FSE_Geotech_Report_for_NFSR_188_Briar_Creek_Road.pdf

Geotechnical Investigation

Bottomless Aluminum Box Culvert FSR 188 Briar Creek Road

Washington County, M.P. 2.40 Washington County, Tennessee

Contract No. AG-4756-P-14-0027

FSE Project No. 314140 08/26/2014

Prepared For: USDA Forest Service

August 26, 2014

USDA Forest Service North Zone Engineering 4400 Unicoi Drive Unicoi, Tennessee 37692-0007

COR: Lynn DiFiore

RE: Geotechnical Investigation

Contract No. AG-4756-P-14-0027

Bottomless Aluminum Box Culvert

FSR 188 Briar Creek Road

Washington County, M.P. 2.40

Washington County, Tennessee

FSE Project No. 313140

As authorized by Contract No. AG-4756-P-14-0027, we have completed a subsurface exploration for the above referenced box culvert to be located at mile post 2.40 on Briar Creek Road. The purpose of the subsurface exploration was to gather subsurface data to allow engineering recommendations as to site preparation, foundation preparation and foundation allowable bearing capacity. The firms of Foundation Systems Engineering, P.C. and Construction Materials Laboratory completed this work.

Please give us a call if you have any questions concerning the data obtained or our recommendations. It has been a pleasure to be of service on this project.

Sincerely, Foundation Systems Engineering, P.C.

Eric M. Peterson, P.E. Jack F. Llewellyn, Jr., P.E.

Geotechnical Engineer Principal-In-Charge Tennessee No. 109536 Tennessee No. 19187

JFL/EMP/sf Enclosures

TABLE OF CONTENTS

1.0 EXECUTIVE SUMMARY

2.0 OBJECTIVE OF SUBSURFACE EXPLORATION

3.0 SCOPE OF SERVICES

4.0 SITE LOCATION AND CONDITIONS

4.1 Photographs

5.0 SUBSURFACE STRATIFICATION

5.1 Soil Overburden

5.2 Bedrock

5.3 Groundwater

6.0 GEOLOGY

7.0 RECOMMENDATIONS

7.1 Box Culvert Site Preparation

7.2 Foundation Type and Allowable Bearing Capacity

7.3 Excavation Safety

8.0 ADDITIONAL RECOMMENDED WORK

9.0 GENERAL QUALIFICATIONS

Lynn DiFiore (COR) Aluminum Bottomless Box Culvert USDA – Forest Service FSR 188 Briar Creek Road, M.P. 2.40

1.0 EXECUTIVE SUMMARY

The existing drainage structure is located on Forest Service Road (FSR) 188 Briar Creek Road at Mile Post (M.P.) 2.40, in Washington County, Tennessee. This is within the North Zone of the Cherokee National Forest. The site is located 2.4 miles east of the intersection of Briar Creek Road and Dry Creek Road, and approximately 3.8 miles, airline, to the northwest of Unicoi, Tennessee. This subsurface exploration was conducted to provide geotechnical engineering recommendations regarding a replacement of the existing concrete box culvert with a new aluminum bottomless box culvert.

Briar Creek Road is an undivided, gravel covered, forest road. Within the area of the subject new culvert the roadway is oriented in an approximate northwest to southeast direction. Briar Creek cross beneath the road in an approximate northeast to southwest direction, with stream flow from approximately northeast to southwest.

The existing structure consists of a concrete box culvert with wingwalls. The structure appears to be supported directly on the underlying Siltstone bedrock unit. Bedrock outcroppings are visible in the creek on both the upstream and downstream sides of the existing box culvert structure.

The upstream side of the box culvert has a deposit of alluvial gravel to cobbles and boulders, with a mixture of limbs and logs, near the entrance. This material appears to have been deposited during past flooding events.

The existing culvert is approximately 7 feet in width (not including wingwalls), 8.5 feet in height and approximately 30 feet in length (headwall to headwall). The bottom of the structure is located approximately 15 feet below the level of Briar Creek Road.

The slope leading down from the roadway to the creek is overgrown in weeds, brush and trees.

Bridge inspection reports and topographic survey with existing features were to be provided; however, we did not receive this data and have assumed that such information was not available for this structure.

The purpose of our exploration was to collect subsurface data with regard to soil type, consistency, site geology and presence of groundwater at the proposed box culvert location, and to provide geotechnical engineering recommendations as to site and foundation preparation, and foundation allowable bearing capacity. To meet our objective we placed three soil borings at the site. The borings were drilled to refusal on the underlying bedrock unit. The bedrock was core drilled a minimum depth of 15 feet at each boring location. Area topographic and geologic mapping was reviewed, along with proposed construction data provided by the Forest Service.

Two soil test borings with Standard Penetration testing and one offset boring (B-1, B-2 and B-2A) were used to investigate subsurface conditions at the proposed new box culvert. The soil test borings were placed using a CME-55 truck-mounted drilling rig, with Standard Penetration testing (ASTM D 1586) performed through hollow-stem augers. Upon refusal on the underlying bedrock unit, NX sized core drilling was performed to a depth of approximately 15 feet into the bedrock at the three boring locations.

The borings encountered fill soils at existing grade. In general, the fill soils consist of firm to very loose, dry to very moist, reddish brown, tan, brown and gray, clayey silty sands mixed with fine to coarse shale, siltstone and sandstone gravel to cobbles and boulders.

The hollow stem augers refused on siltstone at depths of from approximately 12 feet to approximately 18 feet below existing grade. The bedrock at each of the borings was core drilled. An NX sized diamond-studded core bit was used to advance the core drill holes.

Core drilling commenced at boring B-1 at a depth of approximately 18 feet below existing grade. From a depth of approximately 18 feet through our drilling depth of approximately 33 feet, hard to moderately hard, medium gray, siltstone with very soft to soft, partially weathered to weathered, siltstone was encountered. Very soft, broken, weathered seams were encountered at depths of 18’ – 19’; 21’ – 23’; and 30’ – 32’.

Boring B-1 was terminated at a depth of 33 feet below existing grade. Core recovery was 96% and RQD for the rock core interval was 64% (fair rock).

Core drilling commenced at boring B-2 at a depth of approximately 13 feet below existing grade. From a depth of approximately 13 feet through our drilling depth of approximately 28 feet, moderately hard to hard, medium to dark gray, broken, weathered to partially weathered, siltstone was encountered. Very soft, broken, weathered seams were encountered below a depth of 23 feet. Boring B-2 was terminated at a depth of 28 feet below existing grade. Core recovery was 80% from the interval of 13 feet to 23 feet, and 7 percent for the interval of 23 feet to 28 feet. Rock

Quality Designation (RQD) for the rock core interval of 13 feet to 23 feet was 34% (poor rock), and 0% for the interval of 23 feet to 28 feet.

As a result of the poor quality rock encountered at boring B-2, an offset boring B-2A was used to investigate the rock at an offset location approximately 4 feet from B-2.

Core drilling commenced at boring B-2A at a depth of approximately 12 feet below existing grade. From a depth of approximately 12 feet through our drilling depth of approximately 30 feet, very soft to hard, medium to dark gray, broken, weathered to partially weathered, siltstone was encountered. Very soft, broken, weathered seams were encountered below a depth of 22 feet. Boring B-2A was terminated at a depth of 30 feet below existing grade. Core recovery was 58 percent from the interval of 12 feet to 22 feet, and 61 percent for the interval of 22 feet to 30 feet. Rock Quality Designation (RQD) for the rock core interval of 12 feet to 22 feet was 13% (poor rock), and 7% (poor rock) for the interval of 22 feet to 30 feet.

Based on the results of the borings, we recommend that the excavation made for box culvert construction be excavated down to the underlying bedrock unit. We estimate this to be a depth of about 15 feet below existing road level. More or less excavation may be required between boring locations to reach the underlying bedrock unit. The width of the excavation should extend a minimum of 15 feet beyond the perimeter edge of each side the proposed new culvert.

Excavation sidewalls should be sloped no steeper than 1.5H:1V. Excavations should be sloped or shored in accordance with local, state and federal regulations including OSHA (29 CFR Part 1926) excavation and trench safety. The on-site, in-place, fill soil overlying the bedrock is classified under OSHA guidelines as Type C soil (see Section

7.3 below).

Backfill material placed around the box culvert (up to the level of 1 foot above the 100 year flood level of Briar Creek) should consist of free draining coarse grained sand and gravel, with no silt or clay fines.

Care should be taken to ensure that no fine grained sands, silts, and clays are placed as fill up to the level of 1 foot above the 100 year flood level.

Once the free draining fill material reaches the desired level, a minimum 8 ounce per square yard, nonwoven, geotextile should be spread across the top of the fill. The geotextile should use a minimum lap width of two feet between successive roll widths and at all locations where two or pieces of the geotextile will be joined.

Backfill material placed around the box culvert, beginning at the level of 1 foot above the 100 year flood level of Briar Creek (over the top of the nonwoven geotextile) should consist of stone fragments, gravel and sand, gravel or sand with silt or clay.

Material placed as fill around and over the top of the culvert should meet the Group Classification requirements of AASHTO M-145 for material types A-1-a, A-1-b, A-2-4, A- 2-5, or A-3. Soils with AASHTO Group Classifications of A-2-6, A-2-7, A-4, A-5, A-6, A- 7 (A-7-5 & A-7-6) are not suitable for use as backfill material. Maximum particle size should not exceed three inches in greatest dimension. The in-place soil excavated during construction of the new culvert may be reused as fill provided that it meets these recommended soil classification guidelines.

Backfill lift thickness should not exceed 8 inches, loose. The fill should be placed in horizontal lifts. Each lift should be thoroughly compacted before subsequent lifts of fill are placed. The fill should be placed uniformly on both sides of the culvert, taking care to minimize differential (unbalanced) backfill heights on either side of the culvert.

Balanced fill lifts should be placed as per AASHTO Section 26.

Backfill material around and above the box culvert should be compacted to a minimum of 95% of its maximum dry density as determined by the Standard Proctor test, AASHTO T-99. The moisture content of soils meeting the Group A-2-4 and A-2-5 classification requirements should have the moisture content of the material controlled to within the range of +/- 2 percent of Standard Proctor Optimum moisture content during compaction. As noted above, maximum particle size should not exceed 3 inches in greatest dimension. In-place density testing should be performed concurrent with placement of all fill to ensure the desired density is achieved.

Up to the elevation of 1 foot above the 100 year flood level of the creek, the slope face (exposed surface) of the backfill placed around the culvert (both upstream and downstream) should be covered by a heavy duty, nonwoven, geotextile. Riprap should be placed over the geotextile. The riprap size, and thickness of the riprap layer, should be based on the stream hydraulics during maximum flooding. Geotextile damaged during placement of riprap cover should be removed and replaced.

The portion of the slope above the riprap should receive seed and straw as soon after completion as possible, with erosion control matting placed as needed, to prevent washing until a vegetative cover develops. We recommend that the compacted structural fill slope be constructed no steeper than 1.5 horizontal to 1 vertical (1.5H:1V).

We recommend that the proposed aluminum bottomless box culvert be supported using a steel reinforced concrete footing. The footing should bear a minimum of one (1) foot into the Siltstone bedrock material. Bearing a minimum of one foot into the bedrock, the footing may be sized using an allowable bearing capacity of 5000 PSF. The footing should be sized a minimum of 18 inches in width.

The footing excavations should be inspected by a geotechnical engineer prior to placement of reinforcing steel or concrete. Dynamic Cone Penetrometer testing (ASTM STP 399) should be performed as directed by the geotechnical engineer to confirm the assigned bearing capacity.

Excavations should be sloped or shored in accordance with local, state and federal regulations including OSHA (29 CFR Part 1926) excavation and trench safety. The on-site, in-place, alluvial soil overlying the bedrock is classified under OSHA guidelines as Type C soil.

The above summary provides an overview only and should not be used as a separate document or in place of reading the entire report including the appendices. The summary is not a substitute for the following detailed sections of this report. A complete discussion of finding and recommendations are included in the following sections of this report.

2.0 OBJECTIVE OF SUBSURFACE EXPLORATION

The purpose of our exploration was to collect subsurface data with regard to soil type, consistency, site geology and presence of groundwater at the proposed box culvert location, and to provide geotechnical engineering recommendations as to site and foundation preparation, and foundation allowable bearing capacity. To meet our objective we placed three soil borings at the site. The borings were drilled to refusal on the underlying bedrock unit. The bedrock was core drilled a minimum depth of 15 feet at each boring location. Area topographic and geologic mapping was reviewed, along with proposed construction data provided by the Forest Service.

3.0 SCOPE OF SERVICES

Two (2) soil test borings (B-1 and B-2) with Standard Penetration testing were used to investigate the subsurface conditions at the proposed new box culvert. An offset boring (B-2A) was placed adjacent to boring B-2. The borings were placed at locations as selected by our firm. The approximate locations of the borings may be seen on the attached Boring Location Plan. A Boring Location Summary may be seen in Table I of this report. The results of the Standard Penetration testing and general subsurface stratification may be seen on the attached Test Boring Records located in the Appendix of this report.

Standard Penetration testing was performed at 2.5-foot intervals to a depth of 10 feet below existing grade. Below a depth of 10 feet, Standard Penetration testing was performed at 5-foot intervals to our auger refusal depths. A Soil Overburden Data Summary may be seen in Table II of this report.

The underlying bedrock unit was core drilled at all three locations (B-1, B-2, and B-2A).

NX sized rock core drilling was performed. Rock description, core recovery and rock quality designation values may be seen on the attached Test Boring Records. A Rock Core-Drilling Summary may be seen in Table III of this report.

The borings were monitored for groundwater. Upon conclusion, the soil test borings were backfilled with soil auger cuttings.

A brief summary of the test procedures utilized on this project are located in the Appendix of this report.

4.0 SITE LOCATION AND CONDITIONS

The existing drainage structure is located on Forest Service Road (FSR) 188 Briar Creek Road at Mile Post (M.P.) 2.40, in Washington County, Tennessee. This is in the North Zone of the Cherokee National Forest. The site is located 2.4 miles east of the intersection of Briar Creek Road and Dry Creek Road, and approximately 3.8 miles, airline, to the northwest of Unicoi, Tennessee.

Briar Creek Road is an undivided, gravel covered, forest road. Within the area of the subject new culvert the roadway is oriented in an approximate northwest to southeast direction. Briar Creek cross beneath the road in an approximate northeast to southwest direction, with stream flow from approximately northeast to southwest.

The slope leading down from the roadway to the creek is overgrown in weeds, brush and trees.

The existing structure consists of a concrete box culvert with wingwalls. The structure appears to be supported directly on the underlying Siltstone bedrock unit. Bedrock outcroppings are visible in the creek on both the upstream and downstream sides of the existing box culvert structure.

The upstream side of the box culvert has a deposit of alluvial gravel to cobbles and boulders, with a mixture of limbs and logs, near the entrance. This material appears to have been deposited during past flooding events.

The existing culvert is approximately 7 feet in width (not including wingwalls), 8.5 feet in height and approximately 30 feet in length (headwall to headwall). The bottom of the structure is located approximately 15 feet below the level of Briar Creek Road.

Bridge inspection reports and topographic survey with existing features were to be provided; however, we did not receive this data and have assumed that such information was not available for this structure.

The following photographs were taken at the time of our site visit for boring layout.

4.1 Photographs

Briar Creek Road.

Briar Creek

Existing Structure

Alluvial Deposit

Roadway Fill Slope.

Structure

Creek

Bedrock

5.0 SUBSURFACE STRATIFICATION

Two soil test borings and one offset boring (B-1, B-2 and B-2A) were used to investigate subsurface conditions at the proposed new box culvert. The soil test borings were placed using a CME-55 truck-mounted drilling rig, with Standard Penetration testing (ASTM D 1586) performed through hollow-stem augers. Upon refusal on the underlying bedrock unit, NX sized core drilling was performed to a depth of approximately 15 feet into the bedrock at the three boring locations. A brief summary of the soil encountered at the boring locations follows. Additional subsurface details may be seen on the attached Test Boring Records. Subsurface stratification indicated on the boring logs is approximate, and represents our interpretation of the soils encountered at the Standard Penetration Testing intervals.

The borings were located in the field by our firm. The approximate locations of the borings may be seen in the following table.

Table I – Boring Location Summary

Boring Number Location –

North/South

Location –

East/West

Auger Refusal

Depth*

Boring

Termination

Depth* B-1 North (upstream side of road).

East Side Existing

Culvert 18 Feet 33 feet (Rock Core

Drill 18’ – 33’)

B-2 North (upstream side of road).

West Side Existing Culvert

13 Feet 28 feet (Rock Core Drill 13’ – 28’)

B-2A Offset 4’ West Of B-2.

West Side Existing Culvert

12 Feet 30 feet (Rock Core Drill 12’ – 33’)

* Approximate

5.1 Soil Overburden

The following table briefly summarizes soil subsurface stratification. Refer to boring logs for a description of the approximate subsurface stratification encountered.

Table II – Subsurface Stratification Summary

Boring

Number

Surface

Veneer*

Fill* Residual Boring

Terminated B-1 0” – 1” Gravel

1” – 5” Topsoil

5” – 18’ Fill – Firm to very loose, dry to very moist, reddish brown, tan, brown and gray silty sand mixed with fine to coarse shale, siltstone and sandstone gravel.

Mixed with roots at 8.5’ to 12’.

18’ – 33’ Residual – Hard to moderately hard, medium gray, siltstone with very soft to soft, partially weathered to weathered seams.

33’

Surface

Veneer*

Fill* Residual Boring

Terminated B-2 - 0” – 13’ Fill – Firm, moist to very moist, reddish brown, tan, and brown, clayey, silty sand mixed with fine to coarse shale, siltstone and sandstone gravel to cobbles.

13’ – 28’ Residual – Moderately hard to hard, medium to dark gray, broken, weathered to partially weathered, siltstone, with very soft to soft, broken, weathered seams.

28’

B-2A - 0” – 12’ Fill - Firm, moist to very moist, reddish brown, tan and brown, clayey silty sand mixed with fine to coarse shale, siltstone and sandstone gravel to cobbles.

12’ – 30’ Residual – Very soft to hard, medium to dark gray, broken, weathered to partially weathered, siltstone, with weathered seams.

30’

*Stratum depths are approximate. “-“ Stratum not detected.

5.2 Bedrock

The hollow stem augers refused on siltstone at depths of from approximately 12 feet to approximately 18 feet below existing grade. The bedrock at each of the borings was core drilled. An NX sized diamond-studded core bit was used to advance the core drill holes.

Core recovery and rock quality designation were determined for the rock core drilling.

Core recovery is the ratio, expressed as a percentage, of the total length of core recovered to the total length of core advanced. The RQD (Rock Quality Designation) is the ratio, expressed as a percentage, of the summed length of core retrieved in segments longer than 4 inches, to the total length of core advance. These values are related to the quality of the drilling and soundness of the rock. In homogenous sound rock a recovery of 100% may be expected; in rocks with seams a recovery of about 50% is typical; however, in decomposed or seamy rock the recovery may be little or nothing. Rock with an RQD value of 90% or more denotes excellent rock; 75% to 90%, good rock; 50% to 75%, fair rock; and 25% to 50%, poor rock.

Core drilling commenced at boring B-1 at a depth of approximately 18 feet below existing grade. From a depth of approximately 18 feet through our drilling depth of approximately 33 feet, hard to moderately hard, medium gray, siltstone with very soft to soft, partially weathered to weathered, siltstone was encountered. Very soft, broken, weathered seams were encountered at depths of 18’ – 19’; 21’ – 23’; and 30’ – 32’.

Boring B-1 was terminated at a depth of 33 feet below existing grade. Core recovery was 96% and RQD for the rock core interval was 64% (fair rock).

Core drilling commenced at boring B-2 at a depth of approximately 13 feet below existing grade. From a depth of approximately 13 feet through our drilling depth of approximately 28 feet, moderately hard to hard, medium to dark gray, broken, weathered to partially weathered, siltstone was encountered. Very soft, broken, weathered seams were encountered below a depth of 23 feet. Boring B-2 was terminated at a depth of 28 feet below existing grade. Core recovery was 80% from the interval of 13 feet to 23 feet, and 7 percent for the interval of 23 feet to 28 feet. Rock Quality Designation (RQD) for the rock core interval of 13 feet to 23 feet was 34% (poor rock), and 0% for the interval of 23 feet to 28 feet.

As a result of the poor quality rock encountered at boring B-2, and offset boring B-2A was used to investigate the rock at an offset location approximately 4 feet from B-2. Core drilling commenced at boring B-2A at a depth of approximately 12 feet below existing grade. From a depth of approximately 12 feet through our drilling depth of approximately 30 feet, very soft to hard, medium to dark gray, broken, weathered to partially weathered, siltstone was encountered. Very soft, broken, weathered seams were encountered below a depth of 22 feet.

Boring B-2A was terminated at a depth of 30 feet below existing grade. Core recovery was 58 percent from the interval of 12 feet to 22 feet, and 61 percent for the interval of 22 feet to 30 feet. Rock Quality Designation (RQD) for the rock core interval of 12 feet to 22 feet was 13% (poor rock), and 7% (poor rock) for the interval of 22 feet to 30 feet.

Core recovery and RQD for the rock cores may be seen in Table III.

Table III – Rock Core-Drilling Subsurface Stratification Summary

Stratum

Depth, Ft.*

Description Core

Recovery - %

Rock Quality

Designation - %

B-1 0.0” – 18’ Soil Overburden (Fill). NA NA

18’ – 33’ Hard to moderately hard, medium gray, siltstone with very soft to soft, partially weathered to weathered seams.

Weathered Seams: 18’-19’; 21’-23’; 30’- 32’

96 64

B-2 0.0” – 13’ Soil Overburden. NA NA

13’ – 23’

23’ – 28’

Moderately hard to hard, medium to dark gray, broken, weathered to partially weathered, siltstone, with very soft to soft, broken, weathered seams.

Very soft, very broken, weathered siltstone.

B-2A 0.0” – 12’ Soil Overburden. NA NA

12’ – 22’

22’ – 30’

Very soft to hard, medium to dark gray, broken, weathered to partially weathered, siltstone, with weathered seams.

Very broken weathered siltstone.

*Stratum depths are approximate. NA = 0% Recovery & 0% RQD for soil overburden (this material not core drilled).

The underlying siltstone bedrock encountered through our core drilling depths is described as very soft to hard, with soft to very soft, weathered seams. Very soft rock disintegrates or easily compresses to touch and can have a high percentage of soil.

The unconfined compressive strength of very soft rock ranges from 1 to 2,500 psi. Soft rock is coherent but breaks very easily to thumb pressure at sharp edges and crumbles with firm hand pressure. The unconfined compressive strength of soft rock ranges from 2,500 psi to 8,000 psi. Moderately hard rock can be broken off along sharp edges by considerable hand pressure, and can be broken with light hammer blows. Hard rock cannot be broken by thumb pressure but can be broken by moderate hammer blows.

The unconfined compressive strength of hard rock ranges from 8,000 to 20,000 psi.

The unconfined compressive strength of moderately hard rock is near the lower end of the hard rock unconfined compressive strength scale. Very hard rock can be broken only by heavy hammer blows. The unconfined compressive strength of very hard rock is greater than 20,000 psi.

Upon completion of the soil and rock core drilling operation, the bore holes were backfilled with soil auger cuttings.

5.3 Groundwater

By definition, groundwater is the continuous body of subsurface water that fills the soil, rock voids and fissures and is free to move under the influence of gravity. The water table or phreatic surface is the level of zero (atmospheric) pressure in a continuous body of groundwater. The groundwater level is not a static level surface as the term water table implies. Instead, it is the sloping surface of a moving stream of water in the voids and fissures.

Groundwater was not encountered in the borings at the time of drilling. It is likely that a perched or trapped water level would be encountered on top of the Siltstone bedrock unit within the area along Briar Creek. Groundwater should be anticipated in excavations that extend down to creek level and below. The perched or trapped water level can be expected to fluctuate seasonally as well as during periods of inclement and arid weather. For reasons of safety, all borings were backfilled with soil upon completion.

A deeper bedrock aquifer exists at some depth into the bedrock below the ground surface. This depth is well below the level of our borings. A groundwater study was beyond the scope of our exploration.

6.0 GEOLOGY

Physiographically the site is located in the Southeast Valley and Ridge geologic province. This is a region of folded and faulted rock formations of Cambrian to Precambrian age. The subject site is located on the East Sheet of the Geologic Map of Tennessee. The quadrangle has been geologically mapped at a 1:250,000 scale. The area was geologically mapped by John Rodgers and Josiah Bridge. The mapping was published in 1966 by William D. Hardeman, State Geologist.

The project site is mapped to be underlain by the Unicoi Formation. The Unicoi Formation is a member of the Chilhowee Group and is of Middle Cambrian age. The Unicoi Formation is describes as follows: Sequence of gray feldspathic sandstone, arkose, conglomerate, greywacke, siltstone and shale; greenish amygdaloidal basalt flows near middle and base. Thickness 2,000 to 5,000 feet. The formation strikes from northeast to southwest.

Geologic Map Plan View

The project site is mapped to be underlain by the Unicoi Formation (Symbol Cu).

SITE

7.0 RECOMMENDATIONS

We offer the following engineering recommendations based on the geotechnical data obtained from the subsurface exploration and information provided by the Forest Service regarding the box culvert construction.

We understand that the Forest Service is considering installing a bottomless aluminum box culvert with aluminum footing pads or reinforced concrete footings.

7.1 Box Culvert Site Preparation

We recommend that the excavation made for box culvert construction be excavated down to the underlying bedrock unit. We estimate this to be a depth of about 15 feet below existing road level. The width of the excavation should extend a minimum of 15 feet beyond the perimeter edge of each side the proposed new culvert.

Excavation sidewalls should be sloped no steeper than 1.5H:1V. Excavations should be sloped or shored in accordance with local, state and federal regulations including OSHA (29 CFR Part 1926) excavation and trench safety. The on-site, in-place, fill soil overlying the bedrock is classified under OSHA guidelines as Type C soil (see Section

7.4 below).

Backfill material placed around the box culvert (up to the level of 1 foot above the 100 year flood level of Briar Creek) should consist of free draining coarse grained sand and gravel, with no silt or clay fines.

Care should be taken to ensure that no fine grained sands, silts, and clays are placed as fill up to the level of 1 foot above the 100 year flood level.

Once the free draining fill material reaches the desired level, a minimum 8 ounce per square yard, nonwoven, geotextile should be spread across the top of the fill. The geotextile should use a minimum lap width of two feet between successive roll widths and at all locations where two or pieces of the geotextile will be joined.

Backfill material placed around the box culvert, beginning at the level of 1 foot above the 100 year flood level of Briar Creek (over the top of the nonwoven geotextile) should consist of stone fragments, gravel and sand, gravel or sand with silt or clay.

Material placed as fill around and over the top of the culvert should meet the Group Classification requirements of AASHTO M-145 for material types A-1-a, A-1-b, A-2-4, A- 2-5, or A-3. Soils with AASHTO Group Classifications of A-2-6, A-2-7, A-4, A-5, A-6, A- 7 (A-7-5 & A-7-6) are not suitable for use as backfill material. Maximum particle size should not exceed three inches in greatest dimension. As noted, care should be taken to ensure that no fine grained sands, silts, and clays are placed as fill up to the level of 1 foot above the 100 year flood elevation. Material removed during construction of the proposed new culvert may be reused as fill provided that it meets the above outlined classification guidelines.

Nonwoven geotextile (minimum 8 ounce per square yard) should be placed between layers of soil with significantly different gradations to prevent migration of fines.

Backfill lift thickness should not exceed 8 inches, loose. The fill should be placed in horizontal lifts. Each lift should be thoroughly compacted before subsequent lifts of fill are placed. The fill should be placed uniformly on both sides of the culvert, taking care to minimize differential (unbalanced) backfill heights on either side of the culvert.

Balanced fill lifts should be placed as per AASHTO Section 26.

Backfill material around and above the box culvert should be compacted to a minimum of 95% of its maximum dry density as determined by the Standard Proctor test, AASHTO T-99. The moisture content of soils meeting the Group A-2-4 and A-2-5 classification requirements should have the moisture content of the material controlled to within the range of +/- 2 percent of Standard Proctor Optimum moisture content during compaction. As noted above, maximum particle size should not exceed 3 inches in greatest dimension.

Care should be taken during placement and compaction of fill immediately adjacent to the box culvert to prevent damage to the structure. The culvert manufacturer should be consulted regarding maximum equipment weights, compaction equipment, etc. In general, we recommend that for a minimum distance of 4 feet around the perimeter (sides and top) that lightweight (under 20,000 pounds) be used to place fill, and that lightweight vibratory plate or roller compaction equipment be used to compact the backfill. Use of heavy equipment (greater than 20,000 pounds) and rubber tired equipment such as dump trucks, loaders, scrapers, etc. should typically not be used within this 4 foot zone, as there is risk that damage to the aluminum culvert structure would occur. As noted, the culvert manufacturer should provide fill placement compaction equipment guidelines to prevent damage to his product during installation.

In-place density testing should be performed concurrent with placement of all fill to ensure the desired density is achieved. The recommended minimum rate of testing is 1 test per 2500 square feet or less of fill area for each soil fill lift. A qualified soil technician, under the direction of a geotechnical engineer, should perform the soil density testing.

Water flow and hydraulic forces can erode backfill, damage the culvert ends and inundate backfill. Flow into the culvert should be in a straight path or should be directed into the culvert using wingwalls or other channeling structure. Up to the elevation of 1 foot above the 100 year flood level of the creek, the slope face (exposed surface) of the backfill placed around the culvert (both upstream and downstream) should be covered by a heavy duty, nonwoven, geotextile. A minimum 8 ounce per square yard geotextile should be used; however, the geotextile should ultimately be sized to survive the placement of riprap slope protection. Riprap should be placed over the geotextile. The riprap size, and thickness of the riprap layer, should be based on the stream hydraulics during maximum flooding. Care should be taken during placement of the riprap on the geotextile. Geotextile damaged during placement of riprap cover should be removed and replaced.

The portion of the slope above the riprap should receive seed and straw as soon after completion as possible, with erosion control matting placed as needed, to prevent washing until a vegetative cover develops. We recommend that the compacted structural fill slope be constructed no steeper than 1.5 horizontal to 1 vertical (1.5H:1V).

7.2 Foundation Type and Allowable Bearing Capacity

We recommend that the proposed aluminum bottomless box culvert be supported using a steel reinforced concrete footing. The footing should bear a minimum of one (1) foot into the Siltstone bedrock material. Bearing a minimum of one foot into the bedrock, the footing may be sized using an allowable bearing capacity of 5000 PSF. The footing should be sized a minimum of 18 inches in width.

To resist lateral loading, a friction factor of 0.60 may be used for design (footing concrete on weathered Siltstone); and coefficient of passive pressure Kp value of 4 (phi angle of 37 degrees and minimum 1 foot embedment down into the bedrock) may be used for rock sidewalls.

The footing excavations should be inspected by a geotechnical engineer prior to placement of reinforcing steel or concrete. Dynamic Cone Penetrometer testing (ASTM

STP 399) should be performed as directed by the geotechnical engineer to confirm the assigned bearing capacity.

If seams of very soft, weathered material are encountered that do not meet the assigned 5000 PSF allowable bearing capacity, the very soft, weathered material should be excavated to suitable bearing material, with the excavation backfilled to design footing grade with concrete.

We recommend that dowels/rock anchors be extended from the bedrock into the concrete footing to provide resistance to lateral loading and uplift as may be required.

Below the 100-year flood level, the box culvert should be designed to resist equivalent fluid pressure loading of 115 PSF per foot of depth (unit weight of water plus buoyant weight of compacted structural soil fill), plus applicable surcharge loading from culvert approach traffic. This value assumes that there is only a small amount of water moving through the barrel of the box bridge and that water is trapped behind the walls (no free drainage). If water pressure is equal on both sides of the box culvert walls, then the walls should be designed to resist equivalent fluid pressure loading of 50 PSF per foot plus applicable surcharge loading from bridge approach traffic.

Above the 100-year flood elevation, the abutments should be designed to resist equivalent fluid pressure loading of 55 PSF per foot of depth (plus applicable surcharge loading) if the fill is composed of the recommended material, and is placed and compacted as outlined above.

7.3 Excavation Safety

Excavations should be sloped or shored in accordance with local, state and federal regulations including OSHA (29 CFR Part 1926) excavation and trench safety. The on-site, in-place, alluvial soil overlying the bedrock is classified under OSHA guidelines as Type C soil.

The contractor is solely responsible for site safety. All surcharge loading from construction materials, material removed from the excavation (soil, rock, etc.), construction equipment, etc. should be considered when designing shoring. Such material should generally be placed a minimum distance back from the crest of the excavation equal to the depth of the excavation. This information is provided only as a service and under no circumstances should we be assumed to be responsible for construction site safety.

8.0 ADDITIONAL RECOMMENDED WORK

We recommend that our firm be selected to provide all field and laboratory quality control construction material engineering and testing services during construction (structural fill, concrete, etc.). Quality control testing and observation services are recommended to confirm the allowable bearing capacity of excavated footings, to check the in-place density of the backfill material, and to test concrete footings, etc..

9.0 GENERAL QUALIFICATIONS

This report has been prepared for the exclusive use of the USDA Forest Service. This subsurface exploration report has been prepared in accordance with generally accepted geotechnical engineering practice for specific application to the geotechnical design elements of this project. The conclusions and recommendations contained in this report are based upon applicable standards of our practice in this geographic area at the time this report was prepared. No other warranty, expressed or implied, is made. Foundation Systems Engineering, P.C is not responsible for any claims, damages, or liability associated with any other party’s interpretation of this report’s subsurface data or reuse of this report’s subsurface data or engineering analysis without our express written authorization.

The analyses and recommendations submitted herein are based, in part, upon the data obtained from the subsurface exploration. The nature and extent of variations between the borings will not become evident until construction. If variations appear evident, then we will re-evaluate the recommendations of this report. In the event that any changes in the nature, design, or location of the proposed new aluminum bottomless box culvert are planned, the conclusions and recommendations contained in this report will not be considered valid unless the changes are reviewed and conclusions modified or verified in writing.

This report should not be made a part of project plans and specifications; but may be included with bidding documents for the convenience of the bidders.

FOUNDATION SYSTEMS

ENGINEERING, P.C.

2203 ATCHLEY STREET

P.O. BOX 9449

KNOXVILLE, TN 37940

865-577-3361

FAX 573-1817

www.fsepc.com

BORING LOCATION PLAN

FSR 188 BRIAR CREEK ROAD

WASHINGTON COUNTY, TENNESSEE

USDA FOREST SERVICE

Geotechnical Engineering and Consulting