Southfork_Final_Geotechnical_Report.pdf

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SOUTHFORK ROAD

PARK COUNTY, WY

WY 6WX(1)

Final Geotechnical Report Report No. WY-FLAP-6WX (1)-18-01

Prepared by Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch December 2018 i

TABLE OF CONTENTS

SECTION ONE - INTRODUCTION

1.1 BACKGROUND AND LOCATION

1.2 SCOPE AND PURPOSE

SECTION TWO - FIELD EXPLORATION AND LABORATORY TESTING

2.1 FIELD EXPLORATION

2.2 LABORATORY TESTING

SECTION THREE - GEOLOGY, SEISMICITY, AND SITE CONDITIONS

3.1 GEOLOGY

3.2 SEISMIC DEISGN PARAMETERS

3.3 SUMMARY OF SITE CONDITIONS

SECTION FOUR - ANALYSIS AND RECOMMENDATIONS

4.1 FOUNDATIONS - BRIDGE EGF

4.1.1 Bridge Foundation Selection

4.1.2 Driven Pile Foundation Design

4.1.3 Pile Setup

4.1.4 Group Effects on Axial Resistance

4.1.5 Lateral Loads

4.1.6 Settlement

4.1.7 Pile Drivability

4.2 FOUNDATIONS - LITTLE BOULDER CREEK BRIDGE

4.2.1 Bridge Foundation Selection

4.2.2 Factored Bearing Resistance - Strength Limit State

4.2.3 Settlement Evaluation - Service Limit State

4.3 ABUTMENT DESIGN

4.4 EMBANKMENT CONSTRUCTION

4.5 CONSTRUCTION CONSIDERATION

4.6 SPECIFICATIONS

4.7 DISCLAIMER/LIMITATIONS

SECTION FIVE - REFERENCES

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TABLES

TABLE 2.1 Summary of Field Exploration Program TABLE 2.2 Pavement Boring Locations TABLE 2.3 Summaries of Laboratory Index Tests Results TABLE 2.4 Direct Shear Test Results TABLE 3.1 Summaries of Seismic Parameters for Earthquake with 1000-Year Return Period for Site Class D TABLE 4.1 Proposed Bridge Foundation Locations TABLE 4.2 Summary of Pile Design Recommendations TABLE 4.3 LPILE Parameters TABLE 4.4 Lateral Earth Pressures for Bridge Abutments TABLE 4.5 Cut Slope Recommendations

FIGURES

FIGURE 1 Vicinity and Location Map FIGURE 2 Bridge Boring Location Map FIGURE 3 Abutment 1 - Axial Resistance Plot FIGURE 4 Abutment 2 - Axial Resistance Plot FIGURE 5 Factored Bearing Resistance Plot

APPENDICES

APPENDIX A Boring Logs APPENDIX B Laboratory Data APPENDIX C Photographs

Southfork Road, WY FLAP 6WX(1)

SECTION ONE - Introduction

1.1 BACKGROUND AND LOCATION

This report presents the geotechnical investigation findings and provides geotechnical recommendations for the proposed Southfork Road rehabilitation project located approximately 25 miles southwest of the Town of Cody in Park County, Wyoming. The work will take place between mileposts (MP) 27.8 and

42.7 along Park County Road 6WX (Southfork Road) and will consist of the following construction activities: construction of new asphalt pavement from MP 27.8 to 35.3, aggregate resurfacing from MP

35.3 to 42.7, the replacement of bridge EGF over South Fork Shoshone River, the replacement of the Little Boulder Creek bridge, drainage improvements, and minor alignment shifts to optimize roadway geometry. Additional recommendations regarding proposed cuts and fills along the alignment are also provided. The approximate location of the bridges can be found in the vicinity map in Figure 1.

The two-span, 132-foot-long, bridge EGF over the South Fork Shoshone River was constructed in 1978 and is founded on spread footings that are likely above the design scour elevation. Scour evidence has been observed as documented in a 2017 bridge inspection report, particularly at the bridge center pier.

Furthermore, erosion of the upstream embankment near the west abutment has occurred. Proposed construction includes the replacement of the two-span bridge EGF with a single span bridge built at the same location, with the foundations constructed behind the existing abutment walls resulting in a slightly longer bridge length. The existing footings are currently assumed to be left in place and pre-drilling or coring through the footings may be required to construct deep foundations.

The Little Boulder Creek bridge is located on Hunter Creek Road, approximately 1 mile from Southfork Road. Survey of the bridge has not yet been completed. The current proposed replacement concept consists of replacing the bridge in the same location with a pre-fabricated single-span steel bridge founded on shallow foundations.

1.2 SCOPE AND PURPOSE

The scope of work includes geotechnical investigation and analysis to determine the subsurface profiles and ground water conditions at the foundation abutments, estimate material properties for foundation design, and provide AASHTO based design recommendations on foundation types/geometry, bearing resistance, settlement, global stability, and earth pressures. This report presents the findings of the subsurface investigation program and provides geotechnical recommendations for the design and construction of the Southfork Road rehabilitation project.

SECTION TWO – Field Exploration and Laboratory Testing

2.1 FIELD EXPLORATION

An engineer from the Central Federal Lands Highway Division (CFLHD) Geotechnical Group observed the field exploration program that was completed in July and October of 2018. The field investigation for the two bridge sites included site characterization, seismic geophysical testing, and drilling four borings.

The locations of the explorations are presented on Figure 2. A summary of the field exploration is provided in Table 2.1 and additional details are presented in the following paragraphs.

TABLE 2.1 - Summary of the Field Exploration Program

EXPLORATION

DESIGNATION

LOCATION

STATION OFFSET

GROUND

ELEVATION

TERMINATION

ELEVATION

EXPLORATION

DEPTH

BH-01

Bridge EGF Abutment #1

706+49 10-ft LT 6,098 ft 6,018 ft 80 ft

BH-02

Bridge EGF Abutment #2

708+10 10-ft RT 6,095 ft 6,005 ft 90 ft

HC-01

Little Boulder

Creek Not

Available Not

Available 6,432 ft 6,392 ft 40 ft

HC-02

Little Boulder

Creek Not

Available Not

Available 6,433 ft 6,398 ft 35 ft

Note: The exploration locations and elevations were estimated relative to features shown on the 95 percent project plans.

Additionally, six pavement borings, each 5 feet deep, along the Southfork Road alignment and four test pits ranging in depth from 10 to 12 feet at a potential fill borrow source were also completed. Table 2.2 presents the approximate location of the pavement borings and the approximate locations of the test pits are presented on Figure 1. The logs and laboratory test results are presented in Appendix A and Appendix B.

TABLE 2.2 - Pavement Boring Locations

EXPLORATION DESIGNATION LOCATION

PH-01 MP 42.3

PH-02 MP 40.2

PH-03 MP 38.3

PH-04 MP 34.9

PH-05 MP 32.9

PH-06 MP 29.9

GEOPHYSICAL TESTING:

On July 12, 2018, a CFLHD geotechnical engineer performed a seismic test near the proposed east abutment of bridge EGF shown on Figure 2. The intention of the geophysical survey was to supplement the boring data and to provide additional information regarding the seismic Site Class determination. The Multi-Channel Analysis of Surface Waves (MASW) method was selected for the seismic testing since the algorithm and software allows for data collection using “Active and Passive” acoustic sources allowing estimation of shear wave velocities to depths in excess of 100 feet. A series of (24) 4.5-Hz geophones spaced 5 feet apart for a total line length of 115 feet were connected to a Geode seismograph manufactured by Geometrics, Inc. A sledgehammer strike on a metal plate was used to initiate the readings, but only the naturally occurring ambient seismic energy was used as the source.

The field data was reduced by CFLHD geotechnical engineers using SurfSeis 4.2.4 software developed by Kansas Geological Survey. Equipment limitations, a fixed geophone spacing of 5 feet, resulted in data that could not be resolved to the desired depth of 100 feet. The portion of the data that could be reasonably well resolved indicated that the average shear wave velocity within the upper 50 feet is approximately 900 feet per second. Due to the difficulty resolving the data, detailed results are not presented.

EXPLORATORY BORINGS:

Elite Drilling Services, LLC. of Denver, Colorado provided the drilling services using a CME-550 truck-mounted drill rig. The borings at the bridges were advanced using an ODEX air-percussion hammer system while the pavement borings were advanced using 6-inch outside diameter hollow stem augers.

Upon completion of drilling activities, field personnel backfilled the borings with cuttings generated during the drilling.

Drilling was completed in two mobilizations due to equipment damage sustained while drilling boring HC-01. The first mobilization from July 12th to July 14th, 2018 included drilling the borings for bridge EGF, all pavement borings, and boring HC-01. The second mobilization included the drilling of boring HC-02 and the completion of boring HC-01, which was abandoned during the first mobilization when the ODEX bit was broken on cobbles and boulders at a depth of 24 feet.

Disturbed samples were obtained from the borings using the Standard Penetration Test (SPT), in accordance with AASHTO T-206. The SPT involves driving a 2-inch outside diameter, 1.375-inch inside diameter split spoon sampler 18 inches with a 140-pound hammer falling 30 inches and recording the blow counts per 6-inch of driving. An automatic-trip hammer was used to drive the samplers. The SPT N-value is the sum of the blow counts required to drive the sampler over the second and third 6-inch increments. The N-value provides a means for evaluating the relative density of cohesionless soils and consistency or stiffness of cohesive soils.

Difficulties were encountered sampling during borings BH-01 and BH-02 due to the presence of heaving sands below depths of about 40 feet. Once below about 40 feet, the fine to medium grained sands would heave several feet into the ODEX casing once the ODEX bit was removed. The sampler, therefore, could not reach the bottom of the hole to obtain representative blowcounts or samples. When this occurred, grab samples were taken from the ODEX cuttings with the understanding that these samples were highly disturbed and may be representative since the ODEX drilling system tends to pulverize larger particles.

Soil from the SPT split-spoon sampler and from grab samples were placed and sealed in plastic bags and were transported to the CFLHD Materials Laboratory for testing.

Logs of the explorations are presented in Appendix A. Photos of drilling equipment and field exploration activities are included in Appendix C.

2.2 LABORATORY TESTING

Soil samples recovered from the borings were tested in the laboratory to support the field classifications and to provide an estimate of the engineering characteristics and mechanical properties of the soil.

Laboratory tests included gradation (AASHTO T88), classification (AASHTO M145) and Atterberg limits (AASHTO T89 and T90). When the necessary tests were completed, samples were classified using the Unified Soil Classification System (USCS) and AASHTO soil classification system. A summary of the soil test results is shown in Table 2.3.

TABLE 2.3 - Summaries of Laboratory Index Test Results

BORING

NUMBER

SAMPLE

DEPTH, ft

PERCENT

SAND

PERCENT

PASSING 200

LL PI USCS AASHTO

BH-01 14 57 29 25 4 SC-SM A-2-4 (0)

BH-01 24, 29 75 5 NV NP SP-SM A-1-b (0)

BH-01 59, 64 73 27 NV NP SM A-2-4 (0)

BH-02 10 44 56 25 3 ML A-4 (0)

BH-02 20, 25, 30, 35 55 2 - - -

BH-02 55, 60 77 19 NV NP SM A-2-4 (0)

BH-02 70, 75 86 3 NV NP SP A-1-b (0)

Two direct shear tests (ASTM D3080) were performed on samples obtained from the borings to measure the Mohr-Coulomb shear strength parameters of the soil. The disturbed soil samples were remolded to an assumed in place density and moisture content prior to testing. Samples of similar composition were combined to provide a sufficient quantity of material to perform the tests. A summary of the direct shear test results are presented in Table 2.4.

TABLE 2.4 - Direct Shear Test Results

SAMPLE

LOCATION

PEAK STRENGTH PARAMETERS RESIDUAL STRENGTH PARAMETERS

FRICTION

ANGLE

degree

COHESION

INTERCEPT

psf

FRICTION

ANGLE

degree

COHESION

INTERCEPT

psf

BH-01 (59 ft to 64 ft) 33 289 32 90 BH-02 (20 ft to 35 ft) 44 277 32 84

The results of the laboratory tests are presented in Appendix B.

SECTION THREE–Geology, Seismicity and Site Conditions

3.1 GEOLOGY

The project is located within the valley floor between the Carter and Citadel mountains of the Absaroka Range. Geologic mapping of the area indicates that the current alignment is underlain predominantly by alluvial materials that are described as consisting of unconsolidated deposits of silt, sand, gravel, and cobbles. Small portions of the alignment may be underlain by areas mapped as landslide debris. These general descriptions appear to be consistent with the soils encountered in the borings and the laboratory test results. Bedrock is not expected to be encountered during the project, but geologic mapping indicates that it consists of volcanic sandstone, siltstone, conglomerate, and breccia.

3.2 SEISMIC DESIGN PARAMETERS

Recommended seismic response parameters for use in design are based on the 7th Edition of AASHTO, ground motion corresponding to an exceedance probability of 7 percent in 75 years for an earthquake with an approximate 1000-year return period. The 1000-year return period uniform hazard spectrum for the soils at the east abutment of bridge EGF (latitude 44.25415°N, longitude 109.51215°W) for the probabilistic horizontal acceleration values corresponding to specific ground acceleration (PGA) and spectral coefficients, namely the short- and long-period ground acceleration (Ss and S1) for Site Class D and the corresponding Seismic Zone are summarized Table 3.1. Based on the site class definitions specified in Table 3.10.3.1-1 of AASHTO and the limited available blow count and shear wave velocity data, a default Site Class D is recommended to be used for design for the loose to medium dense sands and silts. These seismic parameters can also be used for the Little Boulder Creek bridge. Based on these criteria, a peak ground acceleration (PGA) of 0.128 was assigned to the site.

TABLE 3.1 - Summary of Seismic Parameters for Earthquake with 1000-Year Return Period for Site Class D

Horizontal Peak Ground Acceleration, (PGA) 0.128 g Horizontal Response Spectral Acceleration at Period of 0.2 sec, (Ss) 0.292 g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (S1) 0.100 g

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.60 Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 1.60 Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 2.40

Factored Horizontal Peak Ground Acceleration, (As) 0.197 g Factored Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.458 g Factored Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.240 g

Seismic Zone Zone 2

The nearest active faults to the project, based on a USGS Earthquake Hazard Program database search, are the Upper Yellowstone Valley Faults. These faults follow an east-west trend and are located approximately 24-miles west of the south end of the project area.

3.3 SUMMARY OF SITE CONDITIONS

Bridge EGF The ground surface at the borings for bridge EGF consisted of asphalt pavement. The subsurface conditions at both abutment locations were generally consistent. Both borings encountered a layer of fill material consisting of a mixture of clay, sand, gravel, and cobbles to depths of about 8 to 12 feet.

Underlying the fill material was a layer of low plasticity silty, clayey sand to sandy silt approximately 7 feet thick. Once groundwater was encountered at a depth of 14 to 17 feet, a thick layer of medium dense poorly-graded sand was encountered that extended to a depth of 52 to 53 feet. The poorly-graded sand was predominantly medium to coarse grained, with little gravel or fines. Underlying the poorly-graded sand layer was a silty sand, mostly composed of fine grained sand which eventually graded to a sandy silt to the maximum depths explored, approximately 90 feet.

Due to heaving sands filling the drill casing during drilling, sampling below a depth of about 35 feet was not possible, and apparent density evaluations were not possible by SPT methods. However, apparent density was estimated based on the limited SPT information that was obtained, observations of the drill rig action during drilling, and perceived penetration resistance from the driller.

Groundwater elevations were measured during the subsurface investigation at elevation 6,081 feet in both borings. Fluctuations in the ground water level due to seasonal and climatic effects are expected.

Little Boulder Creek Bridge The gravel surfacing near borings HC-01 and HC-02 were in poorer condition than the gravel surfacing on Southfork Road with a slightly rougher grade and several minor depressions. The areas outside the gravel surfacing near the Little Boulder Creek bridge contained numerous cobbles and large boulders about 3 to 5 feet in diameter with occasional larger boulders exposed at the ground surface and on the banks of the creek. Subsurface conditions at the Little Boulder Creek bridge generally consisted of silty gravel with sand and abundant cobbles and boulders. The frequency of encountering cobbles and boulders generally increased with depth. The presence of cobbles and boulders was not observed in the drill hole or sampler, but inferred from the observed surface conditions, and the drill rig action, that included the damage of the ODEX drill bit. The diameter of the cobbles and boulders could therefore not be determined.

Groundwater was encountered during drilling at approximate elevations of 6,420 and 6,423 feet.

Pavement Borings The subsurface conditions at the location of the pavement borings consisted of either asphalt or gravel surfacing underlain by a fill base course, underlain by silty sand with gravel and occasional cobbles.

Asphalt pavement thicknesses ranged from ½ inch to 3 inches and base thicknesses ranged from 12 inches to 24 inches. The silty sand with gravel subgrade was generally dry to moist and difficult to drill by auger methods indicating that it is likely very dense.

Specific site descriptions are based on field observations, subsurface characterization information, and may vary in material type and strength with distance away from boring locations. This variability is due to topography and land forming processes.

SECTION FOUR – Analysis and Recommendations

The recommendations presented in this report are based on the subsurface conditions observed in the field explorations, laboratory test results, engineering analysis, and experience with similar projects. The following sections include recommendations regarding foundations for bridge EGF, foundations for Little Boulder Creek bridge, abutment design, embankments, construction considerations, and specifications.

4.1 FOUNDATIONS - BRIDGE EGF

The proposed bridge will be constructed in generally the same location but slightly longer than the existing bridge. The proposed single span bridge is approximately 150 feet long and will be supported by deep foundations. Based on the 95 percent design plans, the proposed abutment centerline stations and pile cap elevations are shown in Table 4.1.

TABLE 4.1:- Proposed Bridge Foundation Locations

FOUNDATION APPROXIMATE STATION BOTTOM OF PILE CAP ELEVATION*

Abutment 1 706+55.62 6,087.39

Abutment 2 708+05.62 6,085.35

*The bottom of pile cap elevations were estimated from information presented on the 95% design plans.

4.1.1 Bridge Foundation Selection

Deep foundations were selected as the preferred bridge foundation alternative. Shallow footings were determined to be unfeasible due to the design scour elevation provided by the hydraulics engineer of 6,071.7 feet (approximately 25 feet below existing ground surface).

Deep foundation options were evaluated based on feasibility and costs. Driven piles and drilled shafts are considered feasible based on the subsurface conditions (primarily sand, gravel, and silt) encountered.

Drilled shaft foundations are expected to be more costly than driven piles due to typical local construction practices, the construction staging requirements, and a longer time for construction. Therefore, it is recommended that the bridge be supported on driven H-piles.

4.1.2 Driven Pile Axial Resistance

Preliminary design analyses by the bridge team indicates that six HP 14x102 piles per abutment will be required to resist lateral loads associated with a long unsupported length resulting from the design scour elevation. The piles will gain axial resistance from side and tip resistance within the sand and gravel soils below the scour elevations presented in the project hydraulics report.

Based on the AASHTO guidelines, nominal axial resistance and loads should be factored by the appropriate resistance factor (φ) for Strength, Service, and Extreme Event limit state. Factored resistances are determined from estimated nominal pile resistances and resistance factors that are based on the construction and field verification methods. It is recommended that at least two piles (one at each abutment) be tested using the Pile Driving Analyzer (PDA) and signal matching at end of driving.

Inspector charts based on the wave equations will be developed by the contractor once the driving equipment and accessories are selected. In this case, a resistance factor of 0.65 should be applied to determine the factored resistance at the Strength Limit State (AASHTO Table 10.5.5.2.3-1). Based on this resistance factor, the design resistance lost to scour, and the design load at the Strength Limit State, the required nominal driving resistance is calculated and presented in Table 4.2. Note that if PDA testing is not performed, a resistance factor of 0.40 should be used.

TABLE 4.2:- Summary of Pile Design Recommendations

Foundation Location

Required Factored Nominal Resistance (kips)

Estimated Design Tip

Elevation(2) (ft)

Required Nominal Driving

Resistance

(kips/pile)

Strength Limit State

(Φ=0.65) (1)

Extreme Event Limit State

(Φ=1.0)

Abutment 1 354 230 6,047(3) 435 Abutment 2 354 230 6,045(3) 415

1. Assume PDA testing of at least 2 piles (one at each abutment).

2. Design tip elevation from comparison of axial requirements in the strength limit state and extreme event state, settlement, and lateral load requirements.

3. Minimum tip elevations presented on the bridge plans indicate all piles must reach an elevation of 6,047 and 6,045 to satisfy the lateral load requirements for abutments 1 and 2, respectively. The required axial resistance is expected to be reached at elevations 6,057 and 6,053 for abutments 1 and 2, respectively.

The nominal and factored axial resistances calculated using a static analysis using APILE software are presented on Figures 3 and 4. The estimated design tip elevations presented in Table 4-2 are based on the estimated elevation required for axial resistance based on the results of our static analysis. Minimum tip elevations are expected to be controlled by the required lateral resistance calculated by the structural engineer that will be shown on the project plans. Preliminary results provided by the structural engineer indicate minimum tip elevations of 6,047 and 6,045 feet for Abutments 1 and 2, respectively (estimated pile length of 40 feet). In all cases, the piles should be driven to at least the minimum tip elevation shown on the project plans.

4.1.3 Pile Setup

Pile setup is an increase in the nominal axial resistance that develops over time. When soils are compressed and disturbed due to pile driving, large excess pore pressures develop. These excess pore pressures are generated partly from the shearing and remolding of the soil and partly from radial compression as the pile displaces the soil. The excess pore pressures cause a reduction in the effective stresses acting on the pile, and thus a reduction in the soil shear strength. This results in a reduced pile resistance during, and for a period after driving. After driving, the excess pore pressures will dissipate primarily through radial flow of the pore water away from the pile. With the dissipation of pore pressures, the soil reconsolidates and increases in shear strength. This increase in soil shear strength results in an increase in the static pile resistance and is called soil setup.

It is recommended that the resistance gained by setup not be utilized for determining nominal resistance for the pile foundation since the majority of the soils encountered were cohesionless and the low cohesion silts are expected to have minor setup.

4.1.4 Group Effects on Axial Resistance

The resistance of a pile group to the applied axial loads is not necessarily the sum of the axial resistance of individual piles within the group. The zone of influence from an individual pile in a pile group may overlap with other piles, depending on the pile spacing. Historically the axial efficiency of groups of piles has not been a concern if the center-to-center spacing between piles is greater than 2.5 times the pile diameter (2.5B) or 30.0 inches whichever is greater, to avoid interference between adjacent piles during construction. Therefore, an axial efficiency factor (η) of 1.0 is applied for the pile group with center-to-center spacing of 2.5 diameters or more.

4.1.5 Lateral Loads

Lateral soil-structure interaction analysis of the driven piles is performed by the CFL Bridge Engineer. A strength limit state resistance factor of 1.0 is specified in AASHTO for lateral geotechnical resistance of a single pile or pile group. Factored strength limit state lateral loads should be used in the analysis.

For lateral loading analyses, use the subsurface soil parameters provided in Table 4.3 to estimate the lateral load displacement behavior. The values presented in Table 4.3 do not include reduction factors or load factors.

TABLE 4.3 – LPILE Parameters

APPROXIMATE

ELEVATION

(FT)

DEPTH BELOW

EXISTING GROUND

SURFACE (FT)

LPILE P-Y

MODEL

EFFECTIVE UNIT

WEIGHT (PCF)

FRICTION

ANGLE

(DEG)

SOIL

MODULUS

(PCI)

ABUTMENT No. 1 (BORING BH-01)

6,098 - 6,086 0 - 13 Sand (Reese) 135 38 225 6,086 - 6,079 13 - 19 Sand (Reese) 122 33 225 6,079 - 6,046 19 - 52 Sand (Reese) 67.6(1) 36 125 Below 6,046 Below 52 Sand (Reese) 52.6(1) 32 60

ABUTMENT No. 2 (BORING BH-02) 6,095 - 6,088 0 -7 Sand (Reese) 135 38 225 6,088 - 6,081 7 - 14 Sand (Reese) 122 33 225 6,081 - 6,042 14 - 53 Sand (Reese) 67.6(1) 36 125 Below 6,042 Below 53 Sand (Reese) 52.6(1) 32 60

1. Below groundwater surface.

The soil behavior around the laterally loaded pile is described by the soil P-y curves. Material properties provided are for single piles and do not account for the reduced lateral resistance of piles in a group. P-multipliers are a function of the number of rows of piles and center-to-center pile spacing in the direction of loading. P-multipliers are required even for a single row of piles if the center-to-center spacing of the piles is less than 5 pile diameters. P-multipliers are specified in Table 10.7.2.4-1 in AASHTO. When this analysis method is used, the resistances at the strength limit state as represented by the P-y curves should not be factored since they already represent the nominal conditions.

4.1.6 Settlement

The settlement of the piles driven to the minimum embedment length and nominal axial capacity is expected to be less than one half inch at the bottom of pile cap elevation for the Service I limit state axial load condition.

4.1.7 Pile Drivability

The contractor should conduct drivability analysis using the Wave Equation Analysis Program (WEAP) to select hammers that have sufficient energy to drive the piles to the desired embedment without exceeding the acceptable pile driving stresses and blows per foot presented in the project specifications.

Test piles should be driven while instrumented with PDA to determine production pile driving criteria.

One test pile per abutment located as indicated in the plans should be tested and monitored by an engineer.

The tests should be performed in general accordance with ASTM D 4945. Signal Matching program analyses should be performed to confirm the load resistance of the piles at the end of the test driving program. The production piles should be driven with the same hammer as that used in the test pile.

4.2 FOUNDATIONS - LITTLE BOULDER CREEK BRIDGE

The proposed bridge will be constructed at the same location as the existing bridge, over Little Boulder Creek. The existing span of 28 feet will be increased to 50 feet, with the new abutments being constructed behind the existing abutments. The existing abutments will be removed and a 2H:1V slope will be constructed in front of the abutment walls. Shallow foundations are proposed by the bridge team to bear at an elevation of 6,418 (approximately 14 to 15 feet below existing grade).

4.2.1 Bridge Foundation Selection

Due to the abundant presence of cobbles and boulders interpreted from the drilling results and the observations of the surface conditions, a deep foundation system is not practical. The design scour elevation of 6,420 feet, will result in an embedment depth of 14 to 15 feet, which should be shallow enough to reduce excavation complications. A shallow foundation system constructed on the gravel, cobbles and boulders is therefore recommended. A micropile foundation system may also be practical, but is expected to be more costly than a shallow foundation system.

4.2.2 Factored Bearing Resistance - Strength Limit State

Factored bearing resistance at the strength limit state was estimated using the methods presented in section

10.6.3 of AASHTO. The factored bearing resistance is a function of the subsurface conditions and the proposed footing dimensions including length, width, and embedment depth. Based on the soils encountered in the bearing zone and guidance presented in AASHTO, a resistance factor of 0.45 has been applied. Footing widths have not yet been determined. The evaluation of factored bearing resistance was performed using a footing length (bridge width) of 16 feet provided by the structural engineer and a minimum recommended embedment depth of 3 feet. Figure 5 presents the factored bearing resistance as a function of effective footing width.

Lateral loads on the footings may be resisted by the friction developed between the concrete footing and soil. A nominal sliding resistance friction coefficient of 0.62 is recommended. A resistance factor of 0.8 should be applied for the strength limit state in accordance with AASHTO. Passive resistance should not be utilized to resist lateral loads due to the limited depth of soil below the design scour elevation.

4.2.3 Preliminary Settlement Evaluation - Service Limit State

Due to the assumed light loading typical bridges of the proposed span length and the very dense nature of the cohesionless bearing soils, nominal loading up to approximately 9.5 ksf is estimated to produce settlements less than 1/2 inch.

4.3 ABUTMENT DESIGN

Abutments and wing walls should be designed to resist lateral earth pressures and other applicable lateral loads in accordance with AASHTO. Lateral earth pressure is influenced by the strength of the abutment backfill, the presence or absence of water, and the ability of the abutment or wall to move in response to lateral loads. Other loads, such as live loads, construction loads, and soil compaction loads should also be considered in the design.

Unbalanced water behind an abutment or wall adds significant lateral pressure and should be avoided by using free draining gravity outlets for water. Abutment and wing wall backfill should consist of structural backfill as specified in Section 704.04 of FP-14.

The coefficient of at-rest earth pressure should be used for design if the abutment is so restrained that it cannot be expected to rotate (deflect at the top) 0.002 times the wall height. Where deflection of the abutment can be expected, a coefficient of active earth pressure should be used for wall design. Active and at-rest lateral earth pressures of native materials, properly placed and compacted structural backfill, and unclassified borrow above the water table are presented in Table 4.4. The values are unfactored loads and assume that the surface of the soil slope behind the wall is horizontal.

TABLE 4.4:- Lateral Earth Pressures for Bridge Abutments

Backfill Type Assumed Backfill

Properties Case

Unfactored Equivalent Fluid Density (pcf)

Structural Backfill c = 0 psf = 34 deg.

γ = 125 pcf

Active 32

At-Rest 55

Silty Sand and Silty Gravel

(SM/GM)

c = 0 psf = 32 deg γ = 120 pcf

Active 33

At-Rest 56

4.4 EMBANKMENT CONSTRUCTION

Based on the field observations and test results, temporary short-term excavations should be cut at a maximum inclination of 1V:1.5H for excavations less than 15 feet in height. Slopes may need to be further flattened or shored based on conditions encountered during construction. Safety of construction personnel is the sole responsibility of the contractor. If stability of an excavation becomes questionable during construction, the excavation should be evaluated promptly by a geotechnical engineer. All construction surcharge loads and traffic loads should be kept a minimum distance equal to the depth of the excavation away from the edge of excavations.

Construct permanent long-term embankments with a maximum slope ratio of 1V:2H to maintain slope stability and promote vegetation of the slope. An erosion control mat or other erosion mitigation devices should be placed on the completed slopes to facilitate vegetation. Construct embankments in accordance with Section 204 of FP-14.

Several potential cut slopes were evaluated in the field while preliminary design plans were being developed. In general, the proposed cut slopes are relatively small. Small cut slopes are generally designed based on local precedence and engineering judgment. In general, design by precedence is used when the following conditions apply: 1) new cuts will be made into an existing slope 10 ft or less and at the same angle of inclination, 2) slope height does not increase significantly, 3) there is no evidence of instability,

4) material types at the excavation face appear consistent, and 5) there is no apparent seepage in the cut.

Table 4.5 presents the maximum recommended slope angles for the evaluated slopes.

TABLE 4.5:- Cut Slope Recommendations

Station Range of Potential Cut Slope Recommended Maximum Slope Angle (H:V)

600+25 to 601+25 1.5:1 632+50 to 635+50 1:1 643+00 to 645+00 1.5:1 664+00 to 668+00 1.5:1 804+00 to 805+25 1:1 820+50 to 822+50 1:1 855+00 to 857+00 1:1 860+50 to 863+00 1:1 874+50 to 877+00 1:1

On-site soils encountered within the anticipated excavation and construction limits generally consist of silty to clayey sand and gravel soils. The excavations are anticipated to be in material that is likely to have a shrink/swell factor of approximately 0.90. The recommended shrink/swell factor is based on a combination of standard tabled values for common materials in the FLH Technical Guidance Manual, FLH Project Development and Design Manual (PDDM) Chapter 6, and experience with other CFLHD projects in similar materials.

4.5 CONSTRUCTION CONSIDERATIONS

At the EGF Bridge Site, the contractor will be required to submit specifications on pile driving equipment prior to installation of production piles. The pile hammer should be suitably sized to limit significant driving stresses and subsequent pile damage according to the wave-equation analysis. The final blow count of production piles should be limited to 10 blows per inch.

At the Little Boulder Creek Bridge site, excavation within the cobble and boulder subgrade is anticipated to be difficult. If boulders are encountered in the excavation at the bearing elevation it is recommended that boulders are removed and a minimum of one-foot is subexcavated below the bottom of the footing and laterally to a minimum of 2 feet beyond the foundation footprint and replaced with structural backfill.

The structural backfill should be compacted to a minimum of 95 percent of maximum dry density as determined by ASTM D1557. Lean concrete may also be used to backfill beneath the footing elevation.

If lean concrete is used, the surface should be roughened prior to set-up.

4.6 SPECIFICATIONS

Special provisions were developed to be consistent with geotechnical recommendations stated above and should be incorporated into the special contract requirements (SCR) to amend the FHWA Standard Specification for Construction of Roads and Bridges on Federal Highway Projects; known as FP-14.

4.7 LIMITATIONS

The subsurface explorations and tests described in the Subsurface Investigation Section on Procedures and Results have been conducted in accordance with standard practices and procedures (except as specifically noted). The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface conditions between these locations may vary. The Analysis and Recommendations Section in this report include interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

SECTION FIVE -References

AASHTO, 2014, Standard Specifications for Highway Bridges, Load and Resistance Factor Design, Section 10.

FHWA, 2008, Federal Lands Highway Project Development and Design Manual (PDDM).

FHWA, 2016, Design and Construction of Driven Pile Foundations, Publication number FHWA-NHI-

16-009, September.

Federal Lands Highway, 2006, Technical Guidance Manual (TGM), A Geotechnical Supplement to the

FLH Project Development and Design Manual

Pierce, W.G., and Nelson, W.H., 1969, Geologic Map of the Wapiti Quadrangle, Park County, Wyoming: U.S. Geological Survey GQ-778, scale 1:62,500

Pierce, W.G., 1977, Geologic Map of the Cody 1 Degree x 2 Degree Quadrangle, Northwestern, Wyoming: U.S. Geological Survey I-2500, scale 1:250,000

FIGURES-Vicinity and Boring Location Map, Axial

Resistance Graphs, Factored Bearing Resistance Graph

806010

0 100 200 300 400 500 600 700 800 900 1000

P ile

L e n gt h ft

El e va ti o n ft

Axial Resistance (kips)

Abutment No. 1 Driven H‐Piles (HP14x102)

Ultimate Resistance

Factored Resistance (0.65)

Notes:

1. Top of pile assumed to be at Elevation 6,087 feet.

2. Assumes a minimum of 5 piles or capacity should be reduced by 20%.

3. Assumes dynamic testing will be performed on at least one pile per abutment. Otherwise use resistance factor of 0.40.

Scour Elevation = 6,071 ft

Estimated Top of Pile = 6,087 ft

806005

0 100 200 300 400 500 600 700 800 900 1000

P ile

L e n gt h ft

El e va ti o n ft

Axial Resistance (kips)

Abutment No. 2 Driven H‐Piles (HP14x102)

Ultimate Resistance

Factored Resistance (0.65)

Notes:

1. Top of pile assumed to be at Elevation 6,085 feet.

2. Assumes a minimum of 5 piles or capacity should be reduced by 20%.

3. Assumes dynamic testing will be performed on at least one pile per abutment. Otherwise use resistance factor of 0.40.

Scour Elevation = 6,071 ft

Estimated Top of Pile = 6,085 ft

PROJECT: SOUTHFORK ROAD - LITTLE BOULDER CREEK BRIDGE

SUBJECT: FACTORED BEARING RESISTANCE

2 4 6 8 10 12

Fa ct o re d B e ar in g R e si st an ce ks f)

Effective Footing Width (ft)

APPENDIX A- Boring Logs

G rfc

Te xt

!S O

IL

C

A

LS

S

IF

IC

A

TI

O

N C

H A

R T

L

E G

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D

3/

/2

3:

:5

P

M

GW

GP

GM

GC

SW

SP

SM

SC

ML

CL

OL

MH

CH

OH

PT

Unified Soil Classification System

SOIL CLASSIFICATION CHART & LEGEND

SILTY GRAVELS WITH OR WITHOUT SAND

HIGHLY ORGANIC SOILS

POORLY-GRADED SANDS WITH OR WITHOUT

GRAVEL

CLEAN SANDS

WITH LESS THAN

15% FINES

GRAVELS WITH

15% OR MORE

FINES

GRAVELS

MORE THAN HALF

COARSE

FRACTION IS

LARGER THAN NO.

4 SIEVE

MAJOR DIVISIONS TYPICAL NAMES

WELL-GRADED GRAVELS WITH OR WITHOUT

SAND

POORLY-GRADED GRAVELS WITH OR

WITHOUT SAND

ORGANIC SILTS OR CLAYS OF HIGH

PLASTICITY WITH OR WITHOUT SAND OR

GRAVEL

PEAT AND OTHER HIGHLY ORGANIC SOILS

CLAYEY SANDS WITH OR WITHOUT GRAVEL

C O

A R

S E

-G R

A

IN

E D

S O

IL

S

M O

R E

T H

A N

H A

LF

IS

C O

A R

S E

R T

H A

N N

O . 2

S

IE

V

E

NOTE: Coarse-grained soils with between 5% and 12% passing the No.200 sieve and fine-grained soils with limits plotting in the gray zone on the plasticity chart have dual classifications.

SILTS AND CLAYS

LIQUID LIMIT 50% OR LESS

Unconfined Compression No Recovery

SILTS AND CLAYS

LIQUID LIMIT GREATER THAN 50%

UC

NR

FI

N

E -G

R A

IN

E

D S

O

IL

S M

O R

E T

H A

N H

A

LF

IS

F

IN

E

R T

H A

N N

O . 2

S

IE

V

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SANDS WITH 15%

OR MORE FINES

SANDS

MORE THAN HALF

COARSE

FRACTION IS

FINER THAN NO. 4

SIEVE SIZE

INORGANIC CLAYS OF HIGH PLASTICITY

WITH OR WITHOUT SAND OR GRAVEL

Liquid Limit Plastic Index Moisture Content Dry Density Non Plastic No Valve

Water Level at Time of Drilling

Stabilized Water Level

CLEAN GRAVELS

WITH LESS THAN

15% FINES

Abbreviations

WELL-GRADED SANDS WITH OR WITHOUT

GRAVEL

CLAYEY GRAVELS WITH OR WITHOUT SAND

INORGANIC SILTS OF LOW TO MEDIUM

PLASTICITY WITH OR WITHOUT SAND OR

GRAVEL

INORGANIC CLAYS OF LOW TO MEDIUM

PLASTICITY WITH OR WITHOUT SAND OR

GRAVEL

LL

PI

W

DD

NP

NV

SILTY SANDS WITH OR WITHOUT GRAVEL

ORGANIC SILTS OR CLAYS OF LOW TO

MEDIUM PLASTICITY WITH OR WITHOUT

SAND OR GRAVEL

INORGANIC SILTS OF HIGH PLASTICITY WITH

OR WITHOUT SAND OR GRAVEL

Use primary colors or hyphenated compound primary colors. Use "mottled" or "streaked" if necessary.

4. Color Dry Dry to touch, dusty Moist Damp but no visible water Wet Visible free water

5. Moisture Content

Flat Width/Thickness >3 Elongated Length/Width >3

Flat & Elongated Meets both of the above

Applies to sand, gravel, cobbles and boulders.

Length, width and thickness refer to the greatest, intermediate and least dimensions, respectively.

6c. Particle Shape

N Density N Consistency

Unconfined Compressive Strength qu

(tsf)

Undrained Compressive Strength su

(tsf)

Behavior

0-4 Very Loose 0-1 Very Soft <0.25 <0.125 Extrudes between fingers when squeezed

5-10 Loose 2-4 Soft 0.25-0.50 0.125-0.25 Remolded by light finger pressure

11-30 Medium Dense 5-8 Firm 0.50-1.00 0.25-0.50

Imprinted easily with fingers, remolded by strong finger pressure

31-50 Dense 9-15 Stiff 1.00-2.00 0.50-1.00 Imprinted with considerable finger pressure, indented by finger nail

>50 Very Dense 16-30 Very Stiff 2.00-4.00 1.00-2.00 Barely imprinted by fingers or indented by finger nail

>30 Hard >4.00 >2.00 Not imprinted by fingers or difficult to indent with finger nail

SAND & GRAVEL SILT AND CLAY

3. Consistency and Density:

Angular Sharp edges and relatively plane sides.

Subangular Same as angular with rounded edges.

Subrounded Nearly plane sides but well-rounded corners and edges.

Rounded Smooth curved sides and no edges.

Well-

Rounded Very Smooth surfaces, spherical or ovular, no edges.

6b. Particle Angularity Applies to coarse sand, gravel, cobbles and boulders.

Sieve < #200 Flour or smaller

Fine > #200 to #40 Flour to sugar Medium #40 to #10 Sugar to rock salt Course #10 to #4 Rock salt to pea-sized

Fine #4 to 3/4 in. Pea-sized to thumb Coarse 3/4 in. to 3 in. Tumb to fist Cobble 3 in. to 12 in. Fist to basketball

Boulders > 12 in. Larger than Basketball

Material

Gravel

6a. Particle Size

Silt or Clay

Sand

Particle Size Approximate Scale

Example, fine-grained soil: Lean CLAY with Sand (CL)- stiff, brown, moist, medium plasticity, laminated Example, coarse-grained soil: Silty SAND with Gravel (SM)-medium dense, gray, wet, fine to coarse grained, angular to subangular gravel, weakly cemented Example, fine-grained soil (Long Form):

Clayey GRAVEL with SAND (CL-ML)- loose to soft, dark brownish green to pale brownish gray, wet; fine to medium grained, angular, flat sand; coarse grained, rounded elongated gravel, some chert, trace coarse gravel, and cobbles, medium plasticity, dessicated, weak cementation, low dry strength, rapid dilatancy, moderate HCL reaction, hydrocarbon odor, iron oxide staining, alluvium fill, (Quaternary Alluvium), Additional Description.

1. Group Name (Pg. 3) 9.

2. Group Symbol (Pg. 3) 10.

3. Consistency / Relative Density (Pg. 1) 11.

4. Color (Pg. 1) 12.

5. Moisture (Pg. 1) 13.

6. Particle Size / Shape / Angularity (Pg. 1) 14.

7. Plasticity (Pg. 2) 15.

8. Structure (Pg. 2)

Odor (Pg. 2)

Use the following descriptive sequence when classifying soils, both in the field and when entering data into gINT:

Staining (Pg. 2)

Cementation (Pg. 2) Organics Dry Strength (Pg. 2) Dilatancy (Pg. 2) HCL Rxn (Pg. 2)

Weak Crumbles with little finger pressure Moderate Crumbles with considerable finger pressure Strong Will not crumble with finger pressure

Intact coarse-grained soil

9. Cementation

Nonplastic Thread cannot be rolled at any water content.

Low The thread can barely be rolled and the lump cannot be formed when drier than the plastic limit.

Medium The thread is easy to roll and not much time is required to reach the plastic limit. The thread cannot be rerolled after reaching the plastic limit. The lump crumbles when drier than the plastic limit.

High It takes considerable time kneading and rolling to reach the plastic limit. The thread can be rerolled several times after reaching the plastic limit. The lump can be formed without crumbling when drier than the plastic limit.

Toughness test: Shape the specimen into an elongated pat and rolled on a smooth surface or between the palms into a thread ~1/8”. If the sample is too wet to roll, it should be allowed to dry. Fold the thread and reroll repeatedly until the thread crumbles at a diameter of ~1/8”. This will be near the plastic limit. Note the pressure required to roll the thread near the plastic limit and the strength of the thread. After the thread crumbles, the pieces should be lumped together and kneaded until the lump crumbles. Note the toughness during kneading.

On the basis of observations made during the toughness test, describe plasticity.

7. Plasticity

None No visible reaction Weak Some reaction, bubbles forming slowly Strong Violent reaction, with bubbles forming immediately

13. HCL Reaction 14. Odor 15. Staining None None

Chemical Hyrodcarbon Hyrodcarbon Iron Oxide

Organic

None No visible change Slow Water appears slowly during shaking and does not disappear or disappears slowly during squeezing.

Rapid Water appears quickly during shaking and disappears quickly during squeezing.

12. Dilatancy

1. Mold soil, adding water if necessary, into ~1/2” diameter ball with soft but not sticky consistency.

2. Smooth in palm of one hand with knife blade. Shake horizontally, striking the side of the hand vigorously against the other hand several times. Note the reaction of water appearing on the surface.

4. After Dilatancy has been determined perform the Toughness test (see explanation in #7).

3. Squeeze by closing the hand or pinching the soil between fingers. The reaction is the speed with which water appears while shaking and disappears while squeezing.

None Crumbles into powder with mere pressure of handling.

Low Crumbles into powder with some finger pressure.

Medium Breaks into pieces with considerable finger pressure.

High Cannot be broken with finger pressure, will break between hard surface and thumb.

Very High Cannot be broken between hard surface and thumb.

1. Mold a ball ~1” diameter until it has the consistency of putty, adding water if necessary.

2. From the ball, make at least 3 ½” diameter balls. Allow to air dry.

3. If the specimen contains natural dry lumps, those that are ~1/2” diameter may be used in place of molded balls.

4. Test the strength of the dry balls or lumps by crushing between the fingers.

11. Dry Strength

Stratified Alternating layers > 1/4 inch, note thickness.

Laminated Alternating layers < 1/4 inch, note thickness.

Fissured Contains shears or separations along planes of weakness.

Slickensided Shear planes appear polished or glossy, sometimes striated.

Blocky Cohesive soil can be broken down into harder, angular lumps.

Lensed Inclusion of small pockets of different soils, note thickenss.

Homogeneous Same color and appearance throughout.

Mottled Spots or patches possessing no apparent pattern Varved Distinct laminations of lacustrine sediments predominantly clayey

Desiccated Shrinkage cracks due to dehydration of fine-clayey soil

8. Structure Terms

O

E X

25-50/3" (3" = 33%)

7-6-7 (0" = 0%)

1-2-2 (18" = 100%)

8-12-15 (3" = 17%)

14-12-13 (11" = 61%)

4-10-14 (14" = 78%)

15-10-9

SPT-1

SPT-2

SPT-3

SPT-4

SPT-5

SPT-6

SPT-7

ASPHALT: Approximately 3 inches thick El.

6097.75 ft 0.25 ft

Clayey GRAVEL with Sand: moist, low plasticity, fine grained sand, with cobbles and boulders inferred from drilling action (Fill).

El. 6094 ft 4 ft Silty GRAVEL with Sand: moist , non plastic, fine grained sand, with cobbles and boulders inferred from drilling action (Fill).

Medium dense.

El. 6086 ft 12 ft Silty, Clayey SAND (SC-SM), loose, moist, low to medium plasticity, fine to medium sand, trace gravel in sample.

Wet below 17 feet

El. 6079 ft 19 ft Poorly graded SAND with silt and gravel (SP-SM), medium dense, brown, wet, non plastic.

Alternating beds of fine to medium grained sand and fine gravel.

Station and Offset: 706+49 10 ft Lt.Groundwater Depth:

While Drilling: 17 ft / Elev 6081 ft At Completion: --- After Drilling: ---

Notes:

Elevations approximated from project plan sheets. Surveyed elevation data not available.

Surface Elevation: 6098 ft

State Plane Coors: N 4901171.62 ft E 618749.2 ft Latitude: 44.2541° Longitude: -109.5125°

Weather: Warm/Dry

Date Started: 7/12/18 Date Completed: 7/12/18 Driller/Company: Chris/Elite Hammer Type: 140 lbs Automatic

Drill: CME 550

Logger/Company: D. Robbins/CFLHD

BH-01BORING LOG

Sheet: 1 of 3

Project Location: Park County Road 6WX

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: Southfork Road

E le va tio n (f t)

D ep th ft)

D ril lin g

M et ho d

Field Blow Count (Recovery)No. Test Results

T yp e

SAMPLE

MATERIAL DESCRIPTION

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

B O

R

IN

G L

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H F

O R

K R

O A

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P J

G ra ph ic

L og

E X

10-10-9

(9" = 50%)SPT-8

Poorly graded SAND with silt and gravel (SP-SM), medium dense, brown, wet, non plastic. (continued)

Unable to sample due to heaving sands. Cuttings and drill rig action consistent.

El. 6046 ft 52 ft Silty SAND (SM), grayish brown, wet, non plastic, fine sand.

El. 6038 ft 60 ft Sandy silt (ML), gray, wet, non plastic, fine sand.

Unable to sample to a depth of 80 feet due to aggressively heaving sands.

BH-01BORING LOG

Sheet: 2 of 3

Project Location: Park County Road 6WX

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: Southfork Road

E le va tio n (f…