Geotechnical_NE_FLAP_7136(1)_MONTROSE_BRIDGE.pdf

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HAT CREEK BRIDGE

MONTROSE ROAD 7136

SIOUX COUNTY, NE

NE FLAP 7136 (1)

Final Geotechnical Report Report No. NE-FLAP-7136 (1) -001-16

Prepared by Federal Highway Administration

Central Federal Lands Highway Division

Geotechnical Services Branch October 2017 i

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 SEISMIC DESIGN PARAMETERS

SECTION THREE - SUBSURFACE INVESTIGATION

3.1 FIELD EXPLORATION

3.2 SUMMARY OF SITE CONDITIONS

3.3 LABORATORY TESTING

SECTION FOUR - ANALYSIS AND RECOMMENDATIONS

4.1 BRIDGE FOUNDATION DESIGN

4.1.1 Geotechnical Profile

4.1.2 Groundwater Conditions

4.1.3 Montrose Bridge Foundation Selection

4.1.4 LRFD Driven Pile Foundation Design

4.1.5 Pile Setup

4.1.6 Group Effects on Axial Resistance

4.1.7 Lateral Loads

4.1.8 Settlement

4.1.9 Pile Drivability

4.2 ABUTMENT DESIGN

4.3 EMBANKMENT CONSTRUCTION

4.4 CONSTRUCTION CONSIDERATION

4.5 SPECIFICATIONS

4.6 DISCLAIMER/LIMITATIONS

SECTION FIVE - REFERENCES

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TABLES

TABLE 2.1 Summaries of Seismic Parameters for Earthquake with 1000-Year Return Period TABLE 3.1 Summary of Test Hole Locations and Information TABLE 3.2 Summary of Laboratory Index Tests of Retrieved Soil Samples TABLE 3.3 Electro-Chemical Test Results

TABLE 4.1 Proposed Bridge Foundation Locations

TABLE 4.2 Summary of Geotechnical Design Values

TABLE 4.3 N1(60) Calculation at Bridge Location

TABLE 4.4 Summary of Pile Design Recommendations TABLE 4.5 LPILE Parameters for Soil TABLE 4.6 LPILE Parameters for Shale TABLE 4.7 Lateral Earth Pressures for Bridge Abutments

FIGURES

FIGURE 4.1 Axial Resistance

APPENDICES

APPENDIX A Vicinity & Boring Location Map, Boring Logs, Hammer Efficiency Report APPENDIX B Laboratory Data APPENDIX C Photographs

Montrose Bridge, NE FLAP 7136(1)

SECTION ONE - Introduction

1.1 BACKGROUND AND LOCATION

This report presents the findings of a subsurface investigation and provides geotechnical recommendations for the proposed Hat Creek Bridge replacement located along Montrose Road in Sioux County, Nebraska. The bridge provides access to the Oglala National Grasslands to the north.

Project vicinity and location maps are presented on Figure 1 in Appendix A.

The Central Federal Lands Highway Division (CFLHD) of the Federal Highway Administration (FHWA), in cooperation with the Oglala National Grasslands and Sioux County is proposing to replace the existing deficient approximately102-foot long, 16-foot wide, single-span bridge over Hat Creek to meet the current design load standards per American Association of State Highway and Transportation Officials–Load Resistance Factored Design (referred to as AASHTO) guidelines.

The deficient existing bridge was constructed in 1915 with a timber deck. The bridge abutments are founded on five 6-inch x 8-inch steel piles spaced at about 50 inches on center. Wingwalls consisting of piles with timber lagging approximately 8-feet long with a 45-degree flare are present at both abutments.

Original bid documents provided by Sioux County indicated that the abutment foundation piles were bid to be 30-feet long. The actual constructed pile length has not been verified.

The proposed replacement 106-foot long 20-foot wide bridge will be located near the same alignment as existing. The existing bridge piles will remain but will not be accounted to resist design loads. The replacement bridge abutments will be constructed on top of the existing piles. The roadway leading to the bridge is a low volume road with gravel surface. It is expected that the roadway will be closed during construction and hence, no temporary structure will be required.

1.2 SCOPE AND PURPOSE

The scope of work includes subsurface investigation and analysis for determining the subsurface profiles and ground water conditions at each abutment, determining material physical properties for foundation design, and providing 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 based on engineering analysis for the design and construction of the Hat Creek Bridge replacement. The stationing in this report is based on the preliminary 30 percent project plans, July 2017.

SECTION TWO – Geology and Seismicity

2.1 GEOLOGY

The project is located within the planes region of northwest Nebraska which generally contains alluvial and eolian deposits underlain by sedimentary bedrock. The alluvial deposits are generally characterized by fine grained sand deposits with varying amounts of silt and clay while the eolian deposits are typically comprised of silt with varying amounts of fine grained sand. The bedrock within northwest Nebraska are comprised of tertiary and cretaceous age sedimentary units which are typically present within about 30 to 50 feet of the ground surface.

The geology at the bridge site consists mainly of alluvial fine grained sands, low plasticity clays, and silts underlain by shale bedrock of the Pierre formation at a depth of approximately 35 feet from the ground surface elevation at the bridge abutments. A weathered zone at the transition from soil to bedrock was encountered in both borings and ranged in thickness from one to two feet. The Pierre shale is a marine unit deposited in the late Cretaceous period and consists primarily of a dark gray shale with occasional veins and seams of gypsum and iron oxide. A description of the soil and rock encountered from the borings will be discussed in more detail in following sections.

2.2 SEISMIC DESIGN PARAMETERS

Based on the AASHTO site classification criteria, the predominant subsurface soils, 35 feet of overburden alluvial soil overlaying bedrock, at the bridge site (42.9222 latitude and -103.7425 longitude) can be classified as a stiff soil profile corresponding to Site Class D. 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 bridge site 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) are summarized Table 2.1

TABLE 2.1 - Summary of Seismic Parameters for Earthquake with 1000-Year Return Period

Horizontal Peak Ground Acceleration, (PGA) 0.053 g Horizontal Response Spectral Acceleration at Period of 0.2 sec, (Ss) 0.115 g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (S1) 0.030 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) 0.085 g Factored Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.184 g Factored Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.072 g

Seismic Zone Zone 1

SECTION THREE–Subsurface Investigation

3.1 FIELD EXPLORATION

An engineer from the Central Federal Lands Highway Division (CFLHD) Geotechnical Group observed the field exploration program that was completed on May 15th, 2017. The field investigation included site characterization and drilling two borings, one at each abutment. The individual boring logs represent 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.

Representative soil and rock samples collected during the field exploration program were transported to the CFLHD Materials Laboratory in Lakewood, Colorado for testing. Detailed boring logs are presented in Appendix A. A summary of the laboratory testing program is provided in Appendix B. Photos of drilling equipment and field exploration activities are included in Appendix C.

The location and elevation of individual borings were estimated relative to features shown on the preliminary 30 percent project plans. Boring locations are listed on individual boring logs and are show below in Table 3.1.

TABLE 3.1 - Summary of Test Hole Locations and Information

FOUNDATION

DESIGNATION

BORING

NUMBER

STATION OFFSET

GROUND

ELEVATION

TERMINATION

ELEVATION

BEDROCK

ELEVATION

Abutment #1 BH-01 11+45 5-ft RT 3,606 ft 3,546 ft 3,570 ft Abutment #2 BH-02 13+10 5-ft RT 3,605 ft 3,555 ft 3,570 ft

Vine Laboratories, Inc. of Denver, Colorado provided the drilling services using a CME-55 truck-mounted drill rig. The borings were advanced through the overburden soil and shale bedrock using 4-inch outside diameter solid stem augers. Upon completion of drilling activities, field personnel backfilled the borings with cuttings generated during the drilling in accordance with applicable local, state, and federal regulations.

Disturbed samples were obtained from the borings in accordance with the Standard Penetration Test (SPT), the procedures of which are detailed in AASHTO T-206. An automatic-trip hammer with 90 percent efficiency was used to drive the samplers 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. A 2.5-inch outside diameter, 2-inch inside diameter modified California sampler lined with brass tubes was also used to retrieve soil samples in clay layers. The number of blows required to advance the sampler through every 6-inch increments was recorded. 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.

Representative soil from the split-spoon samples were placed in plastic bags and transported to the CFLHD Materials Laboratory for testing.

CFLHD Geotechnical personnel collected soil/rock samples and prepared field logs of the soils encountered within the borings. Soil identification and descriptions, as shown on the field logs, are based on ASTM D2488, a systematic process for identifying and describing individual soil samples by visual and manual means. When sufficient laboratory testing was completed, select samples from borings were classified using the Unified Soil Classification System (USCS) and AASHTO soil classification system. Both the visual soil identification system and the referenced soil and rock classification systems are summarized in Appendix A.

3.2 SUMMARY OF SITE CONDITIONS

At the field investigation time, the surface conditions at the boring locations consisted of gravel approach roads. Few cobbles or boulders were observed within the vicinity of the bridge location. The creek slope extending from the creek bottom to the east abutment appears to have slumped for a distance extending about 25 feet north and south of the bridge. The head scarp of the surficial slump has an opening of generally less than 6-inches with a 1-foot maximum observed and a vertical offset of generally about 1-foot with localized areas of up to about 3-feet. No obvious deflections or rotations of the existing bridge abutment were observed in relation to the slumped area.

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 process.

Groundwater elevations were measured during the subsurface investigation between elevation 3,588 and 3,589 feet. Fluctuations in the ground water level due to seasonal and climatic effects are expected. The following is a detailed description of materials encountered at each foundation location:

BRIDGE ABUTMENT 1 (STATION 11+45):

The subsurface conditions were investigated at the west abutment by drilling boring BH-01. The subsurface materials encountered broadly consisted of silt and clay layers with one silty sand layer underlain by shale bedrock. The gravel approach road was less than 3-inches thick. Low plasticity silt with varying clay content was encountered below the surface gravel to a depth of 6-feet. The silt layer was underlain by a stiff medium plasticity lean clay to a depth of 20-feet. A very loose layer of fine to medium grained silty sand was present from 20-feet to 25-feet. A soft to firm lean clay layer with a high silt content and seams of fat clay was present overlying the bedrock from 25-feet to 36-feet. The shale bedrock contained a one foot thick weathered layer. Groundwater elevation was encountered at a depth of 18 feet measured at the time of drilling.

SPT measurements in the overburden soils produced N-values ranging between 3 and 21 with the higher blow counts being contained in the stiff lean clay layer between 6 and 20 feet. Refusal blow counts ranging from 50 blows for 2 inches of penetration and 50 blows for 5 inches of penetration were recorded for the shale bedrock.

BRIDGE ABUTMENT 2 (STATION 8+29):

The subsurface conditions were investigated at the east abutment by drilling boring BH-02. The subsurface materials consisted of a silty clay layer underlain by silty sand layer with a fat clay layer before encountering shale bedrock. Similar to boring BH-01, the gravel approach road was less than 3-inches thick. Low plasticity silty clay was encountered below the surface gravel to a depth of 15-feet.

The silty clay layer was underlain by a very loose to loose silty sand layer to a depth of 30-feet. A very firm fat clay layer was present overlying the bedrock from 30-feet to 35-feet. The shale bedrock contained a two-foot thick weathered layer. Groundwater elevation was encountered at a depth of 19 feet measured at the time of drilling.

SPT measurements in the overburden soils produced N-values ranging between 2 and 8 with the blow count of 8 occurring within the fat clay layer at 30 feet. Refusal blow counts ranging from 50 plows for 2 inches of penetration and 50 blows for 5 inches of penetration were recorded for the shale bedrock.

3.3 LABORATORY TESTING

Laboratory index tests on recovered soil samples included; gradation (AASHTO T88), classification (AASHTO M145), Atterburg limits (AASHTO T89 and T90), and natural moisture content (AASHTO T 255) were conducted to provides an estimation of the soil’s mechanical properties. A summary of the soil test results are shown in Table 3.2. Detailed laboratory test results are presented in Appendix C.

TABLE 3.2 - Summaries of Laboratory Index Tests of Retrieved Soil Samples

BORING

NUMBER

SAMPLE

DEPTH,

ft

PERCENT

SAND

PERCENT

PASSING

LL PI

MOISTURE

CONTENT

DRY UNIT

WEIGHT

(PCF)

USCS AASHTO

BH-01 6 6 94 - - 29.2 - - -

BH-01 7.5 - - - - 20.5 106.1 - -

BH-01 10 - - - - 21.4 95.9 - -

BH-01 15 12 88 49 32 32.9 - CL A-7-6(29)

BH-01 20 - - - - 35.0 82.8 - -

BH-02 10 25 75

18.8 - CL-

ML

A-4(4)

BH-02 25 70.6 29.4 NV NP 25.3 115.5 SM A-2-4(0)

Electrochemical tests were conducted on selected soil samples to characterize the aggressiveness of the soil environment and its potential for deterioration of concrete and metallic elements necessitating special design considerations. The corrosion tests included pH (AASHTO T289) and resistivity (AASHTO T288). Since testing determined a minimum resistivity below 5,000 ohm-cm (considered corrosive soils) and a pH of 8.3, additional testing to determine the sulfate ion content (AASHTO T290) and chloride ion content (AASHTO T291) were performed on the soil sample. A summary of the electrochemical test results is shown in Table 3.3.

TABLE 3.3 - Electro-Chemical Test Results.

SAMPLE LOCATION pH

MINIMUM

RESISTIVITY

ohm-cm

SULFATE ION

CONTENT

ppm

CHLORIDE ION

CONTENT

ppm

BH-02 (15 ft to 30 ft) 8.3 597 580 25 BH-01 (2.5 ft to 7.5 ft) 8.5 Not Measured 90 11

Although electro-chemical test results for sulfate and chloride indicated that the soil may be corrosive to buried steel. However, due to the relatively high pH of the soils and the lack of oxygen within the deeper soils, steel loss is not expected to be significant. Additionally, drivability requirements resulted in greater pile thicknesses.

The water-soluble sulfate and chloride concentration levels will affect the corrosion process of concrete and metallic elements. It is recommended that the materials engineer at CFL be consulted to determine the optimum cement type, cementations mixture ratios, and steel corrosion protection measures that will effectively mitigate the effects of corrosive site soils.

SECTION FOUR – Analysis and Recommendations

A generalized subsurface profile was developed from field investigations, and laboratory testing on collected samples and was used for the bridge elements analysis, design, and construction considerations.

4.1 BRIDGE FOUNDATION DESIGN

The primary structure considered for this project is replacing the existing bridge with a new single-span structure approximately 106-foot long and 20-foot wide with a prefabricated superstructure and a minimum 2-½-inch aggregate surface. The proposed bridge will be located at about the same location and elevation as the existing alignment. The elevation of the proposed bridge deck and channel invert at centerline is about 3,605 feet and 3,588 feet respectively. Based on the 30 percent design plans, July 2017, 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 TOP OF PILE ELEVATION

Abutment 1 11+87.71 3,598.39 3,599.39

Abutment 2 12+93.71 3,598.39 3,599.39

It is anticipated that the piles will be embedded a minimum of one foot into the pile cap.

4.1.1 Geotechnical Profile

Generalized subsurface profiles and associated material properties were developed for foundation and abutment design. These profiles are based on the field investigation results, laboratory test results, and presumptive empirical strength characteristics of similar materials. Due to similarities in the two abutment borings, the more conservative profile was selected for design purposes. Selected design values are presented in Table 4.2.

In general, two distinctive cohesive soil layers, overburden material and weathered Pierre Formation shale (cohesive IGM), were encountered in each of the borings at similar elevations. These materials were generally characterized as CL with interbedded 5-foot sand, classified as SM that was encountered between elevations 3,586 and 3,581 feet as overburden material and weathered Pierre Shale at the bottom layer. Ground elevation is 3,606 feet.

TABLE 4.2 – Summary of Geotechnical Design Values

DEPTH

BELOW

GROUND

SURFACE

(FT)

MATERIAL

DESCRIPTION

TOTAL

UNIT

WEIGHT

(PCF)

EFFECTIVE

UNIT

WEIGHT1

(PCF)

UNDRAINED

SHEAR

STRENGTH2

(PSF)

FRICTION

ANGLE

(DEG)

RATE OF

INCREASE

OF SOIL

MODULUS3

(KSI/FT)

SOIL

MODULUS

(PCI)

0 - 20 Silty Clay 120 N/A 2,000 0 N/A 500 20 - 25 Silty Sand 115 52.6 0 32 0.556 20 25 - 37 Fat Clay 116 53.6 500 04 N/A 100 37 - 60 Shale 140 140 24,000 0 N/A 2,000

1Groundwater is estimated at approximately a depth of 17 feet from the surface (Elevation 3,588 feet). Effective unit weight is used below the groundwater surface.

2The undrained shear strength (Su) were estimated for low plasticity clays (PI≤10) and medium to high plasticity clays (11≤PI≤40) using the relationship developed by McGregor and Duncan, 1986.

3The modulus of elasticity for sand (Es) is assumed to increase linearly with depth starting at zero at the ground surface. The rate of increase of soil modulus (nh) is applied per foot of overburden (z) as shown in the equation Es=nh*z (AASHTO 2014, 7th Edition).

4Typcially, the internal friction angle () is considered negligible (=0) in cohesive soils.

The SPT-N values were measured every 5 feet and corrected for a hammer efficiency of 90 percent (based on calibration data provided by the driller) and overburden pressure to obtain the N1(60) values for LRFD foundation design. A summary of the steps used for determining a representative N1(60) value for deep foundation design purposes are shown in Table 4.3. The groundwater table was encountered at an approximate depth of 17 feet from the ground surface at the time of drilling, therefore, pore-water pressure is partially included in calculating the effective overburden stress.

SPT N1(60) values within the overburden materials range from 4 to 21 with the higher values occurring in the lean clay layer. Moderately to slightly weathered shale consistently measuring greater than 50 blows per foot were encountered at 36 (El. 3,570 ft) to 60 feet (end of borings). In general, SPT N-values obtained within shale reached 50 blows prior to penetrating 6 inches (indicative of very stiff material).

In cohesive soils, SPTs are not reliable for predicting strength and compressibility. Fine-grained, cohesive materials show different driving resistances when dry or moist, and if they become highly moist, they may not show the stiffness predicted by the SPT. From the field observations during subsurface explorations, the bedrock is expected to be a suitable foundation material for the H-piles. The shale was able to be drilled using a 4 inch outside diameter solid-stem auger. However, the hard shale will likely result in difficult driving conditions

TABLE 4.3 - N1(60) Calculation at Bridge Location

Boring SPT Depth1, ft σv' 2,ksf N3 N60 4 Cn

5 N1(60)

BH-01

1 2.5 0.3 6 7 1.60 11 2 5 0.6 4 5 1.60 7 3 7.5 0.9 21 22 1.49 33 4 10 1.2 20 21 1.29 27 5 15 1.8 8 11 1.05 11 6 20 2.275 3 4 0.94 4 7 25 2.538 5 7 0.89 6 8 30 2.806 3 4 0.84 3 9 35 3.074 13 19 0.81 15

10 40 3.462 50/5” 66 0.76 50 11 45 3.85 50/4” 74 0.72 53 12 50 4.238 50/2” 66 0.69 45 13 55 4.626 50/4” 74 0.66 48 14 60 5.014 50/2” 68 0.63 43

BH-02

1 5 0.6 4 5 1.60 7 2 10 1.2 5 6 1.29 8 3 15 1.775 2 3 1.06 3 4 20 2.225 3 4 0.95 4 5 25 2.488 5 6 0.90 6 6 30 2.756 8 12 0.85 10 7 35 3.024 42 56 0.81 45 8 40 3.412 50 74 0.77 56 9 45 3.8 50 66 0.73 48

10 50 4.188 50 74 0.69 51 1Begining depth of SPT-N reading

2Effective overburden pressure

3Field SPT-N value 4Calculated using AASHTO equation 10.4.6.2.4-2

4.1.2 Groundwater Conditions

Groundwater elevations have an effect on resistance under axial loads, lateral loads, and pile driving through cohesionless soils. Groundwater was encountered at an approximate depth of 17 feet during drilling, an elevation close to the stream channel as shown on the boring logs in Appendix A.

Groundwater should be anticipated during foundation construction and pile driving operations.

4.1.3 Bridge Foundation Selection

Deep foundations were selected as the preferred bridge foundation alternative. Shallow footings were determined unfeasible due to the existence of near surface soft compressible layers, depth from the abutment elevation to the stream channel, and design/check scour elevations of 3,577.94 (27 feet below existing ground surface).

Deep foundation options were evaluated based on feasibility and costs. Driven piles, drilled shafts, and micropiles were all considered feasible at this project site. Based on encountered subsurface materials at the project site, local construction practices and foundation costs, driven, non-displacement, steel H-piles are recommended for the foundation at the bridge abutments. It is anticipated that piles can be driven to design depth within the shale to meet required lateral and axial design resistances. The piles are designed to have adequate geotechnical and structural axial and lateral resistances for a tolerable settlement of up to ½-inch provided by bridge engineers.

4.1.4 Driven Pile Foundation Design

Driven steel H-piles (HP14x89) will be used as the main foundation system to resist design loads. The piles will gain axial resistance from side and tip resistance mostly within the Pierre shale below the scour depth.

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 methods, testing, and monitoring (such as static load test, dynamic analysis, and wave equation analysis). Table 4.4 presents the service loads and factored loads for each of the abutments as provided by the structural engineer.

It is assumed at least two piles (one at each abutment) will be tested using the Pile Driving Analyzer (PDA) and signal matching at end of driving and after restrike. 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 4.4.

TABLE 4.4:- Summary of Pile Design Recommendations

Pile Type

Cut-off Elev.

(ft)

Service-I Limit State Load (kips)

Total Estimated Settlement (in)

Required Factored Nominal Resistance (kips)

Strength Limit State

(Φ=0.65) (1)

Design Tip Elev.(2)

(ft)

Required Nominal Driving Resistance

(kips)

HP

14x89

3,599 140 ¼ 340 3,563 420

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

2. Minimum design tip elevation from comparison of compression and tension in the strength limit state and extreme event state, settlement, and lateral load requirements.

If the pile driving analyzer (PDA) is not used during installation, a resistance factor of 0.40 should be used to determine the nominal pile resistance. Inspector charts based on the wave equations will be developed by the contractor once the driving equipment and accessories are selected. A set of graphs of the calculated nominal and factored axial resistances for PDA testing and wave equation analysis are presented in Figure 4.1. To meet the required axial and lateral resistances, the piles must be driven to a minimum elevation of 3,563 feet.

Pile installations will likely encounter hard driving within the bedrock material and may result in difficult and slow driving conditions during the installation. We recommend the use of protective pile tips welded to the end of each pile to reduce the possibility of pile damage during driving in bedrock.

FIGURE 4.1:- Axial Resistance

0 200 400 600 800 1000 1200

El e va ti o n ft

Axial Resistance (kips)

Nominal Resistance

Factored Resistance (0.40)

Factored Resistance (0.65)

Notes:

1. No reduction for non‐redundant piles required.

2. Top of pile assumed to be at Elevation 3,598 feet.

3. Scour elevation assumed to be at Elevation 3,578 feet.

Scour Elevation = 3,578 ft

Top of Pile = 3,598 ft

4.1.5 Pile Setup

Pile setup is an increase in the nominal axial resistance that develops over time, predominantly along the pile shaft. 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 at the Montrose Bridge due to the shale encountered.

4.1.6 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 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 smaller to avoid interference between adjacent piles during construction. Therefore, an efficiency factor (η) of 1.0 is applied for the pile group with center-to-center spacing of 2.5 diameters or more. It is anticipated that there will be four piles at each abutment spaced at 52 inches apart, which corresponds to an efficiency factor of 1.0. Embedment of the piles into the pile cap should be at least 12.0 inches to meet AASHTO requirements. AASHTO guidelines consider 4 piles or less as non-redundant and the resistance factor should be reduced by additional 20 percent. However at this site the existing abutments which are supported by 5 piles each will be kept in place and will be accounted on for additional support that is not used in the pile resistance calculations. For this reason, it is assumed that each abutment is supported by 9 piles which is considered redundant support and hence the 20 percent reduction does not apply.

4.1.7 Lateral Loads

Lateral soil-structure interaction analysis of the driven piles is performed by CFL Bridge Engineer on single and group piles. For lateral loading analyses, use the subsurface soil parameters provided in Table

4.5 and 4.6 to estimate the lateral load displacement behavior. The values presented in Table 4.5 and 4.6 do not include reduction factors or load factors. 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.

TABLE 4.5:- LPILE Parameters for Soil

DEPTH

BELOW

GROUND

SURFACE

(FT)

LPILE P-

Y

MODEL

EFFECTIVE

UNIT

WEIGHT

(PCF)

FRICTION

ANGLE

(DEG)

HORIZONTAL

SUBGRADE

MODULUS, Ks

(PCI)

UNDRAINED

COHESION

(PSF)

STRAIN

FACTOR, 50

0 - 12 Stiff Clay without

Free Water 120 N/A N/A 2,000 0.006

12 - 20 Stiff Clay without

Free Water

52.6 N/A N/A 2,000 0.006

20 - 25 Sand

(Reese)

52.6 32 20 N/A N/A

25 - 37 Soft Clay 53.6 N/A N/A 500 0.016

TABLE 4.6:- LPILE Parameters for Shale

Soil Type Weak Rock

Effective Unit Weight (’), pcf 140

Elastic Modulus (E), psi 8000

Uniaxial Compressive Strength (UCS), psi 330

Average RQD 50

Softness Constant (Krm), pci 0.0005

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.

4.1.8 Settlement:

Since the piles will be embedded adequately into bedrock the piles are not subjected to downdrag loads, a detailed assessment of the pile group settlement was not warranted (AASHTO). The settlement of the piles driven to refusal is expected to be less than 0.25 inches.

4.1.9 Pile Drivability

The piles should be driven with a hammer capable of delivering energies in the range of approximately 25,000 to 53,000 foot-pounds of energy per blow. To prevent development of excessive stresses in the piles during the driving operations, the hammer energy (or stroke) should be carefully controlled during the initial stages of pile driving where the pile tip is within the soft soil layer. The minimum driving resistance required will depend on the type of hammer and pile driving equipment used. The contractor should conduct drivability analysis using the WEAP equation to select hammers that will not cause the driving stresses (compression and tension) in the pile to exceed the acceptable levels.

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

One test pile at each 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 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 4.7. The values are unfactored loads and assume that the surface of the soil slope behind the wall is horizontal.

TABLE 4.7:- 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

Unclassified Borrow c = 0 psf = 30 deg.

γ = 125 pcf

Active 37

At-Rest 63

Silty Clay (CL-ML) c = 0 psf = 28 deg γ = 115 pcf

Active 37

At-Rest 61

4.3 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 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.

On-site soils encountered within the anticipated excavation and construction limits generally consist of low plasticity clay and silt 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.

4.4 CONSTRUCTION CONSIDERATIONS

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. It is unlikely that a pile driven using the analyzed criteria will experience damage due to excessive driving stresses.

Driving shoes should be placed on the pile tips to reduce the risk of installation damage while driving the pile through the shale bedrock. Prefabricated H-pile shoes come in various shapes and sizes.

Manufacturers also recommend different shapes for various applications and should be asked to include the shape of the shoe in the pile submittal. Several manufactured driving shoes are available that attach to the H-piles with fillet welds along the outside of each flange. Pile shoes fabricated from cast steel (ASTM A 27) are recommended because of their strength and durability.

4.5 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.

4.6 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, 2016, 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

APPENDIX A-Vicinity and Boring Location Map, Boring

Logs, Hammer Efficiency Report

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CL

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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

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T H

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H A

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IS

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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

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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

0.0 - 6.0 ft SILT (ML): soft to firm, light greenish brown, moist, less than 10% fine grained sand, low to medium plasticity, varying clay content

6.0 - 20.0 ft Lean CLAY (CL): stiff, dark grayish brown with some white streaks, moist, less than 10% fine grained sand, medium plasticity

15.0 ft increased white streaks with black pieces

18.0 ft wet below 18 feet

20.0 - 25.0 ft Silty SAND (SM): very loose, light greenish brown, wet, non-plastic

25.0 - 36.0 ft Lean CLAY (CL): soft to firm, light brown, wet, medium plasticity, high silt content, some thin Fat CLAY (CH) layers

2/3/3

1/2/2

11/10

8/12

2/4/4

1/2

2/2/3

1/2

SPT

SPT

MC

MC

SPT

MC

SPT

MC

1.17 78%

1.50 100%

1.00 100%

1.00 100%

1.50 100%

1.00 100%

1.50 100%

1.00 100%

U .S

.C .S

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

BORING LOG

18ft

5/15/2017

Driller: Vine Laboratories G ra ph ic L og

Description: (Density, Color, Type, Moisture, Other)

R un

/S am p N

o. Length Recov.

feet

% Rec.

Sheet 1 of 2Date: May 2017Project Name: Montrose Bridge

Boring Location: STA 11+45, 5 ft RT

Coordinates: N 42.9224 E -103.7429

Drill: CME 55

Field Logged By: D. Robbins

Revisions/Final By: D. Robbins

Depth Elevation

(feet)

RQD

SPT

Blows per 6 in

Boring No. BH-01

Type of Boring: Solid Stem Auger

Casing Used: N/A

Boring Began: 5/15/17

Ground Elev: 3606.0 ft

Water Depth:

Date:

Time:

Size: 4" O.D.

Completed: 5/15/17

Weather: Sunny, 71°F

B O

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/9 /1

36.0 - 37.0 ft Weathered SHALE: gray to dark gray, hard, some gravel

37.0 - 60.2 ft SHALE: Pierre Formation, gray to dark gray, hard to very hard

BHT at 60.2 ft

2/2/11

50/5"

11/50/4"

50/2"

50/4"

50/2"

SPT

MC

SPT

MC

SPT

MC

3545.8

1.50 100%

0.42 100%

0.83 100%

0.17 100%

0.33 100%

0.00 0%

U .S

.C .S

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

BORING LOG

18ft

5/15/2017

Driller: Vine Laboratories G ra ph ic L og

Description: (Density, Color, Type, Moisture, Other)

R un

/S am p N

o. Length Recov.

feet

% Rec.

Sheet 2 of 2Date: May 2017Project Name: Montrose Bridge

Boring Location: STA 11+45, 5 ft RT

Coordinates: N 42.9224 E -103.7429

Drill: CME 55

Field Logged By: D. Robbins

Revisions/Final By: D. Robbins

Depth Elevation

(feet)

RQD

SPT

Blows per 6 in

Boring No. BH-01

Type of Boring: Solid Stem Auger

Casing Used: N/A

Boring Began: 5/15/17

Ground Elev: 3606.0 ft

Water Depth:

Date:

Time:

Size: 4" O.D.

Completed: 5/15/17

Weather: Sunny, 71°F

B O

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IN

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ID

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/9

0.0 - 15.0 ft Silty CLAY (CL-ML): soft to firm, light greenish brown, moist, less than 10% fine grained sand, low to medium plasticity, varying clay content, some Lean CLAY (CL) layers

15.0 - 30.0 ft Silty SAND (SM): very loose…