WM19-146G Quantico Nat Cemetery Expansion GEOTECH 02212020.pdf

701 Alexander Lee Parkway · Williamsburg, VA 23185 Phone: (757)-564-6452 www.getsolutionsinc.com

REPORT OF

SUBSURFACE

EXPLORATION

AND

GEOTECHNICAL

ENGINEERING

SERVICES

Quantico National Cemetery Expansion

Triangle, Virginia

G E T Project No: WM19-146G

November 27, 2019 Revised January 22, 2020

PREPARED FOR:

Woolpert 1203 Walnut Street, 2nd Floor Cincinnati, OH 45202

November 27, 2019 Revised January 22, 2020

TO: Woolpert

1203 Walnut Street, 2nd Floor Cincinnati, Ohio 45202

Attn: Mr. John E. Martin

RE: Report of Subsurface Exploration and Geotechnical Engineering Services

Quantico National Cemetery Expansion Triangle, Virginia G E T Project No: WM19-146G

Dear Mr. Martin:

In compliance with your instructions, we have completed our Subsurface Exploration and Geotechnical Engineering Services for the above referenced project. The results of this study, together with our recommendations, are presented in this report.

Often, because of design and construction details that occur on a project, questions arise concerning subsurface conditions. G E T Solutions, Inc. would be pleased to continue its role as Geotechnical Engineer during the project implementation.

Thank you for the opportunity to work with you on this project. We trust that the information contained herein meets your immediate need, and should you have any questions or if we could be of further assistance, please do not hesitate to contact us.

Respectfully Submitted, G E T Solutions, Inc.

Philip A. Wunderly, P.E.

Senior Project Engineer Virginia Lic. No. 047135

Bruce R. Spiro, P.E.

Principal Engineer Virginia Lic. No. 015791

Copies: (1) Client

701 Alexander Lee Parkway Williamsburg, VA 23185 Phone: 757-564-6452 Fax: 757-564-6453 info@getsolutionsinc.com

TABLE OF CONTENTS

1.0 PROJECT INFORMATION

1.1 Project Authorization

1.2 Project Site Location and Description

1.3 Project Construction Description

1.4 Purpose and Scope of Services

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

2.2 Laboratory Testing

2.2.1 Soil Classification and Index Testing

2.2.2 Bulk Soil Sample Testing

2.2.3 Analytical Testing

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology

3.2 Subsurface Soil Conditions

3.3 Groundwater Information

3.4 Shrink-Swell Soils Discussion

3.5 Corrosivity Characteristics Discussion

4.0 EVALUATION AND RECOMMENDATIONS

4.1 Clearing and Grading

4.2 Subgrade Preparation

4.3 Structural Fill and Placement

4.4 Suitability of On-site Soils

4.5 Embankment Discussion-Settlement and Slope Stability

4.6 Retaining Wall Discussion

4.7 Earth Pressures from Earthquakes

4.8 Below-Grade Estimated Soil Parameters

4.9 Pavement Design Discussion

4.10 Seismic Evaluation

5.0 CONSTRUCTION CONSIDERATIONS

5.1 Anticipated Excavation Characteristics

5.2 Excavation Stability

5.3 Dewatering

5.4 Site Utility Installation

6.0 REPORT LIMITATIONS

APPENDIX I BORING LOCATION PLANS

APPENDIX II CLASSIFICATION SYSTEM FOR SOIL EXPLORATION

APPENDIX III SUMMARY OF LABORATORY CLASSIFICATION RESULTS

APPENDIX IV BORING LOGS

APPENDIX V GENERALIZED SOIL PROFILES

APPENDIX VI CBR TESTING RESULTS

APPENDIX VII CALCULATIONS

APPENDIX VIII GEOPHYSICAL RESISTIVITY STUDY

Quantico National Cemetery Expansion Triangle, Virginia G E T Project No: WM19-146G

Report of Subsurface Exploration and Geotechnical Engineering Services November 27, 2019 Quantico National Cemetery Expansion Revised January 22, 2020 Triangle, Virginia G E T Project No: WM19-146G

1.0 PROJECT INFORMATION

1.1 Project Authorization

G E T Solutions, Inc. has completed our Subsurface Exploration and Geotechnical Engineering Services for the proposed Quantico National Cemetery Expansion Project in Triangle, Virginia.

The geotechnical engineering services were conducted in general accordance with G E T Proposal No. PVB19-275G dated April 2, 2019 and PWM19-243G dated July 18, 2019.

Authorization to proceed with our services was obtained in the form of Task Order 002 from Mr.

John Martin with Woolpert dated June 23, 2019 and Amendment 001 dated September 30, 2019.

1.2 Project Site Location and Description

The project consists of three (3) sites within Quantico National Cemetery in Triangle, Virginia:

one (1) large site along the central western boundary of the Cemetery and two (2) smaller sites at the north and south ends of the Cemetery. The approximate locations of the project sites are shown on the map in the below figure (adopted from the Joplin and Quantico USGS quadrangle maps dated 2016).

Figure 1. Project Vicinity Map, not to scale (USGS, 2016).

N

Triangle, Virginia G E T Project No: WM19-146G

The primary site is an approximately 14-acre wooded, undeveloped parcel located west of Quantico Drive at its intersection with Thomas Jefferson Road. This site is comprised of broad gently sloped ridges with steeper sloped valleys in between. Based on a review of survey drawings provided by the client, the site grade generally slopes downward from Quantico Drive to the western boundary of the Cemetery. Elevations across the parcel vary from 180 feet to 230 feet, NAVD88.

The northern site is approximately 250 square yards and is located on the south side of Yorktown Road Drive east of the Cemetery staff office building. The site is currently landscaped with a few isolated trees and has an elevation change of approximately 7 feet across the width of the site from east to west (elevation 257 to 264 feet, NAVD88). The southern site is at the service entrance to the Cemetery and consists of a level area (elevation 194 feet NAVD88) on either side of the entrance road.

1.3 Project Construction Description

The proposed development at the primary, centrally located site will consist of the construction of new cemetery plots to include approximately 6,500 pre-manufactured, pre-placed double stacked burial crypts and over 3,500 cremains plots, in addition to approximately 2,000 feet of new paved roadways. Per drawings provided by the client, the crypts are approximately 3 feet wide, 2 feet tall and 7.5 feet long. Excavations to accommodate the crypts are expected to be on order of 8 feet below finished grade elevations. The crypts are to be placed on a bedding layer of VDOT (Virginia Department of Transportation) No. 57 stone, backfilled with select fill and covered with a layer of sand and topsoil. The cremains plots are expected to be 4 feet square; urns will be placed in the plots by hand or small equipment. Cuts and fills to establish the finished grades of the burial areas and the roadway will be up to 20 feet and 12 feet respectively.

The proposed development at the northern site will consist of the construction of an ossuary (a below grade resting place for remains with an above ground decorative memorial) and associated features (sidewalks, stairs, pavers and a memorial wall). The ossuary structure will be approximately 12 feet below grade and will consist of segments of precast concrete pipe and reducers, 72 to 24 inches in diameter. The memorial wall be a retaining wall with a maximum height of approximately 5 feet; the cut at the wall is expected to be less than 5 feet however as there will be approximately 18 inches of exposed height on the higher elevation side of the wall. A minimal amount of fill, 2 feet or less, is expected for establishing finished grades at this site.

The proposed development at the southern site will consist of the construction decorative metal fencing. Site elevations are not expected to be altered at this location.

If any of the noted information is incorrect or has changed, G E T Solutions, Inc. shall be informed so that we may amend the recommendations presented in this report, if appropriate.

1.4 Purpose and Scope of Services

The purpose of this study was to obtain information on the general subsurface conditions at the proposed project site. The subsurface conditions encountered were then evaluated with respect to the available project characteristics. In this regard, engineering assessments for the following items were formulated:

1. General assessment of the soils revealed by the borings performed at the project sites.

Triangle, Virginia G E T Project No: WM19-146G

2. General location of bedrock and construction considerations for crypt and cremains vaults excavations.

3. General location and description of potentially deleterious material encountered in the borings that may interfere with construction progress or structure and pavement performance, including existing fills or surficial/subsurface organics.

4. Construction considerations for soil subgrade preparation (stripping, grading and compaction). Engineering criteria for placement and compaction of approved structural fill material.

5. Evaluation of the on-site soils for re-use as structural fill.

6. Feasibility of utilizing a shallow foundation system for support of the proposed ossuary retaining walls. Design parameters required for the foundation system, including foundation sizes, allowable bearing pressures, foundation levels, and expected total and differential settlements.

7. Assessment of the shallow subsurface soils’ expansive properties and corrosive potential.

8. Estimated below grade soil parameters and construction considerations for the proposed retaining walls and below grade structures.

9. Pavement design recommendations based on field exploration activities, California Bearing Ratio (CBR) tests and our experience with similar soil conditions.

10. Seismic Site Class definition in accordance with the International Building Code (IBC) 2015 requirements, available soil data, and our local experience.

The scope of services did not include an environmental assessment for determining the presence or absence of wetlands or hazardous or toxic material in the soil, bedrock, surface water, groundwater or air, on or below or around this site.

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

In order to explore the general subsurface soil types and to aid in developing associated design parameters and recommendations, the following exploration program was performed:

§ Four (4) 10-foot deep Standard Penetration Test (SPT) borings (designated as CE-1 through CE-4) were drilled within cremains burial areas.

§ Twelve (12) 15 to 20-foot deep SPT borings (designated as CY-1 through CY-12) were drilled within crypt burial areas.

§ Seven (7) 10 to 20-foot deep Standard Penetration Test (SPT) borings (designated as P-1 through P-7) were drilled within the road alignment.

§ Two (2) 20-foot deep SPT boring (designated as O-1 and O-2) were drilled within the ossuary area.

Triangle, Virginia G E T Project No: WM19-146G

§ Two (2) 15-foot deep SPT boring (designated as F-1 and F-2) were drilled within the fence area.

§ A geophysical study, consisting of Earth Resistivity Profiling along seven (7) lines, was performed at the burial site (designated as Lines 1 through 6) and at the ossuary site (designated as Line 7).

The SPT borings were performed with the use of hollow stem auger and rotary wash “mud” drilling procedures in general accordance with ASTM D 1586. The tests were performed continuously from the existing ground surface to depths of 10 to 12 feet and at 5-foot intervals starting at a depth of 13 feet. The soil samples were obtained with a standard 1.4-inch inner diameter, 2-inch outer diameter, 30-inch long split-spoon sampler. The sampler was driven with blows of a 140 lb. automatic hammer falling 30 inches. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded and is shown on the boring logs. The sum of the second and third penetration increments is termed the SPT N-value (uncorrected for automatic hammer and overburden pressure). A representative portion of each disturbed split-spoon sample was collected with each SPT, placed in a glass jar, sealed, labeled, and returned to our laboratory for review.

Resistivity field data was collected using a SuperSting R8 IP® multi-electrode resistivity system manufactured by Advanced Geosciences Inc. Data was collected using the dipole-dipole array with a current of up to 2000 milliamps. For each electrode configuration in the array, measurements were repeated a minimum of two times, and percent error between the repeated measurements were stored for subsequent evaluation of data quality. Lines 1 through 6 each utilized a spacing of five meters (16.4 feet) between electrodes, while Line 7 utilized a spacing of three meters (9.84 feet) between electrodes. The locations of the resistivity electrodes were recorded with a Trimble Pro 6H GPS unit capable of sub-foot accuracy and plotted onto topographic layers in the CAD survey drawings provided by the client. The elevations of each electrode were extracted from the topographic layer and integrated into the resistivity data so that the resistivity sections would reflect the local topographic relief. The results of the resistivity study are included as an Appendix to this report (Appendix VIII).

Bulk subgrade samples (designated as CBR #1 through CBR #6) were collected at or adjacent to each respective pavement boring location as conditions allowed. The bulk subgrade samples were collected from approximately 12 to 36 inches below existing grades and were returned to our AASHTO re:source (formerly AMRL) and US Army Corps of Engineers certified Williamsburg, VA laboratory and subjected to CBR testing in accordance with ASTM standards.

The boring locations were established by and staked in the field by G E T Solutions, Inc. with the use of a hand-held Global Positioning System (GPS) device. Approximate soil boring locations and resistivity survey lines are shown on the attached “Boring Location Plans” (Appendix I) which were developed using the 65% concept layout drawings provided by the client.

2.2 Laboratory Testing

Soil testing provided by G E T Solutions, Inc. was performed in accordance with American Society for Testing and Materials (ASTM) standards. All soils and materials tests were performed in our AASHTO re:source (formally AMRL) and US Army Corps of Engineers certified Williamsburg laboratory.

Triangle, Virginia G E T Project No: WM19-146G

2.2.1 Soil Classification and Index Testing

Representative portions of all soil samples collected during drilling operations were sealed in glass jars, labeled and transferred to our laboratory in accordance with ASTM D 4220 for classification and analysis. Soil descriptions on the boring logs are provided using visual-manual methods in general accordance with ASTM D 2488 using the Unified Soil Classification System (USCS). Soil samples that were selected for index testing were classified in general accordance with ASTM D 2487. It should be noted that some variation can be expected between samples classified using the visual-manual procedure (ASTM D 2488) and the USCS (ASTM D 2487). A summary of the soil classification system is provided in Appendix II.

Representative split-spoon soil samples were selected and subjected to natural moisture, #200 sieve wash, Atterberg Limits and pH testing. These test results are presented in Appendix III and on the soil test boring logs provided in Appendix IV. Generalized subsurface soil profiles are provided in Appendix V.

2.2.2 Bulk Soil Sample Testing

The six (6) bulk soil samples were returned to our AASHTO re:source and US Army Corps of Engineers certified Williamsburg laboratory and subjected to Standard Proctor and CBR testing in accordance with ASTM procedures. A summary of the CBR test results is presented in the following table (Table I); Proctor curves, CBR curves, and Particle Size Distribution curves are provided in Appendix VI.

Table I - CBR Test Results

CBR /

Boring

No.

Depth

(inches)(1)

USCS

Type(2)

Natural Moisture

Passing

#200 Sieve

Atterberg Limits

(LL/PL/PI)

Max.

Dry

Density (pcf)

Optimum Moisture

CBR

Value

Swell

#1 / P-1 12 - 24 CL 8 55.2 31/20/11 105.9 14.7 7.4 0.9

#2 / P-2 12 - 36 CL 11 50.6 39/22/17 105.4 15.6 11.0 1.4

#3 / P-3 12 - 24 CL 13 55.3 28/19/9 103.1 16.6 7.8 1.2

#4 / P-4 12 - 24 SC 12 49.3 27/16/11 111.9 13.6 8.4 0.1

#5 / P-5 12 - 24 CL-ML 9 51.0 23/16/7 114.6 13.0 8.1 0.4

#6 / P-6 12 - 36 CL 10 56.4 26/17/9 113.9 13.2 8.4 0.5

Note: (1) Depth below existing site grades

(2) Visual Classification in absence of specific laboratory tests

2.2.3 Analytical Testing

Composite soil samples were created from 4 to 15 feet below the existing site grades from representative boring locations where excavations for utilities are likely to occur. The samples were created from sealed jar samples of soils recovered from borings CY-2, CY-5 and CY-12.

The composite soil samples were subjected to resistivity testing by the soil box method. A summary of the test results is presented in Table II on the following page.

Triangle, Virginia G E T Project No: WM19-146G

Table II - Resistivity Testing Results

Sample Boring Location Depth (ft)(1)

Resistivity (ohms/cm)

CY-2 6-15 106,700

CY-5 4-12 73,400

CY-12 4-12 133,400

Notes: (1) Depth below existing grades

Unified Facilities Criteria (UFC) 3-570-01, Cathodic Protection, requires protection for buried/submerged steel piping and ductile/cast iron piping when resistivity is less than 30,000 ohm-cm.

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology

Quantico National Cemetery lies within the Coastal Plain physiographic province of Virginia. At the location of the project sites, surficial deposits of marine sediments overlie the Potomac Formation. The Potomac Formation is a complex series of ancient deltaic deposits varying from massive clays (deposited along the leading edge of the delta) to interlayered sands, gravels, silts and clays. Meandering rivers and distributary channels in a delta setting deposited these materials during the early Cretaceous Period. During the late Tertiary, the area was subjected to erosion and fluvial deposition that resulted in broad alluvial terraces consisting of sand and quartz gravel. The Potomac Formation is characterized by crossbedding, channel fills, rapid pinching and swelling of beds, and abrupt changes in grain-size grading. In the area of the project sites, the predominant clay is montmorillonite; the clays of the northern portion of the formation tend to be mainly kaolinite and illite. The Potomac Formation is weakened in the uppermost 20 feet along fractures, joints, and parting planes. As such, the most prevalent geologic processes taking place today are the creep, slumping, and sliding of Potomac Formation clays and Quaternary Period sediments.

3.2 Subsurface Soil Conditions

A summary of the subsurface soil conditions encountered at the SPT boring locations are presented Table III on the following page.

Triangle, Virginia G E T Project No: WM19-146G

Table III - Subsurface Soil Conditions

Average Depth

(Feet)(1) Stratum Description

Ranges of

SPT(2)

N-Values to

0.2 - 0.6 TOPSOIL Ø 2 to 7 inches of Topsoil -

0.1 to

FILL

Ø FILL material generally comprised of Clayey GRAVEL (GC) with varying amounts of Sand and fibrous organic material

FILL materials were only observed at boring location F-2

0.2 - 2 to

10 - 20

IA

Ø CLAY (CL-ML and CL) with varying amounts of Gravel, Sand, Silt and fibrous organic material

The Clays observed above elevation 205 feet, NAVD88 were generally indicative of Coastal Plain deposits, the Clays encountered below this elevation were indicative of Potomac Formation deposits

3 - 43

IB Ø SAND (SC and SM) with varying amounts of Gravel, Silt, Clay, and fibrous organic material 5 - 50+

Notes: (1) Depth below existing grades

(2) SPT=Standard Penetration Test, N-Values in Blows-per-foot (uncorrected)

The resistivity data collected during the geophysical study of the burial and ossuary sites correlate reasonably well with the stratifications and groundwater levels encountered in the SPT soil borings. Though none of the borings encountered auger refusal within the upper 15 to 20 feet below the existing ground surface, Resistivity Lines 4 through 6 revealed a transition to higher resistivities at depths ranging from 13 to 49 feet below the ground surface, interpreted as possibly representing the transition from unconsolidated soils into bedrock. Figure 9 in the included Resistivity Study (Appendix VIII) illustrates the estimated depth to possible bedrock beneath Lines 4 through 6. The estimated depth to this possible bedrock surface ranges from approximately 13 feet (dark red color contours) to 49 feet (dark blue color contours). No other instances of possible bedrock were observed in the other resistivity sections. It should be noted that all geophysical methods are interpretive and additional invasive exploration would be required to verify or refute the interpretations depicted in the included study.

The subsurface descriptions are of a generalized nature provided to highlight the major soil strata encountered. The records of the subsurface exploration are included in Appendix IV (Boring Log sheets) and in Appendix V (Generalized Soil Profiles) which should be reviewed for specific information as to the individual borings. The stratifications shown on the records of the subsurface exploration represent the conditions only at the actual boring locations. Variations may occur and should be expected between boring locations. The stratifications represent the approximate boundary between subsurface materials and the transition may be gradual.

Triangle, Virginia G E T Project No: WM19-146G

It is noted that the “Topsoil” designation references the presence of surficial organic laden soil and does not represent any particular quality specification. It is recommended that this material be tested for approval prior to use as topsoil.

3.3 Groundwater Information

The initial groundwater level was recorded at the boring locations and as observed through the wetness of the recovered soil samples during the drilling operations. The initial groundwater table was measured to occur at a depth of approximately 14 to 19 feet below the existing site grades (approximate elevations of 192 to 243 feet, NAVD88) at boring locations CY-8, O-1, and O-2 (and as interpreted from Resistivity Line 6). The initial groundwater table was not observed at the remaining boring locations to the depths explored (10 to 20 feet below existing grades).

The borings were backfilled upon completion for safety considerations and as such, the initial groundwater levels may not be indicative of static groundwater levels.

During drilling operations, fluid (clay-water slurry) is introduced into the bore hole generally impairing the ability to accurately determine groundwater levels. Additionally, as subsurface soils begin to dry, moisture moves upwards through the soil profile by means of capillary action.

Based on the subsurface soil composition (soils containing more than 30% of fines by weight), the initial groundwater level reading (based on the relative wetness of the soils) could be in part attributed to the capillary action of the soils.

It is noted that each project site may be susceptible to perched water conditions at or near the ground surface as relatively impermeable soils were encountered within the top 10 feet of several borings. Controlling perched water should be addressed by the contractor prior to proceeding with construction. Water seepage, at varying elevations, should be expected within the side walls of open cut areas due to relatively impermeable soils that were encountered above measured groundwater elevations. It is important to note that even small quantities of persistent seepage may complicate construction operations when excavations extend near or below areas of saturated soil. Construction difficulties resulting from near surface groundwater or excess soil moisture will be much less likely if work is conducted during the dry season.

Groundwater conditions will vary with environmental variations and seasonal conditions, such as the frequency and magnitude of rainfall patterns and man-made influences, such as existing swales, drainage ponds, underdrains and areas of covered soil (paved parking lots, sidewalks, etc.). In the project’s area, seasonal groundwater fluctuations of ±3 feet are common; however, greater fluctuations have been documented. We recommend that the contractor determine the actual groundwater levels at the time of the construction to determine groundwater impact on the construction procedures, if necessary.

3.4 Shrink-Swell Soils Discussion

The soils recovered during our field exploration were tested and evaluated for their potential to expand or contract with moisture changes (typically termed shrink-swell). Shallow foundations and other on-grade features constructed on expansive soils at certain depths may be subjected to detrimental uplift or horizontal forces caused by the swelling of these soils as a result of an increase in the moisture content. Conversely, as these Clays lose moisture they may shrink, adversely affecting the foundations. The depth to which soils are normally affected by moisture changes extends from the ground surface to approximately 30 inches below existing grades in this area, depending on site topography and drainage characteristics.

Triangle, Virginia G E T Project No: WM19-146G

The predominant soils within the project site as mapped by the USDA Web Soil Survey include the Caroline fine sandy loam (CaB2 and CaC2), Lunt loam (34D), and the Aura-Galestown- Sassafras Complex (AwE). The soils encountered in the borings appear to be consistent with these soils. The expansive (shrink-swell) potential of these soils, as described by the Soil Survey, is as follows:

§ Caroline fine sandy loam (CaB2 and CaC2): low to moderate (all three sites)

§ Aura-Galestown-Sassafras Complex (AwE): low (fence site)

§ Lunt loam (34D): high (ossuary site)

In order to minimize shrink-swell concerns and possibilities, the following preventative measures are typically practiced:

§ Increasing footing bearing depth.

§ Restrict planting of deep-rooted trees and shrubs within 10 feet of foundations.

§ Moderately moisten the soils within 5 feet of the foundations during hot weather conditions.

§ Tie roof drains to the storm water system and situate downspouts in such a manner to prevent ponding water near the foundation.

3.5 Corrosivity Characteristics Discussion

The AWWA (American Water Works Association) - DIPRA (Ductile Iron Pipe Research Association) 10 point assessment for determining corrosivity potential consists of assigning points to a soil based on its drainage characteristics (poor, fair, or good) and the results of the following analytical tests: pH, Resistivity, Redox potential, and Sulfides content. If the total point value is greater than or equal to 10, the soil is considered to be corrosive to iron pipe and protection would be warranted.

The results of the pH testing (values from 4.22 to 5.13) performed on selected spilt spoon soil samples recovered from the borings and the results of the analytical testing (resistivity values much greater than 3,000 ohm-cm) indicate conditions that are not corrosive to iron pipe and as such are assigned zero (0) points. The fair drainage characteristics of the soils encountered in the borings contribute minimally to corrosive environments and are assigned only one (1) point.

In order to fully evaluate the corrosivity potential of site soils per AWWA-DIPRA standards, Redox potential and Sulfides content testing would need to be completed. However, we would not expect the results of these tests to contribute enough points to result in a total value that would equal or exceed 10. As such, we do not expect site soils to be corrosive to iron pipe or ferrous materials per the AWWA 10-point evaluation method.

4.0 EVALUATION AND RECOMMENDATIONS

Our recommendations are based on the previously discussed project information, our interpretation of the soil test borings and laboratory data, and our observations during our site reconnaissance. If the proposed construction should vary from what was described, we request the opportunity to review our recommendations and make any necessary changes.

Triangle, Virginia G E T Project No: WM19-146G

4.1 Clearing and Grading

The proposed construction areas should be cleared as needed by means of removing the topsoil material, trees, and any other unsuitable materials. It is estimated that a cut of up to 7 inches in depth will be required to remove topsoil material. In addition, based on our experience with similar site conditions, this initial cut to remove organic laden soils could extend to 18 inches or more within wooded areas (burial site). Removing the trees will also consist of stump and large root removal. These events will likely leave holes that may extend several feet in depth throughout the project site. Surface water may accumulate in these holes leading to subgrade deterioration if not properly addressed. These holes should be backfilled as recommended in Section 4.3. It is recommended that the clearing operations extend laterally at least 5 feet beyond the perimeter of the proposed construction area.

Uncontrolled FILL material was observed at boring location F-2 (fence site) and may occur elsewhere at this site within unexplored locations. All Uncontrolled FILL materials must be removed from below the base of all new foundation excavations. Uncontrolled FILL materials are often considered unreliable due to the variable content and uncertainty regarding means of placement. As such, Uncontrolled FILL material left in place can be susceptible to settlement as a result of internal compression of the soils contained within.

Following the initial clearing, the resulting exposed subgrade will generally be comprised of SAND (SM and SC) soils and some CLAY (CL and CL-ML) soils, some of which contain appreciable amounts of fines. The bulk soil samples indicated natural moisture contents at or above their optimum moisture (as determined by means of laboratory testing). Accordingly, combinations of excess surface moisture from precipitation ponding on the site and the construction traffic, including heavy compaction equipment, may create pumping and general deterioration of the bearing capabilities of the surface soils. Therefore, undercutting to remove very soft/loose soils in isolated areas should be expected. The extent of the undercut will be determined in the field during construction based on the outcome of the field-testing procedures (subgrade proofroll). In this regard, and in order to reduce undercutting, care should be exercised during grading and construction operations at the site.

To reduce the potential for subgrade improvements (undercutting due to saturated soils in conjunction with heavy construction traffic), it is recommended that the grading operations be performed during the drier months of the year (historically April through November as indicated by the NCDC Climate Atlas of the United States). This should minimize these potential problems, although they may not be eliminated. If grading is attempted during the winter months, stabilization of wet soils should be anticipated. Methods to address wet soils may include excavation-substitution (undercutting and backfilling with structural fill) or the introduction of chemical additives (cement, lime, etc.). However, during the drier months of the year, wet soils could be dried by discing or implementing other drying procedures (stockpiling or spreading in thin lifts) to achieve moisture contents necessary to achieve adequate degrees of compaction. The project’s budget should include an allowance for subgrade improvements as described above.

The sites should be graded as necessary to enhance surface water runoff to reduce the ponding of water. Ponding of water often results in softening of the near-surface soils. In the event of heavy rainfall within areas to receive fill, we recommend that the grading operations cease until the site has had a chance to dry. If the subgrade becomes deteriorated due to the above-mentioned or other reasons, difficulty maneuvering construction equipment and machinery is likely.

Triangle, Virginia G E T Project No: WM19-146G

The undercut and backfill should be performed under the observation of a representative of G E T Solutions, Inc. who will evaluate the composition of the recovered soils.

Recommendations concerning the subgrade improvements (as necessary) will be provided in the field following the testing procedures.

4.2 Subgrade Preparation

Following the clearing operation, the newly exposed subgrade soils should be densified with a large static drum roller. After the subgrade soils have been densified, they should be evaluated by a qualified geotechnical inspector for stability. Accordingly, the subgrade soils should be proofrolled to check for pockets of loose material hidden beneath a crust of better soil. Several passes should be made by a large rubber-tired roller or loaded dump truck over the construction areas. The number of passes will be determined in the field by the Geotechnical Engineer depending on the condition of the exposed soils. Any pumping and unstable areas observed during proofrolling (beyond the initial cut) should be undercut and/or stabilized at the directions of the Geotechnical Engineer.

It is likely that some subgrade improvements will be required to provide suitable soils for pavement support. The extent of the subgrade improvements will be evaluated in the field during construction based on the outcome of the field-testing procedures (field assessments of subgrade stability). In this regard, and in order to reduce the potential for subgrade improvements, care should be exercised during the grading and construction operations at the site. The project’s budget should include an allowance for subgrade improvements (undercut and backfill with structural fill).

4.3 Structural Fill and Placement

Following the approval of the natural subgrade soils by the Geotechnical Engineer, the placement of the fill required to establish the design grades may begin. Any material to be used for structural fill should be evaluated and tested by an independent testing laboratory prior to placement to determine if they are suitable for the intended use. Materials to replace undercut areas and to achieve finish grades should consist of Imported Structural Fill or On-Site Borrow Fill meeting the following requirements:

On-Site Borrow Fill: Soil material which is free of organics and debris classified as SC, SM, SP, GM, GC, GP, or better with less than 50% passing the No. 200 sieve (Silt or Clay). The Silt and Clay content should have a maximum Liquid Limit of 40 and Plasticity Index of 20. Maximum aggregate size should be limited to 3 inches. Drying or wetting of these materials may be necessary to achieve optimal moistures required for proper compaction. Those soils with high amounts of fines (generally >25%) are moisture sensitive and difficult to compact when wet. Refer to Section 4.4 of this report in regard to reuse of these on-site soils, particularly those with high amounts of fines.

Imported Structural Fill: Soil material imported from local pits for use in general embankment construction should consist of a material classified as SM, SP-SM, SP, GM, GC, GP, or better containing a maximum 20% passing the No. 200 sieve (Silt or Clay) and having a maximum Liquid Limit of 40 and Plasticity Index of 20 and free of rubble, organics, clay, debris, and other unsuitable material. Maximum aggregate size should be limited to 3 inches.

Triangle, Virginia G E T Project No: WM19-146G

All On-Site Borrow fill or Structural fill placed in structural areas (pavements, etc.) should be compacted to a dry density of at least 95% of the Modified Proctor maximum dry density, in accordance with ASTM Specification D 1557. The moisture content of the structural fill should be within ±2 percentage points of the optimum moisture content at the time of placement. In general, the compaction should be accomplished by placing the fill in maximum 8 to 10-inch loose lifts and mechanically compacting each lift to at least the specified minimum dry density. A qualified inspector should perform field density tests on each lift as necessary to assure that adequate compaction is achieved.

Where fill materials will be placed up against existing sloping ground steeper than 6H:1V, the existing slope should be benched. Benching shall consist of a series of horizontal cuts beginning at the intersection with the original ground and continuing along the existing slope surface. Where road alignments intersect sharp transitions between cut and fill, the existing ground should be rounded or gradually sloped away from the transition to provide a more uniform roadbed in the area of the transition. A protective cover of grass or other vegetation should be established on permanent slopes as soon as possible during construction.

Backfill material in utility trenches within the construction areas should consist of structural fill (as previously described) and should be compacted to at least 95% of ASTM Specification D 1557. This fill should be placed in 4 to 6-inch loose lifts when hand compaction equipment is used.

If applicable, care should be used when operating heavy compacting equipment near existing structures to avoid transmission of the vibrations that could cause settlement damage or disturb occupants. In this regard, it is recommended that the vibratory roller remain at least 25 feet away from existing structures; these areas should be compacted with small, hand-operated compaction equipment.

We note that Potomac Clays were encountered at multiple boring locations throughout the crypt and cremains sites. These clays were of minimal thickness and were typically located below an elevation of 205 feet NAVD88. It is noted that massively bedded Potomac Clays located in the Washington D.C. metropolitan area of Virginia and Maryland have been associated with detrimental stability issues (large scale landslides, slumps and slope failures) due to inherent weaknesses within the Clay deposits, particularly when repeated inundation and drying of the Clay occurs (Engineering Geology and Design of Slopes for Cretaceous Potomac Deposits in Fairfax County, Virginia and Vicinity, USGS, 1984). As the Potomac Clays encountered in the soil borings were of minimal thicknesses and no signs of slope instability were observed across the existing site topography during our field operations, we do not expect large scale stability issues to be a concern. However, if thicker deposits of the Potomac Clays are exposed during grading operations, the geotechnical engineer should be contacted in order to assess the conditions and make necessary recommendations to address potential slope stability issues.

4.4 Suitability of On-site Soils

Based on the laboratory testing program, the shallow subsurface SAND (SM and SC) soils encountered at the boring locations appear to meet the criteria of On-Site Borrow Fill as outlined in Section 4.3 of this report. Further classification testing (natural moisture content, gradation analysis, and Proctor testing) should be performed in the field during construction to evaluate the suitability of excavated soils for reuse as structural fill. The project’s budget should include an allowance for imported structural fill.

Triangle, Virginia G E T Project No: WM19-146G

It should be noted that soils with high amounts of fines (generally >25%) are difficult to compact when wet and would typically experience sponginess and instability during compaction if the moisture content is above their optimum moisture. However, when these soils are dried to or just below optimum moisture and are compacted, they perform adequately as fill. As such, the challenge becomes one of manipulating the moisture of these soils to achieve the desired degree of compaction. Also, utilizing proper compaction equipment (such as sheepsfoot rollers in combination with smooth steel drum rollers) generally increases the likelihood of achieving the desired degree of compaction. This is further simplified if attempted during a dry season and establishing proper drainage patterns around the fill (so that they don’t become saturated). It has been our experience that under favorable weather conditions, where the moisture content of similar soils is manipulated to within ±2 percentage points of the optimum moisture content, compaction of these soils is achievable. A single rain event, however, may delay these operations by several days. If the contractor attempts to reuse the onsite cohesive soils, moisture manipulation should be anticipated prior to its reuse. This moisture manipulation could be accomplished by mechanically aerating, discing, and/or scarifying the soils.

4.5 Embankment Discussion - Settlement and Slope Stability

Portions of the burial site will require up to 12 feet of fill to establish finished grades per plans provided by the client. The sides of the proposed fill slopes are designed to be at a ratio of 2H:1V (horizontal to vertical) or flatter.

The magnitude and duration of the settlement associated with the fill embankments is important for construction planning and for embankment performance. Settlement magnitudes were calculated at points where fill slopes corresponded with boring locations and evaluated using the appropriate subsurface information from the borings and laboratory test data (maximum fill height of 5 feet). The subsurface soils at locations of greater amounts of fill will be influenced to depths greater than those explored for this reporting. As such, G E T Solutions, Inc. can make statements only related to the soil conditions within the limits of the depths explored, and specifically excludes any references to the proposed embankments influences on deeper subsurface materials as may be related to settlement performance.

The settlement computations were conducted using a model based on one-dimensional primary consolidation settlement theory. We evaluated the expected consolidation and compression settlements of fine-grained soils (Clay) and the expected elastic settlement of granular (Sand) materials based on our experience with similar soils and on empirical data. As the soils encountered were predominately granular in nature, it is expected that the total settlement (elastic and plastic) induced by the fill materials within the embankments analyzed (fill amounts on the order of 5 feet) will be less than 1 inch and will occur during construction. This estimated settlement is the total settlement to include compression of the subsurface soils and the internal compression of the embankment fill required to achieve finish grades. Again, we note that in order to explore subsurface materials at locations of maximum fill and to address settlements at these locations more accurately, it is recommended to perform deeper Standard Penetration Test (SPT) borings.

To allow for settlements within embankments consisting of greater amounts of fill, construction schedules are generally arranged so that fine grading, pavement construction and utility installation are delayed until after a suitable settlement period has expired. Once rough subgrade elevations have been established in areas that receive in excess of 6 feet of fill, it is recommended to delay further construction of utilities and preplaced burial components for a period of 2 to 3 weeks.

Triangle, Virginia G E T Project No: WM19-146G

Stability analyses of several fill and cut slopes that corresponded with site borings were conducted using the stability analysis software Slide 6.0 by Rocscience, Inc. Slide 6.0 is a 2-D limit-equilibrium slope stability program for determining the factor of safety of circular and non-circular failure surfaces in rock or soil slopes. Circular failure surfaces were evaluated using the Bishop and Morgenstern-Price methods of analysis. The soil parameters used were estimated from the SPT data, the laboratory test program and from our experience with similar materials.

The computer-generated results of the stability analyses are included in Appendix VII.

The results of the stability analyses indicate that embankment slopes (cut or fill) of 2H:1V have acceptable safety factors (1.3 or greater). If slopes steeper than 2H:1V are required, G E T Solutions Inc. requests the opportunity to complete a specific analysis for the location of any steepened slopes in order to verify the safety factor of such a configuration.

4.6 Retaining Wall Discussion

It is expected that the proposed retaining walls at the ossuary site will be cast-in-place walls supported by a shallow foundation. Foundations that bear on natural soils or compacted structural fill can be designed using a net allowable soil pressure of 2,000 psf. The resultant of the soil pressure distribution across the base of the foundation should pass through the center third of the foundation cross section.

In order to develop the recommended bearing capacity of 2,000 psf, and to accommodate for the high expansive (shrink-swell) potential soils at the ossuary site, the base of the footings should have a minimum embedment of 30 inches beneath finished grades and should have a minimum width of 24 inches. In addition, isolated square column footings (if deemed necessary) are recommended to be a minimum of 3 feet by 3 feet in area for bearing capacity consideration. The recommended 30-inch footing embedment is considered sufficient to provide adequate cover against frost penetration to the bearing soils.

In order to reduce the magnitude of lateral loads being applied to the retaining wall, a granular backfill should be used as fill directly behind the wall. These granular soils should be a relatively clean, free-draining, granular material (SAND) classified as SP-SM or better, containing less than 12% passing the No. 200 sieve (0.074 mm). Positive water drainage during construction will be important in order to prevent saturated structural fill from increasing lateral loading on the retaining wall above what is considered adequate for the design of the wall. A “sock drain” or other suitable drainage feature discharging a suitable distance from the wall may be necessary to maintain proper drainage behind the wall during construction. The compaction behind the wall should be in the range of 95% of the Modified Proctor maximum dry density (ASTM D 1557). The soils behind the foundation retaining wall should not be over-compacted. In order to minimize the potential for wall damage due to excessive compaction, hand operated mechanical tampers should be used to compact the granular materials.

The geotechnical engineer or their representative should visit the site during retaining wall construction to verify that the soils in the base of the excavations are consistent with those encountered during the subsurface exploration. At that time, the engineer or their representative will explore the extent of excessively loose, soft, or otherwise unsuitable material within the exposed excavations and perform hand auger borings or use a hand penetration device in the base of the excavations. The necessary depth of penetration will be established during the subgrade observations.

Triangle, Virginia G E T Project No: WM19-146G

Where undercut of loose or soft soils is performed, the design bearing elevation should be re-established by backfilling with VDOT No. 57 Stone. Immediately prior to placement of the stone material, it is suggested that the bearing surfaces be compacted using hand operated mechanical tampers. In this manner, any localized areas which have been loosened by excavation operations should be adequately recompacted.

Soils exposed in the base of the excavations for the retaining wall should be protected against any detrimental change in condition such as from physical disturbance, rain or frost. Surface run-off water should be drained away from the excavations and not be allowed to pond. If possible, all footing concrete should be placed the same day excavations are made. If this is not possible, the footing excavations should be adequately protected.

With regard to the design of the retaining walls to resist lateral earth pressures, the estimated soil parameters provided in following table (Table IV) can be used.

Table IV - Retaining Wall Soil Design Parameters

Soil Type Imported Structural

Fill

(SM, SP-SM, SP,

GM, GC, GP)

CLAY

(CL-ML, CL)

SAND

(SM, SC)

Stratum - IA IB

Estimated Moist Unit Weight (pcf) 122 115 120

Estimated Saturated Unit Weight (pcf) 125 120 125

Estimated Submerged Unit

Weight (pcf) 63 58 63

Friction Angle, f (degrees) 34 5 34

Cohesion, c (psf) 0 750 0

Active Soil Pressure Coefficient, Ka

0.28 0.83 0.28

At-Rest Soil Pressure Coefficient, K0

0.44 0.91 0.44

Passive Soil Pressure Coefficient, Kp

3.5 1.2 3.5

Coefficient of Friction 0.45 0.06 0.45

The above indicated Active, At-Rest, and Passive Coefficients of Lateral Earth Pressure (Ka, K0, and Kp) as shown in Table IV, are based on a horizontal grade above and behind retaining walls. If the final grades above retaining walls are sloped, G E T Solutions Inc. should be notified in order to provide appropriate Lateral Earth Pressure coefficients as these coefficients are greater for sloped ground (in order to account for the angular component of load induced by the sloped ground surface).

Triangle, Virginia G E T Project No: WM19-146G

4.7 Earth Pressures from Earthquakes

The lateral earth pressure may be increased against a retaining wall because of the vibrations of the ground. The combined effect of static and dynamic force (PAE) should be calculated using the following formula (as adopted from Design Manual 7.02, Naval Facilities Engineering Command):

2 +

Where kh is the horizontal acceleration in gravity and H is the height of the wall. The dynamic lateral force, PE, acts at 0.6H above the base of the wall.

Additionally, hydrodynamic pressure should be incorporated into the wall design and be computed as follows:

, = 1.5 (ℎ × ) .

Where Pw,z is the hydrodynamic pressure at depth z below the water surface and h is the depth of the water surface. It is noted that under the combined effect of static and earthquake loads, a factor of safety between 1.1 and 1.2 is acceptable.

4.8 Below-Grade Estimated Soil Parameters

Regarding the…