WY_FLAP_129(1)_Geotech_Rpt_Final_02.02.15.pdf

SAND CREEK ROAD

WY FLAP 129(1)

FINAL GEOTECHNICAL REPORT

Report # WY-FX-0129-15-01

Geotechnical Section

Technical Services Branch

January, 2015

Table of Contents

SECTION ONE--INTRODUCTION

1.1 OBJECTIVE AND SCOPE

SECTION TWO--GEOLOGY AND SEISMICITY

2.1 GEOLOGY

2.2 SEISMIC DESIGN PARAMETERS

SECTION THREE--SUBSURFACE INVESTIGATION

3.1 FIELD EXPLORATION

3.2 SUMMARY OF SUBSURFACE EXPLORATION

3.3 LABORATORY TESTING

SECTION FOUR--ANALYSIS AND RECOMMENDATIONS

4.1 BRIDGE FOUNDATION DESIGN

4.1.1 GRS-IBS DESIGN RECOMMENDATIONS

4.1.2 MICROPILE DESIGN RECOMMENDATIONS

4.1.2.1 GEOTECHNICAL AXIAL RESISTANCE

4.1.2.2 LATERAL LOAD ANALYSIS

4.2 ABUTMENT DESIGN

4.3 CORROSION POTENTIAL

4.4 GABIONS

4.4.1 GABION WALL DESIGN

4.5 SHRINK/SWELL RECOMMENDATIONS

4.6 CONSTRUCTION CONSIDERATIONS

4.7 SPECIFICATIONS

4.8 LIMITATIONS

SECTION FIVE -- REFERENCES

TABLES

TABLE 1: Summary of Seismic Parameters Corrected for Site Class E

TABLE 2: Summary of Design Response Spectrum Data for Site Class E Soil

TABLE 3: Summary of Borings

TABLE 4: Summary of Soil Classification Index Tests

TABLE 5: Summary of Electrochemical Parameters

TABLE 6: Summary of Proposed Bridge Dimensions, Loading conditions and Recommended

Foundation Type

TABLE 7: Estimated Subsurface Material Parameters Used for GRS-IBS Bridge Foundation

Design

TABLE 8: Design Parameters and Analysis Results for the GRS-IBS Abutment Design

TABLE 9: Factored Geotechnical Capacity for Various Bond Diameters and Lengths

TABLE 10: Soil Strength Parameters for LPILE Analysis

TABLE 11: Lateral Earth Pressures for Abutments Founded on Micropiles (Bridges 3 and 4)

TABE 12: Summary of the Stability Analysis Results for a Gabion Wall with 1V:12H Batter.

FIGURES

FIGURE 1: Project Location and Site Map FIGURE 2: Design Response Spectrum Corrected for Class E Soil

FIGURE 3: GRS Construction Notes

FIGURE 4: Sand Creek Bridge #1 Plan and Elevation

FIGURE 5: Sand Creek Bridge #2 Plan and Elevation

FIGURE 6: Sand Creek Bridge #3 Plan and Elevation

FIGURE 7: Sand Creek Bridge #4 Plan and Elevation

FIGURE 8: Sand Creek Bridge #5 Plan and Elevation

FIGURE 9: Sand Creek Bridge #6 Plan and Elevation

FIGURE 10: Gabion Faced Wall W253-2

APPENDICES

APPENDIX A: Field Exploration (Boring Logs)

APPENDIX B: Laboratory Test Results

APPENDIX C: GRS-IBS Analysis

APPENDIX D: Photographs

APPENDIX E: Special Contract Requirements

APPENDIX F: Gabion Wall Design

SECTION ONE--INTRODUCTION

This report presents the foundation recommendations for the six bridges on the Sand Creek

Road, WY FLAP 129(1) project. The Federal Highway Administration (FHWA) Central Federal

Lands Highway Division (CFLHD), in cooperation with the Black Hills National Forest and

Crook County, is proposing bridge replacements at Sand Creek crossings on Sand Creek Road from milepost 3.4 to 5.6. Milepost 0.0 is at the intersection of Beulah, WY at I-90. Figure 1 displays the project location and site map.

FIGURE 1:- Project Location and Site Map

Of the six proposed bridges, four are to be constructed on shallow foundations of Geosynthetic

Reinforced Soil abutments and an Integrated Bridge System (GRS-IBS) with prefabricated pre-stressed concrete girders. The other two bridges are to be constructed of cast-in-place abutments on deep foundations due to scour. The bridges will be two-lanes wide, ranging from 28 to 32 feet, and extend from 38 to 65 feet in length. The project also entails 6 miles of pulverizing and aggregate surfacing. This road serves as the primary access for recreational destinations and private residences along the route.

1.1 OBJECTIVE AND SCOPE

The objectives of this investigation were to develop recommendations concerning structure foundations, subsurface drainage, corrosion potential, and shrink/swell values. In accomplishing these objectives, the scope of work included field exploration, laboratory testing, correlation of available data, and engineering analysis and recommendations. The field investigations included subsurface exploration conducted by CFLHD engineering geologist. The interpretation of laboratory testing, correlation of available data, and engineering analysis was conducted by geotechnical personnel from CFLHD.

SECTION TWO--GEOLOGY AND SEISMICITY

2.1 GEOLOGY

Sand Creek Road is located on the west portion of the Black Hills located in the Great Plains

Geologic Province. The Great Plains Geologic Province is generally characterized by badland topography, sparse vegetation, canyons and rivers but in the western Black Hills it is characterized as red rock cliffs, pine covered hills with younger Eocene age (53 to 55 million years old) igneous intrusions. The rocks of the Great Plains consist of a thick sequence of sedimentary rocks overlying an ancient crust consisting of igneous and metamorphic rocks similar to those exposed in the core of the Black Hills. Over time some of the areas have subsided forming basins, while others have rose forming domes and plateaus. Shallow seas have advanced and retreated many times across the region. Uplift of the Ancestral Rocky Mountains in the late Paleozoic Era generated large quantities of sand and clay sediments that filled basins across the region. As large land masses began to split apart, rivers draining westward from the

Appalachian region flowed into a low mid-continent landscape. During the Tertiary Period, the region was near sea level and brackish inland seas and lakes still existed throughout the Western

Interior region. Mountain building processes that started in the late Cretaceous continued through the mid-Tertiary. Rivers deposited sediments over vast expanses of the exposed plains.

Volcanism also continued and spread airborne ash that eventually mixed with the sediments, stacking up to thousands of feet thick. By the end of the Tertiary Period, dry conditions existed.

During the Quaternary Period, continental glaciation impacted the landscape because of the influence on regional river systems.

The rock outcrops along Sand Creek are sedimentary rocks of Jurassic and Triassic Periods (144 to 245 million years old) and consist of sandstone, siltstone, shale, limestone and chert. It is the harder and more resistant sandstone and limestone that form the boulder outcrops as the shale and siltstone are more easily eroded. The strata is generally west dipping due to the domal uplift of the Black Hills with the older rock in the center and concentrically younger rock along the flanks of the dome that resemble a bulls eye.

The geology underlying the bridges along Sand Creek Road consisted of alluvial soils overlying bedrock consisting of Mesozoic Era sedimentary rock. The alluvial soils consisted mostly of sands, gravels and cobbles; however clays and boulders were also present at some of the bridge locations. The alluvial soils are derived from a combination of Paleozoic Era igneous and metamorphic rocks, Mesozoic Era sedimentary rocks, and harder Tertiary Period volcanics. The bedrock consisted primarily of sandstone but limestone, siltstone and chert were also present.

SEISMICITY

There are no known active faults within the vicinity of the project site and it is geologically located in a low seismic area, as described further in the following section.

2.2 SEISMIC DESIGN PARAMETERS

The American Association of State Highway and Transportation Officials (AASHTO) criteria for seismic design of ordinary bridges, allows for damage to occur when the structure is subjected to 1000-year strong ground motion, but does not allow for collapse of one or more spans and loss of life. Bridges may suffer damage that requires repair or partial replacement.

However, AASHTO requires bridges to withstand small, more frequent earthquakes without damage. For Extreme Event I Limit State Design an earthquake load and resistance factor of 1.00 should be used during the LRFD design of the bridge structure.

Recommended seismic response parameters for the Sand Creek Road Bridges Project design are based on the (AASHTO) LRFD Bridge Design Specifications, 5th edition, 2012, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years

(approximately 1000-year return period). The 1000-year return period uniform hazard spectrum for the bridge site, located at 44.498º N latitude and -104.102º W longitudinal, was obtained in accordance with the AASHTO ground motion maps for the probabilistic horizontal acceleration values corresponding to specific peak ground acceleration (PGA) and the spectral coefficients, namely the short- and long- period ground acceleration (Ss and S1 respectively) and corrected for the soil profile at the bridge sites.

Ground motions caused by earthquakes are influenced not only by the distance from the fault planes, but also by the geology and soils found at the site. Subsurface profiles similar to the ones at the project site, with soil layers overlaying bedrock, will have amplified ground motions and a resonant period governed by the layer thickness and shear wave velocity of the materials. The damage potential of strong ground motions with respect to a structure is typically affected by the period of the strong earthquake motion and the resonant period of both the soil and the structure.

Based on the subsurface profile at the bridge site, the average time-weighted shear wave velocity for the top 100 feet (VS100) of subsurface materials was estimated under 600 feet per second based on observed average Standard Penetration Test (SPT) of blow counts is less than 15 blows per foot. Therefore, the site was classified as Site Class E according to the site class definitions specified in Table 3.10.3.1-1 of AASHTO.

A seismic hazard analysis to establish ground motions for seismic design was conducted. The recommended spectral acceleration coefficient values for probabilistic design with a return period of 1000 years were calculated using the program provided with the AASHTO LRFD

Bridge Design Manual developed by the USGS (2008) entitled “Seismic Design Parameters”, version 2.10 and are summarized in Table 1, Summary of Seismic Parameters Corrected for Site

Class E.

TABLE 1: Summary of Seismic Parameters Corrected for Site Class E

Horizontal Peak Ground Acceleration, (As) 0.101g

Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.230g

Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.092g

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 2.50

Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 2.50

Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 3.50

The 5% damped design response spectrum for Site Class E is shown in Figure 2, Design

Response Spectrum Corrected for Site Class E, and the supporting data is presented in Table 2, Summary of Design Response Spectrum Data for Site Class E.

FIGURE 2:- Design Response Spectrum Corrected for Site Class E

0.00

0.05

0.10

0.15

0.20

0.25

0.00 0.50 1.00 1.50 2.00 2.50 3.00

E la s ti c S e is m ic

C o e ff ic ie n t, S a g

Period, T (sec)

Design Response Spectrum

TABLE 2: Summary of Design Response Spectrum Data for Site Class E

Period

(sec)

Sa

(g) Sd (in)

0 0.101 0 (PGA)(Fpga) = As

0.08 0.23 0.014

0.2 0.23 0.09 (Ss)(Fa) = SDs

0.401 0.23 0.361

0.5 0.184 0.45

0.6 0.154 0.54

0.8 0.115 0.721

1 0.092 0.901 (S1)(Fv) = SD1

1.2 0.077 1.081

1.4 0.066 1.261

1.6 0.058 1.441

1.8 0.051 1.621

2 0.046 1.802

2.2 0.042 1.982

2.4 0.038 2.162

2.6 0.035 2.342

2.8 0.033 2.522

3 0.031 2.702

Based on the long acceleration coefficient SD1 value of 0.092 g calculated as Fv.S1, the bridge site is assigned to seismic hazard Zone 1 according to Table 3.10.6-1 in AASHTO. Seismic hazard zones reflect the variation in seismic risk in different regions needing different requirements for design as depicted in Table 4.7.4.3.1-1 in AASHTO.

SECTION THREE--SUBSURFACE INVESTIGATION

3.1 FIELD EXPLORATION

The initial field exploration program consisting of twelve borings with two at each bridge replacement site was between November 5 and 7, 2013. Two additional borings were drilled between July 28 th through the 30 th at Bridges 3 and 4 due to scour changes forcing deeper foundations. The borings were conducted to characterize the subsurface conditions for replacement of 6 bridges along the route and by CFLHD. Drilling operations in November

2013 were advanced using hollow stem augers conducting Standard Penetration Tests (SPT’s) at 5-foot intervals. In addition to hollow stem augers the borings conducted in July of 2014 employed the use of wire-line core techniques when bedrock was encountered. All of the borings were logged by CFLHD’s engineering geologist. Representative soil samples were classified in the field and transported to the CFLHD Materials Laboratory for testing. Details of the field exploration program and the boring logs are included in Appendix A. A summary of the boring locations and depths are shown in Table 3, Summary of Borings.

TABLE 3: Summary of Borings

BORING

BRIDGE

NUMBER

ABUTMENT(1)

BORING

STATION &

OFFSET

GROUND

ELEVATION

(ft)

GROUNDWATER

ELEVATION (ft)

BORING

DEPTH

(ft)

TERMINATION

ELEVATION

(ft)

B-DWV1

Bridge 1

Abutment 2 102+70

7.0 ft

RT

3665.7 3656.7 30.0 3635.7

B-DWV2 Abutment 1 102+07

13.5 ft

LT

3665.2 3657.2 45.0 3620.2

B-DWU1

Bridge 2

Abutment 2 202+25

14.3 ft

RT

3682.3 3669.8 21.0 3661.3

B-DWU2 Abutment 1 201+75

18.4 ft

RT

3682.0 3669.0 32.0 3650.0

B-DWT1

Bridge 3

Abutment 2

302+16

10.7 ft

RT

3714.6 3706.6 42.5 3672.1

B- DWT1a

302+18

10.7 ft

RT

3714.6 3705.6 73.0 3641.6

B-DWT2 Abutment 1 301+63

8.2 ft

LT

3713.8 3705.8 40.0 3673.8

B-EFL1

Bridge 4

Abutment 2

402+50

10.0 ft

RT

3731.1 3723.1 35.5 3695.6

B-EFL1a 402+52

10.0 ft

RT

3731.1 3722.1 68.0 3663.1

B-EFL2 Abutment 1 401+62

17.0 ft

LT

3731.8 3725.8 35.5 3696.3

B-DWR1

Bridge 5

Abutment 2 502+57

18.0 ft

RT

3755.0 3747.0 46.5 3708.5

B-DWR2 Abutment 1 502+14

12.0 ft

LT

3755.2 3746.7 46.5 3708.7

B-DWN1

Bridge 6

Abutment 2 602+26

19.2 ft

LT

3793.6 3787.6 22.0 3771.6

B-DWN2 Abutment 1 601+93

19.9 ft

RT

3792.8 3785.8 55.0 3737.8

Notes:

(1) Abutment 1 and Abutment 2 correspond to the Down-Station and Up-Station sides of each bridge site, respectively.

3.2 SUMMARY OF SUBSURFACE EXPLORATION

Field test results were recorded in the field on appropriate data sheets at the time of the geotechnical investigation. The data sheets and logs contain information concerning the boring methods; samples attempted and recovered; indications of the presence of various materials such as gravel, cobbles and boulders, organic matter, water levels, and loss of water circulation. Also included in the boring logs are laboratory test results and visual interpretations by the field personnel of the conditions based on the performance of the drilling equipment and samples/cuttings brought to the surface.

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

Groundwater elevations were measured at the time of drilling for all of the borings. Fluctuations in the ground water level due to seasonal precipitation and climatic effects are, however, expected. The following is a detailed description of materials encountered at each structure location.

BRIDGE #1- FORMERLY BRIDGE DWV, MP 3.4

Proposed Bridge #1, located between station 102+16 and station 102+62, is 46-feet long.

Borings B-DWV1 and B-DWV2 were advanced at this location to depths of 30 and 45 feet, respectively.

Boring B-DWV1, located at Station 102+70 and approximately 7 feet to the right of the proposed centerline on Abutment 2 of Bridge #1, was advanced using continuous flight augers to a total depth of 30 feet from a starting elevation of 3665.7 feet. The subsurface materials encountered were a loose to medium dense, brown silty SAND with gravels, cobbles and boulders to a depth of 14 feet overlying one foot of cobbles and boulders from

14 to 15 feet, then grading back to brown silty SAND with gravels, cobbles and boulders from 15 to 29 feet. A red brown SANDSTONE or sandstone boulder was encountered from

29 to 30 feet where auger refusal was obtained. SPT N-values of 6, 20 and 10 for 0 blows per foot were recorded in the overburden material above the sandstone. The blow counts are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 9 feet (Elevation 3656.7 feet) below the ground surface at the time of drilling. Laboratory test results on samples obtained from 5.0 to 11.5 feet indicated the material is non-plastic and classifies as SM in the Unified Soil Classification system

(USCS) and as an A-2-4(0) in the AASHTO system.

Boring B-DWV2, located at Station 102+07 and approximately13.5 feet to the left of the proposed centerline on Abutment 1 of Bridge #1, was advanced using continuous flight augers to a total depth of 45 feet from a starting elevation of 3665.2 feet. The subsurface materials encountered were very loose to medium dense brown silty SAND with gravels, cobbles and boulders to a depth of 30 feet overlying six feet of cobbles and boulders from

30 to 36 feet. A weathered red brown SANDSTONE or sandstone boulder was encountered from 36 to 44 feet before becoming less weathered and harder at 45 feet where auger refusal was obtained. SPT N-values of 2, 14 and 5 blows per foot were recorded in the overburden material above the sandstone. The blow counts are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 8 feet (Elevation 3657.2 feet) below the ground surface at the time of drilling. Laboratory test results on samples obtained from 5.0 to 11.5 feet indicated the material is non-plastic and classifies as SM in the USCS as an A-2-4(0) in the AASHTO system.

BRIDGE #2- FORMERLY BRIDGE DWU, MP 3.8

Proposed Bridge #2, located between station 201+83 and station 202+21, is 38-feet long.

Borings B-DWU1 and B-DWU2 were advanced at this location to the depth of 21 and 32 feet

Boring B-DWU1, located at Station 202+25 and approximately 14.3 feet to the right of the proposed centerline on Abutment 2 of Bridge 2, was advanced using continuous flight augers to a total depth of 21 feet from a starting elevation of 3682.3 feet. The subsurface materials encountered were loose brown silty SAND with gravels, and cobbles to a depth of

8.5 feet where a seam of mostly gravels and cobbles is present to a depth of 10 feet then grading back to a medium dense brown silty SAND with gravels and cobbles from 10 to 20 feet. A red brown fractured SANDSTONE or sandstone boulder was encountered to auger refusal at 21 feet below the ground surface. SPT N-values recorded in the overburden material were of 8, 26 and 37 blows per foot are considered unreliable due to the presence of gravels, cobbles and boulders. An N-Value of 50 blows for 6-inches was recorded in the sandstone or sandstone boulder at the bottom of the borehole. Groundwater was encountered at a depth of 12.5 feet (Elevation 3669.8 feet) below the ground surface at the time of drilling. Laboratory test results on samples obtained from 5.0 to 6.5 feet classify the material as SM in the USCS and as an A-4(0) in the AASHTO system with a liquid limit of

21 and plasticity index of 2. Another sample from 10.0 to 16.5 feet classified as GM in the

USCS system and as an A-1-a(0) in the AASHTO system with a liquid limit of 17 and plasticity index of 2.

Boring B-DWU2, located at Station 201+75 and approximately 18.4 feet to the right of the proposed centerline on Abutment 1 of Bridge 2, was advanced using continuous flight augers to a total depth of 32 feet from a starting elevation of 3682.0 feet. The subsurface materials encountered were loose to medium dense brown silty SAND with gravels, cobbles and boulders to a depth of 20 feet with a boulder from 2.5 to 3.5 feet. The material then grades to mostly gravels and boulders to 29.5 feet. A red-brown SANDSTONE or sandstone boulder was encountered from 29.5 feet to auger refusal at 32 feet below the ground surface. The SPT N-values recorded in the overburden material were 7 and 25 blows per foot and are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 13 feet (Elevation 3669.0 feet) below the ground surface at the time of drilling.

BRIDGE #3- FORMERLY BRIDGE DWT, MP 4.0

Proposed Bridge #3, located between station 301+72 and station 302+16, is 44-feet long.

Borings B-DWT1 and B-DWT2 were advanced at this location to the depth of 42.5 and 40.0 feet respectively. Boring B-DWT1a was drilled at a later date to a total depth of 73 feet.

Boring B-DWT1, located at Station 302+16 and approximately 10.7 feet to the right of the proposed centerline on Abutment 2 of Bridge 3, was advanced using continuous flight augers to a total depth of 42.5 feet from a starting elevation of 3714.6 feet. The subsurface materials encountered were loose to medium dense brown silty SAND with gravels, cobbles and boulders to a depth of 12.5 feet where a seam of mostly gravels, cobbles and boulders is present to a depth of 18 feet then grading to a brown silty SAND with gravels, cobbles and boulders from 18 to 35 feet. The material graded to mostly gravels and cobbles from 35 to

40 feet where a red brown SANDSTONE BOULDER was encountered to auger refusal at

42.5 feet below the ground surface. The SPT N-values recorded in the overburden material were 10 and 11 blows per foot are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 8.0 feet (Elevation

3706.6 feet) below the ground surface at the time of drilling.

Boring B-DWT1a, located at Station 302+18 and approximately 10.7 feet to the right of the proposed centerline on Abutment 2 of Bridge 3, was advanced using continuous flight auger to a depth of 54.0 feet then cored to a total depth 73.0 feet from a starting elevation of

3714.6 feet. The subsurface materials encountered were loose to medium dense brown silty

SAND with gravels, cobbles and boulders to a depth of 12.5 feet where a seam of mostly gravels, cobbles and boulders is present to a depth of 18 feet then grading to a brown silty

SAND with gravels, cobbles and boulders from 18 to 35 feet. The material graded to mostly gravels and cobbles from 35 to 54 feet before encountering bedrock comprised of a brown red to white interbedded SILTSTONE, LIMESTONE, SANDSTONE and SHALE. This bedrock was cored to the bottom of the boring at 73.0 feet. Percent recovery on the bedrock ranged from 52% to 98% with RQD ranging from 0 to 40. Water circulation within the bedrock was fair to none but dominantly poor. Core runs times ranged from about 2 minutes/ft. to 4 ½ minutes/ft. Groundwater was encountered at a depth of 9.0 feet

(Elevation 3705.6 feet) below the ground surface at the time of drilling.

Boring B-DWT2, located at Station 301+63 and approximately 8.2 feet to the left of the proposed centerline on Abutment 1 of Bridge 3, was advanced using continuous flight augers to a total depth of 40.0 feet from a starting elevation of 3713.8 feet. The subsurface materials encountered were loose brown silty SAND with gravels, cobbles and boulders with seams of gravels and cobbles to a depth of 39 feet where a red brown SANDSTONE

BOULDER was encountered to auger refusal at 40 feet below the ground surface. The SPT

N-values recorded in the overburden material ranged from 7 to refusal (10 blows for no penetration), and are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 8.0 feet (Elevation 3705.8 feet) below

Laboratory test results on combined samples obtained from B-DWT1 and B-DWT2 from

5.0 to 6.5 feet classify the material as SM in the USCS and as an A-2-4(0) in the AASHTO system and non-plastic.

BRIDGE #4- FORMERLY BRIDGE EFL, MP 4.4

Proposed Bridge #4, located between station 401+78.5 and station 402+27.5, is 49-feet long.

Borings B-EFL1 and B-EFL2 were advanced at this location to the depth of 35.5 each. Boring B-

EFL1a was drilled at a later date to a total depth of 68 feet.

Boring B-EFL1, located at Station 402+50 and approximately 10.0 feet to the right of the proposed centerline on Abutment 2 of Bridge 4, was advanced using continuous flight augers to a total depth of 35.5 feet from a starting elevation of 3731.1 feet. The subsurface materials encountered were medium dense brown silty SAND with gravels, and cobbles with seams of gravels and cobbles to a depth of 35.0 feet where a red brown SANDSTONE

BOULDER was encountered to auger refusal at 40 feet below the ground surface. One SPT

N-values recorded in the overburden material was 13 blows per foot and is considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 8.0 feet (Elevation 3723.1 feet) below the ground surface at the time of drilling.

Boring B-EFL1a, located at Station 402+52 and approximately 10.0 feet to the right of the proposed centerline on Abutment 2 of Bridge 4, was advanced using continuous flight augers to a depth of 54 feet then cored to a total depth 68.0 feet from a starting elevation of

3731.1 feet. The subsurface materials encountered were medium dense brown silty SAND with gravels, and cobbles to a depth of 30 feet. A seam of mostly cobbles was recorded from

12.5 to 13.5 feet. Mostly GRAVELS and COBBLES were encountered from 30 feet to the bottom of the hole at 68 feet. Percent recovery on the GRAVELS and COBBLES ranged from 26% to 70% with water circulation within the unit was generally poor to none. Core runs times ranged from about 2 to 3 minutes/ft.. Groundwater was encountered at a depth of

9.0 feet (Elevation 3722.1 feet) below the ground surface at the time of drilling.

Boring B-EFL2, located at Station 401+62 and approximately 17.0 feet to the right of the proposed centerline on Abutment 1 of Bridge 4, was advanced using continuous flight augers to a total depth of 35.5 feet from a starting elevation of 3727.8 feet. The subsurface materials encountered were loose brown silty SAND with gravels, and cobbles from 0 to 9 feet and from 12 to 25 feet below the surface. Lenses of mostly gravels and cobbles were encountered from 9 to 12 feet and again from 25 to 35 feet in depth. At 35 feet a red brown

SANDSTONE BOULDER was encountered to auger refusal at 35.5 feet below the ground surface. One SPT N-values recorded in the overburden material was 7 blows per foot and is considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 6.0 feet (Elevation 3721.8 feet) below the ground surface at the time of drilling.

Laboratory test results on combined samples obtained from B-EFL1 and B-EFL2 from 5.0 to 11.5 feet classify the material as SM in the USCS an A-1-b (0) in the AASHTO System and non-plastic.

BRIDGE #5- FORMERLY BRIDGE -DWR, MP 4.8

Proposed Bridge #5, located between station 502+03 and station 502+68 is 65 feet long. Borings

B-DWR1 and B-DWR2 were each advanced at this location to the depth of 46.5 feet.

Boring B-DWR1, located at Station 502+25 and approximately 18.0 feet to the right of the proposed centerline on Abutment 2 of Bridge 5, was advanced using continuous flight augers to a total depth of 46.5 feet from a starting elevation of 3755.0 feet. The subsurface materials encountered were loose dark brown silty SAND with gravels and cobbles to a depth of 11.5 feet overlying a 1.5 foot seam of dark brown clayey SAND, gravels and cobbles to 13 feet. A layer of mostly cobbles to a depth of 18 feet was encountered overlying a dark brown clayey SAND, gravels and cobbles to 32 feet in depth. Bedrock comprised of a white-gray with SILTSTONE with red-brown streaks to 46 feet in depth was found over a light red brown to white chert to auger refusal at 46.5 feet below the ground surface. SPT N-values recorded in the sandy overburden material were of 5 and 6 blows per foot are considered unreliable due to the presence of gravels, cobbles and boulders. An N-

Value of 27 blows per foot was recorded in the siltstone from a depth of 40.5 to 41.5 feet.

Groundwater was encountered at a depth of 8 feet (Elevation 3747.0 feet) below the ground surface at the time of drilling. Laboratory test results on samples obtained from 5.0 to 11.5 feet classify the material as SM in the USCS and as an A-4(0) in the AASHTO system with a liquid limit of 17 and plasticity index of 6.

Boring B-DWR2, located at Station 502+14 and approximately 12.0 feet to the left of the proposed centerline on Abutment 1 of Bridge 5, was advanced using continuous flight augers to a total depth of 46.5 feet from a starting elevation of 3755.2 feet. The subsurface materials encountered were loose to medium dense dark brown silty SAND with gravels and cobbles to a depth of 11.5 feet. Layers of dark brown clayey SAND, gravels and cobbles were found at depths of 11.5 to 13 feet and from 18 to 35 feet. From 13 to 18 feet and 35 to

46 feet layers of mostly GRAVELS and cobbles were found. Bedrock comprised of a light red brown to white CHERT was found at 46 feet and to auger refusal at 46.5 feet below the ground surface. SPT N-values recorded in the sandy overburden material were of 5 and 20 blows per foot are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 8.5 feet (Elevation 3746.7 feet) below

Laboratory test results on combined samples from B-DWR1 and B-DWR2 from 5.0 to 11.5 feet classified as SM in the USCS and as an A-4(0) in the AASHTO system and non-plastic.

BRIDGE #6- FORMERLY BRIDGE -DWN, MP 5.6

Proposed Bridge #6, located between station 601+77.94 and station 602+42.94 is 65 feet long.

Borings B-DWN1 and B-DWN2 were advanced at this location to the depth of 22 and 55 feet

Boring B-DWN1, located at Station 602+26 and approximately 19.2 feet to the left of the proposed centerline on Abutment 2 of Bridge 6, was advanced using continuous flight augers to a total depth of 22 feet from a starting elevation of 3793.6 feet. The subsurface materials encountered were loose brown to gray medium dense brown silty SAND with gravels and cobbles from 0 to 7 feet and from 9.5 to 21 feet below the surface. A lens of mostly COBBLES was found from 7 to 9.5 feet below the ground surface. At 21.5 feet a red brown SANDSTONE or SANDSTONE BOULDER was encountered to auger refusal at 22 feet below the ground surface. The SPT N-values recorded in the overburden material were

16 and 13 blows per foot and refusal (10 blows for zero inches) and are considered unreliable due to the presence of gravels, cobbles and boulders. Groundwater was encountered at a depth of 6.0 feet (Elevation 3787.6 feet) below the ground surface at the time of drilling.

Boring B-DWN2, located at Station 601+93 and approximately 19.9 feet to the right of the proposed centerline on Abutment 1 of Bridge 6, was advanced using continuous flight augers to a total depth of 55 feet from a starting elevation of 3792.8 feet. The subsurface materials encountered were a brown medium dense silty SAND with gravels and cobbles from depth intervals of 0 to 8 feet, 9 to 12 feet, 13.5 to 15 feet 20 to 27.2 feet and 31 to 52.5.

Layers of mostly COBBLES were encountered at depth intervals of 8 to 9 feet, 12 to 13.5 feet, 15 to 20 feet and 27.5 to 31 feet. At 52.5 feet a red brown SANDSTONE or

SANDSTONE BOULDER was encountered to auger refusal at 55 feet below the ground surface. The SPT N-values recorded in the overburden material were 23 and 40 blows per foot and are considered unreliable due to the presence of gravels, cobbles and boulders.

Groundwater was encountered at a depth of 7.0 feet (Elevation 3785.6 feet) below the ground surface at the time of drilling.

Laboratory test results on combined samples from B-DWN1 and B-DWN2 from 5.0 to 11.5 feet classified as SM in the USCS and as an A-1-b (0) in the AASHTO system and non-plastic.

3.3 LABORATORY TESTING

Laboratory testing was conducted on select soil samples obtained during the subsurface investigation to determine material parameters for use in the foundation design. Laboratory test procedures and results, along with grain size curves are presented in Appendix B, Laboratory

Test Results and summarized in Table 4, Summary of Soil Classification Index Tests. Samples showing similar material parameters were combined for a more representative testing size.

Table 4: Summary of Soil Classification Index Tests

BORING

NUMBER

SPT Sample

Sample Depth

(feet)

Percent

Passing

LL PI USCS AASHTO

B-DWV1

Bridge 1

SPT-1, SPT-2 5.0-11.5 28 NV NP SM A-2-4 (0)

B-DWV2 Bridge 1 SPT-1, SPT-2 5.0-11.5 30 NV NP SM A-2-4 (0)

B-DWV2 Bridge 1 SPT-3, SPT-4 15.0-21.5 40 NA NA NA NA

B-DWU1 Bridge 2 SPT-1 5.0-11.5 48 21 2 SM A-4 (0)

B-DWU1 Bridge 2 SPT-2, SPT-3 10.0-16.5 15 17 2 GM A-1-a (0)

B-DWT1 & B-

DWT2

Bridge 3 SPT-1 5.0-6.5 34 NV NP SM A-2-4 (0)

B-DWT1 & B-

DWT2

Bridge 3 SPT-2, SPT-3 10.0-16.5 15 NA NA NA NA

B-EFL1 & B-

EFL2

Bridge 4 SPT-1, SPT-2 5.0-11.5 17 NV NP SM A-1-b (0)

B-DWT1a & B-EFL1a

Bridge 3 & Bridge 4

Bulk 0.0-30.0 37 18 3 SM A-4 (0)

B-DWR1 &

B-DWR2

Bridge 5 SPT-1, SPT-2 5.0-11.5 37 NV NP SM A-4 (0)

B-DWR1 Bridge 5 SPT-4 40.0-41.5 51 17 6 CL-ML A-4 (0)

B-DWN1 &

B-DWN2

Bridge 6 SPT-1, SPT-2 5.0-11.5 17 NV NP SM A-1-b (0)

ALL

BORINGS

- - 0.0-5.0 41 20 4 SC-SM A-4 (0)

Notes: NV = No Value, NP = Non-Plastic, NA = Not Applicable/no test conducted

Electrochemical tests were conducted on one combined representative sample taken in the top 5 feet of all of the borings from the initial round of exploration and another combining the top 30 feet from the borings in the second round of drilling to determine soil corrosivity and potential detrimental effects on concrete and buried metals. Testing for resistivity and pH were performed in general accordance with AASHTO T 288 and T 289, respectively. Tests for sulfate and chloride content were also performed due to resistivity results less than 5000 ohm-centimeters in accordance with AASHTO T 290 and T 291, respectively. A discussion of corrosion requirements, electrochemical test results, and recommendations for corrosion restrictions is resented in Section 4.3, Corrosion Potential. A summary of analytical test results are provided in

Table 5, Summary of Electrochemical Parameters.

Table 5: Summary of Electrochemical Parameters

Boring

Sample

Depth

(feet)

Classification pH Resistivity

(ohm-cm)

Sulfates

(%/ppm)

Chlorides

(%/ppm)

AASHTO USCS

All borings 0-5 A-4 (0) SC-SM 7.8 860 0.021/ 210 0.0353/ 3530

B-DWT1a &

B-EFL1a

0-30 A-4 (0) SM 7.9 2190 0.015/ 150 0.0066/ 66

SECTION FOUR--ANALYSIS AND RECOMMENDATIONS

This section provides general interpretation of site investigations and gives recommendations for design parameters at the proposed bridge site. Generalized subsurface profiles are developed based on data collected during the investigation. Groundwater was encountered at depths between 6 to 13 feet from the ground surface during the investigations.

4.1 BRIDGE FOUNDATION DESIGN

Due to the relative depth of good bearing material, favorable scour and hydraulics conditions, currently loaded bridge abutment structure (mitigating settlement potential), and low structural vertical and lateral loads, a shallow foundation constructed using the Geosynthetic Reinforced

Soil- Integrated Bridge System (GRS-IBS) is recommended for bridges 1, 2, 5 and 6. The GRS-

IBS is the most cost-effective system for Bridges 1, 2, 5, and 6 and can be constructed quickly and efficiently when compared to traditional shallow foundation systems. Generic GRS-IBS design drawings are provided in Attachment D for reference.

Good bearing materials also exists at sites 3 and 4 however, due to an estimated scour depth of

5.5 and 8.7 feet, respectively, it is recommended that Bridges 3 and 4 be constructed on deep foundations using micropiles. The micropiles shall extend below the estimated scour depth.

Table 6 displays a summary of the proposed bridge dimensions, loading conditions and the recommended foundation types for each bridge site. The factored service limit loading conditions per abutment for the new bridge was provided by CFL Bridge Personnel are shown in

Table 6 for the dead and live loading conditions.

Table 6: Summary of Proposed Bridge Dimensions, Loading conditions and Recommended Foundation Type

Bridge

Number

Bridge Length

(Feet)

Bridge Width

(Feet)

Total Bridge

Dead Load Per

Abutment at

Service Limit

State (kips)

Total Bridge

Live Load Per

Abutment at

Service Limit

State (kips)

Recommended

Foundation

Type

Foundation

System or

Elements

1 46 28 146.3 140.8 Shallow GRS-IBS

2 38 28 123.6 128.8 Shallow GRS-IBS

3 44 28 203.1 134.8 Deep Micropiles

4 49 28 211.1 141.8 Deep Micropiles

5 65 36.95 235.1 161.4 Shallow GRS-IBS

6 65 32.33 213.8 161.1 Shallow GRS-IBS

4.1.1 GRS-IBS DESIGN RECOMMENDATIONS

Bridges 1, 2, 5 and 6

The GRS-IBS bridge abutments are generally designed and constructed of a well-compacted granular fill internally reinforced with woven geotextile at a maximum reinforcement spacing of

8-inches and faced with Concrete Modular Blocks (CMU). Based on FHWA GRS-IBS guidelines, GRS-IBS structures are currently limited to 30-feet high with a maximum allowable bearing stress of 4,000 pounds per square foot, neither of which is exceeded in the design of the

Sand Creek Bridges. The following are descriptions of each GRS-IBS component:

Backfill materials are designed to support the applied loads and, therefore, considered a structural element of the GRS-IBS structure. These materials should consist of clean, well-graded, crushed, hard, durable, stone aggregate with a plasticity index of less than 6, a maximum particle size of 2 inches, and less than 12 percent passing the number 200 sieve. The backfill should also have a magnesium sulfate soundness loss of less than 30 percent after four cycles or a sodium sulfate soundness value of less than 15 percent after five cycles.

Aggregate reinforcement should be a biaxial, woven, polypropylene geotextile with a minimum ultimate tensile strength of 4,800 pounds per foot. Limiting the maximum required reinforcement strength at 2 percent strain will ensure long-term performance and serviceability of the reinforcement. The specific type of geotextile used is dependent on the reinforcement spacing and backfill material parameters.

The CMU blocks are readily available as hollow or solid core, flat or cut face units with the following standard dimensions: length = 15⅝ inches, width = 7⅝ inches and, height =

7⅝ inches. The blocks should have a minimum compressive strength of 4,000 pounds per square inch and a water absorption limit of 5 percent. The blocks are connected to the reinforcement layers through friction developed between the blocks. Facing blocks are not considered structural elements and, thus, are not required to resist lateral earth or bridge loads.

The AASHTO load resistance factored design (LRFD) guidelines provided in “FHWA

Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide, January

2011” were used to design the bridge abutments. Since the LRFD resistance factors for the GRS-

IBS are not fully developed due to lack of statistical information available for this system, the

LRFD method has been fit to the allowable stress design (ASD) solution.

An abutment layout was determined based on the geometry of the superstructure, subsurface lithology, topographic surveys, loading conditions, performance criteria, environmental and construction constraints, and guidelines/limitations provided in the FHWA, GRS-IBS manual.

Internal and external stability analyses were conducted to determine the stability factors for the geosynthetic reinforced abutment. Abutment layout and input parameters were then modified to meet the required design factors of safety. Appendix D provides a summary of the design parameters used for the abutment layout and the analysis results.

Material parameters of the foundation soil below Reinforced Soil Foundation (RSF) were estimated for GRS-IBS bridge foundation design based on observations and geology, field investigation, laboratory test results, and known empirical strength characteristics of similar materials. The encountered soils were given conservative presumptive values for the unit weight

(γ), friction angle (φ) and cohesion (c). Table 7 provides a summary of the estimated overburden soil parameters at the proposed RSF for GRS-IBS foundation design purposes. The analysis results and design parameters used in the GRS-IBS abutment design is presented in Table 8.

TABLE 7: Estimated Subsurface Material Parameters Used for GRS-IBS Bridge Foundation Design

NUMBER

ELEVATION AT

BOTTOM OF RSF

(ft)

GROUND

WATER

ELEV(1) (ft)

MATERIAL

DESCRIPTION

UNIT

WEIGHT

ɣ, (pcf)

EFFICTIVE

UNIT

WEIGHT(2)

ɣ’, (pcf)

COHESION

c

(psf)

FRICTION

ANGLE

Փ

(deg) ABUT. 1 ABUT. 2

1 3650.18 3649.76 3657.2 Brown silty sand, gravels, cobbles and boulders

120 57.6 10 34

2 3667.7 3667.4 3669.8

Brown silty sand gravels, cobbles and boulders (GM)

125 62.6 10 34

5 3745.5 3745.78 3747.0

Dark brown silty sand, gravels and cobbles

(SM)

130 67.6 50 35

6 3785.5 3785.0 3787.6

Brown silty sand gravels and cobbles (SM) Interbedded with layers of mostly cobbles.

125 62.6 50 34

Notes:

(1) Highest observed groundwater elevation between Abutment 1 and 2 at the time of subsurface investigations.

(2) Effective unit weight used in design where RSF is below the estimated groundwater elevation.

TABLE 8: Design Parameters and Analysis Results for the GRS-IBS Abutment Design.

MATERIAL PARAMETERS

Bridge Number 1 2 5 6

FOUNDATION SOIL PARAMETERS

Effective unit weight, γf' pcf 57.6 62.6 67.6 62.6

Friction angle, φ f' deg 34 34 35 34

Cohesion, c'f psf 10 10 50 50

Undrained shear strength, cf psf 0 20 0 0

RETAINING BACKFILL SOIL PARAMETERS

Total unit weight, γb pcf 120 125 130 125

Friction angle, φ b' deg 34 34 35 34

Cohesion, c'b psf 10 10 50 50

Undrained shear strength, cb psf 0 20 0 0

REINFORCED BACKFILL PARAMETERS

Total unit weight, γr pcf 137 137 137 137

Friction angle, φ r' deg 38 38 38 38

Cohesion, c'r psf 0 0 0 0

Maximum grain size, dmax in 0.75 0.75 0.75 0.75

REINFORCED SOIL FOUNDATION (RSF) PARAMETERS

Total unit weight, γRSF pcf 137 137 137 137

Effective unit weight, γRSF' pcf 74.6 74.6 74.6 74.6

Friction angle, φ RSF' deg 38 38 38 38

Cohesion, c'RSF psf 50 50 50 50

ROAD BASE SOIL PARAMETERS

Total unit weight, γrb pcf 137 137 137 137

Road base thickness, hrb in 18 18 18 18

GEOSYNTHETIC PARAMETERS & LAYOUT

Bridge Number 1 2 5 6

Ultimate tensile strength of reinforcement, Tf lb/ft 4,800 4,800 4,800 4,800

Reinforcement tensile strength at 2% strain, T@e=2% lb/ft 1,372 1,372 1,372 1,372

Allowable reinforcement strength, Tall lb/ft 1,371 1,371 1,371 1,371

Vertical spacing of primary reinforcement, Sv in 8 8 8 8

Vertical spacing of bearing bed reinforcement, Sv/2 in 4 4 4 4

Minimum number of geosynthetic layers in integration zone layers 3 3 3 3

Geosynthetic spacing in integration zone with minimum number of layers in 9 9 9 9

GEOMETRY

Bridge Number 1 2 5 6

Wall height - top of RSF to top of bearing bed reinforcement, H ft 14 13 8 8

Design clear space - top of uppermost block to bottom of superstructure, de in 4 4 4 4

Set back between back of wall facing and beam seat, ab in 8 8 8 8

Design bearing width, b ft 2.75 2.75 3.22 3.22

Minimum length of bearing bed reinforcement, bbed ft 4.08 4.08 4.55 4.55

Actual base width of wall including the block face, Btotal ft 8 8 6 6

Base length of reinforcement not including the wall face block, B ft 7.36 7.3646 5.3646 5.3646

Wall base to height ratio B/H - 0.53 0.57 0.67 0.67

Minimum width of reinforced soil foundation (RSF), BRSF ft 10.00 10.00 7.50 7.50

Minimum depth of excavation for RSF, DRSF ft 2 2 1.5 1.5

Minimum length of RSF in front of wall face, xRSF ft 2.00 2.00 1.50 1.50

APPLIED BRIDGE LOADS

Bridge Number 1 2 5 6

Total bridge load, Vapplied psf 3,729 3,278 3,333 3,604

Bridge dead load, qb psf 1,900 1,605 1,976 2,054

Bridge live load, qLL psf 1,829 1,673 1,357 1,550

ANALYSIS RESULTS

Bridge Number 1 2 5 6

Total allowable pressure on GRS-IBS abutment, Vallow psf 4,587 4,587 4,587 4,587

Factor of safety against sliding - top of RSF, FSslide,top RSF 2.07 2.04 2.73 2.75

Factor of safety against sliding - bottom of RSF, FSslide,bottom RSF 1.63 1.60 2.20 2.13

FSbearing, (drained condition) 4.42 5.40 8.08 6.30

Vertical strain of GRS-IBS abutment, ev % 0.003 0.003 0.003 0.003

Vertical deformation, Dv in 0.50 0.47 0.29 0.29

Lateral strain of GRS-IBS abutment, eL % 0.006 0.006 0.006 0.006

Lateral deformation, DL in 0.25 0.25 0.28 0.28

Maximum required strength of GRS-IBS geosynthetic reinforcement, Treq lb/ft 837.03 784.98 725.18 758.99

4.1.1.1 Abutment Settlement and Global Stability

Since the abutments are founded on dense gravels and cobbles, immediate elastic settlement and differential settlement are considered negligible. The GRS mass is not rigid and is therefore tolerant to differential settlement. Due to the limited geographic relief in the area and the shallow competent bedrock, global stability is not considered an issue.

4.1.1.2 Wingwall Design Recommendations

The wing walls are constructed from the same materials as the GRS. Wing walls are built at the same time as the abutment face wall and are at either right angle or other angle to the abutment face wall. Wing walls are constructed to support the approach embankment and should be designed to resist earth pressures and to protect against erosion. For this site it is recommended that the same GRS embedment lengths are used along the wing walls.

4.1.2 MICROPILE DESIGN RECOMMENDATIONS

Bridges 3 and 4

A deep foundation system is recommended for the abutments at bridges 3 and 4 due to the calculated scour depth. Furthermore; micropiles are the recommended foundation type as the presence of cobbles and large boulders can lead to potentially difficult conditions for driving piles or drilling large-diameter shafts. Because of their relatively small cross-sectional area, micropiles are assumed to transfer their load to the ground through grout-to-ground skin friction, without any contribution from end bearing. Based on the subsurface exploration sufficient grout-to-ground bond strength to support the required loading conditions at bridges 3 & 4 can be developed in the overburden soils.

4.1.2.1 Geotechnical Axial Resistance

Design loads applied to the top of the micropile will be resisted through the grout-to-ground bonding zone over the bond length of the micropile (portion of the uncased micropile in the overburden soils). The AASHTO LRFD procedures for micropile design were used to estimate the minimum bond length required to resist the applied loads at the strength limit state with a resistance factor (φqs) of 0.55 from AASHTO LRFD manual Table 10.5.5.2.5-1. The grout-to-ground bond strength was assumed using presumptive values listed in AASHTO Table

C10.9.3.5.2-1 and the conservative bond strength value (BOND) of 2 kips per square foot is recommended for the micropile design within the overburden soils encountered at proposed bridges 3 and 4. The micropile resistance for various grout-to-ground bond diameters and lengths was then calculated using the equations 10.9.3.5.1-3 in AASHTO multiplied by the strength limit state resistance factor of 0.55. Table 9 details the factored geotechnical axial resistance at the strength limit state based on the bond diameter and bond lengths.

TABLE 9: Factored Geotechnical Capacity for Various Bond Diameters and Lengths

MICROPILE

GROUT-TO-

GROUND BOND

DIAMETER (in)(1)

GROUT-TO-

GROUND

BOND

STRENGTH

(ksf)

FACTORED GEOTECHNICAL CAPACITY FOR VARIOUS BOND

LENGTHS (per micropile)(3)

34.0 ft 36.0 ft 38.0 ft 40.0 ft 42.0 ft 44.0 ft

68.5 kips(2) 72.6 kips(2) 76.6 kips(2) 80.6 kips(2) 84.7 kips(2) 88.7 kips

8 78.3 kips(2) 82.9 kips(2) 87.5 kip 92.2 kips 96.8 kips 101.4 kips

9 88.1 kips 93.3 kips 98.5 kips 103.7 kips 108.9 kips 114.0 kips

Notes: (1) Factored geotechnical axial capacity is calculated for various bond lengths and grout-to-ground bond diameters of 7, 8, and 9-inches.

(2) Does not meet required capacity using assumed bond strength of 2 kips per square feet. If testing is completed and bond is increased, these may meet required capacity.

(3) Assuming 6 micropiles per abutment.

Case I (micropiles used to transfer applied loads to the overburden soils), Type A (grout placed under gravity head only) micropiles are recommended for use on this project. The geotechnical capacity will be achieved in the overburden soil at the Bridges 3 and 4 which is anticipated to be approximately 54 to 68-feet thick based on subsurface investigations. Therefore, cased and uncased zones of the micropile will both be installed in the overburden soils. The cased portion of the micropile should be a minimum of 10 feet in length and should be cased with a permanent

10.0- inch outside-diameter (OD) casing. The uncased 9-inch grout-to-ground bond diameter should be installed a minimum of 34 feet into the overburden soils. The total micropile length should therefore equal the cased length (10 feet) plus the bond length (34 feet) for a total of 44 feet .

Recommended nominal casing wall thicknesses, including sacrificial steel for the 10-inch outside diameter (OD) casing is 0.5 inch. A continuous-thread, minimum #14 reinforcing steel bar with minimum yield strength of 75 kips, with suitable centralizers firmly fixed to the bar at 5-foot spacing and extending the entire length of the micropile, should be used to assist in transferring axial loads to the uncased bond zone. The bar should extend the entire length of the micropile and through a steel plate installed on top of the casing. The steel plate should be a designed to resist a punching failure of the micropile cap into the base of the abutment.

4.1.2.2 Lateral Load Analysis

Lateral soil-structure interaction analyses are typically performed by the structural engineer using LPILE (Ensoft 2010). The program provides an estimate of the lateral load displacement behavior using the soil reaction-displacement curves (p-y). The pile lateral deflection (y) is related to the soil reaction (p) at various subsurface elevations. In general the curves are nonlinear and are dependent depth, pile diameter, and soil strength.