P691 Final Geotechnical Report.pdf

Report Cover Page

P-691 DBB Aircraft Development & Maintenance Facilities Geotechnical Engineering Report – Revision 2

April 9, 2024 | Terracon Project No. JD215182H

Prepared for:

Pond & Company 3500 Parkway Lane, Suite 500 Peachtree Corners, Georgia 30092

19955 Highland Vista Drive, #170 Ashburn, Virginia 20147

P (703) 726-8030 Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

April 9, 2024

Pond & Company 3500 Parkway Lane, Suite 500 Peachtree Corners, Georgia 30092

Attn: Mr. Mark Hanselman, PE, SE P: (404) 748-4710 E: HanselmanM@pondco.com

Re: Geotechnical Engineering Report – Revision 2 P-691 DBB Aircraft Development & Maintenance Facilities Bonnie Road Patuxent River, MD Terracon Project No. JD215182H

Dear Mr. Hanselman:

We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. PJD225409 dated February 15, 2023. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork, pavements, and the design and construction of foundations and floor slabs for the proposed project.

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

Sincerely, Terracon

Justin R. Kula, EIT Paul E. Burkart, PE Senior Staff Engineer Senior Principal

Geotechnical Engineering Report P-691 DBB Aircraft Development & Maintenance Facilities | Patuxent River, MD April 9, 2024 | Terracon Project No. JD215182H

Facilities | Environmental | Geotechnical | Materials i

Table of Contents Planned Construction

Introduction Project Description Site Conditions Geotechnical Characterization Groundwater Seismic Site Class Liquefaction Infiltration

Field Infiltration Test Results Classification Test Results Recommended Design Infiltration Rate

Earthwork Demolition Site Preparation Subgrade Preparation Existing Fill Fill Material Types Fill Placement and Compaction Requirements Pre-Consolidation Program – Hangar and Apron Area Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Shallow Foundations – Auxiliary Buildings Design Parameters – Compressive Loads Foundation Construction Considerations

Hangar Foundations Shallow Foundations Supported by Ground Improvement Elements –

Hangar Impact Piers Rigid Inclusions Design of Ground Improvement Elements

Auger Cast Piles - Hangar Auger Cast Pile Load Testing Auger Cast Pile Construction Considerations

Floor Slabs Floor Slab Design Parameters Floor Slab Construction Considerations

Pavements Pavement Drainage Pavement Maintenance

General Comments

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Figures GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans Exploration and Laboratory Results Supporting Information

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

Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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Introduction

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed P-691 DBB Aircraft Development and Maintenance Facilities project to be located at Bonnie Road in Patuxent River, MD. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Groundwater conditions

■ Seismic site classification per IBC

■ In-situ infiltration

■ Site preparation and earthwork

■ Demolition considerations

■ Dewatering considerations

■ Foundation design and construction

■ Floor slab design and construction

■ Pavement subgrade and construction considerations

The geotechnical engineering Scope of Services for this project included the advancement of test borings, Cone Penetrometer Tests (CPT), test pits, laboratory testing, engineering analysis, and preparation of this report. Our firm provided a preliminary investigation consisting of 12 soil borings and a geotechnical engineering report for this project on October 28, 2022. Results of the preliminary investigation have also been reviewed as part of this project.

Drawings showing the site and boring, CPT, and test pit locations are shown on the Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs and as separate graphs in the Exploration Results section.

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Project Description

Item Description

Information Provided

■ The Scope of Architect-Engineer Services (SAES) dated 21 September 2022 was provided in an email from POND.

An updated Attachment 10 to the SAES was provided on 13 February 2023.

■ Preliminary site plans

■ Anticipated hangar loading information and anticipated finished floor elevation was provided in an email from POND and Michael Baker on June 26, 2023

Project Description

We understand that the project includes construction of a new hanger building and associated aircraft apron and taxiway, equipment pads, stormwater management, and POV parking lots to support Taxiway Alpha. Three auxiliary buildings – HAZMAT Storage, Sonobuoy Storage, and PEMB Storage – are also included in support of NAS Patuxent River’s mission.

Finished Floor Elevation

■ The anticipated finished floor elevation of the Hangar and apron is approximately EL 47.0.

■ We assume that all the proposed auxiliary buildings will be constructed at about existing grade.

Maximum Loads

■ Typical loads for the hangar are anticipated to range from 50 to 100 kips. However, maximum column loads of up to 1420 and 830 kips are anticipated at the front of the structure.

■ We assume that column loads will not exceed about 225 kips for the three auxiliary buildings.

■ We understand maximum slab on grade loads at the hangar slab and apron will not exceed 250 psf

Grading/Slopes

■ Grading within the hangar and apron area is expected to include up to approximately 10 feet of fill placement.

Portions of this site will also be constructed in up to 4 feet of cut. Areas of stormwater management may include cuts of up to 9 feet.

■ We assume that the proposed HAZMAT Storage, Sonobuoy Storage, and PEMB Storage buildings will be built at about existing grade.

Pavements Pavements to support personal vehicle parking and driveways are anticipated at each of the sites.

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

Site Conditions

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

Item Description

Parcel Information

The project takes place at four sites at NAS Patuxent River, Maryland. The general locations are provided below:

■ Main Hangar

■ Located south and northeast of the intersection of

Millstone Road and Bonnie Road. Coordinates:

38.30111° N, -76.43942° W

■ HAZMAT Storage

■ Located northeast of the intersection of Millstone Road and Peary Road. Coordinates: 38.28239° N, - 76.43568° W

■ Sonobuoy Storage

■ Located north of the intersection of Emory Road and

Hoise Road. Coordinates: 38.28239° N, -76.43649° W

■ PEMB Storage

■ Located northeast of the intersection of Cedar Point Road and Saufley Road. 38.2897° N, -76.42352° W

See Site Location

Existing Improvements

■ The northern portion of the hangar site is currently heavily wooded. Federal facilities and Taxiway Alpha make up the southern and western portion of the hangar site.

■ The HAZMAT, sonobuoy, and PEMB storage sites consist of federal facilities, paved parking areas, and landscaped grassy areas.

Current Ground Cover

Heavily vegetated, landscaped grassy areas, and asphalt taxiways.

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Item Description

Existing Topography (from existing conditions plans)

The elevation at site ranges between elevation EL 35 to EL 48

MSL.

Geology

The site is located within the Coastal Plain Physiographic Province of Maryland. The Coastal Plain consists of a seaward thickening wedge of unconsolidated to semi-consolidated sedimentary deposits from the Cretaceous Geologic Period to the Holocene Geologic Epoch. These deposits represent marginal-marine to marine sediments consisting of interbedded sands and clays. The Coastal Plain is bordered to the east by the Atlantic Ocean and to the west by the Piedmont Physiographic Province.

The dividing line between the Coastal Plain and the Piedmont is locally referred to as the “Fall Line”. This name comes from the waterfalls that form as a result of the differential erosion that occurs as streams cross the Piedmont/Coastal Plain contact.

Specifically, the native soils are alluvial Lowland Deposits of the Quaternary geologic period. The Lowland Deposits are underlain by sediments of the Chesapeake Group. The Chesapeake Group soils consist of (from youngest to oldest) the St. Marys Formation, Choptank Formation, and Calvert Formation, all of the Miocene geologic age. At the sites of this project, the strata immediately underlaying the Lowland Deposits compare favorably with the gray clays of the St. Marys Formation, and the gray silty sands of the Choptank Formation, respectively.

The Choptank Formation contains prominent shell beds with calcareous soils. Existing fill associated with previous site development was also encountered.

Geotechnical Characterization

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

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

Model Layer

Layer Name General Description

1 Existing Fill generally stiff or loose to medium dense, CLAYEY SAND, SILTY SAND, LEAN CLAY, with varying amounts of sand and gravel, FILL, brown, black, orange, moist

Lowland Deposits very loose to dense, POORLY GRADED SAND (SP), SILTY SAND (SM), CLAYEY SAND (SC), varying amounts of gravel, gray, orange, brown, moist

St Marys

Formation soft to medium stiff or medium dense, LEAN CLAY (CL), FAT CLAY (CH), or POORLY GRADED SAND WITH SILT (SP-SM), dark blue gray, moist

Choptank Formation medium dense to very dense, SILTY SAND (SM), SILTY SAND WITH GRAVEL (SM), blue gray, moist, contains shells

Groundwater

Groundwater level observations were made in the field during drilling and up to one day after the completion of the test borings. A summary of the water level readings, where groundwater was encountered, is presented in the table below.

Test Boring Depth to Groundwater (ft) Groundwater Elevation (ft)

A-1 21 EL 22

A-2 24 EL 21

H-1 23 EL 22

P-5 14 EL 32

P-6 14 EL 32

SWM-1 19 EL 24

SWM-2 20 EL 24

SWM-3 22 EL 23

SWM-5 25 EL 15

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Test Boring Depth to Groundwater (ft) Groundwater Elevation (ft)

SWM-7 16 EL 29

SWM-8 16 EL 30

SWM-9 18 EL 28

SWM-13 12 EL 23

SWM-14 8 EL 27

SWM-15 16 EL 19

SWM-16 17 EL 22

SWM-17 9 EL 28

SWM-18 16 EL 26

SWM-19 16 EL 24

B-1 25 EL 18

B-2 10 EL 26

B-3 18 EL 24

B-4 16 EL 29

B-5 15 EL 29

B-6 15 EL 28

B-7 25 EL 18

B-8 23 EL 22

B-9 13 EL 32

B-10 19 EL 26

B-11 24 EL 16

B-12 25 EL 15

The groundwater observations presented herein are considered to be an indication of the groundwater levels at the dates and times indicated. Where more impervious silty and clayey soils are encountered, the amount of water seepage into the borings is limited, and it is generally not possible to establish the location of the groundwater table through short term water level observations. Accordingly, the groundwater information presented

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Facilities | Environmental | Geotechnical | Materials 7 herein should be used with caution. Also, fluctuations in groundwater levels should be expected with seasons of the year, construction activity, changes to surface grades, precipitation, or other similar factors.

Seismic Site Class

A seismic survey was performed at the site to measure the in-situ shear wave velocities of the subsurface, for use in determining the seismic site class in accordance with IBC 2018 requirements. The seismic site class definitions based on the weighted average of shear wave velocity in the upper 100 feet of the soil profile are presented in the IBC and are presented below:

Site Class

Soil Profile Name Weighted Average Shear Wave Velocity, sv (ft/s)

A Hard rock sv > 5,000 ft/s

B Rock 2,500 < sv ≤ 5,000 ft/s

C Very dense soil and soft rock 1,200 < sv ≤ 2,500 ft/s

D Stiff soil profile 600 ≤ sv ≤ 1,200 ft/s

E Soft soil profile sv < 600 ft/s

The results of the seismic shear wave survey are presented in Exploration Results and are presented below. The approximate locations of the seismic arrays are shown on the Exploration Plan.

Seismic Array No.

Weighted Average Shear

Wave Velocity, sv (ft/s) Site Class

L-1 925 D

L-2 922 D

L-3 872 D

L-4 750 D

Based on the results of the shear wave testing, the site soils have been assigned to a site class D per the International Building Code (IBC) 2018.

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Liquefaction

Soil liquefaction is a process by which loose, saturated granular deposits lose a significant amount of their shear strength due to pore water pressure buildup resulting from cyclical loading. Such a reduction/loss of shear strength can result in both settlement and horizontal movement (lateral spreading) of the soil mass. There are several soil characteristics that a soil must have to be prone to liquefaction. In addition, the age and stress history of the soils and the amount and plasticity of soil fines has an effect on the liquefaction potential for a soil. Older deposits have had a greater amount of time to consolidate and are more likely to have been subjected to cyclical loading in the past, which increases a soils resistance to liquefaction.

Based on the results of the four refraction microtremor (ReMi) survey lines completed at the site, the soil profile consists of medium dense sands and soft to medium stiff clays with a shear wave velocity (Vs) of about 750 feet per second (ft/s) in the upper 60 feet.

At about 60 feet depth, shear wave velocities range from about 800 ft/s to 2,300 ft/s.

The shear wave data suggests that the soil profile beneath the site becomes denser with depth. Groundwater was encountered at depths between about 10 and 35 feet below existing site grades.

A liquefaction analysis was performed using representative CPT soundings in the Settle3 program. Graphical results of the analysis are presented in Supporting Information.

Some localized areas of moderate liquefaction potential may be present at the site due to the shallow groundwater and areas of minimal fines content. However, based on liquefaction analysis using representative CPT data, the liquefaction factor of safety is greater than 1 throughout the soil profile. Also, the soils associated with the St Mary’s formation, from about 45 to 65 feet below site grades are less likely to liquefy during cyclical loading due to the presence of plastic fines. It is our opinion that the potential for liquefaction at the site is negligible.

Infiltration

Two methods were used to estimate infiltration capabilities on the subject site: in-situ infiltration testing and published correlations with soil classifications. Details regarding the in-situ infiltration and classification test techniques, the estimated infiltration rates from the individual methods, and the recommended design infiltration rate for the site soils are presented herein.

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Field Infiltration Test Results

In-situ infiltration tests are performed in the field to observe the rate at which water will permeate the soil under saturated conditions. 16 test borings were drilled in areas of planned infiltration. Test borings were initially drilled to depths about 26 feet below the site grades and allowed to remain open for a period of approximately 24 hours to allow any groundwater levels within the boreholes to stabilize. After 24 hours, offset infiltration test holes were drilled at the boring locations to planned infiltration invert elevations. Four-inch diameter PVC casing was set to the bottom of the test holes. The purpose of the casing is to prevent caving of test hole sidewalls. After setting the PVC casing, the borehole was filled with water to saturate the bottom subsoils. The following day, the test hole was refilled with water and the water level in each test hole was recorded every hour for a 4-hour period. Using this procedure, the average change in the water level over the 4-hour period is considered the infiltration rate. Based on the results of the in-situ infiltration tests, the infiltration rates that have been calculated and are presented below in the table below.

Boring Approximate

Test Depth (ft) Approximate Test

Elevation (ft) Field Infiltration

Rate (in/hr)

SWM-1 4.0 EL 39 24.3

SWM-2 4.0 EL 40 24.0

SWM-3 4.0 EL 41 24.9

SWM-4 4.0 EL 37 13.5

SWM-5 4.0 EL 36 12.3

SWM-6 4.0 EL 35 9.6

SWM-7 4.0 EL 41 21.6

SWM-8 4.0 EL 42 20.7

SWM-9 4.0 EL 42 23.4

SWM-13 4.0 EL 31 18.0

SWM-14 4.0 EL 31 13.2

SWM-15 4.0 EL 35 22.2

SWM-16 4.0 EL 34 21.6

SWM-17 4.0 EL 33 25.5

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Boring Approximate

Test Depth (ft) Approximate Test

Elevation (ft) Field Infiltration

Rate (in/hr)

SWM-18 4.0 EL 38 21.0

SWM-19 4.0 EL 36 22.5

Classification Test Results

The classification test method is performed with grain-size sieve analyses including textural analysis on samples obtained from corresponding proposed infiltration depths, to determine the USDA soil texture classifications. Published correlations between USDA classifications and infiltration rates were used to provide estimated hydraulic conductivity values. Since hydraulic conductivity and infiltration values are essentially equal at no head conditions, using the hydraulic conductivity values to estimate the infiltration rates provides a conservative estimate of infiltration for use in design.

Estimated infiltration rates using the USDA soil texture classifications are presented in the table below.

Boring Approximate Test

Depth (ft) USDA Soil Texture

Classification Estimated Infiltration

Rate (in/hr)

SWM-1 4.0 Sand 8.27

SWM-2 4.0 Sand 8.27

SWM-3 4.0 Sand 8.27

SWM-4 4.0 Sand 8.27

SWM-5 4.0 Sand 8.27

SWM-6 4.0 Sand 8.27

SWM-7 4.0 Loam 0.52

SWM-8 4.0 Sand 8.27

SWM-9 4.0 Loamy Sand 2.41

SWM-13 4.0 Loam 0.52

SWM-14 4.0 Sandy Loam 1.02

SWM-15 4.0 Loamy Sand 2.41

SWM-16 4.0 Sand 8.27

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Boring Approximate Test

Depth (ft) USDA Soil Texture

Classification Estimated Infiltration

Rate (in/hr)

SWM-17 4.0 Sand 8.27

SWM-18 4.0 Sand 8.27

SWM-19 4.0 Sand 8.27

Recommended Design Infiltration Rate

It is our opinion that it should be feasible to provide stormwater management through infiltration at all stormwater locations tested. As shown above, the calculated field infiltration rates range from approximately 9.6 inch/hr to 24.9 inch/hr. Based on observations made in the field and the USDA soil texture classifications, it is our opinion that the design infiltration rate from the USDA soil texture classification shown in the table above be used at the locations tested.

It should be noted that the recommended design infiltration rate presented herein is intended for use in design. However, during construction, observations of the subgrade conditions should be made to confirm that the subgrade soils are consistent with the soils analyzed in this report.

Earthwork

Earthwork is anticipated to include demolition, clearing, excavations, a pre-consolidation program, and engineered fill placement. The following sections provide recommendations for use in the preparation of specifications for the work.

Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations, floor slabs, and pavements.

Demolition

The proposed buildings will be constructed in areas of existing facilities which will need to be demolished, as well as exterior sidewalks, pavements, and utilities. We recommend existing foundations, slabs, and utilities be removed from within the proposed building footprint and at least 5 feet beyond the outer edge of foundations.

For areas outside the proposed building footprints and foundation bearing zones, existing foundations, floor slabs, and utilities should be removed where they conflict with proposed utilities and pavements. In such cases, existing foundations, floor slabs, and

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Facilities | Environmental | Geotechnical | Materials 12 utilities should be removed to a depth of at least 2 feet below the affected utility or design pavement subgrade elevation.

Site Preparation

Prior to placing fill, existing vegetation, topsoil, and root mats should be removed.

Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas.

Mature trees are located within or near the footprint of some of the proposed buildings, which will require removal at the onset of construction. Tree root systems can remove substantial moisture from surrounding soils. Where trees are removed, the full root ball and all associated dry and desiccated soils should be removed. The soil materials which contain less than 5 percent organics can be reused as engineered fill provided the material is moisture conditioned and properly compacted.

Based on historic imagery, portions of the sites were developed with buildings that have since been razed. Historic aerial imagery from 1993 is included as an attachment in Supporting Information. Evidence of construction debris and concrete was observed in TP-2 as shown in the test pit photo logs in Exploration Results. We expect additional such debris could be encountered during construction. If unexpected fills or underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction.

Subgrade Preparation

Subgrades should be proofrolled with an adequately loaded vehicle such as a fully-loaded (minimum 20 ton) tandem-axle dump truck. The proofrolling should be performed under the observation of the Geotechnical Engineer or representative. Areas excessively deflecting under the proofroll should be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should be removed. Excessively wet or dry material should either be removed or moisture conditioned and recompacted.

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

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

however, the workability of the subgrade may be affected by precipitation, repetitive

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Facilities | Environmental | Geotechnical | Materials 13 construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

Existing Fill

As noted in Geotechnical Characterization, some borings encountered previously placed fill to depths ranging from about 1 to 4 feet. We have no records to indicate the degree of control, and consequently, the fill is considered unreliable for support of foundation loads. Support of floor slabs and pavements on or above existing fill soils is discussed in this report. However, even with the recommended construction procedures, inherent risk exists 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 following the recommendations contained in this report.

If the owner elects to construct the floor slabs on the existing fill to reduce initial construction costs in exchange for increased potential longer-term distress, the following protocol should be followed. After the planned grading has been completed, the area should be undercut 2 feet within the building area and 10 feet beyond the lateral limits of the building area. Following this overexcavation, the entire area should be proofrolled with heavy, rubber tire construction equipment, to aid in delineating areas of soft or otherwise unsuitable soil. Once unsuitable materials have been remediated, and the subgrade has passed the proofroll test, backfill to finished subgrade elevation can begin.

The existing undocumented fill that was removed can be evaluated for reuse as structural fill.

If the owner elects to construct pavements on the existing fill, the following protocol should be followed. Once the planned subgrade elevation has been reached, the entire pavement area should be proofrolled. Areas of soft or otherwise unsuitable material should be undercut and replaced with either new structural fill or suitable, existing on site materials.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures, pavements, or constructed slopes. General fill is material used to achieve grade outside of these areas.

Excavated on-site soil may be selectively reused as fill below pavement and landscaping areas if it meets acceptable parameters shown below and is free of deleterious materials. Imported fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved

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Facilities | Environmental | Geotechnical | Materials 14 materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

Material property requirements for on-site soil for use as general fill and structural fill are noted in the table below:

Soil Type 1,2 USCS Classification

Acceptable Parameters (for Structural Fill)

Low Plasticity Cohesive

CL, CL-ML

ML, SM, SC

Liquid Limit less than 40 Plasticity index less than 15

Maximum Dry Density > 105 pcf

Granular

GW, GP, GM, GC,

SW, SP

Less than 25% passing No. 200 sieve

1. Structural and general fill should consist of approved materials free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site.

2. Existing fill free of deleterious material may be re-used for fill if it meets the requirements presented above.

Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used 4 to 6 inches in loose thickness when hand-guided equipment (i.e. jumping jack or plate compactor) is used

Same as structural fill

Minimum Compaction

Requirements 1

98% of max. below foundations and within 1 foot of finished pavement subgrade 95% of max. above foundations, below floor slabs, and more than 1 foot below finished pavement subgrade 100% of max below depth of 10 ft where new fill areas exceed 10 feet

92% of max.

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Item Structural Fill General Fill

Water Content

Range 1 -2% to +2% of optimum

As required to achieve min.

compaction requirements

1. Maximum density and optimum water content as determined by the modified Proctor test (ASTM D 1557).

Pre-Consolidation Program – Hangar and Apron Area

Based on the proposed finished floor elevation, we understand that up to 10 feet of new fill placement is required to reach finished subgrades in the proposed hangar and apron areas. Unacceptable settlements will result from consolidation of the compressible clays of the alluvial St Marys Formation beyond the completion of the proposed construction, without a pre-consolidation program.

A settlement analysis using Settle3 software was performed for the proposed fill placement on site. Based on settlement analysis using the Settle3 program, up to approximately 6 inches of total settlement is anticipated from fill placement to achieve site grades in the hangar/apron area without a pre-consolidation program.

Accordingly, it is recommended that the budget and schedule allow for a pre-consolidation program including wick drain installation and earth surcharge in all areas of fill placement in the hangar and apron areas. Wick drains are recommended to assist in the acceleration of compression of the clay layer by allowing a shorter drainage path for water in the pores of the clay layer. Wick drain spacing of 3 feet should be considered for preliminary budgeting purposes, with wick drain lengths estimated at 80 feet from current site grades. The wick drains should be cut off above the ground surface and terminated into horizontal strip drains or in a gravel drainage layer. If selected, the drainage layer should be at least 12-inches thick and consist of free draining open graded aggregate such as AASHTO No. 57 stone or a clean sand such as AASHTO M-6 sand. The top of the drainage layer should be covered with a layer of geotextile filter prior to placement of the new compacted fill and surcharge. We recommend that the wick drains and surcharge extend at least 10 feet beyond the edges of proposed fill placement in building and apron areas.

An earth surcharge is also recommended to pre-consolidate the underlying clay layer.

The fill placed to reach the design subgrade should be placed and compacted in accordance with the earthwork requirements presented in this report. The table below provides the proposed surcharge height to be placed above the proposed finished grades for the hangar/apron area. The earth surcharge should be placed and compacted in one-foot thick lifts, but there are no specific testing requirements other than to verify that the surcharge materials have a moist unit weight of at least 125 pcf. We recommend

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Facilities | Environmental | Geotechnical | Materials 16 that the surcharge be maintained for a minimum waiting period as presented in the table below after the full height of the surcharge is placed.

Location Recommended Earth

Surcharge Height Above Finished Slab Level

Remarks

Hangar/Apron Area 5 ft

Wick drains installed prior to surcharge. Estimated 3 month waiting period after full height surcharge placement

We recommend installing 12 settlement plates, 6 within the hangar and 6 across the proposed apron area, to monitor the settlement. Measurements of the elevation of the settlement plates should be made twice a week from the initial installation until substantial consolidation settlement of the existing soil profile has occurred. Elevations should be obtained by a licensed surveyor to the nearest 0.001 feet. The settlement plates should be protected from construction activities and traffic. We recommend placing the fill and surcharge load at the very beginning of construction in order to reduce the risk of construction schedule overruns.

Grading and Drainage

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

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

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Earthwork Construction Considerations

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

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

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local and/or state regulations including EM 385, Safety and Health Requirement Manual for Naval Facilities Engineering Command (NAVFAC) construction contracts.

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

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

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Construction Observation and Testing

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

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency prescribed by local agencies and local codes.

In areas of foundation excavations, the bearing subgrade should be evaluated by the Geotechnical Engineer. If unanticipated conditions are observed, the Geotechnical Engineer should prescribe mitigation options.

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

Shallow Foundations – Auxiliary Buildings

If the site has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations used at the HAZMAT, Sonobuoy, and PEMB storage sites.

Design Parameters – Compressive Loads

Item Description

Maximum Net Allowable Bearing Pressure 1, 2, 3 2,000 psf

Required Bearing Stratum 4 GeoModel Layer 2, new compacted structural fill meeting the requirements presented in Earthwork

Minimum Foundation Dimensions As determined based on maximum allowable bearing pressure

Ultimate Passive Resistance5

(equivalent fluid pressure) 320 pcf

Sliding Resistance 6 0.35 allowable coefficient of friction -granular material

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Item Description

Minimum Embedment below Finished Grade 7 26 inches

Estimated Total Settlement from Structural Loads 3 Less than about 1 inch

Estimated Differential Settlement 3, 8 Less than about 1/500 (0.002) angular distortion

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Values assume that exterior grades are no steeper than 20% within 10 feet of structure.

2. The allowable bearing capacity can be increased by 33% for transient/seismic loading conditions

3. Values provided are for maximum loads noted in Project Description. Additional geotechnical consultation will be necessary if higher loads are anticipated.

4. Unsuitable or soft soils should be overexcavated and replaced per the recommendations presented in Earthwork.

5. Use of passive earth pressures require the sides of the excavation for the spread footing foundation to be nearly vertical and the concrete placed neat against these vertical faces.

Assumes no hydrostatic pressure.

6. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Frictional resistance for granular materials is dependent on the bearing pressure which may vary due to load combinations. For fine-grained materials, lateral resistance using cohesion should not exceed ½ the dead load.

7. Embedment necessary to minimize the effects of frost and/or seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

8. Differential settlements are noted for equivalent-loaded foundations and bearing elevation as measured over a span of 50 feet.

Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the observation of the Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before foundation concrete is placed.

If existing fill soils are encountered at the base of the planned footing excavations, they should be undercut to natural soils meeting the requirements for structural fill presented in Earthwork. If unsuitable bearing soils are observed at the base of the planned footing excavation, the excavation should be extended deeper to suitable soils or to two feet below the planned footing elevation, whichever is less. The footings could bear directly on these soils at the lower level or on lean concrete backfill placed in the excavations

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Facilities | Environmental | Geotechnical | Materials 20 where unsuitable bearing soils are still present after the two foot undercut. This is illustrated on the sketch below.

Hangar Foundations

The following sections provide two foundation options for support of the hangar. The first option consists of shallow foundations supported by ground improvement elements.

The second option is a deep foundation system consisting of auger cast piles. The final selection of a foundation system should be based on an economic/construction schedule comparison of these options by the general contractor or cost estimator.

Shallow Foundations Supported by Ground Improvement Elements – Hangar

The near surface soils exhibit low to moderate shear strength and high compressibility characteristics. When considering the magnitude of the proposed column loads of the hangar in conjunction with the loads imposed by the proposed fill placement in the building area, the calculated settlement for conventional spread footing foundations on unimproved soils will be unacceptable for the proposed construction.

There is significant variability in the anticipated loading for the proposed hangar. As such, it is expected that two types of ground improvement systems will be required to support the hangar, depending on the magnitude of column load anticipated at the foundation location. Specifically, spread footings may be used to support the proposed hangar when they are founded on soils improved by impact piers in lightly loaded areas (about 100 kip column loads) and by rigid inclusions in heavily loaded areas (about 800 to 1500 kip column loads). The use of ground improvement does not remove the requirement for a pre-consolidation program.

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Impact Piers

Based on our understanding of building loads and grading, we recommend that the spread footings with loads of approximately 100 kips or less may be supported by impact piers. Impact pier elements can be used to reinforce in-situ soils so that they can support conventional spread and strip footings, mats, and slabs. Impact pier elements consist of highly-densified, open-graded aggregate that is placed in controlled lifts using a special high-energy mandrel/hopper system. The mandrel is advanced into the ground to the correct depth, filled with stone via the hopper, and withdrawn in one-foot increments by raising the mandrel/hopper assembly three feet to allow stone to flow into the pier then lowering it two feet to compact the stone. The mandrel transfers the impact compaction energy to the aggregate through the crowd or downward force developed by the track-mounted installation equipment. The Impact pier elements can be used in either virgin soils or fills. Some predrilling may be used to facilitate mandrel penetration through obstructions. By reinforcing and stiffening the foundation soils with Impact pier elements, the improved soil will be capable of supporting a significantly higher allowable bearing pressure.

We recommend that you contact a ground improvement specialty contractor to review and analyze the subsurface data in this report, as well as the proposed structural loads for the project, and provide you with a cost estimate for Impact pier installation. The estimate should include the cost to perform a modulus test on an Impact pier element at the project site. The test should be performed to confirm the element stiffness modulus at the maximum theoretical Impact pier stress. The modulus test should be observed and documented by the project geotechnical consultant. Loading of the test pier should be conducted up to approximately 150 percent of the maximum theoretical stress to which the Impact pier elements will be subjected. At 100 percent of the maximum theoretical Impact pier stress, settlement of the footing supported by the Impact pier element should not exceed one inch.

We recommend that the Impact pier installer’s quality control (QC) program be monitored full-time by the geotechnical engineer of record. The QC program includes verification of Impact pier locations, aggregate lift thickness, and impact crowd per lift.

These items should be documented for each Impact pier element installed to provide a complete record of Impact pier foundation quality.

Rigid Inclusions

Based on our understanding of building loads and grading, we recommend that the heavily loaded spread footings at the hangar with loads ranging from 830 to 1420 kips be supported by Rigid Inclusions. Rigid Inclusions (RI) have been used since 2004 and consist of aggregate mixed with cement, or grout, to form a structural member that can transfer foundation loads down to a competent soil or rock layer. RI capacity is provided

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Facilities | Environmental | Geotechnical | Materials 22 by end-bearing and/or side resistance. A load transfer platform or crushed stone cushion is placed between the top of RI and the footing bottom to limit the stress on the conventional spread footing. Alternatively, an expanded RI head is placed over the main RI shaft to reduce the top-of-RI pressure on the footing or slab. The RI design and the load transfer mechanism is part of the RI contractor’s scope of work.

A shear break is required between the bottom of the spread footing and the top of each RI. The size and thickness of the shear break will depend on the final footing elevations and loading. We recommend that the design team estimate a 6-inch crushed stone pad for the shear break for pre-construction purposes. The RI designer will provide details and specifications as part of the RI design drawings.

A load test should be performed to confirm individual RI capacity and load-settlement characteristics. One load test should be performed on an RI at a location mutually-agreed upon by the RI designer and the Geotechnical Engineer. Loading of the test RI should generally follow the specifications of ASTM D 1143.

We recommend that you contact a ground improvement specialty contractor to review and analyze the subsurface data in this report, as well as the proposed foundation loads and other details for the project, and provide you with a cost estimate for RI design and construction.

The RI contractor’s QC program should include monitoring RI installation, confirming compressive strength of the proposed RI mix design to confirm it meets specifications, and sampling the grout/concrete mix during construction. The geotechnical engineer of record should provide quality assurance (QA) observation of the RI contractor’s QC program.

Design of Ground Improvement Elements

The depths of ground improvement elements, the allowable spread footing bearing pressure, and settlement at the allowable bearing pressure will be confirmed by the specialty contractor during construction by the performance of a modulus test. The final design of the rigid inclusions and impact piers should be completed by the specialized ground improvement contractor. We can provide contact information as necessary to engage a qualified ground improvement contractor. The specific pier design including lengths, support capacities, spacings, and layout should be a coordinated effort between the pier designer and structural engineer.

Auger Cast Piles - Hangar

A deep foundation system consisting of auger cast piles is the most technically feasible deep foundation support system for support of the proposed hangar. Allowable axial

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Facilities | Environmental | Geotechnical | Materials 23 compressive resistance curves are included in Supporting…