Soils Foundation Report.pdf

SOILS AND FOUNDATION

REPORT NO. 08-09

PROJECT AR FSR 400(1)

EMERGENCY LANDSLIDE REPAIR AND ROADWAY RECONSTRUCTION

FALLING WATER ROAD (RICHLAND)

OZARK NATIONAL FOREST

SEARCY COUNTY, ARKANSAS

U.S. Department of Transportation Federal Highway Administration

Eastern Federal Lands Highway Division 21400 Ridgetop Circle

Sterling, VA 20166

March 2010

TABLE OF CONTENTS

REPORT PAGE

INTRODUCTION

General Project Description Regional Geology Soil Survey

PROCEDURES AND RESULTS

General Sampling Field Tests and Measurements Data Summary Laboratory Testing Findings

DESIGN ANALYSIS AND CONCLUSIONS

Design Alternatives Landslide Repair Roadway Embankment Design Analysis Roadway Embankment Landslide Repair

RECOMMENDATIONS

Roadway Embankment Repair Landslide Repair

CONSTRUCTION CONSIDERATIONS

General Roadway Embankment Repairs Anchors

DISCLAIMER/LIMITATIONS CLAUSE

APPENDICES

APPENDIX A – Figures APPENDIX B – Boring Location and Geotechnical Instrumentation Map APPENDIX C – Boring Logs APPENDIX D – Laboratory Data APPENDIX E – Seismic Refraction Data APPENDIX F – Design Calculations APPENDIX G – Typical Details APPENDIX H – Special Contract Requirements (SCRs) APPENDIX I – Representative Photographs

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

SOILS AND FOUNDATION

REPORT NO. 08-09

PROJECT AR FSR 400(1)

LANDSLIDE REPAIR AND ROADWAY RECONSTRUCTION

FALLING WATER ROAD (RICHLAND)

OZARK NATIONAL FOREST

SEARCY COUNTY, ARKANSAS

INTRODUCTION

General

This report presents the result of our geotechnical subsurface investigation design analyses, and recommendations for landslide repair and roadway reconstruction for Project AR FSR 400(1). The project site is located on Falling Water Road (CR-1205/CR-1) in the Ozark National Forest, in Searcy County, Arkansas. The general site location is shown on Figure 1, “Site Location and Vicinity Map” in Appendix A.

Project Description

The project is located approximately 7.5 miles from the intersection with Route 16 and is adjacent to the Richland Wilderness Area. The extent of the failure is approximately 20 acres in size. The failed mass broke away from the parent rock slope forming a very large failure.

The main scarp height is approximately 80 to 100 feet high. Material separated from the vertical scarp moved a horizontal distance of approximately 40 to 50 feet. There are several smaller slides within or on the main failure mass. Two smaller slides within the larger mass moved over the roadway at approximate Stations 11+10 to 13+30 and Stations 16+67 to 17+97 producing failure to the roadway embankment.

The entire slide continues to move. The Forest Service (FS) attempted to remove some of the slide material from the roadway after completion of our subsurface investigation, but more material subsequently slid into the roadway. The road is currently closed to the public.

Representative photographs are shown in Appendix J.

This project starts at Sta.10+00 and extends to Sta. 19+00; the project involves stabilization of the landslide and repair of the roadway embankment. The project also includes drainage improvement using trenches and reconstruction of a failed box culvert at Sta 11+30. The design of the uphill landslide repair and roadway embankment reconstruction was done with consideration for less impact to the wilderness area.

Project: AR FSR 400(1) Landslide Repair – Falling Water Road Ozark National Forest Soils and Foundation Report Searcy County, Arkansas No. 08-09

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Regional Geology

According to United States Geological Survey’s (USGS) “Geologic Map of Arkansas (1976)” the slide is located in the Ozark Region and is underlain by the Hale Formation, Atoka Formations, Pitkia Limestone, Fayette Shale (including the Wedington Sandstone Member), and Batesville Sandstone (including the Hindsville Limestone Member).

The Hale Formation consists of three members: Cane Hill Member, Prairie Grove Member and Bloyd Shale Member. The Cane Hill Member is typically composed of dark gray silty shale interbedded with siltstone and thin-bedded fine-grained sandstone. The Prairie Grove Member is composed of thin to massive, often crossbedded, frequently pitted ("honeycomb weathering"), light-gray to dark-brown, limy sandstone or variously sandy limestone with lenses of relatively pure, crinoidal, highly fossiliferous limestone and oolitic limestone. The Bloyd Shale Member consists of a combination of limestone, sandstone and shale.

The Atoka Formation consists of black to tan shales, interbedded with very thin to thin ripple-bedded micaceous siltstones, and thin to medium bedded, fine to very fine-grained sandstones with sub-angular to sub-rounded quartz grains. Refer to Figure 2 in Appendix A for a “Geologic Map” of the project area.

Soil Survey

According to United States Department of Agriculture “Soil Survey of Searcy County, Arkansas” the surficial soil at the slide consists of Nella-Steprock-Mointainburg complex.

Nella-Steprock-Mointainburg complex is a well drained colluvium derived from sandstone and shale; with skeletal loamy residuum weathered from sandstone; and gravelly and stony loamy residuum weathered from sandstones and siltstone. The formation is distributed on mountain slopes and benches. Refer to Figure 3 in Appendix A for a “Soil Survey Map” of the project area.

PROCEDURES AND RESULTS

General

The Eastern Federal Lands Highway Division’s (EFLHD) Subsurface Exploration Team conducted two subsurface investigation programs at the project site. A preliminary subsurface investigation was conducted from June 18 through 19, 2008. Additional subsurface information was required to complete the design analysis; therefore a second investigation was conducted from April 23 through 26, 2009.

The combined subsurface investigation programs consisted of five (5) borings including Standard Penetration Tests (SPT) and rock core; one (1) auger probe and three (3) seismic refraction survey lines. SPT, rock coring and auger probe were performed on the roadway and at approximately 45 ft from the centerline of the roadway. Borings were advanced to depth using hollow stem augers and a CME 850 rotary, track-mounted drill rig. The seismic

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

refraction survey lines were performed on the slide area not accessible by conventional drilling equipment using a Smartseis S24 System with 24 channels.

The location of each boring and seismic lines may be referenced on the “Boring Location Plan and Profile” sheet in Appendix B.

Sampling

The boreholes were drilled to depths ranging from 21 to 48.8 ft below the existing ground surface. Borings were advanced using 3¾-in. (inside diameter) hollow stem augers. SPT was performed using a 2¼-in. (outside diameter) split-spoon sampler in accordance with AASHTO 7200-87 and AASHTO T206-87. SPT soil samples were typically recovered at 5-foot intervals. Samples were obtained by driving the split-spoon sampler a distance of 24-in., or until auger refusal, into the undisturbed soil under the impact of a 140-lb. automatic hammer free-falling 30 inches. The number of hammer blows required to advance the split-spoon sampler the middle foot of the 24-in. sample interval is designated as the “Standard Penetration Resistance” or N-value. Auger refusal is defined by 50 blows per 1-inch of penetration of the split-spoon sampler. The number of blows required to advance the sampler through each 6-in. interval was recorded on field boring logs. Representative portions of split-spoon samples were preserved in glass jars for laboratory testing. Water levels, if present, were measured in the borings at the time and under the conditions stated on the boring logs.

Rock coring was performed in Borings R-1, R-4, R-5 and R-6 using rotary drilling techniques and samples were retrieved using an NQ core barrel and wireline. Rock core samples were preserved in wooden boxes for laboratory testing.

The sampling sequence along a sampling sequence and associated jar samples for each boring are presented on its appropriate Boring Log in Appendix C.

The geophones along a refraction survey line were spaced at either 10 or 20 feet, and total geophone array lengths ranged from 150 to 315 feet. Shots were typically taken at the first and third sensors, midpoint of the sensor array, tenth and last sensor, and between 20 and 50 feet offsets from each end of the array. The total shots were 11, 12, and 9 for lines 1, 2 and 3, respectively. Shots were produced with a sledgehammer on a striker metal plate.

Geophysical survey results are included in Appendix E.

Field Tests and Measurements

The EFLHD geotechnical crew performed the following field tests and took measurements during the course of the subsurface exploration. A field description of color and texture was made for each recovered sample. The boring locations were determined by measuring from features present on-site and by GPS. Boring elevations were determined from plan topography. The approximate location of borings is as shown on the Boring Location Plan and Profile sheet in Appendix B.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Data Summary

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

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

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

Laboratory Testing

A laboratory testing program was conducted on representative soil samples and rock cores recovered during the subsurface explorations. The primary purpose of the testing program was to aid in classification and evaluation of the engineering properties of soil and rock present at the site. Laboratory tests included grain size distributions (AASHTO T-88), Atterberg Limits (AASHTO T-89, T-90), natural water contents (AASHTO T-265) and unconfined compressive tests (AASHTO T-208) were performed. The results of the laboratory testing program are presented in Appendix D and summarized below in Tables 1 and 2.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Table 1. Summary of Laboratory Test Results for Soil

Moisture Content

Liquid Limit

Plastic Limit Fines Boring

No.

Sample

No.

Sample Depth

(ft) (%) (%) (%) (%)

Classification

R-2

J-2

5 - 7

16.0

64.0

A-7-6(17)

R-2

J-4

15 - 17

11.0

67.6

A-7-5(10)

R-4

J-4

14.5 -16.5

18.2

47.6

A-7-6(5)

R-5

J-3

10 -12

15.3

49.6

A-7-6(8)

R-6

J-3

15 -17

13.2

24.2

A-2-6(0)

J-5

25 - 27

17.5

30.0

A-2-6(0)

Table 2. Summary of Laboratory Test Results for Rock

Boring No.

Sample No.

Sample Depth

(ft)

Unconfined Compressive

Strength (psi)

Description

R-1

C-2

4.0 – 9.0

14, 130

Shale and Sandstone

R-4

C-1

26.7 – 28.7

9, 730

R-5

C-3

38.8 – 40.8

15, 460

46.3 – 48.5

7, 750

R-1

4 – 9

14, 130

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Findings

The site was divided into three zones during the design analysis. Dividing the large slide area into zones assisted with providing an economical slide repair design and is expected to provide uniformity for ease of construction.

The zones were selected based on the topographic mapping, site conditions and subsurface field investigation results. The location, stationing and boring logs used to develop the stratification for each zone are described in Table 3.

Table 3. Zones

Zone Location Station Borings

South

10+00 – 13+30

Center

13+30 – 16+67

R-1, R-2, R-3

North

16+67 – 19+00

R4, R-5

Descriptions of the soil and rock conditions encountered during the subsurface explorations conducted at the site are presented below. The stratification lines designating the interfaces between soil types on the boring logs represent approximate boundaries. The transition between materials may be gradual. One or more of the units may be absent at specific locations.

Zone 1

Zone 1 starts at Station 10+00 and ends at Station 13+30. A failed roadway embankment section is located between Sta. 11+10 to 13+00. Also a failed box culvert is located in this zone at Sta. 11+30. Boring R-6 was used to develop the stratification for this zone. The findings for zone 1 are the following:

WEATHERED SHALE FRAGMENTS LITTLE CLAY – Brown and gray weathered shale fragments with little clay identified as very loose were encountered in moist conditions from ground surface to a depth of 4 ft.

WEATHERED SHALE FRAGMENTS LITTLE CLAY – Brownish orange and gray weathered shale fragments with little clay identified as medium dense were encountered in wet conditions below the soft weathered shale fragments layer to a depth of 15 ft. SPT resistance values recorded within this material were between 11 and 22 blows per foot (bpf). AASHTO soil classification for this layer is A-2-6(0).

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

WEATHERED SHALE FRAGMENTS SOME CLAY – Brown and gray weathered shale fragments with some clay identified as dense to very dense were encountered in moist conditions to a depth of 23 ft. SPT resistance values recorded within this material were between 32 bpf and auger refusal. AASHTO soil classification for this layer is A-2-6(0).

SHALE AND SANDSTONE – Gray and black shale and sandstone identified as relatively sound to sound with fine to course grains was encountered below the weathered shale fragments with some clay layer to a depth of 41.5 ft. Rock core recovery and RQD values were 100%; indicating excellent rock quality with unconfined compressive strength of 7,750 psi.

Zone 2

Zone 2 starts at Station 13+30 and ends at Station 16+67. No roadway embankment failure was found within this zone. Borings R-1, R-2, and R-3 were used to develop the stratification of this zone. The findings for zone 2 are the following:

CLAY SOME WEATHERED SHALE FRAGMENTS – Brown and gray soft clay with some weathered shale fragments identified as soft was encountered in dry conditions from ground surface to a depth of approximately 3 ft in Borings R-1, R-2 and R-3.

CLAY SOME WEATHERED SHALE FRAGMENTS – Brownish gray clay with some weathered shale fragments identified as stiff to hard were encountered in dry conditions below the clay to a depth of approximately 27ft . SPT resistance values recorded within this material were between 10 bpf and auger refusal. AASHTO soil classifications for these layers are A-7-6(17) and A-7-5(10).

WEATHERED SHALE – Brownish gray and black, fine grained shale identified as weathered rock was encountered below the hard clay with some weathered shale fragments to a depth of 39 ft in Boring R-1. Rock core recoveries and RQD values measure were an average of 66% and 21% respectively, indicating very poor to poor rock quality. Unconfined compressive strength tests were requested but could not be performed, because of rock core crumbling during processing.

Zone 3

Zone 3 starts at Station 16+67 and ends at Station 19+00. The failed roadway embankment section within this zone is located between Stations 16+67 and 17+97.

Borings R-4 and R-5 were used to develop the stratification for this zone. The findings for zone 3 are the following:

WEATHERED SHALE FRAGMENTS AND CLAY – Brown and gray weathered shale fragments and clay identified as soft were encountered in moist conditions from ground surface to a depth of 4 ft.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

WEATHERED SHALE FRAGMENTS AND CLAY – Brown and gray weathered shale fragments and clay identified as stiff to hard were encountered in dry conditions below the soft weathered shale fragments and clay layer to a depth of approximately 33 ft . SPT resistance values recorded within this material were between 10 and auger refusal. AASHTO soil classifications for this layer are A-7-6(5) in Boring R-4 and A- 7-6(8) in Boring R-5.

SHALE AND SANDSTONE – Gray and black fine to medium grain shale and sandstone identified as highly weathered to slightly weathered rock was encountered below the weathered shale fragments to an average depth of 49 ft. Average rock core recovery and RQD values were 88% and 59% respectively; indicating fair rock quality. The rock unconfined compressive strength values were 9,730 psi from 26.7 to 28.7 ft in Boring R-4 and 15, 460 psi from 38.8 to 40.8 ft in Boring R-5.

No groundwater was encountered during or after completion of drilling. Fluctuation in the groundwater due to seasonal variations, rainfall, temperature, and other factors should be anticipated.

Seismic Refraction Surveys

Seismic refraction survey lines were performed within the slide at inaccessible locations for the drilling equipment. The seismic surveys were performed in order to identify depth to bedrock, and compare to the conditions encountered in the boring logs. Seismic refraction surveys were performed during April 24th through 26th, 2009. The refraction data was analyzed to create tomographic images of the subsurface soils and rock. Tomographic profiles lines 1, 2, and 3 are included in Appendix E.

The seismic refraction survey results can be used for identification of soil consistency and the inferred location of soil and bedrock strata at the site based on the p-wave velocity. The seismic refraction survey revealed an estimated depth to competent rock between 30 and 100 ft below ground surface. Depth to competent rock was not shown in seismic refraction line 3.

Correlations between soil/rock and p-wave velocity, adjusted based on observations from boring logs and our interpretations of published correlations are presented in Table 4.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Table 4 - Seismic refraction survey results

Soil Type/Density P -wave Velocity (ft/s)

Soft weathered shale fragments and clay

0 -1,500

Stiff to very stiff weathered shale fragments and clay

1,500 - 3,500

Hard weathered shale fragments and clay

3, 500 – 5,000

Soft to moderately hard shale and sandstone

5,000 -7,000

Competent rock (Hard shale and sandstone)

> 7,000

DESIGN ANALYSIS AND CONCLUSIONS

Design Alternatives

Landslide Repair

Design alternatives considered for stabilizing the slide were evaluated in terms of cost, constructability, area of disturbance and long term performance. Alternatives considered for this low ADT area are the following:

1. Excavation and removal of rock and unstable weathered material

2. Excavation of slide material and installation of ground anchors with concrete blocks

3. Anchored or cantilever soldier pile wall with drilled shafts socketed into rock

1. Excavation and removal of rock and unstable weathered material

This alternative consists of flattening the uphill slope by removing the slide debris. The slide debris consists of soil, weathered rock and large boulder with sizes up to 25 ft in diameter. Excavation of approximately 35 to 40 ft is expected to remove the rocks from the top of the slope and provide a stable slope. The benefit of this alternative is that it eliminates the hazard from additional rock fall and reduce future maintenance.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Stabilizing the site using this alternative requires a significant amount of excavation, making this option unfeasible due to high construction cost. This alternative must be combined with other elements to reduce the amount of excavation.

2. Excavation of slide material and installation of anchors with concrete blocks

This alternative consists of flattening the slope by excavating the unstable material to an approximate depth of 30 ft near the top of the slope, then installing ground anchors with concrete blocks and a rock buttress at 5-ft offset from the edge of the roadway embankment. The anchors would intersect the deep failure plane allowing for steeper slopes. This in turn would reduce the amount of excavation at the top of the slope. It would also allow the re-use of on-site rock for construction of the buttress. The buttress and offset distance is designed to keep the material out of the roadway if a future slide occurs. After completion of installation of the blocks and anchors, the blocks will be covered with on-site soil and the slope will be re-vegetated.

3. Anchored or cantilevered soldier pile wall with drilled shafts socketed into rock

An anchored soldier pile wall system would be required if this option was selected because of the high lateral loads. The depth to competent rock and the size of the slide rendered this alternative inapplicable because of concerns with cost for this low ADT road.

Alternative 2 was selected because it was considered the most suitable in terms of cost, constructability, area of disturbance and serviceability.

Roadway Embankment

The roadway embankment failures in zones 1 and 3 require reconstruction between Station 11+10 and 13+00 and Station 16+67 to 17+97. The design alternative selected for the repair of the roadway embankment consists of Geosynthetic Reinforced Soil Slope (RSS) with vegetated facing. This option would provide an economical design, ease of construction and relatively less disturbance.

Design Analysis

Dividing the site into three zones (Zones 1 to 3) provides the ability to make changes to the repair designs between zones resulting in significant cost savings. The geometry of the critical slope sections for each zone was developed using cross sections obtained from EFLHD’s Highway Design Branch.

Landslide Repair

Zones 1, 2 and 3

The proposed landslide repair for the three identified zones consists of removing the slide material and installing ground anchors with concrete blocks at a 12 ft by 12 ft

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

grid pattern. Anchors were designed with 240 kips capacity and 6 ft by 6 ft concrete blocks. The design of landslide slope repair components is described as follows.

Ground Anchors

The selected design alternative consists of installing ground anchors into bedrock (through the failure plane). The ground anchors were designed using principles for ground anchors as presented in FHWA’s Geotechnical Engineering Circular No. 4 (1999) – “Ground Anchors and Anchored Systems” and “Foundations on Rock” by Duncan C. Wyllie. An allowable rock-grout bond stress of 38 psi with a minimum bond length of 26 feet was used. Refer to Appendix F for design calculations.

The stability of the existing slope for each zone was analyzed using soil properties determined from correlation with SPT N-values, p-wave velocity, and guided by typical values from the literature (for shale). These soil properties are presented in Table 7 to 9.

Table 7 – Soil Properties for Zone 1 Slope Stability Analysis

Soil Layer

Unit

Weight (lb/ft3)

Friction Angle (deg.)

Cohesion

(lb/ft2)

Soft to moderately hard shale and sandstone 140 20 5000

Soft weathered shale fragments, little clay 115 15 25

Stiff to very stiff shale fragments, little clay 120 18 25

Hard shale fragments and clay 125 21 350

Soft to moderately hard shale and sandstone 130 23 2000

Hard shale and sandstone 140 40 7000

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Table 8 – Soil Properties for Zone 2 Slope Stability Analysis

Soft to moderately hard shale and sandstone 140 20 5000

Soft clay, some weathered shale fragments 105 10 15

Stiff to very stiff clay, some weathered shale fragments

110 12 20

Hard clay some weathered shale fragments 120 15 500

Soft weathered shale and sandstone 125 20 2000

Table 9 – Soil Properties for Zone 3 Slope Stability Analysis

Soft to moderately hard shale and sandstone 140 20 5000

Soft weathered shale fragments, little clay 110 11 14

Stiff to very stiff shale fragments, little clay 115 14 17

Hard shale fragments and clay 125 17 100

Soft to moderately hard shale and sandstone 125 20 2000

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

The computer program Slope/W (Version 5) was used to analyze and complete the design of the anchored slopes; and to check on global stability. Slope/W calculates the Limit Equilibrium factor of safety with a variety of methods. We selected the Spencer method for stability analyses because the Spencer method satisfies both moment and force equilibrium.

The following lists reinforcement characteristics used in Slope/W, based on 12-ft spacing between the anchors:

Anchor working load - 24,000 lbs/ft width

Bond resistance – 9,311 lbs/ft anchor length/ft width

Bond Length – 26 feet

Reinforcement Direction:

o Zone 1 - 15 degrees o Zone 2 and 3 - 30 degrees

Total Reinforcement Length (including bond length ):

o Zone 1 - First row 90 ft, Second row 100 ft o Zone 2 - Only row 60 ft o Zone 3 -First row 75 ft, Second row 75 ft

Note: If competent rock is encountered at shallower depths anchors lengths shall be adjusted accordingly based on the results of the verification load test.

Distance from the edge of the roadway:

o Zone 1 - First row 52 ft, Second row 77 ft o Zone 2 - One row at 52 ft o Zone 3 – First row 82, Second row 95 ft

The proposed design also includes an approximate offset of 5 ft between the roadway and the toe of the slope. At the toe of the slope, a rock buttress with approximately 10’ wide base and 10’ in height will be constructed using on-site sandstone. The sandstone will be crushed and processed on-site.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Analyses results indicate that the proposed design will provide adequate stability for the slope. Table 10 presents global stability factors of safety for each zone. Refer to Appendix F for examples of landslide repair design calculations.

Table 10 – Factor of Safety

Zone Global Stability Factor of Safety

1 1.2

2 1.2

3 1.3

Roadway Embankment

Geogrid-reinforced roadway embankment reconstruction in Zones 1 and 3 was performed using ReSSA (2.0) slope stability software. Stability calculations were completed for global stability, translational and 3-parts wedge failure modes.

Zone 1

Based on the survey, subsurface exploration and design analyses results this zone requires the replacement of the culvert located at Sta 11+30 and roadway embankment reconstruction between Sta 11+10 and 13+00. The design parameters shown in Table 5 were used for the roadway embankment analysis for this zone.

The proposed embankment repair that satisfied stability requirements consists of:

Excavate roadway embankment to approximate depth of 10 ft at Stations 11+10 to 11+30 and 13+00 to 13+30.

Excavate roadway embankment to approximate depth of 20 ft at Stations 11+30 to 13+00.

Install geogrid reinforcement layers with minimum long term design strength (LTDS) of 2,000 lb/ft at 1.5 ft vertical spacing. Use a minimum geogrid embedment depth of 18 ft from Station 11+10 to 11+30 and 13+00 to 13+30.

Use a minimum geogrid embedment depth of 16 ft from Station 11+30 to 13+00.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Use backfill material (on-site material) consisting of unclassified borrow in accordance with Section 704.06 of the FP-03 and as describe in the Special Contract Requirements.

Table 5 – Design Parameters for Zone 1 Roadway Embankment Analysis

Unclassified borrow 120 32 0

On-site sandstone 140 20 5000

Soft weathered shale fragments, little clay 115 15 25

Stiff to very stiff shale fragments, little clay 120 18 25

Hard shale fragments and clay 125 21 350

The factors of safety obtained for the proposed roadway embankments in terms of global stability, translational and 3-parts wedge failure modes are 1.4, 1.4, and 1.5 respectively for the 20’ high embankment and 1.35, 2.0 and 1.7 for the 10’ high embankment.

Zone 3

Based on the survey, subsurface exploration results and design analyses results this zone requires roadway embankment reconstruction between Sta 16+67 and 17+97.

The design parameters shown in Table 6 were used for the roadway embankment analysis.

The proposed embankment repair that satisfied stability requirements consists of:

Excavate roadway embankment to approximate depth of 10 ft.

Install geogrid reinforcement layers with minimum long term design strength (LTDS) of 2,000 lb/ft at 1.5 ft vertical spacing and an embedment depth of 18 ft.

Use backfill material (on-site material) consisting of unclassified borrow in accordance with Section 704.06 of the FP-03 and as describe on the Special Contract Requirements.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Table 6 – Design Parameters for Zone 3 Roadway Embankment Analysis

Unclassified borrow 120 32 0

On-site sandstone 140 20 5000

Soft weathered shale fragments and clay 110 11 14

Stiff to very stiff weathered shale fragments, and clay

115 14 17

Hard shale fragments and clay 125 17 100

The factors of safety obtained for the proposed roadway embankment design in terms of global stability, translational and 3-parts wedge failure modes are 1.36, 1.7, and 1.7 respectively.

RECOMMENDATIONS

Based on the results of our analyses we recommend the landslide repair to consist of removing slide material and constructing rows of ground anchors with concrete blocks for slope stabilization. In addition, construct a rock buttress at an approximate 5ft offset and Geogrid Reinforced Slope (GRS) roadway embankments at the identified stations in Zone 1 and 3. Our recommendations are as follows:

Landslide Repair

Based on our subsurface field investigations results, lab test results, design analysis, cost analysis and site requirement we recommend landslide repair at all zones to consist of the following:

Regrading Slope and Offset Rock Buttress

Remove slide material and regrade the slope at each zone, as shown on the plans.

At the top of the slope remove an approximately 30 ft depth of slide material and broken rock then grade at 5% toward the face of the slope.

Maintain a minimum offset of 5.0 ft between the edge of the roadway and the toe of the slope.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

At the toe of the slope, construct a rock buttress with approximately 10 ft wide base and 10 ft high. Match the face of the rock buttress with the slope of each zone.

Place underdrain along the back of the rock buttress using # 57 stone and 6” diameter pipe wrapped in Geotextile Type I-C.

Use on-site sandstone for the rock buttress. The sandstone will be crushed and processed on-site.

Ground Anchors

Provide anchors that meet the following requirements:

o Minimum design capacity of 240 kips and a test capacity of

1.33 times the design capacity (320 kips). An anchor consisting of 7 strands of 0.6-in. diameter would meet these criteria.

o Class I corrosion protection.

o Bond length – 26 feet (Bond length should be modified on site based on verification test results. It is expected a shorter bond length will be required to meet design loads.)

o Minimum unbonded zone beyond critical failure zone (unweathered bedrock) – 5 feet.

Install inclinometers and piezometers in the landslide mass accordingly to plans and Section 271. Refer to Figure 1 of Appendix B for Geotechnical Instrumentation Map.

Construct the anchor and block system as follows:

o Minimum design capacity of 240 kips and a test capacity of

1.33 times the design capacity (320 kips). An anchor consisting of 7 strands of 0.6-in. diameter would meet these criteria.

o Excavate for anchors.

o Prepare shotcrete leveling pad, where needed.

o Set 6-ft. by 6-ft. concrete block in place and drill anchor.

o Install blocks and anchors at 12-ft. spacing longitudinally.

o Block and anchors rows distances from the edge of the road:

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Zone 1 - First row : 52 ft; Second row: 77 ft

Zone 2 - First row: 52 ft

Zone 3 - First row : 82 ft; Second row: 95 ft

Perform proof and performance tests in accordance with FP-03 Section 256.08. Lock-off load is 240 kips.

Estimate anchors quantities are the following:

Table 11 – Anchors Quantities

Note: If competent rock is encountered at shallower depths anchors lengths will be adjusted accordingly based on the results of the load test verification.

Backfill over the anchors and blocks with topsoil and seed mix; using on-site material and covered with an erosion control mat type 3.B, if warranted.

Refer to Appendix G for ground anchor layout.

Drainage

Install two drainage trenches, located at approximately Sta 11+75 and 17+10. The trenches should be 5ft wide, 2 ft deep filled with Class 3 riprap underlain by Type IV-F geotextile.

Slope Revegetation

To aid vegetation growth it is recommended that a 6-inch layer of on-site topsoil and seed mix be placed over the repaired slope and encapsulated with a type 3.B erosion control mat after all anchors are

Zone

Total

Anchors

Estimate Unbounded

Zone (ft)

Estimate Bounded

Zone (ft)

1 30 2,060 780

2 30 1,024 780

3 40 1,960 1,040

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

installed and locked-off per Section 256 of FP-03. The erosion control mat will keep the topsoil on the slope and facilitate turf establishment.

Roadway Embankment Repair

Zone 1 and 3

Reconstruct roadway embankment according to Section 204 of the FP-03 and the following recommendations:

Zone 1 - Excavate roadway embankment to approximate depth of 10 ft at Stations 11+10 to 11+30 and 13+00 to 13+30. Excavate roadway embankment to approximate depth of 20 ft at Stations 11+30 to 13+00.

Zone 3 - Excavate roadway embankment to approximate depth of 10 ft at Station 16+67 to 17+97.

Zone 1 and 3 - Along the roadway, extend embankment repair to 10.0 ft beyond failure limits.

Zone 1 - Bench the back of the excavation a maximum of 10.0 ft high and a minimum of 3.0 ft. horizontally. Grade the bottom of the benches on a 5% slope toward the underdrain along the back of the excavation.

Establish the benches on a 1(V):0.5(H) slope.

Zone 3 - Grade the bottom of the embankment on a 5% slope toward the underdrain along the back of the excavation. Establish the back slope of the embankment on a 1(V):0.5(H) slope.

Zone 1 and 3 - Place underdrain at the toe of the embankment and on the first bench along the back of the excavated bench using #57 stone and 6” diameter pipe wrapped in Geotextile Type I-C.

Zone 1 and 3 - Place a drainage layer consisting of #57 stone along the back of the benches with a thickness of 1.0 ft wrapped with Geotextile Type I-C.

Zone 1 and 3 - Provide a minimum of 2 underdrain outlets at the lowest points using a 6” diameter pipe, embedded in #57 stone and wrapped in Geotextile Type I-C.

Zone 1 - Provide geogrid with a minimum LTDS of 2,000 lb/ft. Place the first geogrid layer at 0.5 feet above the bottom of the excavation. On Stations 11+10 to 11+30 and 13+00 to 13+30 extend geogrid layers a minimum of 18.0 ft of embedment depth at 1.5 vertical spacing. On Stations 11+30 to 13+00, extend geogrid layers a minimum of 16.0 ft of embedment depth at

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Zone 3 - Provide geogrid with a minimum LTDS of 2,000 lb/ft. Place the first geogrid layer at 0.5 feet above the bottom of the excavation. Extend geogrid a minimum of 18.0 ft of embedment depth at 1.5 ft vertical spacing.

Zone 1and 3 - Establish the new face of the slope repair on a 1(V):

0.75(H).

Zone 1 and 3 – Use backfill material (on-site material) consisting of unclassified borrow in accordance with Section 704.06 of the FP-03 and as describe on the Special Contract Requirements.

Zone 1 and 3 - To aid vegetation growth, it is recommended that topsoil and seed mix be placed for the first 1-foot behind the face of the wrapped geogrid reinforcement and be encapsulated with a Turf Establishment Mat (TRM). The TRM will facilitate the topsoil and seed placement and vegetation growth. On-site soil can be considered to use as topsoil.

Refer to Appendix G for typical sections.

CONSTRUCTION CONSIDERATIONS

Based on the subsurface field investigations and design analysis results, construction recommendations are as follows:

General

Excavations: All excavations are to be performed in accordance with applicable OSHA standards and with Section 204 of the FP-03 Specifications.

Instrumentation Monitoring and Construction Sequence: The existing slide is active. A monitoring program should be in place and initial baseline readings taken prior to any construction activity at the project site. On zone 1 and 3 install a minimum of two (2) inclinometers at the centerline of the active slide prior to the start of construction. Install the first inclinometer at the toe of the slope. Install the second inclinometer at mid-slope. In zone 2 install a minimum of one (1) inclinometer at the centerline of the active slide prior to the start of construction. Install the inclinometer at mid-slope. Temporary piezometers should be installed to measure groundwater elevations/pore pressures before and during construction. Piezometers should be located in pairs with inclinometers, with a minimum 10 feet spacing to minimize interference between instruments. Make the following minimum instrument readings: prior to the first day of construction, twice for the first week of construction, and weekly throughout the duration of construction. The CO may increase the frequency of readings based on the need for additional information.

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

Roadway Embankment Repairs

Backfill Material: Backfill material for the repaired slope should consist of AASHTO A-2-4 material or better. The maximum dimension of coarse aggregate used for backfill material should not exceed 4 inches. Backfill material should be placed and compacted in lifts not to exceed 12 inches, per Section 204 of the FP-03 Specifications. The portion of the on-site excavated material that meets the unclassified borrow specification may be used as backfill material. Backfill material should be placed and compacted in accordance with Section 204, and the specified maximum dry density should be achieved within a water content of ±2%.

Lightweight compaction equipment should be used within 3-feet of the slope face. This equipment will reduce the possibility of triggering additional movement of the uncompacted fill soils within the existing slope. Examples of acceptable lightweight equipment include small single or double drum, walk behind vibratory rollers or vibratory plate compactors.

Sheepsfoot, grid, or other types of equipment employing a foot are not recommended.

Berm or Ditch: Along the roadway embankment, including Zone 1, 2, and 3 which includes Stations 10+00 to 19+00 add a 6” high berm to divert the water flow away from the embankment face.

Geogrid Handling and Placement: Geogrid reinforcement material should be in accordance with Section 714 as amended and included in Appendix H. The geogrid should come packaged in a sheathing or container suitable to protect the geogrid from damage due to ultraviolet light and abrasion during storage and handling. The geogrid should not be removed from the sheathing or container until the time of placement within the reinforced slope. The geogrid should be free from defects, tears, punctures, flaws, deterioration, or other damage.

Place geogrid reinforcement in horizontal layers and in accordance with the manufacturer’s recommendations and as amended and included in Appendix G. The principle strength direction for the geogrid should be placed perpendicular to the face of the RSS.

Anchors benches

Shotcrete: The anchors will be installed at 15 and 30 degrees from horizontal, meaning that the excavation for individual concrete blocks will be at 75 and 60 degrees from horizontal. A 6-inch thick shotcrete facing should be applied to the excavated bearing surface prior to installation of anchor blocks. The purpose of the shotcrete pad is to prevent sloughing of the freshly excavated bearing pad and provide a uniform bearing surface for the concrete blocks.

Excavate and install anchors in a manner that prevents destabilizing the slope or initiating slope movement. Accomplish backfilling as each horizontal row is competed and do not excavate immediately above or below any incomplete anchor location.

APPENDIX A

Figures

Source: United States Geological Survey (USGS), "Geologic

Pitkia Limestone, Fayette Shale (including the Wedington Sandstone Member), and Batesville Sandstone (including the Hindsville

Bloyd Shale and Praire Grove Member Thin to massive, often crossbedded, frequently pitted light-gray to dark-brown, limy sandstone or sandy limestone. And a combination of

Map of Arkansas (1976)" sandstone and shale.

Limestone Member)

Cane Hill Member Dark gray silty shale interbedded with siltstone and thin-bedded fine-grained sandstone.

HALE FORMATION

3AR ERFO FSR 400(1)

TOTAL

SHEETS

HALE FORMATION

2SE

SHEET

NO.

PROJECTREG

AR

FIGURE 2

GEOLOGIC MAP

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STATE

STERLING, VIRGINIA

RICHLANDS (CR-1205/CR-1)

Source: United States Department of Agriculture (USDA) "Soil Survey of Searcy County, AR " http://websoilsurvey.nrcs.usda.gov/app/

50 EF Nella-Steprock-Mointainburg complex - Mountain slopes, benches, well drained. Colluvium derived from sandstone and and 50 G sandstones and siltstone.

3AR ERFO FSR 400(1)

TOTAL

SHEETS

AR

FIGURE 3

SOIL SURVEY

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL LANDS HIGHWAY DIVISION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

shale. Skeletal loamy residuum weathered from sandstone. Gravelly and stony, loamy residuum weathered from

STATEREG

STERLING, VIRGINIA SE

SHEET

NO.

PROJECT

APPENDIX B

Boring Location and Geotechnical

Instrumentation Map

APPENDIX C

Boring Logs

M:\Projects\fs\ar\400(1)\techserv\geotech\Borings\Boring Log_Soil Description Standard.doc

SOIL BORING GENERAL NOTES

Drilling and Sampling Symbols

SS: Split Spoon - 1 3/8” I.D., 2” O.D., except where noted ST: Shelby Tube - 2” O.D., except where noted PA: Power Auger Sample

Water levels indicated on the boring logs are the levels measured in the boring at the times indicated. In pervious soils, the indicated elevations are considered reliable ground water levels. In impervious soils, the accurate determination of ground water elevations is not possible, even after several days, and additional evidence on ground water elevations must be sought.

VISUAL METHODS FOR SOILS CLASSIFICATION

Component Distinguishing Features

Boulders Larger than 12” (300 mm)

Cobbles 3” to 12” (75 mm to 12 mm)

Gravel Larger than No. 4 sieve and smaller than a 3” sieve, described with any of the following terms (or any combination):

Coarse 3” to 3/4” (75 mm to 19 mm) sieve Medium 3/4” to 3/8” (19 mm to 9.5 mm) sieve Fine 3/8” to No. 4 (9.5 mm to 4.75 mm) sieve

Sand The finest sand grains are just visible to the naked eye, while the largest would pass a No. 4

(4.75mm) sieve (pinhead size). Described with any of the following terms (or any combination):

Coarse No. 4 to No. 10 (4.75 mm to 2.0 mm) sieve Medium No. 10 to No. 40 (2.0 mm to 0.42 mm) sieve Fine No. 40 to No. 200 (0.42 mm to 0.075 mm) sieve

Silt 1. Lumps are easily crumbled when are-dried.

2. Feels gritty between the teeth.

3. A moist pat when shaken in the palm of the hand will appear shiny and wet. When squeezed it will appear dry and dull.

Clay 1. Lumps are comparatively hard when air-dried.

2. Threads (1/8” diameter) of considerable length will support their own weight when held by one end.

3. A moist pat will appear the same whether shaken in the palm of the hand or squeezed.

Order of Description

1. Soil Density (or consistency) – see table below

2. Color

3. Major Grain Size – Composes more than 50% of the sample

4. Modifying Term – “and” : 40% to 50% of the minor grain size

“some” : 30% to 40% “little” : 10% to 30%

“trace” : 10% or less

5. Minor Grain Size(s)

6. Other (plasticity, etc.)

M:\Projects\fs\ar\400(1)\techserv\geotech\Borings\Boring Log_Soil Description Standard.doc

7. Moisture Content (by field test) – “dry” : Absence of moisture, dusty, dry to the touch “moist” : Damp but no visible water

“wet” : Visible free water, usually soil is below water table

8. General Classification – Fill, Residual Soil, Weathered Rock

SOIL DENSITY (OR CONSISTENCY) TABLE

Coarse-Grained Soil (Gravel, Sand) Fine-Grained Soil (Clay, Silt)

Apparent Density SPT (# blows / ft) Consistency SPT (# blows / ft) Very loose 0-4 Very soft 0-2

Loose 5-10 Soft 3-4 Medium dense 11-30 Medium stiff 5-8

Dense 31-50 Stiff 9-15 Very dense >50 Very stiff 16-30

Hard >30

Examples:

1. Dense to very dense, brown to light brown, SILTY SAND, some gravel [A-7-6(10)]

(Moist)

-FILL-

Criteria for Describing Soil Structure

Description Criteria

Bed A sedimentary layer bounded by depositional surfaces.

Blocky A characteristic in which cohesive soil can be broken down into small angular lumps which resist further breakdown.

Bonded Attached or adhering.

Fissured Broken along definite planes of fracture.

Foliated Planar arrangement of textural or structural features.

Frequent More than one per foot of thickness.

Homogeneous Same color and appearance throughout.

Interbedded Alternating soil layers of different composition.

Laminae A very thin cohesive layer.

Layer A general term for material lying essentially parallel to the surfaces against which it was formed.

Lens A lenticular deposit, larger than a pocket.

Occasional One or less per foot of thickness.

Parting A very thin granular layer.

Pocket Small erratic deposits less than 12” in thickness.

Seam A thin layer separating two distinctive layers of different composition or greater magnitude.

Stratified Alternating layers of varying material or color.

Stratum A stratigraphic unit.

Varve A cyclic sedimentary couplet consisting of a coarser and a finer layer representing the variation in depositional energy resulting from the annual freeze-thaw cycle typically found in glaciolacustrine environments.

M:\GEOTECH\6. ERFO Projects\Ozark National Forest, IL_MRosa working\Borings\Coring Log_Rock Core Description Standard.doc

ROCK CORING GENERAL NOTES

Depth and Elevation: Use large marks as 1’ (300mm) increments. Record proper elevations.

Core: Draw sketch of core breaks as it is oriented in the core box (align all core breaks so they fit together properly before drawing sketch). Starting at the top of core measure each piece of core down its centerline to 1/100 of a foot. Record this measurement along the left side of the core sketch at the break.

VISUAL METHODS FOR ROCK IDENTIFICATION

Description: 1. Draw a heavy line through description at depth to which core run penetrated.

2. Describe the rock type.

3. Note the condition of the core break on the right side of the core sketch

Mud seam (MS); Sand seam (SS); Weathered surface (WS); Fresh break (FB)

4. Record coring time in minutes.

5. Record to nearest 1/100 foot the core recovered (after alignment in core box). Discard any debris at top of core, which obviously fill into the core hole.

6. Calculate per cent core recovery and record: CR = feet of core recovered feet cored

Color: Wet the rock with water and describe the color including the color of any unusual or reoccurring markings on the core (i.e. light green with dark green bands, foliation lines).

Foliation: Foliation planes are parallel planes of different minerals forming a banded appearance on the rock.

The foliation planes are usually of a different color than the surrounding rock. Also the rock shears along the foliation planes if struck with a hammer. Record the following:

Close spaced (CS) – 1/8” (3mm) or closer; Medium spaced (MS) – 1/8” to 1/4” (3mm to 6mm);

Open spaced (OS) – 1/4” (6mm) or larger

The angle to the horizontal should be measured (with a protractor) and recorded for the rock core.

(Several different angles can be found in each 5’ to 10’ core.)

Hardness: Very Soft (VS) – Can be deformed or crumbled by hand; Soft (S) – Can be scratched with a fingernail Moderately Hard (MH) – Can be scratched easily with a knife; Hard (H) – Can be scratched with difficulty with a knife; Very hard (VH) – Cannot be scratched with a knife

Weathering: Use the proper number 1 through 5.

1. Unweathered: No evidence of any mechanical or chemical alteration along discoloration evidenced.

2. Slightly weathered: Discoloration is evident, on surface, slight alteration no discontinuities, less than 10% of the volume is altered, strength is substantially unaffected.

3. Moderately weathered: Discoloring is evident, surface is pitted and altered with alteration penetrating will below rock surfaces, weathering "halos” evident, 10% to 50% of the rock is altered, strength is noticeably less than fresh rock.

4. Highly weathered: Entire mass is discolored; alteration pervades nearly all of the rock with some pockets of slightly weathered rock noticeable, some minerals leached away, retains only a fraction of original strength (with wet strength usually lower than dry strength).

5. Decomposed: Rock is reduced to a soil with relict rock structure (saprolite), can be generally molded and crumbled by hand.

Rock Quality Designation (RQD) = Σ[Lengths of all pieces of the core ≥ 4” (100mm)] x 100 Total length of core run

M:\GEOTECH\6. ERFO Projects\Ozark National Forest, IL_MRosa working\Borings\Coring Log_Rock Core Description Standard.doc

Soundness: Use the proper number 1 through 5

1. Weathered RQD = 0% to 25%

2. Highly jointed to Jointed RQD = 25% to 50%

3. Jointed to Relatively sound RQD = 50% to 75%

4. Relatively sound to Sound RQD = 75% to 100%

Rock Quality: Use the proper number 1 through 5

1. Very Poor RQD = 0% to 25%

2. Poor RQD = 25% to 50%

3. Fair RQD = 50% to 75%

4. Good RQD = 75% to 90%

5. Excellent RQD = 90% to 100%

Order of Description

1. Hardness

2. Color

3. Soundness (a.k.a. Weathering and Rock Quality)

4. Main Rock Formation – Composes more than 50% of…