Appendix D - Report of Geotechnical Study.pdf

Report of Geotechnical Study

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Appendix D

Corporate HQ: 3015 Dumbarton Road Richmond, Virginia 23228 T 804.264.2701 F 804.264.1202 www.fandr.com

VIRGINIA • NORTH CAROLINA • SOUTH CAROLINA • MARYLAND • DISTRICT OF COLUMBIA

A Minority-Owned Business

Report of Geotechnical Study

AEDC Addition White Oak, Silver Spring, Maryland

F&R Project No. 72X0178

Prepared For:

Battle Creek Construction 200 Washington Avenue

La Plata, Maryland 20646

Prepared By:

Froehling & Robertson, Inc.

22923 Quicksilver Drive, Suite 111 Sterling, Virginia 20166

September 20, 2019

FROEHLING & ROBERTSON, INC.

Engineering Stability Since 1881

Capital Region, Dulles Operation Center 22923 Quicksilver Drive, Suite 111

Sterling, Virginia 20166 T 703.996.0123 I F 703.996.0124

Battle Creek Construction AEDC Addition

F&R Project No. 72X0178 September 20, 2019

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September 20, 2019

Mr. Matt Hunley Battle Creek Construction 200 Washington Avenue White Oak, Silver Spring, Maryland 20646

Subject: Report of Subsurface Geotechnical Study

AEDC Addition White Oak, Silver Spring, Maryland F&R Project No. 72X0178

Dear Mr. Hunley:

The purpose of this study is to present the results of the subsurface exploration program and geotechnical engineering evaluation undertaken by Froehling & Robertson, Inc. (F&R) in connection with the Arnold Engineering Development Complex (AEDC) Addition project in White Oak, Maryland.

Our services were performed in general accordance with F&R Proposal No. 1974-00191R1 dated July

11, 2019, as authorized by your office. The attached report presents our understanding of the project, reviews our exploration procedures, describes existing site and general subsurface conditions, and presents our geotechnical evaluations and recommendations.

We have enjoyed working with you on this project, and we are prepared to assist you with the recommended quality assurance monitoring and testing services during construction. Please contact us if you have any questions regarding this report or if we may be of further service.

Sincerely, Michelle E. Mittel, E.I.T. Oscar R. Merida Jr., P.E.

Geotechnical Staff Engineer Director of Geotechnical Services

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TABLE OF CONTENTS

SECTION PAGE

EXECUTIVE SUMMARY ................................................................................................................... - 0 -

1.0 PURPOSE & SCOPE OF SERVICES .......................................................................................... - 1 -

2.0 PROJECT INFORMATION ...................................................................................................... - 2 -

2.1 SITE DESCRIPTION................................................................................................................ - 2 -

2.2 PROPOSED CONSTRUCTION .................................................................................................... - 2 -

3.0 EXPLORATION PROCEDURES ............................................................................................... - 2 -

3.1 SUBSURFACE EXPLORATION ................................................................................................... - 2 -

3.1.1 Drilling Program ....................................................................................................... - 3 -

3.2 LABORATORY TESTING .......................................................................................................... - 4 -

4.0 REGIONAL GEOLOGY & SUBSURFACE CONDITIONS .............................................................. - 4 -

4.1 REGIONAL GEOLOGY ............................................................................................................ - 4 -

4.2 SUBSURFACE CONDITIONS ..................................................................................................... - 5 -

4.2.1 General.................................................................................................................... - 5 -

4.2.2 Surface Materials ..................................................................................................... - 5 -

4.2.3 Fill and Possible Fill Materials ................................................................................... - 5 -

4.2.4 Residual Soils ........................................................................................................... - 6 -

4.2.5 Partially Weathered Rock ......................................................................................... - 6 -

4.2.6 Auger Refusal Materials ........................................................................................... - 6 -

4.3 SUBSURFACE WATER ............................................................................................................ - 6 -

4.4 LABORATORY TEST RESULTS ................................................................................................... - 6 -

5.0 PRELIMINARY GEOTECHNICAL DESIGN RECOMMENDATIONS ............................................... - 7 -

5.1 GENERAL ........................................................................................................................... - 7 -

5.2 SHALLOW FOUNDATIONS ...................................................................................................... - 8 -

5.2.1 Settlement for Shallow Foundations ......................................................................... - 9 -

5.3 SEISMIC CONSIDERATIONS ..................................................................................................... - 9 -

6.0 GEOTECHNICAL CONSTRUCTION RECOMMENDATIONS ........................................................ - 9 -

6.1 SITE PREPARATION .............................................................................................................. - 9 -

6.2 STRUCTURAL FILL PLACEMENT AND COMPACTION ..................................................................... - 10 -

6.3 FOUNDATION CONSTRUCTION .............................................................................................. - 11 -

6.4 SURFACE WATER/GROUNDWATER CONTROL ........................................................................... - 12 -

6.5 TEMPORARY EXCAVATION RECOMMENDATIONS ....................................................................... - 12 -

7.0 CONTINUATION OF SERVICES ............................................................................................ - 12 -

8.0 LIMITATIONS .................................................................................................................... - 13 -

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APPENDICES

APPENDIX I

Site Location Plan, Drawing No. 1 Boring Location Plan, Drawing No. 2 Undercut Footing Diagram, Drawing No. 3

APPENDIX II

Classification of Soils for Engineering Purposes Key to Soil Classification Soil Classification Chart Boring Logs (B-1 through B-4)

APPENDIX III

Laboratory Testing

APPENDIX IV

GBA Document “Important Information about Your Geotechnical Engineering Report”

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EXECUTIVE SUMMARY

This Executive Summary is provided as a brief overview of our geotechnical engineering evaluation for the project and is not intended to replace more detailed information contained elsewhere in this report. As an overview, this summary inherently omits details that could be very important to the proper application of the provided geotechnical design recommendations. This report should be read in its entirety prior to implementation into design and construction.

This project consists of the geotechnical evaluation of a site for a new concrete slab and nozzle tracks structure on the south face of Building 430 at the Arnold Engineering Development Complex (AEDC) at White Oak in Silver Spring, Maryland.

The project site is located on AEDC property, the main office of which is located at Bushnell Road, White Oak, MD 20904. The site consists of asphalt and concrete pavement located south of an existing building structure. Site elevations range from approximately EL 277.4 feet to EL 275.5 feet, dipping downward in the south-eastern direction away from the building.

The proposed site development consists of the construction of a new concrete pad with nozzle tracks for moving 30,000 lb equipment in and out of the existing building.

A subsurface exploration consisting of four (4) test borings drilled to depths ranging from 25 to 35 feet was conducted on site to evaluate the subsurface characteristics of the soils.

The subsurface soil profile encountered on site consisted of asphalt and concrete pavement overlying fill materials, possible fill materials, residual soils, partially weathered rock, and auger refusal materials.

Based on the test borings and analysis, we recommend that a shallow foundation system be used for support of the proposed concrete pad and track structure.

Shallow foundations may be designed for a net allowable bearing pressure of 2,000 psf bearing on properly evaluated existing fill, virgin residual soils and/or newly placed structural fill. All foundation subgrades should be evaluated by the geotechnical engineer at the time of construction.

Based on the boring data and in general accordance with ASCE 7-10 for the proposed buildings, a Seismic Site Class “C” should be used to develop the project’s Seismic Design Category for further evaluations relative to Earthquake Load design for the buildings.

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1.0 PURPOSE & SCOPE OF SERVICES

The purpose of the subsurface exploration and geotechnical engineering evaluation was to explore the subsurface conditions in the area of the proposed concrete pad and nozzle track structure and provide geotechnical engineering design and construction recommendations for the proposed structure. These recommendations can be used during the design and construction of the proposed structure.

F&R’s scope of services included the following:

Reviewed and summarized available geologic and subsurface information relative to the project site;

Obtained base access for the Project Engineer and Drill Crews;

Visited the site to observe existing surface conditions and features;

Performed the boring layout and coordinated with Miss Utility;

Executed a subsurface exploration program consisting of:

o Four (4) Standard Penetration Test (SPT) borings drilled to depths ranging from 25 to 35 feet below the existing ground surface;

Prepared typed boring logs;

Performed geotechnical laboratory testing on representative soil samples;

Performed a geotechnical engineering evaluation of the subsurface conditions with regard to their suitability for the proposed structure;

Completed this geotechnical report, prepared by professional engineers.

Our scope of services did not include allowances for meetings, review of plans and specifications, survey of boring locations, permitting, drilling with UXO restrictions, traffic control, environmental recommendations, slope stability analysis, identification and evaluation of wetland or other environmental aspects of the project site, health and safety considerations for non-F&R personnel, or landscape repair.

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2.0 PROJECT INFORMATION

2.1 Site Description

The proposed site is located at the Arnold Engineering Development Complex (AEDC) at White

Oak in Silver Spring, Maryland, as shown on the Site Location Plan (Drawing No. 1) included in

Appendix I of this report.

The site is located on a concrete slab and parking lot south of the existing AEDC Building 430 located on Bushnell Road. The topography of the area is relatively flat with a slight downward slope from northwest to southeast. The site is covered with asphalt and concrete pavement. The area of the proposed structure will range in elevation from approximately EL 277.4 feet to EL

275.5 feet.

An existing 48” diameter vacuum pipe is located on site approximately 50 feet south of Building

430 to the pipe centerline. The pipe is parallel with the south facing wall of the building and dips slightly downward in the northeastern direction. In the vicinity of borings B-2 and B-3, the vacuum pipe is located at an approximate depth of 7.0 feet below the ground surface and at an approximate elevation of EL 269.8 feet. Pipe location, depths, and elevations are estimated based on the Hypervelocity Wind Tunnel – BLDG. 430 Civil Grading & Drainage Plan, Sheet Nos. C-2A and C-4.

2.2 Proposed Construction

Our understanding of the project is based on information provided by your office as well as the

AEDC Addition Storage Build-Out Scope of Work, dated April 30, 2019, and the Arnold

Engineering Development Complex Nozzle Tracks White Oak – AEDC Building 430 Proposed Site

Plan, dated June 10, 2019. We understand that a new concrete pad and nozzle tracks for the transportation of equipment in and out of the AEDC building facility is planned at the site.

Based on the structural loading information provided to F&R at the time of this report, we have assumed structural loading to be on the order of 30 kips for the nozzle equipment that is planned to be transported over the concrete slab in the vicinity of borings B-1 through B-4. Significant site grading changes are not expected as part of this project. If this loading is not representative of the proposed construction, we should be notified to reevaluate recommendations contained herein.

3.0 EXPLORATION PROCEDURES

3.1 Subsurface Exploration

A subsurface exploration program consisting of four (4) Standard Penetration Test borings

(designated B-1 through B-4) was conducted on site. Testing was completed on August 30, 2019, Page - 3 -and September 3, 2019, at the approximate locations shown on the attached Boring Location

Plans (Drawing No. 2, Appendix I). Prior to drilling, F&R personnel marked the boring locations in the field. Ground surface elevations at the boring locations were interpolated to the nearest foot from the provided Arnold Engineering Development Complex Nozzle Tracks White Oak-AEDC

Building 430 Proposed Site Plan, drawn by Battle Creek Construction, LLC, dated June 10, 2019.

Site elevations range from approximately EL 277.4 feet to EL 275.5 feet, dipping downward in the south-eastern direction away from the building. In consideration of the methods used in their determination, the boring locations shown on the attached Boring Location Plan should be considered approximate.

3.1.1 Drilling Program

The test borings were performed in accordance with generally accepted drilling practices using a truck-mounted CME-75 rotary drill rig. The test borings were advanced with augers to pre-selected depths, the center plug was removed, and representative soil samples were recovered with a standard split-spoon sampler (1.375 in. ID & 2 in. OD) in general accordance with ASTM D

1586, the Standard Penetration Test. The split-spoon sampler was driven into the soil by freely dropping a weight of 140 pounds from a height of 30 inches. The number of blows required to drive the split-spoon sampler three consecutive 6-inch increments is recorded, and the blows of the second and third increments are summed to obtain the Standard Penetration Resistance (N-value). For this project, the sampler was driven an additional 6 inches to provide a continuous profile of the subsurface soils. The N-value provides a general indication of in-situ soil conditions and has been correlated with certain engineering properties of soils. Standard Penetration

Testing was conducted using an automatic hammer.

Research has shown that the Standard Penetration Resistance (N-value) determined by the automatic hammer method is different than the N-value determined by the safety hammer method. Most corrections that are published in technical literature are based on the N-value determined by the safety hammer method. This is commonly termed N60, as the rope and cathead with a safety hammer delivers about 60 percent of the theoretical energy delivered by a 140-pound hammer falling 30 inches. Several researchers have proposed correction factors for the use of hammers other than the safety hammer. The correction is shown in the following equation:

N60 = Nfield x CE where Nfield is the value recorded in the field and CE is the drill rod energy ratio for the hammer used. For the automatic hammer utilized during the drilling of this site, a correction factor (CE) of 1.63 was used to convert Nfield values to N60 values – this correction factor is based on previous energy measurements made for the automatic hammer system used during the field exploration

Page - 4 -of this project. The N-values reported on the boring logs included in this report are the actual, uncorrected, field derived values (Nfield). Corrected N60 values were used for all analyses.

Subsurface water level readings were taken in all of the borings during drilling and immediately upon completion of the drilling process. Upon completion of drilling, the boreholes were backfilled with soil cuttings and capped with asphalt or cement patch. Periodic observation of the boreholes should be performed to monitor subsidence at the ground surface, as the borehole backfill could settle over time.

Split-spoon samples were collected within the boring locations in general accordance with ASTM

D 1586-11. A bulk soil sample was obtained at test boring B-3 from 2 feet to 6 feet in depth. The boreholes were backfilled with soil cuttings upon completion of drilling.

Split-spoon soil samples recovered on this project will be stored at F&R’s office for a period of sixty days. After sixty days, the samples will be discarded unless prior notification is provided to us in writing.

3.2 Laboratory Testing

Representative portions of the split-spoon soil samples and the bulk sample obtained throughout the exploration program were placed in glass jars and plastic bags, respectively, and transported to our laboratory. In the laboratory, the soil samples were evaluated by a member of our professional staff in general accordance with techniques outlined in the visual-manual identification procedure (ASTM D 2488) and the Unified Soil Classification System. The soil descriptions and classifications discussed in this report and shown on the attached boring logs are based on visual observation and should be considered approximate. Copies of the boring logs are provided and classification procedures are further explained in the attached Appendix II.

Laboratory tests were performed on the bulk sample and selected split-spoon samples in general accordance with the American Society for Testing and Materials (ASTM) standards. The tests performed were Natural Moisture Content (ASTM D 2216), Atterberg Limits (ASTM D 4318), Mechanical Sieve Analysis with Wash #200 (ASTM D 6913), and Modified Proctor Test (ASTM D

1557). The laboratory testing results are discussed in Section 4.4 of this report and are provided in Appendix III.

4.0 REGIONAL GEOLOGY & SUBSURFACE CONDITIONS

4.1 Regional Geology

The available geologic references, including the 1968 and 1995 Geologic Maps of Maryland, indicate that the site is located on the Wissahickon Formation, formerly mapped as the Sykesville and Laurel Formations.

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The Wissahickon Formation is Late Precambrian in age and consists of boulder gneiss rock. The formation is comprised of thick-bedded to massive, pebble- and boulder-bearing, arenaceous to politic metamorphic rock, typically a medium-grained, garnet-oligoclase-mica-quartz gneiss with an apparent thickness of approximately 15,000 feet.

4.2 Subsurface Conditions

4.2.1 General

The subsurface conditions discussed in the following paragraphs and those shown in the attached boring logs represent an estimate of the subsurface conditions based on interpretation of the boring data using normally accepted geotechnical engineering judgments. The transitions between different soil strata are usually less distinct than those shown on the boring logs.

Although individual soil test borings are representative of the subsurface conditions at the boring locations on the dates shown, they are not necessarily indicative of subsurface conditions at other locations or at other times. Data from the specific soil test borings are shown on the attached boring logs in Appendix II.

The general subsurface profiles encountered consists of asphalt and concrete pavement layers overlying fill materials, possible fill materials, residual soils, partially weathered rock, and auger refusal materials, as shown on the boring logs. These materials are generally discussed in the following paragraphs.

4.2.2 Surface Materials

Test boring B-1 was completed on a concrete pad next to the existing building, and test borings

B-2 through B-4 were completed in an asphalt parking lot south of the existing building.

Approximately 7 inches of concrete was encountered at the ground surface within test boring B-

1, and approximately 6 to 10 inches of asphalt pavement layers was encountered at the ground surface within test borings B-2 through B-4.

4.2.3 Fill and Possible Fill Materials

Fill and possible fill materials were encountered within the test borings underlying the concrete and asphalt pavement layers, extending to approximate depths ranging from 3 feet to 6 feet. Fill and possible fill materials encountered in this exploration mainly consisted of clayey SAND (SC) with gravel and silty SAND (SM). Standard Penetration Test (SPT) N-values ranging from 9 to 23 blows per foot (bpf) were recorded for the soils in this stratum, indicating a loose to medium dense state for granular soils.

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4.2.4 Residual Soils

Residual soils, formed by the in-place weathering of the parent rock, were encountered below the pavement layers and existing fill soils in the test borings below existing site grades at depths ranging from 3 feet to 21 feet. Residual soils encountered in this exploration mainly consisted of clayey SAND (SC) and silty SAND (SM). SPT N-values ranging from 9 to 55 blows per foot (bpf) were recorded for the soils in this stratum, indicating a loose to very dense state for the granular soils. An average SPT N-value of 20 bpf was recorded for the soils in this stratum.

4.2.5 Partially Weathered Rock

Partially Weathered Rock (PWR) is a transitional material between soil and rock which contains the relict rock structure, with very hard consistencies or very dense relative densities. PWR material is defined herein as residual soils exhibiting an SPT N-value in excess of 50 bpf. PWR materials were encountered in the four test borings to depths ranging from 12 feet to 30.2 feet below existing site grades. When sampled, the PWR was described as silty SAND (SM) with gravel.

4.2.6 Auger Refusal Materials

Auger refusal occurs when materials are encountered that cannot be penetrated by the soil auger and is normally indicative of a very hard or very dense material, such as boulders, rock lenses, rock pinnacles, or the upper surface of competent bedrock. Auger refusal was encountered in test borings B-2 and B-4 at depths of 30.2 feet and 25 feet, respectively. Auger refusal conditions with a

CME-75 drill rig do not necessarily indicate conditions impenetrable to other equipment. Auger refusal conditions will likely vary in unexplored areas of the site.

4.3 Subsurface Water

Subsurface water was not encountered in the four test borings during drilling or upon completion of drilling. Cave-in depths ranging from 21.4 feet to 26 feet were recorded within the borings.

Fluctuations in subsurface water levels and soil moisture can be anticipated with changes in precipitation, surface runoff, evaporation, seasonal effects, and other similar factors. Normally, the highest subsurface water levels occur in the late winter and spring and the lowest levels occur in the late summer and fall.

4.4 Laboratory Test Results

The results of the laboratory tests are summarized in Table 1 below, and are presented in

Appendix III of this report.

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Table 1: Soil Classification Test Summary

Boring No.

Sample Depth

(ft)

Water Content

Retained on No. 4

Sieve

Finer than

No. 200 Sieve

Atterberg Limits

USCS

Classification

Max.

Dry

Density (pcf) 1

Optimum Water

Content (%)1 L.L. P.L. P.I.

B-1 3.0 16.1 73.1 26.9 27 24 3 SM - -

B-2 6.0 13.8 76.5 23.5 35 21 14 SC - -

B-2 12.0 7.9 84.3 15.7 23 21 2 SM - -

B-3 2.0 11.2 70.9 29.1 31 17 14 SC 135.7 7.3

B-3 15.0 6.1 86.3 13.7 26 25 1 SM - -

B-4 9.0 10.2 83.6 16.4 30 28 2 SM - -

1Maximum Dry Density and Optimum Moisture Content determined by ASTM D 1557

5.0 PRELIMINARY GEOTECHNICAL DESIGN RECOMMENDATIONS

5.1 General

The following evaluations and recommendations are based on our observations at the site, interpretation of the field data obtained during this exploration, and our experience with similar subsurface conditions and projects. Soil penetration data has been used to estimate an allowable bearing pressure and associated settlements using established correlations. Subsurface conditions in unexplored locations may vary from those encountered. If the structure location, loadings, or elevations are changed, we should be notified and requested to confirm and, if necessary, re-evaluate our recommendations.

Determination of an appropriate foundation system for a given structure is dependent on the proposed structural loads, soil conditions, and construction constraints such as proximity to other structures, etc. The subsurface exploration aids the geotechnical engineer in determining the soil stratum appropriate for structural support. This determination includes considerations with regard to both allowable bearing capacity and compressibility of the soil strata. In addition, since the method of construction greatly affects the soils intended for structural support, consideration must be given to the implementation of suitable methods of site preparation, fill compaction, and other aspects of construction.

The following geotechnical recommendations are provided for cost and project feasibility;

determination of the final design and geotechnical analysis should be completed by the winning design build contractor and design team.

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5.2 Shallow Foundations

The proposed concrete pad and nozzle track structure may be supported on shallow foundations

(i.e., spread footings or turn down mats) bearing on approved, properly-placed, and compacted structural fill, evaluated existing fill material, or residual soils (see Section 6.2, Structural Fill

Placement and Compaction).

Based on the assumed structural loads provided in the Proposed Construction section of this report and the subsurface conditions encountered in our test borings, we recommend that foundations be designed for a maximum net allowable bearing pressure of 2,000 pounds per square foot (psf) for footings bearing on approved subgrades consisting of virgin residual soil or newly placed structural fill. The existing fill materials may be suitable for support of shallow foundations, in accordance with the recommendations discussed in the Site Preparation and

Structural Fill Placement and Compaction sections of this report. An elevated bearing pressure of

3,000 psf may be used if the existing fill soils are removed from the foundation footprint.

To reduce the possibility of localized shear failures, spread and strip footings should be a minimum of 3 feet and 1.5 feet wide, respectively. We recommend that exterior footings be constructed at least 2.5 feet below adjacent grades in order to bear below normal frost depth.

The Hypervelocity Wind Tunnel – BLDG. 430 Civil Plot & Utilities Plan provided by your office shows that approximately 7 feet of fill soil is located above the 48” diameter vacuum pipe in the vicinity of test borings B-2 and B-3. As shown in the attached boring logs, approximately 6 feet of fill was encountered in test borings B-2 and B-3 during our exploration. Based on discussions with your office, it is assumed that the fill soil in this area should remain on site during construction of the concrete pad and nozzle track structure to minimize disturbance to the pipe. Details on the location, depth, and elevation of the vacuum pipe are provided in the Project Information section of this report.

A mat foundation may be used in the vicinity of the existing vacuum pipe to minimize disturbance to the pipe. We recommend that mat foundations have a minimum thickness of 4.0 inches, but may have to be greater in thickness. A granular drainage blanket consisting of 4.0 inches of crushed or washed gravel should be placed beneath the mat foundation for lateral drainage and to act as a capillary barrier. We estimate that a design modulus of subgrade reaction (k) = 72 pci is appropriate for the concrete slab design calculations.

It is recommended that during construction of the proposed structures, an experienced geotechnical engineer or his/her representative should be on site to confirm that the in-situ bearing conditions at the bottom of each footing excavation and mat foundation is adequate for the design bearing pressure recommended in this report.

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5.2.1 Settlement for Shallow Foundations

Based on the boring data, assumed loading information, and provided grading information, we estimate that foundation settlements for the structures will be less than one half of an inch with differential settlement of up to one-half the estimated total settlement. The magnitude of differential settlements will be influenced by the variation in fill placement and compaction across the structures’ footprints, the distribution of loads, and the variability of underlying soils and rock.

Our settlement analysis was performed on the basis of assumed structural loading discussed in the project information section of this report. Actual settlements experienced by the structure and the time required for these soils to settle will be influenced by undetected variations in subsurface conditions, final grading plans, and the quality of fill placement and foundation construction.

5.3 Seismic Considerations

The following Seismic Site Class Definition was established in general accordance with Table 20.3-1 of the ASCE 7-10 as set forth in the International Building Code (IBC) 2015. Our scope of services did not include a seismic conditions survey to determine site-specific shear wave velocity information;

however, Chapter 20 of ASCE 7-10 provides a methodology for interpretation of Standard

Penetration Test resistance values (N-values) to determine a Site Class Definition. Based on the SPT soil testing, we recommend that a Seismic Site Class “C” be used in accordance with ASCE 7-10 for the proposed substation.

6.0 GEOTECHNICAL CONSTRUCTION RECOMMENDATIONS

6.1 Site Preparation

Before proceeding with construction, utilities, concrete and crushed stone, surficial soils and any other deleterious non-soil materials should be stripped or removed from the proposed construction area. During the stripping operations, positive surface drainage should be maintained to prevent the accumulation of water. Existing underground utilities should be re-routed to locations at a minimum of 10 feet outside of any proposed structure footings, or they should be abandoned in place with flowable fill.

After stripping, areas intended to support foundations and new fill should be carefully evaluated by a geotechnical engineer. At that time, the subgrade should be proofrolled with a 20- to 30-ton loaded truck, or other pneumatic-tired vehicle of similar size and weight, under the observation of the geotechnical engineer. Proofrolling should be performed during a time of good weather and not while the site is wet, frozen, or severely desiccated. The purpose of the proofrolling is to locate soft, weak, or excessively wet soils present at the time of construction. Any unsuitable materials observed

Page - 10 -during the evaluation and proofrolling operations should be undercut and replaced with compacted fill and/or stabilized in-place.

The proofrolling observation is an opportunity for the geotechnical engineer to locate inconsistencies in the existing subgrade, especially near existing utilities, where fill may exist, and where new fill placement and foundations are proposed. Any unsuitable materials observed during the evaluation and proofrolling operations should be undercut and replaced with compacted structural fill or stabilized in-place. The possible need for, and extent of, undercutting and/or in-place stabilization required can best be determined by the geotechnical engineer at the time of construction. Once the site has been property prepared, at-grade construction may proceed.

In a dry and undisturbed state, the subgrade soils at the site will provide suitable subgrade support for fill placement and construction operations. However, when wet, the soil can degrade quickly either with or without disturbance from contractor operations. Therefore, good site drainage should be maintained during earthwork operations to help maintain the stability of the soil. Attempting site work during adverse seasonal conditions will have significant effects on the site work budget and schedule, as substantially more undercutting will be required.

6.2 Structural Fill Placement and Compaction

Based on the boring data, controlled fill may be constructed using an off-site borrow source having a classification of GM, GP, SW, SP, SM, and SC as defined by the Unified Soil Classification

System. Fill materials and non-plastic fill soils should have a maximum liquid limit of 40 and plasticity index less than 15. Other materials may be suitable for use as controlled structural fill material and should be individually evaluated by the geotechnical engineer. Controlled fill should be free of boulders, organic matter, debris, or other deleterious materials and should have a maximum particle size no greater than 3.0 inches. In addition, we recommend a minimum

Modified Proctor (ASTM D 1557) maximum dry density of approximately 120 pounds per cubic feet for fill materials. A mixture of on-site soils and boulders/cobbles is not an acceptable fill material.

Up to 6 feet of fill was encountered in the borings within the footprint of the proposed concrete and nozzle track structure. Existing fill materials may be suitable for proposed foundations.

However, the geotechnical engineer on record or his or her representative on site should evaluate the suitability of the fill soil at the time of construction. If weak fill materials are encountered during foundation construction, they should be undercut and replaced with structural fill. An allowance for undercut and replacement should be carried in the construction cost. As an alternative, the foundations’ depths can be extended to suitable virgin soils.

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After acceptance of the soil subgrade, fill materials should be placed in horizontal lifts with a maximum height of 8 inches loose measure. New fill should be adequately keyed into stripped and scarified subgrade soils and should, where applicable, be benched into the existing slopes.

For further details on backfill of undercuts beneath proposed footings, see the attached Undercut

Footing Diagram, Drawing No. 3, located in Appendix I of this report. During fill operations, positive surface drainage should be maintained to prevent the accumulation of water. We recommend that structural fill be compacted to at least 95 percent of the Modified Proctor maximum dry density.

In general, we recommend that the moisture content of fill soils be maintained within two percentage points of the optimum moisture content as determined from the Modified Proctor density test. Excessively wet or excessively dry soils should not be used as fill material without proper drying or wetting. We recommend that the contractor have equipment on site during earthwork for both drying and wetting of fill soils. Each lift of fill should be tested in order to confirm that the recommended degree of compaction is attained.

Where construction traffic or weather has disturbed the subgrade, the upper 8.0 inches of soils intended for structural support should be scarified and re-compacted. Each lift of fill should be tested in order to confirm that the recommended degree of compaction is attained. Field density tests to verify fill compaction should be performed for every 2,500 square feet (approximately every 50x50 foot square) of fill area, with a minimum of two tests per lift. In confined areas, a greater frequency may be required.

6.3 Foundation Construction

All foundation subgrades should be observed, evaluated, and verified for the design bearing pressure by the geotechnical engineer after excavation and prior to reinforcement steel placement. If low-consistency soils are encountered during foundation construction, localized undercutting and/or in-place stabilization of foundation subgrades will be required. The actual need for and extent of undercutting should be based on field observations made by the geotechnical engineer at the time of construction.

Excavations for footings should be made in such a way as to provide bearing surfaces that are firm and free of loose, soft, wet, or otherwise disturbed soils. Foundation concrete should not be placed on frozen or saturated subgrades. If such materials are allowed to remain below foundations, settlements will increase. Foundation excavations should be concreted as soon as practical after they are excavated. If an excavation is left open for an extended period, a thin mat of lean concrete should be placed over the bottom to minimize damage to the bearing surface from weather or construction activities. Water should not be allowed to pond in any excavation.

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6.4 Surface Water/Groundwater Control

Subsurface water for the purposes of this report is defined as water encountered below the existing ground surface. Subsurface water was not encountered during drilling or upon completion of drilling. Based on the groundwater conditions observed during this study, we do not anticipate that groundwater will be encountered during construction. However, perched water may be encountered at localized areas during deep excavations or following prolonged period of heavy precipitation. If perched water is encountered, conventional dewatering measures such as diversion ditches, interceptor drains, and sump pits and pumps will be adequate. Fluctuations in subsurface water levels and soil moisture can be anticipated with changes in precipitation, runoff, and season.

6.5 Temporary Excavation Recommendations

Mass excavations and other excavations required for construction of this project must be performed in accordance with the United States Department of Labor, Occupational Safety and

Health Administration (OSHA) guidelines (29 CFR 1926, Subpart P, Excavations) or other applicable jurisdictional codes for permissible temporary side-slope ratios and/or shoring requirements. The OSHA guidelines require daily inspections of excavations, adjacent areas and protective systems by a “competent person” for evidence of situations that could result in cave-ins, indications of failure of a protective system, or other hazardous conditions. All excavated soils, equipment, building supplies, etc., should be placed away from the edges of the excavation at a distance equaling or exceeding the depth of the excavation. F&R cautions that the actual excavation slopes will need to be evaluated frequently each day by the “competent person” and flatter slopes or the use of shoring may be required to maintain a safe excavation depending upon excavation specific circumstances. The contractor is responsible for providing the

“competent person” and all aspects of site excavation safety. F&R can evaluate specific excavation slope situations if we are informed and requested by the owner, designer or contractor’s “competent person”.

7.0 CONTINUATION OF SERVICES

We recommend that we be given the opportunity to review the foundation plan, grading plan, and project specifications when construction documents approach completion. This review evaluates whether the recommendations and comments provided herein have been understood and properly implemented. We also recommend that Froehling & Robertson, Inc. be retained for professional and construction materials testing services during construction of the project. Our continued involvement on the project helps provide continuity for proper implementation of the recommendations discussed herein.

The Geotechnical Engineer of Record should be retained to monitor and test earthwork activities, Page - 13 -and subgrade preparations for foundations, excavations, and floor slabs. It should be noted that the actual soil conditions at the various subgrade levels and footing bearing grades will vary across this site and thus the presence of the Geotechnical Engineer and/or his or her representative during construction will serve to validate the subsurface conditions and recommendations presented in this report. We recommend that F&R be employed to monitor the earthwork, foundation, and pavement construction, and to report that the recommendations contained in this report are completed in a satisfactory manner. Our involvement on the project will aid in the proper implementation of the recommendations discussed herein. The following is a recommended scope of services:

Review of project plans and construction specifications to verify that the recommendations presented in this report have been properly interpreted and implemented;

Observe and perform testing during earthwork to document that subsurface conditions encountered during construction are consistent with those anticipated in this report;

Observe subgrade preparation including any proofrolling operations, undercutting of soft/loose unsuitable soils, installation of drainage materials, geotextiles and fill placement;

Observe all foundation excavations and footing bearing grades for compliance with the geotechnical recommendations.

8.0 LIMITATIONS

This report has been prepared for the exclusive use of Battle Creek Construction or their agent, for specific application to the Arnold Engineering Development Complex (AEDC) Addition project, in accordance with generally accepted soil and foundation engineering practices. No other warranty, express or implied, is made. Our evaluations and recommendations are based on design information furnished to us; the data obtained from the previously described subsurface exploration program, and generally accepted geotechnical engineering practice. The evaluations and recommendations do not reflect variations in subsurface conditions which could exist intermediate of the boring locations or in unexplored areas of the site. Should such variations become apparent during construction, it will be necessary to re-evaluate our recommendations based upon on-site observations of the conditions.

There are important limitations to this and all geotechnical studies. Some of these limitations are discussed in the information prepared by GBA, which is included in Appendix IV. We ask that you please review this GBA information.

Regardless of the thoroughness of a subsurface exploration, there is the possibility that conditions between borings will differ from those at the boring locations, that conditions are not as anticipated by the designers, or that the construction process has altered the soil conditions. Therefore, experienced geotechnical engineers should evaluate earthwork, pavement, and foundation construction to verify that the conditions anticipated in design actually exist. Otherwise, we assume

Page - 14 -no responsibility for construction compliance with the design concepts, specifications, or recommendations.

In the event that changes are made in the design or location of the proposed structures, the recommendations presented in the report shall not be considered valid unless the changes are reviewed by our firm and conclusions of this report modified and/or verified in writing. If this report is copied or transmitted to a third party, it must be copied or transmitted in its entirety, including text, attachments, and enclosures. Interpretations based on only a part of this report may not be valid.

APPENDIX I

DATE: September 2019

SOURCE: Google Maps

DRAWN: MEM F&R # 72X0178

Site Location Plan Battle Creek Construction

AEDC Addition White Oak, Silver Spring, Maryland

Drawing No.

Approximate Site Location

SCALE: NTS

DATE: September 2019

SOURCE: See Note Above

DRAWN: MEM F&R # 72X0178

Boring Location Plan Battle Creek Construction

White Oak, Silver Spring, Maryland

Drawing No.

SCALE: NTS

Drawing adapted from the Hypervelocity Wind Tunnel – BLDG. 430 Civil Grading & Drainage Plan, Sheet No. C-2A, dated 12/16/1969, prepared by The Marquardt Corporation for the Naval Facilities Engineering Command Chesapeake Division.

Legend Approximate Boring Location

Engineering Stability Since 1881

22923 Quicksilver Dive, Suite 111 Dulles, Virginia 20166

T 703.996.0123 I F 703.996.0124

Undercut Footing Diagram

Client: Battle Creek Construction

Project: AEDC Addition

F&R Project No.: 72X0178

Date: September 2019 Scale: none Drawing No.: 3

Vertical Vertical

Approximate Limits of Undercut Excavation

Approximate Limits of Undercut Excavation

Zone of Excavated Material and Backfill

Zone of Excavated Material and Backfill

Undisturbed Natural Soil or Dense/Stiff Stable Material

Undisturbed Natural Soil or Dense/Stiff Stable Material

A. No Backfill; Footing Bearing on Newly Exposed Stable Material

B. Excavation Backfilled with Lean Concrete or Flowable Fill

C. Excavation Backfilled with Granular Material

D. Excavation Backfilled with Engineered Soil Fill

Footing

Footing

Footing Footing

APPENDIX II

CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

ASTM Designation: D 2487

(Based on Unified Soil Classification System)

Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A Soil Classification

Group Symbol Group Name B

COARSE-GRAINED

SOILS

More than 50% retained on No. 200 sieve

Gravels

More than 50% coarse fraction retaining on No. 4 sieve

Clean Gravels

Less than 5% fines c

Cu ≥ 4 and 1 ≤ Cc ≤ 3 E GW Well graded gravel

F

Cu < 4 and/or 1> Cc >3

GP Poorly graded gravel

F

Gravels with Fines

More than 12 % fines c

Fines classify as ML or MH GM Silty gravel F,G,H

Fines classify as CL or CH

GC

Clayey gravel F,G,H

Sands

50% or more of coarse fraction passes No. 4 sieve

Clean Sands

Less than 5% fines D

Cu ≥ 6 and 1 ≤ Cc ≤3

SW Well-graded sand

I

Cu < 6 and/or 1 > Cc > 3

SP Poorly graded sand

I

Sands with Fines

More than 12% fines D

Fines classify as ML or MH SM Silty sand G,H,I

Fines classify as CL or CH SC Clayey sand G,H,I

FINE-GRAINED SOILS

50% or more passes the No. 200 sieve

Silts and Clays

Liquid Limit less than

Inorganic PI > 7 and plots on or above

“A” line J

CL

Lean clay

K,L,M

PI < 4 or plots below “A” line J ML Silt

Organic Liquid limit - ovendried <0.75

Liquid limit - not dried

OL

Organic clay K,L,M,N

Organic silt K,L,M,O

Silts and Clays

Liquid Limit 50 or more

Inorganic PI plots on or above “A” line CH Fat clay

PI plots below “A” line MH Elastic silt

Organic Liquid limit - ovendried <0.75

Liquid limit - not dried

OH

Organic clay K,L,M,P

Organic silt K,L,M,Q

HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor PT Peat

A Based on the material passing the 3-in (75 mm) sieve

B If field sample contained cobbles or boulders, or both, add

“with cobbles or boulders, or both” to group name.

C Gravels with 5 to 12% fines require dual symbols:

GW-GM well-graded gravel with silt

GW-GC well-graded gravel with clay

GP-GM poorly graded gravel with silt

GP-GC poorly graded gravel with clay

D Sands with 5 to 12% fines require dual symbols:

SW-SM well-graded sand with silt

SW-SC well-graded sand with clay

SP-SM poorly graded sand with silt

SP-SC poorly graded sand with clay

E Cu=D60/D10 Cc = (D30)

/(D10*D60)

F If soil contains ≥ 15% sand, add “with sand” to the group name

G If fines classify as CL-ML, use dual symbol GC-GM, or

SC-SM

H If fines are organic, add “with organic fines” to the group name

I If soil contains ≥ 15% gravel, add “with gravel” to group name

J If Atterberg limits plot in hatched area, soils is a CL-ML, silty clay

K If soil contains 15 to 29% plus No. 200, add “with sand” or

“with gravel,” whichever is predominant

L If soil contains ≥ 30% plus No. 200, predominantly sand, add “sandy” to group name

M If soil contains ≥ 30% plus No. 200, predominantly gravel, add “gravelly” to group name

N PI ≥ 4 and plots on or above “A” line

O PI < 4 or plots below “A” line

P PI plots on or above “A” line

Q PI plots below “A” line

SIEVE ANALYSIS

Screen (in) Sieve No.

1.5 ¾ 4 10 20 40 60 100 200

D60 = 3 mm

D30 = 0.6 mm

D10 = 0.2 mm

Cu = D60/D10 = (3/0.2) = 15

Cc = (D30) /(D10*D60) = (0.6

)/(0.2*3) = 0.6

“U” Line “A” Line

CL or OL

CH or OH

ML or OL

MH or OH

CL-ML

For classification of fine-grained soils and fine-grained fraction of coarse-grained soils:

0 10 20 30 40 50 60 70 80 90 100 110

Liquid Limit (LL)

Plasticity Index (PI)

Equation of “A” line: Horizontal at PI = 4 to LL = 22.5, then PI = 0.73*(LL-20)

Equation of “U” line: Vertical at LL = 16 to PI = 7, then PI = 0.9*(LL-8)

KEY TO SOIL CLASSIFICATION

Correlation of Penetration Resistance with

Relative Density and Consistency

Sands and Gravels Silts and Clays

No. of Relative No. of

Blows, N Density Blows, N Consistency

0 - 4 Very loose 0 - 2 Very soft

5 - 10 Loose 3 - 4 Soft

11 - 30 Medium dense 5 - 8 Firm

31 - 50 Dense 9 - 15 Stiff

Over 50 Very dense 16 - 30 Very stiff

31 - 50 Hard

Over 50 Very hard

Particle Size Identification

(Unified Classification System)

Boulders: Diameter exceeds 12-in. (300-mm)

Cobbles: 3-in. (75-mm) to 12-in. (300-mm) diameter

Gravel: Coarse - ¾-in. (19-mm) to 3 in. (75-mm) diameter

Fine - No. 4 (4.75-mm) sieve to ¾-in. (19-mm) diameter

Sand: Coarse – No. 10 (2.0-mm) to No. 4 (4.76 mm) sieve

Medium – No. 40 (0.425-mm) to No. 10 (2.0-mm) sieve

Fine - No. 200 (0.075-mm) to No. 40 (0.425-mm) sieve

Silt and Clay: Less than No. 200 (0.075-mm) sieve

Modifiers

The modifiers provide our estimate of the amount of silt, clay or sand size particles in the soil sample.

Approximate

Content

Modifiers

Field Moisture

Description

≤ 5%: Trace Dry Absence of moisture, dusty, dry to touch

5 to 10%: Few Moist Damp but no visible water

15 to 25%: Little Wet Visible free water, usually soil is below water table

30 to 45%: Some

50 to 100% Mostly

LETTERGRAPH

SYMBOLS

MAJOR DIVISIONS

SOIL CLASSIFICATION CHART

OH

CH

MH

OL

CL

ML

SC

SM

SP

COARS…