
■ Provide early warning of adverse trends (i.e.,use of alarms and/or implementation of
action levels).
■ Provide the Engineer and Contractor with sufficient data to determine the source of
unanticipated ground movement and to plan remedial measures.
■ Determine when remedial measures need to be implemented to protect the UPRR
tracks and embankment, Mousehole Tunnel utilities, and other improvements.
■ Monitor the degree to which these protective or remedial measures are limiting
deformations, and to provide early warning when alternative means of protection are
necessary.
■ Provide data for settling potential legal disputes.
■ Monitor the performance of temporary construction structures (i.e., temporary
shoring).
■ Confirm design assumptions and provide data that could improve future designs.
We recommend geotechnical instrumentation and monitoring program include:
■ Preconstruction survey and documentation of adjacent existing structures and
facilities.
■ Measured horizontal and vertical movement of existing structures, temporary
construction structures, utilities, and other improvements adjacent to the alignment.
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■ Monitoring opening or closing of existing cracks in adjacent existing facilities.
■ Providing alert, alarm, or other action levels for monitored displacements or other
critical measurements.
The following sections describe information regarding these proposed activities.
14.3.1 Preconstruction Survey
Before beginning geotechnical instrumentation installation or construction, a
preconstruction survey of existing railroad tracks, Mousehole Tunnel and portals, structures, and
utilities along the project alignment and within the potential influence distance of proposed
construction should be undertaken. The survey should document the existing condition of each
facility with diagrams, sketches, photographs, and/or video recordings. For inaccessible
facilities, such as smaller diameter sewers, a closed-circuit television survey should be
performed. The survey records should include, but not be limited to, for example, length and
width of existing cracks,number of cracks, indications and locations of past or current seepage,
condition of Mousehole Portals, condition of paint, etc. Where applicable, the surveys should be
conducted in the presence of representatives of the buildings or facility owner,UPRR, the
Contractor, Caltrans, and the Town of Truckee. A formal report for each surveyed facility
should be developed and signed by each member of the group.
14.3.2 Geotechnical Instruments
The types, numbers, and locations of the geotechnical instruments depend on the
Contractor's proposed construction methods, sequence, and durations, as well as on the
proximity, foundations characteristics, and conditions of adjacent facilities. The instrument
types discussed in the following sections could be considered for use in the geotechnical
instrumentation and monitoring program. Included in this discussion is the suggested minimum
level of instrumentation that should be implemented for the monitoring program. In our opinion,
in addition to the quantities and locations of instruments described below, the contract
documents should also provide for additional points to be installed during construction to assist
the Engineer with evaluating the Contractor's performance and to assist with assessing the
reliability and readings from other instruments.
14.3.2.1 Deformation Monitoring Points (DMPs)
DMPs are fixed markers (survey hubs, pins, or targets), monitored, in conjunction
with standard surveying techniques, to evaluate vertical and horizontal deformations. DMPs are
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an effective method of monitoring ground and adjacent facility movements to assist with
assessing construction-induced impacts. DMPs include surface,near-surface, structure, and
utility settlement points, placed on roadways, utilities, structures, and near the ground surface,
for the purpose of monitoring changes in elevation of existing ground, roadway, structures, and
utilities. All settlement points are monitored by optical or laser survey methods to determine
displacements.
Surface settlement points (SSPs) typically consist of PK nails, survey hubs, or
bonded targets. SSPs are generally installed on new or existing pavement, or curbs, to be
monitored that are adjacent to excavations. We do not anticipate that SSPs will be needed for the
existing pavement of SR 89 or other nearby similar surfaces.
Near-surface settlement points (NSPs) consist of split-end settlement rods driven
into place to ensure that the rods will move with the soil in which they are embedded. Each
settlement rod is protected by and centered in a protective enclosure to prevent damage and
ensure that the settlement rod moves independently of the enclosure. In conjunction with optical
survey equipment,NSPs are used to monitor settlements under rigid pavement and settlements in
unimproved areas between excavations and settlement sensitive structures. We recommend
installation of NSPs along the existing embankment in three alignments parallel to the UPRR
tracks. One alignment would be located between the two mainline tracks, with a center NSP
located above the MUP tunnel alignment and then NSPs extending out at 10 foot spacing
between the tracks to 50 feet from the MUP tunnel centerline. The other two alignments of
NSPs would be installed parallel to the UPRR tracks and downslope along the existing
embankment, established to coincide with the headwalls of the existing Mousehole Tunnel. The
NSPs would be installed at 10 foot spacing, extending 30 feet northeast of the MUP tunnel
centerline, and extending southwest to the headwall of the existing tunnel. The NSPs along the
center of the tunnel alignment could be fitted with prism-style reflective targets for remote
monitoring of the rod positions.
Structure settlement points (STSPs) typically consist of survey targets or stainless
steel bolts, bonded to or mechanically anchored into structure walls or the top of shoring walls.
In conjunction with optical survey equipment, STSPs are used to monitor vertical and horizontal
deformations of existing or temporary construction structures, including temporary excavation
shoring. We recommend installation of three STSPs along the top of each portal headwall for
the existing Mousehole tunnel, spaced evenly along the width. In addition, STSPs should be
installed on the wall of the SR-89 tunnel closest to the construction activity, extending from the
end of the end wall to the other, at approximately 15 foot spacing. Along the lengths of the new
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retaining walls, STSPs should be installed near the top portion of the walls that are in excess of
10 feet in height. These points should be installed at approximately 25 foot spacing along the
wall, where applicable.
Utility settlement points (USPS) are reference points located on top of buried
utilities or structures. In conjunction with optical survey equipment,USPS are used to monitor
settlement of pipelines and buried structures. They should be installed on new and existing
settlement sensitive utilities that are located within 50 feet of planned excavations to monitor
their performance during construction.
14.3.2.2 Inclinometers
Inclinometers are used to monitor lateral movements in embankments, landslide
areas, deflections of retaining walls, and deformations of excavation walls and drilled shafts.
Inclinometers, if needed, should be installed at the vertical walls and at the crest and toe of the
proposed embankments to monitor lateral movement in the retained soil and in the embankment
and underlying soils.
14.3.2.3 Crack Monitors (CMs)
CMs are gages that may be used to measure cracks and joint openings in existing
structures. These gages should be installed on existing cracks and sensitive joints of adjacent
existing structures to monitor their performance during project construction. We anticipate that
CMs will be installed on cracks and sensitive joints in the Mousehole Tunnel and end walls that
may be identified during preconstruction surveys.
14.3.2.4 Optical Survey
Optical survey should include measurement of horizontal and vertical
deformation of existing structures, temporary construction structures, utilities, and other
improvements in conjunction with DMPs. Optical survey should be conducted by a registered
surveyor provided by the Contractor. The optical measuring system should have an accuracy of
at least '/io-inch and all optical survey measurements should be within '/8-inch.
14.3.2.5 Monitoring Frequency
Monitoring frequency would vary widely for each of the instrument systems and
for each category of construction. Instrumentation should be installed prior to construction, and
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a minimum of three measurements, ideally at least one week apart, should be obtained before the
start of construction to provide a stable baseline.
A typical monitoring frequency for DMPs is to monitor all points with each 5 feet
of tunnel advancement. At a minimum, the DMPs should be read once per week. Three sets of
readings should be taken at least 2 weeks prior to start of any excavation or tunneling. Following
construction of the tunnel,weekly readings should continue for a minimum of 2 weeks or until
all points indicate settlement rates of less than 0.1-inches per week. Readings should then be
performed on a monthly basis until the excavation is backfilled and/or the structure is completed.
One last set of readings should be taken at the end of the contract, immediately prior to removal
of the instruments.
14.3.2.6 Response Values
Measurements obtained should be evaluated and compared to established
response values to determine if any action level has been reached with the instrumentation. For
this project,Table 8 summarizes response values have been established for this project.
TABLE 8
SUMMARY OF PROJECT RESPONSE VALUES FOR CONSTRUCTION
Instrument Threshold Value Limiting Value
Surface Monitoring Point 0.25-inch H or V 0.5-inch H or V
and Arrays
Crack Meters +/- 0.25-inch +/- 0.5-inch
Notes:
H=Horizontal
V=Vertical
The threshold values represent a level of movement that warrants attention. The limiting values
represent the maximum level of movement or deformation a structure or utility can tolerate
without compromising safety and serviceability. If the instruments indicate that the threshold
values have been experienced, the Contractor should be required to establish and prepare to
implement remedial measures to mitigate the movement that is occurring. Threshold values are
typically some percentage of limiting values. If the instruments indicate that the limiting value
has been experienced, then remedial measures should be implemented immediately or
construction suspended to prevent damage to the structures being monitored.
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14.3.2.7 Data Reduction and Review
Monitoring of the instrumentation is useful for assessing the need for
implementing mitigation measures, as well as for resolving potential disputes, especially with
respect to the construction impacts on adjacent structures. Baseline measurements should be
established well in advance of construction (one to two months prior).
Because the collected and reduced data may be critical to assessing the successful
undertaking of the project, the data must be made available within a few hours to the Contractor
and owner's representative for their evaluation and should be easy to read and interpret.
Therefore,we recommend that data be reduced and presented within eight hours of the readings
being collected and that the data be presented in useful, legible, and well-labeled plots. Both the
total movement over the project life and the differential movement between the last two readings
should be presented. In general, the plots should include relevant construction information (i.e.,
excavation depth or deep foundation installed and/or stationing of the advancing construction).
Plots might also include geotechnical data, including soil layers and groundwater levels, or other
features that may impact the interpretation of the data.
The data report should document the readings collected and any pertinent
readings that may lead to significant adjustments in construction procedures. The results of the
monitoring should be compared to the response values established for each instrument.
14.4 Hazardous Waste Considerations
Relatively low concentrations of petroleum hydrocarbons as diesel and motor oil were detected
in near surface soils along the retaining wall alignments and within the UPRR embankment soils.
Discussions with representatives of Kiff Analytical indicate that the detected petroleum
hydrocarbons appear to have a higher boiling point that is typical of motor oil but is still reported
as diesel range hydrocarbons. Our review of the gas chromatographs from the tests indicates that
the petroleum hydrocarbons appear to represent a typical motor oil finger print.
Metals such as lead, copper, and zinc were detected at slightly elevated concentrations in one
boring (BV-2). The remaining borings did not reveal elevated concentrations of inorganic
chemicals. Based on the analytical testing, we conclude that the majority of the soil anticipated
to be excavated during construction would be classified as non-hazardous. However, we
recommend additional samples be collected from soil excavated in the vicinity of BV-2.
Samples collected from the excavated soils should be analyzed for STLC of lead, copper and
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zinc to determine if these soils should be characterized as non-RCRA hazardous waste. Our
office can assist in the collection and analysis of these samples.
In addition, we recommend a project-specific sampling and monitoring plan be prepared for the
project to evaluate aerially deposited lead along the project alignment prior to construction. The
sampling and monitoring plan should be prepared in general accordance with Caltrans
guidelines.
14.5 Differing Site Conditions
We assume that the exploratory borings and excavations completed for this project are
representative of the subsurface conditions throughout the construction area(i.e., the subsurface
conditions everywhere are not significantly different from those disclosed by the explorations).
If conditions different from those described in this report are observed or appear to be present
during construction, we should be advised at once so that we can review these conditions and
reconsider our recommendations, where necessary.
Unanticipated soil conditions are commonly encountered and cannot be fully determined by
merely taking soil samples or completing borings. Such unexpected conditions frequently
require that additional expenditures be made to attain a properly constructed project. Therefore,
some contingency fund is recommended to accommodate such potential extra costs.
15.0 EARTHWORK RECOMMENDATIONS
We recommend that site grading, excavation, and filling be performed under the observation of
our firm and in accordance with the recommendations contained in this report. The following
additional requirements should be included in the project plans and specifications.
15.1 Site Clearing and Grubbing
Prior to site grading, construction areas should be cleared of all undocumented fills, deleterious
debris, and all existing underground utilities designated to be removed or relocated including all
backfill. Trees and shrubs designated to be removed should include the entire rootball and all
roots larger than 1/2-inch-diameter.
Difficulty in achieving subgrade compaction or unusual soil instability may be indications of
loose fill associated with prior site usage or utility lines. Should these conditions exist, the
unsuitable materials should be excavated to check for subsurface structures and the excavations
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restored to grade with engineered fill placed and compacted in accordance with Section 15.3 of
this report.
15.2 Engineered Fill Construction
All fill should be placed in thin layers and uniformly compacted to a dense, unyielding condition.
In general, the thickness of the soil layers before compaction should not exceed 8 inches for
heavy, self-propelled, compaction equipment and 4 inches for hand-operated, mechanical
compactors. The appropriate lift thickness would depend on the Contractor's equipment and the
moisture content and quality of the fill material.
Sloping ground steeper than 6H:1 V should be benched prior to receiving engineered fill. Each
bench should consist of a level terrace excavated horizontally at least 4 feet into the hillside.
Benching should be done progressively up the hillside at vertical increments not exceeding 2
feet. Engineered fill placed on slopes steeper than 4H:1 V should be keyed into the natural
ground at the toe of the fill slope. The key should be excavated at least 2 feet into firm
undisturbed material as determined by our representative.
15.3 Structural Backfill
Structural fill should consist of native, on-site granular soils or a well-graded mixture of
imported granular soil that is free of organics, contaminants, and debris. Proper documentation
should be provided by the Contractor assuring the import materials are free of contamination
prior to being transported to the property. Structural backfill should possess a minimum sand
equivalency of 20 when tested in accordance with California Test 217 and meet the following
grading requirements (Caltrans, 2010c)provided in Table 9:
TABLE 9
MINIMUM GRADATION REQUIREMENTS FOR STRUCTURAL FILL MATERIALS
Sieve Size Percent Passing
3-inch 100
No.4 35-100
No. 30 20-100
The suitability of soil for use as structural fill would depend on its gradation and moisture
content. As the amount of fines (portion of soil particles passing a U.S. Standard No. 200 sieve,
based on the minus 3/4-inch fraction) increases, soil becomes more sensitive to small changes in
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moisture content, and adequate compaction becomes more difficult to achieve. Structural fill
placed during wet weather or on wet subgrade soils should contain no more than 5 percent fines.
During dry weather,the fines content could be higher, provided the fill is at suitable moisture
content, or could be moisture-conditioned and compacted to the specified degree. The fines
should be non-plastic, and the moisture content of the soil should be within±2 percent of the
optimum moisture content as determined by ASTM D 1557 (ASTM, 2011). Additional
information on wet weather construction is described in Section 15.5.
Structural backfill should be placed in thin lifts described above and uniformly compacted in
accordance with the following requirements (Table 10):
TABLE 10
RECOMMENDED MINIMUM DEGREES OF STRUCTURAL FILL COMPACTION
Recommended Minimum Percentage of
Location of Fill Modified Proctor Maximum Dry Density*
Beneath Structures 95
Beneath Pavement Areas 95
Landscaped Areas/General Fill(e.g. embankments) 90
Wall Backfill 95
Note:
* As determined by ASTM International Designation: D 1557-09,Methods B,C,or D.
Class 2 aggregate base,when used, must comply with the grading requirements for the sieve
sizes shown in Table 11 and possess the minimum aggregate qualities presented in Table 12
(Caltrans, 2010c). All aggregate base should be properly moisture conditioned to at least the
optimum moisture content and uniformly compacted to not less than 95 percent of the MDD as
determined by ASTM D 1557 (ASTM, 2011).
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TABLE 11
CLASS 2 AGGREGATE BASE GRADING REQUIREMENTS
Percentage Passing
3/4-inch Maximum Dimension
Sieve Size Operating Range Contract Compliance
2-inch -- --
1'/2-inch -- --
1-inch 100 100
3/4-inch 90 to 100 87 to 100
No. 4 35 to 60 30 to 65
No. 30 10 to 30 5 to 35
No. 200 2 to 9 0 to 12
TABLE 12
MINIMUM CLASS 2 AGGREGATE BASE QUALITY
Property Test Method Operating Range Contract Compliance
Resistance Value California Test 301 --- 78
Sand Equivalent California Test 217 25 22
Durability Index California Test 229 --- 35
15.4 Drainage Layer
Retaining walls should be fully drained to prevent the buildup of hydrostatic pressure behind the
wall. The drainage blanket should consist of either open-graded '/2 to 3/4-inch crushed rock or
Class 2 permeable rock that possesses a minimum Sand Equivalency of 75 when tested in
accordance with California test 217 and the grading requirements summarized in Table 13.
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TABLE 13
CLASS 2 PERMEABLE AGGREGATE BASE GRADING REQUIREMENTS
Sieve Size Percentage Passing
1-inch 100
3/4-inch 90-100
%-inch 40-100
No. 4 2540
No. 8 18-33
No. 30 5-15
No. 50 0-7
No. 200 0-3
15.5 Wet Weather Earthwork
Wet weather generally begins about mid-October and continues through about May, although
rainy periods may occur at any time of year. The Town of Truckee currently has a construction
grading moratorium that occurs during the period from October 15 through May 1 (Town of
Truckee, 2001). This should be considered in the construction schedule. Nearly all of the soil at
the site contains sufficient silt and fines to produce an unstable mixture when wet. Such soil is
susceptible to changes in water content, and tends to become unstable and difficult or impossible
to compact if their moisture content significantly exceeds the optimum. If earthwork at the site
continues into the wet season, or if wet conditions are encountered, we recommend the
following:
1. The ground surface in and surrounding the construction area should be sloped to promote
runoff of precipitation away from work areas and to prevent ponding of water.
2. Work areas should be covered with plastic. The use of sloping, ditching, sumps,
dewatering, and other measures should be employed as necessary to permit proper
completion of the work.
3. Earthwork should be accomplished in small sections to minimize exposure to wet
conditions. That is, each section should be small enough so that the removal of unsuitable
soil and placement and compaction of clean structural fill can be accomplished on the same
day. The size of construction equipment may have to be limited to prevent soil
disturbance. It may be necessary to excavate soils with an excavator located so that
equipment does not traffic over the excavated area.
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4. A subgrade stabilization geogrid is recommended for this site where heavy equipment will
traverse areas of the site that do not already contain gravel-based access roads.
5. Fill material should consist of gravel borrow with not more than 7 percent fines by dry
weight passes the No. 200 mesh sieve,based on wet-sieving the fraction passing the 3/4-inch
mesh sieve.
6. No soil should be left uncompacted and exposed to moisture. A smooth-drum vibratory
roller, or equivalent, should roll the surface to seal out as much water as possible.
7. In-place soil or fill soil that become wet and unstable and/or too wet to suitably compact
should be removed and replaced with clean, granular soil described above in item 5.
8. Excavation and placement of structural fill material should be observed on a full-time basis
by a geotechnical engineer(or representative) experienced in earthwork to determine that
all work is being accomplished in accordance with the project specifications and our
recommendations.
9. Grading and earthwork should not be accomplished during periods of heavy, continuous
rainfall.
We suggest that these recommendations for wet weather earthwork be included in the contract
specifications.
16.0 LINHTATIONS
This report should be provided to prospective contractors for information on factual data only
and not as a warranty of subsurface conditions, such as those interpreted from the exploration
boring logs and test pits, and discussions of subsurface conditions included in this report.
The analyses, conclusions, and recommendations contained in this report are based on site
conditions as they presently exist. If there is a substantial lapse of time between submission of
our report and the start of work at the site, or if conditions have changed because of natural
forces or construction operations at or near the site,we recommend that this report be reviewed
to determine the applicability of the conclusions and recommendations considering the changed
conditions and time lapse.
Within the limitations of the scope, schedule, and budget, the analyses, conclusions, and
recommendations presented in this report were prepared in accordance with generally accepted
professional geotechnical engineering principles and practices in this area at the time this report
was prepared. We make no other warranty, either express or implied. These conclusions and
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recommendations were based on our understanding of the project as described in this report and
the site conditions as interpreted from the current explorations.
Our firm should be given the opportunity to review the final plans and specifications to verify
that those documents have been prepared in general accordance with our geotechnical
recommendations.
Shannon&Wilson, Inc. has prepared the document, "Important Information About Your
Geotechnical/Environmental Report," in Appendix H to help you and others in understand the
use and limitations of this report.
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17.0 REFERENCES
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American Concrete Institute (ACI), 2008, Building code requirements for structural concrete and
commentary: ACI Committee 318, ACI 318-08, 471p.
ASTM International (ASTM), 2011, Annual book of ASTM standards, construction, v.4.08, Soil
and rock, (I): D 420—D 5876: West Conshohocken, PA, ASTM International, 1 v.
Brown,V.W., 2009, Geotechnical investigations at Martis Creek Dam, Truckee, CA: U.S. Army
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California Geological Survey (CGS), 2008,Naturally occurring asbestos hazard in Placer
County, California: California Department of Conservation,November 4, 1 sheet, scale
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California Department of Transportation(Caltrans), 2004, Foundation report/geotechnical design
report checklist for earth retaining systems, Memo to Designers 5-20, August, 11 p.
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design reports: Guidelines written by the Division of Engineering Services, Geotechnical
Services,V1.3, December, 26 p.
California Department of Transportation (Caltrans), 2007, Peak ground acceleration map,
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California Department of Transportation (Caltrans), 2009a, ARS Online web tool, v2.0.4,
accessed January 30, 2013: Available: http://dap3.dot.ca.gov/shake stable/v2/index.php
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California Department of Transportation (Caltrans), 2010a, Soil and rock logging, classification,
and presentation manual: Manual written by the Division of Engineering Services,
Geotechnical Services, 90 p.
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written by Caltrans, V1.6,November.
California Department of Transportation(Caltrans), 2010c, Standard specifications: Prepared by
the Business, Transportation and Housing Agency Department of Transportation, 1072 p.
California Department of Transportation (Caltrans), 2011, California amendments to AASHTO
LRFD Bridge Design Specifications (4th ed.), Sacramento, CA.
California Geologic Survey (CGS), 2012, Geologic map of the North Lake Tahoe-Donner Pass
Region,Northern Sierra Nevada, California, Map Sheet 60; CGS Department of
Conservation, Sacramento, CA, 45 p.
Cassella, D., 2006, DMA 2000 multi jurisdiction,multi-hazard mitigation plan for Nevada
County: Nevada County Office of Emergency Services, June 30, 204 p.
Caterpillar, Inc., 2011, Performance handbook(41st Edition),p. 1-75 through 1-79.
Ensoft, Inc., 2010, Computer program LPILEpLus version 5.0.46, technical manual: a program
for the analysis of piles and drilled shafts under lateral loads: Austin, Tex., Ensoft, Inc.
Federal Emergency Management Agency, 2010, Flood insurance rate map,Nevada County, CA
and incorporated areas: National Flood Insurance Program, Map 06057C0529E, 1 sheet,
scale 1" = 500'.
Gates, W.C.B., 1994, Regional slope stabilization of the Truckee River Canyon drainage basin
from Tahoe City, California to Reno,Nevada: Ph.D. thesis in Geology, University of
Nevada at Reno.
Geocon Consultants, Inc. (Geocon), 2009, Site investigation report,Nevada County, California:
Report prepared by Geocon Consultants, Rancho Cordova, CA,job no. 59300-06-82, for
Caltrans, Marysville, CA, December, 10 p.
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Google Earth, 2011, v. 6.1: Available: http://www.earth.goo lg e.com.
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21-1-21072-002-xi fmal.aocx/wp/aay 21-1-21072-002
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Reference: February 2013 21-1-21072-002
U.S.Geological Survey and California Geological Survey,2010, C
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