Geotechnical Report 2 of 3.pdf

PROPOSAL C OVER PAGE

REPORT C OVER PAGE

Geotechnical Engineering Report

Proposed VA Prosthetics Building – Building 50 Renovation

Hampton, Virginia

June 17, 2021

Terracon Project No. 70205252

Prepared for:

Anderson Engineering

Plymouth, Minnesota

Prepared by:

Terracon Consultants, Inc.

Raleigh, North Carolina

Terracon Consultants, Inc. 2401 Brentwood Road, Suite 107 Raleigh, North Carolina 27604

P (919) 873 2211 F (919) 873 9555 terracon.com Virginia Registered 0407004003

REPORT C OVER LETTER TO SIGN

June 17, 2021

Anderson Engineering

13605 1st Avenue N, Suite 100

Plymouth, Minnesota 55441

Attn: Mr. Tom Olesak, Architect Department Manager

P: (763) 412-4045

Re: Geotechnical Engineering Report

Proposed VA Prosthetics Building – Building 50 Renovation

Hampton, Virginia

Terracon Project No. 70205252

Dear Mr. Olesak:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with P70205252 dated December 15, 2020. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

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

Sincerely, Terracon Consultants, Inc.

Mark Weritz, P.E. Andrew A. Nash, P.E.

Senior Engineer Geotechnical Department Manager

Registered VA 041385

Proposed VA Prosthetics Building – Building 50 Renovation ■ Hampton, Virginia

June 17, 2021 ■ Terracon Project No. 70205252

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TABLE OF CONTENTS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

DEEP FOUNDATION

SEISMIC CONSIDERATIONS

FLOOR SLABS

PAVEMENTS

GENERAL COMMENTS

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE MAP AND EXPLORATION PLANS

EXPLORATION RESULTS (Test Boring Logs and Laboratory Data)

SUPPORTING INFORMATION (General Notes and Unified Soil Classification System)

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NTRODUCTION

Geotechnical Engineering Report

Proposed VA Prosthetics Building – Building 50 Renovation

Hampton, Virginia Terracon Project No. 70205252

June 17, 2021

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed VA Prosthetics Facility to be located at the Building 50 site within the VA Medical Center, in Hampton, Virginia. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Foundation design and construction

■ Groundwater conditions ■ Floor slab design and construction

■ Site preparation and earthwork ■ Seismic site classification per IBC

■ Excavation considerations ■ Pavement design and construction

■ Lateral earth pressure

The geotechnical engineering Scope of Services for this project included the advancement of four

(4) test borings to depths of 70 feet below existing site grade.

Maps showing the site and boring locations are shown in the attached Site Map and Exploration

Plans, respectively. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs and as separate graphs in the

Exploration Results section.

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

Location

The project site is located on the east side of McClellan Avenue, approximately 250 feet north of the Black Avenue intersection at the VA

Hampton Medical Center in Hampton, Virginia.

Latitude: 37.01662°N, Longitude: 76.3323°W

Existing improvements

The project is located at the current site of Building 50, which is a two-story building with a brick masonry exterior. Building 50 will be partially demolished for the new Prosthetics Building.

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Item Description

Current Ground

Cover

The ground surface exterior of Building 50 consists mostly of grass turf with scattered sidewalks, mature trees and bushes. A partly collapsed cistern is located immediately south of the building.

Existing Topography Surface elevations range between el 9 and el 11 feet msl.

PROJECT DESCRIPTION

ITEM DESCRIPTION

Project Description

The project consists of the construction of a new Prosthetics Building, which will consist of two stories with approximately 16,200 square feet of finished building space. The existing two-story, brick façade of Building 50 will be left in-place and be incorporated into new building construction. Framing of front of new structure may be cantilevered from new foundation to meet left-in-place façade.

Building Construction Specific proposed building construction is unknown, but is assumed to consist of reinforced concrete, CMU block, and structural steel framing, with concrete slab-on-grade and structural floors.

Finished Floor Elevation Assumed to approximately match the existing site grade.

Maximum Loads

(Assumed)

■ Columns: 200 to 300 kips

■ Walls: 2 to 6 kips per linear foot (klf)

■ Slabs: 150 to 250 pounds per square foot (psf)

Settlement Maximum allowable settlement criteria for the proposed structure will need to be provided by the client.

Grading/Slopes Minimal cuts/fills of less than 2 to 3 feet are anticipated.

Pavements Construction of new pavements are not anticipated.

GEOTECHNICAL CHARACTERIZATION

Site Geology

The project site is situated in the Coastal Plain Physiographic Province with soils consisting of marine sediments that were deposited during successive periods of fluctuating sea level and moving shoreline. The project site overlies thick deposits of Tertiary silty/clayey sands of the Yorktown

Formation, which extend to at least 70 feet below existing grade.

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Subsurface Profile

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 site preparation and foundation options. Conditions encountered at each exploration point are indicated on the individual logs. Laboratory tests for moisture content, Atterberg limits, and grain size were conducted on selected soil samples. The individual logs along with the GeoModel can be found in Exploration Results.

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.

Conditions encountered at each boring location are indicated on the individual boring logs shown in the Exploration Results section and are attached to this report. Stratification boundaries on the boring logs represent the approximate location of changes in native soil types; in situ, the transition between materials may be gradual.

Groundwater Conditions

The boreholes were observed while drilling for the presence and level of groundwater. Groundwater was observed in all test borings at depths ranging from 4.5 to 10 feet below existing ground surface.

Water level readings are indicated on the boring logs in Exploration Results.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. 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. Perched water conditions may exist within and above clayey layers of coastal plain deposits.

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GEOTECHNICAL OVERVIEW

A shallow layer of existing silty sand fill was encountered across the site to a depth of approximately 2 feet. Below the existing fill layer, subsurface conditions consist of very loose to loose silty/clayey sands to a depth of about 45 feet, and medium dense to dense silty sands to a depth of at least 70 feet. A very loose to medium dense, poorly sorted sand layer was encountered at the depth interval of 6 to 17.5 feet below the ground surface. Further details regarding subsurface conditions are summarized in Geotechnical Characterization.

Due to the presence of very loose to loose sand deposits within 25 feet of the ground surface, estimated settlements exceed 1 inch for column loads greater than 150 kips supported on conventional shallow foundations. We therefore recommend the proposed structure to be founded on deep foundations, such as auger cast-in-place concrete piles. At a minimum, deep foundations should extend into the upper portion of the medium dense to dense sand layer that is generally present below a depth of 45 feet. The Deep Foundations section addresses support of proposed structures on deep foundations.

Proposed subgrade level of shallow foundations for ground level screen walls, or other small grade level structures, will likely be located within the surficial existing fill layer that extends across the project site. Existing fill consists of loose to medium dense sand. The Shallow Foundations section addresses support of the small grade level structures on approved subgrade consisting of existing fill, or engineered fill. We recommend footing excavations to be inspected by Terracon for suitable preparation of bearing conditions

Groundwater was measured at depths of 4.5 to 10 feet below grade at the time of drilling in all boring locations. Local sumps and pumps may be suitable to dewater excavations shallower than

4 feet. Well points will be required to maintain dewatered conditions in deeper excavations.

Support of floor slabs, shallow footings, and sidewalks on or above existing fill materials is discussed in this report. However, even with the recommended construction procedures, there is an inherent risk to 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. To take advantage of the cost benefit of not removing the entire amount of undocumented fill, the owner must be willing to accept the risk associated with building over the undocumented fills following the recommended reworking of the material.

The geotechnical engineer shall be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation;

proof-rolling; placement and compaction of controlled compacted fills; backfilling of excavations into the completed subgrade, and just prior to construction of foundations. A more complete discussion of these points and additional information is included in following sections.

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The General Comments section provides an understanding of the report limitations

EARTHWORK

Earthwork is anticipated to include demolition of existing structures and utilities, clearing and grubbing, excavations, and 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.

Site Preparation

After demolition work and prior to placing fill, existing vegetation, root mat, and other unwanted utilities, structures or materials should be removed. Existing utilities that are to be abandoned should be completely removed or filled with grout within proposed building footprints. Utilities to remain in place should be accurately located horizontally and vertically to minimize potential conflicts with new construction.

Stripped materials consisting of vegetation and organic materials should be disposed off site, or used to vegetate landscaped areas. Stripping depths between our boring locations and across the site could vary considerably.

After demolition and site stripping, we recommend proof-rolling exposed soil in areas to receive fill and at subgrade in the cut sections. Proof-rolling should be performed with a minimum 10-ton vibratory roller making a minimum of 10 passes in perpendicular directions. The proof-rolling operations should be observed by a representative of Terracon and should be performed after a suitable period of dry weather to avoid degrading an otherwise acceptable subgrade and to reduce the amount of remedial work required.

If the exposed soil surface exhibits excessive deflection, pumping, or rutting under the proof-rolling operation, we recommend over-excavation of soft/unstable soil and replacement with suitable compacted structural fill or crushed stone. The extent to which over-excavation and replacement will be required will likely be reduced if the site preparation and earthwork are performed during warmer and drier periods of the year. Additional recommendations for site stabilization will depend on the location of the instability and should be provided by the

Geotechnical Engineer based on observations at the time of construction

Existing Fill

As noted in Geotechnical Characterization, test borings encountered existing fill at shallow depths ranging to about 2 feet below existing grade. Existing fill at test boring locations consists of loose to medium dense silty sand. Generally, floor slabs, foundations, and pavements could be

Responsive ■ Resourceful ■ Reliable 6 supported on or above the remaining existing fill soils that have been densified in place and withstand proofrolling. However, there is 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 following the recommendations in Site Preparation.

Excavation Conditions

We anticipate that on-site materials can be excavated with conventional earth moving equipment.

All temporary excavations that may be required during construction should comply with applicable local, state and federal safety regulations, including the current OSHA Excavation and Trench

Safety Standards to provide stability and safe working conditions.

Water was measured at depths of 4.5 to 10 feet at test boring locations. Dewatering of any excavations below a depth of 4 feet may be required. Most dewatering can be accomplished with ditches, sumps and pumps. Well points may be required in larger excavations that extend into saturated sand deposits.

Fill Material Types

Earth fill material should meet the following soil property requirements:

Fill Material1 USCS Classification Acceptable Location for Placement

On-Site Sand Soils or Imported

Sand Soils (max. 25% fines)

SP-SM, SP-SC,

SM, SC

All locations and elevations

Sand / Gravel with less than

10% fines (silt and clay)

GW/GP, SW/SP

VDOT No. 21A beneath pavements and floor slabs or as a replacement material in over-excavated areas.

1. Controlled, compacted fill should consist of approved materials that are free of organic matter and debris. A sample of each material type should be submitted to the geotechnical engineer for evaluation.

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Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift Thickness

9 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

Minimum of 95% of the material’s standard Proctor maximum dry density (ASTM D698).

The top lift of engineered fill should be compacted to a minimum of 98% of the material’s standard Proctor maximum dry density (ASTM D698) for retaining walls, buildings and pavements.

Minimum of 92% of the material’s standard

Proctor maximum dry density (ASTM D698).

Water Content

Range

Within the range of -2% to +3% of optimum moisture content as determined by the standard Proctor test at the time of placement and compaction.

As required to achieve min. compaction requirements

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D 698).

Grading and Drainage

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

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

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Earthwork Construction Considerations

Coastal plain soils can be moisture sensitive and will lose strength and stability and will become difficult to adequately compact as their moisture content increases. Performing site earthwork between during dryer times of the year (typically between June and October) will likely reduce the potential for earthwork problems associated with wet soil.

Performing site preparation and earthwork at other times of the year increases the potential for having to perform remedial work on the subgrade soil. Construction traffic over wet subgrades should be avoided to the extent practical. The site should also be graded to prevent ponding of surface water on the prepared subgrades. If the subgrade should become, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and re-compacted. The use of lime treatment generally reduces the plasticity of clays and silts, makes them less susceptible to moisture fluctuations, and may make them more workable during wetter periods of the year.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of floor slabs and pavements. Construction traffic over the completed subgrade should be avoided to the extent practical. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. If the subgrade should become frozen, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and recompacted prior to floor slab and pavement construction and observed by Terracon.

Surface water should not be allowed to pond and soak into the soil during construction.

Construction staging should provide drainage of surface water and precipitation away from the building and pavement areas. Any water that collects over or adjacent to construction areas should be promptly removed, along with any softened or disturbed soils. Surface water control in the form of sloping surfaces, drainage ditches and trenches, and sump pits and pumps will be important to avoid ponding and associated delays due to precipitation and seepage.

Water was measured at depths of 4.5 to 10 feet at test boring locations. Dewatering of any excavations below a depth of 4 feet may be required. Most dewatering can be accomplished with ditches, sumps and pumps. Well points may be required in larger excavations that extend into saturated sand deposits.

All excavations should be sloped or braced as required by OSHA regulations to provide stability and safe working conditions. Temporary excavations will probably be required during grading operations. The grading contractor, by his contract, is usually responsible for designing and constructing stable, temporary excavations and should shore, slope or bench the sides of the excavations as required to maintain stability of both the excavation sides and bottom. All

Responsive ■ Resourceful ■ Reliable 9 excavations should comply with applicable local, state and federal safety regulations, including the current Occupational Health and Safety Administration (OSHA) Excavation and Trench Safety

Standards.

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 that Terracon is assuming any responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied or inferred.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation and topsoil, proofrolling, and mitigation of areas delineated by the proofroll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of compacted fill in the building areas and 5,000 square feet in pavement areas. One density and water content test should be performed for every 50 linear feet of compacted utility trench backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. If unanticipated conditions are encountered, 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

Small ground level structures, such as screen walls, with total wall loads less than 2 kips per foot, can be supported on shallow wall or spread footings. Provided that foundation subgrade has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations.

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Foundation Design Recommendations

Description Value

Net allowable soil bearing capacity 1 2,000 psf

Minimum embedment below lowest adjacent finished grade for frost protection and protective embedment 2 18 inches

Minimum width for continuous wall footings 16 inches

Minimum width for isolated column footings 24 inches

Approximate total settlement 3 Up to 1 inch

Estimated differential settlement 3

Less than L/500 along walls. Less than

½ inch over 50 feet between interior columns.

Passive Lateral Resistance 300 pcf (unfactored)

Coefficient of Friction 0.35 (unfactored)

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

2. The footing embedment depth recommended exceeds the frost depth for the area. Footings should be embedded at least 12 inches to provide protective embedment.

3. The actual magnitude of settlement that will occur beneath the foundations would depend upon the variations within the subsurface soil profile, the structural loading conditions and the quality of the foundation excavation. The estimated total and differential settlements listed assume that the foundation related earthwork and the foundation design are completed in accordance with our recommendations.

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 factored loads that include wind or seismic conditions. The weight of the foundation concrete below grade may be neglected in dead load computations. Interior footings should bear a minimum of 12 inches below finished grade. Finished grade is the lowest adjacent grade for perimeter footings and floor level for interior footings.

Footings, foundations, and masonry walls should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of control joints at openings or other discontinuities in masonry walls is recommended.

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

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Design Parameters - Uplift Loads

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils. As illustrated on the subsequent figure, the effective weight of the soil prism defined by diagonal planes extending up from the top of the perimeter of the foundation to the ground surface at an angle, , of 20 degrees from the vertical can be included in uplift resistance.

The maximum allowable uplift capacity should be taken as a sum of the effective weight of soil plus the dead weight of the foundation, divided by an appropriate factor of safety. A maximum total unit weight of 100 pcf should be used for the backfill. This unit weight should be reduced to

40 pcf for portions of the backfill or natural soils below the groundwater elevation.

Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the direction 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 unsuitable bearing soils are encountered at the base of the planned footing excavation, the excavation should be extended deeper to suitable soils, and the footings could bear directly on these soils at the lower level or on washed stone or lean concrete backfill placed in the excavations. This is illustrated on the sketch below.

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Over-excavation for structural fill placement below footings should be conducted as shown below.

The over-excavation should be backfilled up to the footing base elevation, with ABC or acceptable fill material placed, as recommended in the Earthwork section.

DEEP FOUNDATION

If supported on conventional foundations, anticipated structural loads of the proposed structure will induce foundation settlements greater than 1 inch; therefore, the proposed structure will be required to be supported on deep foundations. The proximity of nearby healthcare-related structures will exclude installation of driven piles. Based on proposed construction and existing site conditions, auger cast in place (ACIP) piles appear to be the most appropriate type of deep foundation for the project.

The structural capacity of ACIP piles should be checked to assure they can safely accommodate the combined stresses induced by axial and lateral forces. Lateral deflections of piles should be evaluated using an appropriate analysis method, and will depend upon the pile’s diameter, length, configuration, stiffness and “fixed head” or “free head” condition.

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Augered Cast-in Place (ACIP) Design Parameters

Soil design parameters are provided below in the table for the design of non-displacement ACIP foundations. The values provided in the table below may be used to assist the design of ACIP using common software (e.g. LPILE™ by Ensoft). The unit weights shown are assumed total unit weights, the designer should use effective unit weights based on the provided total unit weights for design of the driven piles. A groundwater level of 10 feet below existing grade can be used for design purposes. The values of cohesion, lateral subgrade modulus, and strain values have no factors of safety. The allowable skin friction has a factor of safety of about 2, while the allowable end bearing has a safety factor of 3. The provided skin friction values should be reduced by 2/3 for uplift loading.

These values should be considered approximate.

Factors of safety for skin friction and end bearing, with no load testing performed, shall be 2 and

3 respectively. If load testing is performed the reduction in the safety factor can be determined by the ACIP designer/contractor.

Preliminary ACIP Parameters

Soil Parameters Axial Parameters

(Non-Displacement ACIP) Lateral Parameters

Depth

(feet bgs)1

Assumed

Total Unit

Weight, γT

(pcf)

Cohesion c

(psf)

Friction

Angle

Φ

Allowable

Skin

Friction

(FS = 2)

(ksf)

Allowable

End Bearing

Pressure

(FS = 3)

(ksf)

Strain

Factor, ε50

Lateral

Subgrade

Modulus k (pci)

0 – 5 -- -- -- -- -- -- --

5 – 10 122 -- 30 0.25 1.5 -- 20

10 - 25 122 -- 25 0.40 2.0 -- 20

25 – 45 122 -- 27 0.70 2.0 20

45 – 55 122 -- 32 1.10 6.0 -- 60

55 - 70 122 -- 32 1.35 6.0 -- 60

1. Groundwater is assumed to be 10 feet below ground level

2. Effective Unit Weight γ’ should be use in foundation design

When piles are used in groups, the lateral capacities of the piles in the second, third, and subsequent rows of the group should be reduced as compared to the capacity of a single, independent pile. Guidance for applying p-multiplier factors to the p values in the p-y curves for each row of pile foundations within a pile group can be found in the driven pile section.

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Augered Cast-in-Place Piles Considerations

A minimum center-to-center spacing of three pile diameters should be maintained to limit the possibility of damage to adjacent piles during installation. Compressive stresses in the piles should not exceed 25% of the grout’s 28-day compressive strength and steel reinforcement should meet the structural requirements of the pile as determined by the structural engineer.

Typically, a minimum set time of 18 hours should be provided prior to installation of adjacent piles.

The successful performance of ACIP piles is highly dependent on the quality of installation. In soft/loose ground conditions, there is a risk of soil inclusions or “necking” of the grout column that can significantly reduce the structural capacity of the grout column. We recommend that the pile installation contractor for the project be pre-selected on a qualification basis. As a minimum the contractor’s personnel should have at least 5 years of total experience in the piling industry. All personnel and equipment should be subject to the review of the geotechnical engineer.

We recommend that a test pile be installed within the building area. The load test for compression capacity should be conducted in accordance with ASTM Standard D-1143, “Standard Test

Method for Piles under Static Axial Compressive Load”. The reaction frames and hydraulic jacks by which load will be applied to the pile should have a capacity equivalent to at least 2.5 times the design capacity of the piles. A representative of the geotechnical engineer monitor the installation of the test and reaction piles, the load test program, and evaluate the load test data.

During production installation of the piles, acceptance of the individual piles depends on a number of criteria, including installation time, withdrawal rate during pumping, grout take, tested compressive strength of the grout, etc. Each pile should contain a minimum of 120% of the theoretical “neat-line” volume of grout for its individual length. Each pile must be evaluated separately because of the anticipated variables at the site.

Field monitoring of the pile installation is a direct extension of the design process. Pile installation techniques must be observed, weighed against load test data, and evaluated to determine the acceptance of each pile. Understanding of the subsurface conditions and pile design requirements are necessary to make the routine engineering judgments required during installation. Therefore, the preceding foundation recommendations should be considered valid only if the geotechnical engineer monitors the pile installation.

When piles are used in groups, the lateral capacities of the piles in the second, third, and subsequent rows of the group should be reduced as compared to the capacity of a single, independent pile. Guidance for applying p-multiplier factors to the p values in the p-y curves for each row of pile foundations within a pile group are as follows:

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Front row: Pm = 0.8;

Second row: Pm = 0.4

Third and subsequent row: Pm = 0.3

The load capacities provided herein are based on the stresses induced in the supporting soil strata.

The structural capacity of the piles should be checked to assure they can safely accommodate the combined stresses induced by axial and lateral forces. Lateral deflections of piles should be evaluated using an appropriate analysis method, and will depend upon the pile’s diameter, length, configuration, stiffness and “fixed head” or “free head” condition. We can provide additional analyses and estimates of lateral deflections for specific loading conditions upon request. The load-carrying capacity of piles may be increased by increasing the pile’s section and/or length.

LATERAL EARTH PRESSURES

Design Parameters

The lateral earth pressure recommendations herein are applicable to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity type concrete walls.

Reinforced concrete walls with unbalanced backfill levels on opposite sides 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 free-standing 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.

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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 - 0.29

Sandy Silt/Silty Sand - 0.36

(0.29)S

(0.36)S

(35)H

(45)H

At-Rest (Ko) Granular - 0.46

Sandy Silt/Silty Sand - 0.53

(0.46)S

(0.53)S

(55)H

(65)H

Passive (Kp) Granular - 3.4

Sandy silt/Silty Sand – 2.8

Applicable conditions to the above include:

◼ Granular soil defined as clean sand (USCS Classification SP, SM-SP, or SW) with less than 10% passing the No. 200 Sieve.

◼ 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

◼ In-situ soil backfill weight a maximum of 120 pcf

◼ Horizontal backfill, compacted between 95 and 98 percent of standard 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 low plasticity cohesive soils.

For the granular values to be valid, the granular backfill must extend out and up 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 0.35 should be used as the ultimate coefficient of friction between the footing and the underlying soil.

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Subsurface Drainage for Below Grade Walls

To aid in reducing the potential for hydrostatic pressure behind walls, we recommend installation of a perforated rigid plastic drain line installed behind the base of walls with a collection pipe leading to a reliable discharge. The invert of a drain line around a below-grade building area or exterior retaining wall should be placed near foundation bearing level. The drain line should be sloped to provide positive gravity drainage to daylight or to a sump pit and pump, or other reliable discharge. The drain line should be surrounded by clean, free-draining granular material having less than 5 percent passing the No. 200 sieve, such as No. 57 aggregate. The free-draining aggregate should be encapsulated in a non-woven filter fabric. The granular fill should extend to within 2 feet of final grade, where it should be capped with compacted cohesive fill to reduce infiltration of surface water into the drain system. As an alternative to free-draining granular fill, a pre-fabricated drainage structure may be used. A pre-fabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion, and is fastened to the wall prior to placing backfill.

If adequate drainage is not possible, then combined hydrostatic and lateral earth pressures should be calculated for granular backfill using an equivalent fluid weighing 80 and 90 pcf for active and at-rest conditions, respectively. For silty backfill, an equivalent fluid weighing 85 and 95 pcf should be used for active and at-rest, respectively. These pressures do not include the influence of surcharge, equipment or floor loading, which should be added. Heavy equipment should not operate within a distance closer than the exposed height of retaining walls to prevent lateral pressures more than those provided.

Damp-proofing of the walls below the ground surface is also recommended to aid in preventing seepage of water into the structure during situations of heavy rains and or temporary high water table conditions above the bedrock surface that may not drain immediately.

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SEISMIC CONSIDERATIONS

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

Category. Site Classification is required to determine the Seismic Design Category for a structure.

The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC).

Based on the soil properties encountered at the site and as described on the exploration logs and results, it is our professional opinion that the Seismic Site Classification is E. Subsurface explorations at this site were extended to a maximum depth of 70 feet. The site properties below the boring depth to 70 feet were estimated based on our experience and knowledge of geologic conditions of the general area. A more favorable seismic site classification may be possibly achieved using a geophysical test method such as Multi-Spectral Analysis of Surface Waves

(MASW).

FLOOR SLABS

Design parameters for a floor slab-on-grade assume the requirements for Earthwork have been followed. Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab.

Floor Slab Design Parameters

Item Description

Floor Slab Support Approved native soils or new engineering fill

Estimated Modulus of

Subgrade Reaction

150 pounds per square inch per inch (psi/in) for point loads

Stone Base Course 4 inches of crushed aggregate base course (VDOT 21A)

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.

2. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in Earthwork, and the floor slab support as noted in this table. It is provided for point loads. For large area loads the modulus of subgrade reaction would be lower.

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

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Saw-cut control joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations refer to the ACI Design Manual. Joints or cracks should be sealed with a water-proof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates differential movement between the walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the length of the structural dowels. The Structural Engineer should account for potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

Floor Slab Construction Considerations

Finished subgrade, within and for at least 10 feet beyond the floor slab, should be protected from traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are constructed. If the subgrade should become damaged or desiccated prior to construction of floor slabs, the affected material should be removed and structural fill should be added to replace the resulting excavation. Final conditioning of the finished subgrade should be performed immediately prior to placement of the floor slab support course.

The Geotechnical Engineer should approve the condition of the floor slab subgrades immediately prior to placement of the floor slab support course, reinforcing steel, and concrete. Attention should be paid to high traffic areas that were rutted and disturbed earlier, and to areas where backfilled trenches are located.

PAVEMENTS

New pavements for vehicles are not anticipated for this project. For new sidewalks, we recommend using a Portland cement concrete pavement with a thickness of at least 4 inches underlain by an approved subgrade (upper 6 inches of subgrade compacted to at least 98% maximum dry density of standard proctor, ASTM D698). Concrete should be air-entrained and have a minimum compressive strength of 4,000 psi after 28 days of laboratory curing per ASTM

C-31.

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GENERAL COMMENTS

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration. Natural variations will occur between exploration point locations or due to the modifying effects of construction or weather.

The nature and extent of such variations may not become evident until during or after construction.

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

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

Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client.

Reliance upon the services and any work product is limited to our client, and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

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

Site safety, and cost estimating including, excavation support, and dewatering requirements/design are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

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FIELD EXPLORATION PROCEDURES

Field Exploration

Number of Borings Boring Depth (feet) Planned Location

4 70 feet Building Area

Boring Layout and Elevations

Test boring locations are shown on the Exploration Plan. Exploration locations were established in the field by measuring from existing site features and estimating right angles or by GPS location. The locations of the borings should be considered accurate only to the degree implied by the means and methods used to define them.

Soil Test Borings

The soil test borings were performed using mud-rotatory techniques with a CME 55 rotary drill rig.

Samples of the soil encountered in the borings were obtained using the split barrel sampling procedure.

In the split-barrel sampling procedure, the number of blows required to advance a standard 2-inch outer diameter split-barrel sampler from 6 to 18 inches of the typical total 18- or 24-inch penetration by means of a 140-pound hammer with a free fall of 30 inches, is the standard penetration resistance value (SPT-N). This value is used to estimate the in-situ relative density of cohesionless soils and consistency of cohesive soils. Four soil samples were taken in the upper 10 feet bgs, and at 5-foot intervals below thereafter.

Samples collected in the field were tagged for identification, sealed to reduce moisture loss as appropriate, and taken to our laboratory for further examination, testing, and classification. A field log of each boring was prepared by the drill crew. These logs included visual classifications of the materials encountered during drilling as well as the driller’s interpretation of the subsurface conditions between samples. Final boring logs included with this report represent the engineer's interpretation of field logs and include modifications based on laboratory observation and/or testing of the samples.

An automatic SPT hammer was used to advance the split-barrel sampler in the borings performed on this site. 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 be 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.

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LABORATORY TESTING DESCRIPTION

Laboratory Testing

The project engineer reviews field data and assigns various laboratory tests to better understand the engineering properties of various soil strata.