Geotechnical Engineering Report 03-22-11.pdf

Geotechnical Engineering Report Proposed National Guard Readiness Center

Natick, Massachusetts March 22, 2011

Project No. J1115100

Prepared for:

Gale Associates, Inc.

Weymouth, Massachusetts

Prepared by:

Terracon Consultants, Inc.

Manchester, New Hampshire

TABLE OF CONTENTS

EXECUTIVE SUMMARY ............................................................................................................ I

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 PROJECT DESCRIPTION

2.2 SITE LOCATION AND DESCRIPTION

3.0 SUBSURFACE CONDITIONS

3.1 TYPICAL SUBSURFACE PROFILE

3.2 GROUNDWATER

3.3 LABORATORY ANALYSES

3.3.1 Gradation Testing

3.3.2 Environmental Analytical Testing

3.4 IN-SITU INFILTRATION TESTING

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 GEOTECHNICAL CONSIDERATIONS

4.2 EARTHWORK

4.2.1 Subgrade Preparation

4.2.2 Fill Materials and Placement

4.2.3 Compaction Requirements

4.2.4 Grading and Drainage

4.2.5 General Construction Considerations

4.3.1 Design Recommendations

4.3.2 Construction Considerations

4.4 SEISMIC CONSIDERATIONS

4.4.1 Liquefaction Potential

4.4.2 Seismic Design Criteria

4.5 FLOOR SLABS

4.5.1 Design Recommendations

4.5.2 Construction Considerations

4.6 LATERAL EARTH PRESSURES

4.6.1 Design Criteria

4.7 PAVEMENTS

4.7.1 Design Recommendations

4.7.2 Construction Considerations

5.0 GENERAL COMMENTS

APPENDIX A – FIELD EXPLORATION

Exhibit A-1 – Site Location Map Exhibit A-2 – Subsurface Exploration Location Plan Exhibit A-3 – Geologic Cross Sections Exhibit A-4 – Field Exploration Description Boring Logs B-1 through B-6 Boring Logs B-101 through B-104 Test Pit Logs TP-1 through TP-10

APPENDIX B – LABORATORY TESTING

Geotechnical Laboratory Test Results Environmental Analytical Test Results

APPENDIX C – SUPPORTING DOCUMENTS

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

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EXECUTIVE SUMMARY

A geotechnical exploration has been performed for the proposed National Guard Readiness Center in Natick, Massachusetts. Terracon’s geotechnical engineering scope of services included advancing 10 test borings and 10 test pits within the proposed project area. Borings, designated B-1 through B-6 and B-101 through B-104, were advanced to depths ranging from approximately 31 to 59 feet below the existing ground surface. Test pits, designated TP-1 through TP-10, were excavated to depths ranging from approximately 10 to 11 feet below existing ground surface.

Based on the information obtained from our subsurface exploration, the site can be developed for the proposed project. The following geotechnical considerations were identified:

Soil conditions generally consisted of 1 to 8.5 feet of fill, underlain by a natural sand deposit. Groundwater was encountered at depths of approximately 11 to 17 feet below existing grade.

Existing fill is not suitable for foundation support in its current condition. Where encountered at foundation subgrade, fill should be removed from the foundation-bearing zone to undisturbed natural soil.

Assuming proper site and subgrade preparation, total and differential settlement for the building should be within project specifications.

A site-specific liquefaction evaluation was completed for the proposed building location.

Based on supplemental test boring data, laboratory testing, and the site-specific evaluation, the site does not appear to be susceptible to liquefaction during the design seismic event.

Based on the Massachusetts State Building Code (8th Edition), the seismic site classification is D.

Earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during construction.

The geotechnical executive summary should be used in conjunction with the entire report for design and/or construction purposes. It should be recognized that specific details are not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The section titled General Comments should be read for an understanding of the report limitations.

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GEOTECHNICAL ENGINEERING REPORT

PROPOSED NATIONAL GUARD READINESS CENTER

NATICK, MASSACHUSETTS

Terracon Project No. J1115100

March 22, 2011

1.0 INTRODUCTION

This report presents the results of our geotechnical engineering services performed for the proposed National Guard Readiness Center in Natick, Massachusetts. Our geotechnical engineering scope of services included advancing six test borings and 10 test pits within the proposed project area. Borings, designated B-1 through B-6, were advanced to depths ranging from approximately 31 to 32 feet below the existing ground surface. Test pits, designated TP-1 through TP-10, were excavated to depths ranging from approximately 10 to 11 feet below existing ground surface.

Based on the results of our exploration program, supplemental borings were completed to evaluate the liquefaction potential at the project site. Four test borings, identified as B-101 through B-104, where advanced to depths ranging from 48 to 59 feet below existing ground surface. A Site Location Map, a Subsurface Exploration Location Plan, and Geologic Cross Sections are included in Appendix A as Exhibits A-1, A-2, and A-3 respectively. Logs of the explorations are also included in Appendix A.

The purpose of our services is to provide information and geotechnical engineering recommendations related to the following:

■ Subsurface soil conditions

■ Earthwork construction

■ Seismic considerations

■ Pavement design and construction

■ Groundwater conditions

■ Foundation design and construction

■ Floor slab design and construction

National Guard Readiness Center ■ Natick, Massachusetts March 22, 2011 ■ Terracon Project No. J1115100

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2.0 PROJECT INFORMATION

2.1 Project Description

Item Description Site layout See Exhibit A-2, Subsurface Exploration Location Plan

Building

The project will include constructing a new two-story, slab-on-grade office building with plan dimensions of approximately 100 feet by 316 feet within the central portion of the site, with associated paved parking and access drives surrounding the building. Military vehicle parking is planned on the south side of the property. A subsurface infiltration system is anticipated within the eastern parking area; the size and depth of the infiltration system is not known at this time.

Building Construction Building materials are unknown, but are expected to consist of steel frame and concrete/masonry.

Finished Floor Elevation1 Lowest finish floor elevation is unknown, but is expected to be near existing grade.

Maximum loads Columns: 275 kips Walls: 3.0 klf (assumed) Slabs: 175 psf max

Maximum allowable settlement (assumed)

Columns: 1 inch Walls: ¾ inch over 40 feet Floors: 1 inch

Grading Minor cuts and fills anticipated.

Free-standing Retaining Walls No retaining walls anticipated Below Grade Areas No below grade areas anticipated

2.2 Site Location and Description

Location 149 Speen Road, immediately southwest of Lake Cochituate, in Natick, Massachusetts

Existing improvements

The property is relatively level and currently occupied by one single-story storage building. The site was historically occupied by a large distribution/warehouse with two smaller ancillary buildings and associated paved parking; however, the buildings have been demolished and the project area is unoccupied at this time.

Current ground cover Grass and topsoil

Existing topography1 Site topography is generally level near El 155 feet within the project area.

Note 1: Ground surface elevations are estimated based on contours illustrated on the Layout and Test Pit Plan developed by Gale Associates, Inc. of Weymouth, Massachusetts.

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3.0 SUBSURFACE CONDITIONS

3.1 Typical Subsurface Profile

Based on the results of the explorations, subsurface conditions can be generalized as follows:

Description Approximate Depth to

Bottom of Stratum (feet)

Material Encountered Consistency/Density

Fill 1 to 8.5

Poorly-graded SAND with varying amounts of silt and gravel, portions contained brick and crushed concrete, light brown to gray.

Medium Dense

Glaciofluvial Deposit 48 to 59

Poorly Graded SAND with varying amounts of silt, to Non-plastic SILT, light brown. (SP, ML)

Loose to Medium Dense

Visual soil classifications and conditions encountered at each exploration location are indicated on the individual logs. Stratification boundaries on the logs represent the approximate location of changes in soil types; in-situ, the transition between materials may be gradual. Details for each of the exploration can be found on the test boring and test pit logs in Appendix A. A discussion of field sampling procedures is included in Appendix A.

3.2 Groundwater

The explorations were observed during advancement and after completion for the presence and level of groundwater. Observed groundwater depths and elevations are summarized in the following table:

Exploration Summary of Groundwater Observations

Approximate Depth to Groundwater Below

Ground Surface (feet)

Approximate Elevation (feet)

B-1 While Sampling 16.0 138.9 B-2 Delayed (5 days) 17.1 138.0 B-3 Delayed (6 days) 16.8 138.4 B-4 Delayed (6 days) 17.0 138.2 B-5 While Sampling 10.0 141.1 B-6 While Sampling 12.0 143.0

B-101 While Sampling 17.0 137.4 B-102 While Sampling 15.0 139.4

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Exploration Summary of Groundwater Observations

Approximate Depth to Groundwater Below

Ground Surface (feet) Approximate Elevation

(feet)

B-103 While Sampling 15.0 139.7 B-104 While Sampling 15.0 140.2 TP-2 During Excavation 11.0 143.2

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, run-off, and other factors not evident at the time the borings were performed. Additionally, based on the subsurface conditions and differences between groundwater observations during drilling and the stabilized groundwater readings in the monitoring wells, groundwater may be seasonally perched on the upper silty sand and silt layers. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

3.3 Laboratory Analyses

3.3.1 Gradation Testing

Laboratory testing was performed on soil samples obtained from the test borings to assist in classification and to evaluate relative engineering parameters. Grain-size analyses and Atterberg Limit tests were performed on samples of the glaciofluvial deposit. The results of the tests are included in Appendix B and are summarized below:

GRAIN-SIZE DISTRIBUTION ANALYSES

Sample Identification

Depth (feet)

Geologic Unit

Description Fines Content

(% Passing No. 200 Sieve)

Moisture Content

B-1, SS-10 18 - 20 Glaciofluvial SILTY SAND, brown

(SM) 16 26.4

B-3, SS-7 12 - 14 Glaciofluvial SILTY SAND, brown

(SM) 84 29.4

B-3, SS-13 27 - 29 Glaciofluvial

POORLY GRADED

SAND, trace Silt, Brown

(SP)

3.6 25.3

B-6, SS-10 18 - 20 Glaciofluvial SILTY SAND, brown

(SM) 40 25.5

B-104, SS-9 25 - 27 Glaciofluvial SILT, light Brown (ML) 78 33.0

B-104, SS-11 35 – 37 Glaciofluvial SILTY SAND, Brown

(SM) 23 23.6

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GRAIN-SIZE DISTRIBUTION ANALYSES

Sample Identification

Depth (feet)

Geologic Unit

Description Fines Content

(% Passing No. 200 Sieve)

Moisture Content

B-104, SS-13 45 – 47 Glaciofluvial

POORLY GRADED

SAND, trace Silt, Brown

(SP)

3.2 26.7

B-104, SS-14 50 - 52 Glaciofluvial SILTY SAND, Gray/Brown (SM) 14 24.8

ATTERBERG LIMIT TESTS

Sample Identification

Depth (feet)

Geologic Unit

Description Liquid Limit

(LL)

Plastic Limit

(PL)

Plasticity Index

(PI)

B-103, SS-7 14 - 16 Glaciofluvial SILT, Brown (ML) 26 NP NP B-104, SS-8 20 - 22 Glaciofluvial SILT, Gray/Brown (ML) 25 NP NP B-104, SS-9 25 - 27 Glaciofluvial SILT, light Brown (ML) 23 NP NP

Notes: NP – Non Plastic

3.3.2 Environmental Analytical Testing

Environmental analytical tests were performed on four soil samples and three groundwater samples in accordance with DCAM requirements in January 2011. Soil samples were analyzed for extractable petroleum hydrocarbons (EPHs) with target analytes, and CAM metals.

Groundwater samples were analyzed for EPHs with target analytes, pH, hardness, sulfates, specific conductivity, temperature, and dissolved CAM metals.

A second round of groundwater samples were collected and analyzed for dissolved CAM metals in March 2011 to confirm the January 2011 results because the laboratory noted that the January 2011 groundwater sample containers were inappropriate for the dissolved metals analysis; aliquots were taken from unpreserved containers, filtered and preserved appropriately.

Soil and groundwater samples were collected in general accordance with accepted sampling protocols, transported and submitted to Alpha Analytical, Inc. of Westborough, Massachusetts under proper chain-of-custody procedures. Soil and groundwater analytical test results are summarized in Table 1, which is included with the laboratory test results in Appendix C.

3.4 In-situ Infiltration Testing

Constant head hydraulic conductivity tests were performed within the glaciofluvial deposit at the locations and depths presented in the table below to evaluate the field saturated hydraulic

Responsive ■ Resourceful ■ Reliable 6 conductivity of the soils near the bottom of the proposed subsurface infiltration field. Tests were conducted using a Guelph Permeameter. The hydraulic conductivity for the tests was calculated using the procedures supplied by the manufacturer. The Guelph Permeameter is capable of testing soils with a field saturated hydraulic conductivity ranging 0.014 inch per hour (in/hr) to

14.2 in/hr. Results of the field permeability tests are summarized below.

Test

Location

Approximate Ground Surface

Elevation (ft)

Approximate Depth of Test (in)

Field Saturated Hydraulic

Conductivity (KFS) (in/hour)

Approximate Depth to

Groundwater (in)

Depth to

ESHWT

(in)

TP-8 155.1 48 1.7 N/E N/O

TP-9 155.2 48 >14.2 N/E N/O

Notes: N/E – Not encountered N/O – None observed

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

We recommend the proposed building be supported by conventional spread footing foundations bearing on proofrolled natural glaciofluvial sand or on compacted structural fill placed above the natural sand deposit. The lowest floor slab may be designed as a soil-supported slab bearing on a minimum 12-inch-thick layer of compacted structural fill or crushed stone placed over proofrolled natural glaciofluvial sand or existing granular fill proofrolled and compacted to at least 95 percent of the maximum dry density by ASTM D1557 (Modified Proctor).

Excavated granular fill may be selectively reused as structural fill below a depth of 12 inches from bottom of footings or floor slab, provided it is free of deleterious materials and it can be adequately compacted. Existing granular fill may be used as structural fill directly beneath footings and floor slab if it meets the gradation requirements for imported structural fill discussed herein.

Support of floor slabs and pavements on or above existing fill soils is discussed in this report.

However, even with the recommended construction testing services, there is an inherent risk for the owner that compressible fill or unsuitable material within or buried by the fill will not be discovered. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill, but can be reduced by performing additional testing and evaluation.

If the owner’s risk tolerance is low, relative to potential postconstruction settlement of floor slabs, we recommend removing the existing uncontrolled fill in its entirety and replacing it within

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Based on the depth to groundwater observed during drilling, dewatering is not anticipated for construction of building elements or site utilities. We recommend including a moisture barrier below the building floor slab if proposed floor coverings will be susceptible to moisture-related damage.

Geotechnical engineering recommendations for foundation systems and other earth-connected phases of the project are outlined below. The recommendations contained in this report are based upon the results of field and laboratory testing, engineering analyses, and our current understanding of the proposed development.

4.2 Earthwork

The following presents recommendations for site preparation, excavation, subgrade preparation, and placement of fill for the project. The recommendations presented for design and construction of earth-supported elements, including foundations, slabs and pavements, are contingent upon the recommendations outlined in this section.

Earthwork on the project should be observed and evaluated by Terracon representatives. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project.

4.2.1 Subgrade Preparation

Existing organic topsoil and root zones should be removed from proposed building and pavement areas. Following the required stripping, excavation to rough grade and before placing new fill the natural inorganic soil subgrades should be proofrolled with at least six passes each way of a minimum 10-ton vibratory roller in open areas, or a 1-ton vibratory roller or large plate compactor in trenches before placing new fill.

Due to the uncontrolled backfill from demolition of previous structures, existing fill is not suitable for foundation support in its current condition. Where fill is encountered at foundation subgrade elevation, it should be removed from the foundation bearing zone to undisturbed natural soil and proofrolled as discussed above.

A geotechnical engineer, or his/her representative, should review the subgrade during the proof-rolling process. Soft/unstable zones should be overexcavated from the building footprint and footing bearing zones to competent material and replaced with compacted structural fill or

Responsive ■ Resourceful ■ Reliable 8 crushed stone, as necessary. Overexcavation efforts should be accomplished in accordance with the recommendations presented in Section 4.3.2 Construction Considerations.

Following proofrolling, structural fill or crushed stone may be placed and compacted to achieve design footing/slab subgrade. Where subgrades become wet, unstable and/or difficult to proof-roll, the use of crushed stone should be considered in lieu of structural fill. Crushed stone, when used, should be underlain with a geotextile separation fabric, such as Mirafi 140N or equivalent.

4.2.2 Fill Materials and Placement

Fill materials should consist of mineral soil free from debris or other deleterious material.

Frozen material should not be used and fill should not be placed on frozen subgrades. Crushed stone or other similar noncementitious, poorly-graded materials should not be used as fill or backfill without the prior approval of the geotechnical engineer.

Imported structural fill meeting the criteria defined below should be placed within 12 inches of foundations and the floor slab. Fill should meet the following material property requirements:

Fill Type1 USCS Classification Acceptable Location for Placement

Structural Fill

GW, GP, SW, SP, GW-

GM, GP-GM, SW-SM,

SP-SM 2

All locations and elevations.

Common Fill Varies 3

Common fill may be used for site grading to within 6 inches of finished grade or pavement subgrades.

Common fill should not be used under settlement sensitive structures.

1. Compacted structural fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used. Fill should not be placed on a frozen subgrade.

2. Imported structural fill should meet the following gradation:

Sieve Size

Percent Passing by

Weight

8-inch 100 3-inch 70 – 100* ¾-inch 45 – 95 No. 4 30 – 90 No. 10 25 – 80 No. 40 10 – 50 No. 200 0 – 10

* Maximum 3-inch particle size within 12 inches of the underside of footings or slabs

3. Imported Common fill should have a maximum particle size of 6 inches and no more than 25 percent by weight passing the US No. 200 sieve.

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4.2.3 Compaction Requirements

The recommended compaction and moisture criteria for engineered fill materials follow:

Fill Lift Thickness Vibratory Rollers: 12 inches or less in loose thickness Plate Compactors: 8 inches or less in loose thickness

Compaction Requirements 1 95% maximum Modified Proctor dry density (ASTM D1557, Method C)

Moisture Content – Granular Material Workable moisture levels

1. We recommend testing structural fill for moisture content and compaction during placement. If in-place density test results indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested, as required, until the specified moisture and compaction requirements are achieved.

4.2.4 Grading and Drainage

Positive drainage should be provided during construction and maintained throughout the life of the development. Infiltration of water into utility trenches or foundation excavations should be prevented during construction.

We recommend permanent cut and fill soil slopes be made no steeper than 3 horizontal (H) to 1 vertical (V). Steeper slopes should be evaluated for slope stability. The recommended 3H:1V slopes are based on our experience and are consistent with slope geometries widely used by state and local government agencies. We recommend seeding exposed earth slopes to provide protection against erosion. Seeded slopes should be protected with erosion mats until the vegetation is established.

4.2.5 General Construction Considerations

The individual contractor(s) is responsible for designing and constructing stable, temporary excavations, as required, to maintain stability of the excavation sides and the excavation bottom. Instability in the form of slope raveling, caving, and sloughing should be expected in all excavations and trenches which extend into the granular materials with little to no cohesion.

Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards.

Based upon the encountered subsurface conditions, subgrade soils exposed during construction are anticipated to be easily disturbed by construction traffic and are likely to become unstable when above optimum moisture. Stability of the subgrade will be affected by precipitation, repetitive construction traffic or other factors. If unstable conditions develop, replacement with granular materials may be necessary.

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Dewatering is not anticipated for construction of foundations and utilities; however, groundwater may be seasonally perched in the upper silty sand and silt layers. If dewatering becomes necessary, the contractor should select a dewatering method to lower groundwater at least 2 feet below the excavation subgrade in order to minimize bearing surface disturbance during construction of footings and utilities.

Efforts should be made to prevent surface water runoff from collecting in excavations.

Subgrade soils that become unstable should be replaced with compacted structural fill or crushed stone, as necessary.

4.3 Building Foundations

In our opinion, the proposed building can be supported by a conventional shallow spread footing foundation system. Design recommendations for shallow foundations for the proposed structure and related structural elements are presented in the following paragraphs.

4.3.1 Design Recommendations

Description Value Foundation type Conventional shallow spread footings

Bearing materials Proofrolled natural glaciofluvial deposit or compacted structural fill or crushed stone placed above the proofrolled natural glaciofluvial deposit.

Net allowable bearing pressures 1

3,000 psf (foundations bearing on proofrolled natural glaciofluvial soils)

- or - 4,000 psf (foundations bearing on minimum 18-inch-thick layer of compacted structural fill or crushed stone placed above proofrolled natural glaciofluvial soils)

Minimum strip footing width 16 inches Minimum isolated spread footing width 24 inches Minimum footing embedment below finished grade for frost protection2

48 inches

Total estimated settlement 3 <1 inch Estimated differential settlement 3 <½ inch between columns; < ½ inch over 40 ft.

1. The recommended net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Assumes unsuitable fill or soft soils, where present, will be replaced with compacted structural fill or crushed stone.

2. Perimeter footing and footings beneath unheated areas. Minimum recommended embedment for interior footings beneath heated areas is 18 inches below finished grade.

3. 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.

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The allowable foundation bearing pressures apply to dead loads plus design live load conditions. The design bearing pressure may be increased by one-third when considering total loads that include wind or seismic conditions. The weight of the foundation concrete below grade may be neglected in dead load computations.

Footings should be proportioned to reduce differential foundation movement. Proportioning based on equal total settlement is recommended; however, proportioning to relative constant dead-load pressure will also reduce differential settlement between adjacent footings.

4.3.2 Construction Considerations

Foundations for the proposed building and related structural elements should bear directly on proofrolled natural glaciofluvial sand or a minimum 18-inch-thick layer of compacted structural fill or crushed stone placed above proof-rolled undisturbed natural soil subgrade, as presented in Section 4.3.1.

Overexcavation for compacted backfill placement below footings should extend laterally beyond all edges of the footings at least 8 inches per foot of over-excavation depth below footing base elevation. The soil subgrades should be reviewed and proof-rolled as described in Section 4.2 Earthwork of this report. The overexcavation should then be backfilled up to the footing base elevation with structural fill or crushed stone placed in lifts of 8 inches or less in loose thickness and compacted to at least 95 percent of the material's maximum Modified Proctor dry density (ASTM D1557). The overexcavation and backfill procedure is described in the adjacent figure.

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Foundation excavations should be observed by the geotechnical engineer. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required.

4.4 Seismic Considerations

4.4.1 Liquefaction Potential

The initial test borings (B-1 through B-6) identified loose to very loose glaciofluvial deposits made up of poorly graded sands and silty sands extending to the maximum depth of the explorations (approximately 30 feet below existing grade). Based on the relatively uniform gradation of the deposit, very loose relative density below the groundwater table, and criteria defined in the Commonwealth of Massachusetts Building Code, 8th Edition, it appeared that the site soils may be susceptible to liquefaction during a seismic event. However, these explorations were advanced using standard hollow-stem auger drilling techniques, which can be more susceptible to disturbance, particularly when loose, noncohesive soils are encountered below the water table.

A supplemental investigation was performed to conduct a site-specific liquefaction evaluation.

Four test borings (B-101 through B-104) were advanced to refusal at depths ranging from 48 to 59 feet below existing grade to evaluate further the soil profile using drive-and-wash drilling techniques. In addition, grain-size distribution tests (sieve analyses) and Atterberg Limit tests were performed on select soil samples to evaluate the gradation and plasticity of soil samples of particular concern.

Field and laboratory test results were used to perform site specific liquefaction analyses.

Liquefaction analyses were performed in general accordance with industry standards. Standard penetration tests (SPT’s) were normalized and compensations were made to address silt content. A maximum ground surface acceleration (Amax) equal to 0.13g was used in the analysis based on a 2-percent exceedance in 50 years. Based on the subsurface information, laboratory test data, and our analyses the site does not appear to be susceptible to liquefaction during a seismic event.

4.4.2 Seismic Design Criteria

DESCRIPTION VALUE

Code Used Massachusetts Building Code, 8th Edition1 Site Class D 2 Liquefaction potential in event of an earthquake

Does not appear to be susceptible to liquefaction.

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1. In general accordance with the Massachusetts Building Code, 8th Edition (MBC), Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile.

2. The MBC requires a site soil profile determination extending a depth of 100 feet for seismic site classification. The current scope does not include the required 100-foot soil profile determination.

Borings extended to refusal on bedrock at a maximum depth of approximately 59 feet, and this seismic site class definition considers that bedrock continues below the maximum depth of the subsurface explorations.

4.5 Floor Slabs

4.5.1 Design Recommendations

Description Value

Floor Slab support 1

Minimum 12-inch-thick layer of compacted structural fill or crushed stone placed above compacted existing granular fill or undisturbed natural soil subgrade proof-rolled as discussed in Section 4.2 Earthwork.

Modulus of subgrade reaction (k) 150 pounds per square inch per inch (psi/in)

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 foundation.

The use of a vapor retarder/barrier should be considered beneath concrete slabs 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/barrier, the slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder/barrier.

Additional floor slab design and construction recommendations follow:

Positive separations and/or isolation joints should be provided between slabs and all foundations, columns, or utility lines to allow independent movement.

Control joints should be provided in slabs to control the location and extent of cracking.

Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1R are recommended.

4.5.2 Construction Considerations

Existing inorganic granular fill may be left in place beneath floor slabs, provided it is observed to be free of deleterious materials and buried debris, and relatively firm, dry and stable by the project geotechnical engineer or his/her representative at the time of construction. The existing granular fill subgrades should be reviewed by the geotechnical engineer, proofrolled, and

Responsive ■ Resourceful ■ Reliable 14 compacted to at least 95 percent of the maximum dry density as determined by ASTM D1557 (Modified Proctor) with a minimum 10-ton vibratory roller as described in Section 4.2 Earthwork of this report. Following proofrolling and compaction of the existing fill, compacted structural fill may be placed as necessary to achieve slab subgrade.

4.6 Lateral Earth Pressures

4.6.1 Design Criteria

Reinforced concrete walls with unbalanced backfill levels due to using structural backfill should be designed for earth pressures at least equal to those indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained.

Two wall restraint conditions are shown. Active earth pressure is commonly used for design of freestanding cantilever retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls, but assume compacted granular backfill.

Earth Pressure Coefficients Earth Pressure

Conditions Coefficient for Backfill Type

Equivalent Fluid Density (pcf)

Surcharge Pressure, p1 (psf)

Earth Pressure, p2 (psf)

Active (Ka) Granular - 0.30 40 (0.33)S (40)H At-Rest (Ko) Granular - 0.47 56 (0.47)S (56)H Passive (Kp) Granular - 3.0 360 --- ---

Applicable conditions to the above tables include:

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For active earth pressure, wall must rotate about base, with top lateral movements of about 0.002 H to 0.004 H, where H is wall height

For passive earth pressure to develop, wall must move horizontally to mobilize resistance

Uniform surcharge, where S is surcharge pressure

Backfill compacted to 92 percent of Modified Proctor maximum dry density

Loading from heavy compaction equipment not included

No hydrostatic pressures acting on wall

No dynamic loading

No safety factor included in soil parameters

Ignore passive pressure in frost zone

Backfill placed against structures should consist of granular soils or processed inorganic demolition fill. For the above earth pressures to be valid, the granular backfill must extend out from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively. To calculate the resistance to sliding, a value of 0.40 should be used as the ultimate coefficient of friction between the footing and the underlying soil.

As an alternative to free-draining granular fill, a prefabricated drainage mat may be used. A pre-fabricated drainage mat is a plastic drainage core or mesh covered with filter fabric to prevent soil intrusion that is fastened to the wall and connected to a drainage pipe before placing backfill.

4.7 Pavements

4.7.1 Design Recommendations

Flexible Pavements: Flexible pavement design was based on the American Association of State Highway and Transportation Officials’ (AASHTO) Guide for Design of Pavement Structures (1993). The thickness of each course is a function of subgrade strength, anticipated traffic volume, design life, serviceability factors, and frost susceptibility. In the design process, we used our engineering judgment, a design life of 20 years, and an assumed 18-kip equivalent axle load (EAL) of 100,000 based on preliminary traffic loads (portable generator, truck, and trailer loads) provided by the client. Reference is mad to materials described by the MHD Standard Specifications for Highways and Bridges. The following pavement design is recommended:

Responsive ■ Resourceful ■ Reliable 16

Flexible Pavement Material Pavement Thickness (inches)

Bituminous Concrete Top Course (MHD – M3.11.03, Table A – Dense Mix)

1.5

Bituminous Concrete Binder Course (MHD – M3.11.03. Table A – Binder Course)

1.5

Dense-graded Crushed Stone for Sub-base

(MHD – M2.01.7)

6.0

Processed Gravel for Subbase (MHD - M1.03.1) 6.0

Rigid Pavements: Concrete compactor pad and rigid pavement designs, where required, are based on the AASHTO Guide of Design of Pavement Structures (1993). The thickness of the concrete is a function of subgrade strength, traffic design life, serviceability factors, and frost susceptibility. A 20-year design life and 18-kip EAL of 100,000 were used for rigid pavement design. The following is a summary of design recommendations.

Rigid Pavement Material Heavy-duty

Thickness (inches)

Type II Portland Cement (Reinforced Concrete 4,000 psi) 6.0

Processed Gravel for Subbase (MHD - M1.03.1) 12.0

For dumpster pads, as a minimum, the concrete pavement area should be large enough to support the container and tipping axle of the refuse truck. The outer edges of concrete pavement are susceptible to damage as trucks move from the concrete to the adjacent bituminous concrete. Therefore, the concrete thickness of the outer 2 feet of the concrete pavement should be increased to 12 inches. Dowels should be placed across slab expansion joints to limit differential settlements. Welded wire mesh (¼ inch) should be incorporated into the rigid concrete pavement design to provide tensile strength and increase serviceability. The above sections represent minimum thicknesses and, as such, periodic maintenance should be anticipated.

4.7.2 Construction Considerations

Existing inorganic granular fill may remain in-place beneath the designed pavement section provided it is proofrolled and observed by the geotechnical engineer as discussed in Section 4.2 Earthwork of this report. Base course or pavement materials should not be placed when the

Responsive ■ Resourceful ■ Reliable 17 subgrade surface is wet. Surface drainage should be provided away from the edge of paved areas to minimize lateral moisture transmission into the subgrade.

Preventative maintenance should be planned and provided through an ongoing pavement management program in order to enhance future pavement performance. Preventative maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment.

5.0 GENERAL COMMENTS

Terracon should be retained to review final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide observation and testing services during grading, excavation, foundation construction and other earth-related construction phases of the project.

The analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between borings, 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 an 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.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, express 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

FIELD EXPLORATIONS

FIGURES

AND

FIELD EXPLORATION DESCRIPTION

Res pons ive ■ Res ou rcefu l ■ Reliab le Page 1 of 2

FIELD EXPLORATION DESCRIPTION

Six test borings (B-1 through B-6) were drilled to depths ranging from approximately 31 to 32 feet below the ground surface at the site on January 4 and 5, 2011. Ten test pits (TP-1 through TP-10) were excavated to depths ranging from 10 to 11 feet below existing grades on January 7, 2011. An additional four test borings (B-101 through B-104) were advanced as part of a site specific liquefaction study between February 24, 2011 and March 2, 2011. Supplemental explorations were drilled to refusal at depths ranging from 48 to 59 feet below existing grade.

Explorations were advanced at the approximate locations shown on the attached Subsurface Exploration Location Plan (Exhibit A- 2). Explorations were located as follows:

Borings Location Approximate Depth (feet)

B-1 through B-6 Building Area 31 to 32

B-101 through B-104 Building Area 48 to 59

TP-1 through TP-7, TP-10 Parking Area 10 to 11

TP-8 and TP-9 Parking and Subsurface

Infiltration Area

Test borings were advanced by GeoSearch, Inc. of Fitchburg, Massachusetts using a truck-mounted drill rig and 4¼-inch-inside-diameter hollow-stem augers, or 4-inch-diameter flush-joint casing with drive-and-wash drilling techniques. Borings were located in the field by tape measurement to line-of-sight referencing existing site features. Boring locations were marked in the field for subsequent survey by the project surveyor. The accuracy of boring locations should only be assumed to the level implied by the method used.

Soil samples were generally obtained nearly continuously from ground surface until groundwater was encountered, and at 5-foot intervals thereafter using a standard 2-inch-outside-diameter split-barrel sampler. Standard Penetration Tests (SPTs) were performed in general accordance with industry standards. Density of soil samples are based on N-values, which is determined by adding the number of hammer blows required to drive the sampler from 6 to 18 inches.

An automatic SPT hammer was used to advance the split-barrel sampler in borings B-1 through B-6. A greater efficiency is typically achieved with the automatic hammer compared to the conventional safety hammer operated with a cathead and rope. Published correlations between the SPT values and soil properties are based on the lower efficiency cathead and rope method.

This higher efficiency affects the standard penetration resistance blow count (N) value by increasing the penetration per hammer blow over what would obtained using the cathead and rope method. The effect of the automatic hammer's efficiency has been considered in the interpretation and analysis of the subsurface information for this report.

Res pons ive ■ Res ou rcefu l ■ Reliab le Page 2 of 2

Visual classification of soils is shown on test boring and test pit logs included in Appendix A.

Groundwater conditions were measured in each boring at the time of drilling, stabilized groundwater levels were measured in monitoring wells subsequent to completion of the exploration program.

BORING LOGS B1 THROUGH B-6

SP-SM

SM

SM

SM

SP-SM

SP-SM

SP-SM

SM

SM

SP-SM

SP-SM

SP-SM

154.5

123.5

0.25 0.9

3-inches topsoil.

FILL Poorly graded sand, trace brick.

POORLY GRADED SAND with silt to SILTY SAND, light brown, loose to medium dense.

Sample wet at 6 feet.

Sample dry to moist at 12 feet.

Sample wet at 16 feet.

(GLACIOFLUVIAL DEPOSIT)

BORING TERMINATED AT 32.0 feet.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

1.1

11-9 6-4

8-7 6-6

4-5 4-4

7-6 4-3

4-3 4-4

3-4 6-5

5-5 4-6

3-2 4-4

7-6 5-5

3-4 4-5

2-3 4-5

2-3 4-4

1-2 2-3

SAMPLES TESTS

Approx. Surface Elev.: 155.35 ft

CLIENT

PROJECT

NAME

SITE

LOCATION

Gale Associates

Drop Method:

WS

U S

C S

S Y

M B

O L

The stratification lines represent the approximate boundary lines between soil and rock types: in-situ, the transition may be gradual.

G R

A P

H

IC

L O

G

D E

P T

H , f t.

Natick, MA

BORING STARTED

BORING COMPLETED16

DESCRIPTION

1-4-11

1-4-11

Mike

J1115100

BORING NO. B-1

CME 75

RJF

RIG

LOGGED BY:

Hammer Weight: 140 lbs.

Casing Dia: 4.25 in.

WL

WL

WL

WATER LEVEL OBSERVATIONS, ft

Natick National Guard Readiness Center

FOREMAN

JOB #

Casing Type: HSA

Hammer Type: Automatic

N U

M B

E R

T Y

P E

R E

C O

V E

R Y

, i n.

U N

C O

N F

IN

E

D S

T R

E N

G T

H , p si

P

ID

pp m

O T

H E

R T

E S

T S

S P

T

B lo w s pe r

6"

W A

T E

R C

O N

T E

N T

T E

R R

A C

O N

B O

R

IN

G L

O G

J

.G

P J

T E

R R

A C

O N

7.

G

D T

/2

/1

SP

SM

SP-SM

ML

ML

ML

SM

SP

SP

SP

SP

124.5

0.25

2.5

3-inches topsoil.

FILL Poorly graded sand with fine gravel, trace silt, light brown, moist, medium dense.

POORLY GRADED SAND to FINE SANDY SILT, light brown, loose to medium dense.

Sample wet at 6 feet.

(GLACIOFLUVIAL DEPOSIT)

BORING TERMINATED AT 31.0 feet.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

11-14 12-15

10-11 12-12

6-8 8-7

7-6 6-6

1-3 4-3

6-9 11-15

2-4 4-4

1-4 5-5

2-2 4-5

5-5 6-8

2-2 2-3

SAMPLES TESTS

Approx. Surface Elev.: 155.39 ft

CLIENT

PROJECT

NAME

SITE

LOCATION

Gale Associates

Drop Method:

WD

(3/1/11)

U S

C S

S Y

M B

O L

The stratification lines represent the approximate boundary lines between soil and rock types: in-situ, the transition may be gradual.

G R

A P

H

IC

L O

G

D E

P T

H , f t.

Natick, MA

BORING STARTED

BORING COMPLETED6

16.7

17.1

16.7

DESCRIPTION

1-6-11

1-6-11

Mike

J1115100

BORING NO. B-2

CME 75

RJF

RIG

LOGGED BY:

(1/11/11)

(3/4/11)

Hammer Weight: 140 lbs.

Casing Dia: 4.25 in.

WL

WL

WL

WATER LEVEL OBSERVATIONS, ft

Natick National Guard Readiness Center

FOREMAN

JOB #

Casing Type: HSA

Hammer Type: Automatic

N U

M B

E R

T Y

P E

R E

C O

V E

R Y

, i n.

U N

C O

N F

IN

E

D S

T R

E N

G T

H , p si

P

ID

pp m

O T

H E

R T

E S

T S

S P

T

B lo w s pe r

6"

W A

T E

R C

O N

T E

N T

T E

R R

A C

O N

B O

R

IN

G L

O G

J

.G

P J

T E

R R

A C

O N

7.

G

D T

/2

ML

ML

ML

ML

SM

SP-SM

ML

SM

SP

SP

SP

154.5

0.4 0.9

4.5-inches topsoil.

FILL Poorly graded sand with gravel and brick fragments.

POORLY GRADED SAND to FINE SANDY SILT, light brown, moist to wet, loose to medium dense.

Sample wet at 8 feet.

(GLACIOFLUVIAL DEPOSIT)

BORING TERMINATED AT 31.0 feet.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

14-13 9-8

10-10 11-11

11-5 7-6

4-4 4-6

7-6 5-5

4-4 3-2

2-3 2-2

3-2 2-2

2-3 4-4

2-4 5-7

2-3 3-3

2-2 3-2

2-3 4-4

2-3 5-5

SAMPLES TESTS

Approx. Surface Elev.: 154.97 ft

CLIENT

PROJECT

NAME

SITE

LOCATION

Gale Associates

Drop Method:

WD

(3/1/11)

U S

C S

S Y

M B

O L

The stratification lines represent the approximate boundary lines between soil and rock types: in-situ, the transition may be gradual.

G R

A P

H

IC

L O

G

D E

P T

H , f t.

Natick, MA

BORING STARTED

BORING COMPLETED8

16.3

16.8

16.3

DESCRIPTION

1-5-11

1-5-11

Mike

J1115100

BORING NO. B-3

CME 75

IKC

RIG

LOGGED BY:

(1/11/11)

(3/4/11)

Hammer Weight: 140 lbs.

Casing Dia: 4.25 in.

WL

WL

WL

WATER LEVEL OBSERVATIONS, ft

Natick National Guard Readiness Center

FOREMAN

JOB #

Casing Type: HSA

Hammer Type: Automatic

N U

M B

E R

T Y

P E

R E

C O

V E

R Y

, i n.

U N

C O

N F

IN

E

D S

T R

E N

G T

H , p si

P

ID

pp m

O T

H E

R T

E S

T S

S P

T

B lo w s pe r

6"

W A

T E

R C

O N

T E

N T

T E

R R

A C

O N

B O

R

IN

G L

O G

J

.G

P J

T E

R R

A C

O N

7.

G

D T

/2

SM

ML

SM

ML

SP-SM

SP

ML

SP-SM

SP

SP

SP

152.5

0.3 1.2 2.5

4-inches topsoil.

FILL Crushed concrete with sand.

FILL Bituminous concrete pieces

FILL Poorly graded sand, trace silt, light brown to tan, moist, medium dense.

POORLY GRADED SAND to FINE SANDY SILT, light brown, moist to wet, loose to medium dense.

Sample wet at 8 feet.

(GLACIOFLUVIAL DEPOSIT)

BORING TERMINATED AT 31.0 feet.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

0.8

10-17 16-11

10-10 9-9

15-7 7-9

11-10 9-8

3-4 2-2

1-3 5-5

7-5 5-6

3-3 5-6

6-6 9-10

2-2 6-6

2-3 4-6

2-3 3-4

5-4 6-4

3-5 4-4

SAMPLES TESTS

Approx. Surface Elev.: 155.20 ft

CLIENT

PROJECT

NAME

SITE

LOCATION

Gale Associates

Drop Method:

WD

(3/1/11)

U S

C S

S Y

M B

O L

The stratification lines represent the approximate boundary lines between soil and rock types: in-situ, the transition may be gradual.

G R

A P

H

IC

L O

G

D E

P T

H , f t.

Natick, MA

BORING STARTED

BORING COMPLETED8

16.5

17.0

16.5

DESCRIPTION

1-4-11

1-5-11

Mike

J1115100

BORING NO. B-4

CME 75

RJF/IKC

RIG

LOGGED BY:

(1/11/11)

(3/4/11)

Hammer Weight: 140 lbs.

Casing Dia: 4.25 in.

WL

WL

WL

WATER LEVEL OBSERVATIONS, ft

Natick National Guard Readiness Center

FOREMAN

JOB #

Casing Type: HSA

Hammer Type: Automatic

N U

M B

E R

T Y

P E

R E

C O

V E

R Y

, i n.

U N

C O

N F

IN

E

D S

T R

E N

G T

H , p si

P

ID

pp m

O T

H E

R T

E S

T S

S P

T

B lo w s pe r

6"

W A

T E

R C

O N

T E

N T

T E

R R

A C

O N

B O

R

IN

G L

O G

J

.G

P J

T E

R R

A C

O N

7.

G

D T

/2

SM/ML

SP-SM

ML

ML

ML

SM

ML

123.5

0.4 1.5

8.5

4-inches topsoil.

FILL Poorly graded gravel with sand, gray-brown-green, moist, medium dense.

FILL Poorly graded sand, trace silt, light brown, moist, medium dense, with concrete pieces from 6 to 8 feet.

POORLY GRADED SAND with silt to NON-PLASTIC SILT, light brown, very loose to medium dense.

Sample wet at 10 feet.

(GLACIOFLUVIAL DEPOSIT)

BORING TERMINATED AT 32.0 feet.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

23-30 13-11

12-14 11-9

8-6 5-5

9-11 12-8

8-5 6-5

3-4 5-6

7-8 6-8

5-3 6-5

5-5 5-5

1-woh/12" woh/24"

4-6 6-9

SAMPLES TESTS

Approx. Surface Elev.: 155.58 ft

CLIENT

PROJECT

NAME

SITE

LOCATION

Gale Associates

Drop Method:

WD

U S

C S

S Y

M B

O L

The stratification lines represent the approximate boundary lines between soil and rock types: in-situ, the transition may be gradual.

G R

A P

H

IC

L O

G

D E

P T

H , f t.

Natick, MA

BORING STARTED

BORING COMPLETED10

DESCRIPTION

1-4-11

1-4-11

Mike

J1115100

BORING NO. B-5

CME 75

RJF

RIG

LOGGED BY:

Hammer Weight: 140 lbs.

Casing Dia: 4.25 in.

WL

WL

WL

WATER LEVEL OBSERVATIONS, ft

Natick National Guard Readiness Center

FOREMAN

JOB #

Casing Type: HSA

Hammer Type: Automatic

N U

M B

E R

T Y

P E

R E

C O

V E

R Y

, i n.

U N

C O

N F

IN

E

D S

T R

E N

G T

H , p si

P

ID

pp m

O T

H E

R T

E S

T S

S P

T

B lo w s pe r

6"

W A

T E

R C

O N

T E

N T

T E

R R

A C

O N

B O

R

IN

G L

O G

J

.G

P J

T E

R R

A C

O N

7.

G

D T

/2

SM/ML

SM/ML

SM/ML

ML

ML

ML

SM

SP

ML

SP

154.5

123.5

0.4

4-inches topsoil.

FILL Concrete with sand.

SILTY SAND to NON-PLASTIC SILT, light brown, moist to wet, loose to medium dense.

Sample wet at 12 feet.

POORLY-GRADED SAND from 20 to 25 feet.

POORLY GRADED SAND from 30 to 32 feet.

(GLACIOFLUVIAL DEPOSIT)

BORING TERMINATED AT 32.0 feet.

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

30-33 15-7

10-9 8-7

12-6 6-7

4-7 5-6

3-5 6-7

3-4 6-6

7-4 5-4

2-2 2-2

4-3 5-4

1-2 2-2

3-3 3-3

4-4 5-4

2-3 4-4

SAMPLES TESTS

Approx. Surface Elev.: 155.25 ft

CLIENT

PROJECT

NAME

SITE

LOCATION

Gale Associates

Drop Method:

WD

U S

C S

S Y

M B

O L

The stratification lines represent the approximate boundary lines between soil and rock types: in-situ, the transition may be gradual.

G R

A P

H

IC

L O

G

D E

P T

H , f…