Geotechnical Report

FINAL SUBSURFACE EXPLORATION &

GEOTECHNICAL EVALUATION

Contract No: DTFH71-02-D-00003 Task Order 0003 for

RECONSTRUCTION and REHABILITATION Rock Creek & Potomac Parkway and Beach Drive

Project No. PRA-ROCR 3A6, 10(5)

PHASE V - (99%)

Rock Creek Park

Washington, D.C.

Federal Highway Administration Eastern Federal Lands Highway Division

Sterling, Virginia

March 2004 [Revised April 03, 2009 (revised October 9, 2009)]

Revised December 18, 2009

Prepared By:

KCI Technologies, Inc.

936 Ridgebrook Road

Sparks, Maryland 21152 i

Table of Contents

Table of Contents .................................................................................................................................... i

List of Tables ......................................................................................................................................... ii

List of Appendices ................................................................................................................................ iii

1 INTRODUCTION

1.1 Site Description

1.2 Project Description

2 PROCEDURES AND RESULTS

2.1 Field Exploration

2.2 FWD Testing

2.3 Soil Sampling

2.4 Pavement Condition Survey

2.5 Laboratory Testing

2.6 Geology

2.7 Subsurface Conditions

2.8 Groundwater

3 ANALYSIS

3.1 Pavement Section

3.2 Slope Stability

4 DISCUSSION

4.1 Pavement Rehabiliation

4.2 Slope Stability

5 RECOMMENDATIONS

5.1 General Earthwork Recommendations

5.2 Fill Selection, Placement and Compaction

5.3 Pavements

5.4 Slope Stability

5.5 Excavation Difficulties

5.6 Dewatering and Drainage

5.7 Low pH Soils

6 BASIS OF RECOMMENDATIONS

LIST OF TABLES & FIGURES

Table 1 - Summary of Pavement Cores

Table 2 - Summary of FWD Test Results

Table 3 - Summary of Soil Borings

Table 4 - Summary of Soil Classification Test Results

Table 5 - Summary of Moisture-Density Relationship Test and CBR Results

Table 6 - Summary of Corrosion Test Results

Table 7 - Summary of Auger Refusal

Table 8 - Summary of Traffic Data

Table 9 - Summary of Truck Factors

Table 10 - Summary of Design Correlations

Table 11 - Summary of Load Transfer from FWD Testing

Table 12 - Slope Stability Soil Parameters

Table 13 - Summary of Slope Stability Analysis

LIST OF APPENDICES

APPENDIX A

Figure A-1 Project Location Map Figure A-2 thru A-3 Index Sheets Figure A-4 thru A-16 FWD, Pavement Core, and Boring Location Plans

APPENDIX B

Table B-1 Summary of Boring Information Test Boring Logs (49) Field Classification Sheet for Soil Exploration Unified Soil Classification System Chart AASHTO Classification System of Soil and Soil-Aggregate Mixtures FWD Testing Results Pavement Condition Survey Results

APPENDIX C

Grain-Size Distribution Curve (6) Moisture-Density Relationship (6) California Bearing Ratio Curve (5) Corrosive Testing Results

APPENDIX D

Pavement Design Summary and Calculations Slope Stability Calculations

APPENDIX E

Response to Phase II Comments Response to Phase III Comments Response to Phase IV Comments

Subsurface Exploration & Geotechnical Evaluation

Washington, DC KCI Job No. 01-02046.E

1 INTRODUCTION

In accordance with our proposal dated May 9, 2003, KCI has completed the Subsurface Exploration and Geotechnical Evaluation for Beach Drive, Shoreham Drive, Cathedral Avenue, and Rock Creek and Potomac Parkway (RC&PP).

The purpose of this study was to determine general subsurface conditions at the project site and to evaluate those conditions with respect to geotechnical engineering considerations for the proposed construction. The specific scope of our services on this project consisted of evaluating the existing pavement using Falling Weight Deflectometer (FWD) testing and performing a pavement condition survey and exploring the subsurface conditions using pavement cores and soil borings, determining the USCS and AASHTO soil classification, the moisture density relationship, the California Bearing Ratio (CBR), and the pH for representative samples, evaluating the conditions encountered, developing geotechnical recommendations, and submitting our findings in a report. Based on this geotechnical study, recommendations are provided for the earthwork, flexible pavement sections, repairs, and other geotechnical concerns.

In this section, details of the areas explored are described based on information available at the time of this report.

Washington, DC

1.1 SITE DESCRIPTION

The project is located in an urban area of Washington, D.C. The majority of Beach Drive (Station 99+00 to 439+71) consists of a 2-lane asphalt road with wooded areas on either side. Rock Creek flows along Beach Drive, alternating sides of the roadway as it meanders towards the Potomac River. Along the northern half of Beach Drive, there are picnic areas with asphalt parking lots of varying size. Typically Beach Drive has concrete curbing with grassy shoulders, however there are many locations where rock outcrops or bedrock have been exposed from road cuts. There is a tunnel from Station 112+00 to Station 120+00 towards the beginning of Beach Drive.

RC&PP consists of a four-lane concrete road with an asphalt overlay, with some areas of full depth asphalt pavement. At the beginning of the project (Station 33+20), both directions of the parkway are undivided and then at Station 44+59 the road splits with a wooded and grassy median separating the two directions. Then at Station 78+73 the roadway rejoins and stays together until the intersection with Beach Drive (Station 99+00) and Shoreham Drive (Station 700+00).

Shoreham Drive (Station 700+00 to 710+61) consists of a two-lane asphalt road with concrete curbing.

There are large grassy areas on both sides of the roadway and an asphalt paved walking path on the southbound shoulder.

Cathedral Avenue (Station 900+00 to 907+15) consists of a two-lane road with both concrete and stone curbing. The northbound ramp from Shoreham Drive onto Cathedral Avenue (Station 900+00 to 901+07) consists of flexible pavement with concrete curbs. The remaining portion of Cathedral Avenue (Station 901+07 to 907+15) consists of a concrete paved roadway with an asphalt overlay. There is a grassy shoulder on the southbound side and a wooded area along the northbound side.

Washington, DC

1.2 PROJECT DESCRIPTION

The project consists of reconstructing, rehabilitating, and resurfacing Beach Drive and RC&PP. Portions of Shoreham Drive, Cathedral Avenue, and the ramp to Harvard Street are also included in the limits.

The north project limit is the Maryland State line. The southern project limit is the P Street overpass.

Beach Drive is a two-lane asphalt paved roadway. There are 11 parking areas and 16 intersections within the project limits for Beach Drive. The project area includes 6.5-miles of Beach Drive, 1.6-miles along RC&PP and less than less than a 0.25-mile along Shoreham Drive and Cathedral Avenue. The project will involve milling, pavement patching, asphalt paving, concrete curb and gutter replacement, storm drainage replacement and rehabilitation, pavement marking, guardrail replacement, sign placement and replacement, shoulder stabilization, and other miscellaneous work.

We understand the project to consist of rehabilitating the existing asphalt pavement without changing neither the horizontal nor the vertical alignments; therefore any additional pavement thickness will require complete reconstruction in order to maintain these alignments.

In addition to the pavement rehabilitation, there are two existing areas where possible slope stability is in question. At the first area localized slumps or holes were noted in the median between the northbound and southbound lanes of Rock Creek and Potomac Parkway from Station 519+00 to Station 520+00. The other area is where the existing pavement along Beach Drive near Rapid Bridge between Stations 259+00 to 260+00, south of the police station, is slumping. The slumping is a crescent shaped crack approximately 100-feet in length along the outside wheel path along the southbound lane of Beach Drive.

Washington, DC

2 PROCEDURES AND RESULTS

2.1 FIELD EXPLORATION

The field exploration consisted of pavement cores, Falling Weight Deflectometer (FWD) testing, soil borings with pavement cores, and a pavement condition survey. At the time of this final report all the scheduled fieldwork has been completed and the FWD tests results have been revised based on the pavement thickness encountered in the soil borings and pavement cores.

The pavement cores were performed on October 13, 2003 to determine the type and thickness of the pavement within the project to aid in the FWD evaluation. The pavement cores were obtained at twelve locations within the project as shown in the boring location plan. Table 1 indicates the location, pavement type and pavement thickness. Table B-1 in Appendix B includes the pavement type and pavement thickness encountered in the soil borings.

Table 1 - Summary of Pavement Cores

Core Number Roadway

Project Stationing

Pavement Type

Asphalt Thickness (inches)

Concrete Thickness (inches)

PC-1 Beach Dr. – SB 437+40 Asphalt 6.0 - PC-2 Beach Dr. – SB 352+90 Asphalt 4.75 - PC-3 Beach Dr. – NB 306+00 Asphalt 5.0 - PC-4 Beach Dr. – NB 213+90 Asphalt 4.25 - PC-5 Beach Dr. – SB 167+25 Asphalt 5.0 - PC-6 Beach Dr. – NB 102+80 Composite 2.0 10.0 PC-6a Beach Dr. – NB 103+00 Asphalt 3.5 - PC-7 RC&P Pkwy – SB 60+00 Asphalt 8.5 - PC-8 RC&P Pkwy – NB 501+20 Composite 5.0 6.5 PC-9 Shoreham Dr. – SB 705+63 Asphalt 4.0 - PC-9a Shoreham Dr. – NB 705+75 Asphalt 4.5 - PC-10 Cathedral Ave. - SB 902+15 Composite 3.0 10.0

Note 1: NB: Northbound SB: Southbound Composite: Concrete pavement with an Asphalt overlay Note 2: Pavement Thickness encountered in Soil Borings is shown on Table B-1

Washington, DC

2.2 FWD TESTING

Once the pavement types and thickness were known then the FWD testing was performed on October 14 and 15, 2003 by ERES, under subcontract to KCI. The FWD tests were performed every 500-ft along Beach Drive, Cathedral Avenue, and Shoreham Drive with test locations alternating travel lanes. The FWD testing for RC&PP was performed along the right travel lane for each direction of the four-lane roadway and spaced every 500-feet. FWD tests were also performed at various pavement joints to measure effective load transfer. There were a total of 108 FWD tests performed for this project. The preliminary results of the FWD testing aided in determining the most strategic locations to perform the soil test borings.

The FWD testing was performed using a 9-ft KUAB falling weight deflectometer with a 5.91-inch radius load plate. The target load for analysis was 9,000-lbs and deflections were measured at 7 points located radially from the center of the load plate ranging from 0 to 48-inches. Flexible pavement backcalculation analysis was performed using the 1993 AASHTO pavement design procedure and the composite pavement backcalculation analysis was performed using the 3-sensor Outer Area method. For composite pavement, joint load-transfer efficiency (LTE) tests were performed across areas of visible joint-reflective cracking on approximate 500-ft test spacing. For composite pavement backcalculation analysis, the elastic moduli values for PCC and AC were determined from the backcalculated composite pavement modulus values assuming a ratio of 10:1.

From the pavement cores and the soil borings the thickness values of pavement layers, AC and PCC were determined and were used in the backcalculation analysis. The pavement cores did not include a thickness for the gravel subbase. However, the gravel subbase or roadbase material below the existing pavement was encountered in the soil borings and the thickness was recorded in the boring logs. At the time of the FWD testing the subbase materials was assumed to be contaminated with fine grained soils and was assumed to be not fully functional. For this reason, this layer was not incorporated in the analysis of the subgrade material below the pavement section. The values of Resilient Modulus of Subgrade, Mr for flexible pavements and the Modulus of Subgrade Reaction, k for composite pavements are reported as obtained from the backcalculation formulas. After the soil borings were performed there were sections along Beach Drive and RC&PP where the granular subbase should be consider towards the structural capacity of the pavement section.

Washington, DC

Table 2 summarizes the results from the FWD testing for the existing pavements. The resilient modulus of subgrade was reduced using the standard FHWA reduction factor of 0.33. This reduction factor has only been analyzed by AASHTO on fine-grained, stress-sensitive soils and according to AASHTO, this reduction factor may not be valid for granular soils. Application of this reduction factor provides a more conservative design. These conservative values should be confirmed with the laboratory test results.

Detailed results of the FWD testing are presented in Appendix B.

Table 2 - Summary of FWD Test Results Roadway Stationing Mr k EAC EPCC

Beach Drive

99+00 to 198+20 5,610 - 673,760 - 198+20 to 346+00 5,000 - 428,790 - 346+00 to 376+00 5,820 - 577,940 - 376+00 to 398+50 6,290 - 994,370 - 398+50 to 439+71 4,980 - 968,550 -

RC&PP-Flexible 47+75 to 88+20 6,220 - 1,593,800 - 93+30 to 99+00 6,170 - 407,970 -

RC&PP- Composite 33+20 to 93+30 - 107 608,200 6,082,200 Shoreham Drive 700+00 to 711+00 6,200 - 479,800 - Cathedral 900+00 to 904+35 - 70 1,516,800 12,168,000 Mr: Resilient Modulus of Subgrade, psi EAC: Elastic Modulus of Asphalt Pavement, psi k: Modulus of Subgrade Reaction, pci EPCC: Elastic Modulus of Concrete Pavement

2.3 SOIL SAMPLING

The third phase of the field exploration consisted of drilling 49 standard penetration test (SPT) borings.

The borings were drilled with a truck-mounted drill rig using hollow stem augers. The soil borings were drilled from January 28, 2003 to February 10, 2003. The following table summarizes the location of the borings and Table B-1 in Appendix B summarizes the stationing and elevation of each boring. The boring locations were staked based on existing features and by a hand-held GPS with a 3-meter accuracy with WAAS satellite signal. Elevations were interpreted from topography shown on the site plans. Boring locations are shown in Figures A-4 to A-16.

Washington, DC

Table 3 - Summary of Soil Borings Location Boring Numbers Number Borings

Beach Drive BCH-1 to BCH-17 17 Rock Creek & Potomac Parkway RCP-1 to RCP-10 10 Shoreham Drive SHR-1 to SHR-4 4 Cathedral Avenue CTH-1 to CTH-4 4

Picnic Areas PRK-1 to PRK-5 PRK-7 to PRK-12

Police Station PRK-6 1 Possible Slope Failure SLP-1 and SLP-2 2

Total 49

Forty of the forty-nine borings extended 5-feet below the existing ground surface and the remaining nine borings extended between 10 and 15-feet below the existing ground surface. The deeper borings were located in possible slope failure areas and at deeper storm drain inverts. Soil samples were obtained at 2.5 and 5.0-feet intervals in accordance with the SPT procedure.

In general, the SPT consists of advancing a 2-inch outside diameter sampling spoon 18 inches by driving it with a 140-pound safety hammer falling 30-inches. The values reported on the boring logs are the blows required to advance three successive increments. The first 6-inch increment is considered as seating. The sum of the number of blows for the second and third increments is the "N" value.

In addition, bulk samples were obtained from the auger cuttings of 10 selected borings. Several borings were mapped within the same soil type according to the USDA Soil Survey of Washington, DC and therefore a representative sample was taken from major soil mapping units.

The soils were be classified in general accordance with the Unified Soil Classification System (USCS) and the AASHTO soil classification system. A KCI field engineer recorded the classifications, observations, water and cave in depths and field sampling information on the Test Boring Logs contained in the Appendix B.

Washington, DC

2.4 PAVEMENT CONDITION SURVEY

The fourth phase of the field exploration consisted of performing an initial pavement condition survey in 2003, and a final condition survey to re-evaluate existing pavement conditions in 2009.

At the time of the survey (2003), the stationing along the roadways was not marked; therefore, only crude locations could be noted. The survey noted distresses in the pavement in 500-foot increments. This initial survey provides an estimate of the current condition of the existing pavement and aid in determining if the existing pavement can be rehabilitated or if it needs complete reconstruction. The guidelines and severity levels outlined in the Distress Identification Manual for the Long-Term Pavement Performance Project, 1993 (SHRP-P-338) were used for this survey. The results of this survey are included in the Appendix B of this report.

KCI performed a pavement condition survey in 2009 to re-evaluate the existing pavement prior to restarting the project. The pavement condition survey performed by KCI’s Transportation Division to restart the project compared to that performed in 2003 did not identify significant difference in the pavement condition. Therefore the results of the initial survey as provided in Appendix B are still valid.

2.5 LABORATORY TESTING

The laboratory testing consisted of performing classification and index testing, determining the natural moisture content, the grain-size distribution, the Atterberg limits, the moisture-density relationship, the CBR, the pH and soil resistivity of selected soil samples. Results of the classification testing are summarized in Table 4, the moisture-density relationship results and the California Bearing Ratio results are summarized in Table 5, and the pH, soil resistivity results are summarized in Table 6. Natural moisture content results are shown on the Test Boring Logs in Appendix B. Detailed results of the grain-size distribution, CBR, and moisture-density graphs, pH and soil resistivity test results are also in Appendix C.

Washington, DC

Table 4 - Summary of Soil Classification Test Results Boring No. / Sample No.

DEPTH

(feet) DESCRIPTION % Fines LL% PL% PI USCS AASHTO

BCH-10 / Bulk 1.0-5.0 Silty Sand 40.0% NP NP NP SM A-4

BCH-15 / Bulk 1.0-5.0 Poorly Graded Gravel some Sand, trace Silt

10.7% NP NP NP GP-GM A-1-a

RCP-2 / Bulk 1.0-5.0 Silty Gravel and Sand 18.8% NP NP NP GM A-1-b

RCP-6 / Bulk 1.0-5.0 Silty Sand, little Gravel 31.9% NP NP NP SM A-2-4

CTH-2 / Bulk 2.5-5.0 Silty Sand some Gravel 23.2% 34 28 5 SM A-1-b

SLP-2 / Bulk 1.0-5.0 Silty Sand, trace Gravel 45.8% 29 25 4 SM A-4

“S-#”: Split Spoon Sample % Fines: Percent of material passing the No. 200 Sieve LL: Liquid Limit PL: Plastic Limit NP: Non-Plastic USCS: Unified Soil Classification System

Washington, DC

Table 5 - Summary of Moisture-Density Relationship Test and CBR Results

Sample No.

DEPTH

(feet)

Maximum Dry Density

(pcf)

Optimum Moisture Content

Natural Moisture Content CBR

BCH-10 / Bulk 1.0-5.0 126.1 9.7% 13.9% 6

BCH-15 / Bulk 1.0-5.0 125.3 8.0% 7.5% 3

RCP-2 / Bulk 1.0-5.0 120.6 10.3% 14.5% NT

RCP-6 / Bulk 1.0-5.0 123.5 9.5% 16.4% 11

CTH-2 / Bulk 2.5-5.0 123.1 12.4% 13.9% 18

SLP-2 / Bulk 1.0-5.0 116.3 14.7% 17.4% 5

CBR: California Bearing Ratio at 95% of Maximum Dry Density

NT: Not Tested (insufficient sample amount)

Table 6 - Summary of Corrosion Test Results

Sample No.

Depth (feet) pH

Resistivity (ohm/cm)

BCH-4 / S-2 3.5-5.0 5.2 3,826

BCH-5 / S-2 3.5-5.0 3.4 971

BCH-11 / S-2 3.5-5.0 6.0 3,045

BCH-15 / S-1 1.0-2.5 6.7 6,351

RCP-2 / S-2 1.0-2.5 7.5 2,582

RCP-9 / S-2 3.5-5.0 3.9 7,116

SHR-2 / S-2 3.5-5.0 7.7 5,172

pH: ASTM D4972 Resistivity: ASTM G-57 “S-#”: Split Spoon Sample

Washington, DC

2.6 GEOLOGY

According to the Geologic Map of the Washington D.C. and Vicinity (1964) the majority of the project site is mapped within the Eastern Piedmont Physiographic Province with approximately a fifth of the northern portion and the very southern portion of the project lying within the Coastal Plain Physiographic Province.

Natural soils of the Eastern Piedmont are residual soils, which have formed in place by the weathering of the parent bedrock. Residual soils typically form a profile characterized by a change from soil to completely weathered rock to rock with increasing depths below the ground surface. The project appears to be located within the Oligoclase-mica facies of the Wissahickon Formation, Laurel Gneiss, and Mafic igneous rocks.

The natural soils of the Coastal Plain Physiographic Province located within the project are mostly sedimentary materials consisting of the Patuxent Formation of the Potomac Group, the Wicomico Formation, and Recent Alluvium. The Patuxent Formation typically consists of highly variable, interbedded sand and gravel with pockets of silt and clay. Isolated areas of hematite-limonite cemented sands are also common. The Patuxent Formation is believed to have been deposited in a high-gradient, braided stream complex during the Cretaceous Period. The Wicomico Formation is believed to be old river terrace deposited during the Pleistocene Epoch. This consists of gravel at the base with sand and silt at the higher elevations.

The project is mapped through ten major soil phases indicated in the USDA Soil Conservation Service Soil Survey of District of Columbia. The major soil phases are as listed; Brandywine Gravelly Loam, Codorus Silt Loam, Manor Loam, Glenelg Loam, Codorus-Urban Land Complex, Sassafras Gravelly Sandy Loam, Udorthents, Joppa Gravelly Sandy Loam, Sassafras-Urban Land Complex, and Manor- Urban land Complex.

Washington, DC

Beach Drive predominately lies within Codorus Silt Loam, Manor Loam, and Codorus-Urban Land Complex. The lower portions of Beach Drive also lie in Brandywine Gravelly Loam. Shoreham Drive and Cathedral Avenue are mapped in both Sassafras-Urban Land Complex and Udorthents. These soils have been grading for residential and other urban development. RC&PP are mapped within Codorus- Urban Land Complex and Manor-Urban land Complex. These soils are similar to the soil mapped at Shoreham Drive and Cathedral Avenue. Large areas of dumps, fills, building and domestic rubbish were mapped for the majority of RC&PP. There was an abandoned quarry mapped south of the intersection of Beach Drive and RC&PP.

2.7 SUBSURFACE CONDITIONS

The reader is referred to the Test Boring Logs in Appendix B for details related to the subsurface conditions encountered in the various borings. The stratification lines shown on the Test Boring Logs will represent approximate transitions between material types. In situ, strata changes could occur gradually or at slightly different levels. Also, the borings will depict conditions at particular locations and at the particular times indicated. Some conditions, particularly groundwater conditions between borings could vary from the conditions encountered at the particular boring locations.

Roadway Base Material: The roadway base course material generally consisted of Silty Sand and ½-inch Rounded Gravel. The roadway base material was encountered in all the borings in areas of flexible pavements, except BCH-5, BCH-16, SHR-2, SHR-3, and SHR-4. Borings that encountered a composite pavement section also did not encounter roadway base material below the concrete pavement. The depth of the base material generally extended from about 3.0-inches to 15.0-inches below the existing pavement surface, with a average thickness of 9.5-inches.

Fill: Fill material was encountered in borings BCH-2, BCH-3, BCH-16, BCH-17, PRK-8, PRK-10, PRK- 12, and SLP-2 along Beach Drive. The depth of the fill generally extended to about 3.0-feet below the existing ground surface, except in borings BCH-16, PRK-10, and SLP-2 where the fill extended to approximately 5.0-feet below the existing ground surface. Borings CTH-1 and CTH-2 along Cathedral Avenue also encountered the fill material. The depth of the fill along Cathedral Avenue generally extended to about 5.0-feet below the existing ground surface. Along RC&PP borings, RCP-2, RCP-3, RCP-6, RCP-7, RCP-8, and RCP-10. The depth of the fill along RC&PP generally extended to about 3.0-feet below the existing ground surface, except in borings RCP-2, RCP-3, and RCP-7. The fill material encountered in borings RCP-2 and RCP-3 extended to the termination depths of the borings, Washington, DC approximately 5.0-feet below the existing ground surface. Boring RCP-7 also encountered fill material to the termination depth of approximately 10-feet below the existing ground surface. Fill material was encountered in borings SHR-1, SHR-3, and SHR-4 along Shoreham Drive. The fill material encountered along Shoreham Drive typically extended to 2.5-feet below the existing ground surface, except in boring SHR-3 where the fill material extended to termination depth of the boring of 10-feet below the existing ground surface.

The FILL material encountered in our borings consisted of loose to dense micaceous Silty SAND with varying amounts of man-made materials such as brick, asphalt pavement, crushed stone, and rock fragments [GM and SM] {A-1-a, A-1-b, A-2-4, and A-4}. The SPT N-values typically ranged from 4 blows per foot (bpf) to 58-bpf and averaged 21-bpf. The larger SPT N-values were probably exaggerated by the brick, asphalt pavement, crushed stone, and rock fragments.

Natural Stratum 1 Soils: The natural soils of Stratum 1, generally consisted of loose to medium dense, micaceous Silty SAND with varying percentages of Gravel [SM] {A-1-b and A-2-4}. The SPT N-values typically ranged from 5 to 26-bpf, averaging 15-bpf. These soils were the predominant soils of the project, with most borings terminating in this material. Typically, these soils were encountered below the roadway base material or fill material. The average depth was 5-feet below the existing ground surface, except in borings BCH-3, BCH-6, BCH-10, CTH-2, RCP-6, and SLP-2. In these borings this material extended to approximately 8-feet below the existing ground surface.

Natural Stratum 2 Soils: The natural soils of Stratum 2, at the site generally, consisted of soft to very stiff, SILT with varying percentages of Clay [ML, CL-ML] {A-4 and A-5}. The SPT N-values typically ranged from 3 to 34-bpf, averaging 13-bpf. The material was encountered in boring BCH-3, BCH-5, BCH-11, BCH-12, BCH-13, PRK-11, PRK-12, RCP-1, RCP-4, RCP-6, and RCP-8. For the majority of these borings this material was encountered beneath the roadway base material and extended to the termination depths of the boring, at 5-feet below the existing ground surface, except for borings BCH-3 and RCP-6. In these two borings, Stratum 2 soils were encountered beneath Stratum 1 soils and extended to the termination depths of 10-feet below the existing ground surface.

Washington, DC

Completely Weathered Rock: Residual soil gradually transitions into Completely Weathered Rock with depth. Completely Weathered Rock is defined in this report as residual material which retains the relic rock structure of the parent bedrock and exhibits SPT N-values consistently in excess of 60-blows/foot and less than 50-blows/inch or spoon refusal. Completely Weathered Rock was encountered in borings BCH-2, BCH-8, BCH-15, PRK-4, PRK-9, RCP-6, SHR-1, and SLP-1. Auger refusal was also encountered in the borings listed in Table 7 at depths ranging from 2.0 to 12.0-feet below the existing ground surface. Auger refusal, thus indicated, may result from hard cemented soil, soft weathered rock, coarse gravel or boulders, thin rock seams, or the upper surface of sound continuous rock. Rock coring techniques are required to determine the character and continuity of the refusal materials.

Table 7 - Summary of Auger Refusal

Boring Station Depth of Auger Refusal (feet)

BCH-2 122+03 2.0

BCH-6 197+84 11.5

BCH-8 256+87 3.5

BCH-15 411+40 6.0

PRK-4 245+93 3.0

RCP-6 520+01 11.5

SHR-1 701+61 4.0

SLP-1 259+78 3.0

SLP-2 259+25 12.0

2.8 GROUNDWATER

Groundwater was only encountered in 6 borings during the field exploration. The depth of the groundwater ranged from 2-feet to 9.5-feet below the existing ground surface. Borings PRK-6, PRK-12, and SHR-2 encountered groundwater 2.5, 3.5, and 2.0-feet below the existing ground surface, respectively. Borings BCH-6, BCH-10, and RCP-6 encountered groundwater 9.5, 8.5, and 9.4-feet below the existing ground surface, respectively.

Washington, DC

Moisture was also observed on several sampling spoons during the subsurface exploration near the soil/rock contact; therefore, if the borings were left open for a long period of time groundwater may have been observed at theses depths. In addition, several samples near the contact with fill and under the roadway material were mottled in color. This mottling indicates the drainage is impeded, resulting in temporary periods of saturated conditions. Due to the large spacing between borings throughout the project area, there may be areas where groundwater or seeps may be encountered during the excavation.

A more accurate determination of the hydrostatic water table would require the installation of numerous perforated pipes or piezometers to cover the entire project area, which could be monitored over an extended period of time. The actual level of the hydrostatic water table and the amount and level of perched water should be anticipated to fluctuate throughout the year, depending upon variations in precipitation, surface run-off, infiltration, site topography, and drainage.

Washington, DC

3 ANALYSIS

3.1 PAVEMENT SECTION

We have based our pavement analyses and design on 1993 AASHTO Pavement Design Guide and the pavement design software Darwin 3.2. The 18-kips equivalent single axle load (ESAL) used for our design is based on the current traffic information and 20-year design life. The information from the boring logs, laboratory CBR results, and Mr values from the FWD testing were considered in the evaluation of the pavement sections. Based on field and laboratory testing results, and our experience with similar soils we have used an average subgrade CBR value of five in our analyses. Our pavement design input parameters for the roadway sections are shown in Tables 8 through 10.

The traffic analysis performed in 2003 provided a current Average Daily Traffic (ADT) count for each roadway and percentage breakdown for each vehicle type. We have used 2010 projected ADT as our initial ADT for the pavement section design for all roadways in the project. Table 8 provides the initial design year ADT (2010), Future ADT, the design Equivalent Single 18-kip Axle Load (ESAL) value, and Table 9 provides the vehicle percentage breakdown and truck factor used in our evaluation. We have determined the ESAL for a 20-year design life with the standard FHWA 2-percent growth rate and this is summarized in Table 8.

Table 8 - Summary of Traffic Data

Roadway

Current

ADT

Growth Rate

Future

ADT

Directional Distribution

Factor

Lane Distribution

Factor

20 Year Design

ESAL

Beach Drive Station 99+00 to 439+71

24,000 2% 35,000 0.5 1.0 2,195,938

Shoreham Drive 14,500 2% 21,500 0.5 1.0 1,326,713

Cathedral Avenue 6,500 2% 9,500 0.5 1.0 594,733

Rock Creek & Potomac Parkway 60,000 2% 89,000 0.5 0.5 2,744,923

Washington, DC

Table 9 - Summary of Truck Factors Vehicle Percent of Total Traffic Truck Factor

2 Axle/4 Tires, Passenger Car 91% 0.0007 2 Axle/4 Tires, Pick up 7% 0.0007 2 Axle / 6 Tires, Maintenance Vehicle 1% 0.6 Four or Less Axles / Single Trailer 1% 1.2

Based on the pavement condition surveys, Shoreham Drive exhibits numerous large areas needing full depth patching; therefore, we recommend that the entire roadway section be completely reconstructed.

Table 10 provides the design values used for the evaluation of the current pavement and design of new pavement sections. The Mr values shown in Table 10 were based on FWD test results and were adjusted based on the CBR data. The design correlations from the FWD testing for elastic modulus and estimated existing structural number (SNxeff) are also summarized in Table 10.

Table 10 - Summary of Design Correlations Roadway Project Stationing Design Mr EAC a1 SNxeff Dxeff SNy

Beach Dr.

99+00 to 198+20 13,500 673,758 0.40 2.43 - 2.81 198+20 to 346+00 7,000 428,794 0.34 1.43 - 3.70 346+00 to 376+00 5,800 577,939 0.38 1.75 - 3.97 376+00 to 398+50 6,300 994,374 0.44* 1.96 - 3.85 398+50 to 439+71 5,000 968,547 0.44* 3.20 - 3.20

RC&PP-Flexible 47+75 to 88+20 6,500 1,593,780 0.44* 3.26 - 3.96 93+30 to 99+00 6,165 407,970 0.32 2.59 - 4.08

RC&PP- Composite 33+20 to 93+30 6,500 313,500 0.44* 3.26 6.0 3.96 Shoreham Dr. 700+00 to 711+00 8,000 1,517,000 0.44* 1.38 - 3.33 Cathedral Ave. 900+00 to 904+00 13,680 1,516,800 0.44* 1.35 4.0 3.3 EAC= Elastic Modulus of Asphalt Concrete a1= Structural Layer coefficient of HMA overlay SNxeff=Total effective structural number of the existing pavement structure Dxeff=Effective thickness of in situ PCC Layer reflecting its reduced modulus value SNy=Total structural number required to support the anticipated traffic

* a1 were reduced to the maximum value of 0.44

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Table 11 - Summary of Load Transfer from FWD Testing

Roadway Direction Project

Stationing

Asphalt Thickness (inches)

Concrete Thickness (inches)

Joint Load Transfer Efficiency, LTE (%) Condition

RC&PP

NB 35+67 4.0 4.0 53.4% Marginal NB 39+05 4.0 4.0 56.6% Marginal NB 44+11 5.0 6.5 67.1% Marginal NB 509+69 5.0 6.5 63.0% Marginal NB 519+30 3.0 8.0 48.2% Replace NB 523+84 3.0 8.0 43.5% Replace NB 529+37 3.0 8.0 72.3% Good

RC&PP SB 69+73 2.0 12.0 62.4% Marginal

Cathedral Ave.

NB 900+37 2.0 10.0 43.9% Replace SB 905+61 2.0 4.0 86.2% Good NB 909+73 2.0 4.0 76.5% Good

According to AASHTO guidelines joint efficiencies under 50-percent need restoration and joint efficiency over 70% are consider in good condition. However most of the joint tested along RC&PP were between 50 and 70-percent and should be considered marginal. Marginal meaning that the joint is still transferring the weight, but the traffic loading has begun to damage the pavement and eventually the joint will fail. Rate of failure for the joints can not be quantified at this time, further exploration and evaluation of each joint would be necessary to determine the remaining life and rate of decay for each joint as discussed in Section 5.3 of this report.

3.2 SLOPE STABILITY

As shown in the Appendix A of the Design Scoping Report for RC&PP, we have identified the hole photographed, explored the subsurface along the roadway near this hole, and have evaluated the stability of the embankment where the hole is located. We identified the hole to be in the grassy median between the northbound and southbound lanes of Rock Creek and Potomac Parkway between station 64+00 and 65+00. At the time of the subsurface exploration several other slumps were noted in the grassy median.

The ground surface slopes at 2.7 (H): 1 (V) in this area. These slumps appear to be more of a localized

Washington, DC seepage problem rather than a convention slope stability situation.

During our initial site visit, an area along Beach Drive was identified as an area where a possible slope instability problem may be occurring. The ground surface slopes at a 1.3(H):1(V) in this area. This area is located along Beach Drive from Station 259+00 to 260+100 and KCI determined that the subsurface conditions should be explored. Therefore, KCI moved two of the three slope borings from the RC&PP hole location to the area along Beach Drive.

The cross section at Station 65+50 along RC&PP was used to perform a slope stability analysis on the embankment between the northbound and southbound travel lanes. Soil parameters were established using the soil boring information from borings RCP-5, RCP-6, and RCP-7 and laboratory index tests.

The cross section at Station 260+00 for Beach Drive was used to perform a slope stability analysis on the second embankment. Soil parameters were established using the soil boring information from borings SLPS-1 and SLP-2 and laboratory index tests.

The computer program GSTABL7 was used to perform the slope stability analysis using the Modified Bishop Method. Table 12 below summarizes the shear strength parameters used for both areas. The two cross sections were analyzed for normal groundwater conditions and for rapid draw down, since both areas are in a flood plain. Rapid draw down is a situation where the ground has been fully saturated when Rock Creek has flooded and then quickly recedes leaving heavy saturated soil. This causes the slope to have the most weight and have the weakest soil strength. Based on the requirements stated in Section 6.4.F of the PDDM the minimum Factor of Safety (FS) under normal groundwater conditions would be range from 1.25 to 2.0 range. For this type of facility a minimum FS of 1.3 will be used for the analysis.

The minimum FS for the rapid draw down situation is not described in the PDDM, therefore a minimum FS of 1.1 will be used for this situation, since it represents an extreme event.

Table 12 - Slope Stability Soil Parameters

Material

Unit Weight Shear Strength Cohesion Moist Saturated

RC&PP, Station 65+50 Fill Material 120 pcf 125 pcf φ=28 o c=100 psf Residual Silty Sand 125 pcf 130 pcf φ=31 o - Residual Silt 130 pcf 135 pcf φ=34 o - Bedrock 145 pcf 145 pcf φ=44 o -

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Beach Drive, Station 260+00 Fill Material 120 pcf 125 pcf φ=29 o − Residual Silty Sand 125 pcf 130 pcf φ=32 o − Bedrock 145 pcf 145 pcf φ=44 o − Rock Fill 110 pcf 110 pcf φ=38 o −

Using the above parameters, the slope stability results contained in the Appendix D illustrate the lowest FS for each situation as summarized in Table 13. At Station 65+00, the existing slope is shown to be stable in both conditions. The most likely cause of this distress is localized water seepage. Drains can be used to control the seepage and reduce future damage. At Station 260+00, the existing slope is shown to be below the required FS and the slope needs to be reconstructed. This construction consisted on a free draining rock veneer. This rock veneer provided factors of safety above the minimum values for both conditions.

Table 13 - Summary of Slope Stability Analysis

Location Condition Minimum

Factor of Safety

RC&PP

(Sta. 65+00)

Existing slope under normal groundwater conditions 2.54

Existing slope under rapid draw down conditions 1.44

Beach Drive (Sta. 260+00)

Existing slope under normal groundwater conditions 1.10

Existing slope under rapid draw down Conditions 0.67

Rock veneer slope stabilization under normal groundwater conditions 1.42

Rock veneer slope stabilization under rapid draw down conditions 1.42

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4 DISCUSSION

4.1 PAVEMENT REHABILIATION

With the current information, testing results, and construction constraints, it appears that portions of Beach Drive, RC&PP, Shoreham Drive, and Cathedral Avenue will require complete reconstruction. The remaining portions of the project can be milled and resurfaced. Detailed recommendations are contained in Section 5.3.

From Sta. 99+00 to 198+20 along Beach Drive, the Mr values from the FWD tests once reduce by the FHWA reduction factor produce much smaller values than the closest CBR test result. Therefore, the Mr values in this section will not be reduced. The unadjusted Mr values are closer to the CBR value obtained from a nearby bulk sample. With the uncorrected Mr values, the required structural capacity of the pavement is much closer to the existing pavement. This agrees with the pavement condition survey, since there are fewer distresses in this area than the other areas along Beach Drive. In the other section of Beach Drive, the CBR values agree with the reduced Mr value from the FWD testing and were used in the pavement evaluation.

With the current project restrictions, that the vertical grade should remain unchanged, and constructibility issues associated with the project due to location and water quality requirements, significant portions of the project will need to be reconstructed or will require removing thicker sections of the existing pavement, including portions of the existing aggregate base course, and replacing with asphalt base and surface course layers. This is to improve the structural capacity of the newly rehabilitated pavement sections to support the design traffic load while maintaining the current vertical grade. This is based on data from our pavement condition surveys, FWD testing, soil borings and the laboratory test results for the areas and types of rehabilitation. Based on the FWD tests and laboratory CBR test results, we have used a CBR value of 5 (i.e. Mr of 7500) in evaluating and designing the pavement sections.

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4.2 SLOPE STABILITY

The two areas of the project that present slope stability problems are described in Section 1.2. The results of the Modified Bishops analysis show that the existing slope at RC&PP Station 65+00 has an adequate factor of safety with respect to slope stability. Based on the best available utility information, it appears that there are no utilities in the immediate area that might have caused these localized slumps. Another possible reason for these small slumps are that old gravel pits and dumps, metro fills, building and domestic rubbish fills are mapped within the immediate area to these slumps by The USDA Soil Conservation Service Soil Survey map of District of Columbia. These isolated slumps could be small voids created by poorly placed fill materials that are now collapsing and settling. It is also possible that localized groundwater flow could be causing piping or underground erosion. Therefore, re-grading the areas and localized construction of slope drains would be the appropriate repair of these small slumps.

From the slope stability analysis of the area along Beach Drive near Rapid Bridge between Stations 259+00 to 260+00, it appears that the failure surface is initiating at the toe of the slope and ending at the crack observed in the roadway at the time of this report. The failure appears deep enough that shallow earthwork will not be sufficient to stabilize the slope. The stabilization of this slope will most likely require significant undercutting and earthwork.

There are several stabilization techniques available to stabilize this slope. A retaining wall could be constructed down slope of the failure to stabilize the movement. Another option is to replace the failed portion of the slope with a Reinforced Soil Slope (RSS) combined with brush layering. This method uses geotextile or geogrid to reinforce the slope providing a stable slope at steeper grades. The brush layering will aid in quickly establishing vegetation on steep slopes, reducing erosion and enhancing the visual appearance. The third option to stabilize the slope would be to completely remove the failed soil and replace the soil with a free draining rock veneer. This rock veneer would be benched into the existing slope and covered with existing boulders and rip rap to provide natural aesthetics and would not stand out from the opposite bank. Anchors or soil nails would not be possible to stabilize the slope because of the sanitary sewer located under the northbound lane, which would interfere with the anchors or soil nails.

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Two types of retaining wall would be appropriate for this area are either a H-pile and lagging wall or a crib wall, which has been previously used along Beach Drive. However, bedrock was encountered in the soil borings at the elevation that the retaining wall would be founded; therefore, H-piles will need to be socketed into the rock, requiring large construction equipment. This will also result in some temporary traffic closures and increased cost. Both the H-pile and lagging wall and crib wall will require a facing to improve the appearance of the wall.

A disadvantage of an RSS is that a significant portion of the existing roadway will need to be excavated to place the geotextile or geogrid. This will likely close the entire road to traffic for several weeks. In addition, the excavation would mostly likely encounter boulders and bedrock. To excavate the rock and boulders to install the required lengths of geotextile or geogrid will be expensive.

The third alternative would be to undercut the existing slope and replace with free draining rock fill. This option would require closing at least one lane for several weeks and would require an excavation support system to maintain traffic on the other lane, otherwise the entire roadway should be closed. Unlike the other alternatives, this alternative does not require bedrock excavation. Once competent bedrock is encountered the excavation may be terminated. If boulders are encountered, these boulders can be salvaged and used as facing material to blend into the natural surroundings. For this project, this alternative will most likely be the least expensive considering the rock excavation required in the other alternatives.

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5 RECOMMENDATIONS

The following recommendations have been developed on the basis of the previously described project characteristics and subsurface conditions. If there are any significant changes to the project characteristics or if significantly different subsurface conditions are encountered during construction, KCI should be consulted so that the recommendations of this report can be reviewed.

5.1 GENERAL EARTHWORK RECOMMENDATIONS

Topsoil other organic materials, frozen, wet, soft or loose soils, and other deleterious materials should be removed and wasted before placement of fill. These stripping operations should be performed in a manner consistent with good erosion and sediment control practices.

The initial step in the development of areas outside the existing roadway should be to remove topsoil, root matter and other deleterious materials from the areas to be developed. Typically, deeper undercutting on the order of 2+/- to 3+/- feet will be required where trees must be removed but, otherwise stripping will be limited to the upper 0.5+/- to 1+/- feet in grassy areas. These stripping operations should be performed in a manner consistent with good erosion and sediment control practices.

After stripping, areas to be filled or where pavements or structures will be placed should be proofrolled with a heavily loaded (15-20 ton) dump truck or another pneumatic-tired vehicle of similar size and weight. The purpose of the proofrolling is to provide surficial densification and to locate any isolated areas of soft or loose soils. Unsuitable areas should be undercut and replaced with controlled compacted fill as described in Section 5.2. A geotechnical engineer licensed in the District of Columbia or an engineering technician under the supervision of such an engineer should witness the stripping and proofrolling operations. All stripping and earthwork activities should be performed in a manner consistent with good erosion and sediment control practices.

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5.2 FILL SELECTION, PLACEMENT AND COMPACTION

In general, existing on-site soils free from environmental contamination, building debris, frozen, organic or wet materials and with an AASHTO Soils Classification of A-1-a, A-1-b, A-2-4, A-2-5, A-2-6, and A- 3 can be reused as compacted fill. On site materials with an AASHTO Soils Classification of A-4, A-5, A-7, A-7-5, and A-7-6 are not suitable as backfill to support structures and pavements, but may be reused in landscaping areas. If imported materials are required it should have an AASHTO Soils Classification of A-2-4 or better and a maximum dry density of at least 105-pcf in accordance with the modified Proctor test method (AASTHO T-180).

Fill slopes no steeper than 2(h): 1(v) should be used without reinforcement. Once the proposed ground surface is achieved, the site should be stabilized as quickly as possible to reduce erosion damage and excessive run off. It will likely be necessary to use temporary erosion matting on steeper slopes.

Prior to placement the borrow material should be classified in accordance with AASHTO M 145. For material classified A-1 or A-2-4, determine the maximum density according to AASHTO T 180 method D. For other material classifications, determine the optimum moisture content and maximum density according to AASHTO T 99 method C.

All fill materials in structural and pavement areas should be placed in horizontal, eight-inch maximum loose lifts and compacted. Fill material should be compacted to at least 95-percent of the maximum dry density in accordance with FP-03. In pavement areas, the uppermost one-foot (after compaction) should be compacted to 98-percent of the maximum dry density. Determine the in-place density and moisture content according to AASHTO T 238 and AASHTO T 239 or other approved test procedures.

The moisture content of the fill should be properly controlled during placement. Moisture content of the fill materials should be within plus or minus 2-percent of the optimum moisture content. In-place density tests should be performed by an engineering technician on a full-time basis under the supervision of a geotechnical engineer licensed in the District of Columbia to verify that the proper degree of compaction is being obtained.

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5.3 PAVEMENTS

Based on the FWD test results, soil boring data, laboratory test results, the design ESAL given in Section 3.1, and our engineering judgment, we recommend the following pavement rehabilitation. For areas of complete reconstruction and full depth patching, the subsurface soils should be compacted in accordance with Section 5.2 of this report.

We have provided a summary of the minimum recommended pavement sections for patching, mill and resurface, and reconstruction sections in Appendix D. The proposed pavement sections should match the existing pavement as close as possible.

In addition to the reconstruction and overlay recommendations for the roadways, we recommend that transverse and longitudinal joints in the composite sections be visually inspected after milling. As noted in Section 3.1, joint efficiencies under 50-percent need restoration and joint with efficiencies between 50 and 70-percent should be considered marginal.