512A5-18-302 Final Geotechnical Report.pdf

J & B Hartigan Inc.

Carrollton, Virginia

Geotechnical Subsurface Investigation

Central Emergency Power Distribution Project

VA Medical Center

Perry Point, Maryland

April 2019 i-i associates Environmental, Geotechnical Engineering & Testing

April 29, 2019 linc —. ce

1915 North 12th Street

Toledo, OH 43604-5305 T 419-324-2222

F 419-241-1808 www.ttlassoc.com

TTL Project No. 1762302

Geotechnical Subsurface Investigation Central Emergency Power Distribution Project

VA Medical Center Perry Point, Maryland

Following is the report of the geotechnical subsurface investigation performed by TTL Associates, Inc. (TTL) at the site of the referenced project. This investigation was performed in general accordance with TTL Proposal No. 1762302R1, dated December 19, 2018, and was authorized by Ms. Barbara Brann of 3 & B Hartigan Inc. on January 10, 2019 with J & B Hartigan Inc. Contract # 512A5-18-302 TTL.

This final report contains the results of our study, our engineering interpretation of the results with respect to the project characteristics, and our recommendations for foundation design and construction.

Soil samples collected during this investigation will be stored at our laboratory for 90 days from the date of this report. The samples will be discarded after this time unless you request that they be saved or delivered to you.

Should you have any questions regarding this report or require additional information, please contact our office.

Sincerely, TTL Associates, Inc.

Christopher P. Iott (OH 69734) Chief Geotechnical Engineer ‘Ni’ / R:SUR.IIFA Enginering..Repo I762O2 flL fleoleeli Repo CenimI Emergency Power Dismrihution I’mject VA Medical Center Pe Point MOdoc

Mr. John P. Hartigan J & B Hartigan Inc.

103 Adams Court Carrollton, Virginia 23314

Dear Mr. Hartigan:

•1.f

Vice President

Teamwork - Trust - Leadership Since 1927

GEOTECHNICAL SUBSURFACE INVESTIGATION

CENTRAL EMERGENCY POWER DISTRIBUTION PROJECT

VA MEDICAL CENTER

PERRY POINT, MARYLAND

FOR

J & B HARTIGAN INC.

103 ADAMS COURT

CARROLLTON, VIRGINIA 23314

SUBMITTED

APRIL 29, 2019

TTL PROJECT NO. 1762302

TTL ASSOCIATES, INC.

1915 NORTH 12TH STREET

TOLEDO, OHIO 43604

(419) 324-2222

(419) 241-1808 (FAX)

J & B Hartigan Inc. April 2019

TTL Project No. 1762302 Page i

TABLE OF CONTENTS

Page No.

1.0 Introduction

2.0 Investigative Procedures

3.0 Proposed Construction

4.0 General Site and Subsurface Conditions

4.1 General Site Conditions

4.2 General Soil Conditions

4.3 Groundwater Conditions

4.4 Laboratory Test Results

4.5 Laboratory Permeability Tests

5.0 Design Recommendations

5.1 Foundations

5.1.1 Mat Foundations

5.1.2 Mat Foundation Subgrade Modulus

5.1.3 Light Equipment Foundations

5.2 Seismic Considerations

5.3 Groundwater Control

5.4 Excavations and Slopes

6.0 Construction Recommendations

6.1 Site Preparation

6.2 Fill

6.3 Foundation Excavations

7.0 Qualification of Recommendations

PLATES

Plate 1.0 Site Location Map

Plate 2.1 Test Boring Location Plan – Aerial

Plate 2.2 Test Boring Location Plan – Proposed Plan

FIGURES

Logs of Test Borings B-1 through B-3

Legend Key

Tabulation of Test Data

Grain Size Distribution

Moisture-Density Relationship Data

Unconsolidated-Undrained Triaxial Compressive Strength Test Results

Hydraulic Conductivity (Permeability) Test Results

TTL Project No. 1762302 Page 1

1.0 INTRODUCTION

This geotechnical subsurface investigation report has been prepared for the proposed new central emergency power distribution system at the Perry Point Maryland VA Medical Center. The general location of the project is shown on the attached Site Location Map (Plate 1.0).

This report summarizes our understanding of the proposed construction, describes the investigative and testing procedures, presents the findings, discusses our evaluations and conclusions, and provides our design and construction recommendations for foundations.

This investigation was performed in general accordance with TTL Proposal No. 1762302R1, dated December 19, 2018, and was authorized by Ms. Barbara Brann of J & B Hartigan Inc. on

January 10, 2019 with J & B Hartigan Inc. Contract # 512A5-18-302 TTL.

The purpose of this investigation was to evaluate the subsurface conditions and laboratory data relative to the design and construction of foundations at the referenced site. To accomplish this, TTL performed three test borings, field and laboratory soil testing, and geotechnical engineering evaluations of the test results.

This report includes:

• A description of the subsurface soil and groundwater conditions encountered in the borings.

• Design recommendations for foundations associated with the proposed construction.

• Recommendations concerning soil and groundwater-related construction procedures such as site preparation, earthwork, foundation construction, and related field testing.

This investigation did not include an environmental assessment of the subsurface materials at this site.

TTL Project No. 1762302 Page 2

2.0 INVESTIGATIVE PROCEDURES

Three test borings, designated as Borings B-1 through B-3, were drilled by E2CR, Inc. as directed by TTL on February 27 and 28, 2019 for this investigation. The borings were performed in the general area of the proposed central emergency power distribution system. The test borings were located in the field by E2CR, Inc. based on approximate boring locations indicated by TTL in the project area drawn by J & B Hartigan Inc. on a “Topography Work Sheet – Under Ground

Utility Locations” drawing prepared by George Williams Stephens, Jr. and Associates, Inc., dated February 7, 2019. The approximate locations of the borings are shown on the Test Boring

Location Plans. Plate 2.1 includes boring locations with an aerial background. Plate 2.2 includes boring locations on a proposed site plan.

The test borings were performed in general accordance with geotechnical investigative procedures outlined in ASTM Standards D 1452 and D 5434. The borings performed during this investigation were drilled with a truck-mounted D-50 drill rig utilizing 3¼-inch inside diameter hollow-stem augers. Borings B-1 and B-3 were terminated at a depth of approximately 26½ feet below existing grade. Boring B-2 was terminated at a depth of approximately 30 feet below existing grade.

During auger advancement, soil samples were generally collected at 2½-foot intervals to a depth of 10 feet and at 5-foot intervals thereafter. Split-spoon (SS) samples were obtained by the

Standard Penetration Test (SPT) Method (ASTM D 1586), which consists of driving a 2-inch outside diameter split-barrel sampler into the soil with a 140-pound weight falling freely through a distance of 30 inches. The sampler was driven in three successive 6-inch increments with the number of blows per increment being recorded. The sum of the number of blows required to advance the sampler the second and third 6-inch increments is termed the Standard Penetration

Resistance (N-value) and is presented on the Logs of Test Borings attached to this report. The samples were sealed in jars and transported to our laboratory for further classification and testing.

Shelby tube samples, designated ST on the Logs of Test Borings, were obtained from Boring B-1

(1½ to 3½ feet), Boring B-2 (2 to 4 feet), and Boring B-3 (1½ to 3½ feet). The Shelby tube samples were obtained by hydraulically advancing a 3-inch diameter, thin-walled sampler beyond the hollow-stem auger into relatively undisturbed soil in accordance with ASTM D 1587. The

Shelby tubes were then extracted from the subsoils, and the ends were capped and sealed. The samples were transported to our laboratory where they were extruded, classified, and tested.

TTL Project No. 1762302 Page 3

Bulk samples of auger cuttings were obtained from selected intervals in the borings.

Soil conditions encountered in the test borings are presented in the Logs of Test Borings, along with information related to sample data, SPT results, water conditions observed in the borings, and laboratory test data. It should be noted that these logs have been prepared on the basis of laboratory classification and testing as well as field logs of the encountered soils.

All samples of the subsoils were visually or manually classified using the Unified Soil

Classification System (ASTM D 2487 and D 2488) and tested in the laboratory for moisture content (ASTM D 2216). Dry density determinations and unconfined compressive strength tests by the constant rate of strain method (ASTM D 2166) were performed on the Shelby tube samples from Borings B-1 and B-2, as well as selected intact cohesive split-spoon samples.

Unconfined compressive strength estimates were performed on the remaining intact cohesive samples using a calibrated hand penetrometer. Organic content determinations by the loss-on-ignition (LOI) method (ASTM D 2974) were performed on selected samples. The results of these tests are presented on the Logs of Test Borings and Tabulation of Test Data sheets attached to this report.

An Atterberg limits test (ASTM D 4318) and a particle size analysis with hydrometer testing

(ASTM D 422) were performed on representative samples from Borings B-1 (SS-5 and BS-1) and B-3 (ST-1) to determine soil classification and index properties. The results of these tests are presented on the Logs of Test Borings, Tabulation of Test Data sheets, and Grain Size

Distribution sheet attached to this report.

Standard Proctor moisture-density relationship tests (ASTM D 698) were performed on the bulk samples from Borings B-1 and B-3, and the results are attached to this report. A one-point unconsolidated-undrained (UU) triaxial compressive strength test (ASTM D 2850) was performed on a sample from Boring B-3 (ST-1). The test was performed using a confining pressure approximately equal to the overburden pressure at the midpoint of the sample depth.

The results of this test are attached to this report.

A flexible-wall permeability test (ASTM D 5084) was performed on a bulk sample from Boring

B-1 (BS-1). The test was performed on a sample re-compacted to 100 percent of the maximum dry density at optimum moisture content as determined by the Standard Proctor (ASTM D 698).

A flexible wall permeability test was also performed on a Shelby tube sample from Boring B-3

(ST-1). The results of these tests are attached to this report.

TTL Project No. 1762302 Page 4

Experience indicates that the actual subsoil conditions at a site could vary from those generalized on the basis of test borings made at specific locations, especially at previously developed sites such as this site. Therefore, it is essential that a geotechnical engineer be retained to provide soil engineering services during the site preparation, excavation, and foundation phases of the proposed project. This is to observe compliance with the design concepts, specifications, and recommendations, and to allow design changes in the event subsurface conditions differ from those anticipated prior to the start of construction.

TTL Project No. 1762302 Page 5

3.0 PROPOSED CONSTRUCTION

We understand that the project consists of a new central emergency power distribution system at the Perry Point Maryland VA Medical Center. As part of the project, four (4) new generators will be installed. Four (4) fuel tanks will be installed to facilitate the generators. Additionally, new piping will be installed, and will be supported on pipe racks.

Two (2) capacitors and a load bank will each be supported on individual foundations on the order of 7½ feet by 7½ feet in plan. Each generator and associated fuel tank will be supported on an individual foundation on the order of 15 feet by 50 feet in plan. A new paralleling switch gear and enclosure will be on the order of 25 feet by 65 feet in plan. The structures are planned to be supported on shallow spread foundations.

Final site grades are anticipated to approximate grades present at the time of our investigation.

TTL Project No. 1762302 Page 6

4.0 GENERAL SITE AND SUBSURFACE CONDITIONS

4.1 General Site Conditions

At the time of our investigation, the areas of the proposed development consisted of a grass field with some trees. The surface materials encountered in the borings consisted of approximately

6 inches of topsoil.

4.2 General Soil Conditions

Based on the results of the field investigation and laboratory tests, the subsurface profile encountered underlying the surface materials can be generally described by three strata of cohesive soils with granular soils interbedded.

Stratum I consisted of predominantly soft to medium stiff cohesive soils underlying the surface materials to a depth of 1½ to 3½ feet below existing grade in all the borings. These cohesive soils consisted of lean clay (CL) with varying amounts of sand. Trace organics (determined to be approximately 3 percent or less) were observed in the Stratum I SS-1 samples obtained from

Borings B-1 and B-3. SPT N-values ranged from 3 to 8 blows per foot (bpf). An unconfined compressive strength of 1,500 pounds per square foot (psf) was determined for a Stratum I sample obtained from Boring B-3. A hand penetrometer reading of greater than 9,000 psf

(maximum reading obtainable using a hand penetrometer) was determined for the Stratum I sample obtained from Boring B-2, but this reading was likely influenced by desiccation and is not considered reliable for design. An unconsolidated-undrained (UU) triaxial compressive strength test performed on the Shelby tube sample obtained from Stratum I in Boring B-3 resulted in a cohesion (c) of 530 psf. Moisture contents ranged from approximately 21 to

25 percent.

Stratum II consisted of predominantly stiff cohesive soils underlying Stratum I to depths of

3½ feet and 4 feet in Borings B-1 and B-2, respectively. These cohesive soils consisted of lean clay (CL) with varying amounts of sand. Trace organics (determined to be approximately

2 percent) were observed in the Stratum II sample obtained from Boring B-1. Unconfined compressive strengths ranged from 2,460 to 2,800 psf. Moisture contents ranged from approximately 20 to 21 percent.

TTL Project No. 1762302 Page 7

Stratum III consisted of predominantly very stiff cohesive soils underlying Stratum II in

Borings B-1 and B-2 and underlying Stratum I in Boring B-3 to a depth of 6 to 6 ½ feet. These cohesive soils consisted of lean clay (CL) with varying amounts of sand, as well as silty clay

(CL/ML) with trace sand. SPT N-values generally ranged from 21 to 24 bpf. Unconfined compressive strengths varied from 4,480 to 9,000 psf. Moisture contents ranged from approximately 16 to 17 percent.

Stratum IV consisted of predominantly medium stiff to stiff cohesive soils underlying Stratum

III to termination depths of 26½ to 30 feet below existing grade. These cohesive soils consisted of lean clay (CL) with varying amounts of sand, sandy silt (ML) with trace gravel, as well as silty clay (CL/ML) with trace sand. Trace organics (determined to be approximately 1 to 2 percent) were observed in the upper two Stratum IV samples obtained from Boring B-1. SPT N-values ranged from 8 to 13 bpf. Unconfined compressive strengths ranged from 1,000 to 4,100 psf.

Moisture contents were on the order of 16 to 31 percent.

Interbedded in the Stratum IV soils in all the borings, zones of predominantly medium dense to dense granular soils were encountered at depths ranging from 16 to 30 feet below existing grade.

All the borings were terminated within zones of granular soils. These granular soils consisted of silty sand (SM) with clay and trace gravel, as well as clayey sand (SC) with gravel. Within the granular soils, the SPT resulted in N-values ranging from 8 to 22 bpf. Moisture contents ranged from 12 to 21 percent.

Additional descriptions of the stratigraphy encountered in the borings are presented on the Logs of Test Borings.

4.3 Groundwater Conditions

Groundwater was encountered during drilling in all the borings at a depth ranging from 14½ to

15½ feet below existing grade. Groundwater was observed upon completion of drilling operations in Borings B-1 and B-3 at depths of 3 feet and 9½ feet, respectively. It should be noted that each of the borings was drilled and backfilled within the same day. As such, stabilized water levels may not have occurred over this limited time period. Instrumentation was not installed to observe long-term groundwater levels.

Based on the soil characteristics and moisture conditions encountered in the borings, it is our opinion that the “normal” groundwater table at the site can generally be expected at depths of

TTL Project No. 1762302 Page 8 approximately 15 to 23 feet below existing grade. However, it should be noted that groundwater elevations can fluctuate with seasonal and climatic influences. In particular, “perched” water may be encountered in granular materials that are underlain by relatively impermeable native cohesive soils. Additionally, the water in the lower profile sand layers may be under a head pressure based on the rising water levels in the borings to depths on the order of 10 feet or shallower below existing grade after termination in the granular soils. Therefore, groundwater conditions at the site may vary at different times of the year from those encountered during this investigation.

4.4 Laboratory Test Results

Results of laboratory tests performed for selected samples are summarized below.

Results of the index property tests used to classify the soils are summarized in Table 4.4.A. The

Grain Size Distribution curves for these tests are also attached to this report.

Table 4.4.A Index Property Tests

Boring

Number

(Sample)

Sample

Depth

(feet) In te rp re te d

S tr a tu m Grain Size Distribution

L iq u id

L im it

P la st ic

L im

P st ic y

In ex

M o is tu re

C o n te n t

U S

C S

C la ss

G ra v el a n il t

C y

B-1 (SS-5) 15 to 16½ IV 0 15 45 40 23 18 5 22

CL-

ML

B-1 (BS-1) ½ to 7 ½ I/II/III 0 24 27 49 28 18 10 - CL

B-3 (ST-1) 1½ to 3½ I 0 18 24 58 34 23 11 25 CL

Standard Proctor moisture-density relationship tests were performed on two selected bulk samples to evaluate the soils that will be excavated in the area of the development and placed as new engineered fill. Results of the Proctor tests are summarized in the following table.

Table 4.4.B. Standard Proctor Test Results

Number

(Sample)

Sample

Depth

(feet)

Interpreted

Stratum

USCS

Class.

Maximum

Dry Density

(pcf)

Optimum

Moisture

Content

B-1 (BS-1) ½ to 7½ I/II/III CL 107.3 18.4

B-3 (BS-1) ½ to 10 I/II/III/IV CL 111.9 16.1

Results of laboratory permeability testing are presented in Section 4.5.

TTL Project No. 1762302 Page 9

4.5 Laboratory Permeability Tests

A flexible-wall permeability test was performed in the laboratory for a selected Shelby tube sample to evaluate the hydraulic conductivity of the in-situ soils. Additionally, a flexible-wall permeability test was performed on a selected sample of anticipated borrow soils to evaluate the permeability of these soils when they are recompacted for construction. Please refer to Section

2.2 for information regarding criteria used for recompaction of the test specimens from the bulk sample. Results of the laboratory permeability tests are summarized in the following table.

Table 4.5. Laboratory Permeability Test Results

Number

(Sample)

Approx.

Sample /

Test

Depth

(feet)

Interpreted

Stratum

Hydraulic

Conductivity, k

(cm/sec)

Liquid

Limit /

Plasticity

Index

Percent

Passing

No. 200

Sieve

Initial

Moisture

Content

B-1 (BS-1) ½ to 7 ½ I/II/III 8.5x10-8 28 / 10 76 18*

B-3 (ST-1) 1½ to 3½ I 8.9x10-8 34 / 11 82 26

*Recompacted to optimum moisture content

The range of hydraulic conductivity indicated in the above table from laboratory permeability tests indicates the native cohesive soils have very low permeability. These conditions should be suitable for containment associated with the proposed fuel tanks.

TTL Project No. 1762302 Page 10

5.0 DESIGN RECOMMENDATIONS

The following conclusions and recommendations are based on our understanding of the proposed construction and the data obtained during our field investigation. If the project information or location as outlined is incorrect or should change significantly, a review of these recommendations should be made by TTL. These recommendations are subject to satisfactory completion of the recommended site and subgrade preparation and fill placement operations described in Section 6.0, “Construction Recommendations.”

5.1 Foundations

5.1.1 Mat Foundations

Based on the results of our field and laboratory testing for Borings B-1, B-2 and B-3, Stratum II native stiff to very stiff cohesive soils are generally expected at the anticipated mat slab bearing depth of approximately 32 inches below existing grade (minimum required depth for protection from frost penetration). However, based on the conditions encountered in Boring B-3, Stratum I native predominantly soft to medium stiff cohesive soils may also be encountered at the foundation bearing elevation. The Stratum II soils are considered generally suitable for support of the proposed structures. If Stratum I soils are encountered, they will require over-excavation and replacement with new granular engineered fill as described below. The Stratum I soils extended to a depth of 3½ feet below existing grade in Boring B-3.

Where unsuitable foundation bearing materials are encountered, over-excavation should extend through these materials to suitable bearing soils. Additionally, the base of the over-excavation should be widened one foot for every foot of depth below the planned bearing elevation, with the overexcavation centered along the foundation footprint. The over-excavated areas should be backfilled with dense-graded aggregate, placed in controlled lifts, and compacted to not less than

100 percent of the maximum dry density as determined by ASTM D 698 (Standard Proctor).

Alternatively, the over-excavated areas could be backfilled with lean concrete having a minimum compressive strength of 1,500 pounds per square inch (psi) or other flowable controlled-density fill having a minimum compressive strength of 300 psi. If foundations will be placed at the base of the over-excavation or the lean concrete fill option will be utilized, widening the footing over-excavation will not be required. If the controlled-density fill option is utilized, the footing over-excavation shall be widened as discussed above.

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Following the satisfactory completion of the site preparation and footing excavation inspections outlined in this report, the square mat foundations for structures such as the pad-mounted capacitors and the load bank equipment pad may be supported on mat foundations designed utilizing an average gross allowable bearing pressure of 3,000 pounds per square foot (psf). For the rectangular mat foundations, such as anticipated for the switchgear and enclosure as well as the generators, an average gross allowable bearing pressure of 2,750 pounds per square foot (psf) may be utilized for design. These allowable bearing pressures are based on a nominal factor of safety of 3 applied to the calculated gross ultimate bearing capacity. Foundation bearing materials should be field-verified as being native lean clays (CL) with a minimum unconfined compressive strength of 2,500 psf, or properly placed and compacted new dense-graded aggregate backfill materials.

Due to the existing site development and Stratum I soft cohesive soils, we strongly recommend that the bearing surface at the bottom of all footing excavations be inspected during construction by a TTL geotechnical engineer or qualified representative. Inspection should be performed to verify that the exposed soil conditions at the bearing elevations are consistent with the subsurface conditions encountered in the test borings, and are suitable for foundation bearing. Additionally, the presence of our engineer will help facilitate the timely remediation of unsuitable soil conditions. If the results of hand penetrometer or other strength tests indicate the exposed soil conditions are not suitable for the design bearing pressure, it may be necessary to increase the foundation size to accommodate the lower bearing strengths or to over-excavate and backfill with engineered fill.

It should be noted that footings in unheated areas constructed shallower than the minimum frost penetration depth of 32 inches below finished exterior grades will be susceptible to movement due to freeze-thaw phenomena. Even if turned down edge portions of the foundation are extending to the minimum depth for protection from frost penetration, there is potential for movement due to frost heave in soils above the frost depth. This could occur even when

“non-susceptible frost material,” such as gravel or crushed stone, is placed to support the mat foundation. Therefore, we recommend that the entire mat foundation slab extend to a depth of at least 32 inches below finished exterior grades.

For the smaller capacitors and load bank equipment mat foundations, total settlement at the center of the mat foundation based on an average gross allowable bearing pressure of 3,500 psf was calculated to be less than 1 inch. For the larger generator mat foundations, total settlement at the center of an individual mat foundation based on an average gross allowable bearing pressure

TTL Project No. 1762302 Page 12 of 3,000 psf was calculated to be on the order of 1 to 1¼ inches. Due to the four generator mat foundations adjacent to each other, settlement in the middle of the loaded area may be on the order of 1¼ to 1¾ inches. It is our experience that this magnitude of settlement for a large mat foundation is often tolerable. However, if total settlement of the entire loaded area is limited to

1 inch, the average gross allowable bearing pressure should be reduced to 1,835 psf.

Differential settlement will depend on the rigidity of the mat(s), but even for a relatively

“flexible” mat, the center to edge differential settlement is not expected to exceed one half of the total settlement. For mat foundations extending to the minimum required depth for protection from frost penetration, the mats are likely to behave as nearly rigid foundations, which would result in less differential settlement than indicated above.

5.1.2 Mat Foundation Subgrade Modulus

Generally, mat foundations are designed using a modulus of subgrade reaction (k). In addition, mat foundations are typically designed using finite element method (FEM) analyses or similar methodologies that allow for evaluations of contact pressure, deflection, shear and bending moment for structural reinforcement determinations, and thickness/rigidity considerations. For mat foundation design, we recommend a subgrade modulus (k) of 90 pounds per cubic inch (pci).

The modulus of subgrade reaction value indicated above is based on a unit k-value (kv1 or ks1) assuming an equivalent 1-foot by 1-foot plate load test. Depending on the method of analysis used to model the mat, a correction or adaptation is typically made to the kv1 modulus value based on the width and shape of the loaded area, as well as whether the bearing soils are sands or clays. Care should be taken by the structural designer to understand whether the analytical input requires the kv1 or ks1 modulus value based on a 1-foot by 1-foot plate, or the modulus of subgrade reaction (ks), sometimes identified as kb, which is a corrected value based on foundation width B. For foundations bearing on clays, ks for a full-sized footing or mat is equal to kv1/B. For a mat foundation, this B may not be the entire width of the mat, but the effective width of where the mat is acted upon by line loads or point loads spaced a distance B apart. For typical mat design that does not have uniform load intensity, the point loads or line loads and the associated shear and moment distribution in the mat will result in zones where deflection is at or near zero, and the effective width can be taken as the distance between these zones of “zero deflection.” This is valid as long as the contact pressures associated with the areas of concentrated loads are less than ½ of the ultimate bearing capacity of the soil, the latter of which is independent of foundation width.

TTL Project No. 1762302 Page 13

We recommend that the design of the mat consider what is the actual effective width B of the foundation, but in no case incorporate a ks or kb value less than 10 pci. The design should also consider that the contact pressure is not likely to be uniform within all areas of the mat, and deflection may not be uniform unless the mat is indeed a rigid structural element.

With respect to determination of ks, it is difficult for the geotechnical engineer to determine accurate elastic design parameters for the soil as applicable to structural mat design (i.e., Es, p, or ks). It is our experience that bending moments and computed soil pressures are usually not very sensitive to kv1 values or kb values because the structural member (concrete mat) stiffness or rigidity is generally much greater than the soil stiffness as measured by k of the subgrade.

Regarding subgrade stiffness and mat design, the American Concrete Institute (ACI) recognizes that the structural designer and geotechnical engineer may do a parametric study, varying the value of ks over a range of one-half the furnished value up to five times this value. The results of the parametric study should be reviewed by the geotechnical engineer during the course of the design. If no satisfactory solution is found, then adjustments in the development concept may be appropriate. Adjustments to the mat design may include enlarging the mat in plan or deepening the mat base to reduce the net applied pressure. Such adjustments should be made with the concurrence of the geotechnical engineer. During the final design stage, TTL would be pleased to review analyses and coordinate such efforts with the structural engineer.

5.1.3 Light Equipment Foundations

Based on similar past projects, we presume that some light equipment, such as pipe supports, may include block/mass foundations to resist uplift and overturning. We presume these foundations will be extended to or deeper than the minimum required depth for protection from frost penetration of 32 inches below final grades. As such, the foundation bearing materials are generally expected to consist of Stratum II native predominantly stiff cohesive soils, which are considered generally suitable for support of foundations. Based on Boring B-3, Stratum I soft to medium stiff cohesive soils may be encountered at the foundation bearing elevation. These soils are unsuitable for support of the light equipment foundations, and should be over-excavated and replaced with new granular engineered fill as described in Section 5.1.1. In any case, an inspection of all footing excavations should be completed prior to placement of steel reinforcement or foundation concrete.

TTL Project No. 1762302 Page 14

Following the satisfactory completion of the site preparation and footing excavation inspections outlined in Section 6.0 of this report, the proposed light equipment foundations may be designed using a net allowable bearing pressure of 2,500 pounds per square foot (psf) for wall (strip) footings and column (square) footings. This allowable bearing pressure is based on a nominal factor of safety of 3 applied to the calculated gross ultimate bearing capacity. In using a net allowable soil pressure, the weight of the footings or backfill over the footings need not be included in the structural loads for dimensioning footings. The bearing materials should be field-verified as being native lean clay (CL) with a minimum unconfined compressive strength of

2,500 psf, or properly placed and compacted new engineered fill.

Wall (strip) footings should be at least 18 inches wide and column (square) footings should be at least 30 inches square, regardless of sizing based on design loads and the allowable bearing pressure.

Although loads associated with the light equipment were not provided, utilizing the above allowable bearing pressure and proper foundation inspection techniques, the total settlement associated with these structures should not exceed 1 inch, and differential settlement should not exceed ¾ inch.

For cast-in-place concrete footings, an ultimate friction factor (tan δ) of 0.30 may be utilized along the base of the foundation to resist sliding. A passive earth pressure coefficient (kp) of 3.0 may be utilized, along with a total soil unit weight of 130 pounds per cubic foot (pcf), for the portion of the footing that is below a frost protection depth of 32 inches. If the design includes passive pressure above the frost line, the contribution of passive resistance to sliding or overturning stability should be evaluated in conjunction with the design factor of safety. These values are based on footings poured in intimate contact with at least stiff lean clay or crushed stone backfill in over-excavation areas. It should be noted that some wall/foundation movement or horizontal displacement is needed to mobilize the full passive pressure of the soil. Because of this consideration, some design methods incorporate a higher required factor of safety (e.g., F. S. = 2.0) when using passive pressure contribution to stability, as compared to sliding resistance on the base only (typically, F.S. = 1.5).

5.2 Seismic Considerations

We have reviewed seismic design parameters in accordance with International Building Code

(IBC) criteria. It should be noted that the IBC Seismic Site Characterization is based on the upper

TTL Project No. 1762302 Page 15

100 feet of the geologic profile. The borings for this investigation were terminated at depths of

26½ to 30 feet below existing grades. Therefore, our analysis is limited to the encountered overburden soil profile only.

The IBC criteria for the su-method (for cohesive soil layers with a plasticity index PI > 20) are based on site characterization using undrained shear strengths determined by ASTM D 2166 or

D 2850. Based on the limited scope of this investigation, strengths determined from ASTM

D 2166 and D 2850 methods were supplemented with unconfined compressive strengths determined using a hand penetrometer. For this site, laboratory test results also identified cohesionless soil layers (PI < 20) for which the Nch or N-method is considered.

Based on IBC Section 1613.3.2, which references ASCE 7-10, utilizing the SPT N-value method, the weighted average N-value for the profile was calculated to be approximately

20 blows per foot (bpf). For an average SPT N-value greater than 15 bpf and less than 50 bpf, the site can be characterized as Site Class D (stiff soil) in accordance with ASCE 7-10 Table 20.3-1.

Based on the unconfined compressive strengths determined for the overburden soils at the site, the average undrained shear strength (su) was calculated to be approximately 1,350 pounds per square foot (psf). Using the su-method, based on ASCE 7-10 Table 20.3-1 criteria, the average undrained shear strength falls between 1,000 psf and 2,000 psf, which is also indicative of a Site

Class D “stiff soil” designation.

5.3 Groundwater Control

As stated previously, groundwater was encountered during drilling in all the borings at a depth ranging from 14½ to 15½ feet below existing grade. Groundwater was observed upon completion of drilling operations in Borings B-1 and B-3 at a depth of 3 feet and 9½ feet, respectively. Based on the soil characteristics and moisture conditions encountered in the borings, it is our opinion that the “normal” groundwater table at the site can generally be expected at depths of approximately 15 to 23 feet below existing grade. However, “perched” water may be encountered in granular materials that are underlain by relatively impermeable native cohesive soils.

It is our experience that adequate control of groundwater seepage, perched water, or surface water run-off into shallow excavations should be achievable by minor dewatering systems, such as pumping from prepared sumps. Excavations to depths that would intercept the “normal” water level or perched water in sand seams in the lower soil profile are not anticipated for this project.

TTL Project No. 1762302 Page 16

However, it should be noted that water in the lower soil profile may be under a pressure head based on rising water levels in the borings to depths on the order of 10 feet or shallower below existing grade after termination in the granular soils. In the event excessive seepage is encountered during construction, TTL may be notified to evaluate whether other dewatering methods are required.

5.4 Excavations and Slopes

The sides of temporary excavations for foundations, utility installations, and other construction should be adequately sloped to provide stable sides and safe working conditions. Otherwise, the excavation must be properly braced against lateral movements. In any case, applicable

Occupational Safety and Health Administration (OSHA) safety standards must be followed.

The soils encountered within the anticipated depth of excavation during this investigation consist of the following OSHA type soils:

• OSHA Type A soils (cohesive soils with unconfined compressive strengths of

3,000 pounds per square foot (psf) or greater),

• OSHA Type B soils (cohesive soils with unconfined compressive strengths greater than

1,000 psf and less than 3,000 psf), and

• OSHA Type C soils (cohesive soils with unconfined compressive strengths of 1,000 psf or less).

For temporary excavations in Type A, B and C soils, side slopes should be constructed no steeper than ¾ horizontal to 1 vertical (¾H:1V), 1H:1V, and 1½H:1V, respectively. In all cases, flatter slopes may be required if lower strength soils or adverse seepage conditions are encountered during construction.

For permanent excavations and slopes, we recommend that grades be no steeper than 3H:1V without a more extensive geotechnical evaluation of the proposed construction plans and site conditions.

TTL Project No. 1762302 Page 17

6.0 CONSTRUCTION RECOMMENDATIONS

6.1 Site Preparation

Prior to proceeding with construction operations, all structures, vegetation, topsoil, root mat, and other deleterious non-soil materials should be removed from the proposed construction areas.

The actual amount of required stripping should be determined in the field by a geotechnical engineer or qualified representative.

Upon completion of stripping and clearing, the areas intended to support new fill and structure foundations should be carefully inspected by a geotechnical engineer. Subsequently, the engineer may require proof rolling of the cohesive subgrades utilizing a 20- to 30-ton loaded truck or other pneumatic-tired vehicle of similar size and weight. The truck should make a minimum of two passes in each of two perpendicular directions covering the proposed development area, with additional passes as necessary to achieve required compaction and/or subgrade stabilization.

The purpose of proof rolling the cohesive subgrades is to locate any weak, soft, or excessively wet soils that may be present at the time of construction. Any unsuitable materials observed during the inspection and proof-rolling operations should be undercut and replaced with compacted fill or stabilized in place utilizing conventional remedial measures such as discing, aeration, and recompaction. Once the site has been proof rolled, inspected, and stabilized, the proof-rolled or inspected subgrades should not be exposed to wet conditions.

The results of the inspection and proof-rolling operations will be partially dependent on construction operations, the moisture content of the soil, and the weather conditions prevalent at the time. If pumping or rutting is encountered and difficulty is experienced in the operation of construction equipment, TTL should be notified in order to determine which method of subgrade modification may be best suited for the conditions encountered. Should such conditions be experienced, we may recommend that a small test area be used to determine the necessary depth of undercutting and stone replacement or other remedial action necessary to achieve a stable subgrade condition.

TTL Project No. 1762302 Page 18

6.2 Fill

Material for backfill required to achieve design grades may consist of any non-organic soils having a maximum dry density as determined by the Standard Proctor (ASTM D 698) of

90 pounds per cubic foot (pcf) or greater. On-site soils may be used as engineered fill materials provided that they are free of organic matter, debris, excessive moisture, and rock or stone fragments larger than 3 inches in diameter. Depending on seasonal conditions, the on-site soils may be wet of optimum and may require scarification and aeration to achieve satisfactory compaction. If the construction schedule does not allow for scarification and aeration activities, it may be more practical or economical to utilize imported granular fill.

Containment areas should contain at least 1 foot of clay soils at the surface.

Fill should be placed in uniform layers no more than 8 inches thick (loose measure) and adequately keyed into stripped and scarified soils. All fill within structure areas should be compacted to not less than 100 percent of the maximum dry density as determined by ASTM D

698 (Standard Proctor).

The upper soil profile at the site consists of native cohesive soils. The contractor should be prepared to use a sheepsfoot roller to provide effective compaction of the cohesive subgrade soils. If “clean” granular soils are utilized for new engineered fill, a vibratory smooth-drum roller would provide effective compaction of these materials. In narrow utility or footing excavations, the on-site cohesive soils may be difficult to compact; therefore, a clean granular material may be required in these areas.

Scarified subgrade soils and all fill material should be within 3 percent of the optimum moisture content to facilitate compaction. Furthermore, fill material should not be frozen or placed on a frozen base. It is recommended that all earthwork and site preparation activities be conducted under adequate specifications and properly monitored in the field by a qualified geotechnical testing firm.

6.3 Foundation Excavations

As mentioned in Section 5.1, a geotechnical engineer or qualified representative should perform a detailed footing inspection to verify that the exposed materials are similar to those encountered in the borings, unsuitable bearing materials are over-excavated, and that engineered fill has been properly placed and compacted such that it is capable of supporting the design bearing pressures.

TTL Project No. 1762302 Page 19

We recommend that the shallow spread foundation excavations be concreted as soon as practical after they are excavated and that water not be allowed to pond in any excavation. If it is necessary to leave the bearing surface open for any extended period of time, we recommend that a thin mat of lean concrete be placed over the bottom of the excavation to reduce damage to the surface from water or construction. Foundation concrete should not be placed on frozen or saturated subgrade.

Additional foundation installation recommendations for mat foundations and shallow spread foundations are presented in Section 5.1.

TTL Project No. 1762302 Page 20

7.0 QUALIFICATIONS OF RECOMMENDATIONS

Our evaluation of foundation design and construction conditions has been based on our understanding of the site and project information and the data obtained during our field investigation. The general subsurface conditions were based on interpretation of the subsurface data obtained at specific boring locations. Regardless of the thoroughness of a subsurface investigation, 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. This is especially true for previously developed sites.

Therefore, experienced geotechnical engineers should observe earthwork and foundation construction to confirm that the conditions anticipated in design are noted. Otherwise, TTL assumes no responsibility for construction compliance with the design concepts, specifications, or recommendations.

The design recommendations in this report have been developed on the basis of the previously described project characteristics and subsurface conditions. If project criteria or locations change, a qualified geotechnical engineer should be permitted to determine whether the recommendations must be modified. The findings of such a review will be presented in a supplemental report.

The nature and extent of variations between the borings may not become evident until the course of construction. If such variations are encountered, it will be necessary to reevaluate the recommendations of this report after on-site observations of the conditions.

Our professional services have been performed, our findings derived, and our recommendations prepared in accordance with generally accepted geotechnical engineering principles and practices. This warranty is in lieu of all other warranties either expressed or implied. TTL is not responsible for the conclusions, opinions, or recommendations of others based on this data.

1-3-5 (8)

7-11-13 (24)

3-6-6 (12)

5-5-6 (11)

3-3-5 (8)

4-3-8 (11)

3-6-7 (13)

NI

1.23

4.50

1.30

3.25

0.50

1.50

NP

2.00

NP

SS

ST

SS

SS

SS

SS

SS

SS

TOPSOIL - 6 Inches 0.5'

Moist Medium Stiff Brown LEAN CLAY w/Trace Sand and Organics (CL) @0.5': SS-1 Organic Content = 2.5%

1.5' Moist Stiff Brown LEAN CLAY w/Trace Sand and Organics (CL) @2': ST-1 Organic Content = 2.2%

3.5' Moist Very Stiff Brown LEAN CLAY (CL)

6.0' Moist Stiff Brown SANDY SILT w/Trace Gravel and Organics (ML) @7.5': SS-3 Organic Content = 1.8%

9.5' Moist Stiff Gray LEAN CLAY w/Trace Sand and Organics (CL) @10': SS-4 Organic Content = 1.0%

13.5' Moist Medium Stiff Brown SILTY CLAY w/Trace Sand

(CL-ML)

17.5' Moist Stiff Brown/Gray LEAN CLAY w/Trace Sand (CL)

21.0' Moist Medium Dense Gray/Brown SILTY SAND w/Clay and Trace Gravel (SM)

22.5' Moist Stiff Gray LEAN CLAY w/Sand (CL)

26.0' Moist Medium Dense Gray CLAYEY SAND w/Gravel

(SC)

26.5' Bottom of hole at 26.5 feet.

NOTES A bulk sample was taken from auger cuttings from 0.5 - 7.5'.

LOGGED BY A. Patel

AT TIME OF DRILLING 14.5 ft

AT END OF DRILLING 3.0 ft

0hrs AFTER DRILLING Caved @ 13 ft

GROUND WATER LEVELS:

CHECKED BY CPI

GROUND ELEVATIONRIG NO. D-50DRILLING CONTRACTOR E2CR Doren

DRILLING METHOD 3-1/4 in. HSA

DATE STARTED 2/28/19 COMPLETED 2/28/19

E

LE

V A

T

IO

N (f t)

D E

P T

H (f t)

G R

A P

H

IC

LO

G

R E

C O

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(R

Q D

B

LO

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S (N

V A

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U N

C O

N F

C

O M

P

S T

R

(t sf

D R

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N

IT

W T

(p cf

SPT N VALUE

20 40 60 80

S A

M P

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T

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U M

B E

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20 40 60 80

PL LLMC

MATERIAL DESCRIPTION

BORING NUMBER B-1

CLIENT J & B Hartigan Inc.

PROJECT NUMBER 1762302

PROJECT NAME Central Emergency Power Distribution Project

PROJECT LOCATION VA Medical Center, Perry Point, MD

T T

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TTL Associates, Inc.

1915 N 12th Street Toledo, Ohio 43624 Telephone: 419-324-2222 Fax: 419-241-1808

1-1-3 (4)

7-9-12 (21)

2-5-7 (12)

3-6-9 (15)

3-5-6 (11)

3-17-19 (36)

2-2-9 (11)

17-8-11 (19)

4.50

1.40

2.58

1.75

2.05

1.25

NP

1.50

NP

NP

SS

ST

SS

SS

SS

SS

SS

SS

SS

TOPSOIL - 6 Inches 0.5'

Moist Soft to Medium Stiff Brown LEAN CLAY (CL) 2.0'

Moist Stiff Brown LEAN CLAY (CL)

4.0' Moist Very Stiff Brown LEAN CLAY w/Trace Sand (CL)

6.5' Moist Stiff Gray/Brown LEAN CLAY w/Sand (CL)

9.5' Moist Stiff Gray SANDY SILT w/Trace Iron Oxide Stain Seam (ML)

13.5' Moist Stiff Brown LEAN CLAY w/Sand (CL)

17.5' Moist Dense Brown SILTY SAND w/Gravel (SM)

23.0' Moist Soft to Medium Stiff Gray LEAN CLAY w/Trace Sand (CL)

26.0' Moist Medium Dense Gray CLAYEY SAND w/Trace Gravel (SC)

@28.5': w/Gravel

30.0' Bottom of hole at 30.0 feet.

NOTES A bulk sample was taken from auger cuttings from 0.5 - 10.0'.

LOGGED BY A. Patel

AT TIME OF DRILLING 15.0 ft

AT END OF DRILLING None

0hrs AFTER DRILLING Caved @ 15 ft

GROUND WATER LEVELS:

CHECKED BY CPI

GROUND ELEVATIONRIG NO. D-50DRILLING CONTRACTOR E2CR Doren

DRILLING METHOD 3-1/4 in. HSA

DATE STARTED 2/27/19 COMPLETED 2/27/19

E

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V A

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C O

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S (N

V A

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C O

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C

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P

S T

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(t sf

D R

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N

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W T

(p cf

SPT N VALUE

20 40 60 80

S A

M P

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T

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U M

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20 40 60 80

PL LLMC

MATERIAL DESCRIPTION

BORING NUMBER B-2

CLIENT J & B Hartigan Inc.

PROJECT NUMBER 1762302

PROJECT NAME Central Emergency Power Distribution Project

PROJECT LOCATION VA Medical Center, Perry Point, MD

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TTL Associates, Inc.

1915 N 12th Street Toledo, Ohio 43624 Telephone: 419-324-2222 Fax: 419-241-1808

1-1-2 (3)

7-9-12 (21)

5-5-7 (12)

2-4-5 (9)

4-5-8 (13)

3-4-4 (8)

2-6-16 (22)

0.75

UU

2.24

1.50

0.16

1.50

NP

NP

1.75

NP

SS

ST

SS

SS

SS

SS

SS

SS

TOPSOIL - 6 Inches 0.5'

Moist Soft to Medium Stiff Brown LEAN CLAY w/Sand

(CL)

(w/Trace Organics in SS-1 Sample) @1.5': UU: c = 3.7 PSI = 530 PSF

3.5' Moist Very Stiff Brown SILTY CLAY w/Trace Sand

(CL/ML)

6.0' Moist Stiff Brown SILTY CLAY w/Sand (CL/ML)

9.5' Moist Stiff Brown/Gray LEAN CLAY w/Trace Sand (CL)

@13': Brown w/Sand

16.0' Moist Medium Dense Brown SILTY SAND w/Trace Gravel (SM)

20.0' Moist Loose Brown/Gray CLAYEY SAND w/Gravel (SC)

@22': Dense (Based on resistance to auger penetration)

@23.9': Loose to Medium Dense (Based on less resistance to auger penetration)

25.0' Moist Soft to Medium Stiff Gray LEAN CLAY w/Sand

(CL)

25.5' Moist Medium Dense Purple/Gray CLAYEY SAND w/Gravel (SC)

26.5' Bottom of hole at 26.5 feet.

NOTES A bulk sample was taken from auger cuttings from 0.5 - 10.0'.

LOGGED BY A. Patel

AT TIME OF DRILLING 15.5 ft

AT END OF DRILLING 9.5 ft

1hrs AFTER DRILLING 10.5 ft, Caved @ 14 ft

GROUND WATER LEVELS:

CHECKED BY CPI

GROUND ELEVATIONRIG NO. D-50DRILLING CONTRACTOR E2CR Doren

DRILLING METHOD 3-1/4 in. HSA

DATE STARTED 2/28/19 COMPLETED 2/28/19

E

LE

V A

T

IO

N (f t)

D E

P T

H (f t)

G R

A P

H

IC

LO

G

R E

C O

V E

R Y

(R

Q D

B

LO

W C

O U

N T

S (N

V A

LU

E

U N

C O

N F

C

O M

P

S T

R

(t sf

D R

Y U

N

IT

W T

(p cf

SPT N VALUE

20 40 60 80

S A

M P

LE

T

Y P

E N

U M

B E

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20 40 60 80

PL LLMC

MATERIAL DESCRIPTION

BORING NUMBER B-3

CLIENT J & B Hartigan Inc.

PROJECT NUMBER 1762302

PROJECT NAME Central Emergency Power Distribution Project

PROJECT LOCATION VA Medical Center, Perry Point, MD

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