GEO Report WY FLAP JOH 14(1).pdf

NORTH FORK CRAZY WOMAN CREEK BRIDGE

BIGHORN NATIONAL FOREST

JOHNSON COUNTY, WY

WY FLAP JOH 14(1)

FINAL Geotechnical Report

Prepared by Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch April 2023 ii

SIGNATURE SHEET

Report prepared by: ___________________________________________________________

Devin T. Dixon, P.E., Geotechnical Engineer

Aaron A. Baukus, Geotechnical Engineer Trainee

Report reviewed by: ____________________________________________________________

Brendan L. McGarity, E.I., Geotechnical Engineer

Approved for distribution by: ____________________________________________________

James M. Arthurs, P.E., PhD., Acting Lead Geotechnical Engineer

Distribution

Electronic:

N:\WY\14(1)\Geotech\7_FinalDocs K:\TechServices\Geotech\1. Geotech Project Reports Project Management Project Development, Lead Designer Bridge Hydraulics

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TABLE OF CONTENTS

SECTION ONE - INTRODUCTION

1.1 BACKGROUND AND LOCATION

1.2 SCOPE AND PURPOSE

SECTION TWO - GEOLOGY AND SEISMICITY

2.1 REGIONAL GEOLOGY

2.2 SITE GEOLOGY

2.3 SITE SEISMICITY

2.3.1 Nearby Faults

2.3.2 Seismic Design Parameters

2.4 GEOLOGIC HAZARDS

SECTION THREE - SUBSURFACE INVESTIGATION

3.1 SUBSURFACE EXPLORATION PROGRAM

3.2 LABORATORY TESTING PROGRAM

3.3 SUMMARY OF SITE CONDITIONS

3.3.1 General Topography

3.3.2 Average Temperatures and Precipitation

3.3.3 Surface Reconnaissance

3.3.4 Scour Potential and Erosion

3.3.5 Subsurface Conditions

3.3.6 Groundwater

SECTION FOUR - ANALYSIS & RECOMMENDATIONS

4.1 FOUNDATIONS

4.1.1 Bridge Foundation Selection

4.1.2 Site Characterization

4.1.3 Drilled Shaft Axial Resistance

4.1.4 Group Effects on Axial Resistance

4.1.5 Lateral Loads on Deep Foundations

4.1.6 Settlement

4.1.7 Recommended Shaft Lengths

4.1.8 Field Testing

4.2 ABUTMENT & WINGWALL DESIGN

4.3 PERMANENT EARTHWORKS

4.3.1 Embankment Construction

4.3.2 Shrink/Swell Recommendations

4.4 CONSTRUCTION CONSIDERATIONS

4.5 SPECIFICATIONS

4.6 DISCLAIMER/LIMITATIONS CLAUSE

SECTION FIVE - REFERENCES

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TABLES

Table 2.1 - Summary of Seismic Parameters Corrected for Site Class C Table 3.1 - Summary of Field Exploration Program Table 3.2 - Summaries of Laboratory Index Test Results Table 3.3 - Summaries of R-Value Results Table 3.4 - Summaries of Laboratory Corrosivity Results Table 3.5 - Climate Data Summary Table 4.1 - Proposed Bridge Foundation Location Table 4.2 - Bridge Loading Table 4.3 - LPILE Parameters Table 4.4 - Shaft Lengths Required for Axial and Lateral Loading Table 4.5 - Lateral Earth Pressures for Bridge Abutments & Wingwalls

PLATES

Plate 1 Project Vicinity Map Plate 2 Geology Map Plate 3 Geology Map Legend Plate 4 North Fork Crazy Woman Creek Bridge Geotechnical Boring Locations Plate 5 Wyoming Geologic Hazards Map

APPENDICES

APPENDIX A Field Exploration Program APPENDIX B Laboratory Test Results APPENDIX C Photographs APPENDIX D Drilled Shaft Analysis APPENDIX E Excavation Characteristics of Rock & Rippability Charts

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N. Fork Crazy Woman Creek Bridge, WY FLAP JOH 14(1) April 2023

SECTION ONE - Introduction

1.1 BACKGROUND AND LOCATION

This report presents the results of the geotechnical engineering study and provides recommendations for the replacement of the North Fork Crazy Woman Creek Bridge in Johnson County, Wyoming. The project proposes to replace the bridge crossing over the North Fork Crazy Woman Creek, which is located on County Road 14 (Crazy Woman Canyon Road) approximately

0.7 miles away from the Bighorn National Forest boundary on Forest Road 33. A project vicinity map is presented on Plate 1 of this report.

The North Fork Crazy Woman Creek Bridge was built in 1997 as documented in the most recent inspection reports. However, it was reported by county representatives that the bridge was rebuilt that year by reusing the previous steel girders placed on new abutment caps raised to a higher grade after a flood event washed the bridge out. The bridge now requires replacement due to the current poor condition.

The existing North Fork Crazy Woman Creek Bridge is a single lane, single span, 40-foot-long structure. The superstructure consists of steel rolled beams with steel channel diaphragms, timber plank decking, and timber running planks. The substructure abutments are concrete caps with no wingwalls. Cap support by piles or shafts is unknown, per inspection reports, but seems unlikely as the rock depth appears to be shallow as observed by various outcrops in the vicinity. The caps are keyed into concreted riprap slopes along the banks of the creek, which also appear to be tied into rock outcroppings as can be seen at the east abutment. These concreted riprap slopes appear to be undermined in some locations and several rocks may have fallen out as is visible from gaps left in the concrete joints. The abutments do not appear to have settled despite this deterioration to the overall concreted mass. Original bridge plans do not exist, however, a rough schematic drawing and various inspection reports from the early 2000s, 2010s, 2020, and 2021 were available from the Forest Service. The original bridge design loading is unknown; the bridge is currently posted to an 11-ton Inventory Rating and a 20-ton Operating Rating.

The North Fork Crazy Woman Creek Bridge will be replaced to meet HL-93 legal load standards.

The proposed replacement structure type is assumed to be a steel prefabricated bridge with rolled girders and structural steel decking. The existing bridge elements will be removed, and the mortared riprap is to remain in place. The new abutments will be simple cast-in-place concrete caps and wingwalls supported by deep foundations. Scour is anticipated at the bridge location due to the relatively thick mantle of susceptible soils, and, although relatively shallow rock outcroppings are prevalent at the project site, deep foundations are proposed as spread footers likely cannot be founded on competent rock below the anticipated scour depth at an economically

Page | 2 justifiable price. Considerations related to the abutments for the North Fork Crazy Woman Creek Bridge are presented in Section 4 of this report.

1.2 SCOPE AND PURPOSE

The scope of work included a geotechnical investigation, analysis, and recommendations for bridge foundations for use in design and construction. This involved several tasks including field reconnaissance, subsurface sampling, laboratory testing, interpretation and correlation of field measurements, and geotechnical engineering analysis. Specifically, this investigation was conducted to determine the soil profile at the bridge location and develop recommendations concerning bridge foundations, retaining structures, geologic hazards, and construction considerations.

A hydraulics report has been prepared under separate cover by the CFLHD Hydraulics Engineer.

The hydraulics report includes discussion of flood impacts, such as bridge scour and water surface elevations.

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SECTION TWO - Geology and Seismicity

2.1 REGIONAL GEOLOGY

The project is located within the Middle Rocky Mountains Province. This province is part of the Rocky Mountain System physiographic region. The Middle Rocky Mountains Province is in the western United States with a major portion in Wyoming. Several extensions of the Middle Rockies spread into Montana, Colorado, Utah, and Idaho. Folded mountains, which are anticlinal folds, are the dominant type of mountain in this province. Other types of mountains include volcanic mountains and uplifted fault blocks (NPS, 2018).

Quaternary rocks and deposits that exist within the region include landslide deposits (Qls), terrace deposits (Qt), and older alluvial fan deposits (QTf). Tertiary rocks and deposits include the White River Formation (Twr(?)). Cretaceous rocks and deposits include the Lance and Fox Hills Formations undivided (Klf), Bearpaw shale (Kb), the Mesaverde Formation (Kmv), Cody shale (Kc), the Frontier Formation (Kf), and Mowry shale, muddy sandstone, and Thermopolis shale undivided (Kmt). Lower Cretaceous-Upper Jurassic rocks and deposits include the Cloverly and Morrison Formations undivided (KJm). Other Jurassic rocks and deposits include the Sundance and Gypsum Spring Formations undivided (Jsg). Triassic rock and deposits include the Chugwater and Goose Egg Formations undivided (TR Pcg). Pennsylvanian and Mississippian rocks and deposits include the Tensleep Sandstone and Amsdem Formation undivided (IPMta) and Madison limestone (Mm). Ordovician and Cambrian rocks and deposits include Bighorn dolomite (Ob), Gallatin and Gros Ventre Formations undivided (Ꞓg), and Flathead sandstone (Ꞓf). Archean, or early Precambrian, rocks and deposits include mafic rocks (Am), pyroxenite plug (Aum), and granitic gneiss (Agn) (Van Ploeg & Boyd, 2002).

2.2 SITE GEOLOGY

Although no USGS mapping is available for the overburden material, the soil conditions at the site are assumed to be alluvium based on the project setting and the creek bed deposits observed at the bridge site. The project site is mapped as underlain by Tensleep Sandstone and Amsden Formation undivided (IPMta). Landslide deposits (Qls), mixed alluvial and colluvial deposits (Qac), older alluvial fan deposits (QTf), Sundance and Gypsum Spring Formations undivided (Jsg), Chugwater and Goose Egg Formations undivided (TR Pcg), Madison Limestone (Mm), Bighorn Dolomite (Ob), Gallatin and Gros Ventre Formations undivided (Ꞓg), and Flathead Sandstone (Ꞓf) are also mapped in the vicinity of the site. These observations are consistent with the borings as will be discussed in Section 3 of this report. The deposits and landforms are primarily a result of a period of mountain-building activity known as the Laramide orogeny, which affected the region from about 70 to 40 million years ago. The terrain can be described as mountainous and rugged. A geology map of the project area and corresponding map legend are presented in Plates 2 & 3.

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2.3 SITE SEISMICITY

2.3.1 Nearby Faults

No seismic source or Quaternary faults are mapped within 40 miles for the project (USGS, 2020a).

2.3.2 Seismic Design Parameters

One bridge replacement is proposed for the project. This structure is anticipated to include wingwalls. The materials at the project site include silty to clayey sand, recent creek bed (alluvial) material, and sedimentary rock at shallow, <10 feet, depth. Seismic design parameters for analysis of these structures are discussed below.

The American Association of State Highway and Transportation Officials (AASHTO) criteria for recommended seismic response parameters are based on the (AASHTO) LRFD Bridge Design Specifications, 8th Edition, 2017, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years (approximate 1,000-year return period). The 1,000-year return period uniform hazard spectrum for the North Fork Crazy Woman Creek Bridge project site, located at 44.18761°N latitude and 106.83024°W longitude, was obtained in accordance with the AASHTO ground motion maps.

Based on subsurface conditions encountered during drilling and the approximate topographic USGS Vs30 online map viewer (USGS, 2020b), the onsite rock can be assumed to be very weak to medium strong, highly to completely weathered, and intensely fractured with lower typical shear wave velocity values. Therefore, the site is classified as Class B according to the site class definitions specified in Table 3.10.3.1-1 of AASHTO. The recommended spectral acceleration coefficient values for probabilistic design are summarized in Table 2.1.

Table 2.1 - Summary of Seismic Parameters Corrected for Site Class B Horizontal Peak Ground Acceleration, (PGA) 0.106 g

Horizontal Response Spectral Acceleration at Period of 0.2 sec, (Ss) 0.20 g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (S1) 0.04 g

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.0 Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 1.0 Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 1.0

Factored Horizontal Peak Ground Acceleration, (As) 0.106 g Factored Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.20 g Factored Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.04 g

Seismic Zone Zone 1

Based on the long acceleration coefficient SD1 value of 0.04, the project site is assigned to seismic hazard “Zone 1” in accordance with Table 3.10.6-1 of AASHTO. This assignment means that seismic loading is not likely to control design of structures for the project. Seismic hazard zones

Page | 5 reflect the variation in seismic risk in different regions needing different requirements for design as depicted in Table 4.7.4.3.1-1 of AASHTO.

2.4 GEOLOGIC HAZARDS

Potential geologic hazards at the bridge site include those related to landslides and expansive soils as shown in the geologic hazards map for Wyoming presented in Plate 5. Landslides, including rockfall, can cause major losses to infrastructure and can be influenced or triggered by local geology, geologic structures, hydrology, and precipitation. Human activities, such as road construction and surface water diversion, can also affect the occurrence of a landslide. The Wyoming State Geological Survey has mapped more than 30,000 landslides in the state (WSGS, 2022). The project is nearby to terrain susceptible to mass movement and these events could impact the bridge site. No specific investigation was conducted to evaluate slope stability in the project area; however, risk to the structure is interpreted to be low. Mitigation of landslides is outside the scope of this project.

Expansive soils shrink and swell when subjected to changes in moisture. Soil has the potential to be expansive based on the nature of the soil, its plasticity, clay content, soil structure, and other factors. Proper mitigation measures should be incorporated if roads or structures are built on these soils as the expansion or contraction of the soil can cause cracking, movement, or even failure (WSGS, 2022). The overburden soils at the project site, primarily gravel and sand, are not considered expansive soils. Lab testing results of select soil samples collected during drilling, as discussed in Section 3.2, indicated slightly plastic soils (Plasticity Index, PI < 7) corresponding to a low expansion potential.

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SECTION THREE - Subsurface Investigation

3.1 SUBSURFACE EXPLORATION PROGRAM

A subsurface investigation targeting the bridge site was performed by a Central Federal Lands Highway Division (CFLHD) of the Federal Highway Administration (FHWA) geotechnical engineer on July 26, 2022. The geotechnical subsurface exploration program consisted of drilling a total of one boring to approximately 39 feet deep. This boring was drilled near abutment 2.

Hollow-stem augers were used to drill through the overburden soils until refusal, and rock samples were recovered using HQ diamond core drilling. Standard penetration testing (SPT) and sample collection was performed at 5-foot intervals for the boring when possible. One grab sample of the upper subsurface was also collected. Subsurface conditions were logged, and representative samples were collected and transported to the CFLHD Materials Laboratory in Lakewood, CO, for physical property testing. A log of the exploration and boring location are presented in Appendix A and Plate 4, respectively. Photographs related to this exploration can be found in Appendix C. A summary of the field exploration is provided in Table 3.1. It should be noted that Abutment 1 was inaccessible at the time of the investigation due to the drill rig being over the legal weight limit of the existing bridge and the lack of accessible alternative routes.

Table 3.1 - Summary of Field Exploration Program

EXPLORATION

DESIGNATION LOCATION

APPROXIMATE

GROUND

ELEVATION (ft.)

APPROXIMATE

TERMINATION

DEPTH (ft.)

APPROXIMATE

DEPTH TO

GROUNDWATER

(ft.)

BH22-02 Abutment 2;

STA 14+47, 10 ft. RT 5,888.0 39.2 Not encountered

Note: The exploration locations were estimated relative to existing features. Ground elevations were acquired from CFL survey data.

3.2 LABORATORY TESTING PROGRAM

Soil samples recovered from the boring by SPT 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 moisture content (AASHTO T 255), sieve analysis (AASHTO T 11 and T 27), classification (AASHTO M 145 and ASTM D 2487), Atterberg limits (AASHTO T 89 and T 90), R-value (AASHTO T 190), resistivity (AASHTO T 288), soil pH (AASHTO T 289), and sulfate and chloride content (AASHTO T 290 and T 291). When the necessary tests were completed, samples were classified using the Unified Soil Classification System (USCS) and AASHTO soil classification system. Results of the testing are summarized below in Table 3.2 and are presented in Appendix B.

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Table 3.2 - Summaries of Laboratory Index Test Results

BORING

NUMBER

SAMPLE

DEPTH

PERCENT

GRAVEL

PERCENT

SAND

PERCENT

PASSING

#200

LIQUID

LIMIT

PLASTIC

LIMIT

USCS

CLASS.

AASHTO

CLASS.

(feet)

BH22-02 0 - 4 27 43 30 21 15 SC-SM A-2-4(0)

BH22-02 11 - 14 57 26 17 20 16 GC-GM A-1-b(0)

Soil test results indicated a limited range of material types composed of clayey, silty gravel to silty, clayey sand with gravel classifying as A-1-b to A-2-4 by AASHTO and GC-GM and SC-SM by USCS.

R-value testing of one sample taken directly beneath the asphalt is summarized in Table 3.3.

Table 3.3 - Summaries of R-Value Results

BORING NUMBER SAMPLE DEPTH R-VALUE, SUBGRADE

(feet)

BH22-02 0 - 4 37

Note: Bridge approaches are not paved.

Corrosivity and chemistry testing of a select sample was sent to an outside laboratory for testing and is summarized in Table 3.4.

Table 3.4 - Summaries of Laboratory Corrosivity Results

BORING

NUMBER

SAMPLE

DEPTH RESISTIVITY PH

SULFATE ION

CONTENT

CHLORIDE ION

CONTENT

(feet) (ohm-cm) (ppm) (ppm)

BH22-02 0 - 4 3,320 8.3 11 23

3.3 SUMMARY OF SITE CONDITIONS

This section presents the results of the surface reconnaissance and subsurface exploration.

3.3.1 General Topography

The existing bridge serves as an entrance for drivers along the Crazy Woman Creek Road traveling from east to west into Crazy Woman Canyon. The general topography east of the bridge can roughly be defined as sagebrush and grass covered lowland plains. Gradual hills, gullies, creek crossings, farmland, and ranches can be found east of the project site toward Interstate 25.

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The general topography west of the bridge can be characterized by the bordering Bighorn Mountains, which is a sister range of the Rocky Mountains. The Crazy Woman Creek Road winds past enormous sedimentary, namely sandstone, cliffs and parallels the creek for most of its length.

Boulder clusters of varying sizes can be found in the creek and lush forest greenery surrounds the banks and sloping ground adjacent to the cliffs. The forested area contains primarily lodgepole pine, along with several species of spruce, fir, and aspen.

3.3.2 Average Temperatures and Precipitation

Table 3.5 shows the average maximum and minimum temperatures, average monthly precipitation, and average monthly snowfall data for the period from 1948 to 2005 for the Buffalo, Wyoming (481165) weather station (Western Region Climate Center, 2022).

Table 3.5 - Climate Data Summary

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL

Avg. Max. Temp. (°F) 36.3 39.9 47.1 56.9 66.8 76.6 85.8 84.9 73.8 61.6 45.9 38.6 59.5

Avg. Min. Temp. (°F) 10.0 14.5 21.4 30.6 39.5 48.3 54.5 52.6 42.4 32.0 20.2 12.7 31.6

Avg. Total Precip. (in.) 0.50 0.45 0.73 1.55 2.29 2.27 1.39 0.83 1.30 1.00 0.56 0.43 13.3

Avg. Total Snowfall (in.) 5.7 5.9 5.1 2.5 0.6 0.0 0.0 0.0 0.1 1.9 4.9 6.3 33.0

Avg. Snow Depth (in.) 1 1 0 0 0 0 0 0 0 0 0 1 0

Note:

1) Period of Record: 08/01/1948 to 12/31/2005.

2) Percent of possible observations for period of record: Max. Temp.: 83.8% Min. Temp.: 83.7% Precipitation: 89.7%

Snowfall: 66.6% Snow Depth: 56.4%.

3.3.3 Surface Reconnaissance

The existing roadway is a gravel surface maintained to a width that ranges from approximately 16 to 18 feet with an existing bridge width of approximately 15 feet. The road forms a T-intersection in the northwest quadrant of the bridge site with the Crazy Woman Ranch Entrance. The Crazy Woman Creek is perennial and has adjacent riparian areas. Grouted riprap slopes are present along the embankments of the creek beneath the bridge and appear to be tied into rock outcrops.

However, evidence of undermining of the concreted mass was noted during the scoping trip.

Rock outcroppings are prevalent around the bridge site, particularly upstream of the bridge and surrounding the west abutment. A large bluff, approximately 30 feet high nearest to the road, with exposed rock borders the creek just across the west bridge abutment. The Crazy Woman Canyon Road veers around this bluff before continuing into the canyon. The rock type is consistent with the geology discussed in Section 2. Much of the exposed rock faces have black to gray colored mineral staining, are at least slightly weathered, and show signs of natural fracture patterns and cross-bedding.

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Mostly subangular to rounded boulders up to roughly 4 feet in diameter were observed in the creek channel beneath and surrounding the bridge. These boulders could have been placed around the existing abutments as scour protection and may have been locally sourced during the original bridge construction. Thick vegetation including lodgepole pine, shrubs, and native grass species line both banks of the creek and alluvial soils and sediments encompass the bridge site.

3.3.4 Scour Potential and Erosion

Long-term degradation, contraction scour, and local (abutment) scour depths were estimated by the assigned CFLHD hydraulics engineer. Scour elevations were provided by the CFLHD Hydraulics Group in the Final Hydraulics Report dated April 2023 (CFLHD, 2023). The recommended scour elevation for the bridge abutments was estimated to be 5,867.9 feet for the scour design flood and 5,867.6 feet for the scour check flood. This is approximately 6.4 feet below the assumed channel thalweg for the scour design flood. The North Fork Crazy Woman Creek Bridge foundations will be designed for the estimated scour depths, and no additional bank protection or scour countermeasures are recommended. Please refer to the previously mentioned Final Hydraulics Report for more information.

3.3.5 Subsurface Conditions

The subsurface conditions at Abutment 1 of the North Fork Crazy Woman Creek Bridge were not investigated by drilling. The weight of the drill rig exceeded the legal weight limit of the existing bridge and, thus, crossing the bridge was not allowable. Moreover, the lack of accessible alternative routes and time constraints further complicated the investigation. A surficial reconnaissance was conducted in lieu of drilling at Abutment 1 to establish geologic interpretations for the purpose of achieving a level of knowledge commensurate with good engineering practice.

The subsurface conditions at Abutment 2 of the North Fork Crazy Woman Creek Bridge were investigated by drilling boring BH22-02. Hollow stem auger drilling was used from approximately 0 to 4 feet below the ground surface and standard triple-tube HQ wireline rock coring methods were used from approximately 4 feet below the ground surface to the termination depth of approximately 39 feet. The ground surface surrounding the boring location consisted primarily of gravel soils. The boring encountered surface course material consisting of well graded gravel with silt and sand to approximately 4 inches. The material then transitioned to silty, clayey sand with gravel with some cobbles and rock fragments, and trace boulders and organics to a depth of approximately 9 feet. Highly to completely weathered, reddish brown, sandstone was encountered beneath the silty, clayey sand and extended to the termination depth apart from one approximately 6-inch-thick layer of lean clay encountered around 23.5 feet deep. The sandstone was classified as very weak rock (R1) to weak rock (R2) above the lean clay layer, and very weak rock (R1) to medium strong rock (R3) below the lean clay layer using field identification methods outlined in Exhibit 2.8-A of the FLH Rock Characterization Guidelines (FHWA, 2017b). The Rock Quality Designation (RQD) was consistently zero percent in all the core runs drilled indicating “Very

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Poor” rock mass quality; however, the core recovery in the core runs drilled in the sandstone encountered below the lean clay layer was higher than that of the core runs drilled in the sandstone encountered above the lean clay layer. Portions of the rock above the lean clay layer were interbedded with lenticular shale and siltstone, which had completely weathered to a near residual silty, clayey sand soil matrix. Thin chert layers, less than 6-inches thick, and poorly stratified sand layers, less than 1-inch thick, were encountered within the sandstone around roughly 26 and 30 feet, respectively. The sandstone also displayed thin, horizontal laminae after approximately 34 feet below the ground surface. Further descriptions and drilling notes can be found in the attached boring log under Appendix A.

3.3.6 Groundwater

Groundwater was not encountered during drilling in boring BH22-02. However, fluctuations in the groundwater level due to seasonal and climatic effects are expected and will likely follow water levels in the adjacent creek.

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SECTION FOUR - Analysis & Recommendations

This section presents analysis and recommendations for the bridge foundations, abutment wingwalls, permanent earthworks, and construction considerations for the design and construction of the North Fork Crazy Woman Creek Bridge project. Based on discussions with the project team and the current poor condition, the bridge will be replaced. Generalized subsurface profiles were developed based on field reconnaissance, surficial visual evaluation, and subsurface investigations.

4.1 FOUNDATIONS

The existing single span bridge will be replaced with a steel prefabricated bridge with rolled girders and structural steel decking. The existing bridge superstructure will be removed, the existing concrete abutment caps will be partially removed, and the existing mortared rock beneath the bridge will remain in place. Based on the 95% bridge plan sheets dated for distribution in March 2023, the proposed abutment centerline station and cap elevation are shown in Table 4.1.

Table 4.1 - Proposed Bridge Foundation Location

FOUNDATION APPROXIMATE STATION TOP OF SHAFT ELEVATION1

Abutment 1 13+85.63 5,881.98 FT Abutment 2 14+33.63 5,882.46 FT

1 As presented on the 95% foundation plan.

4.1.1 Bridge Foundation Selection

A drilled shaft foundation system is proposed for the new abutments due to the relatively high axial and lateral loads. The presence of scour precluded the use of a shallow foundation as the scour level is lower than the suitable bearing material. Micropiles were considered but determined impractical from structural and cost standpoints since micropiles have a low lateral load capacity and have been more expensive than drilled shafts at the current market price. A driven pile foundation was also considered but determined impractical due to the presence of hard layers including cobbles, boulders, and sandstone that could cause pile damage during driving. Pre-drilling methods could be used to minimize the potential for pile damage during driving and increase the contractor’s production rate, however this would likely cause additional piles to be needed thus increasing cost.

A drilled shaft foundation is feasible from a geotechnical perspective given the dense strata and presence of boulders and rock. Drilled shafts can provide a small footprint, support large foundation loads, and provide lateral resistance at a shallower elevation than driven piles. Based solely on hydraulic recommendations and assumptions stated in the Final Hydraulics Report

Page | 13

(CFLHD, 2023), scour potential as measured from the thalweg was determined to be present at the bridge abutments. Based on available data, it was determined by the combined team of Bridge, Hydraulics, and Geotechnical Engineers that drilled shafts would provide the best foundation system for this bridge.

Table 4.2 presents the final bridge loads factored for the strength limit state as provided by the CFL bridge engineer in February 2023:

Table 4.2 - Bridge Loading1

FOUNDATION

LOCATION

REQUIRED FACTORED

SHAFT RESISTANCE

(kips)

STRENGTH I

BRIDGE LOAD

PER SHAFT

(kips)

SERVICE I

BRIDGE LOAD

PER SHAFT

(kips) STRENGTH I

(η = 1.0)2 Abutment 1 & 2 165 165 115

1 Bridge loading assumes ×2-24-inch drilled shafts per abutment.

2 Reduction factor for group effects per Section 4.1.4.

4.1.2 Site Characterization

The subsurface profile was assumed to be entirely sand for analysis purposes. Although gravel, clayey-silty sand, cobbles, boulders, rock fragments, and highly to completely weathered sandstone were encountered in the borings, the subsurface materials, in general, were of a sand-like nature and composition. Groundwater was also assumed to be at the channel thalweg elevation of approximately 5,874 feet. These assumptions are conservative, or, in other words, purposefully broad to account for the limited subsurface data collected below the scour depth and estimated tip elevations.

4.1.3 Drilled Shaft Axial Resistance

The drilled shaft axial resistance analysis was performed for 24, 30, and 36-inch diameter shafts at the abutments using the beta method for cohesionless soils presented in section 10.8.3.5.2b of AASHTO. N-values were assumed to be equivalent to 50 blows as auger refusal occurred relatively shallow at approximately 4 feet. The selected drilled shaft diameter of 24 inches was chosen to meet both structural considerations and loading requirements at the lowest estimated cost to the project. The abutment foundations will obtain their resistance through side friction and tip resistance. The factored resistance for the strength limit state was calculated by applying 0.55 and 0.50 resistance factors for side and tip resistance, respectively. Results of the calculations for 24-inch diameter drilled shafts are presented in Appendix D.

4.1.4 Group Effects on Axial Resistance

The resistance of a shaft group to the applied axial loads is not necessarily the sum of the axial resistance of individual shafts within the group. The zone of influence from an individual shaft in

Page | 14 a shaft group may intersect with other shafts, depending on the shaft spacing. Based on published design guidance, the efficiency of groups of drilled shafts has not been a concern if the center-to-center spacing between shafts is greater than three times the shaft diameter (3D) to avoid interference between adjacent shafts, assuming a single row shaft group configuration. An efficiency factor (η) should be applied for spacing less than 3D as shown in Table 10.8.3.6.3-1 of

AASHTO.

Besides the effect of overlapping zones of influence, effects of construction on ground conditions in and around the group can be significant. Excavated deep foundation elements in cohesionless soils tend to decrease the effective stress of the surrounding soils. Poorly controlled shaft construction methods can result in soil loosening during drilling and adversely reduce the lateral stress around other shafts within the group. Casing driven in advance of excavation may increase the relative density and effective stress of the surrounding soil and prevents caving of overburden material. The calculations presented in this report assume that any casing used will extend no deeper than the estimated scour elevation.

4.1.5 Lateral Loads on Deep Foundations

Lateral load analysis was performed by the bridge engineer using the software program LPILE developed by Ensoft, Inc. This program analyzes a single pile or shaft considering deflection as a function of design loads, foundation construction, and subsurface conditions. Table 4.3 provides LPILE input parameters for the foundation soils based on available subsurface information and presumptive engineering correlations. We recommend that lateral support above the scour elevation defined in the CFLHD Hydraulics Report be neglected due to potential loss of material during the design flood event. It is also recommended that lateral support within five feet of the final road grade be neglected due to the potential loss of support from frost penetration or other shallow ground disturbance.

Table 4.3 - LPILE Parameters

APPROXIMATE

ELEVATION

(ft)

DEPTH BELOW

EXISTING

GROUND (ft)

LPILE P-Y

MODEL

EFFECTIVE

UNIT WEIGHT,

ɣ’ (pcf)

FRICTION

ANGLE, Փ

(deg)

HORIZONTAL

SUBGRADE

MODULUS, Ks

(pci)

NORTH FORK CRAZY WOMAN CREEK BRIDGE

5,888 to 5,867.9 (Abutment 1 and 2)

0 to 20.1 (Abutment 1 and 2)

Sand (Reese)

135 38 125

5,867.9 to 5,848.8 (Abutment 1 and 2)

20.1 to 39.2 (Abutment 1 and 2)

Sand (Reese)

135 45 125

Material properties provided are for single shafts and do not account for the reduced lateral resistance of shafts in a group. P-multipliers are a function of the number of rows of shafts and

Page | 15 center-to-center shaft spacing in the direction of loading. P-multipliers are required even for a single row of shafts if the center-to-center spacing is less than 5 shaft 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

A resistance factor of 1.0 for the service limit state is recommended to assess the ability of the foundation to meet the specified deflection criteria. Elastic settlements will occur immediately and be essentially complete at the end of construction and are estimated to be less than one inch at all locations based on the loads provided. Differential settlements are not anticipated. Shaft group settlement is not anticipated.

4.1.7 Recommended Shaft Lengths

The final lengths of the drilled shafts are based on both axial and lateral loading. Table 4.4 below shows the required shaft lengths needed for both axial and lateral capacities. This is based on the selected shaft diameter of 24 inches. The lateral capacities needed to meet loading requirements were determined to control the design shaft tip elevations for the North Fork Crazy Woman Creek Bridge.

Table 4.4 - Shaft Lengths Required for Axial and Lateral Loading

STRUCTURE

ELEMENT

REQUIRED SHAFT LENGTH

FOR AXIAL CAPACITY

(feet)

REQUIRED SHAFT LENGTH

FOR LATERAL CAPACITY

ESTIMATED TIP

ELEVATION

Abutment 1 31 32 5,849.98 Abutment 2 31 32 5,850.46

4.1.8 Field Testing

Steel crosshole sonic logging tubes (1.5-inch diameter steel tubes) should be installed in all drilled shafts prior to concrete placement for integrity testing. The recommended number of access tubes and tube spacing are dependent on the selected shaft diameter, typically one access tube per 12-inches of shaft diameter, with a minimum of three access tubes per shaft. The crosshole sonic logging tests should be conducted in accordance with ASTM D-6760 and FP-14 for quality assurance/quality control of the drilled shafts.

4.2 ABUTMENT & WINGWALL DESIGN

Abutments and wingwalls 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

Page | 16 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 wingwall 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 and properly placed and compacted structural backfill above the water table are presented in Table 4.5. The values are unfactored loads and assume that the surface of the soil slope behind the wall is horizontal.

Table 4.5 - Lateral Earth Pressures for Bridge Abutments & Wingwalls

BACKFILL TYPE

ASSUMED

BACKFILL

PROPERTIES

CASE

UNFACTORED

EQUIVALENT

FLUID DENSITY

(PCF)

NOMINAL

FRICTION

FACTOR

Structural Backfill c = 0 psf φ = 34 deg.

γ = 125 pcf

Active 35 0.67

At-Rest 55 0.67

Native Soil c = 0 psf φ = 38 deg γ = 135 pcf

Active 32 0.78

At-Rest 52 0.78

4.3 PERMANENT EARTHWORKS

4.3.1 Embankment Construction

Embankment construction will be necessary with regards to the concrete wingwalls. Construct permanent long-term embankments with a maximum slope ratio of 1V:2H to maintain slope stability and promote slope vegetation.

4.3.2 Shrink/Swell Recommendations

On-site soils expected to be encountered within the project limits generally consist of silty and clayey sands with varying amounts of gravel. It is estimated that these soils will have a 10 percent shrink percentage, corresponding to a shrink/swell factor of 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 (2006) and experience with other CFLHD projects in similar materials.

Page | 17

4.4 CONSTRUCTION CONSIDERATIONS

Traffic and Access: Access to both sides of the bridge is available for construction bearing in mind the posted 11-ton Inventory Rating and 20-ton Operating Rating of the existing bridge. However, the Forest Service is planning another project along the route during the same construction season involving bridge and/or wall construction, which could complicate access to the North Fork Crazy Woman Creek Bridge from the west side. Access to the adjacent private property driveway near the west end of the bridge will need to be verified.

Roadway Excavation: Excavate using equipment capable of removing the material while preventing material from escaping outside the construction limits.

Based on the subsurface investigation and surface geologic mapping, saprolite, or bedrock that has undergone intense weathering, was encountered to the depths explored at the site. Conventional heavy-duty excavation and ripping are assumed to be capable of completing the shallow excavations in the areas surrounding the abutments of the North Fork Crazy Woman Creek Bridge;

however, final determination of rock rippability is the responsibility of the contractor. Shear wave velocity of the geologic layers was not evaluated by geophysical methods. Excavation considerations for drilled shafts are presented later in this section. Additional information regarding the excavation characteristics of rock and rippability charts can also be found in Appendix E.

Evidence of intact, competent bedrock was not encountered during the subsurface investigation as detailed in this report. However, appropriate construction equipment should be mobilized to the site based on the excavation information detailed above. The handling of boulders of at least 4 feet in diameter will be required for excavations in the project area. The contractor is responsible for the safety of excavations and shoring design.

Existing Bridge Elements: The existing bridge superstructure will be removed and the existing concrete abutment cap will be partially removed. The existing mortared rock beneath the abutments will remain in place.

Drilled Shafts: The contractor will be required to submit a drilled shaft construction plan as required in Section 565.04 of the FP-14 which includes the outlining of proposed methods to maintain borehole stability, manage the excavation of boulders, concrete placement, and dewatering.

Boulders were encountered in boring BH22-02 ranging in size from approximately 12 to 18 inches and larger. Boulders up to roughly 4 feet in diameter were observed in the creek channel and surrounding the bridge. The boulders are composed of very hard to extremely hard rock and will likely require specialized tooling and drilling methods to maintain the shaft alignment. Loose

Page | 18 subsurface materials were also encountered at shallow depths, which may warrant the use of temporary casing. The contractor should review the geotechnical borings to determine the need and extents of temporary casings.

It is anticipated that groundwater will be encountered at the foundation excavations. The likelihood of flowing sands could also present a challenge for the driller as the mixture of fine sand and water could infiltrate the drilling equipment. Pockets of sandy material were encountered to the maximum depth explored during the subsurface excavation. The contractor should be prepared to maintain the excavation through flowing sand conditions.

Dewatering: Dewatering may be needed due to water infiltration from the creek. Perform dewatering according to Section 208.07 of the FP-14.

Slope Instability: Slopes could become unstable during construction operations due to precipitation, flooding events, or heavy loading on soft subgrade soils. Precautions should be taken if movement or cracking is observed. Seepage is a contributor to slope instability and similar dewatering and stabilization methods could be used to suspend slope movement. The contractor is responsible for temporary working platforms including those needed for cranes and shaft drilling rigs.

4.5 SPECIFICATIONS

Special provisions were provided prior to the 95% design milestone to be consistent with geotechnical recommendations stated above and were 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.

4.6 DISCLAIMER/LIMITATIONS CLAUSE

The recommendations in this report are based on the data obtained from exploratory boring(s), field review, and laboratory test results. The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface variations across the site are likely and may not become evident until excavation is performed. The Analysis and Recommendations sections 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.

Page | 19

SECTION FIVE - References

American Association of State Highway and Transportation Officials (AASHTO), 2017, LFRD Bridge Design Specifications, 8th Edition.

Brown, Dan A., Turner, John P., and Castelli, Raymond J., 2010, “Drilled Shafts: Construction Procedures and LRFD Design Methods,” NHI Course No. 132014, Geotechnical Engineering Circular No. 10, Report No. FHWA NHI-10-016, dated May.

Central Federal Lands Highway Division (CFLHD), 2023, “WY FLAP JOH 14(1) North Fork Crazy Woman Creek Bridge Final Hydraulics Report,” dated April.

Federal Highway Administration (FHWA), 2007, Geotechnical Technical Guidance Manual, dated May.

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

Federal Highway Administration (FHWA), 2014, Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects FP-14.

Federal Highway Administration (FHWA), 2017(a), Soil Description and Identification Guidelines, dated December.

Federal Highway Administration (FHWA), 2017(b), Rock Characterization Guidelines, dated December.

Hawthorne Cat, 2018, “Caterpillar Performance Handbook,” Edition 48, dated June.

Isenhower, William M., Wang, Shin-Tower, and Vasquez, Gonzalo L., 2020, “LPILE v2019

Technical Manual: A Program for the Analysis of Deep Foundations Under Lateral Loading,” Ensoft, Inc., dated March.

National Park Service (NPS), 2018, “Series: Physiographic Provinces, Rocky Mountain System Provinces,” updated May 1, < https://www.nps.gov/articles/rockies.htm>.

U.S. Geological Survey (USGS), 2020(a), “Quaternary Fault and Fold Database of the United States,” Interactive fault map & database search, USGS Earthquake Hazards Program, <https://www.usgs.gov/natural-hazards/earthquake-hazards/faults?qt-science_support_page_related_con=4#qt-science_support_page_related_con>.

U.S. Geological Survey (USGS), 2020(b), “Vs30 Map Viewer,” online map, USGS Earthquake Hazards Program, <https://earthquake.usgs.gov/data/vs30/>.

U.S. Geologic Survey (USGS), 2020(c), “U.S. Seismic Design Maps,” USGS Earthquake Hazards Program, <http://earthquake.usgs.gov/designmaps/us/application.php> & <https://earthquake.usgs.gov/ws/designmaps/aashto-2009.json?latitude=34&longitude=- 118&siteClass=C&title=Example>.

Ver Ploeg, A.J., and Boyd, C.S., 2002, “Geologic map of the Buffalo 30’ x 60’ Quadrangle, Johnson and Campbell Counties, Wyoming,” Wyoming State Geological Survey, Map Series Ms59, scale 1:100,000.

Page | 20

Weaver, J.M., (1975), “Geologic Factors Significant in the Assessment of Rippability,” The Civil Engineer in South Africa (Die siviele ilngenieur in Suid-Afrika), Volume 17, Issue 12, pgs. 313-316.

Western Regional Climate Center (WRCC), 2022, “Buffalo, Wyoming Period of Record Monthly Climate Summary,” < https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?wybuff>, Accessed November 21, 2022.

Wyoming State Geological Survey (WSGS), 2022, “Geologic Hazards,” <https://www.wsgs.wyo.gov/hazards/hazards.aspx>, Accessed March 8, 2022.

PLATES

PROJECT VICINITY MAP,

GEOLOGY MAP & LEGEND,

GEOTECHNICAL BORING LOCATIONS, AND

WYOMING GEOLOGIC HAZARDS MAP

STATE PROJECT

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

NOT TO SCALE

PLATE

PROJECT VICINITY MAP

WY

CRAZY WOMAN CREEK BRIDGE

WY FLAP JOH 14(1) NORTH FORK

Project Location

(44.18761°, -106.83024°) Project Location

03/11/2021.

Google Maps, 2021. North Fork Crazy Woman Creek Bridge. Google Maps [online].

MONTANA

IDAHO

SOUTH DAKOTA

NEBRASKA

COLORADOUTAH

Casper

CHEYENNE

Sheridan

Jackson

Rock

Springs

Riverton

KEY MAP OF WYOMING

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

Gillette

Cody

Thermopolis

Worland

Rawlings

U.S. DEPARTMENT OF TRANSPORTATION

NOT TO SCALE

PLATE

GEOLOGY MAP

WY

CRAZY WOMAN CREEK BRIDGE

WY FLAP JOH 14(1) NORTH FORK

Ver Ploeg, A.J. and Boyd, C.S., 2002, "Geologic Map of the Buffalo 30' x 60' Quadrangle, Johnson and Campbell Counties, Wyoming", Wyoming State Geological Survey, Map Series MS 59, Scale 1:100,000

(44.18761°, -106.83024°) Approximate Project Location

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

PLATE

GEOLOGY MAP LEGEND

WY

CRAZY WOMAN CREEK BRIDGE

WY FLAP JOH 14(1) NORTH FORK

U.S. DEPARTMENT OF TRANSPORTATION

NOT TO SCALE

PLATE

HAZARDS MAP

WYOMING GEOLOGIC

WY

CRAZY WOMAN CREEK BRIDGE

WY FLAP JOH(1) NORTH FORK

"2035 Plumas General Plan Update Draft Environmental Impact Report," Seismic and Geologic Hazards, Figure 4.7-1

(44.18761°, -106.83024°)

Approximate Project Location

APPENDIX A

FIELD EXPLORATION PROGRAM

APPENDIX A

FIELD EXPLORATION PROGRAM

A.1 INTRODUCTION

The Central Federal Lands Highway Division (CFLHD) Geotechnical Section completed a field exploration program for WY FLAP JOH 14(1) North Fork Crazy Woman Creek Bridge on July

26th, 2022. The scope of work for the field exploration program included drilling a single boring to a depth of approximately of 39 feet. The sole geotechnical boring was drilled near the east bridge abutment. The field exploration program was coordinated and observed by a Geotechnical Engineer from CFLHD. Field exploration locations are illustrated on Plate 4. The individual boring log is attached. This log represents a compilation of field and laboratory data and description of the soil samples by CFLHD Geotechnical personnel. The methods used to conduct the field exploration program are described below. Photos of drilling equipment and field exploration activities are included in Appendix C. All soil and rock samples collected during the field exploration program were transported to the CFLHD Materials

Laboratory in Lakewood, Colorado for testing. A summary of the laboratory testing program is provided in Appendix B.

A.2

A.3

EXPLORATIONS

Boring(s)

Haz-Tech Drilling of Billings, Montana provided the drilling services for the soil boring.

The boring was completed using a Longyear BK81 truck mounted drill rig. The boring was advanced through overburden using hollow stem augers with drive sampling until practical augur refusal was encountered. After refusal, the boring was advanced using a rock coring and continuous sampling system. Following drilling activities, field personnel backfilled the boring with cuttings generated during the drilling in accordance with applicable local, state, and federal regulations.

If water was encountered at the time of drilling, field personnel measured water levels in the boring. Fluctuations in the ground water level due to seasonal and climatic effects are expected.

SOIL AND ROCK SAMPLING

Boring(s)

Disturbed sampling was attempted from the boring in accordance with the Standard Penetration Test (SPT), the procedures of which are detailed in AASHTO T-206. The

SPT involves driving a 2-inch outside diameter, 1.375-inch inside diameter split spoon aaron.baukus Sticky Note Completed set by aaron.baukus aaron.baukus Sticky Note Accept set by aaron.baukus aaron.baukus Sticky Note Accepted set by aaron.baukus aaron.baukus Sticky Note Accept set by aaron.baukus aaron.baukus Sticky Note Accepted set by aaron.baukus aaron.baukus Sticky Note Accepted set by aaron.baukus aaron.baukus Sticky Note Completed set by aaron.baukus aaron.baukus Sticky Note Completed set by aaron.baukus aaron.baukus Sticky Note Completed set by aaron.baukus aaron.baukus Sticky Note Completed set by…