Geotechnical Report 1 of 3.pdf

May 14, 2021

Report of Geotechnical Study

Project No. 590-220 Construct Rehab Medicine Facility Building 52

Hampton Veterans Affairs Medical Center (HVAMC) Hampton, Virginia 23667

Prepared For:

Charlotte Engineers, LLP

5838 Monroe Road Charlotte, North Carolina 28212

F&R Record No. 61Z-0034

Froehling & Robertson, Inc.

dehlers Typewritten Text

APPENDIX F

Engineering Stability Since 1881

May 14, 2021

Charlotte Engineers, LLP 5838 Monroe Road Charlotte, North Carolina 28212

Attn: Douglas Ehlers, P.E.

Director of Project Management

Re: Report of Geotechnical Study

Project No. 590-220 Construct Rehab Medicine Facility Building 52 Hampton Veterans Affairs Medical Center (HVAMC) Hampton, Virginia 23667

Dear Mr. Ehlers:

The enclosed report presents the results of the subsurface exploration program and geotechnical engineering evaluation undertaken by Froehling & Robertson, Inc. (F&R), in connection with the above-referenced project. Our services were performed in general accordance with Proposal No.

2061-00389G, dated December 11, 2020.

The report presents our understanding of the project information, reviews our exploration procedures, describes the general subsurface conditions at the boring locations, and presents our evaluations, conclusions, and recommendations. There are important limitations to this and all geotechnical reports. Some of these limitations are discussed in the information prepared by the Geoprofessional Business Association (GBA) provided in Appendix I of this report. We ask that you review the referenced GBA information.

Charlotte Engineers, LLP Building 52 F&R Project No. 61Z-0034 Hampton VAMC, VA Page i of ii May 14, 2021

TABLE OF CONTENTS

SECTION PAGE

EXECUTIVE SUMMARY

1.0 PURPOSE & SCOPE OF SERVICE

2.0 PROJECT INFORMATION

3.0 EXPLORATION PROCEDURES

3.1 SUBSURFACE EXPLORATION

3.2 LABORATORY TESTING

4.0 SUBSURFACE CONDITIONS

4.1 REGIONAL GEOLOGY

4.2 SUBSURFACE CONDITIONS

4.2.1 GENERALIZED SUBSURFACE STRATIGRAPHY

4.2.2 SURFICIAL SOIL

4.2.3 GROUNDWATER DATA

5.0 GEOTECHNICAL DESIGN RECOMMENDATIONS

5.1 GENERAL

5.2 OPTION 1 - SUBSURFACE SOIL UNDERCUT AND REPLACEMENT

5.3 OPTION 2 – RAMMED AGGREGATE PIERS

5.4 CONCRETE SLABS-ON-GRADE

5.5 EXPANSIVE SOIL EVALUATION

5.6 LATERAL EARTH PRESSURES

5.7 SEISMIC DESIGN CRITERIA

5.8 LIQUEFACTION EVALUATIONS

6.0 CONSTRUCTION RECOMMENDATIONS

6.1 GENERAL

6.2 SITE PREPARATION

6.2.1 SITE PREPARATION FOR OPTION 1 - SUBSURFACE SOIL UNDERCUT AND REPLACEMENT

6.2.2 SITE PREPARATION FOR OPTION 2 – RAMMED AGGREGATE PIERS

6.3 CONTROLLED STRUCTURAL FILL

6.4 SHALLOW FOUNDATION CONSTRUCTION

6.5 GROUNDWATER CONDITIONS AND DEWATERING

6.6 TEMPORARY EXCAVATION RECOMMENDATIONS

7.0 CONTINUATION OF SERVICES

8.0 LIMITATIONS

F&R Project No. 61Y-0015 Hampton VAMC, VA Page ii of ii May 14, 2021

APPENDICES

APPENDIX I

GBA Publication “Important Information About This Geotechnical Engineering Report”

APPENDIX II

Site Vicinity Map (F&R Drawing No. 1) Subsurface Exploration Plan (F&R Drawing No. 2)

APPENDIX III

Boring Logs (B-1 through B-6) Subsurface Profile

Key to Boring Log Soil Classifications Unified Soil Classification System

APPENDIX IV

Laboratory Test Results

Page 1 of 20 May 14, 2021

EXECUTIVE SUMMARY

This Executive Summary is provided as a brief overview of our geotechnical engineering evaluations for the project and is not intended to replace more detailed information contained elsewhere in this report.

The soil borings encountered existing fill and portions of the natural Stratum 1 soils that included very soft to soft clay. These materials are judged to be unsuitable for support of the planned structure using conventional shallow foundations. Improvement of these soil conditions will be necessary in order to utilize conventional shallow foundations for support of the building. Two options for improvement of the soil conditions were evaluated by this study. These options included undercut of the unsuitable soils and replacement with compacted backfill material, and the use of rammed aggregate piers.

Option 1, Subsurface Soil Undercut and Replacement, consists of the undercut of the unsuitable soils and replacement with compacted backfill material. Based on the provided ground surface elevation data at the boring locations, the bottom of the undercut will need to extend to elevations ranging between Elev. 2 to Elev. 3.5 over much of the site. A shallower undercut extending to between Elev. 5 and Elev. 6 is expected in the southern portion (B-5 & B-6) of the project site, and also at the northwest corner of the project site (B-1). It is important to recognize that the necessary depth of undercut will vary across the site, and may need to be deeper than currently anticipated in some areas. The depth will need to be determined at the time of the undercut by the geotechnical engineer.

Option 2, Rammed Aggregate Piers, could be considered for subsurface soil improvement.

Ground improvement methods using rammed aggregate piers is expected to result in an allowable bearing pressure of approximately 5,000 psf for conventional shallow foundations. A rammed aggregate pier (RAP) speciality foundation construction company would design the RAP elements for to support the proposed structure within the structural design tolerances (i.e., settlement potential, sliding resistance, uplift capacity, etc.). The specialty foundation construction company would need to be provided the foundation plan for the building with column loads at each planned column location. Internal peer review and final RAP design approval would be by the specialty foundation provider.

Page 2 of 20 May 14, 2021

1.0 PURPOSE & SCOPE OF SERVICE

The Department of Veterans Affairs is in the preliminary planning phases of replacing Building 52 located at the Hampton Veterans Affairs Medical Center. Preliminary planning includes the potential geotechnical requirements necessary for foundation support of the structure. This subsurface exploration and geotechnical engineering evaluation has been performed to explore the subsurface conditions at the planned footprint for the new building at the site.

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

Recommendations for foundation design to include allowable soil bearing pressure for shallow foundation design.

Soil subgrade modulus recommendation for use in slab-on-grade design.

Recommendations regarding seismic site classification and an evaluation regarding potential soil liquefaction due to seismic events. A 100-foot deep boring was not proposed and the evaluations are based on data collected from borings and our experience in the area.

Reuse of on-site soils.

Soil materials and compaction requirements of fill material and structural fill for the support of structures.

Temporary excavation.

Groundwater elevations encountered.

Our scope of services did not include attendance to meetings or participation in conference calls following submittal of our geotechnical report, topographic or field surveying, development of quantity estimates, preparation of plans and specifications, private utility clearance, or an environmental site assessment.

2.0 PROJECT INFORMATION

Project information was provided to F&R via email on December 8, 2020. Included with the email were copies of the RFP, Programmatic Agreement between the Hampton Veteran’s Affairs Medical

Center (HVAMC) and Virginia State Historic Preservation Officer.

The project site is located at the HVAMC in Hampton, Virginia. The new replacement Building 52 will be constructed in the footprint of the existing Building 52 after its demolition. This area is relatively flat and is currently landscaped with grass and some small trees. The general location

Page 3 of 20 May 14, 2021 of the project site is shown on the attached Site Vicinity Map included in Appendix II as Drawing

No. 1.

The new building is expected to have plan dimensions of approximately 50 feet by 190 feet. The replacement building will resemble the demolished building in height consisting of two stories with an attic. Construction may be either structural steel supported masonry or cast in place concrete with exterior brick veneer.

The replacement building is anticipated to be designed to be supported by conventional shallow spread foundations. Structural loads for the new building have not been provided. F&R has assumed maximum column loads of 100 kips and wall loads of 4 kips per linear foot for our evaluations.

As the project is currently in the preliminary planning phases, construction drawings are not available. F&R anticipates that the new site grades will approximate the existing site grades with

2 feet or less of cut and fill required.

3.0 EXPLORATION PROCEDURES

3.1 Subsurface Exploration

A subsurface exploration program was performed on April 1, 2021, in the planned area of the new Building 52. The preliminary exploration consisted of six Standard Penetration Test (SPT) borings, designated as B-1 through B-6, at the approximate locations identified on the Subsurface

Exploration Plan that is included in Appendix II as Drawing No. 2. The boring locations were marked at the site by measuring distances from existing site features.

Soil test borings for were performed using a CME track mounted drill rig equipped with an automatic hammer. The boreholes were advanced to depths of 35 feet utilizing mud rotary drilling techniques. Standard Penetration Tests (SPTs) were performed at the boring locations in general accordance with ASTM D1586, continuously from the existing ground surface to a depth of ten feet, and at five-foot intervals thereafter.

Soil samples were obtained with a standard 1.4” I.D., 2”O.D., and 30” long split-spoon sampler with each SPT being driven with a 140-lb automatic hammer falling 30 inches. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded as Nfield at the time of sampling. The sum of the second and third penetration increments is termed the

SPT value, “N.” The first six-inch increment is used to seat the sampler, and the sampler is often

Page 4 of 20 May 14, 2021 driven a fourth increment (after the SPT is completed) in order to obtain additional information that is used to stratify the soils. A representative portion of each disturbed split-spoon sample was collected with each SPT, placed in a glass jar, and returned to our laboratory for review.

The recovered split-spoon samples were visually classified in accordance with ASTM D2488 by an

F&R engineer at the time of drilling. Recovered split spoon samples were again reviewed in-house by an F&R Senior Engineer. The boring logs provided in Appendix III show the subsurface conditions encountered on the dates and at the approximate locations indicated.

The drill rig used for this project was equipped with an automatic hammer. Research has shown that the Standard Penetration Resistance (N-value) determined by the automatic hammer is different from the N-value determined by the safety hammer method. Most correlations 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 roughly 60 percent of the theoretical energy delivered by a 140-pound hammer falling 30 inches.

Because an automatic hammer was used to perform the SPT tests, the sample blows recorded during drilling (Nfield) have been corrected to equivalent N60 safety hammer values. The N60 values reported on the boring logs included in this report were determined from 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. A value of 1.3 was used for CE in accordance with guidelines provided in the Performance and Use of the Standard Penetration Test in Geotechnical Engineering Practice manual published by the Center for Geotechnical Practice and Research at the Virginia Polytechnic Institute and

State University.

By the nature of the work performed, the drilling activities result in disturbances to the site. The completed boreholes were backfilled with soil upon completion. The borehole backfill may subside at some time following our work. F&R assumes no responsibility for borehole subsidence after completion of the field exploration and departing the site. For continued safety, the boreholes should be occasionally observed by others with any needed additional backfilling then being performed.

Page 5 of 20 May 14, 2021

3.2 Laboratory Testing

A geotechnical laboratory testing program was performed on 7 soil samples that were recovered from the borings. The laboratory tests included natural moisture content determinations (ASTM

D2216) and soil classification tests (ASTM D422 without hydrometer, and Atterberg limits ASTM

D4318. A summary of the laboratory results is provided in the following table with complete test results for the soil samples classified in general accordance with United Soil Classification System

(USCS) provided in Appendix IV.

Table 3.2.1- Soil Classification Test Summary

Boring

No.

Sample

Depth

(ft)

Water

Content

Finer than

No. 200 Sieve

Atterberg Limits USCS Classification

L.L. P.L. P.I.

B-1 5.0 21.1 58.5 28 15 13 CL

B-2 7.0 13.0 9.7 NP NP NP SW-SM

B-3 9.0 23.0 29.2 22 17 6 SC-SM

B-3 14.0 20.9 3.7 NP NP NP SP

B-4 24.0 34.5 22.6 NP NP NP SM

B-5 19.0 30.6 15.4 NP NP NP SM

B-6 5.0 20.9 60.2 33 16 16 CL

Page 6 of 20 May 14, 2021

4.0 SUBSURFACE CONDITIONS

4.1 Regional Geology

The project site lies within the Coastal Plain physiographic province of Virginia, which extends from the Fall Zone eastward to the Atlantic Ocean.

Numerous transgressions and regressions of the Atlantic Ocean have deposited marine, lagoonal, and fluvial (stream lain) sediments. The regional geology is very complex, and generally consists of interbedded layers of varying mixtures of sands, silts, and marine clays.

4.2 Subsurface Conditions

The subsurface conditions discussed in the following paragraphs and those shown on the attached boring logs represent an estimate of the subsurface conditions based on interpretation of the field and laboratory data using normally accepted geotechnical engineering judgments.

The subsurface profile for the project stratigraphy has been prepared for convenience only.

Strata breaks designated on the boring logs and profile represent approximate boundaries between soil types. The transitions between different soil strata are usually less distinct than those shown on the boring logs and profile. Although the 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 soil test borings are shown on the boring logs that are included in Appendix III.

4.2.1 Generalized Subsurface Stratigraphy

Subsurface data obtained by the soil borings is presented in the following Figure, Composite

Subsurface Profile, and in Appendix III.

Page 7 of 20 May 14, 2021

Figure 4.2.1: Composite Subsurface Profile

Composite Profile Notes

Surface: Surficial Soil.

Fill: Very Soft to Firm, Brown, Gray or Yellowish Brown, Silty Fine Sandy CLAY with trace organics and construction debris (CL).

Stratum 1: Very Soft to Firm, Yellowish Brown, Silty Fine Sandy CLAY (CL).

Stratum 2: Loose to Medium Dense, Yellowish Brown, Silty Coarse to Fine SAND with little gravel (SM), Very Loose to Loose, Brown, Clayey Medium to Fine SAND with little silt (SC-

SM),

Very Loose to Loose, Brown, Reddish Brown or Yellowish Brown, Coarse to Fine SAND with trace silt and varying amounts of gravel (SP).

Stratum 3: Very Loose to Medium Dense, Reddish Brown, Silty Fine SAND with varying amounts of marine shell fragments (SM).

Stratum 4: Loose to Medium Dense, Gray, Silty Fine SAND with little marine shell fragments (SM).

Page 8 of 20 May 14, 2021

4.2.2 Surficial Soil

As identified by the boring data from this study, a surficial soil layer was encountered at the boring locations. Surficial soil is typically dark-colored soil material containing roots, fibrous matter, and or other organic components, and is generally unsuitable for engineering purposes.

F&R has not performed any laboratory testing to determine the organic content or other horticultural properties of the observed surficial soil materials. Therefore, the term surficial soil is not intended to indicate suitability for landscaping and or other purposes.

The surficial soil depth provided in this report is based on visual observations and should be considered approximate. We note that the transition from surficial soil to underlying materials may be gradual and, therefore, the observation and measurement of surficial soil is subjective.

Actual surficial soil depths should be expected to vary across the site.

4.2.3 Groundwater Data

The groundwater level at the time of drilling was determined based on the observed moisture content of the recovered soil samples. A summary of the groundwater data is provided in the following Table 4.2.3.

Table 4.2.3: Groundwater Elevation Summary

Boring No.

Ground Surface

Elevation

(ft)

Groundwater

Depth Below

Surface At Time of Drilling

(ft)

B-1 9.5 8

B-2 8.4 7

B-3 9.2 9

B-4 8.5 8

B-5 8.8 8

B-6 9.0 8

Groundwater levels fluctuate with seasonal changes, periods of heavy or little rainfall, tidal fluctuations, and other factors. Therefore, our evaluations of the groundwater level do not reveal the actual year-round groundwater conditions.

Page 9 of 20 May 14, 2021

5.0 GEOTECHNICAL DESIGN RECOMMENDATIONS

5.1 General

The following evaluations and recommendations are based on our observations at the site, interpretation of the field and laboratory data obtained during our subsurface exploration, and our experience with similar subsurface conditions and projects. Subsurface conditions in unexplored locations may vary from those encountered.

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, consideration must be given to the implementation of suitable methods of site preparation, fill compaction, and other aspects of construction.

The existing fill and portions of the natural Stratum 1 soils consist of very soft to soft clay. This material is unsuitable for support of the planned building and floor slab. Two subsurface improvement options have been evaluated in order to utilize conventional shallow foundations at the project site. These options are discussed in the following Sections 5.2 and 5.3.

5.2 Option 1 - Subsurface Soil Undercut and Replacement

One option for improvement of the subsurface soil conditions would be to undercut the existing fill and portions of the Stratum 1 that contain very soft to soft clay.

The depth of the undercut necessary for removal of very soft to soft clay will vary across the site.

The data obtained from the soil test borings indicates that the typical depths of necessary undercut will be on the order of 4 to 5 feet below the existing ground surface, with some areas requiring deeper depths on the order of 6 to 7 feet.

Based on the provided ground surface elevation data at the boring locations, the bottom of the undercut will need to extend to elevations ranging between Elev. 2 to Elev. 3.5 over much of the site. A shallower undercut extending to between Elev. 5 and Elev. 6 is expected in the southern portion (B-5 and B-6) of the project site, and also at the northwest corner of the project site

(B-1).

Page 10 of 20 May 14, 2021

It is important to recognize that the necessary depth of undercut will vary across the site, and may need to be deeper than currently anticipated in some areas. The depth will need to be determined at the time of the undercut by the geotechnical engineer as discussed in Section 6.2.1 of this report.

The undercut material should be replaced with compacted structural fill meeting the soil classification and compaction requirements discussed in Section 6.3 of this report.

Due to the anticipation of groundwater being near the bottom of the undercut, it is recommended that the first lift of backfill be placed in an 18-inch thick lift and be compacted with a medium-sized vibratory roller (10-ton minimum) in the static mode. Field density tests on the first lift should be performed within the top 6 inches of the lift. Following lifts of backfill should be placed and compacted in accordance with the recommendations of Section 6.3 of this report.

Conventional shallow foundations could bear in the compacted backfill material. Shallow foundations could be designed for a net allowable soil bearing pressure of 2,000 psf. A coefficient of friction against sliding (tan δ) of 0.35 could be used for concrete foundations bearing in compacted backfill meeting the soil classification and compaction recommendations provided in

Section 6.3.

Continuous foundations should have a minimum width of 18 inches and column foundations should have a minimum width of 24 inches to reduce the possibility of a “punching” shear failure.

The structural elements should be centered on the foundations to provide uniform load transfer, unless the foundations are proportioned for eccentric loads.

Shallow foundations should bear at a depth of at least 18 inches below the finish exterior site grades to lessen the potential for damage from frost penetration and for bearing capacity considerations.

Based on our evaluations for Option 1, foundation settlements for columns loaded to 100 kips and wall loads loaded to 4 klf were estimated to be on the order of 1-inch or less. Differential settlement between new foundations is expected to be approximately one-half of the total settlement

The magnitude of differential settlements will be influenced by the variation in excavation requirements across the footprint of the structure, the distribution of loads, and the variability of underlying soils.

Page 11 of 20 May 14, 2021

Our settlement analysis was performed on the basis of anticipated structural loading and grading assumptions 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 and actual structural loads

5.3 Option 2 – Rammed Aggregate Piers

Ground improvement using a system consisting of impact pier elements such as GeoPier Rammed

Aggregate Piers® (RAP), can be used to reinforce in-situ soils so that they can support conventional spread and strip footings, mats, and floor slabs. Impact pier elements consist of highly densified, open-graded aggregate that is placed in controlled lifts using a special high-energy mandrel and hopper system. The mandrel is advanced into the ground to the correct depth, filled with stone via the hopper, and withdrawn in one-foot increments by raising the mandrel and hopper assembly a short distance to allow stone to flow into the pier then lowering the mandrel to compact the stone. The mandrel transfers the impact compaction energy to the aggregate through the crowd or downward force developed by the installation equipment.

The impact pier elements can be used in either virgin soils or fills. Some predrilling may be used to facilitate mandrel penetration through obstructions or denser soils. By reinforcing and stiffening the foundation soils with impact pier elements, the improved soil will be capable of supporting a significantly higher allowable bearing pressure, while limiting total and differential settlements to acceptable magnitudes.

With improvement of the bearing soils, shallow foundations supported by the impact pier elements for this project may be designed for a maximum allowable bearing pressure of

5,000 psf with post construction settlement of 1-inch or less.

A RAP speciality foundation construction company would design the RAP elements for to support the proposed structure within the structural design tolerances (i.e., settlement potential, sliding resistance, uplift capacity, etc.). The specialty foundation construction company would need to be provided the foundation plan for the building with column loads at each planned column location. Internal peer review and final RAP design approval would be by the specialty foundation provider.

Page 12 of 20 May 14, 2021

5.4 Concrete Slabs-On-Grade

Concrete ground floor slabs may be placed on properly compacted controlled structural fill supported by approved soil subgrade following site preparation as discussed in Section 6.2. A standard modulus of subgrade reaction (“k”) of 200 pci may be used for the design of the slabs constructed on improved subgrades. Slabs should be structurally isolated (float freely) from the foundations to allow for differential movement between the slabs and the structure.

Isolated, heavy load locations on the slab-on-grade and slab-on-grade locations with large spacing between columns should be individually evaluated by the impact pier designer for necessary intermediate ground improvement. With ground improvement, the modulus of subgrade reaction may be increased per any recommendation from the impact pier designer.

A six-inch thick layer of Virginia Department of Transportation (VDOT) Open Graded Coarse

Aggregate No. 57, or No. 78, or clean sand (SP per Unified Soil Classification System) should be placed beneath the floor slab. This granular base would function as a leveling and load distributing material as well as a capillary break beneath the slab.

A vapor retarder should be used beneath slabs that will be covered by tile, wood, carpet, impermeable coatings, and or if other moisture-sensitive equipment or materials will be in contact with the slab. However, the use of vapor retarders may result in excessive curling of concrete slabs during curing. We refer the concrete slab designer to ACI 302.1R-15, Sections

5.2.3 and 13.11, for further discussion on vapor retarders, curling, and the means to lessen potential concrete shrinkage and curling.

Proper jointing of the concrete slabs-on-grade is also essential to reduce cracking. ACI suggests that unreinforced, plain concrete slabs may be jointed at spacing of 24 to 36 times the slab thickness, up to a maximum spacing of 15 feet. Slab construction should incorporate isolation joints along walls and column locations to allow minor movements to occur without damage.

Utility or other construction excavations in the prepared subgrade should be backfilled to a controlled fill criterion to provide uniform support.

Page 13 of 20 May 14, 2021

5.5 Expansive Soil Evaluation

The existing subgrade soils encountered by the soil test boring were evaluated for shrink-swell

(expansion) potential within the active zone, which typically extends to a depth of approximately three to four feet below the ground surface in the region of the proposed site.

The existing soils within the active zone were found to consist of low plasticity sandy clay (CL), clayey sand (SC), or silty sand (SM) in accordance with the Unified Soil Classification System.

Based on correlations provided in geotechnical literature, the soil within the active zone is judged to have a low potential for shrink-swell activity.

5.6 Lateral Earth Pressures

The following information is provided to aid in analysis of soil loads on below-grade concrete structures. These below-grade wall recommendations should not be correlated for use in any other wall design.

Earth pressures on below grade walls are influenced by structural design of the walls, conditions of wall restraint, methods of construction and or compaction, and the strength of the materials being restrained. The most common conditions assumed for earth retaining wall design are the active and at-rest conditions. Active conditions apply to relatively flexible earth retention structures, such as freestanding walls, where some movement and rotation may occur to mobilize soil shear strength. Walls that are rigidly restrained, such as foundation walls or walls for elevator pits, require design using at-rest earth pressures.

A third condition, the passive state, represents the maximum possible pressure when a structure is pushed against the soil, and is used in wall foundation design to help resist active or at-rest pressures. Because significant wall movements are required to develop the passive pressure, the total calculated passive pressure should be reduced by one-half to two-thirds for design purposes.

A granular material should be used for backfill beside the below grade wet and dry well walls.

This material should meet the requirements for controlled structural fill, as outlined in Section

6.3 of this report.

A moist unit weight of 120 pounds per cubic foot and angle of internal friction of 30° should be used for design calculations for below grade walls backfilled with approved granular materials.

Based on these values, recommended lateral earth pressure coefficients and equivalent fluid

Page 14 of 20 May 14, 2021 pressure parameters for design of below grade walls using controlled structural fill as backfill are provided in the following Table 5.6.1:

Table 5.6.1 - Lateral Earth Pressure Design Data

Backfill and Controlled Structural Fill

Earth Pressure

Conditions Coefficient

Recommended Equivalent Fluid Pressure - Drained

(psf/ft)1

Fully Submerged Equivalent Fluid Pressures

(psf/ft)1

Active (Ka) 0.33 40 81

At-Rest(Ko) 0.50 60 91

Passive (Kp) 3.00 360 --

NOTE: 1 – does not include a factor of safety

An appropriate factor of safety should be applied to the recommended equivalent fluid pressures for below grade wall design.

It is anticipated that the equivalent fluid pressure for a drained condition would be used during the construction phase, provided that site dewatering is maintained. Lateral pressure using the equivalent fluid pressure for a fully submerged (non-drained) condition is recommended on this site for long term post construction conditions.

If heavy equipment, foundations, or other surcharge loads are located a short distance from the edge of below grade walls, they may also exert appreciable additional lateral pressures. As a result, the below grade walls should be designed for a uniform lateral pressure acting over the full height of the wall calculated on the basis of 0.6 times the surcharge pressure in addition to the equivalent fluid pressure recommended in Table 5.6.1.

5.7 Seismic Design Criteria

The seismic site class evaluations presented herein reference American Society of Civil Engineers

(ASCE) 7-10 as specified by Section 1613.3.2 of the International Building Code (IBC) 2015. An evaluation of the top 100 feet of the subsurface soil profile in order to determine the seismic site class is outlined Chapter 20 of ASCE 7-10. However, when soil properties are not known in sufficient detail to a depth of 100 feet, a Site Class D shall be used unless the building official or geotechnical data determines Site Class E or F soils are present at the site.

Page 15 of 20 May 14, 2021

F&R did not encounter soils requiring a Site Class E or F by the borings. It is, therefore, recommended that a Site Class D be used for the project site.

We note that the above provided soil Site Classification is based on information available at the time this report is written. Should the classification be so onerous to the project cost that further study is warranted, we can perform a site-specific geo-physical survey to attain sufficient detail to further define the project’s soil Seismic Site Class Definition. This additional testing would be beyond the currently authorized scope of services for this project.

5.8 Liquefaction Evaluations

An evaluation was performed with respect to potential seismic liquefaction of the subsurface soils encountered by the soil test borings. The evaluation was performed using methods developed by Seed and Idriss (1982) and modified by Youd (2001).

An earthquake magnitude of 5.1 was used in the liquefaction analysis based on data obtained from the USGS Unified Hazard Tool. A peak ground acceleration (PGA) of 0.045g and a peak ground acceleration adjusted for the Site Class D (PGAM) of 0.072g was used based on data obtained from the USGS Seismic Design Maps.

Based on the results of the liquefaction analysis, the calculated safety factor with respect to potential liquefaction was found to be greater than the typically recommended minimum value of 1.1. As such, the site is considered to possess an adequate safety factor with respect to potential seismic liquefaction.

6.0 CONSTRUCTION RECOMMENDATIONS

6.1 General

The principal purpose of this section is to comment in general on the items related to the construction and geotechnical engineering aspects of construction that should be expected for this project. It is recommended that the geotechnical engineer be retained to provide soil engineering services during the actual site preparation and construction phases of the project to perform appropriate evaluations to help assure that conditions encountered during the project are similar to conditions encountered in the boring. The geotechnical engineer can also assist in interpretation of differing subsurface conditions that may be encountered and recommend remedial work, if needed.

Page 16 of 20 May 14, 2021

6.2 Site Preparation

Site preparation will be dependent upon the option selected for subsurface soil improvement.

The following sections provide guidelines for site preparation for the two subsurface soil improvement options that were evaluated by this study.

6.2.1 Site Preparation for Option 1 - Subsurface Soil Undercut and Replacement

Site preparation for Option 1, Subsurface Soil Undercut and Replacement, includes the removal of the existing fill material and portions of the natural Stratum 1 soils that contain very soft to soft clay. This recommended undercut should extend horizontally a minimum of 5 feet past the outside edge of shallow foundations. The anticipated depth of the undercut is discussed in

Section 5.2 of this report.

The undercut operations should be observed and documented by the geotechnical engineer. The engineer should verify that the very soft to soft clay has been properly removed from the undercut area prior to placement of backfill.

Construction equipment should not travel directly on the exposed natural soils at the base of the undercut. The initial lifts of backfill should be end-dumped and spread with a dozer. As recommended in Section 5.2, the first lift of backfill should be 18 inches thick and compacted with a medium-sized vibratory roller (10-ton minimum) in the static mode. Subsequent lifts should be 12-inches thick, or less, and compacted with the roller in the vibratory mode.

Large construction equipment, such as loaded dump trucks hauling backfill material, should not be allowed on the construction pad until a minimum of 3 feet of backfill has been placed and compacted.

6.2.2 Site Preparation for Option 2 – Rammed Aggregate Piers

Site preparation for Option 2 should be in accordance with the recommendations provided by the RAP speciality foundation construction company.

At a minimum, site preparation should include the complete removal of abandoned foundations, abandoned underground utilities and structures, surficial soil, tree stumps, roots and any deleterious materials encountered.

Page 17 of 20 May 14, 2021

6.3 Controlled Structural Fill

Controlled structural fill material for backfill for undercut excavations and used to raise the site grades should be non-expansive and free of organic matter, debris, and particles larger than two inches in size. Proposed fill material should be subjected to laboratory tests consisting of, but not necessarily limited to, moisture density determinations (ASTM D698), Atterberg limits (ASTM

D4318), and sieve analysis (ASTM D422). These tests are needed for quality control during compaction and to determine if the fill material is acceptable. Controlled structural fill should classify per the Unified Soil Classification System (USCS) as SW, SP, SP-SM, or SM with a maximum of 20 percent fines passing the No. 200 sieve.

Fill materials should be placed in horizontal lifts with maximum height of 12 inches loose measure and compacted with a vibratory compactor operating in vibratory mode, except as otherwise noted in Sections 5.2 and 6.2.1 of this report. In confined areas such as utility trenches or below grade walls, portable compaction equipment and thin lifts of 3 inches to 4 inches may be required to achieve specified degrees of compaction.

The structural fill should be compacted to at least 95 percent of the standard Proctor (ASTM

D698) maximum dry density in areas where structures are to be supported. In general, we recommend that the moisture content of fill soils be maintained within three percentage points of the optimum moisture content as determined from the standard Proctor maximum dry 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. Field density tests to verify fill compaction should be performed at an appropriate frequency for the area being tested, with a minimum of three tests per lift. In confined areas, such as trench backfill, a greater frequency may be required. Testing areas may be increased and the frequencies reduced based on the size of the structure and discretion of the geotechnical engineer.

Page 18 of 20 May 14, 2021

6.4 Shallow Foundation Construction

The geotechnical engineer or his representative should observe shallow foundation subgrades prior to reinforcement steel placement.

The actual need for, and extent of, remedial procedures should be based on field observations made by the geotechnical engineer at the time of construction. Loose or soft soils between impact pier locations may need localized undercutting. Any over-excavated material may be replaced with controlled structural fill to the planned foundation bearing level. Placement and compaction of controlled structural fill should be in accordance with the recommendations provided in Section 6.3 of this report. No. 57 open graded crushed stone seated in-place with the excavator bucket may be used in-lieu of controlled structural fill. The undercut excavations should be backfilled on a daily basis.

Excavations for foundations should be made in such a way to provide bearing surfaces that are firm and free of loose, soft, wet, or otherwise disturbed soils. If such materials are allowed to remain below foundations that are not impact pier supported, localized settlement may occur.

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. Foundation concrete should not be placed on frozen or saturated subgrades.

6.5 Groundwater Conditions and Dewatering

Groundwater for the purpose of this report is defined as water encountered below the existing ground surface. Based on the data obtained during our exploration program, undercut excavations that are part of the recommendations provided in Section 5.2, Option 1 - Subsurface

Soil Undercut and Replacement, may encounter groundwater where deeper excavation depths are required. The contractor should be prepared to dewater during excavation and initial backfilling operations if groundwater is encountered. It is anticipated that dewatering could be accomplished using conventional sump-and-pump methods; however, the selection of the dewatering system should be made by the contractor.

A perched groundwater condition was judged to occur as result of a recent period of wet weather. Perched groundwater at the site was judged to from 1 to 2 feet below the existing ground surface.

Page 19 of 20 May 14, 2021

6.6 Temporary Excavation Recommendations

Excavations required for 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.

7.0 CONTINUATION OF SERVICES

F&R recommends that we 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.

Additionally, we request the opportunity to review the foundation plans and project specifications when these construction documents approach completion. This review evaluates whether the recommendations and comments provided herein have been understood and properly implemented. The above listed services are not part of the currently authorized scope of services.

8.0 LIMITATIONS

There are important limitations to this and all geotechnical studies. Some of these limitations are discussed in the information prepared by Geoprofessional Business Association (GBA), which is included in Appendix I. We recommend that you review the GBA information.

This report has been prepared for the exclusive use of Charlotte Engineers, LLP, or their agents, for the specific application to the replacement Building 52 Project at the Hampton Veterans

Affairs Medical Center in Hampton, Virginia, in accordance with generally accepted soil and foundation engineering practices. No other warranty, express or implied, is made.

Page 20 of 20 May 14, 2021

Our conclusions and recommendations are based on design information furnished to us at the time the work was performed, the data obtained from the previously described subsurface exploration program, and generally accepted geotechnical engineering practice. The findings and recommendations do not reflect variations in subsurface conditions, which could exist in unexplored areas of the site.

Regardless of the thoroughness of a subsurface exploration, there is the possibility that conditions in other areas will differ from those at the boring location, that conditions are not as anticipated by the designers, or that the construction process has altered the soil conditions.

Therefore, our experienced geotechnical engineers should evaluate foundation construction to verify that the conditions anticipated in design actually exist. Otherwise, we assume 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 project, the recommendations presented in this 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

GBA Publication

“Important Information About This

Geotechnical Engineering Report”

Geotechnical-Engineering Report Important Information about This

Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.

While you cannot eliminate all such risks, you can manage them. The following information is provided to help.

The Geoprofessional Business Association (GBA) has prepared this advisory to help you – assumedly a client representative – interpret and apply this geotechnical-engineering report as effectively as possible. In that way, clients can benefit from a lowered exposure to the subsurface problems that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed below, contact your GBA-member geotechnical engineer.

Active involvement in the Geoprofessional Business Association exposes geotechnical engineers to a wide array of risk-confrontation techniques that can be of genuine benefit for everyone involved with a construction project.

Geotechnical-Engineering Services Are Performed for Specific Purposes, Persons, and Projects Geotechnical engineers structure their services to meet the specific needs of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil-works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client. Those who rely on a geotechnical-engineering report prepared for a different client can be seriously misled. No one except authorized client representatives should rely on this geotechnical-engineering report without first conferring with the geotechnical engineer who prepared it. And no one

– not even you – should apply this report for any purpose or project except the one originally contemplated.

Read this Report in Full Costly problems have occurred because those relying on a geotechnical-engineering report did not read it in its entirety. Do not rely on an executive summary. Do not read selected elements only. Read this report in full.

You Need to Inform Your Geotechnical Engineer about Change Your geotechnical engineer considered unique, project-specific factors when designing the study behind this report and developing the confirmation-dependent recommendations the report conveys. A few typical factors include:

• the client’s goals, objectives, budget, schedule, and risk-management preferences;

• the general nature of the structure involved, its size, configuration, and performance criteria;

• the structure’s location and orientation on the site; and

• other planned or existing site improvements, such as retaining walls, access roads, parking lots, and underground utilities.

Typical changes that could erode the reliability of this report include those that affect:

• the site’s size or shape;

• the function of the proposed structure, as when it’s changed from a parking garage to an office building, or from a light-industrial plant to a refrigerated warehouse;

• the elevation, configuration, location, orientation, or weight of the proposed structure;

• the composition of the design team; or

• project ownership.

As a general rule, always inform your geotechnical engineer of project changes – even minor ones – and request an assessment of their impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical engineer was not informed about developments the engineer otherwise would have considered.

This Report May Not Be Reliable Do not rely on this report if your geotechnical engineer prepared it:

• for a different client;

• for a different project;

• for a different site (that may or may not include all or a portion of the original site); or

• before important events occurred at the site or adjacent to it; e.g., man-made events like construction or environmental remediation, or natural events like floods, droughts, earthquakes, or groundwater fluctuations.

Note, too, that it could be unwise to rely on a geotechnical-engineering report whose reliability may have been affected by the passage of time, because of factors like changed subsurface conditions; new or modified codes, standards, or regulations; or new techniques or tools. If your geotechnical engineer has not indicated an “apply-by” date on the report, ask what it should be, and, in general, if you are the least bit uncertain about the continued reliability of this report, contact your geotechnical engineer before applying it. A minor amount of additional testing or analysis – if any is required at all – could prevent major problems.

Most of the “Findings” Related in This Report Are Professional Opinions Before construction begins, geotechnical engineers explore a site’s subsurface through various sampling and testing procedures.

Geotechnical engineers can observe actual subsurface conditions only at those specific locations where sampling and testing were performed. The data derived from that sampling and testing were reviewed by your geotechnical engineer, who then applied professional judgment to form opinions about subsurface conditions throughout the site. Actual sitewide-subsurface conditions may differ – maybe significantly – from those indicated in this report. Confront that risk by retaining your geotechnical engineer to serve on the design team from project start to project finish, so the individual can provide informed guidance quickly, whenever needed.

This Report’s Recommendations Are Confirmation-Dependent The recommendations included in this…