VA-CWV RHS Geotech Report.pdf

ECS Mid‐Atlantic, LLC Subsurface Exploration and Geotechnical Engineering, and

Permanent Slope Repair Recommendations

Louis A. Johnson VA Medical Center ‐ Landslide

1 Medical Center Drive

Clarksburg, Harrison County, West Virginia

ECS Project Number 40:2492

October 20, 2023

Ms. Claire O’Connor

CB Design Group

421 King Street, Suite 301

Alexandria, Pennsylvania 22314

ECS Project No. 40:2492

Reference: Subsurface Exploration, Geotechnical Engineering Analysis and Permanent Slope

Repair Recommendations

Louis A. Johnson VA Medical Center ‐ Landslide

1 Medical Center Drive

Clarksburg, Harrison County, Pennsylvania

Dear Ms. O’Connor:

As authorized by your acceptance of ECS Proposal No. 40:2993‐GP, dated July 9, 2023, ECS Mid‐Atlantic, LLC (ECS) has completed the subsurface exploration to explore the conditions within the limits of the slope failure at the above referenced location. The following sections discuss the subsurface exploration procedures and present the results of our subsurface exploration and laboratory testing. The information contained in this report is being provided for the use in final design of the recommended slope stabilization methods, to be submitted under separate cover.

PROJECT OVERVIEW

Project Location

The site is located at the Louis A. Johnson VA Medical Center in Clarksburg, Harrison County, West

Virginia. Specifically, the area of concern consists of the hillside along the eastern side of Clarksburg Park

Way along the western side of the Louis A. Johnson Medical Center.

The approximate location of the site is indicated on the Site Location Diagram (Sheet 1 of 7) included in the Appendix of this report.

ECS Project No. 40:2492 Page 2

Project Background

Overview

Based on the information provided, including the Field Reports, prepared by CB Design Group, dated

March 1, 2023, we understand that a small landslide occurred during the summer of 2022. Based on the supplied photos and publicly available topographic mapping, the hillside is approximately 30 feet tall in the area of the landslide. In addition, evidence of a prior landslide was observed to the north of the site.

We understand that this area of the hillside is not located on VA property.

Based on our review of the supplied photos and the Boring Logs, prepared by NGE, red clay materials typically associated with landslide‐prone soils were observed beneath the site. We further understand that on the day of the landslide, VA staff observed water flowing from a single point of discharge, uphill from the landslide.

Proposed Permanent Repair

We were provided with drawing titled Exhibit of Topographic Survey of Slip Area along Clarksburg

Parkway (Drawing No. 299‐23), prepared by Allegheny Surveys, Inc., dated October 5, 2023. This drawing, here after referred to as “Site Plan”, depicts existing site topography post failure. This drawing depicts topographic survey information for the landslide and surrounding area, as well as elevations relative to the test borings drilled and instrumentation installed as part of our current study. The site plan indicated site elevations within the project site ranging between approximately EL. 954 to 998 MSL.

According to the USGS Clarksburg, WV Quadrangle Maps, dated, 2023, elevations within the slide area range from approximately EL. 960 to 940 MSL. A copy of the USGS Topographic map (Sheet 2 of 7) is included in the Appendix of this report.

In order to evaluate the subsurface conditions within the limits of the slope failure, a subsurface exploration consisting of a series of soil borings was performed at the site. Additionally, geotechnical instrumentation consisting of a slope inclinometer was installed in the completed borehole at the crest of the slope to monitor the performance of the slope until formal repair design drawings could be completed and the repair implemented. The scope of services performed as part of this subsurface exploration is outlined in the following section.

Scope of Work

In order to evaluate the subsurface conditions within the vicinity of the failed slope, a total of two (2) test borings, referenced as B‐01 and B‐02, were performed at the site. Boring B‐01 was performed at the crest of the slope, above the observed landslide while B‐02 was performed in an accessible area along the toe of the slope. Please note, the location of Boring B‐02A on the Exploration Location Diagram

(Figure 6 of 7) was performed to confirm the shallow refusal conditions in Boring B‐02.

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The borings were scheduled to extend to auger refusal, anticipate to be approximately 30 feet below existing site grades (bgs). Boring B‐01 encountered auger refusal at an approximate depth of 24.5 feet bgs while B‐02 encountered auger refusal at an approximate depth of 5 feet bgs. Upon auger refusal, approximately 10 feet of rock core was obtained from the B‐01 location. The borings were sampled continuously in an effort to identify the depth to the slip plane of the landslide. Boring B‐01 was converted to an inclinometer upon completion of the test drilling.

The number and general location of the test borings were selected by ECS and staked in the field by an

ECS representative using our Global Positioning System (GPS) equipment. Coordinates were provided to the Allegheny Surveys, Inc., who plotted the test borings on the Exhibit of Topographic Survey of Slip

Area along Clarksburg Parkway drawing, which included existing topographic information. Therefore, ground surface elevations have been included on the attached boring logs. Based on the contour interval utilized on the drawing provided, and considering the accuracy with which the borings were located in the field, the elevations noted on our logs are considered to be accurate to about ±1.0 foot.

Please note the elevations shown on our boring logs are only considered to be as accurate as the topographic survey from which they were obtained.

Following drilling operations, laboratory tests were performed on selected soil and rock samples to identify the samples and to assist in the estimation of properties for the subsurface materials. The results of the subsurface exploration, along with an Exploration Location Diagram (Sheet 7 of 7), are included in the Appendix of this letter. The Exploration Location Diagram was developed from the drawing titled Exhibit of Topographic Survey of Slip Area along Clarksburg Parkway (Drawing No. 299‐

23), prepared by Allegheny Surveys, Inc., dated October 5, 2023.

The purposes of this subsurface exploration were to explore the soil, bedrock and groundwater (if encountered within the depths explored) conditions at the site. We accomplished these purposes by:

1. Drilling soil borings to explore the subsurface soil, weathered bedrock, and groundwater conditions,

2. Converting one (1) of the test boring locations to an inclinometer for the purpose of monitoring the stability of the slope during the design and construction phases of the repair,

3. Performing laboratory tests on selected soil samples to estimate their pertinent engineering properties,

4. Evaluating global stability for the existing site slope and stability improvement measures, including the permanent slope repair,

5. Providing recommendations for methods to repair the slope, and

6. Developing this geotechnical summary letter.

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Our current scope of services was limited to providing the results of our subsurface exploration, laboratory testing, inclinometer monitoring (reported under separate cover), and global stability analysis of the permanent repair options only. Formal design and construction drawings for the repair option selected by the VA will be provided under separate cover.

EXPLORATION PROCEDURES

Subsurface Exploration Procedures

Soil Borings

Prior to drilling operations, West Virginia One Call System (811) was contacted to locate and clear/mark underground utilities at the site. Boring locations were adjusted in the field, if necessary, based on these markings. The soil boring was performed with a Acker Soil Scout track‐mounted auger drill rig which utilized continuous flight, hollow stem augers to advance the boreholes. Drilling fluid was not used during the soil drilling at each boring location.

Representative soil samples were obtained by means of the split‐barrel sampling procedure in accordance with ASTM Specification D‐1586. In this procedure, a 2‐inch O.D., split‐barrel sampler is driven into the soil a distance of 18 inches by a 140‐pound hammer falling 30 inches. The number of blows required to drive the sampler through a 12‐inch interval is termed the Standard Penetration Test

(SPT). This value can be used as a qualitative indication of the in‐place relative density of noncohesive soils. In a less reliable way, it also indicates the consistency of cohesive soils.

Representative soil samples were also obtained from selected depths in Boring B‐01 by means of the

Shelby tube sampling procedure in general accordance with ASTM D1587. For this procedure, a thin‐ walled, steel, seamless tube with a sharp cutting edge was pushed hydraulically into the soil, and a relatively undisturbed soil sample was generally obtained, sealed at the site, and transported to the laboratory for classification and testing. The samples were obtained from an off‐set auger probe at the sample location.

Rock Coring

Rock coring techniques using a NQ‐diamond drilling bit were utilized to advance the Boring B‐01 beyond auger refusal to evaluate the underlying site bedrock, as well as to install the inclinometer into competent materials.

Please note that water is introduced into the borehole during the rock coring process; therefore, where groundwater seepage was not encountered prior to auger refusal, the borings were considered to be dry (i.e. groundwater seepage not encountered). Boring B‐02 was backfilled with the spoils generated during drilling, following completion of drilling operations, while an inclinometer was installed and grouted in Boring B‐01. Excess spoils were spread out in approved grassy areas of the site. Some post‐

ECS Project No. 40:2492 Page 5 drilling settlement should be expected and may require future maintenance to fill in the test locations and avoid a tripping hazard. This maintenance is not included in our scope.

A field log of the soils and rock encountered in the borings was maintained by the ECS representative.

After recovery, each sample was removed from the sampler and visually classified. Representative portions of each sample were then sealed in bags and rock core boxes and transported to our laboratory for further visual examination.

Inclinometers

Following completion of Boring B‐01, inclinometer casing was installed to monitor slope movement. A grooved inclinometer casing was installed to be utilized for measurements of inclination manually by portable inclinometer probe. The inclinometer was installed to an approximate depth of 36 feet. The inclinometer casing was tipped into approximately 10 feet of bedrock.

Three sets of baseline measurements were collected to establish an initial soil profile. Inclinometer readings were obtained at 2‐foot increments within the installed casing. Subsequent measurements were collected as noted previously and used to estimate lateral soil movements. Monitoring was performed by taking measurements of the change in inclination of the sensors relative to the baseline position of the sensors. Following baseline readings, inclinometer monitoring of adjacent soils should generally be performed on a monthly basis for the initial five months, then performed twice during construction. A final reading will be performed one year following construction.

The purpose of the inclinometers is to monitor the failed slope for additional movement during the design and final repair phases of the landslide. Any observed movements are to be reported immediately for discussion and possible additional temporary reinforcement measures. Inclinometer readings to date have been reported in daily field reports under separate cover. At the time of this report, significant movement indicative of additional slope instability was not observed within the inclinometer. ECS will continue inclinometer readings during and after construction to monitor slope movements until the project team deems it appropriate to discontinue monitoring.

Laboratory Testing Program

Representative soil samples were selected and returned to our laboratory to check field classifications and to estimate pertinent engineering properties. The laboratory testing program included visual classifications, moisture content tests, Atterberg limits, grain size analysis, undisturbed direct shear, and a moisture‐density relationship (Proctor) testing on a bulk soil sample. Data obtained from the laboratory tests are included on the respective boring logs or on separate sheets in the Appendix of this report.

Each soil sample was classified on the basis of texture and plasticity in accordance with the Unified Soil

Classification System (USCS). The group symbols for each soil type are indicated in parentheses followed by the soil descriptions on the boring logs. A brief explanation of the Unified System is included with the

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Reference Notes for the Boring Logs in the Appendix. The various soil and rock types were grouped into the major zones noted on the boring logs. The stratification lines designating the interfaces between earth materials on the boring logs and profiles are approximate; in situ transitions may be gradual, rather than distinct.

The soil samples will be retained in our laboratory for a period of 60 days after which they will be discarded unless other instructions are received as to their disposition.

EXPLORATION RESULTS

Regional Geology

Geology

Based on the WVGES Interactive Geologic Map WVGES Interactive Geologic Map

(https://atlas2.wvgs.wvnet.edu/portal/apps/webappviewer), the project site is underlain by the

Quaternary Alluvium (Qal). The Quaternary Alluvium consists deep unconsolidated alluvial deposits of sand, gravel, silt, and clay.

A copy of the Regional Geologic Maps (Figure 3 of 7) is included in the Appendix of this report.

Landslide Susceptibility Mapping

We also reviewed the information contained on the West Virginia Landslides and Slide‐Prone Areas, Clarksburg, WV Quadrangle map, complied by the Peter Lessing and Bryon R. Kulander, dated 1976.

Based on the information reviewed, the site is considered “Relatively Stable Ground.”

As defined in West Virginia Landslides and Slide‐Prone Areas, Clarksburg, WV Quadrangle, Relatively

Stable Ground are areas judged to have very low susceptibility to landslides and contain no known evidence of instability.

A copy of the Landslide Susceptibility Map (Figure 4 of 7) is included in the Appendix of this report.

Mine Subsidence Risk Mapping

In addition to the geologic mapping of the site, we also reviewed the information contained on the West

Virginia Geologic and Economic Survey WVGES (http://www.wvgs.wvnet.edu/). Based on the information reviewed, the project site appears to be located outside the limits of mapped mining operations and does not appear to have been affected by historic mining. A site‐specific mining study was not included as part of our scope of services.

A copy of the WVGES Underground and Surface Mine Map (Sheet 5 of 7) is included in the Appendix of this report.

ECS Project No. 40:2492 Page 7

Soil & Bedrock Conditions

A surficial layer of topsoil with an approximate thickness 6 inches was encountered at each boring location. The topsoil thickness measurements noted by the driller were performed over widely spaced locations. In addition, properly measuring the topsoil thickness within a borehole is difficult and can vary depending on one’s interpretation of topsoil, and therefore such measurements can be subject to interpretive disagreements and quantity disputes. In some cases, a distinct topsoil layer thickness

(transition) is not easily discernible, particularly where site has been disturbed by past development and grading. In these cases, underlying soils containing organic material may also be present, which are not readily identifiable as distinct topsoil. The topsoil thickness can also be significantly greater where trees and heavy brush are present.

Accordingly, these measurements should not be solely relied on for accurate construction quantity estimates. In addition, topsoil stripping of the site beyond the surface topsoil may be necessary in some areas, particularly where trees and heavy brush are present, to remove all soils containing high concentrations of organics. We recommend the Contractor, and/or others, make their own detailed observations and measurements, prior to bidding and construction, to determine the quantities, costs and efforts that will be required for topsoil and other existing surface material (i.e., asphalt pavement, concrete slabs, foundations, etc.) removal and associated replacement with appropriate suitable fill materials.

Existing fill/disturbed soils were not encountered in the borings performed. Natural soils were encountered beneath the surficial groundcover generally consisted of SANDY LEAN CLAY (USCS

Classification CL), SILTY SAND (SM), and SILTY GRAVEL WITH SAND (GM), with varying amounts of Sand, Silt, and Gravel. The natural soils exhibited SPT N‐values ranging between 7 to 54 bpf, corresponding to firm to very hard consistencies for the fine‐grained soils and loose to very dense consistencies for the coarse‐grained soils.

Weathered rock materials were encountered directly below the natural soils in each of the borings at an approximate depth of 14 feet in B‐01 and 4 feet in B‐02. Materials classified as weathered rock generally exhibited N‐values in excess of 60 blows per foot of penetration. The samples classified as weathered rock exhibited very hard in‐situ consistencies and maintained a relic rock structure, while breaking down into soil size particles by hand with little effort. Auger refusal was encountered at an approximate depth of 24.5 feet and 5 feet in Borings B‐01 and B‐02, respectively.

Following auger refusal, Boring B‐01 was extended an additional 10 feet via rock coring techniques to sample and evaluate the underlying bedrock, and to install the inclinometer into competent materials.

Based on visual observation of the recovered rock samples, the project site is underlain by moderately to highly weathered Siltstone bedrock. The recovered samples generally had a Rock Quality Designation

(RQD) of 0 to 42%. The recovery for each individual run ranged from 61% to 92%.

Unconfined compressive strength testing was performed on a rock core sample obtained from Boring B‐

01. The following table summarizes the compressive strength test results:

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Table 1: Compressive Strength of Rock Core Samples

Boring Sample Number Sample Depth (ft.)

Compressive Strength

(psi)

B‐01 RC‐2 31‐32 1,370

Groundwater Conditions

Observations for groundwater were made during sampling and upon completion of soil drilling operations in each of the boring locations. During drilling operations, water was not introduced into the boreholes during soil drilling, and the groundwater position can often be determined by observing water flowing into or out of the boring. Groundwater was encountered during drilling operations in Borings B‐

01 at an approximate depth of 20 feet bgs. Groundwater was not encountered within the depths explored in Boring B‐02. Perched groundwater conditions may also be encountered.

Perched water conditions are common at the soil/weathered rock interface, where surface water becomes trapped on top of the less permeable rock. Perched water within granular seams within the natural soils, at the fill/natural soil interface, or within the landslide‐disturbed materials is also common.

It is possible that water seepage and accumulation may be observed in deeper excavations allowed to remain open for an extended duration.

The highest groundwater observations are normally encountered in late winter and early spring;

therefore, our groundwater observations in our most recent boring are expected to be below the seasonal maximum water table. Variations in the elevation of the groundwater table should be expected, depending upon variations in precipitation, evaporation, surface water runoff, and other factors not immediately evident at the time this geotechnical exploration was performed.

DESIGN RECOMMENDATIONS

In an effort to provide reasonable concepts for the repair of the existing landslide, we have analyzed the following concepts which will provide the necessary long‐term factor of safety of 1.5. The following table summarizes the concepts analyzed for the existing landslide at the site.

Table 2: Summary of Repair Concepts

Concept Reinforcement Measures Factor of Safety (FS)

Reinforced Soil Slope (RSS) Geogrid: Miragrid 3XT, 15 ft lengths spaced every 2 vertical feet 1.5

Rock Buttress R3/R4 Stone & Geogrid: Miragrid 3XT, 5 ft lengths spaced every 5 vertical feet 1.5

Geopier SRT® system

SRT Elements: 4‐foot horizontal spacing across and

6‐foot spacing up the slope; tipped a minimum of 2 feet into weathered rock

1.5

ECS Project No. 40:2492 Page 9

The following sections present soil parameters and concepts for use in determining the most desirable option for landslide repair.

Global Stability

Overview

The landslide is located along a southwestern facing, steeply sloping slope with low‐lying vegetation and sporadic small trees. Based on the Exhibit of Topographic Survey, the slope gradient of the landslide is approximately 1.7 feet horizontal to one foot vertical (1.7H:1V), transitioning to roughly 4.5H:1V above the landslide. A global stability analyses was performed along a representative, topographic cross‐ section which includes the landslide area and the overlying slope above.

Design Parameters Used for Stability Analysis

The analyzed Section A‐A’ was developed from the boring data and the Exhibit of Topographic Survey

(299‐23), prepared by Allegheny Surveys, Inc., dated October 5, 2023.

The soil strength parameters used for our analyses were developed from our interpretation of the

Standard Penetration Test (SPT) data, Atterberg Limit and direct shear test data, and our experience with similar soils on past projects. Cohesion was generally neglected for the materials encountered unless actual laboratory data was available. The following table outlines our soil strength parameters used in our current slope stability analyses.

Table 3: Summary of Assumed Soil Strength Parameters

Soil Designation Soil Description Moist Unit Weight

Friction Angle, Ø

Cohesion

1 New Fill 130 pcf 30° 0 psf

2 R3 or R4 Stone 140 pcf 39° 0 psf

3 Firm Lean Clay 119.4 pcf* 26°* 50* psf

4 Loose Silty Sand 130 pcf 30° 0 psf

5 Medium Dense Silty Gravel with Sand 135 pcf 30° 0 psf

6 Weathered Rock 140 pcf 35° 0 psf

7 Bedrock 140 pcf 40° 0 psf

*Based on the results of laboratory testing

Laboratory test results for the direct shear test of the on‐site soils indicated a phi angle of 33.4 degrees.

However, based on our experience with similar soils, we have conservatively modeled the existing site soils with a phi angle of 26 degrees to account for site variability. Groundwater was encountered between approximate depths of 20 feet bgs in Boring B‐01; however, perched groundwater conditions may also exist. The global stability analysis was performed with an assumed water level consistent with the data obtained in our borings. Perched water conditions within the slope are considered likely and

ECS Project No. 40:2492 Page 10 were included in our analysis using the conservative water level readings encountered and modeled based on the drainage provisions to be included in the fill foundation bench.

The global stability analyses were performed using the Rocscience Slide 2.0 two‐dimensional computer global stability program. The factor of safety against global instability computed by the program is defined as the ratio of the sum of the moments, or forces, resisting and driving along a specified potential failure surface. Hence a factor of safety (FS) greater than 1.0 indicates a stable structure, while a factor of safety less than 1.0 indicates a potentially unstable structure. Because of the margin of uncertainty regarding soil parameters and groundwater conditions in situ, we consider factors of safety of 1.5 as the minimum adequate factor of safety for the permanent slopes at the subject site.

Analysis and Results

Section A‐A’ was developed through the approximate center of the landslide area utilizing the data from our borings and the Exhibit of Topographic Survey drawing. The location of the cross section is shown on the Exploration Location Diagram (Figure 6 of 7) included in the Appendix. The proposed grades along these profiles will consist of the placement of new structural fill used to rebuild the failed slope. The existing subgrade is generally underlain by disturbed materials, natural soils, weathered rock, and bedrock.

Final output from the global stability analysis performed, including a plot of the lowest factor of safety calculated from all of the failure surfaces analyzed for each cross‐section, is included in the Appendix of this report.

Reinforced Soil Slope (RSS) – Option 1

Multiple layers of geo‐grid with lengths of 15 feet long were incorporated into the concept design to preclude the shallow seated failures. The geo‐grid used for our analysis possessed a published value for long‐term tensile strength of 1,403.5lbs/ft (Miragrid 3XT or equivalent) and was applied at 100% coverage along the slope for each layer. The vertical spacing of the grid for the concept design was every

2 vertical feet. Please note that this RSS design option is presented as a “proof of concept” only. ECS will provide final design details as part of our Reinforced Soil Slope Design Drawing set, if this option is selected.

The concept geo‐grid spacing for Section A‐A’ addresses global stability requirements only and was not intended to meet specific standards or requirements. The 2‐foot grid spacing presents a higher potential for surficial sloughing between the geo‐grid layers. Based on the stability results, the slope is expected to be stable in its current configuration from an overall global perspective; however, some surficial sloughing off the face of the slope should be expected. At a minimum, the face of the new slope should be tracked‐in with a dozer prior to seeding. Erosion control blankets or matting could also be utilized to reduce soil movement at the slope face. In order to reduce the need for increased maintenance of the slope face, ECS recommends constructing the RSS with secondary grids as a wrapped face slope.

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Rock Buttress – Option 2

We performed a sensitivity analysis to evaluate the lowest phi angle needed to achieve a factor of safety of 1.5. Based on our analysis, the fill materials used to repair and reconstruct the existing slope will need to consist of R3 or R4 stone and possess a minimum friction angle identified of 39°. Approximate 8 feet of native clay materials should be undercut above the weathered rock materials and replaced with compacted R3 or R4 stone. In addition, multiple layers of geo‐grid with lengths of 5 feet long were incorporated into the concept design to achieve the required factor of safety. The geo‐grid used for our analysis possessed a published value for long‐term tensile strength of 1,403.5lbs/ft (Miragrid 3XT or equivalent) and was applied at 100% coverage along the slope for each layer. The vertical spacing of the grid for the concept design was every 5 vertical feet.

Geopier SRT® system ‐ Option 3

The Geopier SRT® system is a solution for the stabilization of new slopes and active slides up to 15 feet deep. For this process, slide material is either replaced or reused and the slope face is reestablished. The plate elements are then driven through the unstable soil into competent materials. Geopier performed a sensitivity analysis to evaluate the lowest phi angle needed to achieve a factor of safety of 1.5. Based on the results, a preliminary element spacing of 4 feet horizontal by 6 feet vertical with an approximate 2‐ foot embedment into weathered rock. Considering the approximate depth to weathered rock is 15 feet at the Boring B‐01 location and 5 feet in the Boring B‐02 location, we estimate pile lengths will be on the order of 7 to 17 feet long.

Slope Construction Considerations

We anticipate materials to repair the slope will be imported. All materials proposed for use in constructing the site fill slopes should be specifically observed, tested, and approved by the

Geotechnical Engineer at the time of construction. The new fill material will need to possess a minimum friction angle identified in Table 3: Summary of Assumed Soil Strength Parameters. Full‐time observation and compaction testing by the Geotechnical Engineer of record or a qualified testing agency will be required to monitor that the slope is constructed as designed. Additional laboratory testing during construction of the slope, including, but not limited to, Modified Proctor, Classification, Direct Shear, and Slake Durability testing will be required to confirm that the materials utilized in slope construction meet or exceed the soil parameters used for design. We can assume no liability for the performance of any slope not constructed under our full‐time observation and without the prior approval, including all required laboratory testing, of all materials utilized in slope construction for conformance with the required shear strength properties outlined herein.

Due to the time requirements inherent in the ASTM test methods for Modified Proctor, direct shear, Slake durability, and classification testing, and the order in which they need to be performed, it has been our experience that a delay of about 3 to 4 weeks may occur in order to complete the recommended testing to confirm design assumptions. We recommend that project schedules, authorizations dates, and budgets account for these delays in order to prevent earthwork contractor down‐time.

ECS Project No. 40:2492 Page 12

Fill foundation benches should be constructed along the base of all new fill slopes constructed at the site. Based on the results of the test borings performed at the site and our slope stability analyses, the depth of the fill foundation benches should be a minimum of 5 feet bgs and should bear in existing weathered rock materials, as approved by the geotechnical engineer or their approved field representative. Construction‐phase DCP testing should be performed along fill foundation bench excavations to confirm compliance with the intent of the slope benching. Fill foundation benches (toe keys) and intermediate benches should be constructed with subsurface drains which outlet beyond the limits of new fill. Particle sizes for structural fill placed within fill foundation benches shall not exceed 6 inches in any dimension. Slope Construction details are included in the Appendix on Sheet D‐1.

Recommended locations for fill foundation benches are depicted on the Exploration Location Diagram

(Figure 6 of 7) in the Appendix of this report.

Any site utilities, including SWM piping, which will be installed within the footprint of the repair must be installed prior to the start of slope construction. Failure to do so will result in extensive (and costly) re‐work to the slope.

Subgrade Preparation and Earthwork Operations

The subgrade preparation operations should consist of stripping any vegetation, rootmat, topsoil, asphalt, and any other soft or unsuitable material (slide debris) from the proposed fill areas. We recommend that site stripping depths account for the topsoil of any deeper rootball systems (if present) and possible variations in topsoil thickness between boring locations. The stripping area should be extended at least 10 feet, where possible, beyond the planned limits of the proposed embankments.

The limits discussed in this paragraph define the expanded fill slope footprint, including the toe of slope.

After stripping to the desired grade, performing all necessary rough grading, and prior to any structural fill placement, the exposed soils should be carefully examined by the Geotechnical Engineer or their authorized representative to identify any localized loose, yielding, or otherwise unsuitable materials.

After examining the exposed soils, loose or yielding areas can be identified by proofrolling with an approved piece of equipment, such as a loaded dump truck, having an axle weight of at least 10 tons.

Any soft or unsuitable materials encountered during this proofrolling should be removed and replaced with an approved backfill compacted according to the criteria in the section entitled Fill Placement.

Considering the location of the site and understanding that proofrolling may be difficult, at a minimum, the stripped subgrade should be evaluated by the Geotechnical Engineer or approved testing agency using visual observation, DCP, and/or probe methods, etc., prior to new fill placement.

It is recommended that the preparation of any areas to receive structural fill should be observed on a full‐time basis. These observations should be performed by the Geotechnical Engineer, or their authorized representative, to document that all unsuitable materials have been removed, and that the subgrade is suitable for support of the structural fills.

ECS Project No. 40:2492 Page 13

We strongly recommend against utilizing soil bridging lifts to span over soft fill subgrade soils within the proposed development limits. Alternatively, we recommend the use of a reinforcing geotextile or geogrid where excessively soft materials are encountered and cannot be effectively removed by undercutting. These materials should be covered by a minimum of one (1) foot of select granular materials. Alternate reinforcing or stabilization of soft subgrades should be determined in the field by the Geotechnical Engineer.

Fill Placement

The stability of Section A‐A’ is highly dependent upon the materials used to reconstruct the slope. It is very difficult, if not impossible, to determine the friction angle through visual observation. Visual observation is generally limited to soil classification and relative comparison to known lab data. Any materials proposed to reconstruct the slope will need to be approved prior to placement at the site and someone will need to be on site during the trucking operations with the authorization to reject truck‐loads of materials used if the materials visually do not appear to match the design requirements.

Fill materials used to construct for the new fill slopes will need to meet or exceed the classification and soil strength properties used in the slope stability analyses. Suitable materials for use as new fill should generally consist of an approved material, free of organic matter, debris, cobbles, and rock fragments greater than 6 inches. Placement of rock fill is discussed later in this report. The structural fill should also have a Liquid Limit and Plasticity Index less than or equal to 40 and 20, respectively. Unacceptable fill materials include topsoil and organic materials (OH, OL), and high plasticity silt (MH) or clay (CH).

As previously mentioned, full time observation and compaction testing by the Geotechnical Engineer or qualified testing agency will be required to monitor that the slope is constructed as‐designed. Additional laboratory testing during construction of the slope, including, but not limited to, Proctor, classification, and direct shear will be required to confirm that the materials utilized in slope construction meet or exceed the soil parameters used for design. Samples of off‐site borrow material to be placed as new fill should be submitted to the site testing agency at least 2 weeks prior to importing the material to the site to allow for appropriate lab testing to determine if the material meets the design criteria.

The on‐site soils may require moisture content adjustments, such as the application of discing or other drying techniques or spraying of water to the soils prior to their use as controlled fill materials. The planning of earthwork operations should recognize and account for these efforts and increased costs.

The suitability of the off‐site materials for use as new fill and their impact on overall stability should be further evaluated in the field at the time of construction.

Fill materials should be placed in lifts not exceeding 8‐12 inches in loose thickness and moisture conditioned to within ±2 percentage points of the optimum moisture content when compaction equipment consists of a Caterpillar 815 segmented‐pad roller, or approved equivalent, and the compacted soils are relatively homogeneous. Thinner lifts may be required if larger rock fragments are contained within the fill materials or if smaller, remote‐controlled, or hand‐operated compaction

ECS Project No. 40:2492 Page 14 equipment is utilized. The soils should be compacted to a minimum of 95% of the maximum dry density obtained in accordance with ASTM Standard D 1557, Modified Proctor Method.

The expanded footprint of the fill areas should be well‐defined, including the limits of the fill zones at the time of fill placement. Grade control should be maintained throughout the fill placement operations.

All fill operations should be observed on a full‐time basis by a qualified soil technician to determine that the specified compaction requirements are being met. A minimum of one compaction test per 500 square feet of area should be tested in each lift placed. The elevation and location of the tests should be clearly identified at the time of fill placement.

Compaction equipment suitable to the soil type used as fill should be used to compact the fill material.

Theoretically, any equipment type can be used as long as the required density is achieved. Ideally, a smooth, steel drum roller would be most efficient for compacting and sealing the surface soils. All areas receiving fill should be graded to facilitate positive drainage of any free water associated with precipitation and surface runoff.

If a smooth‐drum roller is utilized, the surface of each completed lift should be scarified prior to the placement of the next lift of fill to reduce the potential for the creation of slippage planes within the fill mass.

Fill materials should not be placed on soils that are frozen. All frozen soils should be removed prior to continuation of fill operations. Borrow fill materials should not contain frozen materials at the time of placement. All frost‐heaved soils should be removed prior to placement of fill or stone.

Geotechnical Construction Details

The slope repairs should incorporate the Geotechnical Construction Details shown on Sheet D‐1 in the

Appendix of this report. The following paragraphs outline construction considerations for the details included for this project.

Typical Fill Foundation Bench (Detail 1/Sheet D‐1): Fill foundation benches should be constructed along the base of the slope, at the approximate locations shown on the formal drawing package (issued under separate cover). Based on the results of the test borings performed at the site and our slope stability analyses, the depth of the fill foundation benches should be a minimum of 5 feet bgs and should bear in weathered rock materials, as approved by the Geotechnical Engineer or their approved field representative. Fill foundation benches should be constructed with subsurface drains which outlet beyond the limits of new fill. Particle sizes for structural fill placed within fill foundation benches shall not exceed 6 inches in any dimension, with the exception of the rock buttress option.

Typical Intermediate Fill Bench (Detail 2/Sheet D‐1): Intermediate fill benches should be constructed along the mid‐point of all new fill slopes constructed at the site, at the approximate locations shown on the formal drawing package (issued under separate cover). The width of the intermediate fill benches should be a minimum of 8 feet and should be excavated to bear on medium dense or hard residual soils, ECS Project No. 40:2492 Page 15 as approved by the Geotechnical Engineer or their approved field representative. Intermediate fill benches should be constructed with subsurface drains which outlet into subsurface drains or beyond the limits of new fill. Particle sizes for structural fill placed within intermediate fill benches shall not exceed 6 inches in any dimension, with the exception of the rock buttress option.

Typical Compaction Bench (Detail 3/Sheet D‐1): Compaction benches should be constructed everywhere new fill is placed against and existing slope at the subject site. The width of the compaction benches should be a minimum of 4 feet as a bond between existing residual soils and new, structural fill.

Particle sizes for structural fill placed within intermediate fill benches shall not exceed 6 inches in any dimension, with the exception of the rock buttress option.

Typical Subsurface Drain (Detail 4/Sheet D‐1): Subsurface drains should be installed along fill foundation and intermediate fill benches, along streams or waterways that will be covered by new fill placement, at seepage areas observed before or exposed during excavation, and as necessary to control groundwater. Perforations in subsurface drains shall be placed upward to collect and outlet water into the site stormwater system or beyond the limits of new fill slopes. The need for additional drains should be evaluated in the field based on actual conditions at the time of construction.

Temporary and Permanent Slopes

Our scope of services did not include specific analysis of proposed temporary site slopes. However, in general, temporary excavation slopes cut in the native soils should be no steeper than 1H:1V or as indicated by OSHA protocol. Temporary fill slopes constructed of site native silty or clayey soils should be limited to a maximum gradient of approximately 2.5H:1V. The temporary slopes should also be thoroughly vegetated to help reduce erosion of the surficial soils. During temporary excavation, we recommend that the existing on‐site soils be examined and sloped back at gradients in accordance with

OSHA 29 CFR 1926

Permanent slopes should be constructed in accordance with the final design drawings, as specifically analyzed by ECS. At a minimum, the face of all new fill slopes should be tracked‐in to reduce erosion.

The potential for surface erosion of earth slopes should be reduced by establishing deep rooted vegetation on the slope face as soon as the final slope geometry is achieved. Small landscape berms (< 5 feet in height) may be as steep as 1H:1V but should be compacted as structural fill and thoroughly vegetated immediately upon completion.

General Construction Considerations

Precautionary measures should be taken to document that preparation of the subgrade and foundation bearing surfaces are accomplished by the recommended procedures. These precautions are necessary, as the materials, observed in our borings, are moisture and disturbance sensitive, and will become weakened if water intrudes into the foundation excavations. Therefore, we recommend that all excavations be properly dewatered. The site should be graded such that surface water runoff is directed away from the excavations.

ECS Project No. 40:2492 Page 16

The surface of the site should be kept properly graded in order to enhance drainage of the surface water away from the proposed foundation areas during the construction phase. We recommend that an attempt be made to enhance the natural drainage without interrupting its pattern. The surficial soils contain fines which are considered moderately to highly erodible. The Contractor should provide and maintain positive site drainage during earthwork operations to help maintain the integrity of the surficial soils. All erosion and sedimentation shall be controlled in accordance with sound engineering practice and current local requirements.

CLOSING

This report has been prepared to aid in the evaluation of this site. The report scope is limited to this specific project and the location described.

This report was prepared for the sole use of CB Design Group and their consultants, the only intended beneficiaries of our work. The scope is limited to this specific project and locations described herein and our description of the project represents our understanding of the significant aspects relative to it. No other party should rely on the information contained herein without prior written consent of ECS Mid‐

Atlantic, LLC. We cannot be responsible for the evaluations, opinions, interpretations or conclusions of others based on our data.

We appreciate this opportunity to be of assistance to CB Design Group on this project. If you have any questions regarding the information contained in the accompanying report, or if we may be of further assistance to you in any way during this project, please do not hesitate to contact us.

The information contained in this report is provided for conceptual and budgetary purposes only and is not intended to represent final “For Construction” drawings or details. This report and associated figures does not contain full, “For Construction” level information. Final repair drawings will need to be prepared for the site, prior to construction.

Respectfully, ECS MID‐ATLANTIC, LLC

Jessica Maier, G.I.T. Michael P. Krepsik, P.E Geotechnical Project Manager Geotechnical Department Manager/Principal jmaier@ecslimited.com mkrepsik@ecslimited.com

40 Data/Geotechnical/{eProjects}/2401 ‐ 2500/2492 (Louis A. Johnson VA Landslide, Clarksburg, WV)/e‐Report Prep/40.2492 RSE.doc

ECS Project No. 40:2492 Page 17

APPENDIX

Reference Notes for Boring Logs

Reference Notes for Rock Cores

Boring Logs B‐01 and B‐02

Laboratory Testing Summary (2 pages)

Atterberg Limits (2 pages)

Grain Size Analysis (4 pages)

Proctor Test Results (1 page)

Direct Shear Results (1 pages)

Unconfined Compressive Strength Testing (1 page)

Global Stability Analysis

Existing Conditions (1 page)

RSS – Concept 1 (1 page)

Rock Buttress – Concept 2 (1 page)

Geopier SRT® system – Concept 3 (1 page)

Figures:

Site Location Diagram (Figure 1 of 7)

USGS Topographic Map (Figure 2 of 7)

Regional Geologic Map (Figure 3 of 7)

Landslide Susceptibility Map (Figure 4 of 7)

WVGES Historic Mine Map (Figure 5 of 7)

Exploration Location Diagram (Figure 6 of 7)

Cross Section A‐A’ (Sheet 7 of 7)

Geotechnical Construction Details (D‐1)

REFERENCE NOTES FOR BORING LOGS

MATERIAL1,2

1Classifications and symbols per ASTM D 2488-17 (Visual-Manual Procedure) unless noted otherwise.

2To be consistent with general practice, “POORLY GRADED” has been removed from GP, GP-GM, GP-GC, SP, SP-SM, SP-SC soil types on the boring logs.

3Non-ASTM designations are included in soil descriptions and symbols along with ASTM symbol [Ex: (SM-FILL)].

4Typically estimated via pocket penetrometer or Torvane shear test and expressed in tons per square foot (tsf).

5Standard Penetration Test (SPT) refers to the number of hammer blows (blow count) of a 140 lb. hammer falling 30 inches on a 2 inch OD split spoon sampler required to drive the sampler 12 inches (ASTM D 1586). “N-value” is another term for “blow count” and is expressed in blows per foot (bpf). SPT correlations per 7.4.2 Method B and need to be corrected if using an auto hammer.

6The water levels are those levels actually measured in the borehole at the times indicated by the symbol. The measurements are relatively reliable when augering, without adding fluids, in granular soils. In clay and cohesive silts, the determination of water levels may require several days for the water level to stabilize. In such cases, additional methods of measurement are generally employed.

7Minor deviation from ASTM D 2488-17 Note 14.

8Percentages are estimated to the nearest 5% per ASTM D 2488-17.

Reference Notes for Boring Logs (09-02-2021).doc © 2021 ECS Corporate Services, LLC. All Rights Reserved

COHESIVE SILTS & CLAYS

UNCONFINED

COMPRESSIVE

STRENGTH, QP4

<0.25

0.25 - <0.50

0.50 - <1.00

1.00 - <2.00

2.00 - <4.00

4.00 - 8.00

>8.00

SPT5

(BPF)

CONSISTENCY7

(COHESIVE)

GRAVELS, SANDS & NON-COHESIVE SILTS

SPT5

DENSITY

<5 5 - 10

11 - 30 31 - 50

>50

Very Loose Loose

Medium Dense Dense

Very Dense

WATER LEVELS6

RELATIVE

AMOUNT7

Trace

With

Adjective (ex: “Silty”)

COARSE

GRAINED

(%)8

<5

FINE

GRAINED

(%)8

<5

DRILLING SAMPLING SYMBOLS & ABBREVIATIONS

PARTICLE SIZE IDENTIFICATION

DESIGNATION PARTICLE SIZES

Hollow Stem Auger Power Auger (no sample) Bulk Sample of Cuttings Wash Sample Shelby Tube Sampler Split Spoon Sampler

Rock Quality Designation % Rock Sample Recovery % Rock Core, NX, BX, AX Rock Bit Drilling Pressuremeter TestSS

ST

WS

BS

PA

HSA

RQD

PM

RD

RC

REC

Boulders Cobbles

Gravel:

Sand:

Silt & Clay (“Fines”) Fine Medium

Coarse Fine Coarse

0.074 mm to 0.425 mm (No. 200 to No. 40 sieve) <0.074 mm (smaller than a No. 200 sieve)

0.425 mm to 2.00 mm (No. 40 to No. 10 sieve)

2.00 mm to 4.75 mm (No. 10 to No. 4 sieve)

4.75 mm to 19 mm (No. 4 sieve to ¾ inch) ¾ inch to 3 inches (19 mm to 75 mm) 3 inches to 12 inches (75 mm to 300 mm) 12 inches (300 mm) or larger

>50 31 - 50 16 - 30

9 - 15 5 - 8 2 - 4 <2

Very Hard Hard

Very Stiff

Stiff Firm Soft

Very Soft

ASPHALT

CONCRETE

GRAVEL

TOPSOIL

VOID

BRICK

AGGREGATE BASE COURSE

GW

GP

GM

GC

SW

SP

SM

SC

ML

MH

CL

CH

OL

OH

PT

WELL-GRADED GRAVEL

gravel-sand mixtures, little or no fines

POORLY-GRADED GRAVEL

gravel-sand mixtures, little or no fines

SILTY GRAVEL

gravel-sand-silt mixtures

CLAYEY GRAVEL

gravel-sand-clay mixtures

WELL-GRADED SAND

gravelly sand, little or no fines

POORLY-GRADED SAND

gravelly sand, little or no fines

SILTY SAND

sand-silt mixtures

CLAYEY SAND

sand-clay mixtures

SILT

non-plastic to medium plasticity

ELASTIC SILT

high plasticity

LEAN CLAY

low to medium plasticity

FAT CLAY

high plasticity

ORGANIC SILT or CLAY non-plastic to low plasticity

ORGANIC SILT or CLAY high plasticity

PEAT

highly organic soils

WL (First Encountered)

WL (Completion)

WL (Seasonal High Water)

WL (Stabilized)

FILL POSSIBLE FILL…