B09_Amendment_2_Attachment_15_-_Geotechnical_Report_0002.pdf

TAR EPORT C OVER PAGE

Geotechnical Engineering Report

Rev-2

CHOH Level 33 Retaining Wall Repair

Knoxville, Maryland

August 30, 2021

Terracon Project No. EY205063A

Prepared for:

Quinn Evans Architects

Washington, DC

Prepared by:

Terracon Consultants, Inc.

Germantown, MD

Terracon Consultants, Inc. 20401 Seneca Meadows Pkwy, Germantown, MD

P (214) 354 6100 terracon.com

REPORT C OVER LETTER TO SIGN

August 30, 2021

Quinn Evans Architects

2121 Ward Place, Northwest, 4th Floor

Washington, DC 20037

Attn: Ms. Katie Irwin, AIA, IIDA, LEED AP BD+C – Senior Associate

P: (202) 591-2527

E: Kirwin@quinnevans.com

Re: Geotechnical Engineering Report Rev-2

CHOH Level 33 Retaining Wall Repair

Harpers Ferry Road

Knoxville, Maryland

Terracon Project No. EY205063A

Dear Ms. Irwin:

This report presents the results of our subsurface exploration and provides geotechnical engineering recommendations for repair of the retaining wall in distress near the Chesapeake and

Ohio (C&O) canal towpath mile marker 61.3. This study was performed in general accordance with our Proposal No. PEY205063 dated August 11, 2020 and scope modifications authorized on

February 24, 2021.

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 Consultants, Inc.

Aditya Rayudu, Msc, PE Nancy A. Straub, PE, ENV SP, LEED AP

Project Engineer Senior Associate | Geo. Dept. Manager for

Paul Burkart, PE

Senior Engineering Consultant

Professional Certification. I hereby certify that these documents were prepared or approved by me, and that I am a duly licensed professional engineer under the laws of the State of Maryland, License No. 45404, Expiration Date: 05/19/2022

Geotechnical Engineering Report Rev-2

CHOH Level 33 Retaining Wall Repair ■ Knoxville, Maryland

August 30, 2021 ■ Terracon Project No. EY205063A

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TABLE OF CONTENTS

INTRODUCTION

BACKGROUND

GEOTECHNICAL CHARACTERIZATION

SUMMARY OF FINDINGS

RECOMMENDATIONS FOR REPAIR

CONSTRUCTION CONSIDERATIONS

GENERAL COMMENTS

ATTACHMENTS

SITE LOCATION PLAN AND GEOLOGIC MAP

GEOPHYSICAL INVESTIGATION RESULTS

SUBSURFACE EXPLORATION RESULTS

EXPLORATION AND TESTING PROCEDURES

SKETCHES

Note: Refer to each individual Attachment for a listing of contents.

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INTRODUCTION

Geotechnical Engineering Report Rev-2

CHOH Level 33 Retaining Wall Repair

Knoxville, Maryland Terracon Project No. EY205063A

August 30, 2021

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the repair of an existing distressed retaining wall located at the

Chesapeake and Ohio (C&O) canal towpath near mile marker 61.3 in Knoxville, Maryland. The purpose of these services is to evaluate the source of wall distress and provide recommendations for repair.

BACKGROUND

The C&O canal near mile marker 61.3 between Lock 33 and Lock 34 runs parallel to Harpers

Ferry Road below the Maryland Heights cliffs, as shown in the Site Location Plan. In the early

1830s, excavations were made into bedrock at the base of the cliffs to construct the canal and build a stone “protection” retaining wall using rock from the excavation. A Historic Resource Study by the National Park Service (NPS) states that a considerable portion of the excavation above

Lock 33 would be “quarry rock mixed with earth excavation along a steep hillside”1. Archaeological excavations performed in 19842 showed that in general the retaining walls were constructed of large, flat stones set in a clay mortar. Historical archaeological documents indicate that the wall is generally 30 to 42 inches thick and there is a clay-stone aggregate liner behind the wall. Some walls are constructed in a stepped fashion with upper portion of the wall stepped back from the lower portion wall. Archaeological excavations noted that sections which appear to step back were observed to be actually one wall.

This section of wall has a long history of problems. A one-mile long section of Harpers Ferry Road was deemed unsafe in 1982 and was upgraded as a joint project between Washington County and the NPS. The NPS was responsible for repairing the wall and Washington County for repairing

1 Smith, Edward D. Historic Resource Study, Dam 3 Area: Shenandoah River Lock to Lock 36, Historical data, Chesapeake and Ohio Canal National Historical Park, MD-D.C.-W.VA. National Park Service. 1979.

2 McGarry, Thomas, E. Archaeological Excavations, C&O Canal Harpers Ferry Road and Walls, National Historical Park, Maryland-West Virginia-Washington, D.C. 1984.

Responsive ■ Resourceful ■ Reliable 2 the road and guardrails.3 Preliminary drawings prepared in 1982 indicated four different modes of failure4:

■ Condition 2 – ‘Voids along the bottom of the wall creates instability for the wall above them.’

■ Condition 3 – ‘Complete failure of canal lining wall along the top of wall will encourage further erosion, endangering the road and guardrails.’

■ Condition 4 – ‘Complete failure of road retaining wall will encourage further failure of the road and guard rails as well as the canal lining wall.’

■ Condition 5 – ‘Instability of the upper portion of the canal lining wall poses a danger to both people and the road.’

Figure 1 – Composite Profile of C&O Canal from 1984 Archaeological Report

During our site visit, we observed that the retaining wall appeared to be bulging near the base just above the bottom of the canal. We also noticed that the asphalt roadway pavement at the top of the wall in the area of distress has been recently patched, but appears to have subsequently settled.

3 Letter from Richard Stanton (US Department of Interior) and Ms. Carrie Johnson of Butte, Montana. October

1, 1982

4 Harpers Ferry Road Preliminary Drawings. September 1, 1982. Note that Condition 1 is stable.

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GEOTECHNICAL CHARACTERIZATION

Geology

Based on the Geologic Map of Washington and Frederick Counties, Maryland5, the project site is located within the Piedmont Physiographic Province of Maryland in. As shown on the Geologic

Map, the site is mapped within the Harpers Formation from the Cambrian geologic period, which predominantly consists of residual silt and clay with interbedded sand and gravel overlying dark green-gray phyllitic shale and siltstone.

Field Investigation

To determine the source of wall distress, Terracon performed a combination of site reconnaissance, geophysical explorations, and subsurface investigation. The explorations and investigations were used to help determine:

■ the soil and rock conditions at the base of the wall,

■ groundwater conditions,

■ the composition and density of the backfill and rock behind the wall, and

■ thickness of the stone wall.

Site Reconnaissance

Terracon made a site visit on November 12, 2020 to observe the nature and extent of the distress in the retaining wall. At the time of the visit, approximately 3 inches of ponded water was present in the bottom of the canal. East of a rock outcrop protruding from the face of the wall, the wall appears to sag. Joints between stones in the lower third of the wall appeared to be filled with soil and appeared to be bulging. Soil was not observed between the stones higher on the wall. In several locations, stones have fallen from the lower third of the wall with indications of water flow carrying soil between the stones. On the west end of the wall, a gap could be observed between the blocks and the rock outcrop. The travel lane of Harpers Ferry Road closest to the wall appears to sag and has been patched recently. No drainage swales or water channels to capture and redirect water were observed along the shoulders of the road.

5 Brezinski, D.K., 2009, Geologic map of the Keedysville and parts of Shepherdstown, Harpers Ferry and Charles Town quadrangles, Washington and Frederick Counties, Maryland: Maryland Geological Survey, Quadrangle Geologic Map

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Geophysical Explorations

Terracon performed a combination of Multi-channel Analysis of Surface Waves (MASW) and

Ground Penetrating Radar (GPR). Each of these methods will be discussed in detail on the follow.

Multi-channel Analysis of Surface Waves (MASW)

The MASW method was performed on Harpers Ferry Road behind the top of the retaining wall at the area of distress to determine the depth of rock. The survey was performed in three approximately 170-foot long lines parallel to the retaining wall as presented on the plan in the

Geophysical Investigation Results section. The data was collected using a Geometrics Geode seismograph and a linear array of twenty-four 4.5Hz geophones at 3-foot spacing. MASW is performed by collecting surface waves created by a seismic source consisting of a 10-lb sledgehammer striking an aluminum ground plate. The data is then processed using dispersion analysis software (SurfSeis, engineered by the Kansas Geological Survey) that extracts the fundamental-mode dispersion curve(s). The curves are inverted and modeled to yield a 1D shear-wave velocity profile along the array for a corresponding depth. Using subsets of geophones, many 1D profiles are created along an array and then combined to yield a 2D profile.

The results of the MASW investigation are presented in the Geophysical Investigation Results.

Each profile indicates change in shear wave velocity with depth. Based on the correlation to our boring logs, we interpret that approximately 2,000 ft/sec corresponds to the shear wave velocity of rock. The results appear to indicate that the top of rock varies in depth from approximately 0 to

20 feet below the surface of the existing road, but generally gets shallower the further away from the canal.

Ground Penetrating Radar (GPR)

Terracon used GPR on February 25, 2021 on the face of the stone wall to try to confirm the thickness of the wall and the depth to top of rock in the canal at the base of the wall. A GPR system consisting of a 200 MHz HS antenna made by Geophysical Survey Systems Inc. (GSSI) was used for this exploration. GPR field data collection was performed in general accordance with

ASTM D6432. More information on both the test method and collection procedures can be found in the test standard. The locations surveyed, and results of the geophysical investigation are shown in Geophysical Investigation Results section.

Terracon performed 4 scan lines. Three lines were on the face of the wall at 2, 4, and 6 feet above the bottom of the canal. The fourth scan line was on the bottom of the canal right at the base of the wall. The GPR survey was able to penetrate approximately 6 to 7 feet behind the face of the wall or below the bottom of the canal. The wall scans indicate that the wall appears to vary from

1.5 to 3 feet but generally is at least 2 feet thick. The fourth scan along the base of the wall shows that the depth to rock appears to vary from approximately 2 to 3 feet below the bottom of the canal.

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Test Borings and Test Pits

Due to site access constraints, we performed our subsurface explorations in two phases. The first phase, performed on March 23, 2021, included only work that could be performed from the canal.

This included three soil borings (B-3 through B-5) and two test pits (TP-1 and TP-2). The second phase of our investigation on April 26, 2021 coincided with a planned road closure for another project on Harpers Ferry Road. This second phase of investigation included two soil borings (B-

1 and B-2) and two additional test pits in the canal (TP-3 and TP-4). The results of our field explorations are presented in Subsurface Exploration Results section.

A summary of conditions encountered in the borings and test pits are included in the following table.

Exploration Ground

Surface EL (ft)

Depth to

Bedrock (ft)

Exploration

Depth (ft)

Depth to

Groundwater

(ft)

B-1 284.2 19.5 19.5 NE

B-2 284 2.0 22.0 NE

B-3 260 6.0 11.0 2.5

B-4 260.5 5.0 10.0 NE

B-5 260.0 3.0 8.0 NE

TP-1 260.8 1.7 1.7 1.5

TP-2 260.6 2.5 2.5 1.5

TP-3 260.8 NP 3.0 1.5

TP-4 260.0 NP 3.5 1.5

NE = Not encountered prior to adding water for rock coring

NP = Bottom of soil layer not penetrated

Encountered during drilling

Groundwater observations were made during drilling and borehole cave-in observations were made at completion of each borehole. Full details about the methods used to perform the subsurface explorations and obtain samples can be found in the Exploration and Testing

Procedures section.

Subsurface Conditions

We have developed a general characterization of the subsurface conditions within the site based upon our review of the historic information, geophysical, subsurface exploration, and laboratory data, as well as our understanding of the geologic setting. This characterization forms the basis

Responsive ■ Resourceful ■ Reliable 6 of our geotechnical calculations, evaluation of site preparation, and wall stabilization design options. Stratification boundaries on the boring logs represent the approximate location of changes in soil types. The actual transition between materials may be gradual.

We identified the following layers behind the retaining wall.

Layer Layer Name General Description

Asphalt/Base Course

(0 to 6 inches)

Borings B-1 and B-2, performed in the roadway, encountered 6 to

12 inches of asphalt with 1.5 to 3 feet of base aggregate course.

Natural Coarse-grained Soils

(2 to 19 feet)

Silty SAND (SM), and Silty GRAVEL (GM). Brown, moist, loose to very dense.

3 Bedrock

PHYLLITE. The depth to bedrock varied from 2 feet near the centerline of Harpers Ferry Road to 19.5 feet near the guardrail and wall.

We identified the following subsurface profile in front of the retaining wall:

Layer Layer Name General Description

Topsoil

(0 to 2 inches)

Borings B-3 through B-5 and test pits TP-3 and TP-4 performed in grassy area encountered 2 inches of topsoil consisting of Lean

CLAY with roots.

Natural Fine-grained

Soils

(0 to 2 feet)

Elastic SILT (MH) and Lean CLAY (CL). Dark gray, moist, very soft to medium stiff.

Natural Coarse-grained Soils

(2 to 6 feet)

Silty SAND (SM), and Silty GRAVEL (GM). Brown to gray, moist, medium dense to very dense.

4 Rock PHYLLITE. Encountered at 3 to 6 feet below ground surface

Groundwater Conditions

Groundwater levels and cave-in depths were recorded during drilling and test pitting, and at the completion of exploration at each borehole and test pit location.

Perched groundwater may be encountered at shallower depths. Fluctuations in perched or groundwater levels should be expected with variations in conditions such as precipitation, evaporation, construction activity, etc.

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SUMMARY OF FINDINGS

At the location of the wall distress, bedrock behind the wall is deeper than at other locations.

Based on the results of our explorations and observations, it appears that water is becoming trapped behind the wall after rain events. There is evidence of water flow between the wall stones where stones have fallen. The soil between the stones acts as a lubricant. In addition, water flowed continuously and rapidly into our test pits from the base of the wall during our field investigations. We also observed that Harpers Ferry Road does not have drainage swales or drains to capture and convey surface water runoff from Maryland Heights away from the wall.

Historical records indicate that the wall stones may have been set using a clay mortar and that there may have been a clay and crushed rock liner behind the wall. While we did not encounter a clay mortar or a clay and crushed rock liner in our explorations, we observed soil deposited between the stones in the lower third of the wall where the wall is experiencing the most distress.

Research shows that soils with fines contents above 10 percent have reduced permeabilities especially above 15 percent6. The silty sands and gravels encountered behind the wall in our explorations contained 12 to 17 percent fines.

We believe that trapped water behind the wall cannot drain readily through the wall backfill and the clay/elastic canal liner at the base of the wall. The stacked stone wall does not have the internal structural shear strength to resist these hydrostatic pressures. In addition, the water flow is likely slowly washing out the backfill soils from between the wall stones, resulting in loss of ground and settlement of Harpers Ferry Road.

We also considered whether it may be possible that the distress is due to lateral sliding of the wall at its base. However, we anticipate that the combination of friction between the wall stones and the bedrock foundation and the passive resistance pressures provided by the canal soils create sufficient resisting forces to sliding. In addition, the low internal structural shear strength of the wall makes it unlikely that the wall would slide as a unit. We understand that recent wall surveys indicate that the wall movement has occurred above the ground surface in the canal where no passive soil pressures exist.

RECOMMENDATIONS FOR REPAIR

All solutions to stabilize the wall must include the relief of hydrostatic pressures with the use of wall drains and modifications to drainage along Harpers Ferry Road. All surface water

6 Gomez, B. W., Dewoolkark, M. M., Lens, J. E., & Benda, C. C. (2014). Effects of fines content on hydraulic conductivity and shear strength. Transportation Research Record: Journal of the Transportation Research Board, No.

2462, Transportation Research Board of the National Academies, Washington, D.C., 2014, pp. 1–6.

Responsive ■ Resourceful ■ Reliable 8 should be captured in lined drainage channels and conveyed to drainage pipes for discharge into a storm drain or into the canal. Harpers Ferry Road should be regraded to maintain positive drainage of surface water away from the wall and into the lined drainage channels. Subdrainage provisions at the base of the wall backfill zone and/or drainage outlets at the face of the wall should also be provided in any of the mitigation design scenarios to remove water collected within retained materials behind the wall.

The sections below present three different options for stabilization and repair of the wall that will allow the NPS to maintain the aesthetic appearance of the wall without permanent braces or other exposed structural elements. Each option has its own advantages, disadvantages, costs, and risks. We present each of these options in detail in the following sections.

Option 1 – Remove and Replace

In this first option, all soil behind the wall in the area of distress is removed and replaced with concrete. In this area of distress, there is a zone of saturated soil behind the wall which is applying load to the stone wall and requires a self-supporting material to eliminate the load on the stone wall. This will require closure of Harpers Ferry Road for an extended period of time while the work is being completed. The general sequence repair would follow:

■ stone wall is deconstructed,

■ all fill soils are removed,

■ construct form work,

■ install drains,

■ install dowels into the adjacent bedrock to anchor the concrete into the rock mass,

■ place concrete,

■ remove formwork, and

■ reconstruct stone wall.

This solution would be a low-risk, permanent repair that removes all soil and water loads from the stone wall. However, the work will require a long road closure that will be very disruptive to the community. In addition, this alternative requires a large amount of manual work to deconstruct and reconstruct the stone wall, to build custom formwork and install drains, and to remove fill and replace with concrete. Due to the large amount of manual work, we anticipate that this solution will be the most expensive.

Light-weight concrete could be used instead of normal-weight concrete. Light-weight concrete is similar to normal-weight concrete but the mix uses special light-weight aggregates like perlite, pumice. The custom formwork would need to be much more robust for normal-weight concrete

Responsive ■ Resourceful ■ Reliable 9 compared to light-weight concrete. However, light-weight concrete can take 2 to 3 times longer to dry and costs more per cubic yard compared with normal-weight concrete.

Option 2 – Grout and Stabilize

If the wall retains enough structural integrity to just be spot-repaired, the second alternative we recommend is to stabilize the backfill soils in-situ using chemical grouts. The chemical grouts would be injected from the roadway above using small holes and allowed to penetrate the silty sands and gravels. This will bind up the materials behind the wall to prevent the backfill from applying load to the wall. The grout-improved backfill will have increased shear strengths, reducing the lateral earth pressures that need to be resisted by the stacked stone wall. Once the grouting is complete, horizontal drains would be drilled through the wall from the canal to relieve hydrostatic pressures.

Advantages to this solution include:

■ Minimal community impact since the grouting could be done with brief lane closures or short full-road closures.

■ Full deconstruction and reconstruction of the wall may not be necessary if local repairs to the wall can be performed.

■ Likely the least expensive alternative.

Disadvantages/risks with this solution include:

■ This solution relies on the grout to penetrate the backfill fully and uniformly to create a homogeneous mass. This may be difficult to verify in the field.

■ It is undesirable to have the grout flow in between the stones.

■ The grouting process will take some trial and error to determine the correct grout mix properties that will allow it to penetrate the soils without simply flowing out between the wall stone or expanding, which could create additional lateral pressures on the wall. It is uncertain if the grouted soils will be fully self-supporting or if it will still rely on the stone wall for some lateral support. Therefore, there will be some inherent risk to long-term performance of the wall that would not be assumed with either Options 1 or 3.

■ The chemical grouts may coat or stain the face of the stone wall if the grouts seep between the stones.

■ Long-term grout performance can be impacted by contamination.

We discussed this solution with a chemical grouting contractor to confirm the applicability of this approach. They confirmed that an acrylate grout injected slowly will have very little expansion, if any. They recommended that the best way to make sure the grout does not come though the wall

Responsive ■ Resourceful ■ Reliable 10 would be to set the grout to react faster to minimize the travel. This would be paired with tighter injection spacings to make sure the grout has good, full coverage. In addition, we identified other measures that could be used to protect the stone wall face from grout:

■ Pre-wet the wall and then continuously monitor the wall during grouting with a water tank and a hose for seeps. If any grout comes through the wall, it should be sprayed with water and washed off before it reacts and becomes a gel. In addition, the contractor could keep some oakum rope at the ready to stuff any spots where the grout does start to come out.

■ Apply anti-graffiti products to the face of the wall and then a layer of wax to keep the grout from sticking.

■ Apply vegetable oil or other non-toxic lubricant to the face of the wall to keep the grout from sticking. The contractor was less confident that the vegetable oil approach would be successful.

Any product applied to the face of the wall as a non-stick agent has the potential to also discolor the stone.

Option 2A – Grout, Reinforce, and Rebuild

Option 2A is a variation of Option 2 that can be used if the stone wall is not structurally stable enough to be repaired. Similar to Option 2, the existing wall backfill would be grouted using chemical grouts to improve the shear strength of the existing backfill soils. However, in Option

2A, once the grouting is complete, the wall stones would be removed, and permanent soil nails or anchors will be installed as permanent reinforcement. The grout will provide the necessary soil strength and soil face “stand-up” time needed to install anchors. Once the grouting and nailing is complete, horizontal drains would be drilled through the wall from the canal to relieve hydrostatic pressures, and then the wall would be reconstructed.

Advantages to this solution include:

■ Permanent reinforcement elements will remove the lateral earth pressure impacts to the historical wall stone facing.

■ Reduced community impact compared to Option 1. Similar to Option 2, the grouting could be done with brief lane closures or short full road closures. Nail or anchor installation could be performed from the roadway or the canal. If nail installation is performed from the roadway, a full closure will be necessary. We recommend closure of the closest lane to the wall during wall deconstruction and rebuilding.

■ This will require the full deconstruction and reconstruction of the wall

■ This will likely require the construction of soil berm benches for nail or anchor installation.

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■ This solution relies on the grout to penetrate the backfill fully and uniformly to create a homogeneous mass. This may be difficult to verify in the field. If the grout does not penetrate fully, the vertical face needed for nail or anchor installation may not be possible.

■ The grouting process will take some trial and error to determine the correct grout mix properties that will allow it to penetrate the soils without simply flowing out between the wall stone or expanding, which could create additional lateral pressures on the wall.

■ The chemical grouts may coat or stain the face of the stone wall if the grouts seep between the stones.

■ The design must consider potential corrosion to steel elements.

We anticipate that the nails or anchors will consist of solid bolts drilled into rock and grouted in place using resin cartridges.

Option 3 – Piles

Permanent wall stabilization may also be accomplished using a combination of structural elements such as micropiles, soldier piles and lagging, and tiebacks or anchors. To have stability at the toe of the wall, all piles must be pre-drilled and socketed into rock. Temporary or permanent lagging will be placed between the piles to retain the soil. A structural element such as a waler or a cap beam will be needed to connect the piles at the top so that they perform as a single unit.

Tiebacks or battered micropiles drilled into rock will need to be installed to provide additional lateral restraint.

Advantages to this solution include:

■ Permanent reinforcement elements will remove most of the lateral earth pressure impacts to the historical wall stone facing.

■ Once the pile wall is installed, the road can be reopened to traffic while the stone wall is being reconstructed.

■ This will require the full deconstruction and reconstruction of the wall.

■ This will likely require the construction of a large soil berm bench to stabilize the wall during pile installation.

■ Depending on the contractor’s means and methods and their equipment size, the road will likely need to be closed during construction of the pile wall.

■ The structural wall system may be large in cross-section. The pile cap beam or waler and tieback system may protrude into the space needed for the stone wall reconstruction if the piles are installed at the edge of the existing pavement. If the piles are installed below the

Responsive ■ Resourceful ■ Reliable 12 existing travel lane, the pavement may develop cracks at the interface between the rigid pile elements and the retained soil zone.

■ Since the existing soil backfill will remain in place, additional drainage will need to be added behind the wall.

■ The design must consider potential corrosion to steel elements.

Schematic renderings of these three options are included at the end of this report.

CONSTRUCTION CONSIDERATIONS

We would recommend that the drainage improvements be made to Harpers Ferry Road prior to starting any of the proposed stabilization/repair alternatives to prevent water flow into the work area. In addition, some chemical grouts are hydrophilic and will react in contact with water, which could impact the planned treatment program.

For Options 2 and 2A, we recommend prior to start of work that the contractor demonstrate with a mock-up in either the field or the lab, that their proposed grout will successfully penetrate the anticipated backfill soils without flowing out. In addition, we recommend that the contractor provide a contingency plan in the event that the grouts do not perform in the field as intended.

For all three repair options above, we recommend retaining an experienced contractor that is able to adapt to variable conditions and is sensitive to the historic nature of the site.

GENERAL COMMENTS

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration. Natural variations will occur between exploration point locations or due to the modifying effects of construction or weather.

The nature and extent of such variations may not become evident until during or after construction.

Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials, or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

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Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client.

Reliance upon the services and any work product is limited to our client and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate costs. Any use of our report in that regard is done at the sole risk of the cost estimator as there may be variations on the site that are not apparent in the data that could significantly impact costs. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety and cost estimating are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

ATTACHMENTS

Geotechnical Engineering Report – Rev 2

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 1 of 2

EXPLORATION AND TESTING PROCEDURES

Field Exploration

Number of Borings Boring Depth (feet) Location

2 19.5 to 22 Harpers Ferry Road

3 8 to 11 CHOH Canal MM 61.3

Number of Test Pits Test Pit Depth (feet) Location

2 3 to 3.5 CHOH Canal MM 61.3

Boring Layout and Elevations: Based on our visual inspection of distress in the existing retaining wall, Terracon staked the borings on site using existing site features and near the locations of distress. Approximate elevations and coordinates were obtained from the survey data performed by NPS.

Subsurface Exploration Procedures: Soil borings were performed on March 23, 2021 and April

26, 2021 by Terracon. The borings were advanced using a track-mounted D-50 ATV drill rig, using

3¼-inch inner diameter hollow stem augers. Five Standard Penetration Test SPT samples, using

24-inch long samplers, were obtained from 2 feet below the ground surface in the upper 10 feet of each boring. Sampling interval was increased to 5 feet thereafter (using 18-inch long samplers) in all borings within footprint of building location.

In the split-barrel sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon was driven into the ground by a 140-pound automatic hammer falling 30 inches. The number of blows required to advance the sampling spoon middle 12 inches of the typical total 24-inch penetration or the last 12 inches of a normal 18-inch penetration is recorded as the SPT resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths.

We advanced the borings into rock with the same track-mounted rotary drill rig using NQ2-size double tube solid inner core barrel. Water is added as a drilling fluid to the coring process to keep the hole clean and from becoming jammed. The rock core bit snapped while coring rock in boring

B-1 and were not able to advance the hole deeper than 19.5 feet.

We observed and recorded groundwater levels during drilling and sampling. All borings were backfilled with auger cuttings after completion and borings performed within existing pavements are capped with cold patch.

Test pits were excavated by NPS near the distress locations of retaining wall and were observed, photographed, and logged by Terracon representatives. The NPS used Bobcat-435 hydraulically

Geotechnical Engineering Report – Rev 2

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 2 of 2 controlled backhoe excavator with an approximately 15-inch wide bucket with a clamp. The test pits ranged from 3 to 4 feet wide were extended through soil and refused on top of rock.

The sampling depths, penetration distances, and other sampling information was recorded on the field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory for testing and classification by a Geotechnical Engineer. Our exploration team prepared field boring logs as part of the drilling operations. These field logs included visual classifications of the materials encountered during drilling and our interpretation of the subsurface conditions between samples. Final boring logs were prepared from the field logs. The final boring logs represent the Geotechnical Engineer's interpretation of the field logs and include modifications based on observations and tests of the samples in our laboratory.

Laboratory Testing

We reviewed the field data and assigned laboratory tests to understand the engineering properties of the various soil strata, as necessary, for this project. Based on the material’s texture and plasticity, we described and classified the soil samples in accordance with the Unified Soil

Classification System. Procedural standards noted below are for reference to methodology in general. In some cases, variations to methods were applied because of local practice or professional judgment. Standards noted below include reference to other, related standards. Such references are not necessarily applicable to describe the specific test performed.

◼ ASTM D2216 Standard Test Methods for Laboratory Determination of Water (Moisture)

Content of Soil and Rock by Mass

◼ ASTM D4318 Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of

Soils

◼ ASTM D422 Standard Test Method for Particle-Size Analysis of Soils

The laboratory testing program often included examination of soil samples by an engineer. Based on the material’s texture and plasticity, we described and classified the soil samples in accordance with the Unified Soil Classification System.

Rock classification was conducted using locally accepted practices for engineering purposes;

petrographic analysis may reveal other rock types. Rock core samples typically provide an improved specimen for this classification. Boring log rock classification was determined using the

Description of Rock Properties.

SITE LOCATION PLAN AND GEOLOGIC MAP

Contents:

Site Location Plan

Geologic Map

SITE LOCATION PLAN

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MAP 1 PORTR AIT

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

GEOLOGIC MAP

CHOH Level 33 Retaining Wall Repairs ■ Knoxville, MD

June 1, 2021 ■ Terracon Project No. EY205063A

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

GEOLOGIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY

QUADRANGLES INCLUDE: CHARLES TOWN AND HARPERS FERRY, MARYLAND

SITE

MAP 1 LANDSC APE

1 11X17 LANDSC AE

P 2 PORTR AIT

MAP 2 LANDSC APE

\\M AP 2 11X17 LAND SC APE

\\M AP 2 11X17 LAND SC APE

GEOPHYSICAL INVESTIGATION RESULTS

MASW Investigation Plan

MASW Results

GPR Results

MASW INVESTIGATION PLAN

20401 Seneca Meadows Pkwy Germantown, MD 20876

PH. (301) 354-6100 FAX. (301) 354-6101

EY205063A

5/28/2021

NAS

NAS

ER

ER

AS SHOWN

Project Manager:

Performed by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

MASW PLAN

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

0 20

FEET

LEGEND

B-1 BORING

TP-1 TEST PIT

3A MASW LINE

CHOH Level 33 Retaining Wall Repair Knoxville, MD 1

EXHIBIT

ExhibitMASW ResultsNAS

MEC

NAS

EBR

Project No.

Scale:

File Name:

Date:

EY205063A

As-Shown

March - 2021

Project Manager:

Drawn by:

Checked by:

Approved by:

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

20401 Seneca Meadows Parkway Germantown, MD 20876

PH. (301) 354-6100

Approximate Location of B-1

CHOH Level 33 Retaining Wall Repair Knoxville, MD srayudu Line srayudu Rectangle

GPR Results

20401 Seneca Meadows Parkway Germantown, MD 20876

PH. (301) 354-6100

EY205063A

March - 2021

NAS

MEC

NAS

EBR

As Shown

Project Manager:

Drawn by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

EXHIBIT

--DIAGRAM IS FOR GENERAL LOCATION

ONLY, AND IS NOT INTENDED FOR

CONSTRUCTION PURPOSES

GPR Cross Sections Along Wall Approximately 6 Feet Above the Ground Surface

Potential Approximate Wall Thickness

Approximate Locations of GPR Cross Sections

2 Survey Monitoring Target Locations (not related to GPR Survey)

Knoxville, MD

Approximate MASW Line Locations

20401 Seneca Meadows Parkway Germantown, MD 20876

PH. (301) 354-6100

EY205063A

March - 2021

NAS

MEC

NAS

EBR

As Shown

Project Manager:

Drawn by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

EXHIBIT

--DIAGRAM IS FOR GENERAL LOCATION

ONLY, AND IS NOT INTENDED FOR

CONSTRUCTION PURPOSES

GPR Cross Sections Along Wall Approximately 4 Feet Above the Ground Surface

Potential Approximate Wall Thickness

Approximate Locations of GPR Cross Sections

2 Survey Monitoring Target Locations (not related to GPR Survey)

20401 Seneca Meadows Parkway Germantown, MD 20876

PH. (301) 354-6100

EY205063A

March - 2021

NAS

MEC

NAS

EBR

As Shown

Project Manager:

Drawn by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

EXHIBIT

--DIAGRAM IS FOR GENERAL LOCATION

ONLY, AND IS NOT INTENDED FOR

CONSTRUCTION PURPOSES

GPR Cross Sections Along Wall Approximately 2 Feet Above the Ground SurfacePotential Approximate Wall Thickness

Approximate Locations of GPR Cross Sections

2 Survey Monitoring Target Locations (not related to GPR Survey)

20401 Seneca Meadows Parkway Germantown, MD 20876

PH. (301) 354-6100

EY205063A

March - 2021

NAS

MEC

NAS

EBR

As Shown

Project Manager:

Drawn by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

EXHIBIT

--DIAGRAM IS FOR GENERAL LOCATION

ONLY, AND IS NOT INTENDED FOR

CONSTRUCTION PURPOSES

GPR Cross Section Run Along the Ground in Front of Wall

Approximate Top of Rock

2 Survey Monitoring Target Locations (not related to GPR Survey)

Approximate Locations of GPR Cross Section

SUBSURFACE EXPLORATION RESULTS

Exploration Plan

Boring and Test Pit Logs (B-1 through B-5, TP-1 through TP-4)

Laboratory Test Summary

Atterberg Limits

Grain Size Distribution

Photo Log

General Notes

Unified Soil Classification System

EXPLORATION PLAN

CHOH LEVEL 33 RETAINING WALL REPAIR

HARPERS FERRY ROAD

KNOXVILLE, MARYLAND

20401 Seneca Meadows Pkwy Germantown, MD 20876

PH. (301) 354-6100 FAX. (301) 354-6101

EY205063A

05/10/2021

NAS

NAS N.T.S.

Project Manager:

Performed by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

FIG No.

Workplan

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

TP1

B3 B5

B4

TP2

B1

B2

LEGEND

AS-DRILLED LOCATION OF TEST BORING

(APPROX)

AS-COMPLETED LOCATION OF TEST PIT

(APPROX)

B4

TP2

TP3

TP4

2-3-2-2 N=5

2-4-4-8 N=8

7-10-9-10 N=19

9-8-6 N=14

50/4"

6.2

5.9

ASPHALT (12 Inches)

AGGREGATE BASE COURSE

SILTY SAND (SM), with gravel, brown, moist, loose

SILTY GRAVEL (GM), gray, moist, loose to very dense

Auger refusal at 19.5 feet.

Boring Refusal at 19.5 Feet

1.0

4.0

6.0

19.5

283+/-

280+/-

278+/-

264.5+/-

Hammer Type: Automatic Logged by: Aditya Rayudu

Stratification lines are approximate. In-situ, the transition may be gradual.

T H

IS

B

O R

IN

G

L O

G

IS

N O

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A

LI

D

IF

S E

P A

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T E

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IG

IN

A

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E P

O R

T . G

E O

S M

A R

T L

O G

-N O

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LL

E

Y

3A C

H O

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M E

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W A

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J T

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A T

A T

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P

LA

T E

.G D

T

/2 6/

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

D E

P T

H

F t.)

STRENGTH TEST

F

IE

LD

T

E S

T R

E S

U

LT

S

R E

C O

V E

R Y

In

R Q

D

In

Harpers Ferry Road Knoxville, MD

SITE:

Advancement Method:

3-1/4 Hollow Stem Auger

Abandonment Method:

Boring backfilled with Auger Cuttings Surface Capped with Asphalt

Notes:

Project No.: EY205063A

Drill Rig: D-50

Boring Started: 04-26-2021

BORING LOG NO. B-1

Quinn Evans ArchitectsCLIENT:

Washington, DC

Driller: Terracon (John Labbas)

Boring Completed: 04-26-2021

PROJECT: CHOH LEVEL 33 RETAINING WALL REPAIR

20401 Seneca Meadows Pkwy Germantown, MD

Water was not encountered during drilling

Caved-in at 19 feet

Water was not encountered during drilling

Caved-in at 19 feet

WATER LEVEL OBSERVATIONS

C O

M P

R E

S S

IV

E

S T

R E

N G

T H

(t sf

T E

S T

T Y

P E

S T

R A

IN

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

ATTERBERG

LIMITS

LL-PL-PI

LOCATION

Latitude: 39.3312° Longitude: -77.7353°

G R

A P

H

IC

L O

G

DEPTH ELEVATION (Ft.)

Approximate Surface Elev.: 284.2 (Ft.) +/-

S A

M P

LE

T

Y P

E

13-50/2"6

36.5

57.5

ASPHALT (6 Inches)

AGGREGATE BASE COURSE

Auger refusal at 2 feet

METAMORPHIC BEDROCK - PHYLLITE,

green-gray, medium strong, highly weathered, intensly fractured, low to moderate angle, slightly rough to rough, open joints, clayey soil infilling

Very strong, moderately to slightly weathered, highly to moderately fractured from 12 to 22 feet.

Boring Terminated at 22 Feet

0.5

2.0

22.0

283.5+/-

282+/-

262+/-

Hammer Type: Automatic Logged by: Aditya Rayudu

Stratification lines are approximate. In-situ, the transition may be gradual.

T H

IS

B

O R

IN

G

L O

G

IS

N O

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A

LI

D

IF

S E

P A

R A

T E

D F

R O

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R

IG

IN

A

L R

E P

O R

T . G

E O

S M

A R

T L

O G

-N O

W E

LL

E

Y

3A C

H O

H R

E V

E T

M E

N T

W A

.G P

J T

E R

R A

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N _D

A T

A T

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P

LA

T E

.G D

T

/2 6/

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

D E

P T

H

F t.)

STRENGTH TEST

F

IE

LD

T

E S

T R

E S

U

LT

S

R E

C O

V E

R Y

In

R Q

D

In

Harpers Ferry Road Knoxville, MD

SITE:

Advancement Method:

3-1/4 Hollow Stem Auger within soil NQ core barrel within rock and adding water while coring

Abandonment Method:

Boring backfilled with Auger Cuttings and Bentonite Surface Capped with Asphalt

Notes:

Project No.: EY205063A

Drill Rig: D-50

Boring Started: 04-26-2021

BORING LOG NO. B-2

Quinn Evans ArchitectsCLIENT:

Washington, DC

Driller: Terracon (John Labbas)

Boring Completed: 04-26-2021

PROJECT: CHOH LEVEL 33 RETAINING WALL REPAIR

20401 Seneca Meadows Pkwy Germantown, MDWater was not encountered during drilling

WATER LEVEL OBSERVATIONS

C O

M P

R E

S S

IV

E

S T

R E

N G

T H

(t sf

T E

S T

T Y

P E

S T

R A

IN

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

ATTERBERG

LIMITS

LL-PL-PI

LOCATION

Latitude: 39.3312° Longitude: -77.7353°

G R

A P

H

IC

L O

G

DEPTH ELEVATION (Ft.)

Approximate Surface Elev.: 284 (Ft.) +/-

S A

M P

LE

T

Y

0-0-0-19 N=0

21-12-16-25 N=28

17-50/5"

58.5 52

TOPSOIL

ELASTIC SILT (MH), dark gray, moist, very soft

SILTY SAND (SM), with gravel, brown to gray, moist, medium dense

SILTY GRAVEL (GW), brown, very dense

Auger refusal at 6 feet

METAMORPHIC BEDROCK - PHYLLITE,

green-gray, very strong, slightly to moderately weathered, highly fractured, low to moderate angle, slightly rough

Boring Terminated at 11 Feet

0.1

2.0

4.5

6.0

11.0

260+/-

258+/-

255.5+/-

254+/-

249+/-

9387.4 78-53-25

Hammer Type: Automatic Logged by: Aditya Rayudu

Stratification lines are approximate. In-situ, the transition may be gradual.

T H

IS

B

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IN

G

L O

G

IS

N O

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A

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D

IF

S E

P A

R A

T E

D F

R O

M O

R

IG

IN

A

L R

E P

O R

T . G

E O

S M

A R

T L

O G

-N O

W E

LL

E

Y

3A C

H O

H R

E V

E T

M E

N T

W A

.G P

J T

E R

R A

C O

N _D

A T

A T

E M

P

LA

T E

.G D

T

/2 6/

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

D E

P T

H

F t.)

STRENGTH TEST

F

IE

LD

T

E S

T R

E S

U

LT

S

R E

C O

V E

R Y

In

R Q

D

In

Harpers Ferry Road Knoxville, MD

SITE:

Advancement Method:

3-1/4 Hollow Stem Auger within soil NQ core barrel within rock and adding water while coring

Abandonment Method:

Boring backfilled with Auger Cuttings and Bentonite Surface Capped with Asphalt

Notes:

Project No.: EY205063A

Drill Rig: D-50

Boring Started: 03-23-2021

BORING LOG NO. B-3

Quinn Evans ArchitectsCLIENT:

Washington, DC

Driller: Terracon (Garrett Wilson)

Boring Completed: 03-23-2021

PROJECT: CHOH LEVEL 33 RETAINING WALL REPAIR

DEPTH ELEVATION (Ft.)

Approximate Surface Elev.: 260 (Ft.) +/-

20401 Seneca Meadows Pkwy Germantown, MD

While drilling at 2 feet

WATER LEVEL OBSERVATIONS

C O

M P

R E

S S

IV

E

S T

R E

N G

T H

(t sf

T E

S T

T Y

P E

S T

R A

IN

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

ATTERBERG

LIMITS

LL-PL-PI

LOCATION

Latitude: 39.3311° Longitude: -77.7353°

G R

A P

H

IC

L O

G

S A

M P

LE

T

Y

0-0-8-4 N=8

12-12-12-16 N=24

18-50/5"

54.5 43

TOPSOIL

ELASTIC SILT (MH), brown to gray, medium stiff

SILTY GRAVEL (GM), brown, moist, medium dense to very dense

Auger refusal at 5 feet

METAMORPHIC BEDROCK - PHYLLITE,

green-gray, very strong, slightly to moderately weathered, highly fractured, low angle, slightly rough

Boring Terminated at 10 Feet

0.1

2.0

5.0

10.0

260.5+/-

258.5+/-

255.5+/-

250.5+/-

Hammer Type: Automatic Logged by: Aditya Rayudu

Stratification lines are approximate. In-situ, the transition may be gradual.

T H

IS

B

O R

IN

G

L O

G

IS

N O

T V

A

LI

D

IF

S E

P A

R A

T E

D F

R O

M O

R

IG

IN

A

L R

E P

O R

T . G

E O

S M

A R

T L

O G

-N O

W E

LL

E

Y

3A C

H O

H R

E V

E T

M E

N T

W A

.G P

J T

E R

R A

C O

N _D

A T

A T

E M

P

LA

T E

.G D

T

/2 6/

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

D E

P T

H

F t.)

STRENGTH TEST

F

IE

LD

T

E S

T R

E S

U

LT

S

R E

C O

V E

R Y

In

R Q

D

In

Harpers Ferry Road Knoxville, MD

SITE:

Advancement Method:

3-1/4 Hollow Stem Auger within soil NQ core barrel within rock and adding water while coring

Abandonment Method:

Boring backfilled with Auger Cuttings and Bentonite Surface Capped with Asphalt

Notes:

Project No.: EY205063A

Drill Rig: D-50

Boring Started: 03-23-2021

BORING LOG NO. B-4

Quinn Evans ArchitectsCLIENT:

Washington, DC

Driller: Terracon (Garrett Wilson)

Boring Completed: 03-23-2021

PROJECT: CHOH LEVEL 33 RETAINING WALL REPAIR

20401 Seneca Meadows Pkwy Germantown, MDWater was not encountered during drilling

WATER LEVEL OBSERVATIONS

C O

M P

R E

S S

IV

E

S T

R E

N G

T H

(t sf

T E

S T

T Y

P E

S T

R A

IN

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

ATTERBERG

LIMITS

LL-PL-PI

LOCATION

Latitude: 39.3311° Longitude: -77.7354°

G R

A P

H

IC

L O

G

DEPTH ELEVATION (Ft.)

Approximate Surface Elev.: 260.5 (Ft.) +/-

S A

M P

LE

T

Y

0-3-3-4 N=6

50/2"

56 38

TOPSOIL

ELASTIC SILT (MH), dark gray, moist, medium stiff

SILTY GRAVEL (GM)

Auger refusal at 3 feet

METAMORPHIC BEDROCK - PHYLLITE,

green-gray, very strong, slightly to moderately weathered, highly fractured, low angle, slightly rough

Boring Terminated at 8 Feet

0.1

2.0

3.0

8.0

260+/-

258+/-

257+/-

252+/-

Hammer Type: Automatic Logged by: Aditya Rayudu

Stratification lines are approximate. In-situ, the transition may be gradual.

T H

IS

B

O R

IN

G

L O

G

IS

N O

T V

A

LI

D

IF

S E

P A

R A

T E

D F

R O

M O

R

IG

IN

A

L R

E P

O R

T . G

E O

S M

A R

T L

O G

-N O

W E

LL

E

Y

3A C

H O

H R

E V

E T

M E

N T

W A

.G P

J T

E R

R A

C O

N _D

A T

A T

E M

P

LA

T E

.G D

T

/2 6/

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

D E

P T

H

F t.)

STRENGTH TEST

F

IE

LD

T

E S

T R

E S

U

LT

S

R E

C O

V E

R Y

In

R Q

D

In

Harpers Ferry Road Knoxville, MD

SITE:

Advancement Method:

3-1/4 Hollow Stem Auger within soil NQ core barrel within rock and adding water while coring

Abandonment Method:

Boring backfilled with Auger Cuttings and Bentonite Surface Capped with Asphalt

Notes:

Project No.: EY205063A

Drill Rig: D-50

Boring Started: 03-23-2021

BORING LOG NO. B-5

Quinn Evans ArchitectsCLIENT:

Washington, DC

Driller: Terracon (Garrett Wilson)

Boring Completed: 03-23-2021

PROJECT: CHOH LEVEL 33 RETAINING WALL REPAIR

20401 Seneca Meadows Pkwy Germantown, MDWater was not encountered during drilling

WATER LEVEL OBSERVATIONS

C O

M P

R E

S S

IV

E

S T

R E

N G

T H

(t sf

T E

S T

T Y

P E

S T

R A

IN

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

ATTERBERG

LIMITS

LL-PL-PI

LOCATION

Latitude: 39.3310° Longitude: -77.7352°

G R

A P

H

IC

L O

G

DEPTH ELEVATION (Ft.)

Approximate Surface Elev.: 260 (Ft.) +/-

S A

M P

LE

T

Y

LEAN CLAY (CL), dark gray

SILTY GRAVEL, brown to gray, Blocks of gravel encountered Hand dug pit refusal at 1.7 feet Hand dug Pit Terminated at 1.7 Feet

1.5 1.7

259.5+/- 259+/-

Logged by: Aditya Rayudu Stratification lines are approximate. In-situ, the transition may be gradual.

T H

IS

B

O R

IN

G

L O

G

IS

N O

T V

A

LI

D

IF

S E

P A

R A

T E

D F

R O

M O

R

IG

IN

A

L R

E P

O R

T . G

E O

S M

A R

T L

O G

-N O

W E

LL

E

Y

3A C

H O

H R

E V

E T

M E

N T

W A

.G P

J T

E R

R A

C O

N _D

A T

A T

E M

P

LA

T E

.G D

T

/2 6/

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

D E

P T

H

F t.)

STRENGTH TEST

F

IE

LD

T

E S

T R

E S

U

LT

S

R E

C O

V E

R Y

In

R Q

D

In

Harpers Ferry Road Knoxville, MD

SITE:

Advancement Method:

Abandonment Method:

Boring backfilled with soil cuttings upon completion.

Notes:

Project No.: EY205063A

Excavator:

Test Pit Started: 03-23-2021

HAND DUG PIT LOG NO. TP-1

CLIENT: Quinn Evans Architects

Washington, DC

Operator:…