Atch 8_Geotechnical Report_MUHJ 23 4038_Convert Old Steam Plant_Facility 655.pdf

Report Cover Page

JBLE – Old Steam Plant

Repair Facility 655 Geotechnical Engineering Report

August 5, 2024 | Terracon Project No. K4235092

Hampton, Virginia

Prepared for:

Dills Architects

1432 N. Great Neck Road, Suite

Virginia Beach, VA 23454

701 Alexander Lee Parkway

Williamsburg, VA 23185

P (757) 564-6452

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

August 5, 2024

Dills Architects

1432 N. Great Neck Road, Suite 204

Virginia Beach, VA 23454

Attn: Anna D. Campbell

P: (757) 496-4926

E: acampbell@dillsarchitects.com

Re: Geotechnical Engineering Report

JBLE – Old Steam Plant Repair Facility 655

655 Hunting Avenue

Hampton, Virginia

Terracon Project No. K4235092

Dear Ms. Campbell:

We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. PK4235092 dated

August 15, 2023. Authorization to perform this work was received from the client in the form of an official notice to proceed letter dated October 6, 2023. During the course of completing our scope of work, it was determined that additional field work would be required. Authorization to perform this supplementary work was received from the client in the form of an email notice to proceed on April 23, 2024. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon

James R. Wheeler, P.G. D. Mark Scholefield, P.E.

Principal Senior Principal

Virginia Lic. No. 033932 https://na3.documents.adobe.com/verifier?tx=CBJCHBCAABAAmcf2HG0_QsxQZCK8cQ9ZzkoftNKHAakr

Geotechnical Engineering Report

JBLE – Old Steam Plant Repair Facility 655 | Hampton, Virginia x

August 5, 2024 | Terracon Project No. K4235092

Facilities | Environmental | Geotechnical | Materials i

Table of Contents

Introduction Project Description Site Conditions Geotechnical Characterization

Field Exploration Field and Laboratory Testing Soil Classification and Index Testing

Geologic Setting Seismic Site Class Geotechnical Overview Earthwork

Demolition Site Preparation Subgrade Preparation Existing Fill Excavation Fill Material Types Fill Placement and Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Specialty Foundations Helical Piers

Ground Improvement Floor Slabs General Comments

Figures

GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans

Exploration and Laboratory Results

Supporting Information

Facilities | Environmental | Geotechnical | Materials ii

Note: This report was originally delivered in a web-based format. Blue Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/ http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our Subsurface Exploration and Geotechnical

Engineering services performed for the proposed Old Steam Plant Repair Facility 655 project located at 655 Hunting Avenue in Hampton, Virginia. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Groundwater conditions

■ Seismic site classification per IBC

■ Site preparation and earthwork

■ Demolition considerations

■ Dewatering considerations

■ Foundation design and construction

■ Floor slab design and construction

The geotechnical engineering Scope of Services for this project included the advancement of test borings, laboratory testing, engineering analyses, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and

Exploration Plans. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs and as separate graphs in the Exploration and Laboratory Results attachment.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Facilities | Environmental | Geotechnical | Materials 2

Item Description

Information

Provided

An email request for proposal was provided by Anna Campbell on August 1, 2023. The request included a Statement of Work.

In addition, we participated in a Teams meeting with the

Structural Engineer, Peyton Mulé with NRW Engineering, who provided further understanding of the intended structural improvements associated with this project and provided us with a defined scope of work and boring location plan sent in a follow up email on August 9, 2023.

An additional email received from Peyton Mulé on May 31, 2024, provided further information about new features to be included in the project.

Project

Description

The project includes a full renovation and additions to the existing Facility 655 structure, which is currently identified as the old steam plant, into office space for the ACC CE staff. This is expected to include a minimum of 10 offices, a conference room, a break room, restrooms, mezzanines, electrical room, and storage areas.

Proposed

Improvements

Proposed improvements will likely include a new roofing system, raising the floor level as much as possible and still allow for two levels, demolish and remove steel steam stacks, repair all brick, windows, and other exterior elements, repair any structural issues, and full replacement of the electrical, mechanical, and plumbing systems.

The proposed improvements will also include adding two, one-story additions to the existing structure, one for additional office space and the other for an electrical room.

In order to facilitate the proposed improvements, new foundations, slabs, and a ramp and landing will be required along the exterior.

Existing Building

This is an existing 4,522 ft2 structure that was originally constructed in 1941.

The structure is a one to two story structure with brick load bearing walls with an industrial floor supported on-grade that includes floor trenches. One side of the structure includes several bay/overhead doors.

Existing foundations are unknown but considering the observed subsurface conditions and relatively good condition of the existing brick load bearing walls it is suspected that the existing foundations are likely pile supported.

Facilities | Environmental | Geotechnical | Materials 3

Item Description

Finished Floor

Elevation

Finished floor elevation will be raised approximately 1 foot from its current elevation.

Maximum Loads

Anticipated structural loads were provided by the Structural

Engineer in an email on May 31, 2024, which are as follow:

■ Elevated Storage Floor Columns: 23 kips

■ Office Addition Walls: 0.5 kips per linear foot

■ Electrical Room Addition Walls: 0.2 kips linear foot

■ Slabs and Exterior Ramps: 150 pounds per square foot

(psf)

Grading/Slopes No exterior grading is anticipated. Interior grades will be raised approximately 1 foot.

Building Code 2018 IBC

Terracon should be notified if any of the above information is inconsistent with the planned construction as modifications to our recommendations may be necessary.

Site Conditions

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel

Information

The project is located at 655 Hunting Avenue within Joint Base

Langley-Eustis in Hampton, Virginia.

Latitude/Longitude 37.08306, -76.34193

See Site Location

Existing

Improvements

Existing steam plant structure surrounded by asphalt pavement areas.

Current Ground

Cover

Interior – concrete slabs.

Exterior – asphalt pavements.

Existing

Topography

Based on USGS topography mapping, exterior grades surrounding the existing structure are at an elevation of about 5 feet (NAVD 88).

Facilities | Environmental | Geotechnical | Materials 4

Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration and Laboratory Results and the GeoModel can be found in the

Figures attachment of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model

Layer Layer Name General Description

1 SURFICIAL Asphalt underlain by Aggregate Base or Concrete

2 FILL

Silty and Clayey Sand (SM, SC) and Sandy lean Clay

(CL), both containing varying amounts of Gravel and/or other deleterious material

3 SAND Silty and Clayey Sand (SM, SC)

4 YORKTOWN

Silty Sand (SM), contains marine shell fragments, “Yorktown Formation”

The presence of groundwater at the boring locations was examined during drilling as observed through the relative wetness of the recovered soil samples during the drilling operations. During drilling operations, fluid (clay-water slurry) is introduced into the bore hole generally impairing the ability to accurately determine groundwater levels.

The groundwater was estimated to occur at depths ranging from about 4 to 5 feet below existing grades at the SPT boring locations at the time of drilling, corresponding to elevations of approximately EL 0 to 1 foot (NAVD 88).The boreholes were backfilled upon completion for safety considerations and the surface was capped with asphalt or concrete as applicable.

Groundwater conditions will vary with environmental variations, tidal fluctuations, and seasonal conditions, such as the frequency and magnitude of rainfall patterns and man-made influences, such as existing swales, drainage ponds, underdrains and areas of covered soil (paved parking lots, sidewalks, etc.). In the project’s area, seasonal groundwater fluctuations are common and given the site’s proximity to Back River the groundwater may be influenced by tidal fluctuations. We recommend that the contractor determine the actual groundwater levels at the time of the construction to determine groundwater impact on the construction procedures, if necessary.

Facilities | Environmental | Geotechnical | Materials 5

Field Exploration

In order to explore the general subsurface soil types and to aid in developing associated foundation design parameters, the following exploration program was performed:

◼ Seven (7) pavement cores (designated as SB-1 through SB-7) were cored through the existing pavement around the exterior of the existing steam plant building in order to facilitate the soil borings.

◼ Subsequently, seven (7) 20- to 50-foot deep Standard Penetration Test (SPT) borings (designated as SB-1 through SB-7) were drilled within the pavement core holes located around the exterior of the existing steam plant building.

◼ Initially, four (4) concrete cores (designated as C-1 through C-4) were cored in the existing slab within the existing steam plant building. At core locations C-1 and C-2, the cores could not be advanced deep enough to penetrate through the entirety of the slab due to equipment limitations at that time. At core locations C-

2 and C-3, a hand auger boring was advanced to refusal depths, 2 feet and 1.4 feet below existing grades, respectively.

◼ Given the results of our initial cores within the slab, an additional nine (9) cores

(designated as C-1A, C-2A, C-3A, C-4A, and C-5 through C-9) were added to our scope of work. Cores C-1A, C-2A, C-3A, and C-4A were cored directly adjacent to cores C-1, C-2, C-3, and C-4, respectively. The remaining cores were cored at locations directed by the Structural Engineer. Upon completion of these cores, a hand auger boring was advanced to depths ranging from 3 to 3.5 feet below existing grades. Hand auger refusal was encountered at a depth of 2 feet below existing grades at core location C-4A, where brick was encountered.

◼ Review of historical site data.

The SPT borings were performed with the use of rotary wash “mud” drilling procedures in general accordance with ASTM D 1586. The tests were performed continuously from the existing ground surface to a depth up to 12-feet, and at 5-foot intervals thereafter starting at a depth of 13-feet. The soil samples were obtained with a standard 1.4” I.D., 2” O.D., 30” long split-spoon sampler. The sampler was driven with blows of a 140 lb.

hammer falling 30 inches, using an automatic hammer. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded and is shown on the boring logs. The sum of the second and third penetration increments is termed the

SPT N-value (uncorrected for automatic hammer). A representative portion of each disturbed split-spoon sample was collected with each SPT, placed in a glass jar, sealed, labeled, and returned to our laboratory for review. All SPT boreholes that were completed around the exterior of the existing building were backfilled upon completion with the drilling spoils and the surface was capped with asphalt.

Facilities | Environmental | Geotechnical | Materials 6

The soil borings completed inside the existing building were performed using a hand auger extending to depths ranging from 1.4 to 3.5 feet below existing grades. Auger refusal was encountered at borings C-2, C-3, and C-4A. Refusal encountered at boring

C-4A was due to encountering brick below the slab. The refusal encountered at other locations was unidentifiable. Representative samples were collected while advancing the hand augers generally at 2-ft intervals. The hand auger borings were backfilled with washed Sand and the surface was capped with concrete. Where cores were completed with no subsequent hand auger, the core holes were backfilled with concrete only.

The boring and core locations were established by the Client and Structural Engineer prior to mobilization. The boring and core locations were marked in the field by a representative of Terracon with a handheld GPS device and by corroborating the location with easily identifiable landmarks. The approximate boring and core locations are shown in the Figures attachment of this report.

Field and Laboratory Testing

Soil testing provided by Terracon was performed in accordance with American Society for Testing and Materials (ASTM) standards. All soils and materials tests were performed in our AASHTO re:source and US Army Corps of Engineers certified Williamsburg, Virginia laboratory.

Soil Classification and Index Testing

Representative portions of all soil samples collected during drilling operations were labeled, preserved and transferred to our laboratory in accordance with ASTM D4220 for classification and analysis. Soil descriptions on the boring logs are provided using visual-manual methods in general accordance with ASTM D2488 using the Unified Soil

Classification System (USCS).

Soil samples that were selected for index testing were classified in general accordance with ASTM D2487. It should be noted that some variation can be expected between samples classified using the visual-manual procedure (ASTM D2488) and the USCS

(ASTM D2487). A summary of the soil classification system is provided in the

Supporting Information attachment of this report.

Representative split-spoon soil samples were selected and subjected to natural moisture, #200 sieve wash, and Atterberg Limits testing in order to corroborate the visual classification. These test results, along with the soil test boring logs are presented in the

Exploration and Laboratory Results attachment of this report.

Facilities | Environmental | Geotechnical | Materials 7

Geologic Setting

The project site is located within the Atlantic Coastal Plain physiographic province.

Bedrock of the Late Mesozoic age is present at depths of greater than 2,000 ft, and is overlain by Lower and Upper Cretaceous, Tertiary, Pleistocene and Recent Sediments.

Across the outer Coastal Plain, the Pliocene age Yorktown Formation of the Tertiary

Period is widespread, occurring from Maryland to North Carolina. Its age is estimated between 4.8 million and 2.8 million years and is estimated to have been deposited during three transgressive episodes. The depositional environment was shallow marine in nature, consisting of inner shelf, barrier-island, estuarine and lagoonal patterns. The

Yorktown Formation is a glauconitic, fossiliferous, Silty to Clayey greenish-gray fine

Sand. This material has been pre-consolidated by an increased effective overburden pressure generated due to a drop in the sea level at the end of the Tertiary Period, and by previously overlying sediments, which eroded away as the sea level subsequently lowered.

As sea levels rose during the Pleistocene Epoch of the Quaternary Period, areas within the project limits were filled and overlain by soils of the Tabb Formation; Lynnhaven

Member, which is composed of fluvial and estuarine deposits. The geologic stratigraphy encountered in our subsurface explorations generally consisted of marine deposited

Sands and Clays of this formation.

Seismic Site Class

The seismic design requirements for buildings and other structures are based on Seismic

Design Category. Site Classification is required to determine the Seismic Design

Category for a structure. The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of

ASCE 7 and the International Building Code (IBC). Based on the soil properties observed at the site and as described on the exploration logs and results, our professional opinion is for that a Seismic Site Classification of D be considered for the project. Subsurface explorations at this site were extended to a maximum depth of 50 feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

Facilities | Environmental | Geotechnical | Materials 8

Geotechnical Overview

The subsurface materials below the pavements and slabs consisted of undocumented fill generally comprised of Sand (SM, SC) and Clay (CL), both of which contained varying amounts of Gravel and/or deleterious material (such as asphalt, brick, coal, and/or wood fragments). The undocumented fill extended to depths ranging from 4 to 16.5 feet below existing grades at the SPT boring locations completed around the exterior of the existing steam plant building. Borings completed within the inside of the existing building (which extended to depths ranging from 1.4 to 3.5 feet below existing grades or finish floor elevation) were terminated within the undocumented fill.

Underlying the undocumented fill and extending to SPT boring termination depths (20 to

50 feet below existing grades), the soils were generally comprised of very loose to medium dense Sand (SM, SC). The groundwater was estimated to occur at depths ranging from about 4 to 5 feet below existing grades at the SPT boring locations at the time of drilling, corresponding to elevations of approximately EL 0 to 1 foot (NAVD 88).

There is an inherent risk if foundations, slabs, and utilities were to be supported on the undocumented fill due to the possibility of compressible fills and/or unsuitable material within or buried by the fill, present at this site that may not have been observed within the soil borings. In fact, deleterious materials were encountered within some of the undocumented fill, such as asphalt, brick, coal, and wood fragments. Undocumented fill extended to depths ranging from 4 to 16.5 feet below existing grades at the SPT boring locations. Foundations and slabs supported on undocumented fill could experience excessive total and/or differential settlements that may result in structural damage.

Utilities bearing on undocumented fill could also experience excessive settlement that could result in broken utilities, particularly where connecting new utilities to existing utilities.

For the reasons previously discussed, it is recommended to support all new foundations and slabs on a deep foundation system or utilize a ground improvement system so that any new foundations and slabs are supported by the underlying natural soils or improved, suitable undocumented fill material.

Ground improvement options (such as rigid inclusions or rammed aggregate piers) or other deep foundation systems (such as timber piles or concrete piles) may be suitable to support the new foundations; however, considering the site constraints on this project, such as clearance heights for work inside the existing building, it is expected that most of the options may not be practical. Given the site constraints, helical piers may be one of the most practical approaches to support the new foundations and slabs, which are further discussed in the Helical Piers section in this report. Alternatively, pressure injection grouting is a ground improvement technique that could also be utilized instead of helical piers to support the new foundations and slabs. Pressure injection grouting is further discussed in the Ground Improvement section in this report.

Facilities | Environmental | Geotechnical | Materials 9

If a deep foundation system is utilized for this project, it is recommended to have all new utilities hung from or fixed to pile supported features to also avoid the risk of excessive settlements that could potentially damage the utilities.

This would not be required if pressure injection grouting is utilized instead of a deep foundation system. Also, if a deep foundation system is utilized is it recommended to verify the existing foundations are also supported on a deep foundation system, otherwise differential settlement would be of concern.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration Results section), engineering analyses, and our current understanding of the proposed project. The General

Comments section provides an understanding of the report limitations.

Earthwork

Earthwork is anticipated to include demolition, excavations, and structural fill placement.

The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations and floor slabs.

Demolition

The proposed renovations will be constructed within and around the existing steam plant building, which will require removal of the slabs, some pavements, abandoned utilities, and other infrastructure. We recommend the existing interior slabs and any abandoned utilities be removed inside the existing building. For areas outside the existing building footprint, existing pavements, below grade structures, and abandoned utilities should be removed where they conflict with new additions, ramps, and proposed utilities.

Site Preparation

Prior to placing fill, the existing interior slab should be removed. Also, pavements where they coincide with new additions and ramps to be constructed around the perimeter of the existing building should be removed as well. Pavement removal should extend at least 5 feet beyond the lateral limits of the new additions and ramps.

Facilities | Environmental | Geotechnical | Materials 10

Although no evidence of underground facilities (such as septic tanks, cesspools, and basements) were observed during the exploration and site reconnaissance, such features could be encountered during construction. Utility markings indicating the presence of underground utilities at this site were observed at the time of our field exploration. Also, the presence of undocumented fill was encountered at all of our boring locations. If unexpected fills that are deemed unsuitable by the Geotechnical Engineer or underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction.

Subgrade Preparation

The subgrade should be evaluated by the Geotechnical Engineer or representative.

Where accessible the subgrade should be proofrolled with an adequately loaded vehicle such as a fully loaded tandem-axle dump truck. This profrolling is expected to be limited to areas where the ramp and additions will be located around the exterior of the existing building. The proofrolling should be performed under the observation of the Geotechnical

Engineer or representative. Areas inaccessible to proofrolling, the subgrade should be probed. Areas excessively deflecting under the proofroll or considered unstable based on excessive probe penetrations should be delineated and subsequently addressed by the

Geotechnical Engineer. Such areas should either be removed or modified by treating/applying/mixing. Excessively wet or dry material should either be removed, or moisture conditioned and recompacted.

All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of 10 inches, moisture conditioned as necessary, and compacted per the compaction requirements in this report. Compacted structural fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation construction.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

Facilities | Environmental | Geotechnical | Materials 11

Existing Fill

As noted in Geotechnical Characterization, the soil borings encountered previously placed undocumented fill to depths extending up to 16.5 feet below existing site grades at the boring locations. We have no records to indicate the degree of control, and consequently, the fill is considered unreliable for support of foundation loads. For these reasons we recommend that all foundation and slabs be supported on a deep foundation system, likely consisting of helical piers due to site constraints (height clearance inside existing building). Also, new utilities should be hung from or fixed to pile supported features. Any grade supported features could be subjected to damaging settlements.

Excavation

We anticipate that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill . Structural fill is material used below, or within 5 feet of structures, pavements or constructed slopes.

Existing, on-site materials are not considered suitable for re-use as structural fill.

Imported Fill Materials: Imported fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

Soil Type 1

USCS

Classification

Acceptable Parameters

(for Structural Fill)

Granular

GW, GP, GM, GC,

SW, SP, SP-SM, SM

Less than 20% passing No. 200 sieve

Liquid Limit less than 20

Plasticity Index less than 6

1. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site. Additional geotechnical consultation should be provided prior to use of uniformly graded gravel on the site.

Facilities | Environmental | Geotechnical | Materials 12

Fill Placement and Compaction Requirements

Structural fill should meet the following compaction requirements.

Item Structural Fill

Maximum Lift

Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

4 to 6 inches in loose thickness when hand-guided equipment

(i.e. jumping jack or plate compactor) is used

Minimum

Compaction

Requirements 1

98% of max. below foundations and within 1 foot of finished pavement subgrade

95% of max. above foundations, below floor slabs, and more than 1 foot below finished pavement subgrade

Water Content

Range 1 -2% to +2% of optimum

1. Maximum density and optimum water content as determined by the Standard Proctor test

(ASTM D698).

Utility Trench Backfill

It is recommended to have all new utilities hung from or fixed to pile supported features due to the risk associated with utilities bearing solely on undocumented fill that could potentially experience excessive settlement and result in breaks in the utility line(s). It is noted that hanging or fixing utilities to pile supported features would not be required if pressure injection grouting is utilized on this project in lieu of piles.

Trench excavation should not be conducted below a downward 1:1 projection from existing foundations without engineering review of shoring requirements and geotechnical observation during construction.

On-site materials are not considered suitable for backfill of utility and pipe trenches.

Trench backfill should be mechanically placed and compacted as discussed earlier in this report. Compaction of initial lifts should be accomplished with hand-operated tampers or other lightweight compactors. Where trenches are placed beneath slabs or footings, the backfill should satisfy the gradation and expansion index requirements of engineered fill discussed in this report. Flooding or jetting for placement and compaction of backfill is not recommended.

Facilities | Environmental | Geotechnical | Materials 13

For low permeability subgrades, utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the building. The trench should provide an effective trench plug that extends at least 5 feet from the face of the building exterior. The plug material should consist of cementitious flowable fill or low permeability clay. The trench plug material should be placed to surround the utility line. If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

Grading and Drainage

All grades must provide effective drainage away from the building during and after construction and should be maintained throughout the life of the structure. Water retained next to the building can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential floor slab and/or foundation movements, cracked slabs and walls, and roof leaks. The roof should have gutters/drains with downspouts that discharge onto splash blocks at a distance of at least 10 feet from the building.

Exposed ground should be sloped and maintained at a minimum 5% away from the building for at least 10 feet beyond the perimeter of the building. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork. After building construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance program. Where paving or flatwork abuts the structure, a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Earthwork Construction Considerations

Shallow excavations for the proposed structure are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of grade-supported improvements such as floor slabs and pavements. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

Facilities | Environmental | Geotechnical | Materials 14

The groundwater table could affect excavation efforts, especially for overexcavation and replacement of lower strength soils. A temporary dewatering system consisting of sumps with pumps may be necessary to achieve the recommended depth of excavation or overexcavation depending on groundwater or temporary perched water conditions at the time of construction.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part

1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

Excavations or other activities resulting in ground disturbance have the potential to affect adjoining properties and structures. Our scope of services does not include review of available final grading information or consider potential temporary grading performed by the contractor for potential effects such as ground movement beyond the project limits. A preconstruction/ precondition survey should be conducted to document nearby property/infrastructure prior to any site development activity. Excavation or ground disturbance activities adjacent or near property lines should be monitored or instrumented for potential ground movements that could negatively affect adjoining property and/or structures.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (pavements and slabs), as well as proofrolling and mitigation of unsuitable areas delineated by the proofroll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,000 square feet of compacted fill in the building areas (minimum 3 tests per lift). Where not specified by local ordinance, one density and water content test should be performed for every 100 linear feet of compacted utility trench backfill and a minimum of one test performed for every 12 vertical inches of compacted backfill.

Facilities | Environmental | Geotechnical | Materials 15

It is recommended to implement a test pile program that is monitored by the

Geotechnical Engineer if a deep foundation system, such as helical piers, is utilized on this project. This is further outlined in the Helical Pier section in this report. In addition, it is recommended to have production pile installation monitored by the

Geotechnical Engineer as well.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

Specialty Foundations

Helical Piers

As previously indicated, there is an inherent risk of potential damaging settlements to occur if foundations and slabs were to be supported on the undocumented fill present at this site. Consequently, it is recommended to support all new foundations and slabs on a deep foundation or ground improvement system. Given the site constraints, we are recommending using helical piers to support the new foundations and slabs, but other options could be considered. We request that the Geotechnical Engineer be consulted once the foundation design has been completed.

We have conducted preliminary evaluations for Helical Anchor capacity as it would apply to the subsurface conditions noted at this site. Due to the relative slenderness of a typical Helical Anchor shaft, column buckling may be of concern. Therefore, a Round

Shaft section was analyzed. Buckling stability may also be achieved by grout-column modification of typical Square Shaft anchors if desired.

For preliminary design considerations, it is anticipated that a two to three-helix, round-shaft Anchor, installed to a depth of approximately 25 to 35 feet below existing grade, should be able to achieve an allowable compression capacity of approximately 10 to 15 kips. It is recommended that a minimum safety factor of 2.5 in compression and 3 in tension should be incorporated in the pile design. It should be emphasized, however, that Helical Anchor design is proprietary to the specific manufacturer, and that final design of such foundations should be carried out by the selected manufacturer’s professional representative. Also, since undocumented fill is present at this site, it is possible that refusal conditions are encountered during pile installation if obstructions are encountered within or directly below the undocumented fill. The pile designer should take this into consideration and consider having provisions in place, such as possibly pre-augering if needed, if shallow refusal conditions are encountered.

Facilities | Environmental | Geotechnical | Materials 16

We recommend the installation of at least six (6) test piles and performing a static load test at two of these locations selected by the Geotechnical Engineer to confirm the design helical anchor depth and capacity. The static load tests should be performed no sooner than 7 days after pile installation. The load tests should be performed in accordance with ASTM D 1143 - Quick Test Method for Piles Under Static Axial

Compressive Load and should also run uplift and lateral tests if these types of loads are to be applied. The static load tests should be performed under the observation of the

Geotechnical Engineer or his representative who should record the dial gage readings.

The records of the pile load test should be reviewed by the Geotechnical Engineer and the Structural Engineer to verify the pile design criteria. The production piles should be installed using the same equipment and methods as for the test piles.

Ground Improvement

As an alternative to supporting the new foundations and slabs on deep foundations, the new foundations and slabs could be supported on native soils following the completion of successful ground improvements. Ground improvement methods are proprietary systems designed by licensed contractors who could provide further information regarding support options.

A possible ground improvement alternative that could likely be implemented for this project with the site restrictions taking into consideration include pressure injection grouting. Due to the specialty of this soil improvement procedure, we recommend that a performance specification be used for this system.

We understand if pressure injection grouting is utilized to support the foundations and slabs, the pressure injection grouting design firm will be the geotechnical engineer of record for these foundations and slabs. As such, the design firm would provide the necessary design parameters.

Floor Slabs

It is recommended to support all new slabs on a deep foundation system unless a ground improvement system, such as pressure injection grouting, is utilized.

Facilities | Environmental | Geotechnical | Materials 17

Specific attention should be given to positive drainage away from the structure and positive drainage of the porous fill beneath the floor slab. Porous fill should consist of a minimum 4-inch layer of relatively clean, compacted, poorly graded sand (SP) or gravel

(GP) with less than 5% passing the No. 200 Sieve (0.074 mm). The purpose of the 4-inch layer is to act as a capillary barrier and equalize moisture conditions beneath the slab.

The use of a vapor retarder should be considered beneath concrete slabs on grade covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, when the project includes humidity-controlled areas, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

General Comments

Our analyses and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration.

Variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the

Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Facilities | Environmental | Geotechnical | Materials 18

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly effect excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety and cost estimating including excavation support and dewatering requirements/design are the responsibility of others.

Construction and site development have the potential to affect adjacent properties. Such impacts can include damages due to vibration, modification of groundwater/surface water flow during construction, foundation movement due to undermining or subsidence from excavation, as well as noise or air quality concerns. Evaluation of these items on nearby properties are commonly associated with contractor means and methods and are not addressed in this report. The owner and contractor should consider a preconstruction/precondition survey of surrounding development. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

Figures

Contents:

GeoModels (2 pages)

-45

-40

-35

-30

-25

-20

-15

-10

-5

EL

EV

A

TI

O N

M

S L) fe et

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

SB-1 SB-2 SB-3 SB-4 SB-5 SB-6 SB-7

Legend

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

GeoModel

655 Hunting Ave | Hampton, VA Terracon Project No. K4235092

JBLE - Old Steam Plant Repair Facility 655

701 Alexander Lee Pkwy Williamsburg, VA

First Water Observation

Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time.

Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details.

Asphalt Aggregate Base Course

Sandy Lean Clay Silty Sand

Clayey Sand Concrete

Model Layer Layer Name General Description

1 Asphalt underlain by Aggregate Base or Concrete

3 Silty and Clayey Sand (SM, SC)

4 Silty Sand (SM), contains marine shell fragments, "Yorktown Formation"

Silty and Clayey Sand (SM, SC) and Sandy lean Clay (CL), both containing varying amounts of Gravel and/or other deleterious material

SURFICIAL

SAND

YORKTOWN

FILL

0.4

16.5

0.3

12.5

0.6

16.5

0.5

12.5

0.6

16.5

0.5

16.5

0.5

16.5

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

EL

EV

A

TI

O N

M

S L) fe et

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

C-1 C-1A C-2 C-2A C-3 C-3A C-4 C-4A C-5 C-6 C-7 C-8 C-9

Legend

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

GeoModel

655 Hunting Ave | Hampton, VA Terracon Project No. K4235092

JBLE - Old Steam Plant Repair Facility 655

701 Alexander Lee Pkwy Williamsburg, VA

First Water Observation

Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time.

Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details.

Concrete Sandy Lean Clay

Silty Sand Clayey Sand

Model Layer Layer Name General Description

1 Asphalt underlain by Aggregate Base or Concrete

3 Silty and Clayey Sand (SM, SC)

4 Silty Sand (SM), contains marine shell fragments, "Yorktown Formation"

Silty and Clayey Sand (SM, SC) and Sandy lean Clay (CL), both containing varying amounts of Gravel and/or other deleterious material

SURFICIAL

SAND

YORKTOWN

FILL

1.2

2.6

3.5

0.3

1.8

0.9

1.4

0.9

1.3

0.8

1.5

1.9

1.3

0.8

Attachments

Exploration and Testing Procedures

Field Exploration

Number of Cores Location

7 Pavements around the exterior of steam plant building

13 Slab inside steam plant building

Boring Layout and Elevations: Terracon personnel provided the boring layout using handheld GPS equipment (estimated horizontal accuracy of about ±10 feet) and referencing existing site features. Approximate ground surface elevations were obtained by interpolation from a USGS topographic map (unknown datum). If elevations and a more precise boring layout are desired, we recommend borings be surveyed.

Subsurface Exploration Procedures: The SPT borings were performed with a track-mounted, rotary drill rig using rotary wash “mud” drilling procedures. The tests were performed continuously from the existing ground surface to a depth of 12-feet, and at 5-foot intervals thereafter starting at a depth of 13-feet. The soil samples were obtained with a standard 1.4” I.D., 2” O.D., 30” long split-spoon sampler. The sampler was driven with blows of a 140 lb. hammer falling 30 inches, using an automatic hammer. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded and is shown on the boring logs. The sum of the second and third penetration increments is termed the SPT N-value (uncorrected for automatic hammer).