Geo Report.pdf

Report Cover Page

George Washington and

Jefferson National

Forest Project

Geotechnical Engineering Report

April 15, 2025 | Terracon Project No. JD245007

Prepared for:

AECOM

150 Clay Street, Suite 430

Morgantown, WV 26501

19955 Highland Vista Drive, #170

Ashburn, Virginia 20147

P (703) 726-8030

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

April 15, 2025

AECOM

150 Clay Street, Suite 430

Morgantown, WV 26501

Attn: Steven Fox, PE

P: 615-557-3120

E: steven.fox@aecom.com

Re: Geotechnical Engineering Report

George Washington and Jefferson National Forest Project

101 Main Street

Bedford, Scott, Tazewell, and Wythe Counties, VA

Terracon Project No. JD245007

Dear Mr. Fox:

We have completed the scope of Geotechnical Engineering services for the above-referenced project in general accordance with Terracon Proposal No. PJD227134 dated

May 10, 2023. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of remedial slope repairs.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon

Ahmed Mohamed, PE Paul Burkart, PE

Project Engineer Senior Principal

George Washington and Jefferson National Forest Project |

Bedford, Scott, Tazewell, and Wythe Counties, VA

Facilities | Environmental | Geotechnical | Materials i

Table of Contents

1.0 Introduction

2.0 Project Description

3.0 Site Conditions

4.0 Geotechnical Characterization

4.1 Little Stony Road (FSR-700)

4.2 Punch and Judy Road (FSR-618)

4.3 Dry Run Road (FSR-14)

4.4 Hussy Mountain Horse Camp Road (FSR-14A)

4.5 Blackhorse Gap East Road (FSR-186)

5.0 Groundwater

6.0 Laboratory Test Results

6.1 Index Test Results

6.2 Unconfined Compressive Strength Test Results

6.3 Corrosion Test Results

7.0 Earthwork

7.1 Site Preparation

7.2 Subgrade Preparation

7.3 Existing Fill

7.4 Excavation

7.5 Fill Material Types

7.6 Fill Placement and Compaction Requirements

7.7 Utility Trench Backfill

7.8 Grading and Drainage

7.9 Earthwork Construction Considerations

7.10 Construction Observation and Testing

8.0 Drainage Structures

8.1 Scour

8.2 Bearing Resistance

9.0 Retaining Wall Foundations

9.1 Design Parameters – Compressive Loads

9.2 Design Parameters – Overturning

9.3 Foundation Construction Considerations

9.4 Subsurface Drainage for Below-Grade Walls

10.0 Lateral Earth Pressures

10.1 Design Parameters

11.0 Slope/Global Stability

11.1 Mechanics of Stability

11.2 Geometric Analysis Results

11.3 Unstable or Potentially Unstable Slopes

11.4 Summary Results of the Global/Slope Stability

Facilities | Environmental | Geotechnical | Materials ii

11.5 Temporary Condition/Support of Excavation

11.6 Surficial Slope Stability

12.0 General Comments

Figures GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans

Exploration and Laboratory Results

Supporting Information

Note: This report was originally delivered in a web-based format. Blue Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/ http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials 1

1.0 Introduction

This report presents the results of our subsurface exploration and Geotechnical

Engineering services performed for the proposed slopes and drainage structures to be located along Little Stony Road (FSR-700), Punch and Judy Road (FSR-618), Dry Run

Road (FSR-14), Hussy Mountain Horse Camp Road (FSR-14A), and Blackhorse Gap East

Road (FSR 186) in Bedford, Scott, Tazewell, and Wythe Counties, VA. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Boring logs with field and laboratory data

■ Stratification based on visual soil and rock classification

■ Groundwater levels observed during and after the completion of drilling

■ Site Location and Exploration Plans

■ Subsurface exploration procedures

■ Description of subsurface conditions

■ Engineering design parameters

■ Retaining Wall recommendations for Little Stony Road

■ Bedding recommendations for culverts/drainage structures

■ Global/slope stability for Little Stony Road, Punch and Judy Road, and Dry Run

Road

■ Earthwork recommendations including site/subgrade preparation

■ Lateral earth pressure recommendations

The geotechnical engineering Scope of Services for this project included the advancement of test borings, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and

Exploration Plans. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are summarized in the Laboratory

Test Results section and included on the boring logs and as separate graphs in the

Exploration Results section.

Facilities | Environmental | Geotechnical | Materials 2

2.0 Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information

Provided

• Proposed project description and scope of work document provided by AECOM on April 18, 2023 via e-mail

• Preliminary plan view and cross-sections provided by

AECOM on May 2024 via e-mail

• Contour files for Little Stony Road and Punch and Judy

Road provided by AECOM on June 3, 2024 via e-mail

Project

Description

The exploration of the following roads located in George

Washington and Jefferson National Forest Project:

• Little Stony Road (FSR-700) - A 0.19-mile-long gravel road that has experienced heavy rainfall and flooding which caused slope failure that is an 80-foot drop-off and

55-foot long.

• Punch and Judy Road (FSR-618) – A combined 0.19-mile-long gravel road which has experienced heavy rainfall and flooding which caused damage to the uphill and downhill slope. Four downhill slope failure areas

(approximately 30 feet deep by 30 feet wide each) occurred next to each other on a 326-foot-long section.

• Dry Run Road (FSR-14) – A 6.1-mile-long gravel road which has experienced high flows in the creeks adjacent to the path which caused slope failure and bridge scour in two locations. Portions of the road have been previously stabilized using gabions and riprap.

• Hussy Mountain Horse Camp Road – A 0.4-mile-long path which has experienced heavy rains and high flows along with woody debris clogging, overtopping, and scouring.

• Blackhorse Gap East Road (FSR 186) – A 1.8-mile-long gravel path that experienced heavy rains causing flooding and erosion.

Facilities | Environmental | Geotechnical | Materials 3

Item Description

Drainage

Structures

Based on information provided by the client, the following replacements/improvements to drainage structures are expected:

• Dry Run Road (FSR-14) – replacement of existing embedded drainage culvert with 36-inch dia. drainage structure

• Hussy Mountain Horse Camp Road (FSR-14A) – replacement of the existing low water crossing with a 10 ft x 4.5 ft bottomless box culvert

• Blackhorse Gap East Road (FSR 186) – replacement of the existing culverts with an approximately 19 ft x 5.5 ft bottomless box culvert

Grading/Slopes

Existing grades and slopes vary in height and gradient. Two to three feet of fill is proposed at the Hussy Mountain Horse Camp site to improve vehicle accessibility.

Retaining Walls/

Slope

Stabilization

It is our understanding that two gabion walls will be installed at the Little Stony Road site (between Stations 104+35 to 105+65 and 106+30 to 106+90), and Punch and Judy Road site

(between Stations 203+10 to 207+80 and 211+99 to

212+46.80). The height of the wall was estimated to be a maximum of 9 feet at the Little Stony Road site and 15 feet at the Punch and Judy site. A draped wire mesh system is proposed for the cut slope above the road at the Punch and Judy site (between Station 204+00 to 206+50). It is also our understanding that soil nails will be installed at the Little Stony

Road site between approximately Station 106+00 to 107+00.

Terracon should be notified if any of the above information is inconsistent with the planned construction, especially the grading limits, as modifications to our recommendations may be necessary.

Facilities | Environmental | Geotechnical | Materials 4

3.0 Site Conditions

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel

Information

The project is located within the George Washington and

Jefferson National Forest in Bedford, Scott, Tazewell, and Wythe

Counties, Virginia. The project includes the improvement of five

(5) different areas.

• Little Stony Road (FSR-700) – Latitude 36.864500

Longitude -82.509944 (approximate)

• Punch and Judy Road (FSR-618) – Latitude 37.003889

Longitude -81.461000 (approximate)

• Dry Run Road (FSR-14) – Latitude 36.772222 Longitude -

81.176944 (approximate)

• Hussy Mountain Horse Camp Road (FSR-14A) – Latitude

36.771667 Longitude -81.143000 (approximate)

• Blackhorse Gap East Road (FSR 186) – Latitude

37.406780 Longitude -79.745920 (approximate)

See Site Location and Exploration Plans

Current Ground

Cover Existing gravel path, forest

Existing

Topography

The existing topography along each path is as shown:

• Little Stony Road – Elevation (EL) 2,800 to 2,748

• Punch and Judy Road – EL 2,498 to 2,440

• Dry Run Road – EL 2,400 to 2,314

• Hussy Mountain Horse Camp Road – EL 2,888 to 3,103

• Blackhorse Gap Rd – EL 1,171 to 1,174

Based on profile plans provided by AECOM.

Facilities | Environmental | Geotechnical | Materials 5

Item Description

Expected

Subsurface

Conditions

Little Stony Road: This road at the problem area is underlain by Middlesboro Member of Pennsylvanian Age Lee Formation consisting of interbedded shale, siltstone, sandstones, and coal.

Shale is light gray with irregular laminations. Siltstone is sandy and laminated. Sandstone is fine- to medium-grained, thick to very thick-bedded, and not resistant. According to the geologic map, three different units and thickness of coal beds (Middle

Seaboard coal bed, Lower Seaboard coal bed, and Upper

Horsepen coal bed) are located below the roadway.

Punch and Judy Road: This road is underlain by Brallier

Formation which consists of micaceous shale, siltstone, and sandstone. These units are prone to weathering and erosion.

Dry Run Road/Hussy Mountain Horse Camp

Road/Blackhorse Gap East Road: These areas are underlain by Alluvial deposits consisting of various amounts of silts, sands, gravels, and boulders. Below Alluvium the area is underlain by

Erwin and Hampton Formations which consists of sandstone and quartzite; interbeds of sandy, silty, and micaceous shale that become more abundant toward the base.

4.0 Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration Results and the GeoModel can be found in the Figures attachment of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel. Separate GeoModels were created for each of the five project areas.

Facilities | Environmental | Geotechnical | Materials 6

4.1 Little Stony Road (FSR-700)

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

Residual

Soil

Completely weathered sandstone with silt and gravel, fine-grained, loose to medium dense

7 to 8 feet

2 Sandstone Gray, fine-grained, moderately weathered, weak

9 feet, only encountered in boring LS-2

3 Shale

Laminated with sandstone, moderately weathered, extremely weak

17 to 18 feet

4 Shale Laminated with sandstone, fresh, weak 34 to 36 feet

5 Coal Extremely weak 36 to 37 feet

6 Shale Laminated with sandstone, fresh, medium strong

Undetermined, all borings terminated within this layer at depths ranging from 49.6 to

52 feet

4.2 Punch and Judy Road (FSR-618)

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

1 Existing Fill

Existing fill that can be described as clayey sand with gravel

2 to 7 feet

Native

Granular

Clayey sand with gravel, loose to medium dense 2 to 11 feet

Facilities | Environmental | Geotechnical | Materials 7

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

3 Shale

Silty, laminated to very thinly bedded, moderately weathered, weak

16 to 22 feet

4 Shale

Silty, laminated to very thinly bedded, slightly weathered, weak to medium strong

Undetermined, borings PJ-1 and

PJ-2 terminated within this layer at depths ranging from 35.1 to

41.6 feet

4.3 Dry Run Road (FSR-14)

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

1 Existing Fill

Existing fill that can be described as clayey sand with gravel

2.5 to 6 feet

Interbedded

Sandstone and Shale

Gray and dark gray, very thin to thinly bedded

Undetermined, borings DR-1, DR-3 & DR-4 terminated within this layer at depths ranging from 5.4 to 36.6 feet

The following model layers were unique to boring DR-2:

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

1 Existing Fill

Existing fill that can be described as clayey sand with gravel

1.5 feet

Native

Cohesive

Stiff consistency, lean clay, moderate plasticity

4.5 feet

Facilities | Environmental | Geotechnical | Materials 8

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

3 Dolomite

Gray, medium hard, medium bedding thickness, wavy laminated fabric

Undetermined, boring DR-2 terminated within this layer at a depth of 31.6 feet

4.4 Hussy Mountain Horse Camp Road (FSR-14A)

Model

Layer Layer Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

1 Existing Fill

Existing fill that can be described as silty clayey sand with gravel

4.5 feet

Native

Granular

Medium dense fine to coarse grained sand, non-plastic

7 feet

3 Shale

Gray and brown, weathered, fissile, steep bedding, extremely weak

Undetermined, boring HM-1 terminated within this layer at a depth of 8.9 feet

4.5 Blackhorse Gap East Road (FSR-186)

Model

Layer

Layer

Name General Description

Approximate Depth to the

Bottom of the Layer Below

Existing Site Grades

Existing

Fill

Existing fill that can be described as silty clayey sand with trace gravel

5 to 6 feet

Native

Cohesive

Medium stiff to very stiff consistency, gray to red fat clay with micaceous sand

Undetermined, all borings terminated within this layer at depths ranging from 12 to 15 feet

Facilities | Environmental | Geotechnical | Materials 9

5.0 Groundwater

Groundwater was not encountered during the field investigation. Groundwater level observations were made in the field during drilling and upon completion of the test borings. The groundwater observations presented herein are considered to be an indication of the groundwater levels at the dates and times indicated. Accordingly, the groundwater information presented herein should be used with caution. Also, fluctuations in groundwater levels should be expected with seasons of the year, construction activity, changes to surface grades, precipitation, or other similar factors.

6.0 Laboratory Test Results

The results of moisture content, Atterberg limits, grain size analysis, unconfined compressive strength, and corrosion tests performed on soil samples obtained during the field investigation are summarized herein. Individual test results are presented in

Exploration and Laboratory Results.

6.1 Index Test Results

A range of the moisture content (AASHTO T265), liquid limit (ASTM D4318), plastic limit

(ASTM D4318), plasticity index (ASTM D4318), and fines content (AASHTO T88) of soil samples tested along the project is presented in the table below.

Table 6.1-1: Classification Test Results Summary

Range of

Moisture

Content (%)

Range of

Liquid Limit

Range of

Plastic Limit

Range of

Plasticity

Index (%)

Range of

Fines

Content1 (%)

6.6 – 72.5 NP – 80 NP – 36 NP – 44 9.5 – 94.0

1. The fines content is defined as the percentage of soil by weight passing the #200 sieve.

6.2 Unconfined Compressive Strength Test Results

Unconfined compressive strength tests were conducted on five core specimens. The results of the unconfined compressive strength tests are presented in the table below.

Facilities | Environmental | Geotechnical | Materials 10

Table 6.2-1: Unconfined Compressive Strength Test Results

Site Boring No.

Sample Depth

(ft) Rock Type

Unconfined

Compressive

Strength (psi)

Dry Run

Road DR-2 11.7-12.2 Dolomite 7,934

Little Stony

Road

LS-1 17.5-17.9 Shale 902

LS-2 21.1-21.6 Shale 3,170

Punch and

Judy Road

PJ-1 18.1-18.6 Shale 2,285

PJ-2 21.1-21.6 Shale 8,348

6.3 Corrosion Test Results

The table below lists the results of Red-OX (ASTM G200), pH (AASHTO T289), soluble salts (AWWA 2520B), soluble chlorides (AASHTO T291A), soluble sulfates (AASHTO

T290B), electrical resistivity (AASHTO T288), and soluble sulfides (AWWA 4500-S.A.4c) testing of soil samples collected in the vicinity of existing drainage structures along the project. A summary of results is presented in Exploration and Laboratory Results.

Based on the test results from the corrosion analysis, the electrical resistivity values range from 3,100 to 14,000 ohm-cm, with the lowest value recorded at 3,100 ohm-cm for BG-1. According to AASHTO LRFD Bridge Design Specifications (Section 10.7.5), soils with resistivity less than 2,000 ohm-cm are indicative of corrosion situation. While none of the tested samples fall below this critical threshold, the BG-1 sample (3,100 ohm-cm) and DR-4 sample (6,700 ohm-cm) are on the lower end of the resistivity spectrum, suggesting a low to moderate risk of corrosion for steel.

Based on the test results, the risk of concrete deterioration due to sulfate attack, chloride-induced reinforcement corrosion, and pH-related degradation is minimal. The dissolved sulfate concentrations in the soil samples range from 2 to 39 ppm, which is significantly below the AASHTO LRFD threshold of 1,000 ppm for sulfate-induced expansion and degradation of concrete. This indicates that sulfate attack is not a concern at this site. Similarly, dissolved chloride concentrations are either not detected

(NIL) or very low (maximum 19 ppm in HM-1), which is below the 500-ppm threshold that would pose a risk of reinforcement corrosion. This suggests that corrosion of embedded steel reinforcement due to chloride exposure is very low.

While we have provided our recommendations based on the available test results and industry standards, it is important to note that we are not corrosion specialists. A

Facilities | Environmental | Geotechnical | Materials 11 detailed corrosion analysis, considering all environmental and material-specific factors, may be necessary for a comprehensive risk assessment. For buried metals on-site, consultation with a NACE-certified corrosion professional is strongly recommended to ensure appropriate mitigation measures are implemented.

Mapping by the NRCS includes qualitative severity of corrosion to concrete and steel.

Based on this source, the near-surface materials are rated are presented below for both

Concrete and Steel for each site.

Table 6.3-1: Summary of NRCS Corrosion Mapping

Site Concrete Steel

Little Stony Road High Moderate

Punch and Judy Road Moderate to High Low

Dry Run Road Moderate to High Moderate to High

Hussy Mountain Horse Camp Road High Low

Blackhorse Gap Road High High

7.0 Earthwork

Earthwork is anticipated to include demolition of existing culverts (where applicable) and select areas of asphalt concrete pavement, clearing and grubbing, minor excavations, and engineered fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations, retaining walls, and pavements.

7.1 Site Preparation

Prior to placing fill, existing vegetation, topsoil, trees, brush, downed timber, and root mats should be removed. Complete stripping of the topsoil should be performed within the project limits. Clearing and grubbing should follow and be in accordance with FP-14

Section 201 and 202.

For abandoned existing drainage pipes/culvert a portion of the upstream and downstream should be removed within 48 inches of the subgrade and embankment slope. Abandoned culverts should be sealed with a tight-fitting plug of concrete at least

6 inches thick and at 48 inches from the proposed culvert/structure. Removal and replacement of culvert/structure should be in accordance with FP-14 Section 203.

Facilities | Environmental | Geotechnical | Materials 12

7.2 Subgrade Preparation

All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of 6 inches, moisture conditioned as necessary, and compacted per the compaction requirements in this report. Compacted structural fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation or pavement construction. Subgrade preparation should be in accordance with Section 204 of the FP-14.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

7.3 Existing Fill

As noted in Geotechnical Characterization, borings at each of the five sites encountered previously placed fill to depths ranging from about 1.5 to 7 feet. The fill appears to have been placed in a controlled manner, but we have no records to indicate the degree of control. Support of culverts on or above existing fill soils is discussed in this report. However, even with the recommended construction procedures, there is inherent risk for the owner that compressible fill or unsuitable material, within or buried by the fill, will not be discovered. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill but can be reduced by following the recommendations contained in this report.

7.4 Excavation

We anticipate that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction. Excavations shall be performed in concordance with FHWA FLH FP-14

Sections 208 and 209.

7.5 Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures, pavements, or constructed slopes. General fill is material used to achieve grade outside of these areas.

Facilities | Environmental | Geotechnical | Materials 13

Re-use of On-Site Soil: Excavated on-site soil may be selectively re-used as fill below pavement and landscaping areas and as retaining wall backfill behind the drainage layer if it conforms to the requirements specified in FHWA FLH FP-14 Section 704.

Imported Fill Materials: All imported fill materials should meet the material properties specified in FHWA FLH FP-14 Section 703 for aggregates and Section 704 for soil backfill material. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

7.6 Fill Placement and Compaction Requirements

Embankment Fill: Grade and compact embankment soil backfill material according to

Subsections 204.09 and 204.11 of FHWA FLH FP-14. Determine optimum moisture content and maximum dry density according to AASHTO T 99. Adjust the moisture content of backfill material to within 2 percent of the optimum moisture content.

Compact each layer to at least 95 percent maximum dry density. Place embankment material within the roadway prism in horizontal layers not exceeding 12 inches in compacted thickness. Place embankment material outside the staked roadway prism in horizontal layers not exceeding 24 inches in compacted thickness.

Retaining Wall Backfill: Backfill the area behind retaining walls with structural backfill according to Subsection 209.09 of FP-14. Adjust the moisture content of backfill material to within 2 percent of the optimum moisture content. Compact each layer to 95 percent maximum dry density in accordance with Subsection 209.10. Use an approved lightweight mechanical or vibratory compactor within 36 inches of the wall. Place backfill material in successive uniform lifts no more than 6 inches in compacted thickness.

Aggregate Base Course: Aggregate base course shall be compacted in accordance with

Subsection 301.05 of FHWA FLH FP-14. Determine the maximum density of the aggregate mixture according to AASHTO T 180, Method D. Adjust the moisture content of backfill material to within 2 percent of the optimum moisture content. Compact each layer to at least 95 percent maximum dry density. Place aggregate in successive uniform lifts no more than 6 inches in compacted thickness over the entire roadbed area.

Geotextile: Coarse-grained and fine-grained fill materials should be separated by geotextile placed in accordance with Section 207 of FP-14. The geotextile should conform to the requirements of Subsection 714.01 of FP-14.

7.7 Utility Trench Backfill

Excavate utility trenches in accordance with FHWA FLH FP-14 Subsection 208.03 and

Section 209. Any soft or unsuitable materials encountered at the bottom of utility trench

Facilities | Environmental | Geotechnical | Materials 14 excavations should be removed and replaced with structural fill or bedding material in accordance with FP-14 Subsection 209.07. Trench excavation should not be conducted below a downward 1H:1V projection from existing foundations without engineering review of shoring requirements and geotechnical observation during construction.

Utility trench bedding should be placed in accordance with FP-14 Subsection 209.08(a) for box culverts and structures, and Subsection 209.08(b) for pipe culverts. Bedding material shall conform to Subsection 704.02.

Trench backfill material shall be in accordance with FP-14 Subsection 704.03. Trench backfill should be mechanically placed and compacted in accordance with FP-14

Subsections 209.09 and 209.10. Compaction of initial lifts should be accomplished with hand-operated tampers or other lightweight compactors. For water lines, hand-place backfill to a depth of 12 inches above the top of the pipe. Flooding or jetting for placement and compaction of backfill is not recommended.

7.8 Grading and Drainage

All grades must provide effective drainage away from the pavement and retaining walls during and after construction and should be maintained throughout the life of the structure. Water retained next to pavements and retaining walls can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable pavement distress and retaining wall deflections.

Subsurface drainage for site retaining walls should be in accordance with the recommendations provided in the Retaining Walls section.

7.9 Earthwork Construction Considerations

Shallow excavations for the proposed structure are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of pavements.

Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed.

If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part

1926, Subpart P, “Excavations” and its appendices, and in accordance with FP-14

Subsection 208.03 and Section 209.

Facilities | Environmental | Geotechnical | Materials 15

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

7.10 Construction Observation and Testing

The earthwork efforts should be observed by the Contracting Officer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (vegetation, topsoil, and pavements), evaluation and remediation of existing fill materials, as well as proofrolling and mitigation of unsuitable areas delineated by the proofroll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Contracting Officer prior to placement of additional lifts. Each lift of fill should be tested for density and water content in accordance with AASHTO T310 or other approved test procedures.

In areas of foundation excavations, the bearing subgrade should be evaluated by the

Contracting Officer. If unanticipated conditions are observed, the Geotechnical Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Contracting Officer into the construction phase of the project provides the continuity to maintain the Contracting Officer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

8.0 Drainage Structures

Proposed culverts are planned to be replaced along the existing drainage structures/ culvert along the Dry Run Road, Blackhorse Road, and Hussy Mountain Horse Road alignment. Additionally, no additional fill is planned to raise the grade of the existing pavement. Where soft or very loose soils, unsuitable CH, MH, OH and OL soils, or groundwater is encountered at the structure invert, we recommend undercutting 24 inches along the entire length of the pipe and replacing with 18 inches of No. 57 aggregate completely wrapped in a woven geotextile stabilization fabric, topped with 6 inches of bedding material.

Facilities | Environmental | Geotechnical | Materials 16

8.1 Scour

Selected soil samples obtained from the field investigation were tested for grain size distribution with a hydrometer. The interpretation of D50 and D90 was performed by

Terracon and a summary of the results are presented in Table below. Scour analysis is to be completed by the client.

Table 8.1-1: D50 and D90 Test Results

Site

Location

Boring

No.

Sample

Depth

(ft)

Soil Classification D50

(mm)

D90

(mm)

Blackhorse

Gap Road

BG-1 7.5-9 FAT CLAY (CH) 0.0066 0.04

BG-2 1.5-3

SILTY CLAYEY SAND

(SC-SM)

0.4 16.5

BG

Upstream

WELL-GRADED GRAVEL with SAND

(GW)

16.4 61

Dry Run

DR-1 0-1.5

CLAYEY SAND with GRAVEL

(SC)

0.9 16.5

DR-2 1.5-3

LEAN CLAY

(CL)

DR-4 0-1.5

CLAYEY SAND with GRAVEL

(SC)

1.9 22.5

Hussy

Mountain

Horse

Camp Road

HM-1 0-1.5

SILTY, CLAYEY SAND with GRAVEL

(SC-SM)

2.5 17.7

HM-1 4.5-6

SILTY SAND

(SM)

0.43 1.5

HM Stream 0 WELL-GRADED GRAVEL with SAND

(GW)

1.25 40

Little Stony

Road

LS-1 1.5-3

POORLY GRADED SAND with SILT and GRAVEL (SP-SM)

0.27 23

LS-2 0-1.5

POORLY GRADED SAND with SILT and GRAVEL (SP-SM)

1.15 31.7

Punch and

Judy Road

PJ-1A 2-4

CLAYEY GRAVEL with SAND

(GC)

1.9 28.6

PJ-2A 1-2.5

CLAYEY SAND with GRAVEL

(SC)

0.8 37.8

Facilities | Environmental | Geotechnical | Materials 17

Site

Location

Boring

No.

Sample

Depth

(ft)

Soil Classification D50

(mm)

D90

(mm)

PJ-3 0-1.5

CLAYEY SAND

(SC)

0.93 12.5

PJ-4 0-1.5

CLAYEY SAND with GRAVEL

(SC)

0.46 17.3

8.2 Bearing Resistance

Proposed culverts are planned along the existing culvert alignment. Additionally, no additional fill is planned to raise the grade of the existing pavement. The planned culvert and headwall foundation elevations should bear directly on natural suitable soils, weathered rock, or bedrock. Scour has not been considered in the foundation bearing analysis. It is our understanding that if there is a potential for scour, appropriate scour mitigation measures will be provided as part of the design. The foundation bearing subgrade should be evaluated by the Geotechnical Engineer or assigned representative.

Table 8.2-1: Culvert Design Parameters

Item Blackhorse Gap Dry Run Hussy Mountain

Factored Bearing

Resistance1

2.9 ksf

7.8 ksf to

8.8 ksf

4.9 ksf

Required Bearing

Stratum 2 Residual Soil

Weathered

Rock Weathered Rock

Minimum

Foundation

Dimensions

Width: 2 ft

Length: 16 ft

Width: 4 to

6 ft

Length: 20 ft

Width: 2 ft

Length: 18 ft

Ultimate Coefficient of Sliding Friction 3

0.35 (Residual

Soil)

0.45 (Weathered

Rock)

0.45 (Weathered Rock)

Minimum

Embedment below

Finished Grade 4

2 feet 2 feet 2 feet

Estimated

Settlement

1.23 inches

0.28 to

0.45 inches

0.09 inches

Estimated

Differential

Settlement

≤ 1/2 of total settlement

≤ 1/2 of total settlement

≤ 1/2 of total settlement

1. A resistance factor of 0.45 has been applied based on AASHTO LRFD Table 10.5.5.2.2-1.

2. Unsuitable or soft soils should be overexcavated and replaced per the recommendations presented in Earthwork.

Facilities | Environmental | Geotechnical | Materials 18

3. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should be neglected for foundations subject to net uplift conditions.

4. Embedment necessary to minimize the effects of frost and/or seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

9.0 Retaining Wall Foundations

If the site has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for the gabion retaining wall at Little

Stony and Punch and Judy Road.

9.1 Design Parameters – Compressive Loads

Table 9.1-1: Retaining Wall Foundation Design Parameters

Item Little Stony

Punch and Judy

Road at Station

204+50

Punch and Judy

Road at Station

212+50

Factored Bearing

Resistance1

4.25 ksf 11.8 ksf 15.5 ksf

Required Bearing

Stratum 2 Weathered Rock Weathered Rock Weathered Rock

Minimum Foundation

Dimensions B = 9 feet B = 12 feet B = 9 feet

Ultimate Coefficient of Sliding Friction 3

0.45 (Weathered Rock)

0.50 (Bedrock)

0.45 (Weathered Rock)

0.50 (Bedrock)

0.45 (Weathered Rock)

0.50 (Bedrock)

Minimum

Embedment below

Finished Grade 4

2 feet 2 feet 2 feet

Estimated

Settlement

0.08 inches 0.36 inches 0.37 inches

Estimated

Differential

Settlement

≤ 1/2 of total settlement

≤ 1/2 of total settlement

≤ 1/2 of total settlement

1. A resistance factor of 0.65 has been applied based on AASHTO LRFD Table 10.5.5.2.2-1.

2. Unsuitable or soft soils should be overexcavated and replaced per the recommendations presented in Earthwork.

3. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should be neglected for foundations subject to net uplift conditions.

4. Embedment necessary to minimize the effects of frost and/or seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

Facilities | Environmental | Geotechnical | Materials 19

9.2 Design Parameters – Overturning

Shallow foundations subjected to overturning loads should be proportioned such that the resultant eccentricity is maintained in the center-third of the foundation (e.g., e < b/6, where b is the foundation width). This requirement is intended to keep the entire foundation area in compression during the extreme lateral/overturning load event.

Foundation oversizing may be required to satisfy this condition.

9.3 Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the observation of the Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before the foundation concrete is placed.

Sensitive soils exposed at the surface of footing excavations may require surficial compaction with hand-held dynamic compaction equipment prior to placing structural fill, steel, and/or concrete. Should surficial compaction not be adequate, construction of a working surface consisting of either crushed stone or a lean concrete mud mat may be required prior to the placement of reinforcing steel and construction of foundations.

If unsuitable bearing soils are observed at the base of the planned footing excavation, the excavation should be extended deeper to suitable soils, and the footings could bear directly on these soils at the lower level or on lean concrete backfill placed in the excavations. The lean concrete replacement zone is illustrated on the sketch below.

Facilities | Environmental | Geotechnical | Materials 20

9.4 Subsurface Drainage for Below-Grade Walls

A perforated rigid plastic drain line installed behind the base of walls and extends below adjacent grade is recommended to prevent hydrostatic loading on the walls. The invert of a drain line around a below-grade area or exterior retaining wall should be placed near foundation bearing level. The drain line should be sloped to provide positive gravity drainage to daylight or to a sump pit and pump. The drain line should be surrounded by clean, free-draining granular material having less than 5% passing the No. 200 sieve, such as No. 57 aggregate. The free-draining aggregate should be encapsulated in a filter fabric. The granular fill should extend to within two feet of final grade, where it should be capped with compacted cohesive fill to reduce infiltration of surface water into the drain system.

As an alternative to free-draining granular fill, a pre-fabricated drainage structure may be used. A pre-fabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion, and is fastened to the wall prior to placing backfill.

10.0 Lateral Earth Pressures

10.1 Design Parameters

Structures with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to values indicated in the following table. Earth pressures will be influenced by the structural design of the walls, conditions of wall restraint, methods of construction, and/or compaction, and the strength of the materials being restrained.

Two wall restraint conditions are shown in the diagram below. Active earth pressure is commonly used to design free-standing cantilever retaining walls and assumes wall movement. The “at-rest” condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls (unless stated).

Facilities | Environmental | Geotechnical | Materials 21

Table 10.1-1: Recommended Design Lateral Earth Pressures

Item

Highly Plastic –

Fine grained

Material

(CH/MH)

Low to

Medium Plastic

– Fine grained Material

(CL/ML)

Existing Fill/

Coarse grained Material

(SC-SM,

SP-SM, SC,

GC, GP)

Weathere d Rock

Bedrock

(RQD<50)

Bedrock

(RQD>50)

New Compacted

Fill

Friction Angle, (degrees) 26 28 32 36 38 40 32

Moist Unit Weight (pcf) 110 115 125 130 160 160 125

Active Earth

Pressure Coefficients

Level Backslope

0.39 0.36 0.31 0.26 0.24

Rock Pressure:

250 psf

(Rectangular

Distribution)

0.31

2H:1V

Backslope -- 0.65 0.46 0.36 0.32 0.46

At-Rest Earth

Pressure Coefficients

Level Backslope

0.56 0.53 0.47 0.41 0.38 0.47

2H:1V

Backslope

0.81 0.77 0.68 0.60 0.56 0.68

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils. For the granular values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively.

The lateral earth pressure recommendations given in this section are applicable to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity-type concrete walls. These recommendations are not applicable to the design of modular block - geogrid reinforced backfill walls (also termed MSE walls) or gravity walls (such as gabion walls). Recommendations covering these types of wall systems are beyond the scope of services for this assignment. However, we would be pleased to develop a proposal for evaluation and design of such wall systems upon request.

Where applicable, the design should consider surcharge loads using a rectangular earth pressure distribution. The surcharge pressure ordinate should be obtained by multiplying the surface surcharge pressure by the lateral earth pressure coefficient in table above for the respective backfill condition. In addition to static earth pressures, the structural designer should consider dynamic earth pressures due to seismic loading, as applicable.

Facilities | Environmental | Geotechnical | Materials 22

11.0 Slope/Global Stability

11.1 Mechanics of Stability

Slope stability analyses take into consideration material strength, presence and orientation of weak layers, water (piezometric) pressures, surcharge loads, and the slope geometry. Mathematical computations are performed using computer-assisted simulations to calculate a Factor of Safety (FS). Minor changes to slope geometry, surface water flow and/or groundwater levels could result in slope instability. Reasonable

FS values are dependent upon the confidence in the parameters utilized in the analyses performed, among other factors related to the project itself. The accepted minimum FS for the static permanent slope condition is 1.5 and for the temporary condition 1.3.

11.2 Geometric Analysis Results

A combination of LiDAR points and site-specific topographic survey provided by AECOM were used to develop three cross-sections at areas of interest. The cross-section geometries were based on the LiDAR points which were interpreted on ARCGIS and drawn from 5-ft contour lines. The first cross-section is located at Little Stony Road

Station 106+90 to illustrate a slope failure, proposed gabion wall, and proposed soil/rock nails in the slope below the wall. The second is located at Punch and Judy Road

Station 204+50 to illustrate a slope failure and proposed gabion wall. The third is located at Punch and Judy Road Station 212+50 to illustrate a slope failure and proposed gabion wall. Slope stability analyses were performed for each cross-section.

Parameters for the analyses were derived from our exploratory borings, experience, and laboratory tests. Stability analyses were conducted using the computer program Slide2 version 9.031 developed by Rocscience.

11.3 Unstable or Potentially Unstable Slopes

Based on the results of our field investigation, laboratory testing program, and geotechnical analysis, development of the site is considered feasible from a geotechnical viewpoint provided the conclusions and considerations provided herein are incorporated into the design and construction of the project.

The stability of the slopes at the cross-section locations shown on the Exploration Plan were analyzed based on the provided topography, proposed grading, soil and rock properties derived from our geotechnical exploration, laboratory test results and our experience with similar soil conditions. Soil materials use the Mohr-Coulomb envelope to describe the soil mass strength.

Facilities | Environmental | Geotechnical | Materials 23

Rock materials use the generalized Hoek-Brown failure criterion (Hoek et al., 2002) to describe the rock mass strength. The non-linear strength criterion is expressed as follows:

𝜎1 ′ = 𝜎3

′ + 𝜎𝑐𝑖 (𝑚𝑏 𝜎3 𝜎𝑐𝑖

+ 𝑠) 𝑎

Where:

σ'1 and σ’3 = principal effective stresses σci = uniaxial compressive strength of intact rock material mb, s, and a = empirically determined parameters

Parameters “mb”, “s”, and “a” rely on the geological strength index (GSI), material constant (mi), and disturbance factor (D) (Marinos and Hoek, 2000), of the rock at a given depth. Values of GSI and m i for various rock types and conditions are provided in the Tables below. The GSI was determined for the various bedrock units based on observation of rock outcrops and rock core during our field investigation. The disturbance factor depends upon the degree of disturbance to which the rock mass has been subjected by blast damage and stress relaxation. It varies from 0 for undisturbed, in situ, rock masses to 1 for very disturbed rock masses.

Facilities | Environmental | Geotechnical | Materials 24

Table 11.3-1: Geological Strength Index (GSI) for Jointed Rock Masses (Marinos and Hoek, 2000)

Facilities | Environmental | Geotechnical | Materials 25

Table 11.3-2: Values of the constant mi for Intact Rock (Marinos and Hoek, 2000)

Little Stony Road (FSR-700)

In May 2020, heavy rains reactivated a surficial slope failure on the fill side of Little

Stony Road (FSR-700) near mile post 4.2 that reduced the road's travel width to approximately 12 feet from edge of ditch to edge of failure. A Field Trip Report prepared by Eastern Federal Lands (EFL) describes the dimensions of the slope failure as approximately 54 feet wide by 80 feet tall. These dimensions were verified during our

Facilities | Environmental | Geotechnical | Materials 26 field investigation. The depth of the failure is estimated to be up to approximately 5 feet. Based on the LiDAR topography, the slope gradient within the failure area is approximately 1H:1V. The slope descends approximately 100 feet from the road grade to the flood plain of Little Stony Creek below. Two gabion walls are proposed below the outside edge of the roadway to accommodate grade changes necessary to straighten and re-establish a 12-foot road width. Wall 1 extends from Station 104+35 to 105+65 and Wall 2 from Station 106+30 to 106+90. Each wall will have a maximum exposed height of approximately 6.5 feet, and a maximum total height of 9.0 feet with a maximum base width of 9.0 feet. Soil nails are proposed in the slope below Wall 2 to improve slope stability in the area of the recent surficial slope failure. A slope stability model was prepared to illustrate topography in the area of the surficial slope failure and proposed Wall 2 at Station 106+90 for the purpose of evaluating slope stability. Wall 2 is considered more critical than Wall 1 even though the geometry of each wall is similar, because Wall 2 is located in steeper terrain and above a surficial slope failure.

The slope stability model is based on the results of our field investigation which included drilling two rock core borings in the roadway and field observation of bedrock outcrops.

The borings LS-1 and LS-2 extended to depths of 52 feet and 49.6 feet, below existing ground surface, respectively. The borings encountered approximately 7 feet of overburden soils overlying bedrock. The overburden soils primarily consisted of poorly graded sand with silt and gravel interpreted to be residual soil and completely weathered sandstone bedrock. The bedrock consisted of shale with a single layer of coal. The shale was found to be moderately weathered and extremely weak to a depth of approximately

17 feet; it was fresh and weak to medium strong below. The coal was encountered at a depth of approximately 35 feet and was 1.4 feet to 1.8 feet thick. Shale continued below the coal to the total depth explored of 49.6 feet and 52 feet.

Bedrock outcrops were observed above the roadway in a rock cut slope. The cut slope exposed massive to cross-bedded sandstone.

Portions of the slope model that are outside the limits of our exploration are based on supplemental information obtained from publicly available geologic maps. Bedrock underlying the slope at the Little Stony site is mapped as belonging to the Lower

Pennsylvanian-aged Middlesboro Member of the Lee Formation (Whitlock et al., 1988 – see Exhibit 1B). This member is further subdivided into an upper quartzarenite (Plmu on the geologic map), middle siltstone (Plm on the geologic map), and lower quartzarenite

(not mapped in the vicinity of the project site). The massive to cross-bedded sandstone exposed in the cut slope above the road and in the upper portion of boring LS-2 is consistent with the upper quartzarenite unit. The portion of the slope below the road and down to Little Stony Creek is assigned to the middle siltstone unit and contains the

Middle Seaboard, Lower Seaboard, and Upper Horsepen coal seams.