Appendix_A-1_Geotech_Report.pdf

Supplemental Geotechnical Engineering Report

Welch Elementary/Dover Middle School Replacement Dover, Delaware

November 4, 2016 Terracon Project No. J6155030A

Prepared for:

Zyscovich Architects, Inc.

Miami, FL

Prepared by:

Terracon Consultants, Inc.

South Plainfield, New Jersey

RFP W912BU-17-R-0032

Appendix A-1 Page 1

Terracon Consultants, Inc. 4081 Hadley Road, Unit B South Plainfield, New Jersey 07080

P (908) 546-6161 F (908) 546-6160 terracon.com

November 4, 2016

Zyscovich Architects, Inc.

100 North Biscayne Boulevard, 27th floor Miami, FL 33132

Attn: Mr. Michael McGuinn, AIA P: (305) 372-5222 E: mmcguinn@zyscovich.com

Re: Supplemental Geotechnical Engineering Services Welch Elementary/Dover Middle School Replacement Dover Air Force Base Dover City, Delaware Terracon Project No. J6155030A

Dear Mr. McGuinn:

Terracon Consultants, Inc. (Terracon) is submitting, herewith, the results of our supplemental geotechnical evaluation for the above-referenced project. The purpose of this supplemental evaluation was to obtain additional information on subsurface conditions at the project site and, based on this information, to provide final recommendations regarding foundation options and site development for the proposed development. These services were performed in general accordance with our proposal number PJ6150097, dated May 5, 2015, revised May 26, 2015, and as authorized by the Subcontract Agreement dated June 3, 2015.

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

Sincerely, Terracon Consultants, Inc.

Erich L. Christiansen, P.E. Steven D. Thorne, P.E., D.GE, F.ASCE Senior Associate Principal Geotechnical Department Manager New Jersey Office Manager

Appendix A-1 Page 2

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Site Location

2.2 Project Description

3.0 SUBSURFACE EXPLORATIONS AND CONDITIONS

3.1 Geology

3.2 Typical Profile

3.3 Groundwater

3.4 Infiltration Testing

4.0 DESIGN CONSIDERATIONS AND RECOMMENDATIONS

4.1 Geotechnical Considerations

4.2 Earthwork

4.2.1 Site Preparation

4.2.2 Excavations

4.2.3 Reuse of Materials

4.2.4 Imported Fill Materials

4.2.5 Structural Fill Placement

4.2.6 Groundwater

4.3 Foundations

4.3.1 Shallow Foundation Design Recommendations

4.3.2 Shallow Foundation Construction Considerations

4.4 Seismic Design Considerations

4.5 Slab-on-Grade

4.5.1 Slab-on-Grade Design Recommendations

4.5.2 Slab-on-Grade Construction Considerations

4.6 Pavement Subgrade Preparation

4.7 Pavement Design Parameters

5.0 GENERAL COMMENTS

APPENDIX A – FIELD EXPLORATION

Exhibit A-1 Site Location Map Exhibit A-2 Exploration Location Diagram Exhibit A-3 Field Exploration Description Exhibits A-4 to A-30 Boring Logs Exhibits A-31 to A-55 Test Pit Logs

APPENDIX B – LABORATORY TESTING

Exhibit B-1 Laboratory Testing Exhibits B-2 to B-4 Gradation Curves Exhibit B-5 Atterberg Limits

APPENDIX C – SUPPORTING DOCUMENTS

Exhibit C-1 General Notes Exhibit C-2 Unified Soil Classification System

APPENDIX D – CONE PENETRATION TEST INFORMATION

Appendix A-1 Page 3

Supplemental Geotechnical Engineering Report Welch Elementary/Dover Middle School Replacement Dover, Delaware November 4, 2016 Terracon Project No. J6155030A

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EXECUTIVE SUMMARY

The supplemental geotechnical engineering report has been completed for the Welch Elementary/Dover Middle School Replacement at the Dover Air Force Base located in Dover City, Delaware. The project will consist of a school facility with a plan area of approximately 81,000 square feet, with associated sports fields, running track, playground areas and relocated access roads.

Twenty seven soil borings (B-1 through B-4, and B-101 through B-123), twenty five test pit excavations (TP-1 through TP-10, and TP-101 through TP-115), and eleven cone penetration tests (CPT-1 through CPT-11) were advanced to depths ranging from 5 to 41 feet below the existing surface grades. Subsurface conditions at the site typically consist of sand/silty sand soils with interbedded silt/clay layers.

Uncontrolled fill was encountered above these materials in fifteen of the explorations and ranged from 1 to more than 12 feet in thickness.

The following geotechnical considerations for project design and construction were identified and are discussed in the report:

Uncontrolled fill materials were encountered in two borings conducted in the proposed school building area and extended to depths ranging from 1 to 4 feet. These materials are not suitable for support of the foundations and floor slabs. Since the available data indicates that the fill in the building area is relatively random and limited in depth, we recommend excavating the uncontrolled fill in its entirety where encountered from below the proposed building and ancillary structural areas and replace it with controlled structural fill.

Relatively loose sands are present in some locations within the influence zones of proposed foundations. In order to limit post-construction settlements to conventional levels (approximately 1 inch, or less), we recommend conducting a program of densification of materials within several feet of foundation subgrades.

Following completion of the densification program and removal and replacement of any existing uncontrolled fill materials, the building and ancillary structures may be supported on conventional spread footings with a slab-on-grade. We recommend that the foundations be designed using a net allowable bearing pressure of up to 3,000 pounds per square foot (psf) and the slab-on-grade may be designed using a modulus of subgrade reaction of 150 pounds per cubic inch (pci).

It may also be possible to improve some of the fill in place below the proposed pavement areas, ballfields and playgrounds if the nature and thickness of the fill is consistent with what was encountered within the building. This improvement may consist of in-place densification with a large vibratory compactor, or may require removal of the upper 1 to 2 feet of fill, followed by densification of the remaining fill in place, and replacement of the excavated soils in controlled, compacted layers. The feasibility of this option would depend on the

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The majority of soils generated during construction grading and excavation work are expected to consist of silty sand and silt/clay soils. The sand materials should typically be suitable for reuse as structural fill, provided the materials are moisture conditioned appropriately for compaction and deleterious materials are segregated prior to reuse. The silt/clay layers are moisture sensitive and as such may be difficult or not cost effective to use as controlled compacted fill and backfill. In addition, because of their moisture sensitivity, silt/clay subgrades will be easily softened or disturbed by weather and/or construction vehicle traffic.

Based on our review of the available subsurface data, we recommend that Site Class “D” be adopted for seismic design purposes in accordance with the requirements of the 2015 International Building Code.

A geotechnical engineer from Terracon should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during removal of existing fill, stabilization of disturbed subgrade materials, subgrade preparation;

proofrolling; placement and compaction of controlled compacted fills; backfilling of excavations; and subgrade conditions just prior to construction of foundations and the floor slab.

This summary should be used in conjunction with the entire report for design purposes. Details are not included or fully developed in this summary; the report must be read in its entirety of a comprehensive understanding of the information contained herein. The section titled GENERAL COMMENTS should be read for an understanding of the report limitations.

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SUPPLEMENTAL GEOTECHNICAL ENGINEERING REPORT

WELCH ELEMENTARY/DOVER MIDDLE SCHOOL REPLACEMENT

DOVER, DELAWARE

Terracon Project No. J6155030A

November 4, 2016

1.0 INTRODUCTION

The supplemental geotechnical engineering report for the Welch Elementary/Dover Middle School Replacement located on the Dover Air Force Base (DAFB) in Dover, Delaware (see Exhibit A-1, Site Location Map) has been completed.

Four borings and ten test pits (B-1 through B-4, and TP-1 through TP-10) were conducted as part of our 2015 preliminary geotechnical investigation, dated August 21, 2015. Twenty-three additional soil borings (B-101 through B-123), 15 additional test pit excavations (TP-101 through TP- 115), and 11 cone penetration tests (CPT-1 through CPT-11) were conducted as part of this supplemental investigation. Six of the additional test pits were conducted to evaluate the extent of debris fill encountered during our preliminary investigation in the proposed baseball field area. The explorations from both investigations were advanced to depths ranging up to 41 feet below the existing surface grades. Individual exploration logs from both investigations and an Exploration Location Diagram showing all explorations (Exhibit A-2) are included in Appendix A.

This report describes the subsurface conditions encountered in the explorations and provides a discussion of Supplemental geotechnical considerations and recommendations for construction of the proposed Welch Elementary/Dover Middle School Replacement and associated ball fields and recreational facilities.

The purpose of these services is to provide information and preliminary geotechnical engineering considerations relative to:

subsurface soil conditions seismic considerations groundwater conditions slab design and construction earthwork foundation design and construction pavement design and construction

2.0 PROJECT INFORMATION

Our knowledge of the project is based on information provided to our office including the schematic site layout Figure #3 for the Welch Elementary-Dover Middle School, DAFB, Delaware and general project design information provided by the Client.

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A summary description of the project is presented below:

2.1 Site Location

ITEM DESCRIPTION

Location Center and Lebanon Roads, DAFB Approximate coordinates are LAT: 39.1150° LONG: -75.4862°

Existing improvements Existing building with access roads, small parking lot and track.

Current ground cover Grass lawn and asphalt pavement.

Existing topography Relatively level. Ground surface elevations in the vicinity of the proposed school building reportedly range from approximately Elevation +16 to +18 feet.

2.2 Project Description

ITEM DESCRIPTION

Structures/Improvements The proposed school facility will be a two-story structure with an approximate 81,000 SF ground floor plan area. Improvements will also include sports fields, bleachers, running track and playground areas.

Building construction Steel-frame, with brick-clad, concrete masonry walls Finished floor elevation

(FFE)

Elevation +18 feet

Maximum loads Columns: 350 kips Walls: 15 kips/ft Slab: 250 psf Basement areas None anticipated Pavements Parking and access roadways

Stormwater Management 10 to 15 shallow micro-bioretention facilities spread throughout the site.

Terracon should be provided the opportunity to review the building details and grading information for consistency with the recommendations presented in this report. Any revisions required based on review of that data could be provided in an addenda to this report.

3.0 SUBSURFACE EXPLORATIONS AND CONDITIONS

Subsurface conditions at the site typically consist of sand/silty sand soils with interbedded silt/clay layers. Uncontrolled fill was encountered above these materials in fifteen of the explorations and ranged from 1 to more than 12 feet in thickness.

The geology of the site is presented in the following report section. A discussion of subsurface conditions encountered in our borings follows the geology section.

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3.1 Geology

Based on the USGS Interactive Geological Mapping, the site is located in the Coastal Plain Physiographic Province. The unconsolidated materials in the general area of the site are mapped as the Chesapeake Group, which consists predominantly of silt and sand. The top of the basement bedrock underlying the coastal plain sediments is reported to be greater than 3,000 feet deep in this area.

3.2 Typical Profile

Based on the results of the test borings, test pits and field observations at the time of drilling, subsurface conditions at the project site can be generalized as follows:

Stratum Approximate Depth to Bottom of Stratum (feet) Material Description 1 Consistency / Density

1 1 foot to >12 feet Fill: sandy silt/silty sand, with varying amounts of concrete and brick rubble 2 Variable

Not encountered. All explorations terminated in this stratum.

Natural sand to silty sand, with interbedded silt/clay layers3 Loose to very dense

1. Topsoil or asphalt was present at the ground surface in all explorations. Refer to the table below for conditions at each exploration.

2. Additional debris such as rubber, paper, etc. was encountered in TP-7 from 8 to 12 feet below the existing surface grades.

3. The interbedded silt/clay layers were found in borings B-1, B-4, B-101, B-103 through B-105, B-108, B- 112 through B-113, B-119, and B-121 through B-123, and in test pits TP-2, TP-5, TP-6, TP-8 through TP-10, TP-101 through 105, TP-108 through TP-110, TP-115, and CPT-1 through CPT-11. Minor amounts of gravel were occasionally encountered in this stratum.

Fill was encountered in 15 of the explorations conducted for this study. Two of the explorations encountering fill were in the proposed building area (B-3 and B-121), two in proposed paved/drive areas (B-2 and B-104), and four in proposed stormwater management areas (TP-106 through TP-109). The remaining seven explorations encountering fill were located in the proposed baseball field area. At least 12 feet of buried debris was identified in this area in one test pit (TP-7) during our preliminary study. Test Pits TP-110 through TP-115 were conducted as part of this study to assess the extent of the debris in this area. A plan showing the locations of the baseball field area test pits and the approximate fill depths encountered in this area is attached as Exhibit A-2.1. A summary of the surface materials, depth of fill and termination depths at each of the exploration is provided in the following table:

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Boring & Test Pit Number

Approx. Topsoil (TS) and Asphalt (A) Thickness (in.) Approx. Depth of Fill (ft.)1 Termination

Depth (ft.)

B-1 8 (TS) NE 30.5

B-2 7 (TS) 4 30.5

B-3 7 (TS) 4 30

B-4 3.5 (A) NE 30.5

B-101 3 (TS) NE 41

B-102 6 (TS) NE 6

B-103 12 (TS) NE 6

B-104 12 (TS) 3 6

B-105 12 (TS) NE 6

B-106 7 (TS) NE 6

B-107 2.5 (A) NE 6

B-108 5 (TS) NE 6

B-109 10 (TS) NE 6

B-110 11 (TS) NE 6

B-111 8 (TS) NE 6

B-112 9 (TS) NE 10

B-113 8 (TS) NE 6

B-114 9 (TS) NE 16

B-115 3 (A) NE 6.5

B-116 8 (TS) NE 6

B-117 7 (TS) NE 25

B-118 9 (TS) NE 6

B-119 6 (TS) NE 6

B-120 7 (TS) NE 6

B-121 4 (TS) 1 41

B-122 5 (TS) NE 41

B-123 9 (TS) NE 41

TP-1 18 (TS) NE 5

TP-2 12 (TS) NE 10

TP-3 12 (TS) NE 8

TP-4 12 (TS) NE 8

TP-5 10 (TS) NE 12

TP-6 8 (TS) NE 12

TP-7 6 (TS) >122 12

TP-8 12 (TS) NE 12

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Boring & Test Pit Number

Approx. Topsoil (TS) and Asphalt (A) Thickness (in.) Approx. Depth of Fill (ft.)1 Termination

Depth (ft.)

TP-9 18 (TS) NE 12

TP-10 6 (TS) NE 12

TP-101 8 (TS) 2.5 10

TP-102 12 (TS) NE 10

TP-103 11 (TS) NE 10

TP-104 10 (TS) NE 10

TP-105 10 (TS) NE 10

TP-106 7 (TS) 3 10

TP-107 4 (TS) 4.5 10

TP-108 7 (TS) 2 10

TP-109 8 (TS) 2.5 10

TP-110 8 (TS) 3 7

TP-111 1 (TS) 2 4

TP-112 2 (TS) 2.5 5

TP-113 1 (TS) 2 3.5

TP-114 1 (TS) 3 5

TP-115 1 (TS) NE 12

CPT-1 NA3 NA3 30.51

CPT-2 NA3 NA3 30.18

CPT-3 NA3 NA3 30.02

CPT-4 NA3 NA3 30.02

CPT-5 NA3 NA3 10.01

CPT-6 NA3 NA3 26.74

CPT-7 NA3 NA3 30.02

CPT-8 NA3 NA3 30.02

CPT-9 NA3 NA3 30.02

CPT-10 NA3 NA3 30.02

CPT-11 NA3 NA3 27.72

1. NE indicates fill not encountered

2. Native soils were not encountered in TP-7. Fill extended below bottom of test pit.

3. NA indicates not applicable because CPT data does not show fill or topsoil depths

Conditions encountered at each exploration location are indicated on the individual boring logs, test pits, and CPT logs in Appendix A of this report. Stratification boundaries on the exploration logs represent the approximate location of changes in soil types; in situ, the transition between materials may be gradual. Further details of the explorations can be found on the boring and test pit logs.

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3.3 Groundwater

Groundwater was reported in borings B-1 through B-4, B-101, B-114, B-117, B-121 through B-123, TP-115, CPT-1 through CPT-4, and CPT-6 through CPT-11 at depths ranging from 9 to 18 feet below the existing surface grades. The variable groundwater information observed in the borings may be due to incomplete stabilization of water levels in the boreholes associated with the interbedded silt/clay layers. Groundwater was reported in test pit TP-115 at a depth of 11.5 feet.

Mottling, an indicator of seasonal saturation levels, was observed in the native clay deposits in test pits TP-2, TP-8, and TP-115 at 5 feet, 8 feet, and 9.5 feet below the existing surface grades in these locations, respectively. However, it is our understanding that the natural groundwater levels at the site may have been altered due to historical groundwater withdrawal, so mottling may not represent current seasonal high saturation levels.

More precise information regarding groundwater levels is normally obtained from monitoring well data. We understand that numerous monitoring wells have been installed in the site vicinity as part of prior environmental investigations at the base. One report provided to us, the Area 6 Monitoring Report dated June 2016, indicated water levels present between approximately 3-1/2 and 5-1/2 feet below the ground surface in March of 2016. If additional information regarding fluctuations in water levels over time is desired, review of the historic environmental data would be required.

In addition to the variations noted above, fluctuations in groundwater levels occur because of seasonal variations in the amount of rainfall, runoff, and other factors. Additionally, grade adjustments on and around the site, as well as surrounding drainage improvements, may affect the water table. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

3.4 Infiltration Testing

Double-ring infiltrometer tests were conducted in eleven of the test pits (TP-1, TP-2, and TP-101 through TP-109) at a depth of approximately 5 to 6 feet below grade to provide information regarding potential infiltration rates of surface water. The testing consisted of installing a 4 inch diameter ring and a 6 inch diameter ring of PVC casing each approximately 12 inches in height, seated 2 inches into the soil, and adding water into both to induce seepage. Maintaining vertical seepage in the soil from the inner ring is facilitated by infiltration of water from the outer ring. The flow rate from the inner ring is used for quantifying the design infiltration rate. The test pit locations and their corresponding infiltration rates are as follows:

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Test Pit Number Infiltration Rate (inches/hour (cm/sec))

TP-1 >24 (>0.02)

TP-2 4 (0.003)

TP-101 8.6 (0.006)

TP-102 5.6 (0.004)

TP-103 3.8 (0.003)

TP-104 10.1 (0.007)

TP-105 11.3 (0.008)

TP-106 2.5 (0.002)

TP-107 0.6 (0.0004)

TP-108 3.8 (0.003)

TP-109 0.6 (0.0004)

It should be expected that infiltration rates at the site will vary with depth and location primarily due to changes in soil texture. For example a clay layer was found immediately below the tested depth in TP-2, which impeded flow and testing entirely within the clay layer would likely result in a lower infiltration rate. In addition average horizontal and vertical flow rates will be quite different in this natural deposit due to the stratification of soil types.

4.0 DESIGN CONSIDERATIONS AND RECOMMENDATIONS

4.1 Geotechnical Considerations

Uncontrolled fill materials were encountered in two of the borings (B-3, and B-121) conducted in the proposed school building area and extended to depths ranging from 1 to 4 feet. These materials are not suitable for support of the foundations and floor slabs. Since the available data indicates that the fill in the building area is relatively limited in depth and extent, we recommend excavating the uncontrolled fill it in its entirety from below the proposed building and ancillary structural areas, where encountered, and replacing it with controlled structural fill.

Following removal and replacement of the existing uncontrolled fill materials, it is our opinion that the subsurface conditions at the site are suitable for support of the building and ancillary structures on conventional spread footings with a slab-on-grade. However, given the presence of relatively loose sands at the site, we recommend below that the foundations be designed using a reduced design bearing pressure. Also, to keep estimated post-construction settlements within normal ranges (given the presence of these relatively loose sands), we recommend below that a densification program (discussed in Section 4.3.2) be conducted below proposed foundations, Support of pavement, as well as other settlement-sensitive site development such as tracks, playgrounds, courts, etc., above the existing fill soils is discussed in this report. Even with the recommended construction observation and testing services, there is an inherent risk for the

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This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill, but can be reduced by having an engineer from Terracon observe the subgrade preparation activities and by performing additional testing and evaluation.

4.2 Earthwork

4.2.1 Site Preparation

Prior to any earthwork operations, any subsurface utilities and abandoned subsurface structures, as well as the asphalt surface cover, should be relocated and/or removed within, as well as five feet beyond the proposed construction area. Existing fill, where encountered within the proposed building footprint area, should then be removed within, as well as five feet beyond the proposed footprint area.

Following removal of any subsurface utilities and abandoned subsurface structures, as well as the removal of the asphalt pavement and existing fill, the exposed subgrades the building and pavement areas, as well as any settlement-sensitive site development areas (e.g., the track, playground, basketball court, sidewalks, etc.) should be proofrolled to a dense and unyielding consistency under the observation of a Terracon geotechnical engineer. Any loose/soft or unstable areas identified by the proofrolling should be excavated to the surface of stable soils and replaced with structural fill. Where existing fill is identified by our engineer to be present at subgrade levels, our engineer should evaluate the extent and thickness of the fill, as well as the ability of the fill to be uniformly compacted in place to provide suitable subgrade support for the specific overlying development. Materials that cannot be sufficiently compacted in-place may require selective overexcavation and replacement under the guidance of our engineer.

Following the proofrolling operations, approved fill may be placed and compacted in a controlled manner as described below to attain the required foundation and slab subgrade levels.

4.2.2 Excavations

As a minimum, temporary excavations should be sloped, benched or braced, as required by Occupational Health and Safety Administration (OSHA) regulations, to provide stability and safe working conditions. The contractor, by his contract, is usually responsible for designing and constructing stable, temporary excavations and should shore, slope or bench the sides of the excavations, as required, to maintain stability of both the excavation sides and bottom. All excavations should comply with applicable local, State and federal safety regulations, including the current OSHA Excavation and Trench Safety Standards.

4.2.3 Reuse of Materials

The majority of soils generated during construction grading and excavation work are expected to consist of silty sand and silt/clay soils. The sand materials should typically be suitable for reuse as structural fill, provided the materials are moisture conditioned appropriately for compaction and

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4.2.4 Imported Fill Materials

In the event that imported fill is needed for structural fill beneath the proposed building, we recommend that the material consist of inorganic, readily compactable, well-graded granular soils with no more than 15 percent fines (no more than 15 percent passing the No. 200 sieve).

Additionally, we recommend excluding gradations greater than 6 inches. The moisture content of the fill material should be controlled to within approximately 3% of the optimum moisture content by wetting, aeration, or blending, as necessary to achieve the required compaction.

4.2.5 Structural Fill Placement

Structural fill should be installed in controlled layers uniformly compacted to at least 95 percent of the fill material’s maximum dry density, as determined by ASTM D1557 Test Procedures. The layer thickness should be adjusted as needed depending on the type of compaction equipment used and the condition of the fill materials at the time of construction, but should be no greater than 12 inches in loose thickness. It should be expected that thinner lifts will be required to achieve the required compaction in confined areas where portable compaction equipment is used.

4.2.6 Groundwater

Based on environmental well data provided to us, groundwater was encountered at depths ranging from 3-1/2 to 5-1/2 feet below the ground surface earlier this year. Higher levels may be present at the time of construction depending on the seasonal precipitation rates at that time. It should be assumed that excavations that need to extend below groundwater levels could encounter moderate to rapid seepage. The contractor should provide whatever dewatering equipment necessary to maintain excavation subgrades in a relatively dry condition.

Perched/trapped seepage could also occur where silt/clay layers are present at or near excavation subgrade levels.

4.3 Foundations

Provided the site is prepared in accordance with the above recommendations the proposed structure may be supported on shallow spread foundations. Design recommendations for shallow foundations are presented in the following table and paragraphs.

4.3.1 Shallow Foundation Design Recommendations

Description Value

Net allowable bearing pressure 1 3,000 psf Minimum strip footing width 18 inches

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Description Value Minimum isolated spread footing width 24 inches Minimum embedment below finished grade for frost protection 32 inches

Approximate total post-construction settlement 2 1 inch

1. The recommended net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation.

2. Foundation settlement will depend upon the variations within the subsurface soil profile, the structural loading conditions, the embedment depth of the footing, the thickness of compacted fill, and the quality of the earthwork operations. This estimate also assumes that the densification activities recommended in the following section are performed.

Exterior foundations should be established a minimum of 32 inches below the proposed adjacent exterior grades, or deeper if required by the local building official, to provide protection from frost penetration. Interior foundations located in permanently heated portions of the structure may be established at convenient depths below the ground floor slab, provided they bear on appropriate materials as described above.

4.3.2 Shallow Foundation Construction Considerations

Relatively loose sands are present at the site in some locations within the influence zones of the foundations for the proposed structures. In this condition, settlements larger than those estimated in the table above could occur. Accordingly, we recommend the following densification program be conducted under the observation of a Terracon geotechnical engineer below all continuous wall and isolated footings:

■ The existing soils should first be excavated to a depth of three feet below the planned bottom of foundation level. The excavation should extend laterally a distance of at least two feet from the outside edges of the foundations (more, if needed to accommodate the compaction equipment referenced below).

■ The resulting subgrade should be thoroughly compacted with at least six passes of a large, self-propelled vibratory compactor, with a static drum weight of at least 12,000 pounds.

■ Following compaction, the overexcavation should be backfilled in accordance with the recommendations provided in Section 4.2.5, above.

Following completion of this densification program, the base of foundation excavations should be free of water and loose soil before placing concrete. Any subgrades, however, that become wet, disturbed, or frozen prior to the placement of should be removed and replaced prior to placing concrete. As discussed above, Terracon should be retained to observe the subgrade preparation

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4.4 Seismic Design Considerations

Based on our review of the available subsurface data, we recommend that Site Class “D” be adopted for seismic design purposes in accordance with the requirements of the 2015 International Building Code.

4.5 Slab-on-Grade

4.5.1 Slab-on-Grade Design Recommendations

Description Value

Floor slab support 1 12 inches of compacted structural fill Modulus of subgrade reaction 2 150 pounds per square inch per in (pci)

1. Floor slabs should be structurally independent of building footings or walls to reduce the possibility of floor slab cracking caused by differential movements between the slab and foundations.

2. Value is the minimum expected at this site for point load condition.

Where appropriate, control joints should be saw-cut in the slab to help control the location and extent of cracking. For additional recommendations, the slab designer should refer to the ACI Design Manual.

The use of a vapor retarder should be considered beneath a concrete slab-on-grade that will be covered with wood, tile, carpet or other moisture sensitive or impervious coverings, 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. We also recommend the installation of a six inch layer of clean crushed stone to act as a capillary break between the bottom of the floor slab and the underlying subgrade soils.

4.5.2 Slab-on-Grade Construction Considerations

On most project sites, the site grading is generally accomplished early in the construction phase, and this report assumes that the general slab area will be prepared in accordance with our recommendations above in Section 4.2. However as construction proceeds, the subgrade may be disturbed because of utility excavations, construction traffic, precipitation, etc. As a result, the floor slab subgrade may not be suitable for placement of granular base and concrete, and corrective action will be required.

Therefore, immediately prior to placement of the granular base and concrete, we recommend the area underlying the floor slab be proofrolled again with at least six passes of a minimum 4-ton (static weight) vibratory roller compactor. In areas with limited access, a double-drum walk-behind

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Responsive ■ Resourceful ■ Reliable 12 compactor may be used. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located, and manual probes should be performed by Terracon to confirm the stability of these areas. Areas with unsuitable conditions should be repaired by removing and replacing the affected material with properly compacted fill.

4.6 Pavement Subgrade Preparation

Pavement subgrades should be proofrolled in accordance with the recommendations provided in Section 4.2.1. If the elevation of the proposed pavement section subgrade is above existing grades, the exposed subgrade be proofrolled prior to placing fill. If the elevation of the proposed pavement section subgrade is at or below existing grades, the area should be cut to the pavement subgrade level prior to performing the proofrolling.

Pavement subgrades should be carefully evaluated for disturbance or softening from construction activities or weather as the time for pavement construction approaches. Unless the procedures recommended above are conducted immediately prior to paving, the subgrades should be rechecked and proofrolled again prior to placing the pavement base course with a loaded tandem-axle dump truck. Areas where unsuitable conditions are located should be repaired by replacing the materials with properly compacted fill. When proofrolling/subgrade stabilization has been completed to the satisfaction of the geotechnical engineer, the aggregate base course may be placed.

4.7 Pavement Design Parameters

Provided that the pavement subgrade is prepared in accordance with the recommendations of Section 4.6, we recommend designing the parking lot and drive lane pavement section using a CBR value of 8. Please note, however, that CBR values are highly dependent on the final subgrade material (which varies widely at this site between sand and silt/clay materials) and the condition of the subgrade at the time of construction. A Terracon geotechnical engineer should evaluate the final subgrade to confirm that it is consistent with a CBR of 8, and, if necessary, perform additional CBR testing. Areas where silt/clay soils are present at pavement subgrade levels may require up to 18 inches of overexcavation and replacement with granular soils, or a thicker pavement section based on a reduced CBR value.

Detailed traffic design parameters have not been provided to us, so it is not possible for us to calculate design sections for the project using conventional pavement design procedures at this time. Based on our experience and our understanding of subsurface conditions at the site, we would expect that pavement section layers for light and heavy duty sections would need to be on the order of the following thicknesses:

Appendix A-1 Page 17

November 4, 2016 Terracon Project No. J6155030A

Responsive ■ Resourceful ■ Reliable 13

Layer Light Duty Est.

Thickness (in.)

Heavy Duty Est.

Thickness (in.)

Delaware DOT Asphaltic Surface Course 1.5 2

Delaware DOT Asphaltic Binder Course 2.5 3

Delaware DOT Type II Aggregate Base Course 8 8

If traffic design parameters are provided to us, we could conduct detailed pavement design and modify the pavement sections, if needed.

5.0 GENERAL COMMENTS

The investigation and preliminary conclusions discussed in this report are provided for preliminary planning and feasibility evaluation purposes and are insufficient for final design. A supplemental investigation should be performed once building construction details, structural loads, floor elevations and site grading are identified.

The preliminary recommendations presented in this report are based upon the data obtained from the explorations performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between explorations, across the site, or due to the modifying effects of weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided.

The scope of services for this project 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.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either expressed or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing.

Appendix A-1 Page 18

APPENDIX A

FIELD EXPLORATION

Appendix A-1 Page 19

SITE LOCATION

Welch Elementary/Dover Middle School

Replacement

DOVER AIRFORCE BASE

DOVER, KENT COUNTY, DELAWARE

TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY

QUADRANGLES INCLUDE: DOVER, DE (1/1/1993), LITTLE CREEK, DE (1/1/1993), WYOMING, DE (1/1/1993) and FREDERICA, DE (1/1/1993).

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Appendix A-1 Page 21

November 4, 2016 Terracon Project No. J6155030A

Responsive ■ Resourceful ■ Reliable Exhibit A-3

Field Exploration Description

The approximate exploration locations, which are shown on Exhibit A-2, were estimated from hand held GPS which has an accuracy of about 20 feet. The locations of the explorations should be considered accurate only to the degree implied by the method used to define them. Ground surface elevations were not provided prior to the preparation of this report.

Terracon coordinated the advancement of four test borings (B-1 through B-4) and ten test pits (TP- 1 through TP-10) on July 1 and July 2, 2015. The borings were advanced using a drill rig, operated by J.D. Hynes, Delaware. The borings terminated at depths of approximately 30 feet. Terracon coordinated the advancement of twenty three test borings (B-101 through B-123) and fifteen test pits (TP-101 through TP-115) on August 2 through August 11, 2016. The borings were advanced using a drill rig, operated by Allied Well Drilling, Pennsylvania. The borings were advanced using 2¼-inch I.D. continuous flight hollow-stem augers (HSA). The borings terminated at depths of approximately 2 to 41 feet.

An automatic SPT hammer was used to advance the split-barrel sampler in four of the borings (B- 1 through B-4) performed on this site. A significantly greater efficiency is achieved with the automatic hammer compared to the conventional safety hammer operated with a cathead and rope.

This higher efficiency has an appreciable effect on the SPT-N value. The effect of the automatic hammer's efficiency has been considered in the interpretation and analysis of the subsurface information for this report.

In the split-barrel sampling procedure, the number of blows required to advance a standard 2-inch O.D. split-barrel sampler typically the bottom 12 inches of the total 18-inch penetration by means of a 140-pound safety rope and cathead with a free fall of 30 inches is the Standard Penetration Test (SPT) resistance value “N”. This “N” value is used to estimate the in-situ relative density of cohesionless soils and consistency of cohesive soils.

The soil samples were placed in labeled containers and transported to our laboratory for further review and classification by a Terracon geotechnical engineer. Information provided on the boring logs attached to this report includes soil descriptions, relative density and/or consistency evaluations, boring depths, sampling intervals, and groundwater conditions. The borings were backfilled with auger cuttings and grouted prior to the drill crew leaving the site. The test pits were backfilled upon completion with the excavated materials and the materials were tamped with the excavator bucket during backfilling.

Field logs of the explorations were prepared during drilling. These logs included visual classifications of the materials encountered during drilling as well as interpretation of the subsurface conditions between samples. Final exploration logs included with this report represent further interpretation by the geotechnical engineer of the field logs and incorporate, where appropriate, modifications based on laboratory classification of the samples.

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APPENDIX B

LABORATORY TESTING

Appendix A-1 Page 79

November 4, 2016 Terracon Project No. J6155030A

Responsive ■ Resourceful ■ Reliable Exhibit B-1

LABORATORY TESTING SUMMARY

Moisture content determinations, gradation tests and Atterberg Limits were made for selected samples and the results are shown on the Gradation Curves, Exhibits B-2 to B-4, and Atterberg Limits, Exhibit B-5. Descriptive classifications of the soils indicated on the exploration logs are in accordance with the enclosed General Notes and the Unified Soil Classification System (USCS).

USCS symbols are also shown. A brief description of the USCS is attached to this report.

Classification was by visual/manual procedures.

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APPENDIX C

SUPPORTING DOCUMENTS

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UNIFIED SOIL CLASSIFICATION SYSTEM

Exhibit C-2

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

Group Symbol Group Name B

Coarse Grained Soils:

More than 50% retained on No. 200 sieve

Gravels:

More than 50% of coarse fraction retained on No. 4 sieve

Clean Gravels:

Less than 5% fines C

Cu 4 and 1 Cc 3 E GW Well-graded gravel F

Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F

Gravels with Fines:

More than 12% fines C

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

Fines classify as CL or CH GC Clayey gravel F,G,H

Sands:

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

Clean Sands:

Less than 5% fines D

Cu 6 and 1 Cc 3 E SW Well-graded sand I

Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I

Sands with Fines:

More than 12% fines D

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

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

Fine-Grained Soils:

50% or more passes the No. 200 sieve

Silts and Clays:

Liquid limit less than 50

Inorganic:

PI 7 and plots on or above “A” line J CL Lean clay K,L,M

PI 4 or plots below “A” line J ML Silt K,L,M

Organic:

Liquid limit - oven dried

0.75 OL

Organic clay K,L,M,N

Liquid limit - not dried Organic silt K,L,M,O

Silts and Clays:

Liquid limit 50 or more

Inorganic:

PI plots on or above “A” line CH Fat clay K,L,M

PI plots below “A” line MH Elastic Silt K,L,M

Organic:

Liquid limit - oven dried

0.75 OH

Organic clay K,L,M,P

Liquid limit - not dried Organic silt K,L,M,Q

Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat

A Based on the material passing the 3-inch (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name.

C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay.

D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay

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

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

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

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

J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.

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

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

M If soil contains 30% plus No. 200, predominantly gravel, add

“gravelly” to group name.

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

O PI 4 or plots below “A” line.

P PI plots on or above “A” line.

Q PI plots below “A” line.

Appendix A-1 Page 87

APPENDIX D

CONE PENETRATION TEST INFORMATION

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CONE PENETRATION TEST

The cone penetration tests (CPTu) are conducted using an integrated electronic piezocone penetrometer and data acquisition systemmanufactured by Adara Systems Ltd. of Richmond, British Columbia, Canada.

ConeTec’s piezocone…