B.08.03 - TSF USACE Geotechnical Report.pdf

Prepared by:

U.S. Army Engineer District, Baltimore

Engineering Division Geotechnical Branch

June 2020

US Army Corps of Engineers Baltimore District June 2020

Battalion Operations Facility (BOF) and

Training Support Facility (TSF)

Humphreys Engineer Center Support Activity (HECSA)

Fort Belvoir, Virginia

Final Geotechnical Report

FOR INFORMATION ONLY

TABLE OF CONTENTS

1. PROJECT LOCATION AND DESCRIPTION

2. GEOTECHNICAL SCOPE OF WORK

3. PHASE 1 SUBSURFACE INVESTIGATIONS

a. Flat Plate Dilatometer Tests (DMT)

b. Seismic Piezocone Penetration Tests (SCPTu

c. Test Pits - Locating Limits of Buried Concrete Slab

4. PHASE 2 SUBSURFACE EXPLORATIONS

a. Standard Penetration Testing (SPT)

b. Shelby Tubes (Undisturbed Sampling)

c. Test Pits

d. Infiltration Testing

e. Soil Resistivity Testing

5. LABORATORY SOIL TESTING

6. REGIONAL GEOLOGY

7. SITE SOIL STRATIGRAPHY

8. GROUNDWATER

9. DRAINAGE AND WATER CONTROL

10. TEMPORARY EXCAVATIONS

11. REMOVAL OF BURIED CONCRETE SLAB

12. SATISFACTORY FILL and BACKFILL MATERIALS, MOISTURE CONTROL and

COMPACTION

13. STORMWATER RETENTION

14. PAVEMENTS

a. Criteria

b. Traffic

c. Pavement Sections

d. Subgrade Properties and Requirements

e. Strength and Frost Design Parameters

f. Asphalt Materials

g. Concrete Strength, Joint Spacing, Doweling, & Reinforcing

h. Graded Aggregate Base Course

i. Rapid Drainage Material (RDM) Base

j. Subsurface Drainage (Pavement Subdrains)

k. Separation Geotextile

l. Mill and Overlay of Asphalt Pavements

15. INTERIOR SLABS NOT SUBJECTED TO VEHICULAR TRAFFIC

16. LATERAL EARTH PRESSURES

a. Below Grade Non-Yielding Walls

b. Cantilever Wall

17. FOUNDATIONS

a. Foundations of Existing Structures throughout HECSA

b. Recommended Foundation System for the Battalion Operations Facility (BOF) and

Training Support Facility (TSF)

18. SITE CLASS FOR SEISMIC CONSIDERATIONS

19. GENERAL LIMITATIONS

20. POINT OF CONTACT

APPENDICIES

Appendix A: Location Map and Site Dimensioning Plan

Appendix B: Subsurface Location Plan SPT Boring Logs TP Logs DMT Test Results CPT Test Results

Appendix C: Laboratory Test Results

Appendix D: Infiltration Test Results

Appendix E: Soil Resistivity Test Results

Appendix F: Pavement Details

Battalion Operations Facility (BOF) and Training Support Facility (TSF), Humphreys Engineer Center Support Activity (HECSA), Virginia – Final Geotechnical Report

Final Geotechnical Report Battalion Operations Facility (BOF) and Training Support Facility (TSF), Humphreys

Engineer Center Support Activity (HECSA), Virginia June 2020

1. PROJECT LOCATION AND DESCRIPTION: The proposed projects consist of the construction of a new 42,800 square foot Battalion Operations Facility (BOF) and a new 73,000 square foot Training Support Facility (TSF) located within the boundaries of the Humphreys Engineer Center Support Activity (HECSA) located in Fort Belvoir Virginia.

The proposed BOF and TSF are to be located within and adjacent to an athletic field constructed upon spoils ranging in depths of approximately 4 to 10 feet generated from the construction of the adjacent HQ Operation Facility in 2006. According to Corps of Engineers Construction personnel present during the placement of the spoils in 2006, the spoils were placed in uncontrolled lifts and compactive effort with a tracked dozer. The existing ground elevation at the location of the proposed projects range between 43 and 51-feet. The proposed finished floor elevations of the BOF and TSF are 44.6 feet 45.5 feet respectively. Appendix A contains a Location Map and Site Dimensioning Plan.

Humphries Engineering Center Support Activity (HECSA) is within the 450+/- acre Research and Development tract along Telegraph Road in the extreme northern section of Fort Belvoir. Access to the site is by way of Leaf Road located off of Telegraph Road.

Prior to 1970 the area was occupied by the Civil Defense Protective Structures Development Center; existing structures at that time consisted of several small Fallout Shelters and a large fenced area designated as a radiation level test facility. The ground elevations ranged from a high of approximately 100 feet msl along Telegraph Road to a low of approximately 20 feet msl at Drogue Creek. Since then, the facility has grown to its current size containing the Kingman Building completed in 1972; the Coastal Engineering Research Center (CERC) completed in 1973; the Topographic R&D Building completed in 1974; the Casey Building completed in 1982, the Sensitive Compartmented Information Facility (SCI Facility; Addition to the Topographic R&D Building) completed in 1986, the HQ Operations & Training Facility completed in 2006, and other smaller shops and warehouses.

2. GEOTECHNICAL SCOPE OF WORK: The purpose of this report is to establish the subsurface conditions and provide geotechnical recommendations for the proposed BOF and TSF projects. These geotechnical recommendations include those related to foundations, pavements, earthwork, groundwater, and excavations.

3. PHASE 1 SUBSURFACE INVESTIGATIONS: Phase 1 subsurface explorations were conducted within the proposed project boundaries of the BOF and TSF building sites.

These explorations consisted of eighteen (18) Flat Plate Dilatometer tests in accordance with ASTM D 6635, and eight (8) Seismic Cone Penetration Tests (CPT) in accordance with ASTM D 5778 completed between August and September 2019.

Refusal was encountered at depths of approximately 7 feet below existing grade at the locations of DMT’s 9, 10, 12, 14, 16, 17 and 18 and CPT’s 4, 5, 7 and 8 resulting in terminating the tests at these locations. According to 2002 Google Earth aerial imagery and the results of the May 2019 Geophysical Survey Report completed by Pyramid Geophysics, a concrete slab is located beneath the locations of these ten (10) investigations. The 2006 Google Earth aerial imagery does not show the concrete slab as it is assumed that it was buried beneath the spoils placed in 2006. The approximate limits of the buried concrete slab as shown on the 2002 Google Earth imagery is overlaid on the Boring Location Plan contained in Appendix B. Test pits were conducted to determine the thickness and general limits of the concrete slab.

a. Flat Plate Dilatometer Tests (DMT): Eighteen Flat Plate Dilatometer Tests (DMT) were performed by the Baltimore District U.S. Army Corps of Engineers Field Exploration Unit between August and September 2019 in accordance with ASTM D 6635. Locations of the DMT tests are illustrated on the Boring Location Plan contained in Appendix B and are designated as “DMT” (i.e. DMT -

The DMT was advanced utilizing the 20-ton tracked CPT rig provided and operated by the Savannah District U.S. Army Corps of Engineers Field Exploration Unit. In general the DMT consists of a stainless steel blade having a flat, circular expandable steel membrane mounted flush on one side. The DMT was hydraulically pushed into the ground and the test conducted at 8-inch intervals and advanced until 10,000 kgf refusal was encountered resulting in test depths ranging from 67.6 to 107.9 feet below grade, not including the seven DMTs that refused at 7 foot depths due to the presence of the buried concrete slab. The expandable steel membrane was inflated and the pressures required to mobilize two pre-established strain levels are recorded. DMT results are contained in Appendix B and are presented graphically as “measured” parameters and “interpreted” parameters based upon published correlations. These interpreted parameters are based upon generally accepted correlations as defined in Report Number FHWA-PA-87-024+84-24, GUIDELINES FOR USING THE

CPT, CPTU AND MARCHETTI DMT FOR GEOTECHNICAL DESIGN,

VOLUME III.

b. Seismic Piezocone Penetration Tests (CPT): Eight seismic piezocone penetration tests (CPT) were completed by the Savannah District U.S. Army Corps of Engineers Field Exploration Unit in August 2019 in accordance with ASTM D 5778. Locations of the CPT tests are illustrated on the Boring Location Plan contained in Appendix B and are designated as “CPT” (i.e. CPT - *).

The CPT was advanced utilizing the 20-ton tracked CPT rig provided and operated by the Savannah District U.S. Army Corps of Engineers Field Exploration Unit.

The CPT tests were planned to be conducted to a depth of 125 feet or until refusal, whichever occurred first. However, as indicated previously, refusal was encountered at a depth of 7 feet in four of the eight CPT locations due to the presence of the existing buried concrete slab. Once refusal was encountered at these four CPT locations (CPT’s 4, 5, 7 and 8), the cone rig was relocated a few feet and the test re-attempted (CPT’s 4B, 5B, 7B and 8B) at which time refusal was again encountered at a depth of 6 feet resulting in these four test locations to be abandoned. The remaining four CPT’s (CPT’s 1, 2, 3, and 6) were advanced to depths ranging from 116 to 126 feet. A 20-ton tracked CPT rig was utilized to hydraulically push the 10-ton cone. The CPT consists of a three-channel instrumented 1.5-inch diameter steel probe with a 60 degree apex conical tip hydraulically pushed into the ground that measures cone tip stress (qc), sleeve friction (fs), penetration pore water pressure (u), and shear wave velocity (Vs).

These measurements are used to geotechnically characterize the site utilizing empirical correlations to estimate soil type, strength (undrained shear strength and friction angle), in-situ lateral earth pressures, and tangent modulus. A single geophone (pseudo-interval downhole method) was utilized to measure the shear wave velocity at each one-meter rod break. CPT results are contained in Appendix B and are presented graphically as “measured” parameters and “interpreted” parameters based upon published correlations

c. Test Pits – Locating Limits of Buried Concrete Slab: Six (6) test pits were conducted on 8 and 9 October 2019 along the estimated perimeter of the buried concrete slab to determine the depth to the top of slab and thickness of the slab. A test pit 50 feet west of DMT 6 was conducted on the western edge; test pits between DMTs 8 and 11 and adjacent to DMT 15 were conducted along the southern edge; test pits adjacent to DMT’s 10 and 13 along the northern edge; and a test pit 75 feet east of DMT 17 was conducted along the eastern edge of the buried slab. The depth to the top of slab is approximately 7 feet below grade.

The thickness of the slab varied from 6 to 12 inches. A petroleum odor was observed within the test pit adjacent to DMT 15.

4. PHASE 2 SUBSURFACE EXPLORATIONS: Phase 2 subsurface explorations were conducted within the proposed project boundaries of the BOF and TSF building sites between 3 February and 1 April 2020 by the Baltimore District U.S. Army Corps of Engineers Field Exploration Unit. These explorations consisted of Standard Penetration testing and Shelby tube sampling, test pits, infiltration testing, and soil resistivity testing as discussed below.

a. Standard Penetration Testing (SPT): A total of eleven (11) Standard Penetration Test (SPT) borings were conducted; five (5) within the footprint of the BOF and seven (7) within the footprint of the TSF. All SPT borings were conducted in accordance with ASTMD 1586 to a depth of 126.5 feet. In general, sample intervals were obtained at 2.5 foot intervals until the hard Potomac clays or very dense Potomac sands were encountered at which time the sample intervals were increased to 5.0 feet. Boring B-12 was conducted at 5.0 intervals for the full depth of the hole. Disturbed soil samples collected from the borings were accomplished using the Standard Penetration Test Procedure (SPT) per ASTM D 1586, Standard Test Method for Penetration Test and Split-Barrel Sampling of Soils, using a 1-3/8-inch ID x 2-foot 8-inch long split spoon sampler. Sample spoons were advanced by a 140-pound hammer dropped 30 inches utilizing an automatic hammer. The number of blows required to advance the sample spoon in intervals of 6 inches (for a total 18 inch length sample) were recorded on the logs with the sum of the latter two blow counts (final 12 inches of penetration) referred to as the “Nfield” value. The SPT provides soil samples to evaluate the distribution of soil types and in-situ moisture contents and blow count data which indicates the relative density and consistency of the granular and cohesive soils, respectively. Borings were advanced between sampling utilizing 2 ¼ inch ID hollow stem augers until groundwater was encountered at which time mud was introduced into the boring and the hole finished utilizing mud rotary drilling techniques between SPT sampling. Unconfined compressive strength readings from a pocket penetrometer were taken on cohesive samples in the split spoon sampler. Locations of the SPT’s are illustrated on the Boring Location Plan contained in Appendix B and are designated as “B” (i.e. B - *).

Standard Penetration Testing was conducted utilizing a CME-750 Rubber Tire ATV “Swamp Buggy” mounted drill rig equipped with an automatic hammer and a CME-55 truck mounted rig with an automatic hammer. Both automatic hammers have been calibrated in accordance ASTM D4633-10, Standard Test Method for Energy Measurement for Dynamic Penetrometers, to determine the Energy Transfer Ratio (ETR) which is the ratio of the measured energy transferred to the drill rods to the theoretical potential energy. Based upon the ETR, a corresponding energy ratio correction factor (CE) is computed which can be multiplied to the measured blow counts (Nfield) to obtain the “N60” value (N-value corrected to 60% of the maximum theoretical energy delivered by 140 pounds falling 30 inches). The Energy Transfer Ratio (ETR) and corresponding Energy Correction Factor (CE) for both automatic hammers is 81.4 percent and

1.35 respectively.

b. Shelby Tubes (Undisturbed Sampling): Undisturbed samples utilizing Shelby tube samplers were taken in representative cohesive materials adjacent to SPT borings B-5 and B-9 to conduct undisturbed laboratory consolidation testing as addressed in paragraph LABORATORY SOIL TESTING. Locations and depths where Shelby tube samples were obtained are illustrated below in table Undisturbed Shelby Tube Sample Locations.

Undisturbed Shelby Tube Sample Locations

Drill Hole Shelby Tube Sample Depth (feet)

B-5 15.0 – 17.0

20.0 – 22.0

30.0 – 32.2

45.5 – 47.6

52.5 – 54.2

B-9 27.5 – 29.8

49.0 – 51.3

c. Test Pits: Test Pits were excavated at three locations to depths of 4.0 feet below grade utilizing a backhoe to obtain bulk samples to conduct remolded CBR tests and obtain natural moisture contents. Locations of the Test Pits are illustrated on the Boring Location Plan contained in Appendix B and are designated as “TP” (i.e. TP - *).

d. Infiltration Testing: Infiltration testing was conducted at eight (8) locations

(SWM-1 through 8) within proposed SWM facilities within the BOF and TSF sites on 9 through 13 March 2020 to provide permeability data to support in obtaining SWM permits. In addition, two (2) borings (SWM-9 & 10) were conducted to establish soil profiles and seasonal high groundwater readings. The locations and depths of these ten (10) test locations were provided by the AE.

Infiltration testing was conducted in accordance with the TESTING

GUIDELINES FOR INFILTRATION FACILITIES, FAIRFAX COUNTY,

VIRGINIA, July 2012. Generally, the testing consisted of a pre-soak for a minimum of 12 hours followed by refilling a two foot column of water once per hour for four hours and measuring the infiltration rate hourly. Locations of the infiltration tests and Seasonal High Water Table (SHWT) borings are illustrated on the boring location plan contained in Appendix B and are designated as “SWM” (i.e. SWM - *).

The infiltration data is contained in Appendix D and summarized below in table Summary - Infiltration Test Results. Little to no infiltration was observed and therefore the soils are considered unacceptable (less than 0.5 inches per hour) for infiltration. USDA textural classifications were conducted on representative samples and are provided in Appendix C.

Summary - Infiltration Test Results

LOCATION TOH

ELEVATION

(feet)

TEST

DEPTH/ELEV.

OF TEST HOLE

(feet)

GROUNDWATER

DEPTH/ELEV.

(feet)

INFILTRATION

RATE

(in/hr.)

SWM-1 46.0 15.0/31.0 NE 0.03

SWM-2 46.5 14.8/31.7 NE 4.2 *

SWM-3 46.4 14.8/31.6 10.0/36.4 0.18

SWM-4 41.2 15.0/26.2 13.5/27.7 0.09

SWM-5 40.2 14.9/25.3 14.9/25.3 0.0

SWM-6 39.5 14.8/24.7 NE 0.0

SWM-7 37.9 13.0/24.9 NE 0.03

SWM-8 35.8 11.0/24.8 5.1/30.7 32.07 **

SWM-9 ** 35.3 15.0/20.3 4.9/30.4 NA

SWM-10 ** 35.1 15.0/20.1 4.5/30.6 NA

* SWM-2 was the only boring that terminated in a gravel sand.

** SWM-8 was located adjacent to a grassy stormwater culvert which may have affected the infiltration rates *** SWM-9 & 10 were conducted establish soil profiles and seasonal high groundwater readings. No infiltration tests conducted at these locations.

e. Soil Resistivity Testing: In-situ resistivity readings were taken in accordance with ASTM G57 utilizing an AEMC Model 4630 Digital Ground Resistance and Soil Resistivity Tester utilizing the 4-point measurement method. Testing was conducted adjacent to borings B-4 and B-9. Resistivity readings were taken at probe spacing’s of five, ten, fifteen, twenty, and thirty feet at both locations. The Soil Resistivity Survey Report is contained in Appendix E. The average resistivity values (cm) at B-4 and B-9 were 3334 cm and 2369 cm respectively. Based upon UFC 3-570-02A CATHODIC PROTECTION Table 2- 1, indicates that the corrosion of buried metallic utilities in the soils are “moderate severe”.

5. LABORATORY SOIL TESTING: All laboratory soils testing was completed by the

Baltimore District Corps of Engineers Materials and Instrumentation Unit in accordance with the appropriate ASTM methods. All SPT, TP and SWM jar soil samples were visually inspected and assigned a Unified Soil Classification System (USCS) classification by an experienced laboratory technician. Index properties of samples representative of soil stratification were determined by performing mechanical sieve analysis, Atterberg limits, and in-situ water contents. USDA textural classifications were conducted on samples obtained from the SWM holes. Five consolidation tests with time curves, two consolidation tests without time curves, and four unconfined compressive strength tests were conducted on undisturbed Shelby samples to evaluate the compressibility and shear strength characteristics of the underlying cohesive materials.

One remolded California Bearing Ratio (CBR) tests were completed to evaluate the ability to compact the in-situ subgrade soils based on their in-situ moisture contents relative to the target density, strength, and optimum moisture content. The results of these tests are included in Appendix C and reflected in the Final Boring Logs in Appendix B.

6. REGIONAL GEOLOGY: The site lies within the Coastal Plain province of Virginia.

Approximately 20 to 160 feet of normally consolidated soils overlie the highly preconsolidated Patapsco clay (also referred to as the Potomac clay). Rock is at a depth of several hundred feet. This Patapsco formation is part of the Potomac Group of the Cretaceous Age.

7. SITE SOIL STRATIGRAPHY: A general description of the soil conditions encountered during subsurface investigations conducted within the boundaries of the proposed projects are discussed below. These stratum designations do not imply that the materials encountered are continuous across the site. Actual soil conditions between SPT borings, TP’s, DMT and CPT locations may differ from these descriptions.

Fill: The existing site consists of a grassed field placed upon 4.0 to 12.5 feet of uncontrolled fill consisting of spoils generated during the construction of the adjacent HQ Operations & Training Facility completed in 2006. These fill materials consist of cohesive materials with average pocket penetrometer values conducted on split spoon samples ranging from 1.4 to 2.7 tsf and cohessionless materials with average N60 values ranging from 4 to 8 bpf. A concrete slab is located beneath the fill materials in portions of the site as discussed in paragraph

PHASE 1 SUBSURFACE INVESTIGATIONS.

STRATUM A: Stratum A, located just below the uncontrolled fill and buried concrete slab and extending to a depth ranging between 12.5 to 21.5 below grade consists of poorly graded, well graded, clayey and silty sands (SP, SW, SC, SM) with average N60 values ranging from 2 to 14 bpf. Constrained (Tangent) modulus values obtained from flat plate dilatometer tests (DMT’s) typically range between 100 and 1000 tsf.

STRATUM B: The highly compressible clay layer of Stratum B, encountered beneath Stratum A, extends to a depth ranging between 37.5 and 60.0 feet below grade. Stratum B consists primarily of highly compressible normally to slightly overconsolidated very soft to soft clays (CL, CH,) interbedded with very loose to medium dense clayey sands (SC) and medium to stiff clays. Average pocket penetrometer values (qu) conducted on split spoon samples range from 0.6 tsf to

2.0 tsf. Constrained (Tangent) modulus values obtained from flat plate dilatometer tests (DMT’s) are typically below 300 tsf and corresponding undrained shear strength values between 0.2 and 0.9 tsf.

STRATUM C: Stratum C, encountered below Stratum B, extends to depths ranging between 82.5 to 120 feet below grade. These materials consist primarily of loose to dense granular (cohesionless) materials with average N60 values ranging between 6 and 20 bpf. Constrained (Tangent) modulus values obtained from flat plate dilatometer tests (DMT’s) typically range between 100 and 1000 tsf with triaxial friction angles ranging between 35 and 40 degrees.

STRATUM D: Stratum D, encountered below Stratum C consists of stiff to hard, high plastic, fissured (slickensided) clay (CH) and dense to very dense clayey sands. The formation is known locally as the Patapsco (Potomac) formation and the clay is known locally as the Patapsco (Potomac) clay and is part of the Potomac Group of the Cretaceous Age. Typically, this clay is fissured (slickensided); however, it is only troublesome when unconfined, such as on cut slopes. It is also highly preconsolidated and when undisturbed it has very low compressibility characteristics. When confined, as is the case for supporting the proposed foundations, the soil is an excellent bearing layer and is used to support numerous structures in the Washington D.C. area. Average pocket penetrometer values (qu) conducted on split spoon samples typically exceed 5.0 tsf. Layers of dense to very dense clayey sands are interbedded within the Patapsco clay.

Constrained (Tangent) modulus values obtained from flat plate dilatometer tests (DMT’s) exceed 1000 tsf.

8. GROUNDWATER: Groundwater readings are an indication of the groundwater levels at the time, date, and conditions as indicated on the boring logs. Fluctuations in the groundwater levels will occur due to variations in season, precipitation, temperature, construction activities, site development, change in surface grades, and other factors not evident at the time measurements were taken.

Perched groundwater levels are present throughout the site due to the presence of the clay layer of Stratum B and discontinuous clay lenses both located directly beneath the uncontrolled fill and granular materials of stratum A. Encountered groundwater readings during drilling range from 9.3 to 45.1 feet below grade with corresponding elevations of

37.3 and 1.3 feet respectively.

In addition, the clay layer of Stratum B located above the granular materials of Stratum C, is an aquitard creating an artesian groundwater condition. This was evident by groundwater readings taken more than 24 hours after drilling where the groundwater rose well above the level when initially encountered. Twenty-four hour groundwater readings ranged from as high as 0.5 feet below existing grade to 15.75 feet below existing grade with corresponding elevations of 44.4 and 30.85 feet respectively. The average 24-hr groundwater depth was 7.85 feet below existing grade with a corresponding average elevation of 36.8 feet.

Groundwater readings taken in 2019 during explorations for the adjacent Maintenance and Supply Facility site ranged from 3.8 to 13.9 feet below existing grades with corresponding elevations of 35.2 and 25.8 feet, respectively. The 24-hour ground water readings ranged from 2.1 to 10.2 feet below grade with corresponding elevations of 37.3 and 30.1 feet, respectively.

Two observation wells were installed for the adjacent HQ Operations & Training Facility in 2002 to obtain a more accurate understanding of the groundwater conditions. These wells consisted of dual riser flush mount observation wells installed in drill holes DH-3 and DH-7. Two screens were set in each well to obtain accurate groundwater readings in both the upper unconfined aquifer and the deeper confined aquifer. The shallow perched water levels were recorded at depths of 5.4 and 4.3 feet below grade with corresponding elevations of 31.7 and 33.9 feet, respectively. The deeper groundwater levels were recorded at 12.1 and 12.8 feet below grade with corresponding elevations of 25.0 and

25.4 feet, respectively.

9. DRAINAGE AND WATER CONTROL: Proper drainage and protection measures shall be employed during the progress of the work to prevent soils from being rendered unsuitable for subgrade, fill or backfill. These measures include such things as proper grading, sealing soils with a roller prior to rain events, proper scheduling of earthwork activities (i.e. in summer), etc. Appropriate measures shall be employed as necessary to maintain dewatered excavations.

10. TEMPORARY EXCAVATIONS: Temporary excavations more than 4 feet high shall be shored or cutback no steeper than to a 2H on 1V slope. Temporary excavations adjacent to structures and roadways shall be cut back on a 2H to 1V slope with the top of the excavation beginning 10 feet away from the outside edge of the footing or pavement edge. Temporary excavations that remain exposed for more than 30 days shall be stabilized to prevent surface sloughing (i.e. vegetated or covered with plastic to reduce infiltration). Where site restraints make cutting back the excavation impractical, the excavation shall be shored using a soldier beam and wood lagging system or other equivalent temporary excavation support system. Temporary excavation support systems are typically designed by a specialty contractor and then reviewed by the geotechnical engineer provided by Baltimore District’s Geotechnical Branch. Excavations will be completed in both granular and cohesive soils. Groundwater flow into the excavation resulting from precipitation or perched water tables may result in sloughing of the excavated slopes. Any groundwater flowing into excavations shall be intercepted with sumps and pumps to ensure that the foundation soils in the excavation are not adversely affected. Heavy equipment and stockpiles shall not be located near the top of excavations.

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11. REMOVAL OF BURIED CONCRETE SLAB: As indicated previously, a buried concrete slab was identified during Phase 1 explorations. The concrete slab is located within portions of the footprints of both the TSF and BOF structures as illustrated on the Boring Location Plan contained in Appendix B and discussed in paragraph PHASE 1 SUBSURFACE INVESTIGATIONS. The depth to the top of slab is approximately 8 feet below grade with a corresponding top of slab elevation of 38.5 feet. The thickness of the slab varies from 6 to 12 inches.

The soils above the concrete slab consist of construction spoils generated from the construction of the adjacent HQ Operation Facility in 2006. According to Corps of Engineers Construction personnel present during the placement of the spoils in 2006, the spoils were placed in uncontrolled lifts and compactive effort with a tracked dozer. It is our understanding that the concrete slab will be removed and replaced with onsite soils prior to contract award of the subject project. The intent is to backfill with onsite materials, excluding trash, organics and constructions debris, placed in 8 inch loose lifts and compacted at moisture contents within plus or minus 3 percent of optimum moisture to 90 percent and 95 percent of laboratory maximum density, where possible, in accordance with ASTM D 1557, Procedure C for cohesive and cohesionless soils, respectively.

12. SATISFACTORY FILL and BACKFILL MATERIALS, MOISTURE CONTROL and COMPACTION: : Satisfactory materials for fill, embankment, and backfill shall comprise of any materials classified by ASTM D 2487 as GW, GM, GC, SW, SM, SP, SC, or combinations thereof, properly worked by the Contractor to obtain the specified compaction while maintaining the moisture content as specified hereinafter. CL and ML materials may be used in overlot areas only. The Contractor should, however, be aware of the possible construction difficulties and the very close moisture control required in the proper field placement and compaction of CL and ML materials or combinations thereof. Fill and backfill materials shall not contain organics, compressible materials or trash/debris. The maximum particle size shall be limited to 3 inches in diameter.

Satisfactory fill materials shall be placed in loose lifts not exceeding 8 inches. Lift thickness shall be limited to 6 inches where hand operated compaction equipment is used.

To achieve the desired long-term soil strength characteristics, all fill and backfill materials within the building footprint and beneath pavements shall be compacted at moisture contents within plus or minus 2 percent of optimum moisture to 90 percent and 95 percent of laboratory maximum density in accordance with ASTM D 1557, Procedure C for cohesive and cohesionless soils respectively. In grassed overlot areas, higher moisture contents are allowed as long as 85 percent and 90 percent compaction in accordance with ASTM D 1557, Procedure C for cohesive and cohesionless soils respectively is achieved. Compaction adjacent to walls shall be limited to hand tamping operations within a lateral distance equal to the height of the wall.

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13. STORMWATER RETENTION: As indicated in paragraphs Infiltration Testing, SITE SOIL STRATIGRAPHY, surficial soils are generally impermeable resulting in infiltration rates much less than the required 0.52 inches per hour considered unacceptable for infiltration per the VIRGINIA STORMWATER MANAGEMENT HANDBOOK and therefore are considered unacceptable for infiltration. However, lenses of sands may be exposed during excavations for the construction of other BMP.

14. PAVEMENTS

a. Criteria: Pavements were designed to meet both strength and frost protection requirements for a 25-year service life utilizing PCASE VERSION 2.09 computer software (http://www.pcase.com.). PCASE Version 2.09 software incorporates the latest Department of the Army criteria, UFC 3-250-01Nov 16, PAVEMENT DESIGN FOR ROADS AND PARKING AREAS, for the design of the pavements.

b. Traffic: The asphalt Access Road and concrete loading docks were designed to accommodate 2000 trips of 5-axle trucks per year resulting in 50,000 passes of 5-axle trucks per the 25 year life span of the pavement. Parking areas were designed to accommodate only POV vehicles. Interior concrete pavements and exterior concrete loading docks were designed to accommodate 10 passes per day of a CG50 Fork @ 936 lbs, CAT PC7000D @ 2500 lbs and Raymond 7000 series @ 4500 lbs forklifts resulting in 91,250 passes per forklift over the 25 year service life span.

c. Pavement Sections: The proposed pavement sections illustrated below do not consider construction traffic. Construction traffic may result in failure of the subgrade and pavement section. Asphalt surface courses shall not be placed until pavement areas will no longer be subjected to construction traffic. Failed subgrades and base courses shall be repaired prior to placing asphalt. Pavement details are provided in Appendix F.

HEAVY DUTY BITUMINOUS PAVEMENT SECTION (Access Roads)

1.5 inches Bituminous Concrete Surface Course (9.5mm) Tack Coat

2.5 inches Bituminous Base Course (19mm)

4.0 inches Graded Aggregate Base Course

6.0 inches Rapid Drainage Material (RDM) Base Course Separation Geotextile

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LIGHT DUTY BITUMINOUS PAVEMENT SECTION (POV Parking Stalls)

1.5 inches Bituminous Concrete Surface Course (9.5mm) Tack Coat

2.5 inches Bituminous Base Course (19mm)

4.0 inches Graded Aggregate Base Course

4.0 inches Rapid Drainage Material (RDM) Base Course

EXTERIOR HEAVY DUTY CONCRETE PAVEMENT SECTION (Loading docks)

6.0 inches Concrete (5000 psi compressive strength @28 days)

4.0 inches Graded Aggregate Base Course

5.0 inches Rapid Drainage Material (RDM) Base Course

INTERIOR CONCRETE SLABS SECTION (Subjected to forklift traffic)

6.0 inches Concrete (5000 psi compressive strength @28 days) 10 mil Polyethylene Sheeting Vapor Barrier

6.0 inches Capillary Water Barrier

d. Subgrade Properties and Requirements: The cohesive nature of the surficial soils makes them susceptible to strength loss under adverse moisture conditions. Based upon a comparison between the optimum moisture content obtained from the results of remolded CBR test (ASTM D 1883) and the in-situ natural moisture contents, it is anticipated that unstable subgrade conditions may be encountered throughout the site. These unstable subgrade soils will result in excessive pumping and loss of strength when subjected to vehicular traffic. Based upon the permeability characteristics of these subgrade soils, isolated high in-situ moisture contents, and the potential for winter and spring construction operations, isolated areas of the surficial site soils may be too wet to dry back to within a satisfactory range within a reasonable time frame. Therefore, to provide trafficability to the site and to obtain the required moisture control and compaction requirements beneath pavements and within the building footprints, it should be anticipated that isolated areas of the subgrade soils will have to be stabilized as directed by the Contracting Officer. Where possible, construction of the pavements should be scheduled for dryer seasons when moisture conditions are more favorable.

The subgrade beneath interior slabs and exterior paved areas shall be proof rolled in the presence of the Contracting Officer to identify isolated areas of soft, wet and unstable subgrade soils. Proof rolling shall consist of the application of at least three coverage’s with a loaded (approximately 10 cubic yard dump truck) dump truck weighing a minimum of 10 tons. Soft or loose areas identified beneath interior slabs shall be overexcavated and replaced with materials as defined in paragraph SATISFACTORY FILL AND COMPACTION

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REQUIREMENTS. Areas beneath proposed pavements where substantial pumping of the subgrade is observed and the in-situ moisture contents are 6 percent or greater above optimum moisture shall be stabilized as directed by the Contracting officer. Subgrade stabilization is not required in areas where pumping is not observed when subjected to a 10-ton proof roller or where soil moisture contents are less than 6 percent above optimum moisture. These areas where subgrade stabilization is not required shall be dried back to within plus 2 percent of optimum, plowed, disked, or otherwise broken up, thoroughly mixed, and compacted to at least 90 percent laboratory maximum density for cohesive materials or 95 percent laboratory maximum density for cohesionless materials.

Stabilization will generally consist of the overexcavation of unstable in-situ subgrade materials to a depth of 12 inches beneath the existing grades and extending laterally 5 feet beyond the edge of the unstable area. Replace the 12-inch excavation with Graded Aggregate Base Course. To bridge the wet subgrade soils, the 12-inch lift of Dense Graded Aggregate shall be placed between 90 and 95 percent maximum dry density at optimum moisture in accordance with ASTM D 1557. Vibratory compaction shall be used cautiously to minimize the “wicking up” of moisture from the wet subgrade soils into the stabilization layer therefore jeopardizing the stability of the stabilization (bridging) layer. Prior to placement of the Graded Aggregate Base Course, a soil stabilization geotextile shall be placed directly upon the subgrade. The stabilization geotextile shall be a woven or non-woven geotextile except that heatbonded non-woven and slit film woven geotextile shall NOT be used. The geotextile shall meet the requirements of Class 1 Survivability in accordance with AASHTO M 288. The geotextile shall have MARV hydraulic properties meeting the requirements of AASHTO M 288 geotextile criteria for stabilization (i.e. minimum permittivity of 0.05 sec -1 and an apparent opening size (AOS) equal or less than the No. 40 sieve).

e. Strength and Frost Design Parameters: A California Bearing Ratio (CBR) of 3 was used for the design of the bituminous pavements and a modulus of subgrade reaction (k-value) of 150 pci was used for the design of the interior and exterior concrete slab and pavements. The CBR value is based upon the results of the remolded CBR test. The k-value is based upon an empirical correlation between the in-situ moisture contents and soil type and correlations with the CBR value.

The subgrade is classified as an F-3/F-4 material for frost considerations

f. Asphalt Materials: Asphalt paving shall consist of a Virginia DOT approved “Superpave” mixture. The mix design shall use a PG 64-22 binder, a nominal maximum aggregate size of 9.5 mm for the surface and 19.0 mm for the base and a Design ESAL frequency of 0.3 million to 3 million.

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g. Concrete Strength, Joint Spacing, Doweling, and Reinforcing: Concrete pavements shall have a minimum compressive strength of 5000 psi at 28 days.

All longitudinal and transverse control joints of the reinforced concrete shall be spaced at a maximum distance of 15.0 feet to create square to near square panels.

All joints in concrete pavements shall be doweled. Dowels shall consist of 0.75 inch diameter smooth bars 16 inches in length with a minimum spacing of 12 inches. All dowels shall be placed at a depth midway into the slab. One end of the dowel shall be painted and oiled to prevent bonding with the concrete.

Dowels shall not be placed within thickened edge expansion joints.

h. Graded Aggregate Base Course: Graded Aggregate Base shall meet the requirements for 21A Base in Table II-9 of Section 208 Subbase and Aggregate Base Material of the Virginia DOT Standard Specifications for Roads and Bridges, 2016. Crushed Recycled Concrete shall not be permitted.

i. Rapid Drainage Material (RDM) Base Course: The RDM layer shall be incorporated into the final pavement sections as illustrated in paragraph Subsurface Drainage (Pavement Subdrains). Rapid Drainage Materials shall be continuously graded within the limits of one of the following gradations illustrated below. A 50% - 50% blend of No. 57 and No. 9 coarse aggregate (ASTM D 448) will fall within the gradation band No. 1. A 75% - 25% blend of No. 57 coarse aggregate and concrete fine aggregate (ASTM D 448) will fall within gradation band No. 2. Pennsylvania Department of Transportation OGS Gradation (Section 703.2) will fall within gradation band No. 3. The gradation for the completed RDM base course shall have a coefficient of uniformity (Cu=D60/D10) greater than or equal to 4.

Rapid Drainage Material (RDM) Base Course

Sieve Designation

Percent by Weight Passing Designated Square-Mesh Sieve

No. 1 No. 2 No. 3 2-inch 100 100 100 1-1/2-inch 100 100 100 1-inch 95-100 96-100 100 3/4-inch 82-92 70-83 52-100 1/2-inch 62-80 44-70 --- 3/8-inch 59-73 38-59 36-65 No. 4 40-55 24-33 8-40 No. 8 5-25 20-29 --- No. 16 0-5 12-21 0-12 No. 50 0-2 2-8 --- No. 100 --- 0-3 ---

j. Subsurface Drainage (Pavement Subdrains): A pavement subdrainage system is required beneath pavements to limit frost impacts on the pavements therefore

Page prolonging the pavement life. The pavement subdrainage system shall consist of a layer of RDM (Rapid Drainage Material) base course material within the pavement section and perforated pipe subdrains placed along the edge of roadways and parking areas and at 50 to 75 foot intervals within large paved areas. The subdrains shall be directed to inlets to effectively remove the water collected in the RDM layer. The pipe subdrain inverts shall be established based upon final grades and the inverts of the storm sewers. The subdrains shall consist of a 6-inch minimum diameter pipe surrounded by a minimum of 3 inches of ASTM C33, No. 57 crushed stone on the bottom, 6 inches (minimum) on each side, and sufficient crushed stone above the top of the pipe to extend to the Rapid Drainage Material (RDM) base course within the pavement structure. The subdrain trenches shall be a minimum of 18 inches wide. The crushed stone filter material (ASTM C33 No. 57 stone) shall be completely enveloped in a filtration geotextile. The filtration geotextile shall be a nonwoven geotextile with sufficient flow rate characteristics meeting a Class 2 Geotextile Survivability requirement in accordance with AASHTO M 288 except that heatbonded non-woven geotextiles shall not be used. The geotextile shall have MARV hydraulic properties meeting the requirements of AASHTO M 288 geotextile criteria for filtration (i.e.

minimum permittivity of 0.2 sec -1 and a maximum apparent opening size (AOS) equal or less than the No. 60 sieve).

k. Separation Geotextile: The separation geotextile shall be a non-woven, needle punched material conforming to the requirements for an AASHTO M 288 Class 1 geotextile and having a minimum permittivity of 0.02 sec-1 and a maximum apparent opening size (AOS) of No. 30 sieve.

l. Mill and Overlay of Asphalt Pavements: Any areas requiring mill and overlay shall be conducted to a depth of 2 inches. Cold milling of asphalt pavements shall be conducted per the requirements of Section 515 PLANING OR MILLING PAVEMENT of the Virginia DOT Standard Specifications for Roads and Bridges, dated 2016. Asphalt overlay shall consist of a Virginia DOT approved “Superpave” mixture utilizing a PG 64-22 binder and a nominal maximum aggregate size of 9.5 mm. Milled surfaces shall be cleaned, prepared and tack coated prior to paving per the requirements of the Virginia DOT Standard Specifications for Roads and Bridges, dated 2016

15. INTERIOR SLABS NOT SUBJECTED TO VEHICULAR TRAFFIC: A modulus of subgrade reaction k = 150 pci is recommended for use in design of the building slabs.

The building slab should be underlain by a 10 mil vapor retarder conforming to ASTM E 1745 Class A over a minimum 4” thick capillary water barrier consisting of ASTM C 33 #57 aggregate.

16. LATERAL EARTH PRESSURES

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a. Below Grade Non-Yielding Walls: Building walls and any other below grade walls shall be designed to resist lateral earth pressures developed from the soil behind the walls and any surcharge loads at the top of the walls. Due to the potential for perched water conditions, a drain shall be installed behind the wall;

otherwise the walls shall be designed to accommodate full hydrostatic pressures.

The below grade non-yielding walls (those walls which are restrained at the top), shall be designed for an average at rest equivalent fluid pressure of 54H psf (based upon a Ko of 0.43 and unit weight of 125 pcf).

b. Cantilever Walls: Cantilever walls shall be designed to resist lateral earth pressures developed from the soil behind the walls and any surcharge loads at the top of the walls. Cantilevered walls and other walls not fixed at the top and free to rotate shall be designed for an average equivalent active fluid pressure of 34H psf and an ultimate equivalent passive fluid pressure of 238H (based upon a Ka of 0.27, Kp of 1.9 (0.5 * 3.7), and unit weight of 125 pcf). A sliding friction factor of 0.6 shall be used. A drain shall be constructed behind the walls to eliminate the need to design for full hydrostatic pressure. This office shall be contacted if a sloped backfill is placed behind or in front of the wall such that these recommendations can be modified. Heavy equipment for spreading and compacting backfill shall not be operated closer to foundation or retaining walls than a distance equal to the height of backfill above the top of the grade beam or footing. Hand compaction equipment shall be kept 6 inches from the wall

17. FOUNDATIONS

a. Foundations of Existing Structures throughout HECSA: The design and construction records for the Kingman Building (constructed in 1972), Coastal Engineering Research Center (constructed in 1973), Topographic R&D Building (constructed in 1974), SCI Facility (constructed in 1986), and the HQ Operations & Training Facility (constructed in 2006) were investigated. Due to the highly compressible cohesive materials and loose cohesionless materials present in the upper stratums, shallow foundations were not considered feasible for these structures. Shallow foundations constructed upon these highly compressible soft cohesive materials would have subjected the structures to large intolerable total and differential settlements. In addition, deep excavations into these materials would have resulted in unstable excavation conditions. Therefore, these structures were supported upon deep foundation systems (caissons and auger cast piles) founded into the underlying hard Patapsco clays. Information pertaining to the caissons is illustrated in Table “Existing Foundations Summary”.

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Existing Foundations Summary

STRUCTURE

NUMBER OF

CAISSONS

MAXIMUM

COLUMN

LOADING

(kips)

LENGTHS

(Min/Max)

(feet)

SHAFT

DIAMETER

(Min/Max)

(inches)

BELL

DIAMETER

(Min/Max)

(inches) Kingman Building 122 375 60/96 24/30 42/109

Coastal Engineering Research Center

(CERC)

87 unknown 79/132 24/30 30/96

TOPO R&D 163 688 76/120 30/36 54/114

* SCI Facility

(Addition to ETL).

NA NA NA NA NA

HQ Operations & Training Facility

137 470 96/106 30 42/72

* The SCI Facility is supported upon 16 inch diameter auger cast piles with lengths between 60 and 70 feet. The piles were designed for maximum working load of 150 kips per pile

b. Recommended Foundation System for the Battalion Operations Facility (BOF) and Training Support Facility (TSF): The foundation recommendations are based upon a maximum column loading of 400 kips and finished floor elevation of 44.6 feet for the Battalion Operations Facility and maximum column loading of 300 kips, wall loading of 4 kips/lf and finished floor elevation of 45.5 feet for the Training Support Facility as provided by the Structural Engineer. This office shall be notified if these loadings or elevations are changed.

Due to the presence of the highly compressible cohesive soils of stratum B, it is estimated that total settlements estimated from the flat plate dilatometer (DMT) results will range between 0.41 and 9.0 inches for the Battalion Operations facility and 0.38 and 6.4 inches for the Training Support Facility solely from the footing loadings and an allowable bearing pressure of 2000 psf. A large amount of the

6.4 inches of settlement computed from the results of DMT 4 within the TSF were due to the presence of very soft clay materials between depths of 14 and 16 feet below grade. A large amount of the 9.0 inches of settlement computed from the results of DMT 15 within the BOF were due to the presence of very soft clay materials at a depth of 4 feet below grade and between 13 and 16 feet below grade. These very soft clays were also present in adjacent SPT logs with corresponding low undrained shear strength values from pocket penetrometers and low SPT blow counts illustrated as WOH (weight of Hammer) on the boring logs.

In lieu of supporting the structure on an expensive deep foundation system, the proposed foundation system shall consist of supporting the structure upon conventional shallow foundations in conjunction with soil improvement consisting of aggregate piers. All footings shall bear a minimum of 2.5 feet beneath finished grades.

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To control differential and total settlements and increase the shear strength of the foundation soils, aggregate piers shall be installed beneath the column and wall footings to support the conventional shallow foundations. The aggregate piers shall be columns of compacted aggregate constructed in a columnar-type configuration to produce an intermediate foundation system for support of foundation loads to achieve the degree of improvement. The number of aggregate piers, diameters and depth of piers shall be determined by the Aggregate Pier Designer. The subcontractor’s design shall be prepared by a registered professional Engineer and submitted for government approval as a construction shop drawing. The aggregate piers shall be installed to a sufficient depth with granular backfill material beneath all column foundations and load-bearing wall foundations to provide a minimum allowable soil bearing capacity of 3000 pounds per square foot (psf) with a maximum total settlement of 1 inch and a maximum differential settlement of 0.5 inches. Prior to installation of the aggregate piers, a modulus test, to verify the aggregate pier design shall be performed at the location of the worst soil conditions. It shall be the aggregate pier contractor's responsibility to determine and implement the systems and criteria to ensure that the specified performance is achieved.

18. SITE CLASS FOR SEISMIC CONSIDERATIONS: The site classification for seismic design is based upon the weighted average for the upper 100 foot soil profile as defined by chapter 20 of ASCE 7-10, Minimum Design Loads for Buildings and Other Structures. The site is categorized or classified using either shear wave velocity (Vs), standard penetration resistance (N) per ASTM D 1586, or the soil undrained shear strength (Su). The shear wave velocity method is the most accurate and reliable method for categorizing the site. Partial Table 20.3-1 Site Classification of the ASCE-7 is presented below.

Table 20.3-1 Site Classification from ASCE-7

Site Class Soil Profile Name

Shear Wave Velocity…