CHOH 206(1) 913(1) 928(1) Final Geotech Report S.pdf

SOILS AND FOUNDATION REPORT

NO. 03-22

PROJECT CHOH 206(1), 913(1), 928(1)

REPLACEMENT OF EDWARDS FERRY, DARGAN BEND, AND FIFTEEN MILE

CREEK BRIDGES, AND CONSTRUCTION OF CULVERT 82

CHESAPEAKE AND OHIO CANAL NATIONAL HISTORICAL PARK

MARYLAND

U.S. Department of Transportation Federal Highway Administration

Eastern Federal Lands Highway Division 22001 Loudoun County Parkway

Building E-2, Suite 200 Ashburn, VA 20147

February 2022

TABLE OF CONTENTS

REPORT PAGE

1 INTRODUCTION

1.1. General

1.2. Project Description

2 GEOLOGIC SETTING

3 PROCEDURES AND RESULTS

3.1. General

3.2. Sampling

3.3. Field Tests and Measurements

3.4. Data Summary

3.5. Laboratory Testing

3.6. Findings

4 DESIGN ANALYSIS AND CONCLUSIONS

4.1. General

4.2. Seismic Design Considerations

4.3. Bridge Loading

4.4. Foundation Type Considerations

5 RECOMMENDATIONS

5.1. Bridge Foundations

5.1.1. Compression Resistance

5.1.2. Lateral Deflection

5.2. Abutment Walls

5.3. Micropile Load Testing

5.4. Corrosion Protection

5.5. Scour Consideration

6 CONSTRUCTION CONSIDERATIONS

7 DISCLAIMER/LIMITATIONS CLAUSE

8 REFERENCES

APPENDICES

APPENDIX A – Figures APPENDIX B – Boring Location Plans and Subsurface Profiles APPENDIX C – Boring Logs APPENDIX D – Laboratory Testing Results APPENDIX E – Design Analysis APPENDIX F – Selected Photographs

Note: Design changes subsequent to publication of this report and prior to the project’s advertisement will be documented by a memo inserted after the title page.

Project: CHOH 206(1), 913(1), 928(1) Bridge Replacement Chesapeake and Ohio Canal Soils and Foundation Report Maryland No. 03-22

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

SOILS AND FOUNDATION REPORT

NO. 03-22

PROJECT CHOH 206(1), 913(1), 928(1)

REPLACEMENT OF EDWARDS FERRY, DARGAN BEND, AND FIFTEEN MILE

CREEK BRIDGES, AND CONSTRUCTION OF CULVERT 82

CHESAPEAKE AND OHIO CANAL NATIONAL HISTORICAL PARK

MARYLAND

1 INTRODUCTION

1.1. General

This report summarizes the results of our subsurface exploration, laboratory testing, and design analyses and presents recommendations regarding the foundations for the replacement of Edwards Ferry, Dargan Bend, and Fifteen Mile Creek bridges. The project is located in Chesapeake and Ohio Canal National Historical Park, Maryland. The Project Location Maps are provided in Figure 1, Appendix A.

Included in this report are our foundation recommendations for Culvert 82 bridge located at Brunswick, MD between Edwards Ferry and Dargan Bend sites. A geotechnical engineering study for the subject culvert was performed in the summer of 2020 by DMY Engineering Consultants Inc. on behalf of YRU Consulting Inc. All the subsurface data provided in this report and related to Culvert 82 bridge, is pertinent to the summer 2020 report.

1.2. Project Description

The purpose of this project is to replace Edwards Ferry, Dargan Bend, and Fifteen Mile Creek bridges and construct a Culvert 82 bridge located in Chesapeake and Ohio Canal National Historical Park, MD. The historical canal runs parallel to the meandering Potomac River. Table 1 summarizes the location, utilization, and bridge condition remarks per site.

Table 1 - Project Locations Summary

Project site

NPS

Mile

Marker County

EFLHD

Structure Number

Approximate Coordinates* Remarks

Edwards Ferry 31 Montgomery 3100-001P N 39.103712°

W 77.472348°

Used for search and rescue, water supply, access to a boat ramp, and historical canal lockhouse. A temporary bridge was installed in March 2021.

The new single-span bridge will be 42 ft long and 12 ft wide.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Project site

NPS

Mile

Marker County

EFLHD

Structure Number

Approximate Coordinates* Remarks

Dargan Bend 65 Frederick 3100-005P N 39.363945°

W 77.740232°

Used for search and rescue, water supply, access to a boat ramp, and bike trail.

The new single-span bridge will be 44 ft long and 12 ft wide.

Fifteen Mile

Creek 141 Washington 3100-013P N 39.625705°

W 78.386084°

Used for search and rescue, water supply, access to a boat ramp, and access to a campground.

The new single-span bridge will be 44 ft long and 12 ft wide.

Culvert 82 51 to 52 Frederick N/A N 39.307468° W 77.585516°

Floodwaters washed away the historical culvert in May 2018.

The new single-span bridge will be 115 ft long and 8 ft wide.

* Coordinate system WGS84

2 GEOLOGIC SETTING

The Geologic map of the Chesapeake and Ohio Canal National Historical Park and Potomac River Corridor (USGS, 2008) indicates that the project is located on the Piedmont, Blue Ridge, and Valley and Ridge Provinces with rocks ranging from Triassic, Cambrian, and Devonian ages. Ancient alluvial deposits are also present since the historical canal is a part of the Potomac River’s floodplain. The bedrock at Edwards Ferry’s site is predominantly a ferrous, reddish to purple-brownish Shale and Siltstone (TRcbb). Terrace (sand, gravel, and boulders) and alluvium deposits (unconsolidated clay, silt, sand, and gravel) overlay Edwards Ferry’s site. The bedrock at Dargan Bend’s site is predominantly a light to dark bluish-gray Metasiltstone and Metasandstone (Ꞓch);

some alluvium deposits overlay the bedrock at the site. Terrace deposits are present at Fifteen Mile Creek’s site underlain by an olive and greenish-gray to dusky red Sandstone, Siltstone, and Shale (Df). Refer to DMY Engineering Consultants Inc. of June 16, 2020 report for the site Geology of Culvert 82 bridge. Table 2 summarizes the site geology characteristics per site. Site geology maps are provided in Appendix A.

Table 2 - Sites Geology Summary

Project Site Geologic Period Province Formation Parent Rock

Edwards Ferry Upper Triassic Piedmont Bull Run Shale and Siltstone

(sedimentary)

Dargan Bend Lower Cambrian

Between the Blue Ridge province and Great Valley section

Harpers

Metasiltstone and

Metasandstone (metamorphic)

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Project Site Geologic Period Province Formation Parent Rock

Fifteen Mile Creek Upper Devonian Valley and Ridge Foreknobs

Sandstone, Siltstone, and

Shale

Culvert 82* Proterozoic Blue Ridge Neoproterozoic Catoctin

Biotite Granite Gneiss

(metamorphic)

* DMY Engineering Consultants Inc. report of June 16, 2020

3 PROCEDURES AND RESULTS

3.1. General

The Eastern Federal Lands Highway Division’s (EFLHD) Subsurface Exploration Team performed the drilling and coring operations for this project between April 9th and April 23rd, 2021. The fieldwork consisted of drilling six (6) soil borings (BH21-01 through BH21-06) and coring four (4) borings.

Soil borings were staked out by EFLHD field personnel by referencing ground-surface topography, measuring distances from existing surface features, estimating right-angles, and the use of a hand-held GPS unit. Due to the field methods used, boring locations shown in the Borings Location Map should be considered approximate. Ground surface elevations at the boring locations were determined from the topography plans provided by the Survey Division. Borings were advanced to auger refusal or termination depths using hollow-stem augers by a CME 750 ATV-mounted rotary drill rig. Rock coring was performed in selected borings, and core samples were retrieved using an NQ core barrel and wireline. Upon completion of the drilling operation, the boreholes were backfilled with auger cuttings and patched with cold asphalt mix. The approximate borings location are graphically depicted on the Boring Location Plans and Subsurface Profiles presented in Appendix B. Field data are summarized in Table 3.

Table 3 - Summary of Field Data

Project site

Boring No. &

Remarks X

Longitude* Y

Latitude* Ground surface elev. (ft)**

Ground water depth (ft) Termination depth (ft)

Edwards Ferry

BH 21-01

East abutment -77.472298° 39.103778° 205.5 22.0 39.0

BH 21-02

West abutment -77.472410° 39.103658° 205.5 19.0 30.0

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Project site

Boring No. &

Remarks X

Longitude* Y

Latitude* Ground surface elev. (ft)**

Ground water depth (ft) Termination depth (ft)

Dargan Bend

BH 21-03

East abutment -77.740102° 39.364043° 291.5 15.0 34.2

BH 21-04

West abutment -77.740248° 39.363817° 290.5 19.0 30.1

Fifteen Mile

Creek

BH 21-05

East abutment -78.386159° 39.625714° 463.5 5.0 33.0

BH 21-06

West abutment -78.385867° 39.625605° 461.5 Not found 34.2

Culvert 82***

B-1 West abutment Not provided 253.0 23.0 33.3

B-2 East abutment Not provided 254.0 28.0 38.5

Note: All depths are below existing site grades

* WGS84

** NAVD 1988

*** DMY Engineering Consultants Inc. report of June 16, 2020

3.2. Sampling

Borings were advanced to the auger refusal depths using 3¾-in. (inside diameter) hollow stem augers. Standard Penetration Testing (SPT) was performed using a 2¼-in. (outside diameter) split-spoon sampler per AASHTO T 206. SPT soil samples were typically recovered at 5.0 ft intervals until refusal. Samples were obtained by driving the split-spoon sampler a distance of 24-in., into the undisturbed soil under the impact of a 140-lb.

automatic hammer free-falling 30 inches. The number of hammer blows required to advance the split-spoon sampler to the middle foot of the 24-in. sample interval is designated as the “Standard Penetration Resistance” or N-value. The number of blows required to advance the sampler through each 6-in. interval was recorded on field boring logs. The relative consistency of cohesive samples, if encountered, was estimated using a calibrated pocket Penetrometer.

Representative portions of split-spoon samples were preserved in glass jars for laboratory testing. Rock cores were placed in wooden boxes. All soil and core samples were later transported to EFLHD’s Materials Testing Laboratory in Sevierville, Tennessee for laboratory testing and storage. The sampling sequence and associated jar samples for each boring are presented on its appropriate Boring Log in Appendix C.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Groundwater level readings were made in the boreholes at the times and under the conditions stated on the boring logs. However, fluctuations in groundwater level due to seasonal variations, rainfall, temperature, and other factors not evident at the time measurements were made should be expected.

3.3. Field Tests and Measurements

The EFLHD geotechnical crew performed field tests and took measurements during the subsurface exploration. A field description by color and texture was made for each recovered soil sample. Percent core recovery (CR) and Rock Quality Designation (RQD) were determined for each core run.

3.4. Data Summary

The results of field tests and measurements were recorded on the driller’s logs and appropriate data sheets in the field. These data sheets and logs contain information concerning the boring methods, samples attempted and recovered, indications of the presence of various materials such as gravel, pebbles, organic matter, and observations of groundwater. They also contain interpretations by the exploration foreman of the subsurface conditions based on the performance of the equipment and cuttings brought to the surface by the drilling tools; therefore, the field data represents both factual and interpretative information.

The boring logs in Appendix C represent a compilation of field and laboratory data and descriptions of the soil and rock samples by a geotechnical engineer. These records occasionally may not include all data recorded on driller’s logs and field data sheets but do include all information considered relevant to the design and preparation of this report.

3.5. Laboratory Testing

A laboratory testing program was conducted on representative soil and rock samples recovered during the subsurface exploration. The primary purpose of the testing program was to aid in the classification and evaluation of the engineering properties of soils and rock present at the site. Laboratory tests included natural moisture content (AASHTO T 265), Atterberg limits (AASHTO T 89 & T 90), particle size analysis (AASHTO T 11/T

27) and pH testing (AASHTO T 289).

Unconfined compressive strength (ASTM D 7012) tests were performed on representative rock core samples to evaluate their strength parameters. All tests were conducted following applicable ASTM/AASHTO standard test methods. The results of the laboratory testing program are presented in Appendix D and summarized in Table 4, and Table 5 below.

Refer to DMY Engineering Consultants Inc.’s June 16, 2020 report for information regarding the subsurface exploration of Culvert 82 bridge.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Table 4 - Summary of Laboratory Test Results - Soil Samples

Boring No. Sample No. Sample Depth (ft)

Moisture Content (%)

Fines

(%) AASHTO USCS

BH 21-01 J-5 20-22 20.72 32.9 A-2-4(0) SM

BH 21-02 J-3 10-12 17.25 43.2 A-6-3 SC

BH 21-03 J-4 15-17 24.62 46.2 A-4(0) SM

BH 21-04 J-3 10-12 25.48 72.1 A-6(11) CL

BH 21-04 J-4 15-17 21.41 64.7 A-6(11) CL

BH 21-05 J-3 5-7 10.85 23.9 A-1-b SM

J = Jar sample USCS: Unified Soil Classification System

Table 5 - Summary of Laboratory Test Results - Rock Cores

Boring No.

Depth to

Auger Refusal (ft)

Run Depth (ft)

Approx.

Rock elev.

(ft) RQD (%) UCS rock core test (psi)

BH 21-01

East abutment 25.0 30.5 - 39 180.5 9 to 90 N/A

BH 21-02

West abutment 25.0 N/A 180.5 No recovery N/A

BH 21-03*

East abutment 25.1 25.1 – 34.2 266.4 75 to 95 5,200

BH 21-04

West abutment 25.0 N/A 265.5 N/A N/A

BH 21-05

East abutment 18.4 18.4 - 33 445.1 0 N/A

BH 21-06

West abutment 25.0 25.0 – 34.2 436.5 91 to 100 3,550

B-1 West abutment 33.3 N/A 219.7 N/A N/A

B-2 East abutment 33.5 N/A 220.5 42 N/A

N/A = Not Applicable

* pH = 5.73

3.6. Findings

The boring logs in Appendix C represent a compilation of field and laboratory data and descriptions of the soil samples by a geotechnical engineer. These records occasionally may not include all data recorded on driller’s logs and field data sheets, but do include all information considered relevant to the design and preparation of this memo.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

The Boring Location Plan and Subsurface Profile sheets in Appendix B represent generalized subsurface profiles illustrating the general soil conditions that may be anticipated. A brief description of the soil conditions encountered in the borings is presented below. The stratification lines designating soil types and the interfaces between soil types in the boring logs in Appendix C represent approximate boundaries. The transition between materials may be gradual. Each of the soil types has been grouped according to its engineering properties and classification. It should be noted that one or more of the units may be absent at specific locations.

Edwards Ferry (Borings BH 21-01 and BH 21-02)

Stratum I - Fill: Clayey SAND with Gravel (SC) Fill material was encountered in the borings and extended to an approximate depth of

15.0 ft below existing site grades. The fill consisted primarily of clayey sand with gravel (SC). SPT N-values recorded within the fill layer ranged from 5 to 7 blows/ft (bpf), indicating loose relative density.

Stratum II - Natural Deposits: Silty SAND with gravel (SM) Underneath the fill, silty sand with gravel (SM) was encountered. N-values recorded ranged from 0 blow per foot (bpf) to 50 bpf, indicating very loose to very dense relative densities. This stratum extended to auger refusal depths.

Stratum III - Bedrock: Shale and Siltstone Dark brown shale and siltstone were encountered in Borings BH 21-01 and BH 21-02 at a depth of 25.0 ft, below existing site grades. Rock quality designation (RQD) values ranged from 9% to 90% in Boring BH21-01 indicating highly weathered to sound rock.

Rock coring was terminated at a depth of 39.0 ft below existing site grades in Boring BH 21-01.

Groundwater Groundwater was encountered at an approximate depth of 22.0 ft and 19.0 ft below existing site grades in Boring BH 21-01 and BH 21-02, respectively.

Dargan Bend (Borings BH 21-03 and BH 21-04)

Stratum I - Fill: Silty SAND (SM) and Lean CLAY with Sand (CL) Fill material was encountered in the borings and extended to an approximate depth of

10.0 ft below existing site grades. The fill consisted primarily of silty sand (SM) and lean clay with sand (CL) with various amounts of gravel. N-values recorded within the fill layer ranged from 4 bpf to 24 bpf, indicating very loose to medium dense relative densities, and firm to stiff consistencies.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Stratum II - Natural Deposits: Silty SAND (SM), Lean CLAY with sand (CL), and Sandy lean CLAY (CL) Underneath the fill, layers of silty sand (SM), lean clay with sand (CL), and sandy lean clay (CL) were encountered. N-values recorded within this stratum ranged from 0 bpf to 50 bpf, indicating very loose to very dense relative densities, and firm to stiff consistencies. This stratum extended to auger refusal depths.

Stratum III – Bedrock: Metasiltstone and Metasandstone Gray metasiltstone and metasandstone were encountered in Borings BH 21-03 and BH 21-04 at a depth of 25.0 ft, below existing site grades. RQD values ranged from 75% to 95% in Boring BH 21-03 indicating moderately weathered to sound rock. Rock coring was terminated at a depth of 34.2 ft in Boring BH 21-03.

Groundwater Groundwater was encountered at an approximate depth of 15.0 ft and 19.0 ft below existing site grades in Boring BH 21-03 and BH 21-04, respectively.

Fifteen Mile Creek (Borings BH 21-05 and BH 21-06)

Stratum I - Fill: Silty SAND with Gravel (SM) Fill material was encountered in the borings and extended to an approximate depth of

10.0 ft below existing site grades. The fill consisted primarily of silty sand with gravel (SM). N-values recorded within the fill layer ranged from 3 bpf to 10 bpf, indicating very loose to loose relative densities.

Stratum II - Natural Deposits: Silty SAND with gravel (SM) and Sandy lean CLAY (CL) Underneath the fill, layers of silty sand (SM) and sandy lean clay (CL) were encountered.

N-values recorded within this stratum ranged from 6 bpf to 50 bpf, indicating loose to very dense relative densities, and firm to hard consistencies. These layers extended to auger refusal depths.

Stratum III - Bedrock: Sandstone, Siltstone, and Shale Dark Gray sandstone, siltstone, and shale were encountered in Borings BH 21-05 and BH 21-06 at depths of 18.4 ft and 25.0 ft, below existing site grades, respectively. The rock core retrieved at Boring BH 21-05, was of poor quality with an RQD value of 0% followed by no recovery. RQD values ranged from 91% to 100% in Boring BH 21-06.

Rock coring was terminated at depths of 33.0 ft and 34.2 ft below existing site grades in Borings BH 21-05 and BH 21-06, respectively.

Groundwater Groundwater was encountered at an approximate depth of 10.0 ft below existing site grades in Boring BH 21-05.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Culvert 82 Bridge (Borings B-1 and B-2)

The subsurface profile for this site is listed in the DMY Engineering Consultants Inc.

report of June 16, 2020.

4 DESIGN ANALYSIS AND CONCLUSIONS

4.1. General

Foundation design was performed in general accordance with AASHTO LRFD Bridge Design Specifications, 9th Edition, 2020.

4.2. Seismic Design Considerations

Table 6 presents the Seismic Site Class per project site based on the criteria contained within AASHTO Table 3.10.3.1-1, and the results of our subsurface exploration. Table 7 provides seismic design parameters according to the USGS Seismic Design Maps web application based on the approximate coordinates of the project site locations as presented in Table 1. Table 8 presents AASHTO Seismic Zone classifications per project site based on the seismic design parameters presented in Table 7, and as per AASHTO 3.10.3-3.10.6. See Appendix E for computations.

Table 6 - AASHTO Seismic Site Class Project Site Seismic Site Class

Edwards Ferry E

Dargan Bend D

Fifteen Mile Creek E

Culvert 82 D

Table 7 - USGS Seismic Design Maps parameters Seismic Design

Parameter Description Edwards

Ferry Dargan

Bend Fifteen

Mile Creek

Culvert 82

PGA Horizontal Peak Ground Acceleration 0.04g 0.04g 0.04g 0.04g

Ss Short-period (0.2-second) spectral acceleration 0.09g 0.09g 0.09g 0.09g

S1 1-second spectral acceleration 0.031g 0.031g 0.032g 0.031g

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Table 8 – AASHTO Seismic Zone Classifications

Project Site SD1 Seismic Zone Classification Remarks

Edwards Ferry 0.109g 1 The retaining structure located in N

39.103712° W 77.472348° does not require a seismic analysis

Dargan Bend 0.074g 1 The retaining structure located in N

39.363945° W 77.740232° does not require a seismic analysis.

Fifteen Mile Creek 0.112g 1 The retaining structure located in N

39.625705° W 78.386084° does not require a seismic analysis

Culvert 82 0.074g 1 The retaining structure located in N

39.307468° W 77.585516° does not require a seismic analysis.

SD1 = 1-Second Period Acceleration Coefficient

4.3. Bridge Loading

Structural loads provided by the Bridge Division are listed in Table 9 below.

Table 9 - Structural Loads

Load Edwards Ferry Dargan Bend Fifteen Mile Creek Culvert 82

STRENGTH LIMIT STATE

Max axial (STR V) - Single Pile 86.95 kip 89.02 kip 80.27 kip 61.0 kips Lateral Fx (STR I) - Single Pile 10.83 kip 12.25 kip 10.94 kip 8.0 kips Lateral Fy (STR I) - Single Pile 0.264 kip 0.170 kip 0.167 kip NA Total axial (STR V) - Pile group 338.54 kip 538.55 kip 522.94 kip 192 kips Lateral Fx (STR I) - Pile group 86.64 kip 147.00 kip 131.28 kip 48 kips Lateral Fy (STR I) - Pile group 2.11 kip 2.00 kip 2.00 kip NA

SERVICE LIMIT STATE

Max axial (SERV I) - Single Pile 56.14 kip 58.72 kip 53.05 kip 45.0 kip Lateral Fx (SERV I) - Single Pile 6.88 kip 7.92 kip 7.08 kip 5.5 kip Fx = Lateral Load on X direction; Fy = Lateral load on Y direction The X-direction is longitudinal to the bridge; the Y-direction is transversal to the bridge Total axial load corresponds to the total load applied to the pile group

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

4.4. Foundation Type Considerations

Based on the subsurface profile encountered and the proposed construction, several alternatives were considered for the bridge foundations. Decision criteria included cost, constructability, environmental impacts, limits of disturbance, and familiarity with similar projects and soil profiles. Table 10 provides a summary of the foundation types considered.

Table 10 - Foundation Type Summary

Foundation Type Advantages Disadvantages Footings • Affordable

• Well known construction procedure

• Non-specialized labor

• Anticipated differential settlement due to presence of fill

• Deep excavation may be needed to support footings on firm natural soil

• May interfere with unknown foundations at the site

• Foundation subjected to scour Precast-Prestressed Concrete and Driven Steel Piles

• Concrete piles are more resistant to corrosion than steel piles

• Steel piles are a common foundation type – leading to lower costs

• Quick installation

• No maintenance

• Good QA/QC while driving

• End-bearing piles are likely to be used and tip protection may be needed

• Significant noise and vibration impacts during driving

• Possible presence of cobbles and boulders creates installation risks

Micropiles • High load capacity in both tension and compression

• Minimal vibrations and disturbances

• Installation is possible in difficult or limited access site

• Can be socketed in the bedrock to provide higher load capacity and scour resistance

• Moderate lateral load capacity

• Require a specialty contractor

Based on the considerations presented in Table 10, we conclude that micropiles present the most economic and suitable foundation alternative.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

5 RECOMMENDATIONS

5.1. Bridge Foundations

A micropile is defined as “a small-diameter (usually less than 300 mm (12 in.)), drilled and grouted non-displacement pile that is typically reinforced. A micropile is constructed by drilling a borehole, placing steel reinforcement, and grouting the hole” (FHWA, 2005).

A system of micropiles socketed in bedrock is recommended to support the abutments of the new bridges. Table 11 provides a summary of micropile design properties and assumptions considered for design. Core steel reinforcing bar should extend the full height of the micropile, from the top anchor plate completely through the minimum length competent rock bond zone. Steel casing should extend from the abutment cap to the top of bedrock.

Table 11 - Micropile Design Properties and Assumptions

Property Edwards Ferry

Dargan Bend*

Fifteen Mile

Creek* Culvert

Number of Rows of Micropiles, Ny 2 2 2 2 Number of Columns of Micropiles, Nx 4 5 5 3 Total Number of Micropiles per Foundation Element 8 10 10 6 Micropile Row Center-to-Center Spacing, Sy (in) 38 54 54 30 Micropile Column Center-to-Center Spacing, Sx (in.) 54 30 30 60

Micropile Outside Diameter, OD (in.) 9.625 9.625 in 9.625 7.00 Micropile Insider Diameter, ID (in.) 8.681 8.681 8.681 6.000 Wall Thickness, tw (in.) 0.472 0.472 0.472 0.50 Micropile Casing Yield Stress, fy.Ncasing (ksi) 80 80 80 80

Reinforcing Bar Diameter, Dbar (in) 2.5 2.5 2.5 2.5 Reinforcing Bar Size #20 #20 #20 #20 Reinforcing Bar Yield Stress, fy.steel (ksi) 80 80 80 80 Grout Unconfined Compressive Strength, fc_grout (ksi) 6 6 6 6 Minimum Depth of Bond Zone Embedment in Rock, Lb (ft) 15.0 6.0 14.0 5.0 Grout-to-Ground Bond Value, αb (ksf) AASHTO Table C10.9.3.5.2-1 4.3 10.8 4.3 18.0

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

* Lateral Analysis is conservatively based on 10 micropiles. The abutment has a trapezoidal shape with a total of 16 micropiles.

5.1.1. Compression Resistance

Micropile design was evaluated in general accordance with AASHTO Article 10.9 and FHWA (2005). A resistance factor (φqs) of 0.55 was utilized for grout-to-ground bond resistance, as listed in AASHTO Table 10.5.5.2.5-1. Table 12 provides the computed nominal and factored compression resistances (also referred to as geotechnical bond capacity or grout-to-ground bond resistance).

Side resistance along the cased length of micropiles and tip resistance along the uncased length of micropiles were neglected for the determination of compression resistances.

Compression resistance calculations and computer output are included in Appendix E.

Table 12 – Calculated Compression Resistance

Resistance Edwards Ferry

Dargan Bend

Fifteen Mile Creek Culvert 82

Nominal Compression Resistance (kip) 162.5 163.3 151.7 164.9 Factored micropile axial resistance (kip) 89.4 89.8 83.4 90.7

5.1.2. Lateral Deflection

Lateral deflections were evaluated and micropiles were sized to bound service limit state deflections to less than 1 inch. In accordance with AASHTO Table 10.5.5.2.3-1, a lateral resistance factor (φlat) of 1.0 was utilized. Sample lateral deflection computer output is included in Appendix E, with output files provided for factored (maximum) and service limit load conditions under fixed head fixity. A summary of results for the various loadings considered is provided in Table 13.

Table 13 – Lateral Analysis Results

Project Site Lateral Loading

Loading Condition

Maximum Lateral

Deflection at Top of Pile

(in)

Maximum Bending

Moment in Pile

(kip-ft)

Maximum Shear in Pile

(kip)

Edwards Ferry Fx Maximum

0.21 60.8 13.4

Fy 0.004 1.1 0.3 Fx Service 0.1 30.2 6.9

Dargan Bend

0.22 77.2 17.7

Fy 0.003 1 0.2 Fx Service 0.094 33.8 7.9

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

Project Site Lateral Loading

Loading Condition

Maximum Lateral

Deflection at Top of Pile

(in)

Maximum Bending

Moment in Pile

(kip-ft)

Maximum Shear in Pile

(kip)

Fifteen Mile Creek

0.216 63.9 14.6 Fy 0.003 0.9 0.2 Fx Service 0.104 30.8 7.1

Culvert 82 Fx Maximum 0.4 36.3 9.4 Fy NA NA NA NA Fx Service 0.138 17.8 5.5

Fx = Lateral Load on X direction; Fy = Lateral load on Y direction The X-direction is longitudinal to the bridge; the Y-direction is transversal to the bridge

5.2. Abutment Walls

According to FP-14, Section 258, structural fill should be used for the construction of abutment walls. Table 14 presents the range of soil properties recommended for the design of the abutment walls. These soil properties should be used to compute the Active (Ka), Passive (Kp), and At-Rest (Ko) Earth Pressure Coefficients.

Table 14 - Soil Design Parameters for Abutment Walls

Parameter Value

Moist Soil Unit Weight, γ (pcf) 120 - 124

Friction Angle, φ (deg.) 30 - 32

5.3. Micropile Load Testing

Micropile load testing should be performed in accordance with Subsection 567.06 of the FP-14. Design and Alignment Load values for the piers and abutments are listed in Table 15 below.

Table 15 - Loads for Micropile Testing and Stressing

Load Edwards Ferry

Dargan Bend

Fifteen Mile Creek Culvert 82

Design Load, DL (kip) 56.14 58.72 53.05 45

Alignment Load, AL (kip) 5.6 5.9 5.3 4.5 DL = Unfactored design load AL = Alignment load (no greater than 0.1DL)

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

5.4. Corrosion Protection

Based on laboratory test results provided in Appendix D, and according to FHWA (2005) and AASTHO (2020) Article 10.7.5, soils present on the project site can be classified as non-aggressive. FHWA (2005) provides a corrosion protection recommendation for micropiles as presented in Table 16 below.

Table 16 – Corrosion Protection Recommendations for Micropiles

Loading Tension1 Compression

Ground Non-aggressive Non-aggressive

Casing Do not rely on casing for load capacity None

Core Steel Reinforcing Bar1 Grout Cover2 Grout Cover2

1 Permanent tension or temporary tension (e.g., wind, seismic, impact) on critical structures. For temporary tension on normal structures, corrosion protection for compression may be used. The recommendations for corrosion protection for micropiles subject to tension loadings should also be used for that length of the micropile subject to tension due to lateral loads and/or overturning moments at the ground surface.

2 Minimum 1 inch in soil and 0.5 inches in rock. If protective coatings (epoxy, galvanization, or encapsulation) are provided in compression, the minimum cover may be 0.25 inches in soil or rock.

5.5. Scour Consideration

A scour analysis was not performed for the subject project bridges. Nevertheless, it was recommended that the deep foundation for all the bridges is set on rock. Refer to Table 11 for the minimum embedment depth into bedrock per site.

5.6. Culvert 82 Bridge Trail Embankments

On the east side approach of Culvert 82 Bridge, the historical trail extends on an embankment, from approximately Sta. 100+20 to 101+80. The embankment trail height ranges from 5 ft to 17 ft with the highest sections being between Sta. 165+00 to 101+80.

The embankment trail slopes are close to 1.5H:1V. Due to the steepness of the slope, surficial failures are possible.

The program Slide2 by Rocscience was used to perform slope stability analyses using the Bishop Simplified analysis method. Multiple circular slip surfaces are created within the boundary conditions of the slope and the lowest Factor of Safety (FS) is computed. Slope stability analyses were performed on Sta. 101+65, which corresponds to the highest embankment section.

The alternatives considered, together with slope stability results, are presented in Table

17. Appendix E provides the models and soil properties used for the slope stability

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

analyses. Based on PDDM (2012), the recommended minimum FS for an embankment is

1.3. Our analyses indicate that an RSS with 1.5H:1V would yield a minimum factor of safety of 1.34. Alternatively, a 2H:1V select borrow fill embankment would yield a minimum factor of safety of 1.36.

Table 17 – Culvert 82 Bridge Trail Slope Embankment Alternatives

Slope Alternative* FS

1.5H:1V Slope reconstruction using Select Borrow 1.03 1.5H:1V Slope reconstruction using riprap 1.04 1.5H:1V Reinforced Soil Slope (RSS) 1.31 2H:1V Slope reconstruction using Select Borrow 1.36

* Materials used in the analyses as per FP-14

Based on the results, we recommend the embankment trail to be reconstructed on a 2H:1V slope using select borrow material, as per FP-14, Subsection 204.02(b).

6 CONSTRUCTION CONSIDERATIONS

Excavation - All excavations should be performed following applicable Federal, state, local, and OSHA standards and in accordance with Section 204 of the FP-14 Specifications.

Structural Backfill and Backfill Drainage -Weep holes with 6-inch diameter through abutment walls and wingwalls should be installed at a maximum spacing of 10 feet.

Weep holes should be installed above the top of the backfill at the front face. All weep holes should be approved for non-perforated PVC pipes per Subsection 708.05 of the FP- 14 Specifications. Approved geocomposite drains as per Subsection 714.02 of the FP-14 Specifications should be placed against the back face of the walls. The geocomposite drains should extend from the top of the weep holes to the bottom of the proposed aggregate base course at approaches. Type II-B geotextile fabric should be placed between the on-site soil backfill material and the granular select borrow for separation/filtration. Backfilling behind and in front of all walls and pier footings should be done following Subsection 208.09 and compacting per Subsection 208.10 of the FP-14 Specifications.

Micropile Casing Termination at Bedrock - Drilling methods proposed by the Contractor should ensure that an adequate seal is achieved between the micropile casing and the top of bedrock (top of bond zone) to ensure borehole stability during micropile excavation and grout placement, in accordance with FP-14 Subsection 567.05. To determine the required depth of installation due to the potential for variable depths to bedrock across the project sites, careful observation of drilling tools and response during drilling will be

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

required to determine the depths to the top of bedrock at each micropile location. The casing may extend beyond the top of bedrock (to lower elevations).

Grout Placement in Bond Zone/Bedrock - Contamination of the bond zone due to ingress of soils should be prevented. Investigation of the bottom of the excavated hole prior to grout placement should be completed using mechanical probing devices or other suitable electronic methods. The excavated hole should be cleared of any contaminants that would negatively impact the required grout-to-rock bond strength. Due to the potential for voids in the weathered bedrock anticipated for the bond zone, grout levels in micropiles should be carefully observed following initial grouting to determine if any grout loss is occurring at any location along the micropile. Contractor submittals as required by FP-14 Subsection 567.04 should also include a remedial plan in the event that grout losses or leakage are observed during grouting.

Embankment Slope Trail Reconstruction – All embankment reconstruction should be performed following Section 204 of the FP 14 Specifications.

7 DISCLAIMER/LIMITATIONS CLAUSE

The subsurface explorations and tests described in the section Procedures and Results have been conducted in accordance with standard practices and procedures (except as specifically noted). The results of these exploration and tests represent conditions at the specific locations indicated. Subsurface conditions between these locations may vary.

The Analysis and Conclusions sections and the Recommendations section of this report include interpretations and recommendations developed by the Government in the process of preparing this report. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

Prepared by:

Lourdes P. Boulware, Ph.D.

Geotechnical Engineer

Reviewed by:

Mounir Abouzakhm, P.E.

Division Geotechnical Engineer

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VA

8 REFERENCES

AASHTO (2020). LRFD Bridge Design Specifications, 9th Ed. Washington, DC:

American Association of State Highway and Transportation Officials.

Geologic map of the Washington West quadrangle, District of Columbia, Montgomery and Prince George's Counties, Maryland, and Arlington and Fairfax Counties, Virginia. Authors: Fleming, A.H., Drake, A.A., and McCartan, Lucy. Scale - 1:24,000, USGS (1994). Retrieved on October 27, 2020: https://ngmdb.usgs.gov/Prodesc/proddesc_277.htm

FHWA (2005), "Micropile Design and Construction, NHI Course No. 132078, Reference Manual", Washington D.C., National Highway Institute, U.S. DOT, FHWA

(FHWANHI05039).

FHWA (2014). Standard Specifications For Construction of Roads and Bridges on Federal Highway Projects, Washington D.C.: US Department of Transportation.

FLH. (2017). Rock Characterization Guidelines. Washington D.C.: US Department of Transportation - FHWA.

FLH. (2017). Soil Description and Identification Guidelines. Washington D.C.: US Department of Transportation - FHWA.

https://ngmdb.usgs.gov/Prodesc/proddesc_277.htm

APPENDIX A

Figures

U.S DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGINIA

FIGURE 1

REG

Site Location and Vicinity Map EAST

STATE

MD

PROJECT

NP CHOH

260(1), 913(1), 928(1)

SHEET

NO.

TOTAL

SHEETS

Data to create map retrieved from ArcGIS Online t

0 8 16 24 324 Miles

NP CHOH 206(1), 913(1), 928(1)

Fifteen Mile Creek bridge

Dargan Bend bridge

Edwards Ferry bridge

Culvert 82

U.S DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGINIA

FIGURE 1

REG

Site Location and Vicinity Map EAST

STATE

MD

PROJECT

NP CHOH

260(1), 913(1), 928(1)

SHEET

NO.

TOTAL

SHEETS

Data to create map retrieved from ArcGIS Online t

0 0.3 0.6 0.9 1.20.15 Miles

NP CHOH 206(1), 913(1), 928(1)

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGINIA

FIGURE 1

REG

Site Location and Vicinity Map EAST

STATE

MD

PROJECT

NP CHOH

260(1), 913(1), 928(1)

SHEET

NO.

TOTAL

SHEETS

Data to create map retrieved from ArcGIS Online t

0 0.55 1.1 1.65 2.20.275 Miles

Dargan Bend bridge

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGINIA

FIGURE 1

REG

Site Location and Vicinity Map EAST

STATE

MD

PROJECT

NP CHOH

260(1), 913(1), 928(1)

SHEET

NO.

TOTAL

SHEETS

Data to create map retrieved from ArcGIS Online t

0 0.3 0.6 0.9 1.20.15 Miles

Fifteen Mile Creek bridge

Geology of the Chesapeake and Ohio Canal National Historical Park and Potomac River Corridor Authors: Scott Southworth, David K. Brezinski, Randall C. Orndorff, John E. Repetski, and Danielle M. Denenny

Retrieved on June 28, 2021: https://pubs.usgs.gov/pp/1691/ Scale - 1:24,000, Professional Paper 1691, USGS (2008)

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGNIA

FIGURE NO. 2

Geologic Map

STATE PROJECT SHEET

NO.

TOTAL

SHEETS

MD NP CHOH 206(1), 913(1), 928(1) 1 3

Authors: Scott Southworth, David K. Brezinski, Randall C. Orndorff, John E. Repetski, and Danielle M. Denenny

Retrieved on June 28, 2021: https://pubs.usgs.gov/pp/1691/ Scale - 1:24,000, Professional Paper 1691, USGS (2008)

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGNIA

FIGURE NO. 2

Geologic Map

STATE PROJECT SHEET

NO.

TOTAL

SHEETS

MD NP CHOH 206(1), 913(1), 928(1) 2 3

Dargan Bend bridge

Authors: Scott Southworth, David K. Brezinski, Randall C. Orndorff, John E. Repetski, and Danielle M. Denenny

Retrieved on June 28, 2021: https://pubs.usgs.gov/pp/1691/ Scale - 1:24,000, Professional Paper 1691, USGS (2008)

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

ASHBURN, VIRGNIA

FIGURE NO. 2

Geologic Map

STATE PROJECT SHEET

NO.

TOTAL

SHEETS

MD NP CHOH 206(1), 913(1), 928(1) 3 3

Fifteen Mile Creek

APPENDIX B

Borings Location Plans and Subsurface Profiles

B H

1-

B H

1-

1-

B H

1-

B H

APPENDIX C

Boring Logs

APPENDIX D

Laboratory Testing Results

SOIL DATA

NO. AASHTODESCRIPTIONDEPTHSAMPLESOURCESYMBOL

Project No.:

Project:

Client:

Particle Size Distribution Report

PE

R

C

EN

T

FI

N

ER

100 10 1 0.1 0.01 0.001200 GRAIN SIZE - mm

% COBBLES

% GRAVEL

CRS. FINE

% SAND

CRS. MEDIUM FINE

% FINES

SILT CLAY

in in in

1- 1/ in in

3/ in

1/ in

3/ in

#4 #1

#2

#3

#4

#6

#1

#1

#2

0.0 0.0 26.2 10.9 2.6 27.4 32.9

(ft.)

CHOH 206(1)913(1)928(1)

Chesapeake & Ohio Canal NHP, MD

FHWA/EFLHD

Edwards Ferry BH-1/J-5 20-22 Silty sand with gravel A-2-4(0)

Particle Size Distribution Report

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

0.0 0.0 20.8 14.2 4.7 17.1 43.2

Edwards Ferry BH-2/J-3 10-12 Clayey sand with gravel A-6(3)

Project No.:

Project:

Client:

Particle Size Distribution Report

PE

R

C

EN

T

FI

N

ER

100 10 1 0.1 0.01 0.001200 GRAIN SIZE - mm

% COBBLES

% GRAVEL

CRS. FINE

% SAND

CRS. MEDIUM FINE

% FINES

SILT CLAY

in in in

1- 1/ in in

3/ in

1/ in

3/ in

#4 #1

#2

#3

#4

#6

#1

#1

#2

0.0 0.0 2.0 3.6 14.2 34.0 46.2

(ft.)

CHOH 206(1)913(1)928(1)

Chesapeake & Ohio Canal NHP, MD

FHWA/EFLHD

Dargan Br. BH-3/J-4 15-17 Silty sand A-4(0)

Particle Size Distribution Report

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

0.0 0.0 3.4 16.0 0.7 7.8 72.1

Dargan Br. BH-4/J-3 10-12 Lean clay with sand A-6(11)

0.0 0.0 0.8 13.1 4.8 16.6 64.7

Dargan Br. BH-4/J-4 15-17 Sandy lean clay A-6(11)

Project No.:

Project:

Client:

Particle Size Distribution Report

PE

R

C

EN

T

FI

N

ER

100 10 1 0.1 0.01 0.001200 GRAIN SIZE - mm

% COBBLES

% GRAVEL

CRS. FINE

% SAND

CRS. MEDIUM FINE

% FINES

SILT CLAY

in in in

1- 1/ in in

3/ in

1/ in

3/ in

#4 #1

#2

#3

#4

#6

#1

#1

#2

0.0 10.9 23.2 16.3 8.3 17.4 23.9

(ft.)

CHOH 206(1)913(1)928(1)

Chesapeake & Ohio Canal NHP, MD

FHWA/EFLHD

15 mi Br BH-5/J-3 5-7 Silty sand with gravel A-1-b

Particle Size Distribution Report

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

0.0 8.9 21.1 18.5 18.2 14.2 19.1

15 mi Br BH-5/J-4 10-12 Silty sand with gravel A-1-b

0.0 0.0 0.2 2.0 2.1 29.1 66.6

15 mi Br BH-6/J-3 10-12 Sandy lean clay A-6(11)

INDEXLIMITLIMITCONTENTNO.

PLASTICITYLIQUIDPLASTICWATERDEPTHSAMPLE

NATURAL

SOURCESYMBOL

Project No.:

Project:

Client:

LIQUID AND PLASTIC LIMITS TEST REPORT

(ft.) USCS

CHOH 206(1)913(1)928(1)

Chesapeake & Ohio Canal NHP, MD

FHWA/EFLHD

SM3211820.720-22BH-1/J-5Edwards Ferry

LIQUID AND PLASTIC LIMITS TEST REPORT

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

SC16351917.210-12BH-2/J-3Edwards Ferry

10 30 50 70 90 110

LIQUID LIMIT

PL

AS

TI

C

IT

Y

IN

D

EX

CL-ML

CL or OL

CH

or OH

ML or OL MH or OH

Dashed line indicates the approximate upper limit boundary for natural soils

INDEXLIMITLIMITCONTENTNO.

PLASTICITYLIQUIDPLASTICWATERDEPTHSAMPLE

NATURAL

SOURCESYMBOL

Project No.:

Project:

Client:

LIQUID AND PLASTIC LIMITS TEST REPORT

(ft.) USCS

CHOH 206(1)913(1)928(1)

Chesapeake & Ohio Canal NHP, MD

FHWA/EFLHD

SM5272224.615-17BH-3/J-4Dargan Br.

LIQUID AND PLASTIC LIMITS TEST REPORT

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

CL16392325.510-12BH-4/J-3Dargan Br.

CL20371721.415-17BH-4/J-4Dargan Br.

10 30 50 70 90 110

LIQUID LIMIT

PL

AS

TI

C

IT

Y

IN

D

EX

CL-ML

CL or OL

CH

or OH

ML or OL MH or OH

INDEXLIMITLIMITCONTENTNO.

PLASTICITYLIQUIDPLASTICWATERDEPTHSAMPLE

NATURAL

SOURCESYMBOL

Project No.:

Project:

Client:

LIQUID AND PLASTIC LIMITS TEST REPORT

(ft.) USCS

CHOH 206(1)913(1)928(1)

Chesapeake & Ohio Canal NHP, MD

FHWA/EFLHD

SMNP18NP10.85-7BH-5/J-315 mi Br

LIQUID AND PLASTIC LIMITS TEST REPORT

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

SMNPNVNP12.010-12BH-5/J-415 mi Br

CL20381818.210-12BH-6/J-315 mi Br

10 30 50 70 90 110

LIQUID LIMIT

PL

AS

TI

C

IT

Y

IN

D

EX

CL-ML

CL or OL

CH

or OH

ML or OL MH or OH

APPENDIX E

Design Analysis

Seismic Site Class computation as per AASTHO (2020 CHOH 206(1), 913(1), 928(1) Edwards Ferry

From To

Clayey SAND with gravel 0.0 15.0 15.0 7 7 5 6 2.37 Silty SAND with gravel 15.0 25.0 10.0 0 3 2 6.67

BEDROCK 25.0 39.0 14.0 100 100 0.14

From To

Clayey SAND with gravel 0.0 15.0 15.0 10 7 7 8 1.88 Clayey SAND with gravel 15.0 25.0 10.0 10 100 55 0.18

BEDROCK 25.0 30.0 5.0 100 100 0.05

Site Class definition E

Average N (blows/ft) di/Ni

Note: When using Method B, values are for cohesionless soils and cohesive soil and rock layers within the upper 100 ft. Where refusal is met for a rock layer, Ni should be taken as 100 blows/ft.

Site Class Definition - AASHTO Table 3.10.3.1-1

BORING ID - BH21-02

Soil Unit Depth (ft) Layer

Thickness (ft)

Ni (blows/ft) Average N (blows/ft) di/Ni

BORING ID - BH21-01

Soil Unit Depth (ft) Layer

Thickness (ft)

Ni (blows/ft) N

N

N N

Prepared by: Lourdes Boulware

United States Department of Transportation Federal Highway Administration (FHWA) Eastern Federal Lands Highway Division (EFLHD) Technical Services - Geotechnical

Project: CHOH 206(1), 913(1), 928(1) Edwards Ferry Seismic Zone classification

≔NBar 10 ≔Site_Class if else

>NBar 50 ‖“C” if else

>NBar 15 ‖“D”

‖“E” =Site_Class “E”

Site Factors - AASHTO 3.10.3.2

≔PGA 0.040

Since PGA < 0.1 then ≔Fpga 2.5

≔SS 0.09

Since SS < 0.25 then ≔Fa 2.5

≔S1 0.031

Since S1 < 0.1 then ≔Fv 3.5

Eastern Federal Lands Highway Division (EFLHD) Technical Services - Geotechnical

Project: CHOH 206(1), 913(1), 928(1) Edwards Ferry Seismic Zone classification

Modified Horizontal Response Spectral Acceleration Coefficients - AASHTO 3.10.4.2

≔As =⋅Fpga PGA 0.1 g

≔SDS =⋅Fa SS 0.225 g

≔SD1 =⋅Fv S1 0.109 g

≔Ts =――

SD1

SDS

0.482 s

≔To =⋅0.2 Ts 0.096 s

≔Sa =―――

SD1

⋅1.5 Ts

0.15 s

≔Tm , ‥0.0 0.001 1.5

Design Response Spectrum (AASHTO 3.10.4.1)

Seismic Zones - AASHTO 3.10.6

≔Seismic_Zone if else

≤SD1 0.15

‖ 1 if else

≤SD1 0.30

‖ 2 if else

≤SD1 0.50

‖ 3

‖ 4 =Seismic_Zone 1

Conclusion The retaining structure located in N 39.103712° W 77.472348° does not require a seismic analysis.

1/20/22, 11:47 AM https://earthquake.usgs.gov/ws/designmaps/aashto-2009.json?latitude=39.103712&longitude=-77.472348&siteClass=C&title=Ex… https://earthquake.usgs.gov/ws/designmaps/aashto-2009.json?latitude=39.103712&longitude=-77.472348&siteClass=C&title=Examplehttps://earthqua… 1/6

"request": { "date": "2022-01-20T16:47:18.741Z", "referenceDocument": "AASHTO-2009", "status": "success", "url": "https://earthquake.usgs.gov/ws/designmaps/aashto-2009.json?

latitude=39.103712&longitude=-77.472348&siteClass=C&title=Examplehttps://earthquake.", "parameters": { "latitude": 39.103712, "longitude": -77.472348, "siteClass": "C", "title": "Examplehttps://earthquake."

"response": { "data": { "pga": 0.04, "fpga": 1.2, "as": 0.048, "ss": 0.09, "fa": 1.2, "sds": 0.108, "s1": 0.031, Eastern Federal Lands Highway Division (EFLHD) Technical Services Geotechnical

Project: CHOH 206(1), 913(1), 928(1) Micropile design for Edwards Ferry Bridge Replacement

Design Calculations Description Design calculations to determine the micropile's bearing resistance for Edwards Ferry bridge replacement are shown in this report.

The calculation below shows the bearing resistance for a micropile embedded at least 15.0 ft into bedrock.

References

AASHTO (2020), "LRFD Bridge Design Specifications", 9th Edition, Washington D.C. American Association of State Highway and Transportation Officials.

FHWA (2005), "Micropile Design and Construction, NHI Course No. 132078, Reference Manual", Washington D.C., National Highway Institute, U.S. DOT, FHWA (FHWA NHI 05 039).

Assumptions

* Micropile Classification based on construction type Type A (AASHTO 10.9 )

* Top of micropiles is approximately at elevation 201.5 ft

* Scour elevation Not considered but micropile analysed as no friction from depth 0 to 21.0 ft

* Neglect tip resistance based on AASHTO C10.9.3.5.1

* Micropiles will utilize permanent casing until bedrock depth plus plunge depth (into bedrock)

* Approximate bedrock elevation

E abutment ~ 180.5 ft based on BH 21 01 > moderately to highly weathered rock with RQD from 9% to 90% W abutment ~ 180.5 ft based on Boring BH 21 02 > highly weathered rock

* Micropiles tip elevation:

E abutment ~ extend up to elevation 165.5 ft W abutment ~ extend up to elevation 165.5 ft

Model (AASHTO 2020) Figure AASHTO C10.9.1 1 presents a typical detail after (FHWA) Sabatini et. al 2005

By: Lourdes Boulware, Ph.D.

Reviewed By: Girmay Weldegiorgis, PE

Design Date: 12/22/2021

M:\PROJECTS\choh\206(1) 913(1) Etc\Techserv\Geotech\Design Analysis\Edwards Ferry\CHOH 206(1),913(1),928(1)_Edwards Ferry - GeoCalcs_FINAL.mcdx

Eastern Federal Lands Highway Division (EFLHD) Technical Services Geotechnical

Project: CHOH 206(1), 913(1), 928(1) Micropile design for Edwards Ferry Bridge Replacement

Allowable Geotechnical Bond Capacity (Nominal Axial Micropile Resistance)

= = +RR Rn qp Rp qs Rs (10.9.3.5.1 1)

C10.9.3.5.1 Micropiles are typically designed based on bond into soil and rock neglecting tip resistance due to their relatively small diameter and high grout to ground bond resistance.

Therefore = = + > =RR Rn qp Rp qs Rs RR qs Rs

= factored resistance of a micropileRR = resistance factor for grout to ground bond resistance (dim)qs = nominal grout to ground bond resistance (kips)Rs = (10.9.3.5.1-3)Rs qs As = unit grout to ground bond resistance (ksf)qs

= area of grout to ground bond surface ( ) = As ft2 db Lb

Table 10.5.5.2.5 1

(10.9.3.5.1-3)

10.9.3.5.2 — Nominal grout to ground bond resistance

= Rs db b Lb (10.9.3.5.2-1)

≔db 9.625 in Assumed Diameter of micropile drill hole through bonded length

≔b 4.3 ksf Nominal micropile grout to ground bond strength Table C10.9.3.5.2-1

≔Lb 15 ft Assumed micropile bond length

≔Rs =⋅⋅⋅db b Lb 163 kip Nominal resistance of a micropile

Note: Acording to the Geologic Map, the insitu rock is classified as Shale and Siltstone. Both are sedimentary rocks. In Table C10.9.3.5.2-1, values are provided for soft and hard shales. b

Based on the subsurface investigation, the insitu rock encountered is characterized as highly weathered rock. Based on RQD rock mass quality is very poor. Therefore, the type of rock assumed for the table will be soft shale. Grout to ground values for this type of material range from 4.3 ksf to 11.5 ksf. The lower bound value of 4.3 ksf is used for preliminary computations.

Also, based on other references, the average grout to ground bond strength for soft shale is 4.85 ksf. Thus, the value from Table C10.9.3.5.2-1 is conservative.

≔qs 0.55 Resistance factor for grout to ground bond resistance (dim) Table 10.5.5.2.5 1

≔RR =⋅qs Rs 89.4 kip Factored Geotechnical Resistance

By: Lourdes Boulware, Ph.D.

Reviewed By: Girmay Weldegiorgis, PE

Design Date: 12/22/2021

M:\PROJECTS\choh\206(1) 913(1) Etc\Techserv\Geotech\Design Analysis\Edwards Ferry\CHOH 206(1),913(1),928(1)_Edwards Ferry - GeoCalcs_FINAL.mcdx

Eastern Federal Lands Highway Division (EFLHD) Technical Services Geotechnical

Project: CHOH 206(1), 913(1), 928(1) Micropile design for Edwards Ferry Bridge Replacement

Rock…