07_Geotech_WPP_GDR_1.pdf

DRAFT

GEOTECHNICAL DATA REPORT

NAMA 318722 – West Potomac Park Seawall Washington, DC

Schnabel Reference #: 22410101.000 November 23, 2022

November 23, 2022

Mr. Kent Brogger, PE HDR / Moffatt-Nichol Joint Venture 1670 Broadway, Suite 3400 Denver, CO 80202

Subject: Project NAMA 318722, Geotechnical Data Report, West Potomac Park Seawall, Washington, DC (Schnabel Reference 22410101.000)

Dear Mr. Brogger:

SCHNABEL ENGINEERING DC, INC. is pleased to submit our geotechnical data report for this project.

This study was performed in accordance with our proposal dated December 17, 2021 and incorporated into HDR Task Order/Agreement No: 001/10001000731212, dated April 21, 2022 and fully executed on May 19, 2022. The task order was issued under the Master Federal Subconsultant Agreement, Agreement No. 1000100071112, dated and fully executed on May 9, 2022.

We appreciate the opportunity to be of service for this project. Please call us if you have any questions regarding this report.

Sincerely, SCHNABEL ENGINEERING DC, INC.

Joan Bentel, PE Senior Associate

Bill Khouri, PE Principal

JB:BK:

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FINAL.DOCX

November 23, 2022 Page i Schnabel Engineering, LLC.

Project 22410101.000 ©2022 All Rights Reserved

GEOTECHNICAL DATA REPORT

NAMA 318722 - WEST POTOMAC PARK SEAWALL

WASHINGTON, DC

TABLE OF CONTENTS

1.0 SCOPE OF SERVICES

2.0 DESCRIPTION OF SITE AND PROPOSED CONSTRUCTION

2.1 Site Description

2.2 Proposed Construction

3.0 SUBSURFACE EXPLORATION PROGRAM

3.1 Subsurface Exploration and Field Testing

3.2 Previous Explorations by Others

4.0 LABORATORY TESTING PROGRAM

4.1 Soils Testing

4.2 Rock Testing

4.3 Previous Testing by Others

5.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

5.1 Regional Geology

5.2 Site Geology

5.3 Generalized Subsurface Stratigraphy

5.4 Groundwater

6.0 IN-SITU FIELD TESTING

6.1 Cone Penetrometer Testing

7.0 LABORATORY TESTING RESULTS

7.1 Index Testing

7.2 Strength and Consolidation Testing

7.3 Organic Content Testing

7.4 Corrosivity Testing

7.5 Unconfined Compressive Strength of Rock

APPENDICES

Appendix A: Subsurface Exploration Data Appendix B: In Situ Test Results Appendix C: Soil and Rock Laboratory Test Data Appendix D: Subsurface Exploration Data by Others Appendix E: Soil Laboratory Test Data by Others

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1.0 SCOPE OF SERVICES

Our proposal dated December 17, 2021, incorporated into the HDR Task Order/Agreement No.:

001/1000100073121 defines the scope of services for this project. The scope of services includes the following:

• Develop approximate boring and sound location plan.

• Preparation of a subsurface exploration work plan.

• Full-time boring inspection by a junior engineer from our office during drilling activities at West

Potomac Park.

• Preparation of a geotechnical data report, to include:

o Estimated subsurface conditions and groundwater levels within the area explored based on data collected in the subsurface exploration.

o Estimated subsurface profiles and groundwater levels within the area explored based on data collected in the subsurface exploration. Two subsurface profiles have been created.

o Boring logs with soil description, classification, and depth of fill, groundwater observations, and any other observations made during the exploration, including the ground surface elevations at boring locations.

o Laboratory testing results.

o In-situ field testing results.

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2.0 DESCRIPTION OF SITE AND PROPOSED CONSTRUCTION

2.1 Site Description

The subject site run along the Potomac river and is bounded by Arlington Memorial Bridge to the north, Ohio Drive SW to the east, the Ohio Drive SW Inlet Bridge to the south and the Potomac River to the west. A Site Vicinity Map is included as Figure 1. The West Potomac Park wall extends from the Arlington Memorial Bridge to the Ohio Drive SW Inlet Bridge and the wall length is 4,671 ft.

Portions of the existing West Potomac Park (WPP) seawall and adjacent shoreline have eroded over time due to age, highwater and poor drainage. The WPP seawall will be repaired and designed to consider climate resiliency and to preserve the West Potomac Park landscape. The repair is also planned to decrease the National Park Service (NPS) maintenance duties (such as debris clean-up caused by high tides).

We obtained the site information from information shared by HDR and through our site visits.

2.2 Proposed Construction

We understand that the repair will consist of constructing a new wall with raised grades and that deep foundations will be needed to support the new seawall.

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3.0 SUBSURFACE EXPLORATION PROGRAM

A subsurface exploration and field-testing program were performed to identify the subsurface stratigraphy underlying the site and to evaluate the geotechnical properties of the materials encountered. This program included test borings and in-situ testing (i.e., cone penetration testing and dilatometer testing).

Exploration methods used are discussed below. The appendices to this report contain the results of our exploration.

3.1 Subsurface Exploration and Field Testing

3.1.1 Test Borings

E2CR drilled thirteen (13) test borings under our observation between June 15, 2022 and August 10, 2022. The Standard Penetration Test (SPT) was performed at selected depths in the borings. Appendix A includes specific observations, remarks, and logs for the borings, classification criteria, drilling methods, and sampling protocols. Figures 2A and 2B, included at the end of this report, indicates the approximate test boring locations. We will retain soil and rock samples up to 45 days beyond the issuance of this report, unless you request other disposition.

It should be noted that originally sixteen (16) standard penetration test (SPT) borings were planned (WPP-B-05, WPP-B-09 and WPP-B-13); however, three of the locations were converted to cone penetration test (CPT) probes (WPP-CPT-04, WPP-CPT-05 and WPP-CPT-06).

In addition to the SPTs performed in the test borings, in-situ testing was performed to further establish the geotechnical properties of the materials encountered at the site. Cone penetration and dilatometer testing was performed.

3.1.2 In Situ Testing

3.1.2.1 Cone Penetration Testing

In-Situ Soil Testing, LC performed cone penetration testing (CPT) at six locations on the site (designated as WPP-CPT-01, WPP- CPT-02, WPP-CPT-03, WPP-CPT-04, WPP-CPT-05, and WPP-CPT-06). The CPTs were performed to depths of 45.7 ft to 85.5 ft. Details of the CPTs and test results are included in Appendix B.

3.1.2.2 Dilatometer Testing

In-Situ Soil Testing, LC performed flat-blade dilatometer testing (DMT) at three locations on the site (designated as WPP-DMT-01, WPP-DMT-02, and WPP-DMT-03). The DMTs were performed to depths of 48.5 ft to 72.5 ft. Details of the DMTs and test results are included in Appendix B.

3.1.3 Instrumentation

Four inclinometers were installed at borings WPP-B-01, WPP-B-06, WPP-B-11, and WPP-B-16 to depths ranging between 55.4 ft and 108.5 ft, or between EL -49.9 (ft) and EL -102.1 (ft). Two vibrating wire piezometers were installed at borings WPP-B-03 and WPP-B-14 to depths ranging between 20 ft and 30 ft, or between EL -15.9 (ft) and EL -25.1 (ft).

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GEI Consultants, Inc. is providing all monitoring and reporting services for the installed instrumentation.

3.1.4 Coordinates

GEI Consultants, Inc. surveyed the as-drilled boring and in-situ testing locations. Please note that the as-built coordinates and elevation provided for WPP-CPT-03 (provided by GEI on September 30, 2022) is not in the location of where the sounding was advanced and is erroneous WPP-CPT-03 was advanced within two to three feet from the as-staked coordinate which has been considered herein. Elevations and coordinates are shown in the tables below:

Table 3.1: As-Drilled Coordinates and Elevations for SPT Borings

Boring ID Vertical Datum

Ground Surface

Elevation (feet)

Northing (feet)

Easting (feet)

Horizontal Datum

Latitude (deg)

Longitude (deg)

WPP-B-01 NAVD88 5.48 444864.70 1297430.70 NAD 83 38.888185 -77.052356

WPP-B-02 NAVD88 5.45 444561.33 1297675.19 NAD 83 38.887352 -77.051497

WPP-B-03 NAVD88 4.11 444348.27 1297876.85 NAD 83 38.886768 -77.050788

WPP-B-04 NAVD88 2.3 444139.07 1298060.73 NAD 83 38.886193 -77.050141

WPP-B-06 NAVD88 3.06 443685.90 1298538.03 NAD 83 38.884950 -77.048464

WPP-B-07 NAVD88 4.36 443428.83 1298815.80 NAD 83 38.884244 -77.047487

WPP-B-08 NAVD88 4.56 443184.01 1299062.23 NAD 83 38.883573 -77.046621

WPP-B-10 NAVD88 4.19 442831.12 1299427.86 NAD 83 38.882604 -77.045336

WPP-B-11 NAVD88 4.97 442638.18 1299636.36 NAD 83 38.882075 -77.044603

WPP-B-12 NAVD88 5.08 442456.11 1299851.26 NAD 83 38.881575 -77.043848

WPP-B-14 NAVD88 4.86 442021.38 1300354.33 NAD 83 38.880382 -77.042080

WPP-B-15 NAVD88 6.41 441915.65 1300545.67 NAD 83 38.880092 -77.041408

WPP-B-16 NAVD88 5.15 441939.69 1300724.42 NAD 83 38.880158 -77.040780

Table 3.2: As-Drilled Coordinates and Elevations for In-Situ Testing

Test ID Vertical Datum

Ground Surface

Elevation (feet)

Northing (feet)

Easting (feet)

Horizontal Datum

Latitude (deg)

Longitude (deg)

WPP-CPT-01 NAVD88 5.75 444868.02 1297436.45 NAD 83 38.888194 -77.052336

WPP-CPT-02 NAVD88 5.6 443189.64 1299077.68 NAD 83 38.883588 -77.046567

WPP-CPT-03 -- 5(a) -- -- -- 38..88016(b) -77.04077(b)

WPP-CPT-04 NAVD88 4.72 443903.08 1298330.19 NAD 83 38.885546 -77.049194

WPP-CPT-05 NAVD88 4.37 443003.78 1299253.62 NAD 83 38.883078 -77.045949

WPP-CPT-06 NAVD88 5.85 442271.04 1300076.25 NAD 83 38.881067 -77.043058

WPP-DMT-01 NAVD88 5.66 444565.57 1297674.12 NAD 83 38.887364 -77.051500

WPP-DMT-02 NAVD88 4.3 443424.31 1298816.49 NAD 83 38.884232 -77.047485

WPP-DMT-03 NAVD88 5.17 442630.45 1299645.94 NAD 83 38.882053 -77.044570

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(a) Ground surface elevation assumed to be similar to surveyed WPP-B-16 location, WPP-CPT-03 and WPP-B-16 were located within close proximity to one another.

(b) Latitude and longitude of as-staked location included since as-built coordinates provided for WPP-CPT-03 are erroneous and do not match the location where the test was performed in the field.

3.2 Previous Explorations by Others

AECOM previously performed a subsurface exploration for the nearby Potomac River Tunnel. Appendix D contains logs for nineteen (19) borings from that exploration. These data were developed by others and we were not present during collection of this information. We have reviewed the data for reasonableness, but we assume no responsibility for the completeness and accuracy of this information.

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4.0 LABORATORY TESTING PROGRAM

SaLUT laboratory performed tests on selected samples obtained during the subsurface exploration. The testing aided in the classification of materials encountered in the subsurface exploration and provided data for use in the development of preliminary geotechnical parameters. Moisture contents and index test results are shown on the boring logs in Appendix A. The remainder of the test results is included in Appendix C.

4.1 Soils Testing

4.1.1 Index Testing

Natural moisture content, Atterberg limit, and gradation tests on 68 jar samples and 8 tube samples were performed representing Stratum A1, A2, B1, and B2, to provide soil classifications and parameters for use with published correlations with soil properties. The results are presented in the Summary of Laboratory Tests in Appendix C and are summarized (for each stratum) in Section 7.0.

4.1.2 Strength and Consolidation Testing

Two (2) unconsolidated-undrained (UU) triaxial shear tests and four (4) direct shear tests were performed on tube samples of soils representing Stratum B2. One direct shear test was performed on a tube sample representing Stratum B1. These tests were performed to evaluate the shear strength of these materials. Additionally, seven (7) one-dimensional consolidation tests were performed on tube samples of soils representing Stratum B2 to evaluate the compressibility characteristics of these soils. The test results are presented in Appendix C and summarized in Section 7.0.

4.1.3 Organic Content Testing

Organic content testing was performed on seven (7) jar samples and nine (9) tube samples of Stratum B2, and one tube sample of Stratum B1. The organic content values ranged between 3.56 percent and

9.69 percent. The test results are included in Appendix C and summarized in Section 7.0.

4.1.4 Corrosivity Testing

Corrosion potential testing was performed on eight composite (blended) soil samples, two samples from Stratum A1/A2, two samples of Stratum B1, and four samples of Stratum B2 collected during our on-site investigation. These samples were tested for resistivity, redox potential, sulfides, pH, sulfate content, and chloride content. These results are provided in Appendix C and summarized in Section 7.0.

4.2 Rock Testing

Unconfined compressive strength testing (without moduli curves; ASTM D7012 – Method C) was conducted on rock core samples obtained from three of the boring locations (WPP-B-01, WPP-B-06, and WPP-B-16). Results are included in Appendix C and summarized in Section 7.0.

4.3 Previous Testing by Others

Summary tables of laboratory testing performed by others for the Potomac River Tunnel project (AECOM) are included in Appendix E. Please note that detailed lab results can be found in the Potomac River Tunnel contract documents. These data were developed by others and we were not present during the

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performance of these tests. We have reviewed these data for general reasonableness, but we assume no responsibility for the completeness and accuracy of this information.

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5.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

5.1 Regional Geology

The site is located within the Atlantic Coastal Plain physiographic province, which consists of a heterogeneous wedge of unconsolidated sedimentary deposits overlying steeply dipping bedrock. The sedimentary deposits thicken southeastward to about 1,500 ft at the Atlantic Ocean. The upper Coastal Plain sediments consist primarily of Pleistocene age terrace deposits typically composed of interbedded sands, gravels, silts, and clays. The terrace deposits are underlain by fluvial marine sedimentary deposits of the Cretaceous age.

The sedimentary deposits overlay residual soils that are predominantly fine sandy silts and silty fine sands with traces of mica that have developed in-place from the weathering of the underlying bedrock.

The weathering creates a zone of decomposed or “disintegrated” rock that can possess rock-like qualities that can extend to a significant depth. The bedrock below the sedimentary deposits and residual soils consists of crystalline rock (igneous and/or metamorphic rock) of Proterozoic and Paleozoic ages.

5.2 Site Geology

During our exploration, we encountered the following stratigraphy:

• Stratum A1: Existing Fill and Probable Fill (Fine-Grained)

• Stratum A2: Existing Fill and Probable Fill (Coarse-Grained)

• Stratum B1: Recent Alluvial Deposits (Coarse-Grained)

• Stratum B2: Recent Alluvial Deposits (Fine-Grained)

• Stratum C: Residual Soils

• Stratum D: Disintegrated Rock

• Stratum E: Bedrock

Significant filling of this area took place early in the 20th century during reclamation of the West Potomac Park. The existing fill and probable fill soils are believed to be a result of previous grading and dredging reclamation activities. The recent alluvial deposits encountered at the site and are believed to have been deposited from the adjacent Potomac River and the Tiber Creek tributary. If any terrace deposits were present at the site historically, they were extensively eroded and replaced with recent alluvial deposits.

5.3 Generalized Subsurface Stratigraphy

We characterized the following generalized subsurface stratigraphy based on our recent subsurface exploration included in Appendix A. The stratum designations do not imply continuity of materials encountered elsewhere on site but reflect the general description and characteristics of the subsurface materials at the boring locations.

Ground Cover: (Topsoil) At most of the borings between about 2 to 10 inches of topsoil was encountered. At borings WPP-B-08 and WPP-B-10, 24 inches to 30 inches of topsoil was encountered. These depths may vary at other locations at the site.

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Stratum A1: Fill and Probable Fill (Coarse-Grained) Below the ground cover and interlayered with Stratum A2, the borings encountered coarse-grained fill and probable fill soils to maximum depth of 15.0 ft. The fill and probable fill material generally consisting of well graded sand, silty sand, clayey sand, well graded gravel with sand, poorly graded sand with gravel, and poorly graded sand with silt, containing various amounts of gravel, roots, asphalt, brick, rock fragments, pieces of plastic, slag, organics, clay pockets, silt pockets, quartz fragments, glass, and mica. Based on the SPTs, this stratum exhibits generally variable density and consistency. SPT N-values within the coarse-grained fill layer ranged between 1 blow per foot (bpf) and 35 bpf. The average SPT N-value for this material was 4 bpf to 5 bpf indicating that the soil is generally very loose to loose.

Stratum A2: Fill and Probable Fill (Fine-Grained) Below the ground cover and interlayered with Stratum A1, the borings encountered fine-grained fill and probable fill soils to maximum depth of 23.5 ft. The fill and probable fill material generally consisting of sandy lean clay, lean clay with sand, elastic silt, lean clay, sandy elastic silt, sandy lean clay with gravel, sandy silt, and fat clay with sand, containing various amounts of gravel, shells, roots, wood fragments, wood pieces, asphalt, concrete, brick, rock fragments, pieces of foam, organics, ceramic pieces, sand pockets, glass, and mica. Based on the SPTs, this stratum exhibits generally variable density and consistency. SPT N-values within the fine-grained fill layer ranged between WOH over one foot and 50 blows over 3 inches. The average SPT N-value for this material was 4 bpf to 5 bpf indicating that the soil is medium stiff.

Stratum B1: Recent Alluvial Deposits (Coarse-Grained) Below Stratum A1 and A2 and interlayered with the fine-grained deposits of Stratum B2, most of the borings encountered coarse-grained alluvial deposits extending up to 83.5 ft below existing grades. These alluvial deposits generally consist of gray, dark brown, brownish gray, reddish brown, olive, dark gray, light brown, dark olive and brown clayey SAND (SC), silty SAND, silty, clayey SAND (SC-SM), well-graded SAND with silt (SW-SM), poorly-graded SAND with clay (SP- SC), poorly-graded SAND with silt (SP-SM), and poorly-graded SAND (SP), containing varying amounts of mica, organics, roots, gravel, wood fragments, shells, clay seams, lean clay pockets, sandy lean clay pockets, silt pockets, and quartz fragments. Based on the SPTs, this stratum is generally very loose to medium dense (SPT values varied from WOH over one foot and 14 bpf).

The average SPT N-value for this stratum was 4 bpf to 5 bpf indicating that the stratum is generally very loose.

Stratum B2: Recent Alluvial Deposits (Fine-Grained) Below Stratum A1 and A2 and interlayered with the coarse-grained deposits of Stratum B1, the borings encountered fine-grained alluvial deposits extending up to 93.5 ft below existing grades.

These fine-grained deposits generally consist of dark gray, dark brown, gray, brown, dark olive, olive, tan, light gray, and reddish brown LEAN CLAY(CL), sandy ELASTIC SILT (MH), ELASTIC SILT with sand (MH), sandy LEAN CLAY (CL), LEAN CLAY with sand (CL), FAT CLAY (CH), ELASTIC SILT (MH), sandy SILT (ML), FAT CLAY with sand (CH), and SILT (ML), containing varying amounts of mica, gravel, sand seams, organics, clayey sand seams and pockets, sand lenses, shell fragments, cemented sands, quartz fragments, and wood fragments. Based on the SPTs, this stratum exhibits generally very soft to very hard consistency (SPT values varied from WOH over one foot and 50 blows over 2 inches). The average SPT N-value for this stratum was

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4 bpf to 5 bpf indicating that the stratum is generally soft to medium stiff. Pocket penetrometer values ranged between 0 tons per square foot (tsf) and greater than 1.25 tsf, with an average pocket penetrometer value of 0.4 tsf.

Stratum C: Residual Soils Below Stratum B2 in boring WPP-B-02, a 4 ft thick residual soil layer was encountered at a depth of 43.5 ft below surface grades. The residual soil layer consists of gray silty SAND (SM), containing traces amounts of mica. Based on the SPT performed in this stratum, the stratum exhibits generally medium dense (an SPT value of 28 bpf was obtained).

Stratum D: Disintegrated Rock Residual disintegrated rock was encountered below Stratum B1, B2, and C and extended to depths ranging between 47.4 ft to 103.0 ft below the ground surface in most of the borings, except boring WPP-B-14. The Stratum D material consisted of dark gray, light gray, bluish gray, and gray DISINTEGRATED ROCK sampled as poorly-graded gravel with silt and gravel, silty sand, poorly-graded gravel with sand and clay, clayey gravel, silty sand with gravel, poorly-graded gravel with clay, poorly-graded gravel with sand, gravelly sand with clay, and lean clay containing varying amounts of rock fragments, quartz fragments, and mica. Based on the SPTs performed, this stratum is generally very dense (SPT values varied between 50 blows per 5.5 inches and 50 blows over 0 inches).

Stratum E: Bedrock Below the disintegrated rock of Stratum D, bedrock (Stratum E) was encountered at all boring locations. Rock coring extended to depths of 57.4 ft and 113 ft below existing exterior grades.

The bedrock classifies as gray, dark gray, light gray, and bluish gray SCHIST with varying amounts of mica. The rock was weak to medium strong, slightly to highly weathered, and slightly to intensely fractured. The Rock Core Recovery (REC) of the cores varied between 55 and 100 percent and the Rock Quality Designation (RQD) ranged between 0 percent and 95 percent.

Residual soils are derived through the in-place physical and chemical weathering of the underlying rock.

Disintegrated rock is defined as residual material with SPT N values between 60 blows per foot and refusal. Refusal is defined as an N value of 50 blows for a penetration of 1 inch or less. We encountered disintegrated rock at depths between 47.3 ft and 93.5 ft below existing grades, or between about EL -41.8

(ft) and EL -88.4 (ft).

We observed refusal on rock at depths between 47.4 ft and 103.0 ft below existing grades, or between about EL -41.9 (ft) and EL -97.9 (ft).

The above stratification is shown in detail on the boring logs in Appendix A. Numbers after the description of the soil strata in the above tabulation indicate the minimum and maximum penetration resistances, or N values, recorded in each stratum. The sampling procedures used to determine N values are also presented in Appendix A.

The soil group symbols, indicated on the boring logs and in the generalized subsoil stratum descriptions above, represent the Unified Soil Classification System (USCS) group symbols and are based on visual observation of the specimens recovered, per ASTM D-2488. The criteria for visual identification of soil

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specimens are presented in Appendix A. It should be noted that there may be differences between visual classifications and laboratory classifications based on ASTM D-2487.

5.3.1 Methane

During drilling activities, Schnabel utilized RAE Systems MultiRae Pumped Portable Multi-Gas Monitors (10.6eV) to monitor combustible gas due to the presence of methane at the subject site. The lower explosive limit percent (%LEL) was recorded every 5 ft during advancement and removal of the drilling augers at the Standard Penetration Test (SPT) borings. Please note that Schnabel was not originally recording the %LEL at the start of the project; however, once we were notified that methane had been encountered on the Tidal Basin side, we arranged for the delivery and use of the MultiRae gas monitors.

During drilling if a %LEL of greater than 50 percent was recorded drilling was stopped to allow the methane to vent off. Once the %LEL was below the 50 percent threshold drilling was allowed to proceed.

Please note that gas detectors display a gas's presence as a percentage of its LEL. An atmosphere free of methane would show 0% LEL on the gas detector, but an atmosphere containing 5% methane would display 100% LEL.

A summary of the %LEL readings at each borehole location is provided in the table below.

Table 3: %LEL Readings During Drilling Activities

Boring No.

Depth Where 99%LEL

Reading or Greater Registered (ft)

Notes

WPP-B-01 N/A(1) %LEL not measured in this borehole.

WPP-B-02 43.5 10 to 33% LEL at 38.5 ft- 40 ft.

WPP-B-03 N/A(1) %LEL not measured in this borehole.

WPP-B-04 N/A(1) %LEL not measured in this borehole.

WPP-B-06 --(2)

WPP-B-07 55

WPP-B-08 60 - 76.5

Bubbling noted at 57 ft.

WPP-B-10 66.5 - 75.5 26%LEL at 50 ft; 43%LEL at 59 ft

WPP-B-11 58.5

WPP-B-12 --(2) 20-33%LEL at depth of 58.5 ft.

WPP-B-14 52

WPP-B-15 68.5

Methane re-registered at 70 ft when pulling augers.

WPP-B-16 N/A(1) %LEL not measured in this borehole.

(1) %LEL not measured in boreholes WPP-B-01, WPP-B-03, WPP-B-04 and WPP-B-16. MultiRae readers were mobilized to the site once Schnabel was made aware of methane being encountered on the Tidal Basin side.

(2) No %LEL readings of 99% or greater were recorded.

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When methane was detected, our field personnel visually observed bubbling of water within the augers and, in some instances, projection of water and grout through the drill rods/augers. Additionally, hissing and bubbling were also noted by our field personnel when methane was detected.

5.4 Groundwater

Groundwater was encountered during drilling at depths between 5 ft and 12 ft below existing grades, or between about EL +0.2 (ft) and EL -10 (ft). The deeper encountered water level is believed to be due to a restrictive (fine-grained) layer in the upper portion of the fill material (Stratum A1). Discarding that measurement from the data, the encountered groundwater depth ranged between 5 ft and 10 ft below grade, or between about EL +0.2 (ft) and EL -4.5 (ft). Upon completion of the drilling, prior to pulling augers, groundwater was recorded at three of the borings between depths of 2 ft and 10 ft below existing grades, or between about EL +4.4 (ft) and EL -2.5 (ft). Groundwater readings were not taken upon completion at the remainder of the borings. All boreholes were grouted upon completion, except where instrumentation was installed.

The CPT and dilatometer soundings encountered groundwater at depths ranging between 0.6 ft and 5.9 ft below surface grades, or between about EL +5 (ft) and EL +0 (ft).

The vibrating wire piezometer data should be utilized to assess the groundwater level at the site, accounting for low tide and high tide. In general, we anticipate that the groundwater level will be close in elevation to the adjacent Potomac River (anticipated to be at about EL +0 (ft)) with variations of +/- 5 ft.

The groundwater levels on the logs indicate our estimate of the hydrostatic water table at the time of our subsurface exploration. Fluctuation of the hydrostatic water table can depend on variations in tidal action, precipitation, surface runoff, pumping, evaporation, leaking utilities, the nearby Potomac River and other similar factors.

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6.0 IN-SITU FIELD TESTING

6.1 Cone Penetrometer Testing

6.1.1 Brief Description of the Cone Penetrometer Test

The cone penetrometer consists of a 44-mm diameter cone and a 44-mm diameter friction sleeve that sits directly above the cone. The penetrometer contains strain gages to record the force on the cone and the friction sleeve. The penetrometer is attached to the end of a string of drill rods and is hydraulically advanced at a rate of 2 cm/sec. The force on the cone (tip resistance) and on the friction sleeve (friction resistance) is recorded approximately every 3 cm of penetration, providing a continuous record of tip resistance and friction resistance.

Piezocones are penetrometers fitted with pore pressure transducers to record the pore water pressure within the soil as the cone is advanced.

In-Situ Soil Testing, LC performed cone penetration testing (CPT) at six locations on the site (designated as WPP-CPT-01, WPP- CPT-02, WPP-CPT-03, WPP-CPT-04, WPP-CPT-05, and WPP-CPT-06). The CPTs were performed to depths of 45.7 ft to 85.5 ft. Details of the CPTs and test results are included in Appendix B.

6.1.2 Brief Description of the Flat-blade Dilatometer Test

The flat-blade dilatometer is a 95-mm wide, 15-mm thick blade with a wedge-shaped bottom edge. In the center of one face of the blade is a 60-mm diameter diaphragm. The dilatometer is attached to the end of a string of drill rods and is hydraulically advanced into the soil. At selected locations, the advancement is stopped and the dilatometer test is performed. The dilatometer test involves pneumatically pushing the circular diaphragm into the soil a distance of 1.1 mm. The pressure required to move the diaphragm is recorded at the beginning of movement (A reading), at the full extension of the diaphragm (B reading), and when the diaphragm returns to its initial position (C reading). After completion of the test, the blade is advanced to the next depth and the test repeated.

In-Situ Soil Testing, LC performed flat-blade dilatometer testing (DMT) at three locations on the site (designated as WPP-DMT-01, WPP-DMT-02, and WPP-DMT-03). The DMTs were performed to depths of 48.5 ft to 72.5 ft. Details of the DMTs and test results are included in Appendix B.

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7.0 LABORATORY TESTING RESULTS

7.1 Index Testing

Natural moisture content, Atterberg limit, and gradation tests on 68 jar samples and 8 tube samples were performed representing Stratum A1, A2, B1, and B2. The results are presented in the Summary of Laboratory Tests in Appendix C and the following summarizes the results of the laboratory testing for each of the strata encountered in the borings:

Stratum A1/A2: Fill and Probable Fill Twenty-one (21) jar samples of Stratum A1 and Stratum A2 material were tested for moisture content. The laboratory testing measured the following properties:

Moisture Content: 8.5% to 40.1%

Stratum B1: Recent Alluvial Deposits (Coarse-Grained) Twenty-three (23) jar samples and one tube sample of Stratum B1 material were tested. The material classified as silty, clayey SAND (SC-SM), well-graded SAND with silt (SW-SM), silty SAND (SM), and poorly graded SAND with silt (SP-SM). Seven jar samples and the tube sample from this stratum were tested for index properties and sixteen (16) samples were tested for moisture content only. The laboratory testing measured the following properties:

Moisture Content: 15.2% to 58.4% Liquid Limit: Non-plastic to 28 Plasticity Index: Non-plastic to 4 % Passing No. 200 Sieve: 10% to 42%

Stratum B2: Recent Alluvial Deposits (Fine-Grained) Twenty-four (24) jar samples and seven (7) tube samples of Stratum B2 material were tested.

The material classified as LEAN CLAY (CL), ELASTIC SILT with sand (MH), ELASTIC SILT (MH), sandy LEAN CLAY (CL), LEAN CLAY with sand (CL), FAT CLAY (CH), sandy SILT (ML), and FAT CLAY with sand (CH). Seventeen (17) jar samples and the seven (7) tube samples from this stratum were tested for index properties and twelve (12) samples were tested for moisture content only. The laboratory testing measured the following properties:

Moisture Content: 30.3% to 79.3% Liquid Limit: 41 to 96 Plasticity Index: 14 to 52 % Passing No. 200 Sieve: 58% to 99%

7.2 Strength and Consolidation Testing

Two (2) unconsolidated-undrained (UU) triaxial shear tests and four (4) direct shear tests were performed on tube samples of soils representing Stratum B2. One direct shear test was performed on a tube sample representing Stratum B1. These tests were performed to evaluate the shear strength of these materials. Additionally, seven (7) one-dimensional consolidation tests were performed on tube samples

November 23, 2022 Page 15 Schnabel Engineering, LLC.

of soils representing Stratum B2 to evaluate the compressibility characteristics of these soils. The test results are presented in Appendix C and summarized below:

Table 7.1: Unconsolidated-Undrained (UU) Triaxial Shear Tests – Stratum B2

Boring ID No. Depth (ft) Test Elevation (ft)

Undrained Shear

Strength (psf)

WPP-B-06 16.5 - 18.5 EL -14.4 237.6

WPP-B-14 60.0 - 62.0 EL -56.1 303.8

Table 7.2: Direct Shear Testing Results

Boring ID No. Stratum Depth (ft) Test Elevation (ft)

Peak Strength Friction Angle

(degrees) Cohesion (psf)

WPP-B-03 B2 16.5 - 18.5 EL -13.4 26.3 216

WPP-B-06 B1 36.5 - 38.5 EL -34.4 34.2 0

WPP-B-08 B2 43.0 - 45.0 EL -39.4 27.6 604.8

WPP-B-10 B2 63.0 - 65.0 EL -59.8 28.7 288

WPP-B-12 B2 51.0 - 53.0 EL -46.9 27.5 0

Table 7.3: Consolidation Testing Results for Stratum B2

Boring ID No. Depth (ft)

Test Elevation

(ft)

Initial Void Ratio

Pre- Consolidation Pressure (tsf)

Virgin Compression

Index (Cc)

Recompression Index (Cr)

WPP-B-03 16.5 - 18.5 EL -13.4 1.19 0.6 0.33 0.05

WPP-B-06 46.5 - 48.5 EL -44.4 1.49 1.1 0.6 0.09

WPP-B-08 43.0 - 45.0 EL -39.4 1.44 0.6 0.41 0.09

WPP-B-10 63.0 - 65.0 EL -59.8 1.62 0.9 0.66 0.12

WPP-B-12 51.0 - 53.0 EL -46.9 1.59 0.2 0.40 0.07

WPP-B-14 70.0 - 72.0 EL -67.1 1.47 0.5 0.45 0.09

WPP-B-16 35.0 - 37.0 EL -30.8 1.58 0.9 0.64 0.11

7.3 Organic Content Testing

Organic content testing was performed on seven (7) jar samples and nine (9) tube samples of Stratum B2, and one tube sample of Stratum B1. The organic content values ranged between 3.56 percent and

9.69 percent. The test results are included in Appendix C and summarized in the table below:

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Table 7.4: Organic Content Testing Results

Boring ID No. Stratum Depth (ft) Test

Elevation (ft)

As Received Moisture

Content (%)

Organic Content (%)

WPP-B-01 B2 43.5 - 44.2 -38.4 56.8 8.2

WPP-B-03 B2 16.5 - 18.5 -13.4 48.3 5.9

WPP-B-03 B2 48.5 - 50.0 -45.2 78.8 9.4

WPP-B-06 B2 16.8 - 18.5 -14.4 45.8 4.9

WPP-B-06 B1 36.5 - 38.5 -34.4 25.6 3.6

WPP-B-06 B2 46.5 - 48.5 -43.4 47.5 5.8

WPP-B-06 B2 60.0 - 61.5 -57.7 70.8 9.7

WPP-B-08 B2 43.0 - 45.0 -39.4 42.3 4.8

WPP-B-10 B2 45.0 - 46.0 -41.3 45.7 5.8

WPP-B-10(a) B2 63.0 - 65.0 -59.8 63.8 6.7

WPP-B-11 B2 48.5 - 50.0 -44.3 47.8 8.7

WPP-B-12 B2 51.0 - 53.0 -46.9 40.5 4.1

.WPP-B-14 B2 60.0 - 62.0 -56.1 53.1 3.9

WPP-B-14 (a) B2 70.0 - 72.0 -66.1 49.7 3.6

WPP-B-15 B2 68.5 - 70.0 -62.9 48.6 6.3

WPP-B-16 B2 35.0 - 37.0 -30.8 55.4 4.7

WPP-B-16 B2 63.5 - 65.0 -59.1 51.3 6.8

(a) Note: The organic content of these samples was unintentionally tested twice, during different assignments from the main laboratory (SaLUT) to one of their subcontracted laboratories. The additional testing values are included in the Laboratory Assignment No. 2 organic content test results in Appendix C.

7.4 Corrosivity Testing

Corrosion potential testing was performed on eight composite (blended) soil samples, two samples from Stratum A1/A2, two samples of Stratum B1, and four samples of Stratum B2 collected during our on-site investigation. These samples were tested for resistivity, redox potential, sulfides, pH, sulfate content, and chloride content. These results are provided in Appendix C. The table below summarizes these results:

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Table 7.5: Summary of Corrosivity Test Results

Boring ID No. Stratum USCS Sample

Depth (ft)

In Situ Resistivity (ohm-cm)

Redox Potential

(mV)

Sulfides (mg/kg) pH

Chloride Content (mg/kg)

Sulfate Content (mg/kg)

WPP-B-04 A1/A2 13.5 - 17.5 2600 619 6.2 6.2 81 520

WPP-B-04 B2 ML 25.0 - 31.5 4700 625 8.7 5.8 36 190

WPP-B-04 B2 MH 45.0 - 51.5 3060 611 11 5.9 46 800

WPP-B-15 A1 5.0 - 9.0 1980 580 23 5.5 75 320

WPP-B-15 B1 SP-SM / SC 18.5 - 25.0 2640 629 18 5.3 79 230

WPP-B-15 B1 SM 38.5 - 45.0 3010 592 < 5.5 5.5 28 240

WPP-B-15 B2 CL 58.5 - 65.0 10100 526 < 6.1 5.8 30 190

WPP-B-15 B2 CL 73.5 - 80.0 4510 483 7.8 7.2 68 330

7.5 Unconfined Compressive Strength of Rock

We performed unconfined compressive strength (UCS) tests and bulk density measurements on three rock core specimens. Table 7.6 summarizes the results of UCS tests on rock cores.

Table 7.6: Unconfined Compressive Strength of Rock Cores

Boring ID No. Rock Type Approximate Depth (ft)

Approximate Elevation (ft)

Unconfined Compressive Strength (psi)

WPP-B-01 Schist 48.3 - 48.7 -43.0 9,185

WPP-B-06 Schist 72.5 - 72.9 -69.6 11,607

WPP-B-16 Schist 109.7 - 110.1 -96.7 6.814

November 23, 2022 Schnabel Engineering, LLC.

FIGURES

Figure 1: Site Vicinity Map Figures 2A and 2B: Approximate Boring and In-Situ Sounding Location Plans

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NAMA 318722 - WEST PARK POTOMAC SEAWALL

PROJECT NO. 22410101.000

SITE VICINITY

MAP

FIGURE 1

OHIO STREET SW

Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P, NRCan, Esri Japan, METI, Esri China (Hong Kong), Esri Korea, Esri (Thailand), NGCC, (c) OpenStreetMap contributors, and the GIS User Community Esri, HERE, Garmin, (c) OpenStreetMap contributors Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community Projection: WGS 1984 Web Mercator Auxiliary Sphere

© Schnabel Engineering, 2022. All Rights Reserved.

WASHINGTON, DC

APPENDIX A

SUBSURFACE EXPLORATION DATA

Subsurface Exploration Procedures General Notes for Subsurface Exploration Logs Identification of Soil Descriptive Criteria for Rock Core Logging Supplemental Rock Descriptive Terms Boring Logs, WPP-B-01 through WPP-B-04, WPP-B-06 through WPP-B-08, WPP-B-10 through WPP-B-12, and WPP-B-14 through WPP-B-16 Figure A-1: Subsurface Cross Sections A-A’ Figure A-2: Subsurface Cross Section B-B’

SUBSURFACE EXPLORATION PROCEDURES

Test Borings – Hollow Stem Augers

The borings are advanced by turning an auger with a center opening of 2¼ or 3¼ inches. A plug device blocks off the center opening while augers are advanced. Cuttings are brought to the surface by the auger flights. Sampling is performed through the center opening in the hollow stem auger by standard methods after removal of the plug. Usually, no water is introduced into the boring using this procedure.

Test Borings – Mud Rotary

Drillers advanced the borings using mud rotary drilling techniques. The boring is advanced with a drill string consisting of a 3⅞-inch diameter tri-cone roller bit attached to A-sized drilled rods. Bentonite drilling fluid is pumped through the drill rods to flush cuttings to the surface. The borehole remains full of drilling fluid to maintain the sides of the borehole. At the designated depth, the drillers removed the drill string and collected a sample using standard methods. Water level data is indicated on the logs.

Standard Penetration Test Results

The Standard Penetration Test (SPT) is performed in the borings at regular depth intervals to collect soil samples. The numbers in the Sampling Data column of the boring logs represent SPT results. Each number represents the blows needed to drive a 2-inch O.D., 1⅜-inch I.D. split-spoon sampler 6 inches, using a 140-pound hammer falling 30 inches. The sampler is typically driven a total of 18 or 24 inches.

The first 6 inches are considered a seating interval. The total of the number of blows for the second and third 6-inch intervals is the SPT “N-value.” The Standard Penetration Test is performed according to

ASTM D1586.

Soil Classification Criteria

The group symbols on the logs represent the Unified Soil Classification System Group Symbols (ASTM D2487) based on visual observation and limited laboratory testing of the samples. Criteria for visual identification of soil samples are included in this appendix. Some variation can be expected between samples visually classified and samples classified in the laboratory.

Disintegrated rock is defined as residual material with SPT N-values between 60 blows per foot and refusal. Refusal is defined as an N-value of 50 blows for a penetration of one inch or less.

Pocket Penetrometer Results

The values following “PP=” in the sampling data column of the logs represent pocket penetrometer readings. Pocket penetrometer readings provide an estimate of the unconfined compressive strength of fine-grained soils.

Rock Core Drilling

The drillers core drilled rock using special core bits set with carbide steel or diamond, depending upon the rock texture. The bit was fitted onto a double-tube, swivel-type core barrel in which an exterior tube and bit rotate, and an interior barrel remains stationary to receive the rock core. Drillers circulated water between the barrels and across the bit face to provide cooling and to flush away cuttings. The size of bits is indicated on individual boring logs.

The length of rock core recovered expressed as a percentage of the total length cored is shown on the logs. Rock Quality Designation (RQD) is also given for rock core drilled with NX-size core drilling equipment. RQD is defined as the total length of NX-size rock fragments recovered that are greater than 4 inches in length, discounting drilling breaks, expressed as a percentage of the total length cored. RQD is preferred to core recovery as a measure of engineering characteristics of rock.

Volatile Organic Vapor Screening

The headspaces of soil samples collected during our subsurface exploration were screened for the presence of volatile organic vapors with a Photoionization Detector (PID). The PID provides an indication of the concentration of organic vapors in the headspace in parts per million (ppm). The PID detects a variety of organic vapors but does not detect the presence of methane. PID readings are presented in the sampling data column of the test boring logs.

Boring Locations and Elevations

Boring locations were staked by the design team and then, if stakes were pulled at the time of drilling were re-staked by Schnabel personnel using coordinates from the original stakeout. Approximate boring locations are shown on Figure 2A and 2B. As-drilled (as built) elevations and coordinates were obtained by GEI Consultants, Inc. The as-drilled elevations are indicated on the boring logs. Locations and elevations should be considered no more accurate than the methods used to determine them. Please note that the coordinates and elevation provided for WPP-CPT-03 are based on the as-staked coordinates obtained in the field. The CPT location as-advanced was within in a few feet from the as-staked location. The WPP-CPT-03 elevation is based on the nearby WPP-B-16 boring as-drilled elevation.

GENERAL NOTES FOR

SUBSURFACE EXPLORATION LOGS

1. Numbers in sampling data column next to Standard Penetration Test (SPT) symbols indicate blows required to drive a 2-inch O.D., 1⅜-inch I.D. sampling spoon 6 inches using a 140 pound hammer falling 30 inches. The Standard Penetration Test (SPT) N-value is the number of blows required to drive the sampler 12 inches, after a 6-inch seating interval. The Standard Penetration Test is performed in general accordance with ASTM D1586.

2. Visual classification of soil is in accordance with terminology set forth in “Identification of Soil.”

The ASTM D2487 group symbols (e.g., CL) shown in the classification column are based on visual observations.

3. Estimated water levels indicated on the logs are only estimates from available data and may vary with precipitation, porosity of the soil, site topography, and other factors.

4. Refusal at the surface of rock, boulder, or other obstruction is defined as an SPT resistance of 50 blows for 1 inch or less of penetration.

5. The logs and related information depict subsurface conditions only at the specific locations and at the particular time when drilled or excavated. Soil conditions at other locations may differ from conditions occurring at these locations. Also, the passage of time may result in a change in the subsurface soil and water level conditions at the subsurface exploration location.

6. The stratification lines represent the approximate boundary between soil and rock types as obtained from the subsurface exploration. Some variation may also be expected vertically between samples taken. The soil profile, water level observations and penetration resistances presented on these logs have been made with reasonable care and accuracy and must be considered only an approximate representation of subsurface conditions to be encountered at the particular location.

7. Key to symbols and abbreviations:

S-1, SPT Sample No., Standard Penetration Test 5+10+1 Number of blows in each 6-inch increment

SH-1, SH Sample No., 2" or 3" Shelby Tube Sample Rec=24", 100% Recovery in inches, Percent Recovery

Run #1, CORE Core No., Rock Core Run = 5.0 ft Run length in feet REC = 60", 100% Recovery in inches, Percent Recovery RQD = 60", 100% RQD in inches, Percent RQD

LL Liquid Limit MC Moisture Content (percent) PID Photoionization Detector Reading (ppm) PL Plastic Limit PP Pocket Penetrometer Reading (tsf) %Passing#200 Percent by weight passing a No. 200 Sieve

S

IDENTIFICATION OF SOIL

I. DEFINITION OF SOIL GROUP NAMES (ASTM D2487) SYMBOL GROUP NAME

Coarse-Grained Soils More than 50% retained on No. 200 sieve

Gravels – More than 50% of coarse fraction retained on No. 4 sieve Coarse, ¾” to 3” Fine, No. 4 to ¾”

Clean Gravels Less than 5% fines

GW WELL GRADED

GRAVEL

GP POORLY GRADED

GRAVEL

Gravels with fines More than 12% fines

GM SILTY GRAVEL

GC CLAYEY GRAVEL

Sands – 50% or more of coarse Fraction passes No. 4 sieve Coarse, No. 10 to No. 4 Medium, No. 40 to No. 10 Fine, No. 200 to No. 40

Clean Sands Less than 5% fines

SW WELL GRADED

SAND

SP POORLY GRADED

SAND

Sands with fines More than 12% fines

SM SILTY SAND

SC CLAYEY SAND

Fine-Grained Soils 50% or more passes the No. 200 sieve

Silts and Clays – Liquid Limit less than 50 Low to medium plasticity

Inorganic CL LEAN CLAY

ML SILT

Organic OL ORGANIC CLAY

ORGANIC SILT

Silts and Clays – Liquid Limit 50 or more Medium to high plasticity

Inorganic CH FAT CLAY

MH ELASTIC SILT

Organic OH ORGANIC CLAY

ORGANIC SILT

Highly Organic Soils Primarily organic matter, dark in color and organic odor PT PEAT

II. DEFINITION OF SOIL COMPONENT PROPORTIONS (ASTM D2487)

Examples

Adjective Form

GRAVELLY

SANDY

>30% to <50% coarse grained component in a fine-grained soil

GRAVELLY LEAN CLAY

CLAYEY

SILTY

>12% to <50% fine grained component in a coarse-grained soil

SILTY SAND

“With” WITH GRAVEL

WITH SAND

>15% to <30% coarse grained component in a fine-grained soil

FAT CLAY WITH GRAVEL

WITH GRAVEL

WITH SAND

>15% to <50% coarse grained component in a coarse-grained soil

POORLY GRADED GRAVEL WITH SAND

WITH SILT

WITH CLAY

>5% to <12% fine grained component in a coarse-grained soil

POORLY GRADED SAND WITH SILT

III. GLOSSARY OF MISCELLANEOUS TERMS

SYMBOLS ........................ Unified Soil Classification Symbols are shown above as group symbols. A dual symbol “-” indicates the soil belongs to two groups. A borderline symbol “/” indicates the soil belongs to two possible groups.

FILL ...................................... Man-made deposit containing soil, rock and often foreign matter.

PROBABLE FILL .................. Soils that contain no visually detected foreign matter but which are suspect with regard to origin.

DISINTEGRATED ROCK

(DR)

Residual materials with a standard penetration resistance (SPT) between 60 blows per foot and refusal. Refusal is defined as an SPT of 100 blows for 2" or less penetration.

PARTIALLY WEATHERED

ROCK (PWR)

Residual materials with a standard penetration resistance (SPT) between 100 blows per foot and refusal. Refusal is defined as an SPT of 100 blows for 2" or less penetration.

BOULDERS & COBBLES ..... Boulders are considered rounded pieces of rock larger than 12 inches, while cobbles range from 3 to 12-inch size.

LENSES ............................... 0 to ½-inch seam within a material in a test pit.

LAYERS ............................... ½ to 12-inch seam within a material in a test pit.

POCKET ............................... Discontinuous body within a material in a test pit.

MOISTURE CONDITIONS ..... Wet, moist or dry to indicate visual appearance of specimen.

COLOR ................................. Overall color, with modifiers such as light to dark or variation in coloration.

DESCRIPTIVE CRITERIA FOR ROCK CORE LOGGING

Rock is defined as natural subsurface material yielding SPT blow counts of N ≥ 100/2 inches (Martin, 1977). Rock descriptions may include the following descriptive elements, as applicable, generally in the order indicated. Supplemental descriptors may also be used, depending on project performance objectives and available information.

ROCK TYPE, strength, weathering, fracturing, color, recovery, RQD

Rock Type General terms are used following the NRCS (2001) rock type classification chart based on visual identification.

Some of the NRCS rock types common to our geographic area of practice are listed below. Mineralogical modifiers may be added where they help define distinct units (e.g., Garnet-Muscovite Schist).

Sedimentary: Conglomerate, Sandstone, Mudstone, Siltstone, Claystone, Shale, Limestone, Dolomite, Coal, Chert Igneous: Pegmatite, Granite, Diorite, Gabbro, Diabase, Rhyolite, Monzonite, Andesite, Basalt Metamorphic: Gneiss, Schist, Phyllite, Slate, Quartzite, Marble, Amphibolite, Hornfels

Strength (modified from Hoek, 2001) The estimated Uniaxial Compressive Strength associated with each rock strength term is based on the field strength index test for intact rock samples as follows.

• Extremely Strong >36,000 psi Specimen can only be chipped with a geological hammer.

• Very Strong 15,000 - 36,000 psi Specimen requires many blows of a geological hammer to fracture it.

•…