ND.FLAP.704(1)795(1).Magpie and Whitetail Crossings.Geotech Rpt FINAL.February 2023_Driven Piles Box Cul.pdf

MAGPIE AND WHITETAIL CROSSINGS

BILLINGS COUNTY, ND

ND FLAP 704(1) AND 795(1)

FINAL Geotechnical Report

Prepared by

Federal Highway Administration Central Federal Lands Highway Division

Geotechnical Services Branch

February 2023 ii

SIGNATURE SHEET

Report prepared by: ___________________________________________________________

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

Report reviewed by: ____________________________________________________________

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

Approved for distribution by: _____________________________________________________

James M. Arthurs, P.E., Ph.D., Acting Lead Geotechnical Engineer

Distribution

N:\ND\704(1)795(1)\Geotech\7_FinalDocs

K:\TechServices\Geotech\1. Geotech Project Reports

Project Management (PDF only)

Project Development, Lead Designer (PDF only)

Bridge (PDF only)

Technical Services, Hydraulic (PDF only)

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TABLE OF CONTENTS

SECTION ONE - INTRODUCTION

1.1 Background and Location

1.2 Scope and Purpose

SECTION TWO - GEOLOGY AND SEISMICITY

2.1 Regional Geology

2.2 Site Geology

2.3 Seismic Design Parameters

2.4 Geologic Hazards

SECTION THREE - SUBSURFACE INVESTIGATION

3.1 Subsurface Exploration Program

3.2 Laboratory Testing Program

SECTION FOUR - ANALYSIS & RECOMMENDATIONS

4.1 Subsurface Conditions

4.2 Bridge Foundations

4.2.1 Bridge Foundation Selection

4.2.2 Driven Pile Axial Resistance

4.2.3 Pile Setup

4.2.4 Group Effects on Axial Resistance

4.2.5 Lateral Loads

4.2.6 Settlement

4.2.7 Pile Lengths

4.2.8 Pile Drivability and Testing

4.2.9 Scour Potential and Erosion

4.3 Box Culvert Design

4.3.1 Settlement and Consolidation

4.3.2 Bearing Resistance

4.3.3 Foundation Preparation

4.3.4 Lateral Loads

4.4 Abutment and Wingwall Design

4.4.1 Bearing Resistance

4.4.2 Settlement and Consolidation

4.4.3 Foundation Preparation

4.4.4 Lateral Loads

4.5 EARTHWORKS

4.5.1 Embankment and Fill Construction

4.5.2 Cut Slopes & Temporary Shoring

4.5.3 Shrink/Swell recommendations

4.6 Construction Considerations

4.7 Disclaimer/Limitations Clause

SECTION FIVE - REFERENCES

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TABLES

Table 1:- Summary of Seismic Parameters Corrected for Site Class D

Table 2:- Summary of the Field Exploration Program

Table 3:- Summary of Laboratory Index Test Results

Table 4:- Summary of Laboratory Corrosivity Results

Table 5:- Proposed Bridge Foundation Locations

Table 6:- Bridge Loads and Driven Pile Configuration

Table 7:- LPILE Input Parameters1

Table 8:- Calculated Pile Lengths for Axial and Lateral Capacity

Table 9:- Material Properties and Inputs for Settlement Analysis

Table 10:- Box Culvert Settlement Analysis Results

Table 11:- Design Parameters

Table 12:- Resistance Factors (Φ) for each limit state

FIGURES

Figure 1.1: Existing Conditions at Whitetail Creek Crossing

Figure 1.2: Existing Conditions at Magpie Creek Crossing

PLATES

Plate 1:- Location Map

Plate 2:- Geology Map

Plate 3:- Geotechnical Boring Locations

Plate 4:- Bearing Resistance for Box Culvert

Plate 5:- Bearing Resistance for Box Culvert Wingwalls

APPENDICES

APPENDIX A - Field Exploration Program

APPENDIX B - Laboratory Test Results

APPENDIX C - Photographs

APPENDIX D - Pile Static Load Analysis file:///C:/Users/Brendan.McGarity/Documents/GEOTECH/Projects/ND/ND%20FLAP%20704(1)%20&%20795(1)/6_DraftDocs/DRAFT%20Geotechnical%20Report%20(002).docx%23_Toc98149629 file:///C:/Users/Brendan.McGarity/Documents/GEOTECH/Projects/ND/ND%20FLAP%20704(1)%20&%20795(1)/6_DraftDocs/DRAFT%20Geotechnical%20Report%20(002).docx%23_Toc98149630

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Magpie and Whitetail Crossings ND FLAP 704(1)795(1) February 2023

SECTION ONE - Introduction

1.1 BACKGROUND AND LOCATION

This report presents the results of the geotechnical engineering assessment and provides recommendations for culvert and bridge construction work to be performed on Whitetail Creek and Magpie Creek crossings in Billings County, North Dakota. The project is located near and within the Little Missouri National Grassland. The project proposes to improve two existing low-water crossings that provide access to the Little Missouri National Grassland with concrete box culverts at Whitetail Creek and a 3-span bridge at Magpie Creek. The project sites are in undeveloped grassland adjacent to the Whitetail Creek and Magpie Creek. A site map is presented on Plate 1 of this report.

The project roadways provide access to camping, fishing, hiking, and day use facilities. The existing stream crossings at Whitetail Creek and Magpie Creek consist of unimproved low water crossings. The crossings are inadequate and frequently overtop, resulting in significant maintenance costs, vehicle damage, and impassability.

1.2 SCOPE AND PURPOSE

The overall objective of this project is to improve the existing crossings to reduce maintenance and improve safety for the traveling public. A two-barrel concrete box culvert is proposed at

Whitetail Creek and a 3-span bridge is proposed at Magpie Creek to improve the stream crossing conditions and improve safety for the traveling public. Work also consists of placing embankment fill to raise roadway grades and reconstruction of the gravel surface roadway approaches to the stream crossings. Outlet protection at the box culvert and abutment protection at the bridge are proposed. Ancillary construction including signage and revegetation will also be performed.

The scope of work included a geotechnical investigation, analysis, and recommendations for culvert foundations, bridge foundations, and cuts and fills within the project limits for development of design through construction. This involved several tasks including field reconnaissance, subsurface sampling, laboratory testing, interpretation and correlation of field measurements, and geotechnical engineering analysis. Specifically, this investigation was conducted to determine the soil profiles at the proposed culvert and bridge locations and develop recommendations concerning foundations, retaining walls, embankments, material shrink/swell, geologic hazards, and construction considerations for design and construction of structures and slopes within the alignment. The stationing in this report is based on the preliminary 70% project plans, dated

October 2022.

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Figure 1.2: Existing Conditions at Whitetail Creek Crossing (July 24, 2018)

Figure 1.1: Existing Conditions at Magpie Creek Crossing (July 24, 2018)

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SECTION TWO - Geology and Seismicity

2.1 REGIONAL GEOLOGY

The project is located in the Unglaciated Missouri Plateau Section of the Great Plains physiographic province. The area is described by Carlson (1983) as part of the Little Missouri

Badlands. The region is underlain by marine sedimentary deposits dating back to the Precambrian era. Within these sedimentary sections, periods of emergence and subsequent erosion are marked by regional unconformities. The surface and near subsurface is typically underlain by Tertiary sedimentary deposits that have been variably lithified. More resistant beds are typically composed of sandstone or limestone. Numerous lignite (low-grade coal) beds are present in the sedimentary deposits. “Clinker” or “scoria” is formed by baking of sediments where the lignite has burned.

During the most recent glacial period, the Little Missouri River was captured by the ice-marginal

Missouri River. Subsequent warming and thawing lead to a lower regional base level, with streams and tributaries continuing to cut back into uplands. At this time, the Little Missouri River was incised approximately 200 to 500 feet into the relict upland surface. This created an area that was generally characterized by gently rolling uplands interrupted by buttes and ridges capped by more resistant rocks. Badlands areas continue to widen as the back-cutting erosion progresses northward. Landslides are common due to oversteepened slopes.

2.2 SITE GEOLOGY

Geologic mapping of the Whitetail Creek crossing is limited to 1:100,000 scale mapping (Carlson, 1983). This mapping depicts the Whitetail Creek crossing as underlain by the Tertiary Sentinel

Butte Formation (Tsb), which is described as alternating beds of variably lithified sandstone, mudstone, claystone, clinker, and lignite. More recent 1:24,000 scale mapping was completed for the Magpie Creek Crossing (Gonzalez, 2004). This mapping depicts the Magpie Creek crossing as underlain by modern and older alluvial deposits (Qal & Qoal), consisting of sediment ranging in size from clay to gravel. These surficial deposits are underlain by the Tertiary Bullion Creek

Formation (Tbc), which is described as alternating beds of variably lithified sandstone, mudstone, claystone, clinker, and lignite. Thickness of the Tertiary deposits at both sites is greater than 100 feet (Carlson, 1983).

It should be noted that although the project is underlain by formational units, these materials are not classified as rock for engineering purposes. These units are relatively young and have been subject to variable consolidation and cementation. These materials are typically considered stiff to very stiff soils in terms of strength and engineering behavior.

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No seismic source and Quaternary faults are mapped within 40 miles of the project area (U.S.

Geological Survey, 2021).

Refer to Plate 2 to view the geologic map and further unit descriptions that correspond to the project sites.

2.3 SEISMIC DESIGN PARAMETERS

Recommended seismic response parameters are based on the American Association of State

Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications, 8th

Edition, 2017, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years (approximate 1,000-year return period). The 1,000-year return period uniform hazard spectrum for the Whitetail Creek Crossing (47.19855º N latitude and

103.30238º W longitude) was obtained in accordance with the AASHTO ground motion maps.

The site was classified as “Class D” according to site class definitions specified in Table 3.10.3.1-

1 of AASHTO based on a stiff to very stiff soil profile without bedrock within 100 feet of the surface. The recommended spectral acceleration coefficient values for probabilistic design are summarized in the following table.

Table 1:- Summary of Seismic Parameters Corrected for Site Class D

Peak Seismic Ground Acceleration Coefficient, (As) 0.031

Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDS) 0.074

Horizontal Response Spectral Acceleration at Period of 1.0 sec (SD1) 0.039

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.6

Site Factor at Short-Period of Acceleration Spectrum, (Fa) 1.6

Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 2.4

Based on the long acceleration coefficient SD1 value of 0.039, the site is assigned to seismic hazard

Zone 1 in accordance with Table 3.10.6-1 of AASHTO. Seismic design parameters were also determined for Magpie Crossing. Due to similar geology and proximity of the two sites, the

Magpie site displayed very similar seismic parameters and was also assigned to seismic hazard

Zone 1. 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. Based on a classification of Zone 1, seismic loading is not anticipated to impact the design of structures for the project sites.

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2.4 GEOLOGIC HAZARDS

The project sites are located in a relatively flat lying area on a sequence of unconsolidated to lightly consolidated sediments. These materials can potentially have low bearing resistance and high settlement potentials. This hazard can be mitigated by appropriate foundation soil preparation and structural design. Coal and lignite beds are mapped in the area and were found during the subsurface investigation. These beds may be corrosive and contribute to increased acidity of surrounding soils. Landslides are mapped in the project area but are unlikely to affect the proposed culvert and bridge crossings due to the low topographic relief at the project sites. Flooding is also a concern in the project area and can be mitigated by appropriate hydraulic design of the project structures.

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SECTION THREE - Subsurface Investigation

3.1 SUBSURFACE EXPLORATION PROGRAM

A subsurface investigation targeting the proposed stream crossings was performed by a Central

Federal Lands Highway Division (CFLHD) of the Federal Highway Administration (FHWA) geotechnical engineer on October 24, 2018. The geotechnical subsurface exploration program consisted of drilling a total of three (3) borings to approximately 40 feet in depth. The original project scope proposed a series of box culverts at the Magpie Crossing, but the scope changed to a bridge structure in 2022 prior to the 70% design milestone. Thus, boring depths at Magpie are shallower than typical borings at bridge locations. One boring was drilled at the Whitetail Creek crossing and two borings at the Magpie Creek crossing. Standard penetration testing (SPT) and sample collection was performed at 5-foot intervals in each boring. Subsurface conditions were logged, and representative samples were collected and transported to the CFLHD Materials

Laboratory in Lakewood, CO, for physical property testing. Logs of the explorations and boring locations are presented in Appendix A and Plate 3, respectively. Photographs related this exploration can be found in Appendix C. A summary of the field exploration is provided in Table

2.

Table 2:- Summary of the Field Exploration Program

EXPLORATION

DESIGNATION

STATION OFFSET

GROUND

ELEVATION

TERMINATION

ELEVATION

EXPLORATION

DEPTH

BH18-01 204+09 34-ft LT 2,528 ft 2,488.5 ft 39.5 ft

BH18-02 106+24 8-ft LT 2,138 ft 2,098.5 ft 39.5 ft

BH18-03 107+71 12-ft RT 2,137 ft 2,097 ft 40 ft

Note: The exploration locations were estimated relative to existing features with stationing based on the preliminary

70% design plans. Ground elevations were estimated from CFLHD survey data.

3.2 LABORATORY TESTING PROGRAM

Soil samples recovered from the borings by SPT were tested in the laboratory to support the field classifications and to provide an estimate of the engineering characteristics and mechanical properties of the soil. Laboratory tests included moisture content (AASHTO T255), sieve analysis

(AASHTO T11 & T27), classification (AASHTO M145 & ASTM D2487), Atterberg limits

(AASHTO T89 & T90), and corrosivity of soils (AASHTO T288, T289, T290, T291). When the necessary tests were completed, samples were classified using the Unified Soil Classification

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System (USCS) and AASHTO soil classification system. Results of the testing are shown below in Table 3 and 4, and are presented in Appendix B.

Table 3:- Summary of Laboratory Index Test Results

BORING

NUMBER

SAMPLE

DEPTH, ft

PERCENT

GRAVEL

PERCENT

SAND

PERCENT

PASSING

LL PI USCS AASHTO

BH18-01 3 0 69 31 21 5 SC-SM A-2-4(0)

BH18-01 8 1 73 26 NV NP SM A-2-4(0)

BH18-01 18 0 10 90 56 39 CH A-7-6(37)

BH18-01 23 3 8 89 50 35 CH A-7-6(32)

BH18-02 3 16 63 21 21 7 SC-SM A-2-4(0)

BH18-02 13 0 8 92 38 19 CL A-6(18)

BH18-02 23 0 11 89 50 29 CH A-7-6(27)

BH18-03 9 0 2 98 30 12 CL A-6(11)

BH18-03 19 0 46 54 NV NP ML A-4(0)

Soil test results indicated a relatively shallow layer of silty to clayey sand (SC-SM and SM) overlying silts and clays with varying quantities of sand (CL, CH, and ML). The sands typically classified as A-2-4 soils by AASHTO, while the silts and clays classified as A-4, A-6, and A-7-6 soils by AASHTO.

Soil corrosivity testing of a bulk, streambed sample from the Magpie crossing site was sent to an outside laboratory for testing. Results are summarized below in Table 4.

Table 4:- Summary of Laboratory Corrosivity Results

SAMPLE

LOCATION

SAMPLE

DEPTH, ft

RESISTIVITY,

ohm-cm

PH

SULFATE

CONTENT,

ppm / %

CHLORIDE

CONTENT,

ppm / %

Magpie Crossing

Streambed 0-5 1,969 8.3 170 / 0.017 9 / 0.009

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SECTION FOUR - Analysis & Recommendations

This section presents analysis and recommendations for bridge foundations, box culvert foundations, embankments, cut slopes, material shrink/swell, and construction considerations for the design and construction of the Magpie and Whitetail Crossings project. Based on discussions with the project team, proposed improvements as of the 70% design plan set includes new bridge construction for the Magpie Crossing and new concrete box culverts for the Whitetail Crossing.

Generalized subsurface profiles were developed based on field reconnaissance, surficial visual evaluation, and subsurface investigations.

4.1 SUBSURFACE CONDITIONS

Bedrock was encountered during the subsurface exploration, but as discussed in subsection 2.2, it is considered soil for engineering characterization. The surficial deposits consist of relatively uniform moist silty, clayey sand. The SPT testing indicates that the subsurface materials are loose sands and very stiff to hard clays, signifying that the upper deposits are unconsolidated, and the deeper clays are overconsolidated. Potential for consolidation and settlement under loading is high due to these characteristics. Additionally, 1- to 2.5-foot-thick coal/lignite layers are found at shallow depths (less than 15 feet) capping the clay layer. The coal/lignite may be corrosive and contribute to increased acidity of surrounding soils. This will be further discussed in the foundation preparation subsections (4.3.3 and 4.4.3) and construction considerations (4.6).

Shallow groundwater was encountered at both project sites. Groundwater was 3 to 4 feet deep at

Magpie Crossing and 9 feet deep at Whitetail Crossing. Surface and subsurface water is likely to be encountered as construction will take place in or near seasonally active stream channels.

Considerations for implementation of dewatering and water diversion techniques are noted in the construction considerations subsection (4.6).

4.2 MAGPIE CROSSING BRIDGE FOUNDATIONS

A new bridge structure is proposed for the Magpie Crossing location. The bridge is anticipated to be a 114-foot long three-span structure. Based on the 70% design plans, the proposed abutment centerline station and cap elevation are shown in Table 5.

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Table 5:- Proposed Bridge Foundation Locations

Foundation

Location Station Centerline Elevation Pile Cap Elevation

Abutment 1 (SE) 106+43.00 2,147.42 2,142.33

Pier 1 106+80.00 2,147.22 2,144.53

Pier 2 107+20.00 2,147.02 2,144.33

Abutment 2 (NW) 107+57.00 2,146.82 2,141.72

4.2.1 Bridge Foundation Selection

A driven pile foundation system is proposed for the new bridge at the Magpie Crossing location.

A deep foundation was selected due to deep scour and settlement concerns associated with shallow footings at this site. Originally, a multi-celled box culvert was considered at this location, but due to large settlement and hydraulic inadequacy, a bridge structure with deep foundations was selected for design and construction prior to the 70% milestone. Drilled shafts were also considered for a deep foundation but were determined to have a higher cost and longer construction time compared to driven piles based on recent construction and bid history. Additionally, due to remote location of the bridge sites, transportation of concrete to the site would be challenging.

A driven pile foundation is feasible from a geotechnical perspective. Piles will be drivable through the moist, hard clay subsurface and develop required resistance at reasonable depth. Open-ended steel pipe piles are the recommended pile type due to the cohesive nature of the subsurface. Scour potential was determined to be present at the abutments and piers and is discussed in detail in the

Draft Hydraulics report dated September 28th, 2022.

The following factored bridge loads were provided on January 25th, 2023, by the CFL bridge engineer, and are shown in Table 6.

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Table 6:- Bridge Loads and Driven Pile Configuration

Foundation

Location

Max Factored

Axial Load per

Pile (kip)

Piles per Bent Pile Diameter (inch)

Abutment 1

(SE)

142 3 18

Pier 1 230 3 24

Pier 2 230 3 24

Abutment 2

(NW)

142 3 18

4.2.2 Driven Pile Axial Resistance

The driven pile axial resistance analysis was performed on 18-, 24-, and 30-inch diameter piles at the abutments and piers for 3, 4, and 5 pile configurations. Ultimately, three 18-inch piles at the abutments and three 24-inch piles at the piers were selected for final design based on pile drivability and minimization of estimated total pile length. Analysis was performed in Microsoft

Excel using the API method (modified alpha-method) for cohesive soils outlined in the NHI driven pile design manual (FHWA, 2016). The API method was selected due to its applicability in design for highly overconsolidated clays with high undrained shear strengths, as recommended in the NHI drive pile design manual (FHWA, 2016). The abutment and pier foundations, characterized as friction piles, will obtain their resistance through both side friction and tip resistance developed in the clay subsurface, below the scour elevation.

Based on AASHTO guidelines, the nominal axial loads and resistance should be factored by the appropriate resistance factors for the Strength, Service, and Extreme Event limit states. The resistance factor selected depends on construction and field verification methods. It is recommended that at least 4 piles (one at each abutment and pier) be tested using the Pile Driving

Analyzer (PDA) and signal matching at the end of driving. Inspector charts based on the wave equations will be developed by the contractor once the driving equipment and accessories are selected. In this case, a resistance factor of 0.65 should be applied to determine the factored resistance at the Strength Limit State (AASHTO Table 10.5.5.2.3-1). Based on this resistance factor, the design resistance lost to scour, and the design load at the Strength Limit State, the required nominal driving resistance was calculated. If PDA is not performed, a resistance factor of

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0.40 should be used instead, and the minimum tip elevation and required nominal driving resistance should be reevaluated.

Results of the calculations are presented in Appendix D and calculated pile lengths, minimum tip elevation, and required nominal driving resistance are discussed in subsection 4.2.7.

4.2.3 Pile Setup

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

Setup occurs more rapidly in cohesionless soils and more slowly in fine grained soils as pore water pressures dissipate. In some cases, setup in clays may continue to develop over a period of weeks and even months, and in large pile groups it can develop even more slowly. Although the on-site soils are fine grained and cohesive in nature, pile setup is not anticipated to result in significant additional capacity as the clays are hard, overconsolidated, and are not highly saturated.

4.2.4 Group Effects on Axial Resistance

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

10.7.1.2). However, pile groups in clay soils under certain pile cap ground conditions may warrant a reduction factor when spacings are greater than 2.5B. An efficiency factor (η) varying from 0.65 at spacing of 2.5B to 1.0 at 6.0B (found by interpolation) should be applied in instances where the pile cap is not in firm contact with the ground and if the soil at the surface is soft (AASHTO

10.7.3.9) If the cap is in firm contact with the ground, or if the cap is not in firm contact with the ground but the soil is stiff, no reduction in efficiency is required.

Pile groups at abutment locations will be in firm contact with the ground. Pile groups at the pier locations will not be in firm contact with the ground but the soil is stiff. Therefore, an efficiency factor (η) of 1.0 is applied for the pile group at all abutment and pier locations.

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4.2.5 Lateral Loads

Lateral load analysis was performed by the CFLHD bridge engineer using the software program

LPILE developed by Ensoft, Inc. This program analyzes a single pile or shaft considering deflection as a function of design loads, foundation construction, and subsurface conditions. A strength limit state resistance factor of 1.0 is specified in AASHTO 10.7.3.12 for lateral geotechnical resistance of a single pile or pile group. Factored strength limit state lateral loads should be used in the analysis.

Table 7 below provides LPILE input parameters for the foundation soils based available subsurface information and presumptive engineering correlations. These values do not include load or resistance factors. Additionally, it is recommended that lateral support above the scour elevation be neglected due to the potential loss of material during the design flood event.

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Table 7:- LPILE Input Parameters

APPROXIMATE

ELEVATION1

DEPTH

BELOW

EXISTING

GROUND

SURFACE

LPILE P-Y

MODEL

EFFECTIVE

UNIT WEIGHT

STRENGTH

PARAMETER2

FRICTION

ANGLE

STRAIN

PARAMETER

γ' c or k Փ ε50

(FT) (FT) Description (PCF) (PSI or PCI) (DEGREE)

Abutment 1 (SE, BH18-02)

2,138 – 2,135 0 – 3 Sand 120 25 28 -

2,135 – 2,130.5 3 – 7.5 Sand 57.6 20 28 -

2,130.5 – 2,1283 7.5 – 10

Lignite (Stiff Clay

Above the Water

Table)

120 50 - .005

2,128 – 2,098.54 10 – 39.5 Stiff Clay Above the

Water Table 120 50 - .005

Piers 1 & 2 (No Borehole Data)

2,136 – 2,117 0 – 19 Stiff Clay Above the

Water Table 120 27.8 - .005

2,117 – 2,0614 19 - 75 Stiff Clay Above the

Water Table 120 50 - .005

Abutment 2 (NW, BH18-03)

2,137 – 2,133 0 – 4 Sand 120 25 28 -

2,133 – 2,132 4 – 5 Sand 57.6 20 28 -

2,132 – 2,130 5 – 7 Stiff Clay Above the

Water Table 120 27.8 - .005

2,130 – 2,1293 7 – 8

Lignite (Stiff Clay

Above the Water

Table)

120 50 - .005

2,129 – 2,117 8 – 20 Stiff Clay Above the

Water Table 120 27.8 - .005

2,117 – 2,0974 20 – 40 Stiff Clay Above the

Water Table 120 50 - .005

1Neglect support above the scour elevation (2126.42 feet) at both abutments and both piers 2Undrained shear strength (c, psi) for use in clay soils and soil modulus (k, pci) for sands 3Neglect support in lignite layer 4Stiff clay layer may be assumed to extend to greater depth if needed for modeling. Borings did not advance past 40 feet in depth as a bridge structure was not anticipated at the time of the subsurface investigation

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 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 condition.

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4.2.6 Settlement

Settlement of piles driven to anticipated tip elevation and nominal axial capacity were estimated in accordance with section 10.7.2.3.2 of AASHTO. Settlement of the pile group at each abutment and pier is expected to be approximately ½-inch or less.

4.2.7 Pile Lengths

The final lengths of the driven piles are based on both axial and lateral loading, and minimum embedment. Table 8 below shows the calculated pile lengths needed for both axial and lateral capacities. The information in Table 8 is based on the selected pile diameter of 18 inches at the abutments and 24 inches at the piers. The minimum tip elevations presented in Table 8 are based on the estimated elevations required for lateral resistance. Even though estimated lengths for axial compression resistance at the abutments are longer than estimated lengths for lateral resistance by

2 feet, axial compression will not control the minimum tip elevation, as this depth is solely based on bearing resistance, and not other concerns such as excessive settlement, uplift, downdrag, or liquefaction (AASHTO C10.7.6). The nominal bearing resistance will be verified by field testing at each structural element and may be achieved prior to the minimum tip elevation required for lateral deflection, fixity for resisting lateral loading, and structural requirements. In all cases, the piles should be driven to at least the minimum tip elevation shown on the project plans, even if required resistance is developed at a shallower depth. As discussed in subsection 4.2.2, if no PDA testing is performed, the resistance factor must be reduced to 0.40, and the minimum tip elevation and required nominal driving resistance per pile must be revisited.

Appendix D of this report presents a visual representation of axial, single pile capacity versus pile length.

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Table 8:- Calculated Pile Lengths for Axial and Lateral Capacity

STRUCTURE

ELEMENT

MAX

FACTORED

AXIAL

LOAD PER

PILE

REQUIRED

PILE

LENGTH

FOR AXIAL

CAPACITY

REQUIRED

PILE

LENGTH FOR

LATERAL

CAPACITY

MINIMUM TIP

ELEVATION1,2

REQUIRED

NOMINAL

DRIVING

RESISTANCE

PER PILE3

(KIP) (FT) (FT) (FT) (KIP)

Abutment 1 (SE) 142 29 27 2115 225

Pier 1 230 35 35 2110 282

Pier 2 230 35 35 2110 282

Abutment 2

(NW)

142 31 29 2113 194

1Estimated minimum tip elevation based on satisfying all strength, service, and extreme event limit state requirements 2Estimated minimum tip elevation controlled by lateral load requirements. Piles must be driven to this depth or greater.

3The required nominal driving resistance per pile must be achieved in addition to the minimum penetration depth

4.2.8 Pile Drivability and Testing

The contractor should conduct drivability analysis using the Wave Equation Analysis Program

(WEAP) to select hammers that have sufficient energy to drive the piles to the required embedment without exceeding the allowable pile driving stresses and blows per foot presented in the project specifications. Test piles should be driven while instrumented with PDA to determine production pile driving criteria. One test pile per abutment and pier location, as indicated on the plans, should be tested and monitored by an engineer as outlined in the project specifications. The tests should be performed in 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 used for the test piles. If the contractor elects to bring another hammer on-site, the process of drivability analysis and test pile installation outlined above must be repeated for the new equipment.

4.2.9 Scour Potential and Erosion

Final long-term degradation, contraction scour, and local scour (abutment scour and pier scour) depths were determined by the hydraulics engineer. Total scour elevation was determined to be

2,126.42 for both abutments and piers. A detailed scour depth analysis is presented in Section 4.4 of the Draft Hydraulics Report.

Page | 16

4.3 WHITETAIL CROSSING BOX CULVERT DESIGN

A box culvert is proposed to replace the existing, unimproved low water crossing at Whitetail

Creek, consisting of two 12-foot span by 10-foot height concrete box culverts. Based on the subsurface exploration, the culvert will be founded on silty, clayey sand overlying very stiff fat clay. It is recommended for the box culvert to be founded on geotextile wrapped granular fill to address anticipated settlement.

4.3.1 Settlement and Consolidation

Soils typically experience two types of volume change related to loading: short-term

(immediate/elastic) settlement and long-term (primary consolidation) settlement. The classification and index testing of the on-site soils indicate that settlement due do structural loading will induce both elastic and consolidation settlement. It should be noted that no consolidation testing was performed on recovered soil samples. The soil properties for settlement analysis were selected based on correlations with index properties and used to estimate the total settlement potential for the box culverts. Due to the uncertainty of clay soil properties, a range of values (low, medium, high) were used in the analysis to better inform design. The range of values was determined by applying the minimum, average, and maximum index property values from lab testing on the on-site soils to the correlation equations.

Total settlement was evaluated using the Settle3 software from Rocscience. Analysis was first performed assuming native soil as the foundation material. Further analysis then included varying thicknesses of geotextile wrapped granular fill (12 to 36 inches) as options to reduce the magnitude of total settlement. In addition, differential settlement was calculated across the culverts both parallel and perpendicular to the travel way. Material properties and inputs used for analysis may be found in Table 9. Results of the settlement evaluation for the recommended granular fill thickness of 12-inches is presented in Table 10.

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Table 9:- Material Properties and Inputs for Settlement Analysis

Whitetail Crossing

Material

Type

Qualitative

Designation

Settlement

Type γ

(kcf)

Es

(ksf) Cc Cr OCR

Cv

(ft2/yr) e0

Clay

Low

Consolidation

0.12 - 0.360 0.0436 5.94 109.5 0.567

Middle 0.12 - 0.387 0.0475 3.39 83 0.618

High 0.12 - 0.414 0.0514 1.7 65.7 0.67

Silty, Clayey

Sand

- Elastic 0.12 48 - - - - -

Lignite - Elastic 0.13 1,467 - - - - -

Granular

Fill

- Elastic 0.14 4,000 - - - - -

Table 10:- Box Culvert Settlement Analysis Results

Whitetail Crossing

Scenario Qualitative

Designation

Immediate

Settlement

(in)

Primary

Consolidation

(in)

Total

Settlement

(in)

Differential

Settlement Parallel to Travel Way

(in)

Differential

Settlement

Perpendicular to Travel Way

(in)

No

Improvements

Low 0.44 1.40 1.84 0.72 0.74

Middle 0.44 1.47 1.91 0.74 0.76

High 0.44 2.63 3.07 1.82 1.85

12-inch

Granular Fill

Low 0.32 1.36 1.68 0.64 0.66

Middle 0.32 1.44 1.76 0.67 0.70

High 0.32 2.46 2.78 1.64 1.67

With no improvements, the results of the analysis indicate an estimated total settlement ranging from 1.84 to 3.07 inches with 0.74 to 1.85 inches of differential settlement. In addition, Table 10 above estimates settlement for the geotextile wrapped granular fill, but it should be noted that

Settle3 software is unable to account for the addition of geotextile. Therefore, the actual magnitude of total and differential settlement is likely less than what was calculated as the geotextile wrapping will provide additional strength and stability to the foundation. Analysis results also indicate that approximately 50% to 60% of total settlement will occur within the first

3 months after installation of the box culverts.

Page | 18

4.3.2 Bearing Resistance

Ultimate bearing resistance of the culverts is dependent on the dimensions of the foundation elements and characteristics of the bearing material. For these calculations, a foundation length of

32 feet was used based on the proposed culvert length. Bearing resistance for the strength, extreme event, and service limit states are shown in Plate 4. This plate presents both the AASHTO presumptive service limit load and the strength limit load based on the calculations as described below. The fine-grained cohesive on-site soils provide insufficient bearing capacity and excessive settlement is anticipated. Total settlement is still estimated to be outside AASHTO LRFD Bridge

Design Specifications (2017) standard serviceability limits (less than 1-inch) after following recommended foundation preparation that includes over-excavation and replacement with geotextile wrapped granular fill (1.68 to 2.78 inches estimated total settlement). Foundation preparation is detailed in the proceeding subsection.

For the Whitetail Crossing site, the presumptive bearing resistance of the silty, clayey sand is estimated to be between 2 to 4 ksf, with a recommended 3 ksf value of use. Provided values were obtained from Table C10.6.2.6.1-1 of AASHTO LRFD Bridge Design Specifications, 8th Edition, 2017. The bearing resistance values presented in this table are based on a maximum settlement of one inch and only apply at the service limit state (resistance factor of 1.0). The base of the box culverts should extend below the depth of frost potential, which is 32-inches based on National

Oceanic and Atmospheric Administration (NOAA) data and should be protected from scour as recommended by the hydraulic engineer.

Soil parameters recommended for culvert and retaining wall design are presented in Table 11.

These values are unfactored loads and assume that the surface of the soil slope behind the wall is horizontal.

Table 11:- Design Parameters

1Cohesion should not be relied upon when calculating active or at-rest pressures acting on structural elements

The AASHTO LRFD resistance factors for various limit states are presented in Table 12.

MATERIAL

TYPE

UNIT

WEIGHT

γ (pcf)

FRICTION

ANGLE

φ (deg)

COHESION

INTERCEPT

c (psf)

ACTIVE

EQUIVELENT

FLUID

DENSITY

(pcf)

AT-REST

EQUIVALENT

FLUID

DENSITY

(pcf)

NOMINAL

FRICTION

FACTOR

On-Site Soils 120 28 501 44 64 0.53

Structural

Backfill 130 34 0 37 58 0.67

Granular Fill

(foundation material)

140 35 0 - - -

Page | 19

Table 12:- Resistance Factors (Φ) for each limit state

LIMIT STATE BEARING SHEAR RESISTANCE TO

SLIDING

PASSIVE PRESSURE

RESISTANCE TO SLIDING

Strength I 0.45 0.80 0.50

Service I, Extreme

Event I & II

1.00 1.00 1.00

4.3.3 Foundation Preparation

Elastic settlement and potentially some primary settlement, are anticipated to be induced during construction due to equipment loads, compaction, and stages of box culvert and embankment placement. Additionally, the Settle3 model estimates that 50% to 60% of the total settlement will occur within the first 3 months after installation of the box culverts. If the construction schedule allows, and it is deemed feasible within the construction area, application of a pre-load is recommended to induce settlement prior to placement of the box culverts.

To minimize the potential for excessive total and differential settlements it is recommended to:

• Over-excavate by 12 inches to accommodate the granular fill section.

• Allow the excavated area to dry to the most reasonable extent possible. Dewatering should be performed if necessary.

• Compact the excavated foundation in accordance with FP-14 Section 209.10

• Perform construction monitoring of foundation stability as necessary

• Install 12-inch-thick geotextile wrapped granular fill section

The 12-inch geotextile wrapped granular fill section is recommended to prevent on-site soils from migrating into the fill, provide a stable foundation for construction, and distribute loads to help alleviate differential settlements. However, settlement is still anticipated after construction due to the weight of the box culverts, the majority of which (approximately 70%) will take place within the first year after construction.

Prepare the foundation subgrade according to FP-14 Section 209 and project SCRs. If coal/lignite is encountered during excavation, which is likely, it should be completely removed due to its inconsistency and potential for differential movement across its interface with other clay units.

The foundation is anticipated to contain unsuitable materials and be wet and unstable. Unsuitable material and poor conditions are expected to continue with depth. It is recommended to allow the excavated area to dry to the most reasonable extent possible, with dewatering if necessary. It is then recommended to compact the excavated foundation and perform construction monitoring of foundation stability as necessary.

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The granular fill section will consist of a minimum of 12 inches of granular backfill wrapped with separation geotextile once a compacted foundation is established. Granular backfill should meet the requirements of FP-14 Subsection 703.03(a) and be compacted in accordance with FP-14

Subsection 209.10. Fully encapsulate the granular fill with a separation geotextile, Class 1

(woven), Type C per FP-14 Subsection 714.01. If recommended by the culvert designer or manufacturer, place a layer of bedding material on the wrapped granular fill section to provide a level surface for placing the culverts.

The box culvert is in a seasonally active stream channel; therefore, surface and subsurface water are likely to be encountered during construction. Surface water should be diverted around the culvert construction area. If subsurface water is encountered, the foundation excavations should be provided with appropriate dewatering and/or water diversions.

4.3.4 Lateral Loads

The culverts should be designed to resist lateral loads based on the parameters reported in Table

11. The equivalent fluid densities do not include any surcharge for sloping backfill surfaces or other loads. These equivalent fluid densities do not include load factors or factors of safety; the designer should apply appropriate factors based on their design methodology. Below the mean water level, design the culvert wall for hydrostatic loading.

Lateral loads imposed on the structures are resisted by development of friction between the base of the structure footing and the supporting soils. The nominal friction factors presented in Table

12 above should be used for the design of the culverts.

4.4 ABUTMENT AND WINGWALL DESIGN

Cast-in-place concrete headwalls and wingwalls associated with the proposed culverts are anticipated, along with bridge abutment wingwalls. Abutments and wingwalls should be designed to resist lateral earth pressures and other applicable lateral loads in accordance with the AASHTO

LRFD. Lateral earth pressures are influenced by the strength of the backfill, presence of water, and ability of the wall to deflect in response to loading. Other loads including live loads, construction loads, and soil compaction loads should also be considered in the design. Subsurface drainage should be incorporated into the wall to prevent the buildup of hydrostatic pressures behind the wall. Design of concrete structures should be based on the material parameters presented in Table 11 above.

Page | 21

4.4.1 Bearing Resistance

Bearing resistance was not considered for the Magpie bridge abutment wingwalls. The wingwalls are planned to be cantilevered off the end wall and will not require a footing. The following subsection applies only to the Whitetail box culvert wingwalls.

Ultimate bearing resistance of the box culvert wingwall foundations is dependent on the both the length and width of the foundation elements. For the purpose of these calculations, a foundation length of 25 feet was assumed based on the proposed culvert size (12-foot by 10-foot) and proposed embankment side slopes (1V:2.5H). The presumptive bearing resistance of the silty, clayey sand is estimated to be between 2 to 4 ksf, with a recommended 3 ksf value of use. Provided values were obtained from Table C10.6.2.6.1-1 of AASHTO LRFD Bridge Design Specifications, 8th

Edition, 2017. The bearing resistance values presented in this table are based on a maximum settlement of one inch and only apply at the service limit state (resistance factor of 1.0).

Plate 5 presents the ultimate bearing capacity of the foundation soils for various foundation widths.

The appropriate resistance factor should be applied to the ultimate capacity to determine the factored capacity. Resistance factors for various limit states are presented in Table 12.

4.4.2 Settlement and Consolidation

Settlement of the culvert retaining walls is anticipated in the same nature as the box culvert. The classification and index testing of the on-site soils indicate that immediate settlement will occur due to the structural loading, but the primary form of settlement will be long-term (primary consolidation).

4.4.3 Foundation Preparation

Prepare the foundation soils for the culvert retaining walls in accordance with FP-14 Section 209 and as directed for the concrete box culverts (subsection 4.3.3), including use of a geotextile wrapped 12-inch granular fill section.

No foundation preparation is required for the Magpie bridge abutment wingwalls.

4.4.4 Lateral Loads

Retaining structures should be designed to resist lateral pressures depending on the restraint conditions. Retaining walls that can deflect (active condition) should be designed to resist loads based on the active equivalent fluid density presented in Table 11Error! Reference source not found.. Walls that are restrained (at-rest condition) should be designed based on the at-rest equivalent fluid density. If structural backfill is placed within the active or at-rest zones behind the retaining wall, reduced equivalent fluid densities may be used. The equivalent fluid densities do not include any surcharge for sloping backfill surfaces or other loads. These equivalent fluid

Page | 22 densities do not include load factors or factors of safety; the designer should apply appropriate factors based on their design methodology. Below the mean water level, design the walls for the full hydrostatic condition.

Lateral loads imposed on the structures are resisted by development of friction between the base of the structure footing and the supporting soils. The nominal friction factors presented above for the culverts may be used for the design of cast-in-place footings established on similar soils to the culverts.

4.5 EARTHWORKS

4.5.1 Embankment and Fill Construction

Embankment construction is anticipated in relation to the construction of the proposed box culverts, bridge structure, wingwalls, and approach road reconstruction. Soils in the project area are typically silty, clayey sands, including existing embankment fills, and very stiff clay may be found at greater depth. The existing embankment fills were constructed at slopes of approximately

1(V):2(H) and are performing well. It is assumed that similar materials will be used for the proposed embankment expansions. Therefore, the expanded embankments should be constructed with maximum 1(V):2(H) side slopes to maintain slope stability and reduce potential for erosion.

The expansions should be keyed into the existing ground and compacted in accordance with the requirements of Section 204 of the FP-14.

4.5.2 Cut Slopes & Temporary Shoring

Cut slopes are anticipated for construction of the box culverts, bridge foundations, and associated wingwalls. Shoring may be desirable depending on preferences to limit areas of disturbance.

Groundwater is likely to be encountered during construction and dewatering could be necessary.

Design and safety of this work is the responsibility of the contractor. The work shall be performed in a manner to minimize hazards and exposure to the public, construction personnel, and equipment.

4.5.3 Shrink/Swell Recommendations

For estimating shrink/swell values, silty, clayey sands are assumed to be the predominate material located in the cut areas. The recommended shrink/swell factors are based on a combination of standard tabled values for common materials in the FLH Technical Guidance Manual (2006) and experience with other CFLHD projects in similar materials.

The silty, clayey sand on-site materials are assumed to swell 15 percent (Swell Factor 1.15) if wasted without tight density control during placement. If the on-site soils are incorporated into

Page | 23 embankments with tight density control during placement, a shrink of 10 percent (Swell Factor

0.90) should be used.

4.6 CONSTRUCTION CONSIDERATIONS

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

The natural soils are relatively uniform both laterally and vertically. Few boulders were visible in stream banks adjacent to the project site; up to approximately 2 feet in diameter. Based on this, we do not anticipate difficult excavation conditions for conventional, heavy-duty construction equipment in good working order. Occasional boulders requiring special handling may be encountered in excavations for culverts or retaining walls. Additionally, the coal/lignite layers encountered during the subsurface investigation indicated very hard material (SPT refusal or blow counts > 50), but hollow stem augers were able to advance through the material and it is presumed rippable. The contractor should mobilize equipment capable of handling such materials (i.e.

hydraulic rams and excavators).

Excavation will encounter wet, loose silty, clayey sands and possibly clay. These materials will likely be unstable and consideration for shoring may be necessary.

Culvert and Wingwall Foundation Preparation: The soils in the stream channel are likely to be soft and saturated in their natural condition. This report recommends replacing the on-site materials below the culverts and wingwalls with a wrapped granular fill section. Recommendations detailed in subsections 4.3.3 and 4.4.3 should be followed.

If issues related to foundation subgrade stability are encountered during construction, the CFLHD geotechnical engineer should be contacted to provide further guidance.

Dewatering: The box culverts and wingwalls are located in or near seasonally active stream channels; therefore, surface and subsurface water are likely to be encountered during construction.

Surface water should be diverted around the culvert or wingwall construction…