Geotech Rpt.pdf

Report of Geotechnical Exploration

TN ERFO FS CHRKE804 2020-2(1)

Cherokee National Forest, Tennessee

Briar Creek Road(FSR188) – Ranger District – Unaka

Paint Mountain Road(FSR54) – Ranger District – Unaka

Flatwoods Road(FSR87) – Ranger District - Watauga

Prepared for:

U.S. Federal Highway Administration (FHWA) Eastern Federal Lands Highway Division

September 25, 2024

REPORT OF GEOTECHNICAL EXPLORATION

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Table of Contents

1.0 INTRODUCTION

2.0 GEOLOGIC SETTING

3.0 SUBSURFACE EXPLORATION PROGRAM

3.1 SUBSURFACE EXPLORATION

3.2 FIELD TESTING AND SAMPLING

3.3 LABORATORY TESTING

4.0 SUBSURFACE CONDITIONS

4.1 GENERAL

4.2 BRIAR CREEK

4.2.1 MP 599 (Borings 599-A, 599-B)

4.2.2 MP 633 (Borings 633-A, 633-B)

4.3 FLATWOODS

4.3.1 MP 659 (Borings 659-A, 659-B)

4.3.2 MP 660 (Borings 660-A, 660-B, 660-C)

4.4 PAINT MOUNTAIN

4.4.1 MP 590 (Borings 590-A, 590-B, B-2)

5.0 ANALYSIS AND RECOMMENDATIONS

5.1 GENERAL

5.2 SEISMIC HAZARD ANALYSIS

5.3 SLOPE STABILIZATION RECOMMENDATIONS

5.3.1 Briar Creek

5.3.2 Flatwoods

5.3.3 Paint Mountain

5.4 MSE RETAINING WALLS

5.5 CONSTRUCTION CONSIDERATIONS

5.5.1 General Considerations

5.5.2 Wall Construction

6.0 REFERENCES

7.0 CLOSING

LIST OF TABLES

Table 1. Summary of Soil Laboratory Test Results Table 2. Summary of Rock UCS Tests Table 3. Summary of Borings Table 4. Soil Parameters for MSE Walls Table 5. Existing Subsurface Soil Parameters Table 6. Summary of External Stability Analysis - Static Table 7. Summary of External Stability Analysis - Seismic

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LIST OF FIGURES

Figure 1. Aerial View

LIST OF APPENDICES

Appendix A. Exploration Location Plans Appendix B. Boring Logs Appendix C. Laboratory Test Results Appendix D. Subsurface Profiles Appendix E. MSE Wall Analyses Appendix F. Geocell Information Appendix G. Site and Rock Core Photographs

Introduction

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1.0 INTRODUCTION

The United States Department of Transportation, specifically the Federal Highway Administration (FHWA)

– Eastern Federal Lands Highway Division, is planning to repair storm and flood damage to five locations in the eastern part of the Cherokee National Forest in Tennessee. The five slide locations are located in areas designated as Briar Creek Road (FS 188) in Washington Co., Flatwoods Road (FS 87) in Sullivan Co., and Paint Mountain Road (FS 54) in Greene Co. The damage along the five locations generally includes upslope and/or downslope landslides and slope instabilities. Figure 1 shows the approximate locations of the damaged areas.

Figure 1. Aerial View (Google Maps, 2024)

Tennessee

Virginia

North Carolina

Geologic Setting

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2.0 GEOLOGIC SETTING

The three areas, Briar Creek, Flatwoods, and Paint Mountain are located in the Appalachian Ridge and Valley Physiographic Region. This region consists of numerous linear parallel ridges and valleys that trend northeast to southwest, the general direction of the entire Appalachian range. Most of these ridges are low, but some of the higher ones are commonly called mountains. The overburden soils generally consist of relatively thin deposits of alluvial, colluvial, and material weathered from the parent bedrock.

These soils are comprised of clay, silt, sand, and gravel along with weathered fragments of the parent rock. Slopes tend to be steep with ribbed topography reflecting underlying bedrock.

The Geologic Map of Tennessee, East Sheet (Tennessee Department of Conservation, 1966) indicates that the Flatwoods project site is underlain by Ordovician-age Sevier shale consisting of calcareous, bluish-gray shale; with thin gray limestone layers; sandstone, siltstone, and locally, conglomerate to the east. The Briar Creek area is underlain by Cambrian-age dark greenish-gray, silty and sandy, micaceous shale; with numerous layers of medium-grained, feldspathic, thinly bedded sandstone and gray feldspathic sandstone, arkose, conglomerate, graywacke, siltstone and shale. The Paint Mountain area is underlain by Cambrian-age dark greenish-gray, silty and sandy, micaceous shale; with numerous layers of medium-grained, feldspathic, thinly bedded sandstone. According to the Tennessee Landforms website, the state contains more than 54,000 sinkholes, of which over 40 percent are located in the Ridge and Valley Physiographic Region.

3.0 SUBSURFACE EXPLORATION PROGRAM

3.1 SUBSURFACE EXPLORATION

Stantec created an exploratory plan that included 11 test borings to depths of about 20 to 30 feet below the existing roadway surface at the specific slide areas. The Tennessee 811 One Call System was contacted by Stantec to locate and clear the public utilities. A Stantec field engineer provided oversight during the field exploration. Upon completion of the field work, Stantec surveyed the as-drilled locations of the test borings and provided ground surface elevations. The borings were advanced in general accordance with AASHTO guidelines. Borings were performed with a CME 45 truck-mounted drill rig using 3¼-inch inside diameter (ID) hollow stem augers to advance the borings through the overburden materials.

3.2 FIELD TESTING AND SAMPLING

Each boring was logged and sampled in the field by a geotechnical engineer. Soils were logged paying particular attention to the soil type, consistency, moisture content, and color. Standard penetration test (SPT) samples were obtained at selected 2½ foot intervals within the upper 20 feet until auger refusal was reached. The SPT is performed by advancing a 2-inch O.D. split-spoon sampler, in three 6-inch

Subsurface Exploration Program

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 3 increments, with a 140-pound automatic hammer dropping 30 inches at select depth intervals in the boring. The number of hammer blows needed to advance the sampler each 6-inch increment is recorded.

The sum of the blow counts from the last two 6-inch increments is called the field N-value. Where auger refusal was encountered, rock coring was performed for depths of about 10 to 15 feet.

Where bedrock coring was performed, NQ-size equipment was used. Recovery, core loss, and rock quality designation (RQD) values were recorded as percentages for each coring run. The recovery is a measurement of the core sample obtained from a core run. The loss is the difference between the core run and the recovery. The RQD is measured by dividing the sum of all pieces of intact rock core longer than four inches in a run by the total length of the core run. These values are shown on the boring logs contained in Appendix B.

The borings were checked for the presence of groundwater during drilling. Groundwater levels were not recorded at completion due to the addition of water during rock coring. The borings were backfilled with soil cuttings upon completion and, where necessary, capped with a roadway patch.

3.3 LABORATORY TESTING

The soil and rock samples obtained from the borings were returned to Stantec’s geotechnical laboratory for additional laboratory testing. Engineering classification testing was performed on samples reflecting each of the main soil horizons. The engineering classification tests conducted on the samples were sieve and hydrometer analysis (ASTM D 422) and Atterberg limits (ASTM D 4318). The samples were classified according to the Unified Soil Classification System (USCS) and the American Association of State

Highway Transportation Officials (AASHTO) classification method. Soil corrosivity testing consisting of pH (ASTM D 4972) and electrical resistivity (ASTM G 187) was performed on select soil samples.

Samples of rock core were subjected to unconfined compressive (UC) strength testing (ASTM D 7012, Method C). Laboratory test results are presented in Appendix C.

Table 1. Summary of Soil Laboratory Test Results

Boring No.

Sample Depth (ft)

AASHTO

Classification

USCS

Classification

MC

Gravel

Sand

Silt/Clay

590-A 1.5-5.5 A-1-a (0) GC-GM 2.2 55.1 29.8 15.1 590-A 9-14.7 A-1-a (0) GC-GM 2.8 65.4 20.9 13.7

590-A 14.7-18 A-2-4 (0) SC-SM 14.6 31.8 39.1 29.1

590-B 1.5-3 A-1-b (0) GC-GM 6.6 40.5 37.5 22.0 599-B 0-4.4 A-1-b (0) SC-SM 11.2 36.5 40.1 23.4

633-A 1-5 A-2-4 (0) GW-GC 6.4 50.3 41.0 8.7

633-A 6-10 A-1-a (0) SC-SM 6.5 39.6 46.3 14.1

633-A 11-15 A-2-4 (0) SC-SM 6.5 28.8 52.9 18.3

633-A 16-20 A-1-b (0) SM 8.7 35.9 50.3 13.8 633-B 1-5 A-1-a (0) GW-GC 5.6 52.8 36.9 10.3 633-B 6-10 A-1-a (0) GW-GC 7.7 50.4 38.1 11.5

633-B 11-17.5 A-2-4 (0) GP-GM 13.7 50.5 38.4 11.1

Subsurface Conditions

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Boring No.

Sample Depth (ft)

AASHTO

Classification

USCS

Classification

MC

Gravel

Sand

Silt/Clay

659-A 1-2.5 A-2-6 (0) SC 11.6 20.0 49.0 31.0

659-A 3-6.7 A-2-4 (0) GP-GC 5.1 48.3 40.4 11.3

659-B 1-7.5 A-2-6 (0) GW-GC 11.7 70.2 22.3 7.5

660-A 1-2.5 A-2-4 (0) GC 13.5 49.2 33.7 17.1

660-A 3.5-7.5 A-2-4 (0) GM -- 45.3 40.0 14.7

660-B 1-5 A-2-6 (0) GC 15.3 47.7 26.4 25.9

660-B 6-7.5 A-2-4 (0) SM 11.3 4.2 62.0 33.8

660-B 8.5-15 A-2-4 (0) GC 9.7 48.8 27.6 23.6

660-C 1-2.5 A-2-6 (0) SC 13.6 30.4 40.5 29.1

660-C 3.5-5 A-2-4 (0) SM 19.3 28.1 42.1 29.8

Table 2. Summary of Rock UCS Tests

Boring No. Sample Depth (ft)

Compressive Strength psi ksf

590-A 25.6-26.0 11840 1705 590-A 29.3-29.8 8500 1224 599-A 17.3-17.7 10890 1568 599-B 6.7-7.1 13430 1934 599-B 14.2-14.6 11820 1702 659-A 20.5-20.9 2368 341 659-B 13.4-13.8 2094 301 659-B 16.7-17.1 853 123 660-A 15.5-15.9 2856 411 660-C 10.5-10.9 1278 184

4.0 SUBSURFACE CONDITIONS

4.1 GENERAL

Due to the steep terrain, Stantec performed all exploratory activities on the existing roadways. A summary of the borings is presented in Table 3. Exploration locations are shown on the site plans provided in Appendix A and the boring logs are provided in Appendix B.

Table 3. Summary of Borings

General Location

Boring No.

Latitude Longitude

Ground Surface

Elevation (feet)

Explored Depth (feet)

Briar Creek

599-A 36.2237035° -82.402078° 2077.5 18.8 599-B 36.2236205° -82.401888° 2083.3 18.1 633-A 36.229491° -82.3784495° 2423.1 25.8 633-B 36.2295384° -82.3781653° 2419.7 20.0

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General Location

Boring No.

Latitude Longitude

Ground Surface

Elevation (feet)

Explored Depth (feet)

Flatwoods

659-A 36.514508° -82.0391154° 1776.5 24.0 659-B 36.5145938° -82.038985° 1775.5 18.8 660-A 36.5148247° -82.0383457° 1773.3 20.0 660-B 36.5148014° -82.0385896° 1773.6 21.2 660-C 36.5146842° -82.0388809° 1774.8 14.5

Paint Mountain

590-A 35.9470755° -82.8970807° 1320.6 30.5 590-B 35.9472179° -82.8969801° 1323.1 7.2 590-B2 35.947184° -82.8970079° 1322.1 30.0

The surface conditions along the roads for Briar Creek and Paint Mountain typically consisted of a crushed aggregate road base, while Flatwoods consisted of 2 to 3.5 inches of asphalt.

The subsurface conditions at the five slope/wall locations generally consisted of varying thicknesses of granular soils overlying relatively shallow bedrock. Most of the samples tested were of relatively low plasticity (i.e., predominately granular). SPT N-values ranged from 6 to over 50 blows per foot. Some of the blow counts and subsequent N-values may be misleading due to the larger particle sizes encountered (i.e., gravel, cobbles, and boulders). Moisture contents of the samples ranged from 2 to 26 percent with the majority of values between 4 and 14 percent. Corrosivity tests were performed on select soil samples with pH values ranging from 4.2 to 7.6 and soil resistivity values ranging from about 8100 to 29,200 ohms-cm. Typically, a pH value of 4.5 or less or a resistivity less than 2000 ohms-cm is indicative of an aggressively corrosive environment.

The borings encountered auger refusal at depths of about 2 to 20 feet below the ground surface. Auger refusal is a point in the drilling process where if the driller were to continue drilling then there is a greater chance that significant damage to the augers or the drill rig is likely to occur. Rock coring was generally performed where auger refusal was encountered. Rock Quality Designation (RQD) values ranged from 0 to 70 percent with the majority of values between 0 and 40 percent.

Groundwater observations made during drilling generally indicate no static groundwater level above bedrock. Groundwater levels were not taken upon completion of drilling due to the addition of drilling fluids during the coring process. Boreholes were not left open for extended periods of time and were backfilled upon completion of drilling due to their location on the existing roadway and for safety concerns.

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4.2 BRIAR CREEK

4.2.1 MP 599 (Borings 599-A, 599-B)

Natural Deposits

Natural deposits at the boring locations consisted of gravel with silt and sand (GP-GM) and silty, clayey sand with gravel (SC-SM) extending to depths of 2.5 to 4 feet below the existing ground surface. The relative density of these materials ranged from loose to medium dense. Bedrock was encountered below these materials.

Auger Refusal

Auger refusal was encountered in bedrock at depths of 2.5 to 4.3 feet below the existing ground surface.

Rock Coring

Rock coring was performed to depths of 18.1 to 18.8 feet below the existing ground surface and encountered sandy shale and dolostone. Unconfined compressive strength tests of the dolostone ranged from 10,890 to 13,430 psi.

Groundwater

No groundwater was encountered during exploration activities.

4.2.2 MP 633 (Borings 633-A, 633-B)

Natural Deposits

Natural deposits at the boring locations consisted of gravel with clay and sand (GW-GC), silty, clayey sand with gravel (SC-SM), silty sand with gravel (SM), and gravel with silt and sand (GP-GM) extending to depths of 19 and 20 feet below the existing ground surface. The relative density of these materials ranged from loose to very dense. Bedrock was encountered in Boring 633-A at a depth of 19 feet.

Auger Refusal

Auger refusal was encountered in bedrock at a depth of 20 feet below the existing ground surface at Boring 633-A. Bedrock was not encountered in Boring 633-B.

Rock Coring

Rock coring was performed to a depth of 25.8 feet in Boring 633-A and encountered sandstone overlying sandy shale.

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Groundwater

No groundwater was encountered during exploration activities.

4.3 FLATWOODS

4.3.1 MP 659 (Borings 659-A, 659-B)

Natural Deposits

Natural deposits at the boring locations consisted of clayey sand with gravel (SC) and gravel with clay and sand (GP-GC and GW-GC) extending to depths of 5.5 to 8 feet below the existing ground surface.

The relative density of these materials ranged from loose to medium dense. Bedrock was encountered below these materials.

Auger Refusal

Auger refusal was encountered in bedrock at depths of 8 to 8.8 feet below the existing ground surface.

Rock Coring

Rock coring was performed to depths of 18.8 to 24 feet below the existing ground surface and encountered siltstone, shale, and shale interbedded with siltstone. Unconfined compressive strength tests of the shale and shale interbedded with siltstone ranged from 853 to 2368 psi.

Groundwater

No groundwater was encountered during exploration activities.

4.3.2 MP 660 (Borings 660-A, 660-B, 660-C)

Natural Deposits

Natural deposits at the boring locations consisted of clayey gravel with sand (CL), silty gravel with sand (GM), clayey gravel with sand (GC and GM), and silty sand (SM), silty and clayey sand with gravel (SC), and silty and clayey gravel with sand (GC-GM) extending to depths of 7 to 14.9 feet below the existing ground surface. The relative density of these materials ranged from medium dense to very dense.

Bedrock was encountered below these materials.

Auger Refusal

Auger refusal was encountered in bedrock at depths of 8 to 14.5 feet below the existing ground surface.

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Rock Coring

Rock coring was performed to depths of 14.5 to 21.2 feet below the existing ground surface and encountered siltstone interbedded with sandstone, siltstone, limestone, and shale interbedded with limestone. An unconfined compressive strength test of the limestone was 2856 psi and for the shale interbedded with limestone was 1278 psi.

Groundwater

No groundwater was encountered during exploration activities.

4.4 PAINT MOUNTAIN

4.4.1 MP 590 (Borings 590-A, 590-B, B-2)

Natural Deposits

Natural deposits at the boring locations consisted of silty, clayey gravel with sand (GC-GM), silty, clayey sand with gravel (SC-SM), and gravel with sand (GM) extending to depths of 7.2 to 17.5 feet below the existing ground surface. The relative density of these materials was medium dense. Significant boulders were encountered in Borings 590-B and 590-B2 to depths of 20 feet below the existing ground surface.

The relative density of these materials ranged from medium dense to dense. Bedrock was encountered below these materials.

Auger Refusal

Auger refusal was encountered on boulders and in bedrock at depths of 7.2 to 17.5 feet below the existing ground surface.

Rock Coring

Rock coring was performed to depths of 30 to 30.5 feet below the existing ground surface and encountered siltstone interbedded with sandstone, siltstone, sandstone interbedded with dolostone, sandy dolostone, and shale interbedded with limestone. Unconfined compressive strength tests of the sandy dolostone were 11,840 psi and 8500 psi for the shale interbedded with limestone.

Groundwater

No groundwater was encountered during exploration activities.

Analysis and Recommendations

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5.0 ANALYSIS AND RECOMMENDATIONS

5.1 GENERAL

In February and April of 2020, a series of heavy rain events caused significant roadway damage within the Cherokee National Forest. The damaged roadways reduce/prevent roadway public access into various points of the Cherokee National Forest. Damages include large landslides, roadway and shoulder washouts, clogged or damaged culverts, and other miscellaneous conditions. The FHWA has contracted with Stantec to perform geotechnical explorations laboratory testing and provide design recommendations for remediation of slopes in the affected areas. Three areas designated as Briar Creek, Flatwoods, and

Paint Mountain contain a total of five specific slide locations.

The geotechnical explorations were performed on the existing roadways either uphill or downhill of the particular landslide. The lack of access to the uphill and downslope areas of the slides, due to safety and environmental concerns, generally limited exploration activities in these areas. Observation of the slopes along the respective alignments and the overall condition of the roadways indicates the adjacent hillsides to be generally stable. From our observations the downhill slope failures do not appear to be directly impacting the existing roadways, i.e., no distress or apparent cracking in the roadway surface or sinking of the shoulder. From the photographs provided and those taken during exploratory activities it appears that most of the slide activity is surficial in nature and not a deep-seated failure. The recommendations that follow are based on the information discussed in this report, and the interpretation of the subsurface conditions encountered at the site during our fieldwork.

5.2 SEISMIC HAZARD ANALYSIS

The three project sites are mapped generally within the East Tennessee Seismic Zone (ETSZ). Most earthquakes in the ETSZ generally occur in the highly tilted and folded rock layers and are thought to originate in the Precambrian basement structures not related to Appalachian orogeny. The ETSZ is located mainly in the Valley and Ridge province of the southern Appalachians and is the second-most seismically active area in the eastern United States, after the New Madrid seismic zone. The seismic hazard of the ETSZ is difficult to assess, as there are no obvious surface faults found previously except a few recent paleo seismic field surveys, and no recorded historical earthquakes of magnitude greater than 5 (C. Daniels, et al).

In accordance with AASHTO Section 3.10, the overburden soils at the three sites, Briar Creek, Flatwoods, and Paint Mountain, were classified by their stiffness for Site Class. Stantec conducted a review of the soil profile data for the borings completed for this exploration. Using the boring from each area with the deepest overburden profile, Stantec analyzed the soil and bedrock profile using the average Standard Penetration Test (Method B) over the upper 100 feet of profile in accordance with AASHTO

Section 3.10.3.1. In general, the soil profile over a depth of about 100 feet consists of layers of granular soils (2.5 to 20 feet) overlying bedrock. The granular soils were typically medium dense to very dense.

Based on the analysis each of the three areas can be classified as Site Class C. Stantec used this site

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 10 class designation along with the values from the national ground motion maps (PGA, Ss, S1) to obtain the applicable site factors (Fpga, Fa, Fv). Applying the site factors and resulting acceleration coefficients indicates that these sites may be designed within Seismic Zone 1.

5.3 SLOPE STABILIZATION RECOMMENDATIONS

Several slope remediation methods were suggested in the provided information for the various sites.

These consisted of “hard faced” options such as gabion walls, soil nails and steel mesh netting, soil nails and shotcrete cover, and a rockery wall. Stantec discussed several “softer faced, green” options with an FHWA geotechnical representative and recommended vegetated MSE wall systems and vegetated

Geocell slope coverings. These systems are more flexible, generally easier to construct, and less expensive than typical hard faced wall systems.

Stantec created several cross sections along the various alignments to evaluate the stability of existing slopes. Based on our visual observations along the roadway the existing soil slopes appear to be relatively stable. Most soil slopes do not appear to be excessively steep (steeper than 1H:1V) and given the relatively shallow depth to bedrock the soil cover is expected to be relatively thin. Based on the numerous rock outcroppings and boulders visible both up and down slopes and the size and density of foliage, we estimate the overburden soils on slopes to be approximately 2 to 3 feet thick or less where bedrock is shallow. The overburden soils on slopes are likely residual in nature i.e., weathered from the parent bedrock and similar to what was encountered in the borings. In addition to the laboratory test results, Stantec used correlations from FHWA manuals to estimate the soil parameters used in the stability analyses. References are listed in Section 6.

Typically for highway work a minimum factor of safety of 1.3 (1.1 for seismic) would be considered acceptable for slope stability. However, slope stability analyses do not typically account for the presence of boulders, rock out cropping in the slope, or vegetation such as underbrush and trees that have root balls that may anchor into the top of rock. These also help with slope stabilization but cannot be quantified within the analysis.

5.3.1 Briar Creek

Briar Creek Road consists of two sites at MP 599 and MP 633. The slide at MP 599 is assumed to be 100 feet long and 15 feet high. The slide at MP 633 is assumed to be 160 feet long and 12 feet high.

Both slide locations are downhill of their respective roadways.

5.3.1.1 MP 599

Based on site observations and photographs, the slide at MP 599 appears to be surficial. From our constructed cross sections, the slope appears to be roughly 1H:1V. From Borings 599-A and B the overburden thickness ranges from about 2.5 to 4 feet below the roadway surface. Bedrock consisted of weathered and fractured dolostone. Stantec assumed that the slope overburden is roughly the same as the overburden thickness at the roadway. Based on this assumption, then any proposed gravity wall system installation would require the excavation of bedrock, which would be considered expensive. Soil

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 11 nails/rock bolts would also be an expensive remediation and may require benching into the existing slope to construct. Since the apparent slope failure appears to be surficial, Stantec recommends using a geocell product to rebuild and protect the slope after grading has removed the scarp. A geocell solution provides a way to grow and maintain a vegetated slope as steep as 1H:1V. A geocell solution should also reduce the risk of erosion and future slides at this location. Stantec contacted a geocell supplier to determine the feasibility of this technique and provide a preliminary estimate. As geocell products tend to be supplier specific and supplier designed (propriety design), we have included some preliminary information in Appendix F to assist in the decision-making process. We would anticipate that regrading and the application of a “green type” of slope remediation would be more desirable and cost effective than extensive excavation and a conventional wall system.

5.3.1.2 MP 633

Based on site observations and photographs, the slide at MP 633 appears to be surficial as well and the slope appears to be roughly 1H:1V. From Borings 633-A and B the overburden soils range from 19 to 20 feet below the existing roadway surface. However, bedrock was not encountered in Boring 633-B.

Based on the elevation where bedrock was encountered in Boring 633-A (elev. 2404.1), we anticipate that bedrock should be about 2 to 3 feet below the bottom of Boring 633-B. A retaining wall type structure was suggested for this location. Given the depth of the overburden soils at these locations, Stantec recommends using an MSE wall type structure with a vegetated face to repair the face of the slope and reduce the risk of future incidents.

An MSE wall type structure with a maximum height of 12 feet should be sufficient to remediate the slide area and provide for a slightly wider roadway width. A wall batter of approximately 18 degrees (~3V:1H) with a 5-foot bench should fit within the confines of the existing slope and roadway. Design and analysis of the proposed MSE wall is presented in Section 5.4 below.

5.3.2 Flatwoods

Flatwoods Road consists of two sites next to each other at MP 659 and MP 660. The slide at MP 659 is assumed to be 80 feet long and 65 feet high and is located upslope of the road. The slide at MP 660 is assumed to be 225 feet long and 10 feet high and located downhill of the road.

5.3.2.1 MP 659

The slide location at MP 659 is upslope from the roadway. A section approximately 65 feet high by 80 feet wide has been completely denuded due to the topsoil and foliage sloughing off the hillside. From photographs and site observations by the field engineer the hillside appears to be comprised of highly weathered bedrock and shallow pockets of soils weathered from the parent rock. Given the steepness of the slope, roughly 1H:1V, and that the slope has been exposed for roughly 4 years, the overall condition appears to be stable and there is little evidence of erosion. There was no access to the top of the slope, therefore, Borings 659-A and B were performed on the road at the toe of the slope. Bedrock was encountered at depths of 5.5 and 8 feet and consisted of siltstone and shale.

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A suggested remediation method for this slope included soil nails and a steel mesh netting. Stantec recommends using a geocell product to rebuild and protect the slope after any necessary grading is complete. A geocell solution provides a way to grow and maintain a vegetated slope as steep as 1H:1V.

A geocell should also reduce the risk of erosion and future slides/sloughing at this location. Stantec contacted a geocell supplier to determine the feasibility of this technique and provide a preliminary estimate. As geocell products tend to be supplier specific and supplier designed (propriety design), we have included some preliminary information in Appendix F to assist in the decision-making process. We would anticipate that regrading and the application of a “green type” of slope remediation would be more desirable and cost effective than an anchor and steel mesh system.

5.3.2.2 MP 660

Based on site observations and photographs, the slide at MP 660 appears to be surficial and the slope appears to be roughly 1.25H:1V. From Borings 660-A, B, and C the overburden soils range from 7 to 15 feet below the existing roadway surface. The overburden soils generally consisted of medium dense to dense silty clayey sand and clayey gravel. Bedrock consisted of siltstone, limestone, and shale. A retaining wall type structure was suggested for this location. Given the depth of the overburden soils at these locations, Stantec recommends using an MSE wall type structure with a vegetated face to repair the face of the slope and reduce the risk of future incidents.

An MSE wall type structure with a maximum height of 12 feet should be sufficient to remediate the slide area and provide for a slightly wider roadway width. A wall batter of approximately 18 degrees (~3V:1H) with a 5-foot bench should fit within the confines of the existing slope and roadway. Design and analysis of the proposed MSE wall is presented in Section 5.4 below.

5.3.3 Paint Mountain

The Paint Mountain site consists of one slide location at MP 590. From site observations and photographs, the slide at MP 590 appears to be mostly surficial and, from the cross sections, the slope appears to be roughly ¾H to 1H:1V. From Borings 590-A, B, and B2 the overburden soils range from

17.5 to 20 feet below the existing roadway surface with numerous cobbles and boulders. Bedrock consisted of sandstone, dolostone, shale and siltstone. A 20-foot-tall rockery wall was suggested at this location, however, the design footprint for a rockery wall will encroach on the existing roadway. A rockery wall uses large, stacked stones to create the wall face and body with a roughly 12-inch wide granular backfill zone behind the stacked stone. This type of wall system does not lend itself to supporting surcharge loads (i.e., traffic) on the stacked stones or granular backfill. Additionally, the Rockery Design and Construction Guidelines, FHWA-CFL/TD-06-006 (2006) recommends that rockery walls not exceed 12 to 15 feet unless a tiered wall system is used. A tiered wall system would require a larger wall footprint. Given the depth of the overburden soils at this location, Stantec recommends using an MSE wall type structure with a vegetated face to repair the face of the slope and reduce the risk of future incidents. In addition, there is a 15-inch corrugated metal pipe that exits the downstream side of the hillside. The upstream side is buried. Stantec recommends that the existing pipe be backfilled with a non-shrink grout and a new culvert pipe be placed at a suitable upstream depth to carry drainage beneath

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 13 the road. The outfall of the culvert pipe may need to extend from the face of the slope in order to reduce the risk of erosion of the wall.

An MSE wall type structure with a height of 15 feet should be sufficient to remediate the slide area and maintain the existing roadway width. A wall batter of approximately 14 degrees (~4V:1H) with a 5-foot bench should fit within the confines of the existing slope and roadway. Design and analysis of the proposed MSE wall is presented in Section 5.4 below.

5.4 MSE RETAINING WALLS

Three MSE type retaining walls are planned at MP 633, MP 660, and MP 590. The MSE wall was chosen based on its flexibility, ease of construction, relative low cost compared to other wall systems, and the ability to vegetate the wall face. Analysis of the MSE walls were performed in general accordance with AASHTO LRFD Bridge Design Specifications, 9th edition, 2020. The maximum wall height was determined based on the top of wall elevation (near the roadway), the height of the slide, and an embedment depth of 3-feet. In review of online sources, the frost depth for the eastern Tennessee area is approximately 2 feet. Since all three walls are to be located on an existing slope a bench was located at the toe of the wall. The bench also provides support for bearing and slope stability. The wall batter was determined based on the need to fit the proposed wall in the existing slope and not infringe upon the existing roadway width.

In evaluating the design for a "gravity-type" reinforced soil retaining wall (MSE), the external and internal stability should be analyzed. The internal stability analysis will be performed by the wall internal reinforcement designer. The external stability analysis for eccentricity, sliding, bearing resistance and global stability considered the subsurface conditions, the height of the MSE wall and an initial minimum reinforced length of 0.7 times the height of the wall. The reinforcement length was increased/decreased in increments of 0.5 feet to meet external stability requirements. Stantec utilized the computer program MSEW+ in the analysis of the MSE walls. Global stability was analyzed using Slope/W by GeoStudio, 2019. The MSE wall analyses are presented in Appendix E.

Stantec compared and estimated the friction angle values of the existing soils using three different methods from: 1) NAVFAC 7.01, 1986, 2) Peck, Hanson, and Thornburn from Wolff, 1989, and 3) Peck, Hanson, and Thornburn from Kulhawy & Mayne,1990. Based on corrected N-values the internal friction angles ranged from about 31 to 45 degrees and higher. In Stantec’s opinion some of the higher values may be attributed to larger particle sizes (large gravel, cobbles, and boulders) in the soil matrix, therefore, internal friction angles were limited to a maximum of 36 degrees. Since the encountered soils are granular, the soil parameters for short term (undrained conditions) and long term (drained conditions) are essentially the same. A groundwater table was not encountered, likely due to the granular soils, fractured bedrock, and sloping terrain. The tables below summarize the soil parameters used in the analysis of MSE walls and global stability.

In accordance with the AASHTO 11.10.5.3, the reinforced fill portion of the wall must have an internal friction angle (φ) equal to 34 degrees, a cohesion of 0, and an estimated unit weight of 120 pounds per

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 14 cubic foot (pcf). The retained soil must have a minimum internal friction angle (φ) equal to 30 degrees, a cohesion of 0, and an estimated unit weight of 120 pcf. The existing soils can likely be reused as retained and embankment fill, provided they meet the minimum parameters as summarized in the table below and any additional requirements by the MSE wall manufacturer. If differing conditions are discovered during construction, Stantec should be contacted to verify that the design is valid for the actual conditions.

Table 4. Soil Parameters for MSE Walls

Soil Fill Type Unit Weight

(pcf)

Short Term/Long Term

Friction Angle (φ’)

Cohesion (c’)

Bedrock 160 40 4000 Embankment Fill 120 32 0 Reinforced Fill 120 34 0 Retained Fill 120 30 0 Free Draining Base 120 34 0

Table 5. Existing Subsurface Soil Parameters

Wall Location

Depth range above wall base (feet)

Soil Type Unit

Weight (pcf)

Short Term/Long Term

Depth range below wall base (feet)

Friction Angle (φ)

Cohesion (c)

MP 633

0-12 Gravel w/clay and sand 120 36 0 12-20 Gravel w/silt and sand 120 36 0

MP 660

0-12 Clayey Gravel w/sand 120 34 0 12-15 Clayey Gravel w/sand 120 34 0

MP 590

0-15 Silty Clayey Gravel w/sand 120 35 0 15-17 Silty Clayey Sand w/gravel 120 32 0

For external stability, the following four standard modes of failure are typically evaluated:

1) sliding using a resistance factor (ϕ = 1)

2) limiting eccentricity (overturning)

3) bearing resistance using a static resistance factor (ϕ = 0.65)

4) global stability using a static resistance factor (ϕ = 0.75)

5) bearing resistance using a seismic resistance factor (ϕ = 0.9)

6) global stability using a seismic resistance factor (ϕ = 0.9)

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 15

The load factors and geotechnical resistance factors used in the analyses are presented with the analyses in Appendix E. With LRFD analysis methodology, the goal is to have the factored resistance greater than the factored load. The term capacity to demand ratio, CDR, is used to quantify the ratio of the factored resistance to the factored load. CDR values of one or greater indicate acceptable results.

The global stability analyses display the results as a factor of safety. The inverse of the factor of safety is equivalent to the resistance factor. For global stability, a factor of safety (FOS) greater than 1.3 is recommended.

A limitation with the MSEW+ program occurs in the calculation of bearing resistance. The program utilizes only one set of soil parameters in the calculation of bearing resistance (those at the bearing elevation) instead of all the parameters for a soil profile. To compensate for this limitation, a limit equilibrium bearing resistance analysis was performed when an MSEW+ bearing resistance CDR value was less than 1. This allows consideration of the layered subsurface profile beneath the base of the wall, including the presence of shallow bedrock. For a limit equilibrium bearing capacity analysis an area equivalent to the unit width footprint of the wall is loaded with an applied bearing pressure. The resulting failure surface models a classic bearing capacity failure surface and the resulting factor of safety is used to “dial in” the applied bearing pressure that results in a factor of safety of 1.0. Because of the shallow bedrock at MP 633 and MP 660 the necessary applied bearing pressure to reach a factor of safety of 1.0 is very high. Stantec cut off the bearing capacity analysis at the point where the failure surfaces started to enter the bedrock. The CDR for bearing capacity is equal to the factored bearing resistance from the limit equilibrium analysis divided by the factored load from the MSEW+ analysis. The global stability and limit equilibrium bearing resistance analyses utilized the respective profiles from the table above. Tables 6 and 7 presents a summary of the external stability analyses (static and seismic) performed for the MSE walls.

Table 6. Summary of External Stability Analysis - Static

MSE Wall Analysis Condition Sliding Limiting

Eccentricity Bearing

Global Stability

Wall Location & Backslope

Approx. Height & Reinforcement Length (L) CDR ≥ 1 e/L ≤ 0.333 CDR ≥ 1 FOS ≥ 1.3

MP 633

Wall Height: 12 ft

L=12 ft

2.16 0.0052 3.96 a 1.36

MP 660

Wall Height: 12 ft

L=10 ft

1.78 0.0271 3.67 a 1.56

MP 590

Wall Height: 15 ft

L=12 ft

1.75 0.0385 3.23 a 1.47 a - Bearing required the use of limit equilibrium bearing analysis.

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 16

Table 7. Summary of External Stability Analysis - Seismic

MSE Wall Analysis Condition Sliding Limiting

Eccentricity Bearing

Global Stability

Wall Location & Backslope

Approx. Height & Reinforcement Length (L) CDR ≥ 1 e/L ≤ 0.333 CDR ≥ 1 FOS ≥ 1.1

MP 633

Wall Height: 12 ft

L=12 ft

1.86 0.0911 1.31 1.10

MP 660

Wall Height: 12 ft

L=10 ft

1.54 0.1401 4.58 a 1.31

MP 590

Wall Height: 15 ft

L=12 ft

1.43 0.1589 4.05 a 1.25 a - Bearing required the use of limit equilibrium bearing analysis.

The analyses assume proper drainage is maintained and that no hydrostatic water pressure is developed behind the walls. Therefore, for naturally occurring soils, consideration should be given to the installation of a permanent subsurface drainage system located at or near the base of the MSE walls. It is important that the drainage system be protected by a filter fabric to prevent fines from clogging the pipe.

5.5 CONSTRUCTION CONSIDERATIONS

5.5.1 General Considerations

Based on the information obtained at the boring locations and our understanding of the proposed construction, we anticipate that shallow excavations and grading will likely not encounter groundwater.

However, if perched groundwater is encountered or surface water run-off enters shallow excavations during construction, it can likely be removed by using a pump and filtered sump possibly in combination with collection trenches. We also recommend that excavated soil not be stockpiled immediately adjacent to the top of an excavation, nor should equipment be allowed to operate close to unsupported excavations. The Contractor is responsible for maintaining stable excavations. In addition, all excavations should conform with Occupational Safety and Health Administration (OSHA) requirements.

Cohesive soil, if encountered on this project, should be classified as Type A or B, depending on its strength characteristics. The granular soils should be classified as Type C (according to OSHA) and should be treated accordingly.

5.5.2 Wall Construction

In general, engineered fill for walls and embankments should be placed in horizontal lifts not exceeding 8 inches in loose lift thickness and compacted to at least 95 percent of the modified Proctor density (ASTM

D 1557). It should also be noted that the acceptable thickness of loose lifts of engineered fill and/or the number of passes required by the compaction equipment to achieve compaction to the density recommended in this report will be a function of the type of compaction equipment and techniques used, the soil type, as well as proper control of the soil moisture content and the season in which construction

References

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 17 takes place. In addition, periodic field density tests should be performed during fill placement to determine the adequacy of the compactive effort. Large high energy compaction equipment is not recommended as it may cause hillside instability either above or below the proposed wall. Given that granular soils were predominantly encountered at the boring locations and based on relative densities ranging from medium dense to very dense, we anticipate little to negligible post construction settlement should occur.

6.0 REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), Load and Resistance Factor Design (LRFD) Bridge Design Specifications, 9th Edition, 2020.

Clara Daniels, Zhigang Peng, A 15-year-long catalog of seismicity in the Eastern Tennessee Seismic Zone (ETSZ) using matched filter detection, Earthquake Research Advances, Volume 3, Issue 1, 2023, 100198, ISSN 2772-4670, https://doi.org/10.1016/j.eqrea.2022.100198.

NAVFAC Soil Mechanics Design Manual 7.01, September 1986.

Federal Highway Administration (FHWA), Geotechnical Engineering Circular (GEC) No. 5, Evaluation of Soil and Rock Properties, FHWA-IF-02-034, April 2002.

Federal Highway Administration (FHWA), Soils and Foundations Reference Manual – Volume I, FHWA- NHI-06-088, December 2006.

7.0 CLOSING

This evaluation has been conducted in accordance with generally accepted soil and foundation engineering practices. The conclusions and recommendations contained in this report are based on the field observations and subsurface information from the exploratory borings performed for this project. It is important to recognize that subsurface conditions can vary over relatively short distances. The boring/sounding logs and related information depict approximate subsurface conditions only at the specific boring locations noted and at the time of drilling. Conditions at other locations may differ from those occurring at the boring locations. Also, the passage of time may result in a change in the subsurface conditions at the boring locations.

Closing

\\US0537-PPFSS01\shared_projects\2026252113\600 Disc\609 Geotech\Report 18

Construction operations involving wall and slope construction and other earthwork should be performed in the presence of a qualified engineer who is experienced in observation and testing of these operations.

The engineer should operate under the direct supervision of a Professional Engineer experienced in geotechnical engineering.

Darren Pleiman, P.E. Eric Kistner, P.E.

Senior Geotechnical Engineer Principal

APPENDIX A

Exploration Location Plans

ELEV: 2419.6990

E: 3036495.3640

N: 709999.8920

BH - 633-B

ELEV: 2423.0690

E: 3036412.2380

N: 709979.5660

BH - 633-A

PROJECTED POINTS

IE= 2413.65'

C

M P

IE= 2415.09'

GPS

REB & CAP

JH

BM

BH

GPS

REB & CAP

N

:0

A

M

J u n e

M

P

S h e e t] c p w w o r k in g

\i n f r a

\l r a k e s \d

\B r ia r C r e e k

.d g n

MP 633

PROJECT

NUMBER

SHEET

NPS Drwg No. xxxxxx NPS PMIS No. xxxxxx

APPENDIX B

Boring Logs

3- 1/

4" H

S A

N Q

C O

R E

10-13-11 (13" = 73%)

10-12-16 (6" = 33%)

50/3" (3" = 100%)

14-14-8 (2" = 11%)

5-10-6 (12" = 67%)

7-7-4 (12" = 67%)

4-6-23 (12" = 67%)

Rec = 83%

RQD = 0%

Rec = 100%

RQD = 37%

Rec = 100%

RQD = 68%

SS-1

SS-2

SS-3

SS-4

SS-5

SS-6

SS-7

RC-1

RC-2

RC-3

Difficult drilling from 2.5 to 8.5 ft Mostly sandstone fragments

Mostly sandstone fragments

Water seepage at 15.0 ft

Mostly sandstone fragments from

17.0 to 17.5 ft

Horizontal fractures from

23.5 to 27.4 ft

Elv. 1295.0 ft UC = 11840 psi

Vertical fracture at 27.8 ft

Elv. 1291.3 ft UC = 8500 psi

GRAVEL - 3 INCHES

0.3 ft / El. 1320.3 ft

SILTY, CLAYEY GRAVEL WITH SAND (GC-GM), brown with light gray, medium dense, dry.

Possible boulders/cobbles from 0.5 to 6.5'

6.5 ft / El. 1314.1 ft SANDSTONE BOULDER, light gray.

8.5 ft / El. 1312.1 ft

SILTY, CLAYEY FRAGMENTS WITH SAND (GC-GM),

brown with light gray, medium dense, dry to damp, contains few iron oxide stains.

15 ft / El. 1305.6 ft SILTY, CLAYEY SAND WITH GRAVEL (SC-SM), brown, medium dense, moist to very moist.

Moderately organic from 15.0 to 15.5' Contains some iron oxide stains from 17.0 to 17.5'

17.5 ft / El. 1303.1 ft SANDSTONE INTERBEDDED WITH DOLOSTONE, fine to medium grained, gray becoming brown with gray, weak to very weak, highly weathered, highly fractured, soft to medium hard, contains many iron oxide stains.

23.5 ft / El. 1297.1 ft SANDY DOLOSTONE, gray, strong to very strong, slightly weathered, moderately to slightly fractured, hard to very hard.

Highly fractured from 24.0 to 24.2'

27.4 ft / El. 1293.2 ft SHALE INTERBEDDED WITH LIMESTONE, fine grained, dark gray with gray, strong to very strong, slightly weathered, moderately to slightly fractured, hard to very hard.

30.5 ft / El. 1290.1 ft Refusal at 17.5 ft.

Bottom of borehole at 30.5 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)

Core Rec., RQD, and Frac. Freq.

No.

T yp e

Test Results

SAMPLE

590-A Sheet: 1 of 1

Project Location: Cherokee National Forest, TN

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: TN ERFO FS CHRKE804 2020-2(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

BORING LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 8/

:3

C :\U

S E

R S

\Y O

U M

O U

S S

I\O N

E D

R

IV

E

S T

A N

T E

C \A

T T

A C

H M

E N

T S

\D E

S K

T O

P \C

H E

R O

K E

E N

A T

IO

N

A L

F O

R E

S T

\2

\T N

E R

F O

S

IT

E

.G P

J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: No Groundwater Encountered At Completion: ---

Boring backfilled with soil cuttings.

20 40 60 80

Recovery

RQD

Surface Elevation: 1320.6 ft Datum: NAVD88

State Plane Coors:N 601969.7948 ft E 2886794.2754 ft Latitude: 35.9470755° Longitude: -82.8970807° Datum: NAD83

Weather: Sunny

Date Started: 4/7/24 Date Completed: 4/7/24 Driller/Company: A. Clements/Stantec

Hammer Efficiency: 87.1 % Logger/Company: Y. Oumoussi/Stantec

Drill CME-45 Hammer Type: 140 lbs Automatic

G ra ph ic

L og

4" H

S A

6-7-10 (16" = 89%)

19-15-18 (5" = 28%)

13-50/2" (5" = 63%)

SS-1

SS-2

SS-3

Mostly sandstone fragments

Boulder material

GRAVEL - 3 INCHES

0.3 ft / El. 1322.8 ft

SILTY, CLAYEY GRAVEL WITH SAND (GC-GM), brown with light gray, medium dense, dry.

4 ft / El. 1319.1 ft POORLY GRADED GRAVEL (GP), little sand, trace silt, light gray with brown, dense, dry.

6.5 ft / El. 1316.6 ft SILTY GRAVEL WITH SAND (GM), light gray with brown, very dense, dry.

7.2 ft / El. 1315.9 ft Auger bent due to sandstone boulder at 7.2'. Boring offset 15' @ 205 degrees SW, see Boring Log 590-B2.

Bottom of borehole at 7.2 ft.

D ril lin g

M et ho d

Field Blow Count (Recovery)No.

T yp e

Test Results

SAMPLE

590-B Sheet: 1 of 1

Project Location: Cherokee National Forest, TN

20 40 60 80

PL LLWC

N VALUE

20 40 60 80

Project Name: TN ERFO FS CHRKE804 2020-2(1)

E le va tio n (f t)

D ep th ft)

MATERIAL DESCRIPTION

BORING LOG

U. S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

FEDERAL LANDS HIGHWAY DIVISION

F H

W A

L O

G

F H

W A

_D A

T A

T E

M P

LA

T

E .G

D T

/2 8/

:3

C :\U

S E

R S

\Y O

U M

O U

S S

I\O N

E D

R

IV

E

S T

A N

T E

C \A

T T

A C

H M

E N

T S

\D E

S K

T O

P \C

H E

R O

K E

E N

A T

IO

N

A L

F O

R E

S T

\2

\T N

E R

F O

S

IT

E

.G P

J

Groundwater Depth:

Notes:

After Drilling: ---

While Drilling: No Groundwater Encountered At Completion: ---

Boring backfilled with soil cuttings.

Surface Elevation: 1323.1 ft Datum: NAVD88

State Plane Coors: N 602022.561 ft E 2886822.397 ft Latitude: 35.9472179° Longitude: -82.8969801° Datum: NAD83

Weather: Partly cloudy

Date Started: 4/8/24 Date Completed: 4/8/24 Driller/Company: A. Clements/Stantec

Hammer Efficiency: 87.1 % Logger/Company: Y. Oumoussi/Stantec

Drill CME-45 Hammer Type: 140 lbs Automatic

G ra ph ic

4" H

S A

N Q

C O

R E

6-8-8 (0" = 0%)

Rec = 32%

RQD = 8%

Rec = 18%

RQD = 10%

Rec = 94%

RQD = 0%

Rec = 100%

RQD = 7%

SS-4

RC-1

RC-2

RC-3

RC-4

Drilled without sampling from

0 to 9.0 ft

Horizontal and diagonal fractures from

20.0 to 30.0 ft

GRAVEL - 3 INCHES

0.3 ft / El. 1321.8 ft

SANDSTONE BOULDERS/COBBLES INTERBEDDED

WITH SOIL LAYERS.

10 ft / El. 1312.1 ft SANDSTONE BOULDERS, light gray.

6-12" soil layers inbetween.

15 ft / El. 1307.1 ft SANDSTONE BOULDERS, light gray and brown.

Few soil layers inbetween.

20 ft / El. 1302.1 ft

SILTSTONE INTERBEDDED WITH SANDSTONE,

brown with gray, very weak to weak, highly weathered, highly fractured to fractured, soft to medium hard, contains many iron oxide stains.

28 ft / El. 1294.1 ft…