RFI__10_Perry_Point_VA_Community_Living_Center-_Geotech._Report_(Rev._2-9-15).pdf

GEOTECHNICAL ENGINEERING

STUDY

Community Living Center

VAMHCS

Perry Point VA Medical Center

Perryville, Maryland

PREPARED FOR:

POLT DESIGN GROUP

PREPARED BY:

CENTURY ENGINEERING, INC.

10710 GILROY ROAD

HUNT VALLEY, MARYLAND 21031

June, 2013

(Revised 2/9/15)

CEI NO. 028017.08

IMPORTANT INFORMATION

ABOUT YOUR

GEOTECHNICAL ENGINEERING REPORT

More construction problems are caused by site subsurface conditions than any other factor. As troublesome as subsurface problems can be, their frequency and extent have been lessened considerably in recent years, due in large measure to programs and publications of ASFE/The Association of Engineering Firms Practicing in the Geosciences.

The following suggestions and observations are offered to help you reduce the geotechnical-related delays, cost overruns and other costly headaches that can occur during a construction project.

A GEOTECHNICAL ENGINEERING

REPORT IS BASED ON A UNIQUE SET OF

PROJECT-SPECIFIC FACTORS

A geotechnical engineering report is based on a subsurface exploration plan designed to incorporate a unique set of project-specific factors. These typically include the general nature of the structure involved, its size and configuration; the location of the structure on the site and its orientation; physical concomitants such as access roads, parking lots, and underground utilities, and the level of additional risk which the client assumed by virtue of limitations imposed upon the exploratory program. To help avoid costly problems, consult the geotechnical engineer to determine how any factors that change subsequent to the date of the report may affect its recommendations.

Unless your consulting geotechnical engineer indicates otherwise, your geotechnical engineering report should not be used:

• when the nature of the proposed structure is changed, for example, if an office building will be erected instead of a parking garage, or if a refrigerated warehouse will be built instead of an unrefrigerated one;

• when the size or configuration of the proposed structure is altered;

• when the location or orientation of the proposed structure is modified;

• when there is a change of ownership, or

• for application to an adjacent site.

Geotechnical engineers cannot accept responsibility for problems which may develop if they are not consulted after factors considered in their report's development have changed.

MOST GEOTECHNICAL "FINDINGS"

ARE PROFESSIONAL ESTIMATES

Site exploration identifies actual subsurface conditions only at those points where samples are taken, when they are taken. Data derived through sampling and subsequent laboratory testing are extrapolated by geotechnical engineers whom then render an opinion about overall subsurface conditions, their likely reaction to proposed construction activity, and appropriate foundation design.

Even under optimal circumstances actual conditions may differ from those inferred to exist, because no geotechnical engineer, no matter how qualified, and no subsurface exploration program, no matter how comprehensive, can reveal what is hidden by earth, rock and time. The actual interface between materials may be far more gradual or abrupt than a report indicates. Actual conditions in areas not sampled may differ from predictions. Nothing can be done to prevent the unanticipated, but steps can be taken to help minimize their impact. For this reason, most experienced owners retain their geotechnical consultants through the construction stage, to identify variances, conduct additional tests which may be needed, and to recommend solutions to problems encountered on site.

SUBSURFACE CONDITIONS

CAN CHANGE

Subsurface conditions may be modified by constantly changing natural forces. Because a geotechnical engineering report is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a geotechnical engineering report whose adequacy may have been affected by time. Speak with the geotechnical consultant to learn if additional tests are advisable before construction starts.

Construction operations at or adjacent to the site and natural events such as floods, earthquakes or groundwater fluctuations may also affect subsurface conditions, and thus, the continuing adequacy of a geotechnical report. The geotechnical engineer should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary.

GEOTECHNICAL SERVICES ARE

PERFORMED FOR SPECIFIC PURPOSES

AND PERSONS

Geotechnical engineers' reports are prepared to meet the specific needs of specific individuals. A report prepared for a consulting civil engineer may not be adequate for a construction contractor, or even some other consulting civil engineer. Unless indicated otherwise, this report was prepared expressly for the client involved and expressly for purposes indicated by the client. Use by any other persons for any purpose, or by the client for a different purpose may result in problems. No individual other than the client should apply this report for its intended purpose without first conferring with the geotechnical engineer. No person should apply this report for any purpose other than that originally contemplated without first conferring with the geotechnical engineer.

A GEOTECHNICAL ENGINEERING

REPORT IS SUBJECT TO

MISINTERPRETATION

Costly problems can occur when other design professionals develop their plans based on misinterpretations of a geotechnical engineering report. To help avoid these problems, the geotechnical engineer should be retained to work with other appropriate design professionals to explain relevant geotechnical findings and to review the adequacy of their plans and specifications relative to geotechnical issues.

BORING LOGS SHOULD NOT BE

SEPARATED FROM THE

ENGINEERING REPORT

Final boring logs are developed by geotechnical engineers based upon their interpretation of field logs (assembled by site personnel) and laboratory evaluation of field samples.

Only final boring logs customarily are included in geotechnical engineering reports. These logs should not under any circumstances be redrawn for inclusion in architectural or other design drawings because drafters may commit errors or omissions in the transfer process.

Although photographic reproduction eliminates this problem, it does nothing to minimize the possibility of contractors misinterpreting the logs during bid preparation.

When this occurs, delays, disputes and unanticipated costs are the all-too-frequent result.

To minimize the likelihood of boring log misinterpretation, give contractors ready access to the complete geotechnical engineering report prepared or authorized for their use. Those who do not provide such access may proceed under the mistaken impression that simply disclaiming responsibility for the accuracy of subsurface information always insulates them from attendant liability.

Providing the best available information to contractors helps prevent costly construction problems and the adversarial attitudes, which aggravate them to disproportionate scale.

READ RESPONSIBILITY

CLAUSES CLOSELY

Because geotechnical engineering is based extensively on judgment and opinion, it is far less exact than other design disciplines. This situation has resulted in wholly unwarranted claims being lodged against geotechnical consultants. To help prevent this problem, geotechnical engineers have developed model clauses for use in written transmittals. These are not exculpatory clauses designed to foist geotechnical engineers' liabilities onto someone else.

Rather, they are definitive clauses which identify where geotechnical engineers' responsibilities begin and end.

Their use helps all parties involved recognize their individual responsibilities and take appropriate action. Some of these definitive clauses are likely to appear in your geotechnical engineering report, and you are encouraged to read them closely. Your geotechnical engineer will be pleased to give full and frank answers to your questions.

OTHER STEPS YOU CAN TAKE TO

REDUCE RISK

Your consulting geotechnical engineer will be pleased to discuss other techniques that can be employed to mitigate risk. In addition, ASFE has developed a variety of materials that may be beneficial. Contact ASFE for a complimentary copy of its publications directory.

i

TABLE OF CONTENTS

LETTER OF TRANSMITTAL

PREFACE

TABLE OF CONTENTS .................................................................................................................... i

1.0 PURPOSE AND SCOPE

2.0 SITE AND PROJECT DESCRIPTION

3.0 FIELD AND LABORATORY WORK

4.0 SUBSURFACE CONDITIONS

5.0 EVALUATIONS AND RECOMMENDATIONS

5.1 General Site Preparation

5.2 Fill Selection, Placement, and Compaction

5.3 Shallow Foundations

5.4 Ground-Supported Slabs

5.5 Below Grade Walls

5.6 Groundwater and Drainage

5.7 Preliminary Stormwater Management

5.8 Hot Mix Asphalt (HMA) Pavement

5.9 Rock Excavation

5.10 Seismic Design

6.0 ADDITIONAL SERVICES RECOMMENDED

7.0 REMARKS

APPENDIX

Perry Point VA Medical Center June 20, 2013 Community Living Center (Revised 2/9/15) CEI Job No. 028017.08

GEOTECHNICAL ENGINEERING STUDY

PERRY POINT VA MEDICAL CENTER

COMMUNITY LIVING CENTER

CENTURY JOB NO. 028017.08

1.0 PURPOSE AND SCOPE

The purpose of this study was to determine the general subsurface conditions at the site and to evaluate the conditions with respect to geotechnical engineering considerations for the proposed construction. More precisely, the scope of the study included the following objectives:

1. To determine the existing subsurface conditions, including the soil and groundwater conditions, within the areas of proposed construction.

2. To recommend the appropriate foundation and/or slab systems for the proposed building structures, along with necessary design criteria.

3. To provide design recommendations for the proposed site retaining walls.

4. To evaluate subsurface conditions for preliminary design of stormwater management (SWM) facilities.

5. To assess subgrade conditions at the proposed access roadway and parking areas, and to provide recommendations for flexible pavement design.

6. To determine and discuss any likely geotechnical-related design or construction constraints.

An evaluation of the site with respect to potential construction problems and recommendations dealing with the earthwork and inspection during construction are also included. The inspection is considered necessary to verify the subsurface conditions and to ensure that the soils-related construction phases are performed properly. The Appendix contains a summary of the field and laboratory work on which this report is based.

We previously provided a Pre-Design geotechnical engineering report for the proposed Community Living Center, dated December 5, 2011. Please refer to the Pre-Design report for additional subsurface information, evaluation, and geotechnical recommendations.

2.0 SITE AND PROJECT DESCRIPTION

The project site is located on the 400 acre Perry Point VA Medical Center campus to the south of Perryville, Maryland, as indicated on Figure No. 1 “Vicinity Map,” in the Appendix.

The VA Medical Center is located on Perry Point to the east of the Susquehanna River. The campus is developed with roads and numerous buildings including offices, residential care facilities, hospitals and other medical facilities. The proposed development includes a new 155-bed Community Living Center with associated infrastructure, access roadways, and stormwater management facilities.

The project site consists of a 28± acre parcel located to the south of Avenue D, between Eighth Street and Tenth Street. The project site is generally open and clear and consists of mainly grassy areas with about 10 to 12 large mature trees. Existing improvements on the site include: a parking lot, shed and construction trailer in the northern part of the site; a pavilion with benches, a tennis court, basketball court with lighting, and a baseball field with backstop and bleachers in the middle portion of the site; and a pumping station and perimeter roadway along the Susquehanna River at the south side of the site.

The site includes numerous underground utilities and manholes. Existing utilities within the project site include buried electrical, domestic water, chilled water, sanitary, and storm drain systems. It is possible that other types of underground utilities are located in the areas of proposed construction. It is very important that the type and location of all utilities in the areas of proposed construction be determined early in the project design phase.

The project site is generally flat to gradually sloping with existing ground surface elevations ranging from about EL. 25 in the north along Avenue D, to about EL. 10 in the south along the perimeter roadway. The site grades slope gradually downward from north to south towards the Susquehanna River. The slope of the existing ground surface approaches about 4% in the southern portion of the site.

The Community Living Center project has been defined and the proposed site layout and site grades have been established. The proposed Community Living Center will consist of seven (7) single-story U-shaped residence buildings, a 2-story community building, and an enclosed walkway structure connecting the buildings. A site retaining wall will be constructed to divide the site into an Upper Level to the north, and a Lower Level to the south. The Upper Level will include three of the Residence Buildings with FF El. 25, and the Community Building with a second floor at FF El. 25 and a first floor at FF El. 12. The Lower Level will include four of the Residence Buildings with FF El. 12.

To create the Upper and Lower levels of the site, the retaining wall will extend east to west for approximately 1,000-ft. in length, and up to 13-ft. in height. The retaining wall will be included as the back wall of the Walkway Structure, which will provide an enclosed passageway between the Lower Level Residence Buildings and the Community Building.

The roof of the Walkway Structure will provide a connecting sidewalk between the Upper Level Residence Buildings and the second floor of the Community Building. At the east end of the Walkway Structure an enclosed Walkway/Tunnel will extend to the north to provide a connection to the main campus.

The Upper and Lower Level Residence Buildings will incorporate “green roof” features. The building structures will consist of slab-on-grade construction, steel framing, and concrete slab on metal deck construction, and will be supported on shallow foundations. The retaining wall will be a cast-in-place reinforced concrete cantilever wall. The structural engineer has provided a maximum column load of 115 kips, and a wall load of 2 kips per linear foot for the proposed structures. Floor slab live loads range from 40 psf to 150 psf.

The new construction will require paved roadways including a fire access road encompassing the new building structures, and an access road with a drop-off area at the main entrance to the living center. The new construction will include paved at-grade parking facilities. The use of porous pavement at the parking facilities is under consideration for stormwater management.

New utilities for the proposed development will include water, chilled water, communications, electric, storm drain, and sanitary sewer systems. Stormwater management facilities will be required for the new site development. For stormwater management, the use of best management practices (BMPs) based on Environmental Site Design (ESD) principles is required in accordance with the Maryland Department of the Environment (MDE). The SWM design concept has not been fully developed; therefore, the planned in-situ borehole infiltration testing was postponed until further notice.

3.0 FIELD AND LABORATORY WORK

To determine the general subsurface conditions, Connelly & Associates, Inc. drilled thirty-nine (39) test borings, and four (4) additional “offset” test borings, to depths ranging from 8.2-ft. to 25.0-ft. below the existing ground surface, with a truck-mounted CME 45C drilling rig. The four (4) additional “offset” test borings were drilled at locations where refusal materials were encountered before the planned boring depth was reached. Century marked the boring locations in the field, and we determined the ground surface elevations at the boring locations.

The borings were advanced with hollow-stem augers, and soil samples were obtained at 2.5-ft. and 5.0-ft. intervals by driving a split-spoon sampler in accordance with the Standard Penetration Test (SPT) ASTM D-1586. Groundwater and cave-in levels were monitored during the period of the fieldwork. The preliminary stormwater management (SWM) borings were monitored for groundwater at a minimum of 24-hrs. after completion of the test borings.

The boring locations are shown on Figure No. 2 “Boring Location Plan,” in the Appendix.

Soils obtained from the sampling device were sealed in glass sample jars for transportation to the soils testing laboratory. The soil samples were visually examined by the Geotechnical Engineer and then described and classified according to the Unified Soil Classification System (ASTM D 2487 and D 2488). Bulk bag samples were recovered from the pavement borings for laboratory analysis required for compaction and pavement design.

In the laboratory, selected soil samples were tested for moisture content (ASTM D 2216), and index properties: Atterberg Limits (ASTM D 4318) and particle size distribution (minus No. 200 sieve) (ASTM D 422). Any field classifications were revised as necessary. Bulk bag samples were submitted for determination of the moisture density relationship in accordance with the Modified Proctor (ASTM D 1557), and the California Bearing Ratio (CBR) (ASTM D1883). The results of the laboratory testing are contained in the Appendix.

Test Boring Logs, which graphically illustrate the soil descriptions, strata divisions, sampling data, and field test data, are included in the Appendix of this report. Also included is a reference sheet which defines the terms and symbols used on the Test Boring Logs and explains the Standard Penetration Test procedure.

4.0 SUBSURFACE CONDITIONS

The Geologic Map of Maryland (1968) shows that the project site is located in the Coastal Plain province near the contact with the Eastern Piedmont Physiographic province referred to as the fall zone. The Geologic Map of Cecil County (1968) indicates that the project site is located in an area characterized by the Lowland Deposits of Quaternary Age. These recent deposits consist of varying combinations of gravel, sand, silt and clay, with cobbles and boulders near the base.

The USDA-NRCS National Cooperative Soil Survey (http://websoilsurvey.nrcs.usda.gov) of Cecil County, Maryland (Version 7, July 31, 2009) shows that the project site is located in an area consisting primarily of soils of the Butlertown silt loam unit, the Mattapex-Urban land complex, and the Beltsville silt loam unit (see the USDA Soil Map, in the Appendix).

The Butlertown silt loam and Beltsville silt loam soil units are characterized as silty eolian deposits over sandy or loamy fluviomarine deposits. The Butlertown unit consists of Silt Loam, Loam, and Loamy fine Sand soil types. The Beltsville unit consists of Silt Loam, Loam, Very gravelly sandy clay Loam, and Gravelly coarse sandy Loam soil types. These are moderately well drained soils that do not meet hydric criteria. The Mattapex-Urban land complex soils generally consist of Silt Loam, Fine sandy Loam, and Loamy Sand soil types.

The subsurface materials encountered at the project site can be described as coastal plain deposits overlying boulders or weathered rock. These deposits generally consist of mostly cohesive soils including SILT, Silty CLAY and CLAY; and lesser amounts of granular soils such as SAND, Sandy SILT, Silty SAND, and Clayey GRAVEL. The natural soil deposits include layers of very dense cobbles and/or boulders. Some man-placed fill materials were encountered. The reader is referred to the Test Boring Logs in the Appendix for details related to the subsurface conditions encountered in the various borings. It should be noted that stratification lines shown on the Test Boring Logs represent approximate transitions between material types. In-situ, strata changes could occur gradually or at slightly different levels.

The Test Boring Logs depict conditions at particular locations and at the particular times indicated. Some conditions, particularly groundwater conditions, could change with time.

Also, soil and groundwater conditions between borings could vary from the conditions noted at the boring locations.

All of the borings encountered topsoil at the ground surface ranging from about 2-inches in thickness to as much as 12-inches in thickness. Fill materials consisting of Silty SAND (SM) (FILL); and Sand, Gravel and Slag (FILL), were encountered to depths of about 2-ft. to 4-ft.

below existing grade at two of the pre-design test boring locations. Fill materials including concrete or brick materials were encountered to depths ranging from 2-ft. to 6.5-ft. below existing grade at four of the test boring locations. Hard augering was noted at boring S-5 from 1.5-ft. to 6.5-ft. where concrete materials were recovered in the sampler.

Natural soils consisting of coastal plain deposits were encountered at all boring locations.

Most of the borings encountered very soft to medium stiff Silty CLAY (CL) and SILT (ML), extending to depths of 1.5-ft. to 2.5-ft. below existing grade. These natural soils are underlain by variable cohesive and granular soil layers generally consisting of stiff to very stiff Silty CLAY (CL, CL-ML), Sandy SILT (ML) and Clayey SILT (ML), overlying and including layers of medium dense to very dense, Silty SAND (SM), SAND (SM) with varying amounts of Gravel and Rock Fragments (SM, SP, GM), and Clayey GRAVEL (GC). Some of the test borings encountered a zone of dense cobbles and/or boulders beneath these deposits at depths between about 5-ft. to 13-ft. below the existing ground surface. Where these dense layers were encountered it is noted on the test boring logs as “hard drilling” or “augers grinding”.

Weathered rock material is generally defined as a transitional material from residual soil to rock, with a SPT N-value between 60 blows per foot and 50 blows per 1-inch of penetration.

Weathered rock consists of rock that has been significantly weathered, but has not decomposed into a material that behaves like a soil. Weathered rock consisting of very http://websoilsurvey.nrcs.usda.gov/ dense Silty SAND and GRAVEL (SM-GM), with rock fragments, was encountered at depths ranging from 12-ft. to 19-ft. below existing grade and extending to the termination depth of test borings S-3, S-5, S-11A, S-12, S-13, and S-15.

The upper surface of rock, or bedrock, is defined as material with a SPT N-value greater than 50 blows per 1-inch of penetration (or less penetration). Rock is also defined as material that conventional augers cannot cut through, noted as auger refusal on the Test Boring Logs. Although auger refusal materials were encountered, the refusal materials likely consist of large cobbles or boulders.

Auger and/or split-spoon refusal materials were encountered in three of the previous test borings taken during the pre-design phase at depths ranging from 5.5-ft. to 11.5-ft. below existing grade. Auger refusal materials were encountered in four of the current test borings at depths ranging from 12.7-ft. to 20.0-ft. below existing grade. The composition of the refusal materials was not determined; however, the borings were offset and re-drilled to the planned depths. The refusal materials may consist of cobbles, or possible boulders; and where weathered rock materials were encountered, the refusal materials may be an indication of the upper surface of bedrock or a rock layer.

Groundwater was encountered in most of the deeper structural test borings at depths ranging from 9-ft. to 19-ft. below existing grade. The groundwater levels and caved depths of the structural borings were observed and noted as “dry” on the test boring logs before backfilling. The SWM test borings were left open for at least 24-hours, and the depth to groundwater and the caved depth of each boring are noted on the test boring logs, and presented in the summary table of Section 5.7 of this report.

The actual level of the hydrostatic water table and the amount and level of perched water should be anticipated to fluctuate throughout the year, depending upon variations in precipitation, surface run-off, infiltration, site topography, and drainage.

5.0 EVALUATIONS AND RECOMMENDATIONS

The following recommendations have been developed on the basis of the previously described project characteristics and subsurface conditions. If there are any significant changes to the project characteristics or if significantly different subsurface conditions are encountered during construction, Century should be consulted so that the recommendations of this report can be reviewed, and revised as necessary.

Our findings indicate that the site can be developed for the proposed building structures utilizing conventional spread footing support and ground-supported slab construction. In the area of the proposed buildings, we recommend proper abandonment, removal, and/or relocation of all structures, existing underground utilities, and other site improvements prior to building construction. The building demolition, underground utility removal, and replacement with compacted structural fill should be completed as described herein, prior to construction of new foundations.

Project specifications should include provisions for groundwater control, and hard excavation, or rock removal. Temporary and permanent subsurface drainage systems will be required for groundwater control during construction and for the design-life of the proposed construction. In addition to very dense natural materials consisting of rock, boulders, and/or weathered rock, it is possible that buried concrete foundations or partially demolished structures will be encountered particularly in the northeast portion of the site.

We recommend compaction of the subgrade in the building areas and roadway prior to placement of compacted structural fill and roadway embankment fill. The use of off-site borrow material for compacted structural fill should be anticipated. At the construction stage, special consideration should be given to the proper monitoring of earthwork, footing excavations, and concrete placement in all structural areas.

5.1 General Site Preparation

The initial step in development of the site should be clearing and grubbing of trees and shrubs, followed by the removal of topsoil and any other deleterious materials from the areas to be developed. The clearing, grubbing, and topsoil stripping operations should be performed in a manner consistent with good erosion and sediment control practices. Grubbing operations should include the removal of the major root systems of trees and the tree stumps.

All existing structures (including all above and below ground construction) within the areas to be developed should be removed prior to the initiation of new construction.

The building demolition should include removal of all structural components including foundations. Removal should include asphalt paving, concrete curb, underground pipes, and utilities etc. that might interfere with the new construction. The excavations for the removal of underground utilities and all other below-grade construction must be backfilled with compacted structural fill as described herein.

We suggest that all available information regarding the existing utilities at the site be reviewed during the design phase, and prior to new construction. If underground utilities are to be removed or relocated prior to the initiation of construction, provisions should be made in the construction specifications and budget to restore the subgrade to a stable condition. Restoration should include backfilling and compaction of the excavated areas with structural fill as recommended in Section 5.2 of this report.

Topsoil, mulch, rootmat, and any deleterious materials should be removed from the areas to be developed. These stripping operations should be performed in a manner consistent with good erosion and sediment control practices. It is anticipated that stripping operations in general will be limited to removal of the upper 6-in. in grassy areas. All materials having significant organic content should be removed in the stripping operations.

After the initial stripping process is completed, areas of the site to receive fill, or areas of the site at-grade where structures or pavements will be located, should be proofrolled. The proofrolling operations should be performed using a 20-ton loaded dump truck or another pneumatic-tire vehicle of similar size and weight. The purpose of the proofrolling will be to locate any near-surface pockets of soft or loose soils requiring undercutting, stabilization, or in-place densification.

Prior to fill placement, we recommend that the entire subgrade in the proposed building areas be scarified and thoroughly compacted by multiple passes with a 10-ton vibratory steel drum roller. Portions of the proposed roadway subgrade will also require scarification and compaction prior to placement of embankment fill, or construction of the pavement section in cut areas. A Geotechnical Engineer or experienced Soils Technician should witness the proofrolling and compaction operations and should determine which areas need further undercutting, scarification, compaction, and/or stabilization.

Care should be exercised during the grading operations at the site. Where fine-grained subgrade soils are exposed, the action of heavy construction equipment may cause pumping and deterioration of those soils if conducted in the presence of water. The grading should, therefore, if at all possible, be carried out in a dry season. Adequate drainage should be provided during construction. This should minimize these potential problems, although they may not be eliminated. If such problems arise, the Geotechnical Engineer should be consulted for an evaluation of the conditions.

Overexcavated areas resulting from the removal of unsuitable material should be backfilled with properly compacted suitable material in accordance with the procedures discussed in Section 5.2 of this report.

5.2 Fill Selection, Placement and Compaction

All material to be used as fill or backfill should be inspected, tested and approved by the Geotechnical Engineer. Although most of the excavated material from the site appears to be suitable for use as fill, it is likely that some of the required structural fill material will need to be imported from off-site sources. On-site soils which are free from debris, waste, frozen material, organics and other deleterious components can be re-used as general site fill. However, some difficulty in achieving proper compaction of the fine-grained soils should be anticipated. Some moisture conditioning of the on-site soils will be required for proper compaction.

Compacted structural fill placed in structural areas such as under floors slabs or footings should consist of soil with a Unified Soil Classification of SM or better (i.e.

GW, GP, GM, SW, and SP). The fill material should have no more than 35 percent fine materials, and should have a liquid limit less than 40 and a plasticity index less than 10. Roadway embankment fill materials should consist of soils meeting the Unified Soil Classifications of structural fill, and may also include GC, SC, CL, and ML, or a combination of these groups. All fill should be free of rock or gravel with particle size greater than 4-inches in any dimension.

Compacted structural fill should be placed in 8-inch maximum horizontal loose lifts and should be compacted to a minimum of 95 percent of the Modified Proctor (ASTM D-1557) maximum dry density. Wall backfill and fill placed in non-structural areas should be compacted to a minimum of 92 percent of the Modified Proctor maximum dry density. The moisture content of the compacted fill should be within 2 percentage points of the optimum moisture content. A sufficient number of in-place density tests should be performed by an Engineering Technician on a full-time basis to verify that the proper degree of compaction is being obtained. Roadway embankment fill should meet the compaction requirements for structural fill, except that the upper 1-ft. of roadway subgrade should be compacted to a minimum of 97 percent of the Modified Proctor (ASTM D-1557) maximum dry density.

In building areas the fill should extend two feet horizontally for each foot of fill, or a minimum of five feet beyond building lines where floor slabs or pavements are constructed on fill. Fill slopes no steeper than 2(H): 1(V) should be used.

5.3 Shallow Foundations

We understand that the proposed finished floor elevation of the upper level Residence Buildings is at El. 25.0 and the lower level Residence Buildings and Community Building is at El. 12.0. With shallow foundations at typical depths for frost protection, it appears that the proposed building foundations will be located within existing natural soils, or new compacted structural fill.

It is our opinion that the proposed building structures may be supported on conventional spread footing foundations bearing on firm natural soils, or compacted structural fill as described herein. The footings should be designed for maximum allowable soil contact pressures of 3,000 lbs./sq. ft. To preclude punching shear failures, wall footings should be at least 16 inches wide and column footings should be at least 24 inches wide.

As indicated by test borings S-7 and SWM-13, undercutting soft soil materials to depths of about 3 to 4 feet should be anticipated in portions of the proposed lower level building areas. If required during construction, the undercut areas should be replaced with compacted structural fill.

We recommend that a perimeter foundation drainage system be provided along the lower level building foundations. At the lower level of the Community Building, we also recommend that a perimeter foundation drainage system be provided along the building wall/retaining wall foundation about one foot below the lower level floor slab.

The drainage system should use a 4-in. min. diameter slotted polyethylene drainage pipe. The drainage pipe should be surrounded with filter graded aggregate, and/or wrapped in a drainage geotextile to preclude infiltration of soil fines into the drainage system. The foundation drain should provide gravity drainage to a stable outlet location.

Exterior footings and footings in unheated areas should be located at depths of at least 2.5-ft. below final exterior grades so as to provide adequate protection from frost heave. If the structure is to be constructed during the winter months or if the building interior will likely be subjected to freezing temperatures after footing construction, then all footings should be provided with adequate frost cover protection. Otherwise, interior footings can be located on suitable materials at nominal depths below finished floor grade. Footing excavations should be protected from the detrimental effects of precipitation, groundwater seepage, surface run-off, and frost.

All footing excavations should be inspected by a Geotechnical Engineer or experienced Soils Technician prior to the placement of concrete. The purpose of the inspection is to verify that the exposed materials will be capable of supporting the design footing pressure. If soft or loose pockets are encountered in the footing excavations, the unsuitable materials should be removed and footings should be located at a lower elevation. Alternatively, the unsuitable materials could be undercut and replaced with new fill, placed and compacted in accordance with the recommendations of this report, or backfilled with flowable fill, or lean (2000 psi) concrete.

5.4 Ground-Supported Slabs

Floor slabs should be supported on approved firm soils or on new compacted structural fill. The slab subgrade should be prepared in accordance with the procedures outlined in Sections 5.1 and 5.2 of this report. The floor slab may be designed with a modulus of subgrade reaction (k) of 125 pci, if constructed with the recommended granular base placed on prepared subgrade.

We recommend that the floor slabs be supported on a granular base consisting of a minimum 6-inch layer of clean granular materials such as washed sand, washed sand and gravel, or screened, crushed stone. These materials will require acquisition from off-site sources. A suitable moisture barrier should be provided under the concrete slab. These procedures will provide a moisture break that will help to prevent capillary rise and dampness of the floor slabs.

On most projects there is a significant time lag between initial grading and the time when the contractor is ready to place the slab on grade. Environmental conditions and construction traffic often disturb the subgrade soils. Provisions should be made in the construction specifications for restoration of the subgrade to a stable condition prior to placing the floor slab system.

5.5 Retaining Walls

The Walkway Structure back walls, Walkway/Tunnel walls, and the Community Building lower level north wall will consist of cast-in-place concrete cantilever retaining walls.

Retaining walls should be designed to resist lateral earth pressures developed from soil backfill and any surcharge loading. Hydrostatic pressures can be eliminated from the wall design if the recommended wall drainage system is used. Perimeter wall drains (foundation drains) in conjunction with suitable waterproofing of the below grade building walls/retaining walls are recommended and will aid in providing dry structures.

The wall should include a minimum 3 ft. (horizontal distance) zone of free draining select granular materials (such as size No. 57 stone) in order to prevent hydrostatic pressure build-up behind the wall. An alternative would be to specify an appropriate manufactured sheet drain product such as Amerdrain, Enkadrain or Miradrain.

Since the different types of wall drainage products available have unique characteristics, the installation procedures should be conducted in accordance with manufacturer’s recommendations and reviewed by the project engineer. The remainder of the backfill should consist of low-plasticity granular material such as Silty SAND (SM) or better material. Use of cohesive or semi-cohesive materials such as Silty CLAY (CL) should not be used for backfill behind the wall.

The cantilever retaining walls should be supported on spread footing foundations bearing on firm natural soils, or compacted structural fill. We recommend that the footings for the cantilever retaining walls be designed for a maximum allowable soil contact pressure of 3,000 lbs./sq.ft.

The earth pressure behind a wall depends on the nature of backfill and the amount of restraint at the top of wall. Since a cantilever retaining wall will be allowed to move at the top, active earth pressures will be developed behind the wall. If the recommended granular materials are used, an equivalent fluid pressure of 40 psf/ft.

should be used for wall design with level backfill. A coefficient of active earth pressure, Ka= 0.33 and a soil unit weight of 120 pcf were assumed.

The effect of surcharge loading and/or sloping backfill must be considered for the wall design. A minimum factor of safety of 1.5 is recommended for sliding, and a minimum factor of safety of 2.0 is recommended for overturning. A coefficient of friction f = 0.40 is recommended for calculating sliding resistance between the concrete wall footing and the soil subgrade.

Wall backfill materials should be placed and compacted in accordance with Section

5.2 of this report. It will be necessary to use smaller walk behind compaction equipment near the wall to attain the proper degree of compaction and avoid damaging the wall due to the heavier loads produced by larger construction equipment. If walk behind equipment is utilized, the maximum loose lift thickness should be reduced to 4-inches.

5.6 Groundwater and Drainage

Groundwater was encountered in most of the structural building test borings at depths ranging from about 9-ft. to 19-ft. below the ground surface. Groundwater levels encountered in the previous drilled borings ranged from about 1.3-ft. to 17.8-ft.

below grade, with an average depth of about 9-ft. The static groundwater levels noted in some of the stormwater management test borings are presented in a summary table in the following section of this report.

The test borings indicate static groundwater within the anticipated depth of excavations for the new construction. It is likely that groundwater will present problems during construction; however, it is expected that groundwater flows will be minor, due to relatively shallow perched groundwater conditions. It is anticipated that groundwater encountered during excavation for the construction can be controlled by ditching and pumping from sumps.

The site design must include provisions for adequate drainage, and to prevent surface water and groundwater intrusion into the building construction. This may be accomplished through the use of swales, catch basins, and/or underdrains to provide drainage, and to minimize any increase in moisture content of the subgrade soils. All pavement or parking areas should be sloped away from the structures to prevent ponding of water around the buildings. The site drainage should also be such that the run-off onto adjacent properties is controlled properly.

5.7 Preliminary Stormwater Management

We have evaluated the site subsurface conditions at the requested locations, in general accordance with the Maryland Department of the Environment, “2000 Maryland Stormwater Design Manual, and May 2009 revisions” Appendix D. Fifteen

(15) SWM test borings were conducted at locations selected by the SWM design engineer. Field infiltration testing was suspended until the SWM design can be further developed.

We understand that the use of best management practices (BMP) based on Environmental Site Design (ESD) principles is required for SWM. The following information is provided for planning stormwater management measures:

1. Location of groundwater table

Groundwater was not encountered during drilling of the SWM test borings.

Groundwater was detected at a +24-hour interval after completion of two of the SWM test borings. Stormwater management test boring information with regard to groundwater is as follows:

Test

Boring

Ground

Surface

Elevation

(ft.)

Depth of

Boring

(ft.)

+24-hr.

Depth to

Groundwater

(ft.)

Caved

Depth of

Boring

(ft.)

Final

Groundwater

Elevation (ft.)

SWM-1 22.5 10.0 dry 6.5 ~~~

SWM-2 21.5 10.0 6.5 7.5 15.0

SWM-3 23.7 10.0 6.3 7.0 17.4

SWM-4 18.9 10.0 dry 7.0 ~~~

SWM-5 21.1 10.0 dry 8.0 ~~~

SWM-6 22.9 10.0 dry 4.0 ~~~

SWM-7 22.4 10.0 dry 5.0 ~~~

SWM-8 22.9 10.0 dry 6.0 ~~~

SWM-9 23.7 10.0 dry 6.5 ~~~

SWM-10 12.9 10.0 dry 6.0 ~~~

SWM-13 13.9 9.4 dry 7.0 ~~~

SWM-17 19.1 10.0 dry 6.0 ~~~

SWM-18 11.8 10.0 dry 7.0 ~~~

SWM-19 14.4 10.0 dry 6.0 ~~~

SWM-20 13.4 9.8 dry 6.0 ~~~

2. Textural character of the strata units within the subsoil profile

The soils encountered at the SWM test borings are natural soils consisting of silty, clayey, and sandy soils, with gravel. The following U.S.D.A. Textural Classifications and estimated infiltration rates were determined by laboratory testing:

Boring Depth (ft.)

U.S.D.A.

Textural

Classification

Hydrologic

Soil

Grouping

Minimum

Infiltration

Rate (in./hr.)

SWM-1 5.0-6.5 Loam B 0.52

SWM-3 5.0-6.5 Silt Loam B 0.27

SWM-7 2.5-4.0 Silt Loam B 0.27

SWM-9 2.5-4.0 Loam B 0.52

SWM-10 5.0-6.5 Silt Loam B 0.27

SWM-20 5.0-6.5 Loam B 0.52

3. Depth to Bedrock

Materials characterized as bedrock were not encountered within the depths of the SWM test borings. However, dense to very dense materials classified as SAND and GRAVEL were encountered in some of the stormwater management test borings as indicated below:

Boring

Ground

Surface

Elevation

(ft.)

Depth to

Dense or

Very Dense

Materials (ft.)

Elevation

(ft.)

SWM-2 21.5 7.5 14.0

SWM-6 22.9 8.5 14.4

SWM-13 13.9 7.5 6.4

SWM-18 11.8 2.0 9.8

SWM-19 14.4 8.0 6.4

SWM-20 13.4 9.5 3.9

4. Infiltration testing

In-situ infiltration testing was not conducted. The stormwater management design concept was not developed to the point where specific field infiltration test locations and elevations could be requested by the SWM designer. We understand that in-situ infiltration testing will be required for each of the BMP facilities and will be requested when the SWM design is developed further.

Based on the “2000 Maryland Stormwater Design Manual Vols. I & II,” a minimum field infiltration rate of 0.52 inches per hour is required for infiltration trench and basin practices; lower rates preclude the use of these infiltration practices. Also, it is required that infiltration structures be located only in areas where the bottom of the structure will be 4-feet above the seasonally high groundwater table and/or bedrock.

The results of our preliminary evaluation indicate that infiltration methods may be feasible for providing stormwater management for the proposed BMP facilities at selected locations. When the SWM design has been further developed, the proposed BMP facilities should be evaluated by field infiltration testing.

We understand that porous pavement is under consideration for the at-grade parking facilities. It is not likely that the parking lot subgrade soils will be suitable for infiltration. Due to the anticipated low infiltration rate of cohesive subgrade soils, the use of an underdrain system should be anticipated where porous pavements are used. The underdrain system may be constructed using an arrangement of 4-in.

min. diameter perforated drainage pipe. The drainage pipe should be surrounded with filter graded aggregate, and/or wrapped in a drainage geotextile to preclude infiltration of soil fines into the drainage system. The underdrain system should provide gravity drainage to a stable outlet location such as the storm drain system.

Additional SWM test borings, groundwater depth measurements, field infiltration testing and evaluation will be required for final stormwater management design.

5.8 Hot Mix Asphalt (HMA) Pavement

Some of the test borings were performed for evaluation of the subgrade conditions along the proposed access roadway and parking areas. The subgrade soil samples recovered from the test borings primarily consist of Silty CLAY (CL-ML), SILT (ML), and Silty SAND (SM), with Gravel or rock fragments. Representative bulk bag samples were collected from Test Borings P-2A, P-3, and P-5 to depths of 5-ft.

below existing grade. The samples were submitted to the laboratory for determination of the moisture-density relationship, and to determine the California Bearing Ratio (CBR) for use in pavement design. The laboratory test results for the pavement subgrade soil samples are summarized in the following table:

Pavement

Boring

Maximum

Dry

Density

(pcf)

Optimum

Moisture

Content

CBR value

P-2A 125.7 10.3 21

P-3 124.5 11.3 50

P-5 123.5 11.4 39

The results of the CBR testing (ASTM D 1883), and Modified Proctor moisture-density relationship (ASTM D 1557) (AASHTO T-180) are provided in the Appendix.

Based on the laboratory test results, and the subsurface information determined by the test borings, we recommend using a limited design CBR value of 20 for the HMA pavement design. This is generally considered to be excellent pavement subgrade.

The pavement subgrade soils generally consist of cohesive and granular soil types (silts, clays, and sandy soils) and will require proper methods of preparation to achieve the design requirements for HMA pavement construction. Requirements for pavement subgrade preparation, and fill placement is described in Sections 5.1 and

5.2 of this report.

Design traffic information was not provided; however, we understand that predominantly light to moderate traffic volume consisting of passenger vehicles and single unit trucks is anticipated for the proposed access roadway. The roadway will also be used by service vehicles and occasionally by heavy trucks.

Using a soil subgrade CBR value of 20, an assumed design E-18 of 500,000, and the AASHTO Pavement Design Method for a 20-year design period, we have determined that a minimum design structural number of 2.1 will be appropriate for pavement thickness design. We recommend the following for flexible HMA pavement design:

HMA Pavement

1.5” HMA Superpave 9.5mm for surface – PG64-22, Level 1 2.5” HMA Superpave 12.5mm for base – PG64-22, Level 1 6.0” Graded Aggregate Base (GAB)

The hot mix asphalt pavement should be designed, mixed and constructed in accordance with the Maryland State Highway Administration Standard Specifications for Construction and Materials, July 2008, and any revisions or additions.

If the HMA pavement will be subjected to heavy construction loads, we should be notified so that we can review the proposed conditions, and develop recommendations for an alternate paving section if necessary.

We recommend that a minimum cross slope, or crown, of 1.5 percent be provided for proper surface drainage of the HMA pavement. The ground surface or shoulder area adjacent to the pavement should be graded to provide positive surface drainage, and prevent standing water along the edge of pavement.

A Geotechnical Engineer or experienced Soils Technician should monitor the roadway subgrade preparation in accordance with the procedures outlined in Sections 5.1 and 5.2 of this report. The technician should witness the proofrolling and compaction operations and should determine which areas need undercutting, scarification, and additional compaction.

5.9 Rock Excavation

Refusal materials described as possible boulders were encountered in seven of the test borings at depths ranging from 5.5-ft.