Soils Foundation Report.pdf

SOILS AND FOUNDATIONS REPORT

NO. 08-07

PROJECT PRA-NATR 3O16

MULTI-USE TRAIL

(OLD CANTON ROAD TO RESERVOIR OVERLOOK)

NATCHEZ TRACE PARKWAY

MADISON COUNTY, MISSISSIPPI

PMIS No. 55898

U.S. Department of Transportation Federal Highway Administration

Eastern Federal Lands Highway Division 21400 Ridgetop Circle

Sterling, VA 20166

May 2008

TABLE OF CONTENTS

PAGE

INTRODUCTION

GENERAL

PROJECT DESCRIPTION

GEOLOGIC SETTING

REGIONAL GEOLOGY

SOIL SURVEY

PROCEDURES AND RESULTS

GENERAL

SAMPLING

FIELD TESTS AND MEASUREMENTS

DATA SUMMARY

FINDINGS

LABORATORY TESTING

DESIGN ANALYSIS AND CONCLUSIONS

BRIDGE FOUNDATIONS

EMBANKMENTS/FILL SLOPES

RETAINING WALL

PAVEMENT

RECOMMENDATIONS

BRIDGE FOUNDATIONS

ABUTMENT WALLS

RETAINING WALL

PAVEMENT

CONSTRUCTION CONSIDERATIONS

DISCLAIMER/LIMITATIONS CLAUSE

BIBLIOGRAPHY

APPENDICES

APPENDIX A..……………………………………....................…………………………...Figures

APPENDIX B..……………………………...............Boring Location Plan and Subsurface Profile

APPENDIX C..…………………………………………....…………………………...Boring Logs

APPENDIX D.……………………………………………...........………...Laboratory Test Results

APPENDIX E.……………………………………….……………..Design Analysis Computations

APPENDIX F….........................................................................................................Typical Details

APPENDIX G.……………………………………………..............Special Contract Requirements

APPENDIX H.………………………………………………...........…Representative Photographs

Note: Design changes made subsequent to distribution of this report and prior to project advertisement will be documented in a memo inserted after the title page.

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

EASTERN FEDERAL LANDS HIGHWAY DIVISION

STERLING, VA

SOILS AND FOUNDATIONS REPORT

NO. 08-07

MULTI-USE TRAIL

(OLD CANTON ROAD TO RESERVOIR OVERLOOK)

PMIS No. 55898

INTRODUCTION

GENERAL

This report summarizes the results of our subsurface explorations, laboratory testing, and design analyses and presents recommendations for bridge foundations and pavements for Project PRA-NATR 3O16. The project is located along the Natchez Trace Parkway in Madison County, Mississippi. The general site location is shown on Figure 1 in Appendix A.

PROJECT DESCRIPTION

Project PRA-NATR 3O16 consists of the construction of a multi-use trail along the Natchez Trace Parkway near the City of Jackson in Madison County, Mississippi. The proposed multi-use trail was originally envisioned to be constructed in three phases as described in the 1995 Environmental Assessment Report for the project. However, Eastern Federal Lands Highway Division (EFLHD) has since divided the trail into four phases. This phase represents the first phase of construction and consists of the construction of approximately 2.3 miles of paved trail from Old Canton Road to the Ross R.

Barnett Reservoir Overlook parking area (between mileposts 103.7+/- and 105.8+/-). The multi-use trail’s profile will closely follow existing ground elevations, and generally follows the alignment in the approved Environmental Assessment for the project.

The scope of work for Project PRA-NATR 3O16 consists of the construction of 2.26 mile long multi-use trail consisting of a 10 foot wide travel way with 2 foot shoulders and includes construction of 3 trail bridges. The three proposed bridges will span Brashear’s Creek, Rice Road, and a yet unnamed stream. Additional water crossings will be accomplished by extending existing culverts along the Parkway and constructing new culverts, where needed. Additionally, a small connector road is to be constructed between the existing Post Road and the proposed multi-use trail. The trail will generally be located outside the viewshed of the Parkway.

SOILS AND FOUNDATION REPORT NO. 08-07

MULTI-USE BIKE TRAIL

GEOLOGIC SETTING

REGIONAL GEOLOGY

According to the Department of the Interior (1954), “Geology of the Jackson Area Mississippi,” the project site is located within the Jackson Prairie Belt Physiographic Province of the Gulf Coastal Plain.

The geology in the vicinity of the proposed project consists of recent wind and river deposited surficial soils overlying older sediment formations. The most recent deposits consist of alluvial silts, sands, gravels and clays within the flood plains of the Pearl River and its tributaries. Areas of the older stream terrace deposits of red sand and gravel and a surficial formation of weathered loess (wind-blown silt and clay) exist at higher elevations. The surficial loess formation has been eroded, transported, and reworked from the true loess deposits of western Mississippi. The alluvium and terrace deposits are typically 18 to 36 ft thick, while the surficial loess is typically only a few feet thick.

The alluvium, terrace deposits and loess are underlain by the highly plastic, highly expansive Yazoo Clay Formation of the Tertiary Jackson Group (informally, Yazoo Clay). The Yazoo Clay is comprised of an upper weathered phase and a lower unweathered phase. The weathered phase is typically 15 to 30 ft thick and is characterized by an olive-brown to yellow-brown color. Typically, the weathered Yazoo Clay contains glauconitic, fossiliferous clayey sand lenses. The unweathered phase of the Yazoo Clay is typically up to 300+ feet thick and is characterized by a distinct blue-gray color. The unweathered Yazoo Clay is typically fossiliferous and calcareous with thin beds and laminae of fine-grained micaceous sand, thick lenses of cross bedded sand, and large quantities of microfossils and mollusks. Refer to Figure 2 of Appendix A, for a bedrock geologic map of the area.

SOIL SURVEY

According to the United States Department of Agriculture (1982), “Soil Survey of Madison County, Mississippi,” the project site is underlain predominantly by soils of the Byram-Loring Unit, and to a lesser extent the Loring-Grenada-Calloway Unit in the vicinity of Brashears Creek. Byram-Loring soils consist of moderately well drained silty soils that have a fragipan. These soils are typically on ridges and side slopes of uplands and stream terraces. Soils of the Loring-Grenada-Calloway Unit are characterized as moderately well drained and somewhat poorly drained silty soils that have a fragipan. These soils are typically on stream terraces and uplands. Both the Byram-Loring and the Loring-Grenada-Calloway soil units are formed within silty material. The Byram soils were also formed in underlying clayey deposits.

Soils from these units are unsuitable for use as fill material. Refer to Figure 3 of 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 a subsurface investigation program at the project site between February 20 and March 5, 2007. The subsurface investigation program consisted of drilling a total of 36 boreholes along the proposed alignment. The boreholes drilled are generally classified into two groups, shallow/pavement borings and deep/bridge borings. The shallow borings, designated P-1 through P-24, were drilled to depths varying

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between 12.0 and 15.0 ft. The deep borings, designated B-1 through B-12, were typically drilled to depths of greater than 20.0 ft. All borings were advanced to termination depths using a CME 850, rotary, track-mounted drill rig. Boring Location Plans and generalized Subsurface Profiles are provided in Appendix B.

SAMPLING

The boreholes were drilled to depths ranging from 12.0 to 57.0 ft below the existing ground surface.

Borings were advanced using 3¾ -in. (inside diameter) hollow stem augers. Standard Penetration Tests (SPT) were performed using a 2¼ -in. (outside diameter) split-spoon sampler in accordance with AASHTO 7200-87 and AASHTO T206-87.

Representative portions of split-spoon samples were preserved in glass jars. Three (3) undisturbed/thin-walled Shelby tube samples of soil were collected at the site in accordance with AASHTO T207. The undisturbed/thin-walled samples were preserved within their respective sample tubes. All samples were later transported to EFLHD’s Materials Testing Laboratory in Sevierville, Tennessee for laboratory testing and storage.

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

FIELD TESTS AND MEASUREMENTS

Boring locations were determined from features present on-site and by referencing the existing roadway.

Boring elevations were determined by extrapolation of topographic lines from site maps provided by EFLHD’s Survey Section. SPT soil samples in the shallow borings were typically continuously recovered by driving the split-spoon sampler a distance of 24-in., or until refusal, into the undisturbed soil under the action of a 140-pound automatic hammer free-falling 30 inches. Deep borings were typically recovered at 5.0 ft intervals. The number of hammer blows required to advance the split-spoon sampler the middle 1.0 ft of the 24-in. sample interval is designated as the “Standard Penetration Resistance” or N-Value. Split-spoon refusal is defined by 50 blows per 1-in. 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. The relative consistency of each cohesive sample was estimated using a calibrated pocket Penetrometer. A field description by color and texture was made for each recovered soil sample. The depth to groundwater, if present, was measured at the time of completion of each boring, again prior to backfilling the borehole and occasionally at 24-hours after completion of drilling.

DATA SUMMARY

The EFLHD Subsurface Investigation Team performed the following field tests and measurements during the course of the subsurface exploration. 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 team leader 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.

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The boring logs in Appendix C 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 at the times and under the conditions stated on the boring logs. The following table presents a summary of the water readings made during our investigation.

Table 1 – Groundwater Readings

Boring No. Station Ground Surface

Elevation (ft)

Depth to Water

(ft)

Elevation of Water

(ft)

B-1 3+50 306.3 12 294.3 B-2(1) 5+00 297.8 20 277.8 B-3 8+25 299.8 17 282.8 B-4 20+50 291.3 0 291.3 B-6 47+00 292.8 17 275.8 B-7 50+00 290.9 20 270.9 P-11(1) 59+00 300.4 1.8 298.6 P-12 62+00 305.4 1.1 304.3 P-13(1) 67+00 327.5 3.0 324.5

(1) Readings taken at 24-hours after completion of drilling; all othe were measured at time of drilling and again prior to backfill rs ing

Due to the presence of lenses of sand, located either above or between layers of relatively t is ent.

FINDINGS

Boring logs describing the subsurface conditions encountered in each boring may be referenced in ce ns below impermeable silts and clays, the site has the potential of having perched water conditions. I unlikely that groundwater conditions will affect construction activities along most of the alignm Nonetheless, fluctuations in groundwater level due to seasonal variations, rainfall, temperature, and other factors not evident at the time measurements were made should be expected.

Appendix C of this report. Boring Location Plan sheets in Appendix B present generalized subsurfa profiles illustrating the general geologic conditions that may be anticipated at the bridge abutments and piers, and below pavement sections. Descriptions of the soil conditions encountered during the subsurface explorations conducted at the site are presented below. The categories and descriptio are indicative of the various types of subsurface soils encountered and does not suggest stratification.

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Pavement Borings

A total of 24 pavement borings, designated P-1 through P-24, were drilled along the proposed multi-use trail alignment. As indicated on the boring logs, many sections of the proposed multi-use trail is blanketed by a layer of very soft to soft organic clay, which are in turn underlain by two major strata, namely: Clays with interbedded Sand and/or silty Sand layers; and clay of the Yazoo Formation.

Pavement borings were continuously sampled from ground surface to depths varying between 12 and 17 ft.

Fill – Fill soils associated with embankment construction for the Brashears Creek Bridge along the Natchez Trace Parkway was encountered in Boring P-1. The fill material is characterized as red, medium-to-coarse sand with trace amounts of clay. SPT N-values recorded within this stratum ranged between 6 and 17 blows per foot (bpf), indicating loose to medium dense soil conditions. The soils in this stratum were typically moist to wet.

Topsoil/Organic Clay – This stratum is characterized by medium stiff, gray to tan sandy clay, organic clay, silty organic clay, organic lean clay, silty lean clay and lean clay [A-6]. SPT N-values recorded within this stratum ranged from weight-of-hammer (WOH) to 8 bpf, indicating very soft to medium stiff soil consistency. This stratum was typically encountered at ground surface and ranged in thickness from 2 to 3 ft; occasionally this stratum is up to 5 ft thick.

Topsoil/Organic Clay soils were typically moist to wet and exhibited poor bearing resistance as was observed by pumping, weaving and significant rutting of these soils under the movement of our drill rig. It is unlikely that construction equipment will be able to traverse these soils in their natural condition. Consequently, undercutting or chemical stabilization of these soils will be necessary.

Alluvial and Terrace Deposits – This stratum is comprised of interbedded lenses of clay and sand.

The clay soil chiefly occurs in the upper parts of the deposit and consists of sandy clay, silty clay, silty lean clay, and lean clay [A-4, A-6]. The middle and lower parts of this stratum are occasionally characterized by fine-to-medium Sand with varying amounts of silt, clay, and trace amounts of gravel. Fine organic matter is also typically encountered within this deposit.

SPT N-values recorded within the upper part of the deposit ranged between 6 and 50 bpf, indicating medium stiff to hard soil consistency. Middle and lower parts of the deposits had SPT N-values ranging between 7 and 27 bpf, indicating loose to medium dense soil conditions. Occasionally the middle and lower parts of the deposits is dense to very dense with SPT N-values between 31 and 57 bpf.

Most pavement borings were terminated within this stratum at depths varying between 11 and 17 ft.

Soils within this stratum were typically moist to dry.

Yazoo Clay (Weathered) – The weathered phase of the Yazoo Clay Formation was encountered in Borings P-19, P-20 and P-21, between Stations 97+00 and 110+30. This stratum was encountered underlying the alluvial and terrace deposit stratum at a depth of 12 ft, except in Boring P-19 where it was encountered below the topsoil/organic clay at a depth of 3 ft. The weathered phase of the Yazoo Formation consists of gray-brown to brown fat clay, with trace amounts of sand, silt and occasional fine roots [A-7-5, A-7-6]. SPT N-values recorded within this stratum ranged between 5 and 37 bpf, U.S. DEPARTMENT OF TRANSPORTATION

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indicating medium stiff to hard soil consistency. The soils in this stratum were typically moist to dry.

Pavement borings were terminated within this stratum, where encountered.

The groundwater table was encountered in Borings P-11, P-12 and P-13 only, at an average depth of approximately 2 ft.

Bridge Borings

A total of twelve bridge borings, designated B-1 through B-12, were drilled along the alignment of the proposed multi-use trail. Originally, four bridges were proposed along the alignment in order to traverse creeks and the Culley Creek Floodplain. The bridge that traversed the Culley Creek Floodplain has since been eliminated and the multi-use trail’s alignment has been shifted northward in order to avoid construction within the floodplain. As a result, Borings B-5, B-6 and B-7 will not be included in the following discussion of subsurface conditions at bridge locations.

Brashears Creek Bridge

Two borings (B-1 and B-2) were advanced near the abutments of the proposed single span structure that will carry the multi-use trail over Brashears Creek. These borings generally encountered fill material overlying the weathered phase of the Yazoo Clay Formation at the west abutment location and alluvial and terrace deposits overlying the weathered phase of the Yazoo Formation at the east abutment.

Fill – Fill soils associated with embankment construction for the Brashears Creek Bridge along the Natchez Trace Parkway was encountered at ground surface in both borings. The fill stratum is characterized by red-yellow, fine-to-medium Sand overlying light brown to tan sandy clay. SPT N-values recorded within this stratum ranged from 5 to 7 bpf, indicating loose sand conditions and soft clay consistency. The bottom of this stratum was encountered at an average Elevation

295.7 ft. Thickness was measured to be 2.5 ft at the east abutment and 10 ft at the west abutment.

Topsoil/Organic Clay – The fill stratum is underlain by a layer of gray to dark brown organic Clay at the east abutment. This layer of material appears to be the original ground surface at this location, prior to embankment construction for the existing Brashears Creek Bridge. SPT N-values recorded within this stratum ranged from WOH to 5 bpf, indicating very soft to medium stiff soil consistency. The bottom of this stratum was encountered at Elevation 285.8 ft.

Thickness was measured to be approximately 10 ft.

Alluvial and Terrace Deposits – This stratum was encountered underlying the topsoil/organic clay stratum in Boring B-2 only. The alluvial and terrace deposits layer is characterized by clayey, fine-to-medium Sand [A-6]. SPT N-values recorded within this stratum ranged from 6 to 11, indicating loose to medium dense soil conditions. The bottom of this stratum was encountered at an average Elevation 273.8 ft. Thickness was measured to be approximately 12 ft.

Yazoo Clay (Weathered) – The weathered phase of the Yazoo Clay Formation was encountered underlying the fill soils and alluvial and terrace deposits, at Borings B-1 and B-2, respectively.

The Yazoo Clay of this stratum is characterized by gray to tan, sandy fat clay. Occasionally there are pockets of clayey sand within the deposit [A-6]. The weathered Yazoo was measured to be 5

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ft thick in Boring B-2, with corresponding bottom Elevation 268.8 ft. Boring B-1 was terminated within this stratum at a depth of 37 ft. Thickness was measure to be approximately 5 ft in Boring B-2. SPT N-values recorded within this stratum ranged between 5 and 21 bpf, indicating medium stiff to very stiff soil consistency.

Yazoo Clay (Unweathered) – The unweathered phase of the Yazoo Clay Formation was encountered underlying the weathered phase in Boring B-2 at a depth of 29 ft. The unweathered Yazoo is characterized by blue-gray, calcareous fat clay. Frequently shell fragments are encountered within this stratum. An SPT N-value of 10 bpf was recorded within this stratum, indicating stiff soil consistency. Boring B-2 was terminated within this stratum at a depth of 31.0 ft.

The groundwater table was encountered between Elevation 294.3 and 277.8 ft.

Rice Road Bridge

Two borings (B-8 and B-9) were advanced near the abutments of the proposed single span structure that will carry the multi-use trail over Rice Road. These two borings were supplemented with two borings (*B-2 and *B-5) that were drilled, in conjunction with Project PRA-NATR 3O14, at pier locations for the existing Rice Road Bridge. These two borings will be used to provide a generalized subsurface profile at the pier location of the proposed trail bridge. The original ground surface elevation at the location of Borings *B-2 and *B-5 is approximately 6 ft higher than the surface elevation at the location of the trail bridge; as a result, only subsurface information from below the 6 ft depth for these borings will be used.

Fill – Fill soils associated with embankment construction for the existing Rice Road Bridge along the Parkway, was encountered at ground surface in Borings B-8 and B-9. The fill stratum is characterized by red-brown to red-yellow, clayey sand, silty sand, and Sand. SPT N-values recorded within this stratum ranges between WOH and 32 bpf, indicating very loose to dense soil conditions. The bottom of this stratum was encountered between Elevation 329.5 and 320.7 ft.

Thickness varies between 2.5 and 10 ft.

Alluvial and Terrace Deposits – This stratum was encountered underlying the fill soils at depths varying between 2.5 and 10 feet, and is characterized by red-brown to brown, clay, sandy clay, and silty sand. SPT N-values recorded within this stratum ranged from 12 to 42 bpf, indicating stiff to hard clay consistency; and medium dense to dense sand conditions. The bottom of this stratum was encountered between Elevation 320.7 and 313.1 ft. Thickness varies between 5 and 15 ft.

Yazoo Clay (Weathered) – The weathered phase of the Yazoo Clay Formation was encountered underlying the alluvial and terrace deposits in all borings. The Yazoo Clay of this stratum is characterized by gray to light brown, fat clay [A-7-6]. SPT N-values recorded within this stratum ranged between 7 and 18 bpf, indicating medium stiff to very stiff soil consistency. The bottom of this stratum was generally encountered between Elevation 310.7 and 295.7 ft. Thickness was measured to be an average of 14.2 ft.

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Yazoo Clay (Unweathered) – The unweathered phase of the Yazoo Clay Formation was encountered underlying the weathered phase in all borings. The unweathered Yazoo Clay is characterized by blue-gray, calcareous fat clay. Frequently shell fragments are encountered within this stratum. SPT N-values recorded within this stratum ranged between 13 and 42 bpf, indicating stiff to hard soil consistency. All borings were terminated within this stratum at an average depth of 40.7 ft.

All borings were terminated within this stratum at an average depth of 40.75 ft.

Unnamed Stream Bridge

Two borings (B-10 and B-11) were advanced near the abutments of the proposed single span structure that will carry the multi-use trail over two unnamed creeks, designated as Twin Creeks.

These borings encountered a layer of soft organic clay fill material overlying the weathered and unweathered phases of the Yazoo Clay Formation.

Topsoil/Organic Clay – This stratum consists of yellow-brown, organic clay. SPT N-values recorded within this stratum ranged from 2 to 3 bpf, indicating very soft to soft soil consistency.

The soils in this stratum were typically wet to moist. The bottom of this stratum was encountered at an average Elevation 300.2 ft. Thickness was measured to be 5 ft.

Yazoo Clay (Weathered) – The weathered phase of the Yazoo Clay Formation was encountered underlying the topsoil/organic clay layer in both borings. The Yazoo Clay of this stratum is characterized by gray to light brown, fat clay [A-7-6]. The bottom of this stratum was generally encountered at an average Elevation 280.2 ft. Thickness was measured to be an average of 20 ft.

SPT N-values recorded within this stratum ranged between 6and 15 bpf, indicating medium stiff to stiff soil consistency.

Yazoo Clay (Unweathered) – The unweathered phase of the Yazoo Clay Formation was encountered underlying the weathered phase in all borings. The unweathered Yazoo is characterized by blue-gray, calcareous fat clay. Frequently shell fragments are encountered within this stratum. SPT N-values recorded within this stratum ranged between 9 and 17 bpf, indicating stiff to very stiff soil consistency.

All borings were terminated within this stratum at an average depth of 44.5 ft.

LABORATORY TESTING

The laboratory testing program for this project was conducted in two phases as described below. All tests were conducted in accordance with applicable AASHTO/ASTM standard test methods.

Phase I

The primary purpose of Phase I laboratory testing was to aid in the classification and evaluation of the engineering properties of soils present at the site. Additionally, tests were performed to provide a general understanding of the suitability of subgrade soils for lime or cement treatment. Phase I laboratory tests were performed on 21 jar samples and two undisturbed Shelby tube samples and included natural

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moisture content (AASHTO T-265), Atterberg limits (AASHTO T-89 & T-90), particle size analysis (AASHTO T-88), classification (AASHTO M-145), pH (AASHTO T-289), and consolidation (AASHTO T-216).

Phase I laboratory test results are summarized in Tables 2 and 3. Laboratory test result sheets are provided in Appendix D.

Table 2 – Index Properties of Soils at BRIDGES & CULVERTS

Soil Classification Boring No.

Sample No.

Sample Depth

(ft)

Water Content

LL PL PI Fines

(%) pH AASHTO Description

Brashears Creek Bridge B-1 J-3 10–12 34.2 71 19 52 81.6 7.7 A-7-6(45) fat Clay

B-1 ST-2 33–35 19.4 33 13 20 76 – A-6(13) fat Clay

B-2 J-8 19–21 16.3 29 14 15 44.4 – A-6(3) clayey Sand

Rice Road Bridge

*B-2 J-4 15–17 32.4 90 27 63 97.9 – A-7-6(72) fat Clay

*B-2 J-9 40–42 39.2 89 30 59 96.2 – A-7-6(67) fat Clay

*B-5 J-3 10–12 11.8 22 9 13 36.2 – A-6(1) clayey Sand

B-9 ST-1 18–20 45.6 127 24 103 99.9 – A-7-6(120) fat Clay

Unnamed Stream Bridge

B-10 J-10 25–27 40.4 111 37 74 99.5 7.9 A-7-5(90) fat Clay

Culvert Crossing (Sta. 106+50)

B-12 J-6 20–22 44.0 102 39 63 97.4 – A-7-5(75) fat Clay

Table 3 – Index Properties of Soils below PAVEMENT SECTION

Soil Classification Boring No.

Sample No.

Sample Depth

(ft)

Water Content

LL PL PI Fines

(%) pH AASHTO Description

P-2 J-5 10–12 25.8 28 13 15 94.8 – A-6(12) silty Clay

P-4 J-2 2–4 26.6 36 23 13 98.7 7.4 A-6(14) lean Clay

P-5 J-2 2–4 12.4 24 16 8 67.8 – A-4(3) silty Sand

P-6 J-1 0–2 29.0 40 24 16 98.2 – A-6(18) lean Clay

P-7 J-3 5–7 12.7 31 15 16 93.5 – A-6(14) lean Clay

P-8 J-2 3–5 20.3 37 26 11 96.9 – A-6(12) lean Clay

P-9 J-3 5–7 19.8 29 20 9 91.4 – A-4(7) lean Clay

P-10 J-1 0–2 30.5 27 16 11 95.6 – A-6(9) lean Clay

P-12 J-2 3–5 26.3 34 22 12 80.3 – A-6(9) lean Clay

P-18 J-4 10–12 12.6 36 17 19 67.8 – A-6(11) lean Clay

P-19 J-4 10–12 37.6 116 35 81 98.5 – A-7-5(95) fat Clay

P-21 J-4 10–12 9.4 60 24 36 96.8 – A-7-6(40) fat Clay

P-23 J-3 5–7 12.1 34 19 15 95.9 – A-6(14) lean Clay

Fill – No laboratory tests were performed on soil samples recovered within this stratum

Topsoil/Organic Clay – Laboratory tests performed on soil samples recovered within this stratum indicate that the soil has liquid limits between 27 and 40, with an average of 34. The plasticity indices ranged between 11 and 16, with an average of 13. Fines content of the material ranged between 80 and 98 percent, with an average of 91 percent. The moisture content ranged between 26 and 30 percent, with an average of 28 percent.

Alluvial and Terrace Deposits – Laboratory tests performed on soil samples recovered within this stratum indicate that the soil has liquid limits between 24 and 37, with an average of 32. The plasticity indices ranged between 8 and 19, with an average of 13. Fines content of the material ranged between 36 and 99 percent, with an average of 79 percent. The moisture content ranged between 12 and 29 percent, with an average of 17 percent. A pH value of 7.4 was recorded within this stratum.

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Yazoo Clay (Weathered) – Laboratory tests performed on soil samples recovered within this stratum indicate that the soil has liquid limits between 33 and 127, with an average of 67. The plasticity indices ranged between 20 and 103, with an average of 51. Fines content of the material ranged between 76 and 100 percent, with an average of 93 percent. The moisture content ranged between 9 and 42 percent, with an average of 32 percent. A pH value of 7.7 was recorded within this stratum.

Consolidation properties of soil from this stratum are as summarized in Table 4 below.

Table 4 – Consolidation Properties of Soils

Boring No.

Sample No.

Sample Depth

(ft)

Specific Gravity, GS

Dry Density, γd

(pcf) P'c

(psf) Cc Cr eo

B-1 ST-2 33–35 2.68 105 6990 0.14 0.02 0.594

B-9 ST-1 18–20 2.68 72.5 5650 0.38 0.13 1.308

P'c = Preconsolidation Pressure; Cc = Compression Index; Cr = Recompression Index, eo = Initial Void Ratio

Yazoo Clay (Unweathered). Laboratory tests performed on soil samples recovered within this stratum indicate that the soil has liquid limits between 89 and 111, with an average of 100. The plasticity indices ranged between 59 and 74, with an average of 66. Fines content was an average of approximately 98 percent. The moisture content was an average of approximately 40 percent. A pH value of 7.9 was recorded within this stratum.

Phase II

The second phase of laboratory testing was performed upon review of the results of Phase I testing.

Phase II tests were performed to determine the swell potential and California Bearing Ratio (CBR) of soils within the upper 15 ft of the subgrade and to aid in the mix proportioning for the design of pavement/subgrade stabilization using either a lime or cement stabilizer. The soils tested were largely alluvial and terrace deposit soils that were characterized during Phase I testing as lean clays (A-6).

Laboratory tests performed included CBR (ASTM D1883), and Effectiveness of Admixtures for Soil Stabilization (ASTM D4609). Laboratory test results are summarized below in Table 5. Laboratory test result sheet are provided in Appendix D.

CBR test results on untreated soil samples yielded an average value of 7.5%, correlating to a resilient modulus of approximately 9,000 psi. The topsoil/organic clay layer, encountered within the upper 3 ft of the subgrade along the alignment, is estimated to have a CBR value of < 3, correlating to a resilient modus value of approximately 5,000 psi.

The swell potential of untreated soils ranged between 0.5 and 0.6, indicating low to marginal swell potential. The swell potential of A-6 soils tested ranged between 0.5 and 0.6, indicating low to marginal swell potential. However, past experience in the Jackson, Mississippi area has shown that A-6 soils do

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undergo measurable expansion, typically resulting in moderate to severe cracking of pavement sections constructed to bear directly on these materials. The Mississippi State Highway Department has indicated that it is standard practice to treat A-6 subgrade soils with six percent hydrated lime by weight. Our tests results reinforce this recommendation.

Table 5 – Standard Proctor and CBR Results Standard Proctor

California Bearing Ratio

Boring No.

Sample No.(1)

Sample Depth

(ft) Treatment Max

Density (pcf)

Optimum Moisture

CBR

Swell

Swell Potential(2)

Raw 112.2 15.6 7 0.6 Marginal 4% 111.8 14.9 135 0.5 Low

6% 110.9 15 192 0.3 Low

P-5

P-8 S1 0–12

Cement

8% 112.1 14.5 231 0.5 Low

Raw 113.6 14.4 8 0.5 Low 2% 110.9 16.6 35 0.5 Low 4% 108.6 16.7 36 0.2 Low

P-18

P-23 S2 0–12

Lime

6% 107.6 16.7 38 0.1 Low

(1) Sample S1 and S2 is a mixture of bulk soil samples obtained from Borings P-5 and P-8; S2 is a mixture from Borings P-18 and P-23.

(2) The swell potential of soils evaluated in accordance with Table 10.4.6.3-1 of AASHTO (2007)

Laboratory tests indicate that a hydrated lime stabilizer was slightly more efficient than the cement stabilizer in reducing the swell potential of lean clays along the alignment. Both stabilizers markedly improved the bearing resistance of subgrade soil. The CBR value of lime-treated subgrade soils increased to an average of 36 percent, correlating to a resilient modulus of approximately 25,000 psi. The cement stabilizer increased the CBR of soils to an average of 187 percent, correlating to a resilient modulus of approximately 73,000 psi. It is unlikely that a cement stabilizer will be effective in increasing the stability of the topsoil/organic clay layer.

DESIGN ANALYSIS AND CONCLUSIONS

Design analyses for construction of bridge abutments and piers, bridge approaches, retaining walls, and pavement sections were performed based on the strength parameters of onsite soils encountered within the depth of our explorations.

BRIDGE FOUNDATIONS

Previous bridges constructed along the Natchez Trace Parkway (NATR) were supported on deep foundation systems consisting of both driven piles and drilled shafts. During the design process for

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Project PRA-NATR 3O14 a survey of foundation alternatives, their cost, and their performance was conducted of all previous NATR projects. It was determined that driven piles are the most feasible and economical deep foundation system for the subsurface conditions encountered in many areas along the Parkway. Accordingly, driven piles are considered to be the most feasible and economical type of deep foundation system for this project. 14-in. and a 16-in. square, precast, prestressed concrete (PPC) piles are considered to be the most suitable and economical type of driven pile foundation for this project.

Design analyses were performed based on data obtained from our subsurface investigation program and laboratory test results, where available. The soil properties presented in Table 6 below were developed based on empirical correlations between available laboratory test results and SPT N-values. Design analyses were performed using a generalized subsurface profile at each structure location and using the material properties below and the subsurface profiles as presented in Appendix B.

Table 6 – Soil Parameters for Analysis

Material Type Unit Weight, γ

(pcf)

Average SPT N-value

(bpf)

Friction Angle, Φ

(deg.)

Cohesion, c (psf)

Fill 120 12 - -

Organic Clay 90 – 105 5 - 400

Sandy Clay 125 25 - 1, 500

Clayey Fine Sand 120 9 30 -

Silty Fine Sand 127 38 33 -

Weathered Yazoo 110 – 120 9 - 1, 800 – 2, 200

Unweathered Yazoo 115 – 130 13 - 2, 500 –3, 200

Scour

No scour analysis was performed for the bridges on this project as a scour analysis is not required for non-roadway bridges. However, after reviewing the proposed abutment locations and material types in the borings at the bridge sites, the following scour assumptions were made: no scour will take place at the Rice Road Bridge location, and approximately 15 ft of long-term scour (channel degradation and contraction scour) will take place at the east abutment of the Brashears Creek Bridge and 10 ft of long term scour will occur at the Twin Creeks Bridge location. These scour depths were specified in our design analyses for the Brashears Creek and Twin Creeks Bridge sites.

Bottom of footing elevations were established based on review of boring logs and the Preliminary Hydraulics Report of September 13, 2007. Bottom of footing elevations for use in determining pile tip elevations are as shown in Table 7.

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Table 7 – Proposed Bottom-of-Footing Elevations

Structure Location Bottom-of-Footing

Elevation (ft)

Brashears Creek Bridge Abutment(s) 296

East 333 Abutments

West 326 Rice Road Bridge

Piers 320

Unnamed Stream Bridge Abutment 302

Axial Capacity

The nominal (ultimate) resistance of individual piles was evaluated in accordance with FHWA (2006), Design of Driven Pile Foundations, and Section 10 of AASHTO (2007), LRFD Bridge Design Specifications. The FHWA computer program DRIVEN (v1.2) was used to calculate axial capacities for driven piles at each of the three bridge sites.

Design analyses suggest that 14-in. or 16-in. square PPC piles will be adequate for providing support of structure loads. The analyses indicate that axial pile capacity will be developed by a combination of skin friction and end-bearing in the weathered and unweathered phases of the Yazoo Clay Formation.

Design bearing graphs which summarize nominal pile resistance versus depth are presented in Appendix E. DRIVEN analysis computation output files may also be referenced in Appendix E.

Uplift Capacity

Single pile uplift resistance was evaluated in accordance with Subsection 9.7.2 of FHWA (2006). The uplift capacity of individual piles at the abutment and piers are presented as a function of depth on design bearing graphs in Appendix E.

Settlement

Settlement of driven concrete pile foundations bearing a minimum of 10 ft in the medium stiff to very stiff Yazoo Clay Formation should be less than ½ -inch.

Lateral Capacity

Subsurface conditions encountered at the east abutment of the Brashears Creek Bridge are the least likely to provide adequate lateral capacity resistance for piles installed at the three bridge sites. Accordingly, lateral pile capacity analyses were performed using a generalized subsurface profile based on Boring B-2 and using the computer program LPILE Plus (v4.0). Design analyses were performed for the 14-in. and 16-in. PPC piles with an estimated embedment length of 40 ft. Pile length variations of +/- 5 ft should be expected. Actual pile lengths will be determined by dynamic pile load testing.

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Lateral capacity analyses were performed using the maximum shear loads and moments, at the Strength I limit state, as presented in Table 8.

Table 8 – Lateral Loading Conditions

STRUCTURE LOCATION

Brashears Creek Rice Road Unnamed

Streams

LIMIT

STATE LOADS

Abutments Abutments Piers Abutments

Shear (kips) 135 87 – 87

Trans. 55 39 110 53 Service I Moment (k-ft) Long. 1,009 457 397 468

Analysis results indicate that the lateral resistance provided by subsurface soils is adequate to limit pile head deflections to 1-in. or less.

Output files from the LPile analyses are provided in Appendix E.

EMBANKMENTS/FILL SLOPES

The only significant embankment fills along the alignment are at bridge approaches. Approach fills at the Brashears Creek Bridge and the Rice Road Bridge are an average of approximately 7.5 ft high. The approach embankment for the Unnamed Stream Bridge is approximately 4.0 ft high.

Stability

Slope stability analyses were performed for the critical embankment fill slope on the project, which is located at the east abutment of the Brashears Creek Bridge. Although the approach embankments for the Rice Road Bridge are several feet higher than the embankments for the Brashears Creek Bridge, the foundation soils at Brashears Creek are significantly softer and thus present a more critical case for slope stability. Boring B-2 indicates that the soils in this area are fill soils to approximately Elevation 295 ft. Directly underlying the fill material is an approximate 10 ft thick layer of soft to very soft organic clay. The organic clay stratum is underlain by loose to medium dense sand to Elevation 273.8 ft and by the Yazoo Clay Formation to the termination depth of Boring B-2 at Elevation 269 ft. The east abutment at Brashears Creek has a maximum fill slope height of 8 ft. The majority of embankment material will be placed as backfill behind the proposed retaining wall at this location.

For foundations soils, soil strength parameters were selected based on SPT N-values and the results of laboratory testing; and are generally in accordance with the strength parameters presented in Table 6. The computer program ReSSA(2.0) was utilized for the stability analyses. Design analyses indicate that the resulting short-term and long-term safety factors were both at least 1.3 and both had the same critical circle.

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Settlement

It was determined that settlement would be more critical at the east abutment of the Brashears Creek Bridge versus that at approach embankments for the other bridges, largely due to the presence of the soft organic clay stratum at this location. Magnitude of settlement analyses were performed using the soil strength parameters in Table 6 and using correlations to the soil index properties presented in Tables 2 and 3. Settlement analyses were performed in accordance with AASHTO (2007).

Using the method presented in FHWA (2000), “FHWA-NHI-00-045: Soils and Foundation Workshop Manual,” it was concluded that all settlement would be in the recompression range based on the liquidity index being considerably less than 0.7. The settlement calculations using this method indicate that a maximum total consolidation settlement of 4.1-inches will occur within subsurface soils. No time rates of settlement analyses were performed. It is anticipated that most of the settlement should occur during construction, shortly after the embankment is constructed to its full height.

Embankment fill slopes steeper than 2(H):1(V) would likely require the use of rock embankment fill or geosynthetic reinforcement to provide adequate long-term stability. Placement of rock embankment fill would likely destabilize the slope. Additionally, incorporating either the use of rock fill for embankment construction or the placement of geosynthetic reinforcement would incur considerable additional cost to the project. Therefore, fill slopes steeper than 2(H):1(V) should not be considered.

Design analysis computations are presented in Appendix E.

RETAINING WALL

In order to prevent placing embankment fill material within the floodplain south of the Brashears Creek Bridge, it is proposed to construct a retaining wall along the south end of both abutments. The proposed grades at this location suggest that the retaining wall have exposed heights of 6 and 8 feet for the east and west walls, respectively. Borings B-1 and B-2, drilled at the abutment locations for this bridge, indicate that the proposed walls will likely bear within fill soil at approximately Elevation 296 ft. The wall to be constructed at the east abutment location was evaluated for stability due to the nature and consistency of foundation soils at that location.

The following two retaining wall alternatives were evaluated for support of the proposed embankment.

The wall alternatives were evaluated on the basis of cost, stability, constructability, and aesthetics.

1. Concrete Cantilevered Wall – Consists of a traditional reinforced cast-in-place concrete retaining wall designed to bear within the existing soils at approximately Elevation 296 ft.

2. Sheet-pile Wall – This wall alternative consists of driving interlocking sections of steel sheet-pile from ground surface to a depth of embedment within the Yazoo Clay Formation. This wall alternative was considered due to the use of a similar wall to support embankment fills for the west abutment of the Parkway Bridge at Brashears Creek.

The concrete cantilevered retaining wall was determined to be the most suitable wall alternative for this application. The concrete cantilevered wall does not require any specialized equipment for construction and can be constructed in conjunction with abutment construction for the proposed trail crossing over

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Brashears Creek. Additionally, a stone veneer may be applied to the face of the wall to improve its aesthetics.

Stability Analyses

Stability of the proposed retaining wall was analyzed in accordance with AASHTO (2007). The wall height varies along the alignment to a maximum of 8 ft. Configuration of the wall was chosen based on the proposed ground cross section at Station 5+00.

Bearing capacity, sliding, and overturning were checked by hand in accordance with AASHTO (2007).

Global stability was checked using the computer program ReSSA(2.0).

Design analyses indicate that a concrete cantilevered retaining wall bearing at Elevation 296 ft does not satisfy global stability requirements. The calculated failure circle extends almost to the bottom of the soft to very soft organic clay stratum; a depth of approximately 10 ft below existing ground surface. Removal and replacement of the organic clay stratum was determined to be impractical due to the depth and thickness of the stratum. Consequently, it is recommended that the proposed retaining wall at the east abutment be designed to bear on a deep foundation system. The wall at the west abutment should be designed to bear on a spread footing foundation.

Design analysis computations are presented in Appendix E. A typical wall section is presented in Appendix F.

PAVEMENT

Pavement design is based on the findings of our subsurface field investigation, laboratory testing, and design experience in the vicinity of the proposed multi-use trail. The multi-use trail is intended for pedestrian and bicycle traffic with occasional maintenance truck traffic. Therefore, a typical AC pavement section will be used along the alignment and will be modified based on the discussions below.

The prevailing concern with regard to pavement construction along the alignment is the presence of the highly expansive Yazoo Clay Formation. Our subsurface investigation indicates that the Yazoo Clay is located an average of 12 ft below existing grades. Organic clay, lean clay and clayey sand soils were encountered overlying the Yazoo Clay within the upper 12 ft of the subgrade. Laboratory tests were conducted on bulk samples of near surface soils in order to evaluate the expansion potential of predominantly A-6 (lean clay) soils. Additionally, soil-stabilizer mixture design was performed to determine the optimal percentage by dry unit weight of lime or cement admixtures for decreasing the swell potential and increasing the bearing resistance of these soils.

Laboratory tests indicate that the in-situ swell potential of the A-6 soils tested ranged between 0.5 and

0.6 percent, indicating low to marginal swell potential. However, past experience in the Jackson, Mississippi area has shown that A-6 soils do undergo measurable expansion and heave of the ground surface, typically resulting in moderate to severe cracking of pavement sections constructed to bear directly on these materials.

The Mississippi Department of Transportation (MDOT) has indicated that it is standard practice to treat A-6 subgrade soils with six (6) percent hydrated lime by weight. Mixture design laboratory tests were

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performed to estimate the optimum amounts of lime or cement needed to treat subgrade soils and produce an adequate pavement subbase. Laboratory tests indicate that both the cement and lime stabilizer are effective for reducing the swell potential of lean clays along the alignment, with the hydrated lime stabilizer being slightly more efficient. Both stabilizers markedly improved the bearing resistance of subgrade soils. The lime stabilizer increased the bearing resistance of subgrade soils by an average of 450%. Soils treated with the cement stabilizer showed an average increase in CBR value of 2,700%.

We evaluated the two stabilizers on the basis of its respective efficiency in reducing the swell potential and increasing the bearing resistance of subgrade soils. Additionally, both stabilizers were evaluated on the basis of cost, workability during construction, and crack susceptibility of the treated soil. It was concluded that the hydrated lime stabilizer was the better alternative for treating the in-situ lean clay soils.

Design evaluations along cut and fill sections of the trail were evaluated as follows:

Fill Sections

Along fill sections of the roadway a layer of organic clay was encountered and measure to be an average of 2.5 ft thick. The nature of this material makes it unsuitable for direct support of pavement sections.

Consequently, we evaluated three methods for improving the bearing resistance of the organic clays. The three methods evaluated included:

1. Subexcavation and replacement with suitable material

2. In-place chemical treatment using hydrated lime; and

3. Geosynthetic stabilization.

The subgrade stabilization options listed above were evaluated on the basis of cost, efficacy, and constructability. Geosynthetic stabilization was determined to be the most cost-effective alternative for stabilizing pavement sections overlying organic clay soils.

Cut Sections

Expansion of the Yazoo Clay Formation is not a major concern along sections of the roadway that will require fill embankments, but is a concern along sections of the roadway requiring cuts for trail construction. Road cuts between Station 86+50 and 120+60 are an average of 5.5 ft and will encounter the Yazoo Clay and expose this material to fluctuations in moisture content. The Yazoo Clay is especially sensitive to moisture changes and will expand dramatically with increases in moisture content and undergo appreciable contraction with reductions in the moisture content.

Portions of subexcavated material with a liquid limit less than 45 and a plasticity index less than 25 may be improved with lime to enable its use as select topping. It is unlikely that subexcavated soils between Station 90+00 and Station 100+00 will satisfy this requirement.

Design of flexible pavement structures for trail construction over the organic clay was performed in accordance with AASHTO (1993).