Attachment122_OpsCtrPhaseII_final_GeotechRpt_Sept2019.pdf

Defense Supply Center Richmond

DLA Operations Center Phase II

Richmond, Virginia

Geotechnical Design Document Report

100% Submittal

Submitted by:

Geo-Environmental Section

U.S. Army Corps of Engineers

Norfolk District

September 2019

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Table of Contents

1. INTRODUCTION

1.1. GENERAL

1.2. PROJECT DESCRIPTION

1.3. PX GASOLINE STATION PLUME

2. GEOTECHNICAL EXPLORATIONS

2.1. GENERAL

2.2. HISTORICAL SOIL BORINGS

2.3. MONITORING WELLS

2.4. OPS CENTER PHASE I EXPLORATIONS

2.5. OPS CENTER PHASE II EXPLORATION PROGRAM

2.5.1. STANDARD PENETRATION TEST (SPT)

2.5.2. CONE PENETRATION TEST

2.5.3. LABORATORY TESTING

2.6. EXPLORATION LOCATIONS

3. SUBSURFACE CONDITIONS

3.1. REGIONAL GEOLOGY

3.2. SUBSURFACE STRATIGRAPHY

3.3. GROUNDWATER CONDITIONS

4. DESIGN

4.1. GENERAL

4.2. SINGLE STORY BUILDING AREAS

4.2.1. GENERAL

4.2.2. BEARING CAPACITY

4.2.3. SETTLEMENT

4.3. FIVE STORY BUILDING AREA

4.3.1. GENERAL

4.3.2. AXIAL CAPACITY

4.3.3. SETTLEMENT

4.3.4. COMPARISON WITH PHASE I O-CELL LOAD TESTS

4.3.5. LATERAL CAPACITY

4.4. TWO STORY BUILDING AREA

4.4.1. DRILLED PIERS

4.5. SEISMIC SITE CLASSIFICATION

4.6. PAVEMENT DESIGN

4.7. SOIL CORROSIVITY

5. CONSTRUCTION RECOMMENDATIONS

5.1. SITE PREPARATION

5.2. FOUNDATION CONSTRUCTION

5.2.1. GENERAL

5.2.2. POTENTIAL SOIL CONTAMINATION

5.2.3. DRILLED PIER FOUNDATION

5.3. STRUCTURAL FILL

5.4. SOIL PROPERTIES

5.5. COMPACTION REQUIREMENTS

5.6. SUIITABILITY OF ON-SITE SOILS FOR REUSE

5.7. GROUNDWATER

5.8. TEMPORARY EXCAVATION SUPPORT SYSTEM

5.9. STORMWATER MANAGEMENT PONDS

6. LIMITATIONS

7. REFERENCES

LIST OF PLATES

Plate 1. DSCR Location Map Plate 2. DLA Ops Center Phases I and II Footprints Plate 3. DLA Ops Center Phase II, Road Map Plate 4. Overall Exploration Location Map Plate 5. Exploration Location Map, Road J Plate 6. Exploration Location Map, Road K Plate 7. Exploration Location Map, Road L Plate 8. Axial Capacity, 3-Foot Diameter Drilled Piers

LIST OF TABLES

Table 2-1. Phase II Laboratory Testing Program Table 2-2a. Exploration Location Information (Lat-Long) Table 2-2b. Exploration Location Information (Virginia South State Plane) Table 4-1. Preliminary Loading and Settlement Recommendations Table 4-2. Allowable Capacity of Individual 3-Foot Diameter Drilled Piers Table 4-3. Estimated Settlement of Individual 3-Foot Diameter Drilled Piers Table 4-4 Comparison of Compression Capacity and Settlement Table 4-5. Allowable Capacity of Individual 2.5-Foot Diameter Drilled Piers Table 4-6. Estimated Settlement of Individual 2.5-Foot Diameter Drilled Piers Table 4-7. Soil Corrosivity Test Results Table 5-1. Recommended Soil Properties

LIST OF ENCLOSURES

Enclosure 1. Exploration Logs Enclosure 2. Laboratory Test Data Enclosure 3. LPILE Output Summary Enclosure 4. Seismic Site Classification Enclosure 5. PCASE Design

The following Excel design spreadsheets are available in the Geo-Environmental Section, Norfolk District, but are not provided in the report:

Shallow Foundation Design Calculations (Bearing Capacity and Settlement) Axial Capacity, 3-Foot Diameter Drilled Piers Axial Capacity, 2.5-Foot Diameter Drilled Piers Drilled Pier Settlement

Defense Supply Center Richmond DLA Operations Center Phase II

Geotechnical Design Document Report

1. INTRODUCTION

1.1. GENERAL

The Defense Supply Center Richmond (DSCR) is a 631-acre facility just south of the city of Richmond, Virginia, in Chesterfield County. DSCR serves as the aviation demand and supply chain manager for the Defense Logistics Agency (DLA). The mission of DLA Aviation is to support the military by providing items when and where they are needed.

The purpose of the Operations Center (Ops Center) project is to relocate personnel from older, energy-inefficient buildings within DSCR to a new, intelligent, energy efficient facility. The Ops Center is being constructed in two phases. Phase I completed construction in spring 2018 and is occupied and functional. Design of this Phase II began in fall 2017 and is scheduled for completion in January 2020. Construction of Phase II is expected to be in calendar year 2020- 2022, depending on receipt of construction funds.

1.2. PROJECT DESCRIPTION

The Phase II portion of the project consists of a 281,000-square foot office building, an adjacent parking lot, and a geothermal well field along with ancillary facilities (utilities, sidewalks etc.).

The project site is located on the southern portion of the DSCR facility between Road L on the south, Road J on the north, Fifth Street on the west, and Sixth Street on the east. The building will be located where the western portions of Warehouses 32 and 33 are currently. Warehouse 32 will be partially demolished for the Ops Center Phase II construction and Warehouse 33 will be completely demolished. The parking lot will be located where the eastern portion of Warehouse 33 is now. The geothermal well field will be located within the new parking lot.

There are numerous underground utilities around and between Warehouses 32 and 33 that will need to be removed and/or replaced. The Phase II building footprint and general architecture is expected to be an almost mirror-image of the Phase I building.

An overall location map for DSCR is shown on Plate 1. Location maps with the approximate footprints of the Ops Center Phase II building and parking lot are shown on Plates 2 and 3.

1.3. PX GASOLINE STATION PLUME

In 1987, a routine inventory check of the PX Gasoline Station indicated about 4,000 gallons of unleaded gasoline had leaked from an underground storage tank (UST). The PX Gasoline station is located about 1,300 feet northwest of the proposed Ops Center Phase II building. The UST was removed in July 1987. Groundwater monitoring wells were installed in 5 phases between 1988 and 2010 to monitor shallow groundwater in the area. A plume of contaminated groundwater was documented moving from the gas station to the southeast between 1988 and 2011, when regular sampling of the monitoring wells was discontinued. The Norfolk District sampled some of the monitoring wells in March 2017 to determine if the plume had migrated beyond the 2011 limits. The sampling showed that the overall plume configuration does not appear to be migrating to any significant extent. The 2017 monitoring well sampling report is available from DSCR and the Norfolk District. Two of the recommendations from the report are that a passive vapor collection system be installed under the new building and that monitoring wells closest to the new building construction be sampled again prior to advertisement of the construction contract to confirm the conditions.

2. GEOTECHNICAL EXPLORATIONS

2.1. GENERAL

Design of the DLA Ops Center Phase II building and parking lot was based on historical and current explorations near Warehouses 32 and 33. Logs of explorations are in Enclosure 1.

2.2. HISTORICAL SOIL BORINGS

Existing geotechnical data in the vicinity of Warehouses 32 and 33 is limited. Two shallow soil borings (9FA-1 and 9FA-2) were drilled along the western portion of Road J (between Warehouses 32 and 33, within the proposed Ops Center Phase II building footprint) in February 1963 for the conversion of that area into a parking lot. These borings were 4-6 feet deep. Two shallow soil borings (Hole 1 and Hole 2) were drilled along the eastern portion of Road K (between Warehouses 32 and 33, just north of the proposed Ops Center Phase II parking lot) in February 1973 for the design of utility foundation pads. These borings were 18 feet deep.

2.3. MONITORING WELLS

Several shallow monitoring wells were installed in the vicinity of Warehouses 32 and 33 between 1988 and 2010 to monitor groundwater in the area (B32-MW1, B32-MW2, PX-20, PX- 41, PX-42, PXET-02, PXET-01, PX-35, and PX-45). Unfortunately, the drilling logs and well installation diagrams could not be located except for PX-35, which is located on the west side of Warehouse 33 near the intersection of 5th Street and Road K.

2.4. OPS CENTER PHASE I EXPLORATIONS

Two soil borings (12DH-28 and 12DH-29) and three cone penetration tests (CPTs) (12CPT-4, 12CPT-5, and 12CPT-9), conducted along Road J (north of Warehouse 32) in 2012 for the design of the Ops Center Phase I building, were used in the design of the Ops Center Phase II building. The SPT holes were 50-70 feet deep and the CPTs were 33-35 feet deep. 12CPT-9 was a seismic CPT.

2.5. OPS CENTER PHASE II EXPLORATION PROGRAM

2.5.1. STANDARD PENETRATION TEST (SPT)

Five deep soil borings (2F-17-1 through 2F-17-5) and one shallow boring (2F-17-6) were conducted for the design of the Ops Center Phase II building and parking lot. The deep borings were 75 to 90 feet deep and the shallow boring was 10 feet deep. The SPTs were conducted between 27 September and 2 October 2017 using a truck-mounted MobileDrill B-60 SPT rig and crew from the Savannah District of the Corps. The borings were sampled continuously to 16 feet depth and then every 5 feet to the bottom of the hole (BOH). Soil samples were mostly obtained with a standard 1.4” I.D., 2” O.D., and 30-inch long split-spoon sampler driven with a 140-pound automatic hammer falling 30 inches. The number of blows required to drive the sampler for 6 inch penetration increment was recorded. At four locations, undisturbed Shelby tube samples were collected instead of split spoon samples. A bulk sample for CBR testing was collected from the drill cuttings from boring 2F-17-6. The recovered soil samples were visually classified in the field in accordance with ASTM D 2488 by a geotechnical engineer from the Norfolk District. A portion of the recovered soil from the split spoons was placed in plastic jars and returned to the Norfolk District Office for review and laboratory testing assignment. The Shelby tubes and the bulk sample were taken to Savannah by the drill crew for later transportation to the testing laboratory.

Boring 2F-17-3, located along Road K, encountered shredded wood in the first sample collected (0.5 to 2.0 feet below ground surface or bgs). The upper four feet of drill cuttings from that hole smelled like creosote. That was the only unusual odor encountered during the drilling program.

The perched groundwater level was recorded during drilling of the SPT borings. The groundwater level in those borings was recorded at the end of drilling. When a hole completion coincided with the end of a work day, the augers were left in the hole overnight and the groundwater level was recorded first thing the next morning before the augers were pulled and the holes backfilled. For safety reasons, other SPT holes were not left open overnight and the augers were pulled and the holes backfilled at drilling completion.

The SPT holes were filled with drill cuttings and then covered with a cold asphalt patch. Excess drill cuttings were placed in drums and sampled for Diesel Range Organics (DRO). The analytical samples were non-detect and the drums were picked up for disposal as non-hazardous waste by Reco Biotechnology of Richmond.

A temporary standpipe piezometer was installed in boring 2F-17-2 after the augers were pulled.

The temporary piezometer consisted of ¾-inch, Schedule 40 PVC pipe with a 10-foot slotted screen between 5 and 15 feet bgs. The annulus was backfilled with concrete sand to 3-feet below grade and the upper 3-feet was backfilled with drill cuttings. A vented PVC cap sealed the pipe overnight. The water level in the standpipe well was recorded the next morning and the standpipe was removed.

2.5.2. CONE PENETRATION TEST

Three CPTs, designated CPT-17-1 through CPT-17-3, were conducted for the design of the Operations Center Phase II building. The CPTs were 44.1 to 46.5 feet deep and encountered refusal in a dense clayey sand and gravel soil layer. The CPTs were conducted on 26 September with a rig and crew supplied by the Savannah District. Cone resistance, friction resistance, and pore pressure were recorded at approximate 0.65-foot intervals. The CPT holes were filled with concrete sand and then covered with a cold asphalt patch. The field test data was reduced by a geologist with the Savannah District using established correlations.

CPT-17-2 was a seismic CPT. Downhole seismic shear wave velocity testing was performed in accordance with ASTM D 7400 utilizing the CPT rig with two receivers. Testing was performed at 1 meter intervals to a depth of 40.81 feet.

2.5.3. LABORATORY TESTING

Laboratory testing of selected samples was performed by the Savannah District Materials Testing Regional Center of Expertise lab in Marietta, Georgia. Table 2-1 summarizes the testing program. Test results are in Enclosure 2.

Table 2-1. Phase II Laboratory Testing Program

Test Reference Quantity Gradation with hydrometer ASTM D422 5 Gradation w/o hydrometer ASTM D422 25

Atterberg limits ASTM D 4318 29 Water Content ASTM D2216 43

Specific Gravity ASTM D854 4 Corrosivity Suite (pH, sulphates, chlorides, electrical resistivity

ASTM D4972, ASTM G187 3

Consolidation ASTM D2435 2 Unconfined Compression ASTM D2166 3

Modified Proctor ASTM D1557 1 California Bearing Ratio (CBR) ASTM D1883 1

2.6. EXPLORATION LOCATIONS

Due to the existing warehouse buildings, all explorations (historical and current) for the Ops Center Phase II had to be conducted in “lines” along Roads J, K, and L. Due to the need to keep traffic moving along the roads, all explorations conducted in 2017 specifically for the Ops Center Phase II were conducted in parking spaces along the sides of Roads K and L. CPT-17-1, CPT- 17-2, and SPTs 2F-17-1 through 2F-17-3 were located in parking spaces along the north side of Road K. CPT-17-3 and SPTs 2F-17-4 through 2F-17-6 were located in parking spaces along the south side of Road L. The explorations along Road L could not be conducted in the grass/concrete strip south of Warehouse 33 and north of Road L, or in the short-term parking strip on the north side of Road L due to extensive underground utility lines in those areas. The bulk sample was originally planned to be collected in a grassy area between Warehouse 33 and Road L, but was collected from the drill cuttings from boring 2F-17-6 instead due to extensive underground utilities in the original location.

Coordinates and elevations (where available) of all explorations are in Table 2-2. Coordinates and elevations of the Operations Center Phase I explorations were surveyed. Coordinates of the Operations Center Phase II explorations were obtained with a hand-held GPS unit at the time of drilling. Those points were plotted in Google Earth and minor adjustments were made based on photographs and notes of the drill sites collected during drilling. Elevations of the Phase II explorations are approximate from the site topography in the 35% design submittal. Coordinates of the historical explorations were obtained by “eyeball” plotting of the points as shown on old maps into Google Earth. The elevation of PX-35 is approximate from the site topography in the 35% design submittal. Elevations of the other historical explorations are uncertain. Where elevations are written on the logs, the vertical datum is not known. Location of all explorations is shown on Plate 4. Separate location maps for explorations on Roads J, K, and L are on Plates 5 through 7. Exploration logs are in Enclosure 1.

Table 2-2a. Exploration Location Information (Lat-Long)

Exploration Number

Latitude (degrees)

Longitude (degrees)

Elevation (feet

NAVD88)

Historical Explorations

9FA-1 37.414495 -77.442607

9FA-2 37.414809 -77.441774

Hole 1 37.414880 -77.439375 Hole 2 37.415063 -77.438543

PX-35 37.413309 -77.442725 120

Ops Center Phase I Explorations

12DH-28 37.414710 -77.441719 119.9

12DH-29 37.414866 -77.441316 119.7

12CPT-4 37.414710 -77.441719 119.9

12CPT-5 37.414866 -77.441316 119.7

12CPT-9 37.414931 -77.441566 119.8

Ops Center Phase II Explorations 2F-17-1 37.413801 -77.442205 120 2F-17-2 37.414052 -77.441527 120 2F-17-3 37.414341 -77.440772 120 2F-17-4 37.412999 -77.441776 119.5 2F-17-5 37.413526 -77.440236 121 2F-17-6 37.414172 -77.438512 121

CPT-17-1 37.413801 -77.442205 120

CPT-17-2 37.414052 -77.441527 120

CPT-17-3 37.413197 -77.441200 120

Table 2-2b. Exploration Location Information (Virginia South State Plane)

Northing Easting Elevation (feet

NAVD88)

Historical Explorations

9FA-1 3676193.647 11790002.408

9FA-2 3676310.680 11790243.034

Hole 1 3676344.348 11790939.424 Hole 2 3676413.691 11791180.291

Northing Easting Elevation (feet

NAVD88)

PX-35 3675761.462 11789972.976 120

Ops Center Phase I Explorations

12DH-28 3676274.815 11790259.411 119.9

12DH-29 3676332.924 11790375.807 119.7

12CPT-4 3676274.815 11790259.411 119.9

12CPT-5 3676332.924 11790375.807 119.7

12CPT-9 3676355.775 11790302.940 119.8

Ops Center Phase II Explorations 2F-17-1 3675942.282 11790121.982 120 2F-17-2 3676035.874 11790317.855 120 2F-17-3 3676143.553 11790535.931 120 2F-17-4 3675651.685 11790249.841 119.5 2F-17-5 3675848.573 11790694.920 121 2F-17-6 3676089.395 11791192.941 121

CPT-17-1 3675942.282 11790121.982 120

CPT-17-2 3676035.874 11790317.855 120

CPT-17-3 3675725.649 11790416.309 120

3. SUBSURFACE CONDITIONS

3.1. REGIONAL GEOLOGY

The project site is located within the Coastal Plan Physiographic Provence of Virginia in close proximity to the “fall line”. The fall line is a natural boundary between the Piedmont Physiographic region and the Coastal Plain. The Piedmont has a complex history from many intense geologic forces and primarily contains two divisions of rock; the Late Proterozoic and Paleozoic igneous and metamorphic rocks, and lower Mezozoic (Triassic) sedimentary rocks.

The Coastal Plain contains unconsolidated marine and fluvial sediments ranging from clay to gravel, poorly to well sorted, increasing in thickness towards the east.

The near surface soils were judged to be consistent with the Bacon’s Castle Formation of the Coastal Plain over a lower Tertiary Deposit which may be the Old Church Formation.

3.2. SUBSURFACE STRATIGRAPHY

The subsurface conditions discussed in this section and those shown on the boring logs represent interpretations of the boring data and are for information only. The lines designating strata breaks on the boring logs and those indicated below represent approximate boundaries between soil types, as the transition may be gradual or may occur between samples.

The generalized subsurface stratigraphy below is our interpretation of the soil stratigraphy and subsurface conditions at the project site based on the subsurface explorations. The interpretation necessarily assumes uniform subsurface conditions across the site, which is probably, but not necessarily, correct. The general descriptions below should not be considered as a substitute for the boring logs.

Due to existing structures at the site, explorations were conducted in three “lines” along existing Roads J, K, and L. Structural fill material may exist underneath the existing buildings that was not encountered in the boring logs. The asphalt pavement thickness at the exploration locations varied between 5 and 8 inches, with no aggregate base in places. Although not encountered at the exploration locations, DSCR and Ops Center Phase I construction personnel report that concrete, potentially up to 12 inches thick, likely occurs underneath the pavement along Roads J, K, and L. Concrete underneath the asphalt pavement is more likely to occur within the traffic lanes than within the parking spaces where the explorations were conducted.

The first stratum encountered (Stratum I) is a reddish-brown clayey or silty sand or sandy clay classifying as SC, SM, and CL. This material extends to depths of 12 to 18 feet below ground surface. Uncorrected SPT N-values range from 1 to 34 blows per foot (bpf) with an average of 11 bpf. In general, the lower N-values occur at the bottom of the stratum, where perched groundwater exists on top of the underlying fat clay stratum. The moisture content ranged from 9.2% to 56.5% with an average value of 18.9%. The percent fines (percent passing the No. 200 sieve) varies from 8 to 81 percent with an average value of 24 percent. The Liquid Limit (LL) varies from 21 to 68 with an average value of 44 and the Plasticity Index (PI) varies between 3 and 40 with an average value of 22. CPT tip resistance is highly variable between 27 and 450 tons/ft2.

Stratum II is a dark gray fat clay classifying as CH. This material varies in thickness from 14 to 24 feet and extends to depths of 33 to 36 feet below ground surface. Uncorrected SPT N-values range from weight-of-hammer to 8 bfp with an average of 4 bpf. The moisture content ranged from 40.5% to 61% with an average value of 52.7%. The percent fines varies from 80 to 99 percent with an average value of 93 percent. The LL varies from 51 to 112 with an average value of 90 and the PI varies from 22 to 97 with an average value of 69. CPT tip resistance varies between 5.6 and 35.5 tons/ft2.

Stratum III is a dense to very dense whiteish-gray to dark gray mixture of clay, sand, and gravel classifying as GC, SM, SP-SM, and SC. This material varies in thickness from 35 to 42 feet and extends to depths of 68 to 78 feet below ground surface. Uncorrected SPT N-values range from 7 to 81 with an average value of 45; note that these values do not include the 17 SPT refusals (out of 46 total attempts). Moisture content varies between 11.4% and 22.1% with an average value of 16.4%. The percent fines varies from 4 to 22 percent with an average value of 9 percent. The LL of the fine fraction varies from 45 to 108 with an average value of 72 and the PI of the fine fraction varies from 24 to 82 with an average value of 47. CPT tip resistance varies between 15.5 and 505 tons/ft2, and all three CPTs encountered refusal in this stratum. CPT refusal was determined by judgement when continued pushing with high force did not advance the probe, and further force increase could result in damage to the transducers on the cone and/or the rods. CPT refusal in dense gravelly soils such as Stratum III is common.

Underneath Stratum III is decomposed rock. The rock is olive green in color and was very difficult to remove from the split spoon, but once out of the spoon it very easily crumbled into silt and fine sand-size particles. The decomposed rock does not appear to be Petersburg Granite, which outcrops in the surrounding area.

3.3. GROUNDWATER CONDITIONS

During drilling, perched groundwater (on top of the fat clay layer) was encountered between depths of 8 to 15.5 feet bgs. The perched water level in a temporary standpipe piezometer in exploration 2F-17-2 after approximately 24 hours was 5.9 feet bgs. Water levels in the SPT boreholes at the end of drilling varied from 36.5 to 63.5 feet bgs. Water levels in two borings where the augers were left in the hole overnight (approximately 14 hours) were 36.7 and 54.6 feet bgs. Groundwater levels fluctuate over time due to rainfall, nearby irrigation, nearby well pumping, and other factors. The field measurements reported herein do not reveal the actual year-round groundwater conditions.

4. DESIGN

4.1. GENERAL

The subsurface conditions encountered at the Ops Center Phase II site are similar to the conditions encountered under the Ops Center Phase I site, therefore the recommendations will be similar to those made for the Phase I part of the project. In general the site consists of an upper layer of reddish-brown silty or clayey sand or sandy clay. The upper layer is followed by a soft, dark gray fat clay. Underlying the clay is a layer of dense clayey sand and gravel. Underlying the dense sand and gravel is green decomposed rock.

Foundation loads will vary greatly across the building footprint. The Ops Center Phase II structure will be one, two, or five stories tall depending on location within the proposed building footprint (see Figure 1). The 5-story portion of the building is called “the tower” by the design team. In the construction plans, the building has been divided into 7 areas, labeled Area A through Area G. The tower consists of areas A and D, the two-story portion of the building consists of Areas F and G, and the single-story portions consist of Areas B, C, and E. Figure 2 shows the Area designations.

Foundation design is based in large part on bearing capacity and settlement. Differential settlement, defined as the difference in settlement between two points on a structure (generally two load-bearing columns or foundation elements) is usually more of a concern than the overall total settlement. Excessive differential settlement can cause distress in structural members. For this project a maximum differential settlement criteria of 0.002L, where L is the length between foundation elements, will be used. This criteria was used on the Ops Center Phase I building and is also the criteria given in many building codes for steel and concrete framed buildings. The project structural engineer agreed with this criteria.

The existing ground surface elevation within and around the proposed building footprint varies between 119.00 and 122.00 feet. The proposed finished floor elevation is 123.95 feet.

According to Table E-2 of UFC 3-301-01, the depth of frost penetration at DSCR is 18 inches;

therefore, the bottoms of footings and pile caps should be 3 feet below ground.

Figure 1. Proposed building height.

Figure 2. Building areas

4.2. SINGLE STORY BUILDING AREAS

4.2.1. GENERAL

The single story portion of the proposed building is expected to have a shallow spread footing foundation system, similar to the single story portion of the Phase I building. Final column loads for the single story portion of the proposed Phase II building vary from 15 to 116 kips. Loadings were not provided for columns that are supporting an outdoor canopy that is connected to the building. It is anticipated that those columns will have very low axial loads. The canopy footings were designed for uplift by the structural engineer.

4.2.2. BEARING CAPACITY

Bearing capacity is the ability of the soil to resist shear failure under loading. The procedure in EM 1110-2-1905, Bearing Capacity of Soils, was used to calculate bearing capacity. The standard bearing capacity equation is:

Qult = CNcc + 1/2B’N + ’pNqq

Where:

Qult = Ultimate bearing capacity (psf) C = Soil cohesion (psf) B = Footing width (feet) ’ = effective unit weight of soil beneath the foundation within the failure zone (pcf) ’p = Effective stress at the foundation depth (psf) Nc, NandNq = Dimensionless bearing capacity factors c, and q = Dimensionless correction factors for foundation geometry

Shallow column footings in this project are square, ranging in size from 4 feet to 10 feet.

According to the structural engineer, the lateral loads and moments controlled the shallow footing dimensions more than the axial loading. An excel spreadsheet was used to calculate the bearing capacity of shallow foundation elements. Since the depth of footings below finished floor elevation varied along with the footing size and the axial loading, bearing capacity was analyzed at each column location. The spreadsheet is available for review in the Norfolk District office. All column loadings are well below the allowable bearing capacity for the associated footing.

The design also includes wall footings, varying between 2 and 3.5 feet in width. The bearing capacity was calculated for each footing type. As for the square column footings, the wall footing loading is well below the allowable bearing capacity.

4.2.3. SETTLEMENT

Shallow foundation settlement was estimated using the Schmertmann CPT method using an excel spreadsheet, which is available at the Norfolk District office. The first calculation was for column B-15, which has the highest footing loading per unit area. The closest CPT to column B- 15 is 12CPT-4, which is one of the Phase 1 CPTs along Road J. Settlement was calculated at

0.315 inches. Assuming a minimum axial loading (and settlement) of zero, the minimum length between shallow foundation elements required to meet the L/500 criteria is 13 feet. Shallow foundation elements greater than 13 feet apart will automatically meet the L/500 criteria. The only place (aside from an exterior canopy) where shallow foundation elements are closer than 13 feet is columns B-15 and C-15. Settlement of column C-15 was calculated using 12CPT-4 as

0.138 inches, which passes the differential settlement criteria.

The most common wall footing type is 3 feet wide; other widths are primarily used in the lobby doorway area. Settlement of a 3-foot wide wall footing was calculated at less than 0.1 inch due to it’s own loading. Wall footings connect to either square shallow footings or pile caps, and the wall footings will move as the square footings/pile caps move.

To evaluate differential settlement where the lobby (Area C) connects to the tower (area D), the settlement of column B-14 was calculated using the closest CPT (12CPT-4). The calculated value of 0.237 inches was transferred to the pile settlement spreadsheet (discussed in a subsequent section of this report) and compared with the pile settlement calculated for column E-

14. In addition, the settlement calculated for shallow footing column C-15 was compared with tower column E-15. The L/500 criteria was met in both situations.

To evaluate differential settlement where the single-story section (Area E) connects with the 2-story section (Areas F and G), the settlement for single-story column XN-X14.8 was calculated using the closest CPT (SCPT-17-2) and compared with the pile settlement of 2-story column XM-X7. The L/500 criteria was met. Because these two columns are the closest together and also have the highest differential axial loading of any column pair along this connection, no other column pairs were checked along this connection.

The connection between the single-story section (Areas B and E) and the tower (Areas A and D) was not checked for differential settlement because all column pairs are greater than 25 feet apart along this connection.

4.3. FIVE STORY TOWER

4.3.1. GENERAL

Due to the high expected column loadings of the 5-story portion of the proposed building and the presence of the soft clay layer (Stratum II), a deep foundation system will be required. Drilled piers are recommended, similar to the Phase I building. Driving piles, even steel pipe piles, would be very difficult if not impossible into the very dense Stratum III soil layer, and pile driving would produce noise and vibrations that would disturb workers in the nearby buildings.

Final column loads from the structural engineer show the axial loads vary between 104 and 763 kips. A pile diameter of 3 feet was chosen for this analysis because that is the diameter of the drilled piers for the Phase I building.

4.3.2. AXIAL CAPACITY

Axial capacity from the SPT borings was analyzed using an excel spreadsheet using the method in Naval Facilities Engineering Command (NAVFAC) DM 7.02, Foundations and Earth Structures. Typically soil properties (unit weight, friction angle, cohesion) were obtained from laboratory tests or from established correlations with the SPT N-value. Results are summarized in Table 4-2 and the spreadsheet is in Enclosure 5. All Results are shown graphically on Plate 8.

Because the calculated capacities are very close for all the SPT explorations, Table 4-2 shows the allowable capacity calculated for SPT boring 2F-17-2. This boring is located in the approximate center of the building and the calculated capacity is in the middle of all the calculations. Pile lengths less than 45 feet below the existing ground surface are not recommended, as piles should extend at least 5 feet into the bearing layer.

Axial capacity from the CPT explorations was analyzed using an excel spreadsheet using the Aoki and De Alencar Method. Because the CPTs experienced refusal well above the total depth of the SPT borings, the CPT data is used primarily as a check for the SPT analysis. Results from the CPT analysis are similar to the SPT analysis for Stratums I and II, but are lower than the SPT analysis for compression capacity and higher than the SPT analysis for tension capacity. This could be due to the difficulty of pushing a CPT probe through gravelly soils impacting the tip resistance and sleeve friction measurements.

Based on the column loading, three different pile lengths will be utilized for the tower: DP4 (60 feet long), DP3 (50 feet long), and DP2 (45 feet long).

A group pile capacity will be less than the sum of the individual pile capacities if the center-to-center pile spacing within the group is less than about 5 pile diameters (15 feet).

Table 4-2. Allowable Capacity of Individual 3-Foot Diameter Drilled Piers

Pile Tip Depth Below Ground Surface (ft)

Allowable Compression Capacity (kips)

Allowable Tension Capacity (kips)

45 622 152 50 708 182 55 798 215 60 892 250 65 951 285 70 1011 321 75 1071 357 80 1131 393

4.3.3. SETTLEMENT

The procedure from NAVFAC DM 7.02 and EM 1110-1-1904 was used to estimate the settlement of a single pile. An excel spreadsheet was used to calculate the settlement of each pile using the final loadings supplied by the structural engineer. The spreadsheet is available in the Norfolk District office. Settlement ranges from a maximum of 0.569 inches to a minimum of

0.088 inches. Using those two values, the minimum length between foundation elements that meets the L/500 criteria is 20 feet. Foundation elements closer than 20 feet were manually checked for differential settlement. Three column pairs are spaced exactly at their L/500 length.

Those pairs are: L-4 and N-6 in Area A; H-18 and H-19 in Area D; and N-18 and L-19 in Area D. One column pair (I.6-14 and L-14 in Area D) is spaced less than the L/500 length. All four of these column pairs are located at staircases where the columns are closely spaced with a large differential loading. These areas do not meet the minimum requirements for differential settlement and the structural designer should incorporate measures to reduce the potential for differential settlement such as distributing the loads more equally or spacing columns further apart.

4.3.4. COMPARISON WITH PHASE I O‐CELL LOAD TESTS

The Ops Center Phase I project included Osterberg Cell (O-Cell) load tests on two test piles.

The test piles were 55 feet long and a nominal 34-inch width. Table 4-4 is a comparison of the load test results and the axial compression capacities and settlements estimated during design of Phase II.

Table 4-4 Comparison of Compression Capacity and Settlement

Item Phase I O-Cell Load Test

Phase II Calculation

Load (kips) 600 600 Settlement (inches) 0.17 0.188

4.3.5. LATERAL CAPACITY

The computer program LPILE, developed by Ensoft, was used to evaluate lateral pile capacity.

Four columns were selected for analysis;

The highest lateral load and moment for the DP4 piles A high lateral load and moment for the DP4 piles with a deep pile cap The highest lateral load and moment for the DP3 piles The only DP2 pile where lateral load and moment were supplied

To determine how different loading conditions impacted the piles, three loading conditions were evaluated for each column;

Loading Case 1: Axial load, lateral load, and moment as supplied by structural Loading Case 2: Axial load as supplied by structural, lateral load and moment reduced by 50% Loading Case 3: Axial load reduced by 50%, lateral load and moment as supplied by structural

Because lateral loads and moments were only supplied for one DP2 pile, an additional loading case was evaluated for that pile only; axial load as supplied by structural with lateral load and moment increased by 30%.

The LPILE output is shown graphically in Enclosure 3; the LPILE printouts are available in the Norfolk District office. Varying the axial load and the depth of the pile cap had negligible impact on the deflection, bending moment, and shear force of the piles. Varying the lateral load and moment had significant impacts. The highest calculated deflection is about 0.15 inches for the DP3 pile.

4.4. TWO STORY BUILDING AREA

There was no 2-story section of the Phase I building so no two story foundation recommendations were made in Phase I. Final axial column loads from the structural engineer vary between 25 and 267 kips. Drilled piers 2.5-feet in diameter was selected for the 2-story building area.

4.4.1. DRILLED PIERS

The axial capacity and settlement calculations were repeated for drilled piers 2.5-feet in diameter. Drilled piers less than 2.5 feet in diameter are not recommended based on feedback received from a Contractor on a previous job. The Contractor had difficulty moving the concrete tremie into and out of the rebar cages for 2-foot diameter piles with (quality control) inspection tubes inside the rebar cage. Axial capacity results are in Table 4-5 and the spreadsheets are available at the Norfolk District office.. As for the 5-story building area, pile lengths less than 45 feet below existing ground surface are not recommended. The axial capacity of a 2.5-foot diameter, 45-foot long pile is well above the column loads. If drilled piers are used for the 2-story building area, they may be spaced further apart than drilled piers for the 5-story building area, although this could result in high shear and bending moment stresses in grade beams, the floor slab, and other structural elements.

Table 4-5. Allowable Capacity of Individual 2.5-Foot Diameter Drilled Piers

Pile Tip Depth Below Ground Surface (ft)

Allowable Compression Capacity (kips)

Allowable Tension Capacity (kips)

45 457 125 50 524 150 55 567 175

The calculated settlements vary between 0.025 and 0.267 inches. Using those two values, the minimum length between columns that meets the L/500 differential settlement criteria is 10 feet.

Column pairs located closer than 10 feet were manually checked for differential settlement and all pairs meet the L/500 criteria. The connection of the tower to the 2-story portion was also manually checked for differential settlement and meets the criteria.

The LPILE computer program was used to analyze lateral loading and deflection. Results are summarized in Enclosure 3; LPILE printouts are available in the Norfolk District. Three columns were selected for analysis;

Relatively high lateral load and moment with a relatively low axial load Highest lateral load and moment Relatively low lateral load and moment

Each column was analyzed for the same 3 loading conditions as for the tower. As for the tower, varying the axial load had a negligible impact on the results while varying the lateral load and moments had a significant impact. All columns/loading cases analyzed had maximum deflections of less than 0.1 inch.

4.5. SEISMIC SITE CLASSIFICATION

A seismic site classification in accordance with ASCE 7-05 Chapter 20 was conducted. The analysis was based on the shear wave velocity profiles from the seismic CPTs and the standard penetration test data. The analysis is in Enclosure 7. A Seismic Site Class of “D” is recommended for this site, which is the same site class recommended for Phase I. The USGS Ground Motions website recommends the following values based on the 2016 version of ASCE 7-05 Chapter 20:

Fa = 1.6

SS = 0.215

SMS = 0.345

SDS = 0.23

S1 = 0.054

SM1 = 0.129

SD1 = 0.086

Seismic Design Category “B”

4.6. PAVEMENT DESIGN

There are three separate pavement types within this project:

Light duty asphalt, used within parking spaces Medium duty asphalt, used for the driving lanes within the parking lot Concrete, used for the supply truck and fire truck lanes

The PCASE computer program was used to design the pavement sections. PCASE takes user input of the traffic pattern (types of vehicles and number of passes), subgrade soil CBR, and the pavement design life (25 years). The program accounts for frost penetration. Traffic patterns were determined as follows:

Light duty asphalt: A large truck or SUV making 4 passes (in-out beginning and end of day and in-out at lunch) on all 261 work days a year and 2 passes (in and out) on 10% of the 104 weekend days a year. This is considered the maximum loading with regards to both vehicle weight and number of passes.

Medium Duty Asphalt: The parking lot has 446 spaces. Assumed half of all vehicles are passenger cars, 30% are small truck/SUV, and 20% are large truck/SUV. Assumed 40% of all vehicle types make 4 passes/workday and 60% of all vehicle types make 2 passes/workday, and 10 percent of all vehicle types make 2 passes/weekend day. This loading is considered to be conservative without being excessively so based on the designers observations of parking lots at DSCR during drilling, monitoring well sampling, and other site visits.

Concrete: The traffic pattern used in the design of Phase I.

The PCASE output is in Enclosure 8. The pavement sections are as follows:

Light duty asphalt: 2” asphalt over 6” aggregate (VDOT 21A or 21B) Medium duty asphalt: 2” asphalt surface mix (SM-9.5A) over 3” of asphalt base (BM-

25) over 8” aggregate Concrete: 7 inches of 650 psi flexural strength concrete over 6 inches of aggregate

4.7. SOIL CORROSIVITY

Because concrete will be placed below ground as part of this project, corrosivity testing was conducted on soils at the proposed building site. A corrosivity suite, consisting of chloride, sulphate, pH, and resistivity tests, was conducted for each of the three soil types at the site.

Results are in Table 4-7. Based on FHwA criteria, Stratum II, the fat clay, is a corrosive environment based on high sulfate concentration, low pH, and low resistivity. Stratum III is also a corrosive environment based on slightly elevated sulfate concentration. Sulfates attack concrete, especially in low pH environments, causing cracking and spalling of the concrete. It is recommended that the structural engineer specify Type II Portland cement (or Type I plus a pozzolan if Type II is not available locally) as defined by ASTM C 150 to provide moderate sulfate resistance.

Table 4-7. Soil Corrosivity Test Results

Soil Unit Chloride (ppm)

Sulfate (ppm) pH In-Situ Resistivity (ohm-cm)

Inundated Resistivity (ohm-cm)

Stratum I 19 41 4.67 40,000 155,000 Stratum II 7.7 1200 4.4 790 795 Stratum III 5.3 240 8.21 2,000 1,700

Criteria (FHwA)

>100 >200 <4.5 <2,000

5. CONSTRUCTION RECOMMENDATIONS

5.1. SITE PREPARATION

It is recommended that a geotechnical engineer be retained during construction to provide soil engineering services for site preparation and foundation construction phases of the project. The geotechnical engineer can perform appropriate evaluations to help assure proper support of the proposed construction.

Site preparation for the building, sidewalks, and pavements should include complete removal of demolition debris, man-placed fill soils, surface vegetation, topsoil, organic material, trees and bushes, tree stumps, and roots. The depth of removal of these materials is typically expected to be on the order of 12 inches. Deeper grubbing should be expected to remove stumps and root mats. Stripping should be performed to a horizontal distance of at least ten feet beyond the limits of the building footprint and 5 feet beyond the limits of sidewalks and pavements. The construction area should also be cleared of soft, wet, or disturbed soils. Over-excavated areas should be backfilled with compacted structural fill. At all times during construction, positive surface drainage should be maintained to prevent the accumulation of water.

After clearing, grubbing, and stripping, the exposed subgrade soils should be compacted to the moisture content and percentage of maximum dry density in the specifications for the type of subgrade (building, pavement etc.). Compaction should be observed by a geotechnical engineer and the Contracting Officer’s Representative. Compaction should be performed during a time of good weather and not while the site is wet, frozen, above planned grade, or severely dessicated.

Any unsuitable materials that are observed to yield or rut noticeably during compaction should be undercut and replaced with compacted structural fill.

A shallow perched water table can be expected on this site and proper planning will be required.

The near surface subgrade soils are moisture sensitive and will lose stability if these soils become wet and are subjected to construction traffic. As a result, site preparation should be performed during an extended period of dry weather. Undercutting or reworking of the near surface soils may be necessary if the exposed subgrade soils become unstable during construction.

The shallow subgrade soils were noted to mostly be above the optimum moisture needed for compaction (based on laboratory tests); therefore, they will require drying by aerating or disking before being compacted to develop a suitable subgrade for structures and pavements. Any fill materials, aggregates, and/or concrete should be placed as soon as possible over the approved subgrade in order to reduce exposure to weather and construction activity. It is important to stress that the subgrade needs to be properly prepared and protected during construction to minimize the degradation of these soils.

5.2. FOUNDATION CONSTRUCTION

5.2.1. GENERAL

Foundation subgrades shall be observed, evaluated, and verified for the design bearing pressure by a geotechnical engineer after excavation and prior to placement of the capillary water barrier and vapor barrier. This evaluation could include hand auger probes to verify the subsurface soil conditions below the foundation elements.

If soft, unsuitable soils, or deleterious fill materials are encountered during foundation construction, localized undercutting of the foundation subgrades will be required. Undercut excavations in the proposed building footprint should be wider than the amount of deleterious materials. The need for, and extent of, undercutting should be based on field observations made by a geotechnical engineer at the time of construction. Any over-excavation should be backfilled with properly compacted structural fill.

Excavations for foundations should be made in such a way to provide bearing surfaces than are firm and free of loose, soft, wet, or otherwise disturbed soils. Concrete and asphalt should not be placed on frozen or saturated subgrade. If such materials are allowed to remain below foundation elements, settlements will increase. Foundation excavation should be concreted as soon as practical after they are excavated. If an excavation is left open for an extended period, a thin mat of lean concrete should be placed over the bottom to minimize damage to the bearing surface from weather or construction activities. Water should not be allowed to pond in any excavation.

All concrete slabs, including building floors and mechanical/electrical equipment pads, shall be founded on a minimum of 4” of capillary water barrier. The capillary water barrier shall consist of crushed stone meeting the gradation requirements of VDOT #57 aggregate. The capillary water barrier should be compacted with a minimum of two passes of a hand-operated plate-type vibratory compactor. A plastic sheet vapor barrier shall be placed between the capillary water barrier and the slab concrete.

5.2.2. POTENTIAL SOIL CONTAMINATION

In one SPT (2F-17-3) the first sample (0.5’-2’) included shredded wood, and the first 4’ of drill cuttings smelled like creosote. Both the drillers and the Resident Engineer for the Phase I construction thought it was probably an old railroad tie. The intent was to locate 2F-17-3 outside of the building footprint but that was an “eyeball” guess based on the design charette report and the hole may have been just barely within the building footprint. Although no other contamination was encountered during the foundation explorations, given the long history of DSCR it is possible that petroleum contamination could be encountered during project excavation. If contaminated soil is encountered during project excavation it should be excavated and replaced with structural fill or select granular material. The contaminated soil would have to be disposed of off-post in accordance with all Federal, State, and local laws and regulations.

5.2.3. DRILLED PIER FOUNDATION

It is anticipated that the 2-story portion of the building will be supported by 2.5’ diameter drilled piers. It is anticipated that the 5-story portion of the building will be supported by 3’ diameter drilled piers.

5.2.3.1. PILE LOAD TEST

Two Osterberg Load Cell (O-Cell) tests were conducted for the Phase I building. It is recommended that one O-Cell load test be conducted for this Phase II design. This load test will be conducted in the summer of 2019 during the design phase of the project. The load testing shall be performed in accordance with ASTM D 1143 using the “Quick Load Test method for Individual Piles” up to a total test load of 600 kips, followed by the “Loading in Excess of Standard Test Load” up to 800 kips or until failure of the test pile occurs.

A minimum of four displacement transducers mounted 90 degrees apart is required to monitor movement at the O-Cell. A set of movement transducers shall be installed to measure movement at the top and from a reference frame. All movement data shall be recorded.

The test pile shall be instrumented with pairs of vibrating wire strain gages located at two different levels; (1) top of bearing layer (Stratum III) and (2) at the pile tip to obtain information about the shaft friction developed within different subsoil strata. These strain gages shall be “Vibrating Wire Rebar Strain Meters” (Sister bars). Two strain gages shall be installed at each depth mounted 180 degrees apart.

The load test shall not be performed until the concrete has achieved the design compressive strength as verified by compressive strength tests on cylindrical samples. The minimum waiting period is 7 days after test pile installation.

5.2.3.2. CONSTRUCTION RECOMMEDATIONS

Installation shall be in accordance with ACI 336.1 utilizing the slurry displacement method. The contractor shall retain a licensed Geotechnical Engineer in the Commonwealth of Virginia to perform or directly oversee production pier construction.