W912EP21R0003 VIARNG STT VMS Geotechnical Data Report 00 31 32.pdf

GEOTECHNICAL ENGINEERING REPORT

Vehicle Maintenance Shop

Virgin Islands Army National Guard Facility

Charlotte Amalie, St. Thomas, USVI

USACE-Memphis District April 19, 2021

DRAFT

K3CTCWW9

Draft

K3CTCWW9

Draft

VIARNG-STT VMS

USACE-MVM

1.0 INTRODUCTION

The Memphis District (MVM) of the US Army Corps of Engineers (USACE) has completed a geotechnical assessment of the proposed Vehicle Maintenance Shop (VMS) at the existing Virgin Islands Army National Guard (VIARNG) facility located on the Nazareth Military Compound, Charlotte Amalie, St. Thomas, USVI. This report contains the results of the subsurface exploration, on-site geophysical testing, and geotechnical engineering analysis and recommendations for the proposed site development, foundations design, site-specific seismic parameters, and design of below grade and retaining walls. This work was performed for the Middle East District (MED) of the USACE.

2.0 SCOPE OF SERVICES

The scope of services performed for this project was developed in coordination with the MED Project Delivery Team (PDT). The scope of services for this geotechnical evaluation included the following:

Perform a subsurface evaluation consisting of excavating test pits, conducting multiple geophysical seismic refraction tests, and drilling multiple test borings with associated laboratory testing of select samples.

Describe the general Geologic setting and address the risk of possible geologic hazards including shrink/swell potential, seismicity, and liquefaction potential.

Determine the Site Class based on the on-site measured shear wave velocity profiles.

Provide Spectral Accelerations (Ss and S1) and Peak Ground Acceleration (PGA) values based on mapped values from the 2018 International Building Code (IBC2018).

Develop foundation recommendations for the proposed building including allowable bearing pressures, recommended foundation depth, and estimated foundation settlements.

Recommend static and earthquake lateral earth pressure coefficients for use in design of site retaining walls and below-grade cistern walls.

Design gabion retaining wall and evaluate global stability.

Provide pavement designs for flexible and rigid pavement sections.

Provide recommendations considering any potential construction or long-term groundwater issues.

Develop recommendations for site preparation and construction of earthwork features.

3.0 EXISTING SITE CONDITIONS AND PROPOSED CONSTRUCTION

3.1 Existing Site Conditions

The existing VIARNG facility (Nazareth Military Compound) is located in the southeastern part of St. Thomas on Red Hook Road. The facility occupies an area of approximately 15 acres and has existing maintenance and office structures located on site. Figure 1 is a general site vicinity map of the facility.

Figure 1. Vicinity Map of Nazareth Military Compound and Project Site.

The project site is located in the northern portion of the VIARNG facility (see Figure 1), adjacent to the existing maintenance shop. The areas to the north and east of the project site are undeveloped with relatively short vegetation, to the south mainly consist of a paved road leading to the existing maintenance shop, and to the west is the existing maintenance shop. The project site is mainly level with a roughly 10-foot tall slope on the eastern portion with a drainage ditch at the base of the slope. The western portion of the level ground surface is covered with asphalt pavement and much of the eastern portion is covered in vegetation, some of which is maintained and some of which is unmaintained. Several small temporary structures are located on the project site as well.

Several underground utilities were located across the site consisting of storm water drainage, oil separator, and electric.

Figure 2. Typical Existing Site Conditions.

3.2 Proposed Construction

The proposed project will consist of the construction of a 4,700 sq-ft VMS. The VMS will be utilized for organizational and support maintenance of combat and tactical vehicles. The VMS will provide a general purpose work bay, storage room, battery room, bulky equipment storage, and support spaces such as mechanical and electrical rooms. A below grade cistern (30,000-gallons) will be provided under the eastern portion of the VMS.

The cistern will supply potable water for the proposed structures and also water for use in firefighting operations. The water supply for the cistern will come from collection of rain water from the roofs of the structures. The base of the cistern will be located approximately 9 feet below final grade

The VMS structure will consist of a pre-engineered steel moment framed structures with CMU exterior and interior walls which are not loadbearing. The structure is anticipated to be supported on shallow spread foundations, and the cistern portion will be supported on a mat foundation. The loading for the structure is as follows:

Structure Dead Load

(kips) Dead + Live Load

(kips) Uplift (kips)

VMS 87 220 52

The floor slab will be grade supported and is assumed to have loading of 100 psf or less. The cistern will be cast-in-place concrete.

Other site improvements include pavements, utilities, and security fencing. The VMS will be surrounded by rigid concrete pavement. Vehicle types and volumes were not provided but will be assumed based on typical conditions for this type of facility.

Site grading will require a maximum of approximately 16 feet of fill in the eastern portion of the site in order to construct a level pad for the VMS. This grading will also require repositioning of the existing ditch at the base of the existing slope. The extended embankment will be supported using a gravity gabion wall system.

4.0 GEOLOGY

4.1 Regional Geology

The basement rock of the Virgin Islands was formed in the Cretaceous period approximately 145 to 65 million years ago. This rock is comprised of the Caledonia formation, the Cane Valley Formation, and the Judith Fancy Formation. The Judith Fancy Formation is the youngest layer of this zone. These rock formations are tuffaceous rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Above the rocks of the Cretaceous period is the Jealousy Formation which was deposited during the Eocene era (55 to 34 million years ago).

Pyroclastic flows are preserved on Saint Thomas, together with limited fossil-bearing limestone deposits and calcite cement in upper rock units. The Outer Brass Limestone deposited during a lull in volcanic activity in the Turonian and Santonian. The limestone unit also contains calc-silicate rocks, marble and conglomerate bound together with calcareous cement and including both marble and andesite clasts.

In the Late Cretaceous, the overlying Tutu Formation took shape with volcanic turbidite and rare pyroxene basalt. Silt or sand-sized material is most common unlike the Louisenhoj Formation boulders, suggesting a more distant volcanic source. In fact, sediments become finer, ascending upward into the Picara Member and Mandal Member. Striking slump folds and deformation of limestone and conglomerate beds is common.

5.0 SUBSURFACE EXPLORATION PROGRAM

Personnel from MVM and VIARNG performed an initial subsurface exploration on site consisting of test pits and seismic refraction tests in September 2020. An additional subsurface exploration program consisting of 7 test borings was completed by GeoCim in March 2021 under contract with the USACE. These explorations were conducted to identify the subsurface and groundwater conditions underlying the site, to estimate the geotechnical properties of the materials encountered, and determine the shear wave velocity profile for seismic analyses. The subsurface explorations were performed considering the proposed building and site layout information. The initial test locations are shown on Figure 3, and the test boring locations are shown in Figure 4.

Figure 3. Test Pit (TP) and Seismic Test (ST/SL) Locations.

Figure 4. Soil Test Boring Locations.

5.1 Subsurface Exploration and Field Testing

5.1.1 Geotechnical Borings

A total of 7 test borings were drilled across the site, with 4 borings drilled within the VMS footprint, 2 borings in the drainage ditch area, and one boring adjacent to the existing VMS facility. The borings were staked in the field by USACE personnel. The borings ranged in depths from approximately 6 feet to 40 feet below existing ground surface. The borings were advanced utilizing a combination of hollow stem augers, roller bits, and rock coring. Disturbed samples were collected using the Standard Penetration Test (SPT) method with a standard split spoon sampler. Grab samples of the rock material were collected from the return fluid while drilling with the roller bit, and rock core samples were collected during the rock coring process. The samples collected were shipped to the laboratory for classification testing. Logs of the test borings and laboratory results are provided in the appendix.

5.1.2 Test Pits

A total of 2 test pits were excavated using a rubber tired backhoe with a 2-foot wide bucket (see Figure 5). Personnel from MVM chose the test pit locations and supervised the excavation activity.

The backhoe and operator were provided by the VIARNG. The test pits were extended to depths of approximately 4 and 7.5 feet below grade. Bulk samples were collected from the test pits for visual classification. After completion, the test pits were backfilled with excavated soil and compacted in lifts with the excavator bucket. Logs of the subsurface conditions encountered at each test pit location are provided in the appendix.

Figure 5. Excavation of Test Pits.

5.1.3 Seismic Refraction Testing

Seismic refraction tests were performed at 2 locations across the site as depicted in Figure 2. The test arrays consisted of one linear array and one embedded equilateral triangular array. Figure 6 shows the embedded equilateral triangle array test setup on site. The seismic data for all arrays were collected using 4.5-Hz surface geophones. The linear array utilized 24 geophones spaced at 7-foot intervals resulting in an array length of 161 feet. The triangular array utilized 10 geophones with an outermost triangle side length of 40 feet. For all tests the data were recorded using a DAQlink, 24-bit seismic acquisition system using a 1 millisecond sampling rate. Record lengths were 15 seconds in duration, and approximately 20 individual recordings were performed for each test location. The recordings consisted of both ambient background noise as well as the inclusion of active noise generated by personnel running along the geophone arrays and by dropping heavy objects on the ground surface.

Figure 6. Embedded Equilateral Triangle Array Test Setup.

The shear wave velocity profiles were determined using an analysis technique termed Spatial Autocorrelation (SPAC). This method uses standard compression wave recording equipment to record both active and ambient noise to produce one-dimensional shear wave profiles down to depths as shallow as 10’s of feet to depths greater than 200 feet, depending on the geophone spacing and the noise frequency content recorded. In addition, by overlapping individual tests and interpolating across the individual one dimensional results, two dimensional cross-sections of shear wave velocities can be determined. No specific energy source is required to record ambient noises as it is generated by nearby sources (i.e. wind blowing on trees, vehicle traffic, construction activities, pedestrians, etc.). This method has been shown to be very effective for determining the upper 100 feet average shear wave velocity and thus the IBC/ASCE 7 site classification.

This method involves the evaluation of spectra and phase velocity dispersion of surface waves to determine the subsurface velocity and stiffness structure. The dispersion of surface waves references the principle that the velocity of surface wave varies as a function of the frequency of the recorded waveform which are directly related to the variations in the physical properties of the subsurface materials. The subsurface material properties considered in these analyses include the compression wave velocity, shear wave velocity, density, and layer geometry, of which, the shear wave velocity is the dominant variable controlling the characteristics of the surface wave. In general, typical assumed values for the material density and compression wave velocity (actually the ratio of shear to compression wave velocities) are utilized in the inversion and the shear wave velocity and material layers are iterated to determine the shear wave velocity profile.

The SPAC method utilizes the velocity-frequency wavefield transformation to separate the surface wave energy from the body waves, air waves, and incoherent noise. The SPAC method assumes the surface wave ambient sources are randomly distributed in time and space, and for a particular frequency, the phase velocity is equal to that which best fits a 1st order Bessel function to the SPAC function.

The general analysis steps involve using the SPAC method to extract the surface wave dispersion curve from the recorded waveforms and then using an inversion technique for the extracted dispersion curve to model a shear wave velocity profile. The computer program Surface Plus 9.1 from GeoGiga Technology Corporation was utilized to calculate the dispersion curve and pick points along the maximum frequency of the dispersion curve. The picked dispersion curve points were utilized to perform the inversion which allows for the determination of the shear wave velocity profiles. Based on the array geometries and the frequency content recorded, the shear wave velocity profiles were modeled to a depth of 110 feet below existing grade. Images of the dispersion curves, the modeled inversion curves, and the final shear wave velocity profiles are provided in the appendix.

6.0 LABORATORY TESTING

Laboratory testing was conducted on representative samples collected in the test borings. The testing performed consisted of classification type testing to include moisture content (ASTM D2216), percent passing the #200 sieve (ASTM D1140), mechanical sieve analysis (ASTM D6913), and Atterberg limits (ASTM D4318). Undisturbed samples could not be obtained due to the high coarse grained content of the existing soils on site. The results of the laboratory testing are provided on the boring logs in the appendix.

7.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

7.1 Site Geology

The soils in the vicinity of site were mapped by the USDA Soil Conservation Service and published in the Natural Resources Conservation Service (NRCS) Reports. This survey reports that the soil types in the vicinity of the Nazareth Military Compound are comprised of Fredriksdal Clay Loam, Susannaberg Clay Loam, and Dorothea Clay Loam.

7.2 Subsurface Stratigraphy

The subsurface materials encountered at the test pit and boring locations consisted of both soils and rock. The soil and rock samples retrieved were visually classified in the field and then classified based on laboratory test results. The soils generally consisted of various amounts of clay, sand, silt, and gravel, but in general the majority of the soils are predominately coarse grained soils. The soils were classified as Clayey Sand (SC) with gravel, Silty Gravel (GM) with sand, Silty Sand (SM) with gravel, Clayey Gravel (GC) with sand, Clay (CL) with sand and gravel, and Sandy Clay (CL). The soils in the upper 5-8 feet at Borings 20-STT-01 to 20-STT-05 were inspected to be fill soils placed during construction of the embankment for the existing VMS and paved areas.

It is noted that relatively large amounts of trash and construction debris were encountered in Test

Pit #2, and it is anticipated that this is an isolated condition in the embankment fill. At some boring locations up to about 5 feet of soils were generally encountered below the embankment fill soils which were considered to be natural in-situ soils. The moisture contents of the soils were generally evaluated to be relatively dry to moist. The standard penetration test N-values indicated the soils were generally medium dense to very dense.

Rock was encountered below the soils at the boring locations. Based on field observations by the drilling personnel, subsurface conditions transitioned from predominately soils to highly weathered rock at depths of approximately 5 to 10 feet (about elevation 70-73 feet) in the embankment area (Borings 20-STT-01 to 20-STT-05) and from the ground surface to about 2 feet (about elevation 67 feet) in the existing ditch east of the embankment (20-STT-06 and 20-STT-07). Auger refusal was encountered at depths of 6 to 15.5 feet (about elevation 65.5-76 feet) in the embankment area and at 4 to 8 feet (about elevation 63-72 feet) in the existing ditch area. Most of the drilling in the rock was performed with a roller bit to verify the continuity of the rock at depth. Core, SPT, and grab samples of the rock material were collected for visual inspection. The rock material was visually classified as fine-grained volcanic rock weakly metamorphic. The cores obtained indicated the rock material was highly fractured with an RQD of zero.

7.3 Groundwater

Groundwater measurements were made in the test pits during excavation and in the test borings during drilling. Groundwater was not observed in the test pits or borings.

8.0 GEOLOGICAL HAZARDS

Potential geologic hazards that may affect the proposed construction and the project site are described in the following sections and will be important considerations for the project development.

8.1 Shrink/Swell Potential

The existing clayey soils encountered on site are classified as possessing a low potential to experience volume changes with changes in moisture content based on the Atterberg limits and the relatively high sand and gravel content of the samples.

8.2 Seismic Site Classification

Based on available information, the seismic hazard at the site is considered to be moderate to high. Utilizing the shear wave velocity profiles determined in the upper 100 feet, the Vs,100 varied between 3,640 to 4,190 ft/s with an average site value of 3,915 ft/s. The average site shear wave velocity profile would indicate a Site Class B however due to the thickness of the near surface soils the site will be assigned as Site Class C in accordance with the IBC2018 and ASCE 7-16.

Based on the online ‘ATC Hazards by Location’, the site spectral accelerations and peak ground acceleration for ASCE 7-16 were determined to be: Ss=1.23g (spectral acceleration at 0.2-sec), S1=0.43g (spectral acceleration at 1.0-sec), and PGA=0.49g. Based on the Site Class and site accelerations the site coefficients were determined to be: Fa=1.2, Fv=1.5, and Fpga=1.2.

8.3 Liquefaction

Due to the clay content, density of the soils encountered, and the lack of groundwater, liquefaction is not considered to be a potential hazard at the site.

9.0 SITE GRADING AND EARTHWORK

Based on available site topographic information, the site grading will require no cut and a maximum fill of approximately 16 feet to achieve finish floor elevation for the building pad and to achieve proposed finished pavement site grade. Recommendations for clearing and grubbing, subgrade preparation, fill placement, and excavation are presented in subsequent sections.

9.1 Clearing and Grubbing

The construction area should be cleared and grubbed to remove all existing vegetation, topsoil, concrete slab, construction debris, and other unsuitable materials buried under the ground surface. These operations should be completed to a minimum distance of 5 feet beyond the limits of the construction area. The depth of grubbing and stripping should be determined in the field based on visual observations and proper judgment. The spoil generated during these operations should be removed from the site and disposed of as directed by the owner.

9.2 Subgrade Preparation

Subgrades to receive compacted fill for foundations, floor slabs, or pavement support should be stripped of vegetation, debris, and organic matter. Compacted fill subgrades should consist of suitable natural soils as detailed herein.

Loose or soft near-surface soils were not encountered in the test pits or borings; although, they may be found at other areas onsite or in areas where subgrades have been disturbed by construction activities. Any loose or soft soils encountered during construction should be undercut, moisture conditioned as necessary, and recompacted as described in the following section or removed from site and replaced with imported fill soils. Undercut of unsuitable soils beneath compacted fill for support of foundations should extend a minimum of 5 ft or the depth of undercut horizontally beyond the proposed building footprint, foundation area, and limits of fill.

Prior to fill or foundation construction the subgrade should be proof-rolled with a fully loaded 10 ton on-road dump truck, or equivalent, under the observation of a geotechnical engineer or other qualified individual. Areas that exhibit excessive pumping or rutting should either be undercut or be scarified, moisture conditioned, and recompacted as described in the following section. Other alternative methods of subgrade stabilization may be considered to include: crushed stone working platforms, lime or cement treatment, or other methods determined to be suitable by a geotechnical engineer or other qualified individual. The compacted fill subgrades should provide sufficient stability to allow placement of subsequent lifts and compaction of fill as specified in the following section.

Traffic on stripped or undercut subgrades should be limited to reduce disturbance of underlying soil. Maintaining positive drainage and sealing of subgrades with a smooth drum roller should be performed to maintain subgrades free of water and to minimize disturbance of the subgrade soils before placing compacted fill, floor slabs, or pavement section materials. Existing foundations and utilities should be completely removed and replaced with compacted fill.

9.3 Compacted Fill

Compacted fill and backfill in building and pavement areas should consist of suitable material classifying as SC, SM, SP, SW, GC, GM, GP, or GW in accordance with ASTM D2487. Fill soils should be free of topsoil, roots, organic matter, debris, and trash and should have a Liquid Limit and Plasticity Index less than 40 and 15, respectively. Fill materials should not contain particles larger than 2 inches.

Compacted fill should be placed in maximum 10-inch thick horizontal, loose lifts. Fill should be compacted to at least 95 percent of the maximum dry density per ASTM D1557 (modified Proctor), except that the top 12 inches in pavement areas should be compacted to at least 98 percent of the same standard. The fill soils should be moisture conditioned at the time of compaction to be within plus or minus 2 percentage points of the optimum moisture content.

Backfill placed in excavations, trenches, and other areas that large compaction equipment cannot access should be placed with a maximum loose lift thickness of 6 inches. Backfill should meet the material, placement, and compaction requirements outlined above.

Soils used for compacted fill placement should be evaluated during construction for conformance with the project specifications and the recommendations included herein. Specifically, evaluation should include moisture content, Atterberg limits, and dry density tests at the frequencies indicated in the project specification.

9.4 Excavations

Excavations for construction of the cistern and shallow foundations shall be performed in accordance with the requirements of EM 385-1-1. The contractor shall provide stable excavation slopes to protect those working within the excavation and his constructed works. The maximum excavation slope shall be no steeper than 1.5H:1V. Based on the depths of soils and rock materials encountered in the borings, the contractor should anticipate the need for excavation into rock materials consisting of weathered to competent rock for construction of the cistern and gabion basket wall foundations. It is anticipated that the rock excavations can be accomplished using hydraulic jack hammers or other appropriate and approved methods. Rock blasting will not be permitted.

10.0 FOUNDATION RECOMMENDATIONS

The foundation design is based on the current site grading plan and the loads provided by other members of the PDT. Based on the subsurface conditions and the design foundation loads, the use of spread footings will be acceptable for support of the site structure. The cistern may be supported on a mat foundation.

10.1 Spread Footings

Spread footings will be suitable for support of the proposed VMS. The base of the spread footings is currently designed to be approximately 9 feet below grade, which is the same depth as the cistern foundation. This will mitigate any potential differential settlements between the cistern/mat foundation support on rock at the eastern end of the structure and the western end of the structure which will be supported on shallow foundations. Crushed stone (#57) may be compacted under the footings if unacceptable soils are encountered at the proposed footing depth and require undercut. The #57 crushed stone should be compacted to a minimum density of 98 percent of maximum dry density as determined from ASTM D1557. Isolated and continuous footings supported as detailed herein may be designed considering a net allowable soil bearing pressure of 3,000psf. This bearing pressure provides a factor of safety against general bearing capacity failure of at least 3. Settlements of the spread footings constructed as detailed herein are expected to experience settlements of less than 1 inch. Differential settlements between footings are expected to less than ½ inch. Resistance to lateral loads on footings may be designed using an ultimate friction coefficient of 0.65 and a minimum factor of safety of 1.5.

Isolated and continuous footings should have minimum widths of 30 inches and 24 inches, respectively. Footings should be founded at least 30 inches below finished grade. Where footing depths between adjacent footings vary, the slope between the bottom edges of adjacent footings should not be steeper than 1H:1V. Finished site grades should be set to permit positive drainage of surface water away from the building.

The above allowable bearing pressures may be increased by 33 percent for wind and seismic loads when used in conjunction with load combinations defined in IBC Section 1605.3.2, Alternative Basic Load Combinations for use with allowable stress design. This increase is not applicable for other allowable stress load combinations, strength design, or load and resistance factor design.

10.2 Mat Foundation

The cistern may be supported on a mat foundation. The base of the mat foundation will be approximately 9 feet below final site grade, and the mat will be approximately 24 feet by 79 feet in plan. The depth of rock is approximately 7-10 feet at the cistern location. Any soils remaining between the mat foundation excavation and rock should be undercut and backfilled with either lean concrete or #57 crushed stone. The #57 crushed stone should be compacted to a minimum density of 98 percent of maximum dry density as determined from ASTM D1557. It was determined that the weight of soil to be removed to construct the cistern is greater than the applied weight of the structure and water. Therefore, considering the rock support and overall reduction in applied stress conditions, the potential for a bearing capacity failure for the mat is nil, and settlements are anticipated to be minimal to nil.

11.0 FLOOR SLAB RECOMMENDATIONS

The proposed floor slabs should be designed using a modulus of subgrade reaction based on a 1-ft by 1-ft plate test, k1, of 200pci. The subgrade soils supporting the floor slabs should be compacted as recommended above for a minimum depth of 12 inches. A minimum 10-mil thick impermeable plastic membrane should be placed over the compacted subgrade to serve as a vapor barrier.

Final floor slab subgrades should be proof-rolled under the observation of a geotechnical engineer or other qualified individual prior to placing the plastic membrane. The Contractor should compact floor slab subgrades to repair any disturbance that may occur due to construction operations before placing the plastic membrane and concrete. Since floors will be grade supported, footing and utility excavations should be backfilled with compacted fill as defined previously in this report.

The floor slab should be designed with steel mesh or fiber-reinforced concrete to minimize temperature cracking. Proper curing methods should be initiated immediately after placement of the concrete to minimize cracking due to hydration. The floor slab should be designed with adequate joints or saw-cuts to control cracking.

12.0 LATERAL EARTH PRESSURES

The below grade walls of the cistern should be designed to resist lateral earth pressures developed from the surrounding soil, backfill, and surcharge loads. Earth pressures are calculated based on a moist soil unit weight of 120pcf and a drained friction angle of 33 degrees. Backfill placed adjacent to walls are assumed to be free draining and a wall drainage system is assumed to be provided such that hydrostatic forces do not occur. Active and passive earth pressure coefficients should be used in the design of earth retaining walls that are free to rotate or translate laterally, and at-rest earth pressure coefficient should be used for design of earth retaining walls that are restrained from movement or rotation. The table below includes the recommended earth pressure coefficients. The values in this table were developed assuming level site conditions for backfill and toe components of the wall.

Earth Pressure Coefficients for Below Grade Walls and Site Retaining Walls

Backfill Slope or Toe Slope Conditions

Active Earth Pressure At-Rest Earth Pressure Passive Earth Pressure

Static, Ka

Dynamic, ΔKae

Static, Ko

ΔKoe

Static, Kp

ΔKpe

Level 0.30 0.13 0.46 0.32 3.4 -0.38

In addition to lateral earth pressures from backfill and surrounding soils, braced and site retaining walls should also be designed to resist surcharge loads that are located within a lateral distance from the wall equal to the height of the wall. Lateral earth pressures from surcharge loads can be estimated with a uniform lateral pressure equal to the lateral earth pressure coefficient (table above) times the vertical surcharge pressure. Wall footings founded on new compacted fill or natural soils may be designed using an ultimate friction coefficient of 0.65 with a minimum factor of safety of 1.5.

Using the Mononobe-Okabe equation for level backfill conditions, we recommend the seismic component for design of retaining walls that are free to rotate or translate laterally should utilize the dynamic active and dynamic passive earth pressure coefficients provided in the table above, Kae and Kpe, respectively. The design seismic coefficient, kh, of 0.196 was utilized to determine the dynamic earth pressure coefficients for walls free to rotate or translate laterally. This design seismic coefficient was assumed to be equal to ½ of the design PGA of 0.392g, adjusted for site conditions. For retaining walls that are restrained from lateral translation or rotation, the design seismic loading should be based on the dynamic at-rest earth pressure coefficient, Koe. In order to account for higher seismic loads being transmitted to the stiffer wall element, the dynamic at-rest earth pressure coefficient is determined using the full design PGA of 0.392g. The resultant force for the active and at-rest seismic earth pressure stress distribution should be considered to act at a height equal to 0.6H above the base of the wall, where H is the height of the retained soil above the wall base. The resultant force for the passive seismic earth pressure distribution should be assumed to act at a height of 1/3D above the base of the wall, where D is the depth of soil at the toe of the retaining wall. The location of all resultant forces for static earth pressure distributions should be considered to act at a height of 1/3 the height of H or D as appropriate.

The earthquake loads should be considered additive to the static earth pressure loads.

12.1 Gabion Retaining Wall

The eastern edge of the building pad embankment will require fill of up to approximately 16 feet to achieve design grade. The eastern edge of the embankment will be supported using a gravity gabion retaining wall. Figure 7 is an illustration of the typical gabion wall configuration.

Figure 7. Typical Gabion Wall Configuration.

Various gabion wall heights and configurations were evaluated due to the varying height of wall required along the embankment. The wall heights evaluated varied in height from 4 to 16 feet.

Rock or lean concrete Geotextile Fabric Wrap

The gabion wall was designed using individual basket with heights of either 3 or 4 feet and widths of either 3 or 4.5 feet. Each level of gabion baskets should be stair stepped back a minimum of

1.5 feet. The back face of the gabion wall should be vertical. The gabion baskets should be constructed of 9 gage galvanized wire with 3-inch square mesh. The infill of the baskets should consist of stones with nominal dimensions no less than 4 inches and no greater than 8 inches and arranged to minimize voids within each basket. The backfill against the gabion wall should consist of #57 crushed stone that is completely wrapped on all sides in a nonwoven geotextile (Mirafi 180N or equivalent). The base of the wall will be founded on existing rock. The first layer of gabion baskets may be placed directly on the level rock surface, or a lean concrete leveling pad may be constructed on which to place the first basket layer. The level rock surface or lean concrete leveling pad should be roughened to ensure good contact with the basket.

The internal stability of the gabion wall was design in accordance with the National Highway Institute Course No. 13236. Evaluations were performed for both static and earthquake loading conditions considering sliding, overturning, and bearing. Active earth pressures were utilized in the design consistent with those discussed in the previous section. Passive earth pressures were not utilized as the ditch was assumed to be located at the base of the wall with an exposed rock channel bottom. A case was analyzed assuming water in the ditch rose to a height of 4 feet (top of bottom basket level) which would saturate the basket infill and backfill soils; however, neither destabilizing hydrostatic pressure on the gabion wall or stabilizing hydrostatic pressures on the backfill were considered due to the porous nature of the backfill and gabion wall. A uniform surface stress of 250psf was applied at the ground surface to represent potential equipment or vehicle loads. The backfill was assumed to have a unit weight of 120pcf and a drained internal friction angle of 33 degrees. The unit weight of the baskets and rock infill was assumed to be 105pcf. The contact friction angle between the rock and basket was assumed to be 38 degrees, resulting in a friction coefficient of 0.78. The design criteria for the gabion wall was taken from Table 4-1 of EM 1110-2-2502. The results of the wall evaluation are provided in the following table. The calculations are provided in the appendix.

The global stability of the gabion wall, backfill, and embankment was analyzed using limit equilibrium slope stability methods. These analyses were performed using GeoStudio SlopeW computer program. The analyses were conducted using the Spenser method of slices with circular

Wall Height Wall Base

(ft) (ft) Calculated Required Calculated Required Calculated Required

4 4.5 2.6 1.5 100% base compression 75% base compression >3.0 3.0 7 6 2.2 1.5 100% base compression 75% base compression >3.0 3.0

10 7.5 2.0 1.5 100% base compression 75% base compression >3.0 3.0 11 7.5 1.9 1.5 100% base compression 75% base compression >3.0 3.0 14 10.5 2.1 1.5 100% base compression 75% base compression >3.0 3.0 16 10.5 1.8 1.5 100% base compression 75% base compression >3.0 3.0 4 4.5 1.4 1.33 >50% base compression 50% base compression >2.0 2.0 7 6 1.5 1.33 >50% base compression 50% base compression >2.0 2.0

10 7.5 1.5 1.33 >50% base compression 50% base compression >2.0 2.0 11 7.5 1.5 1.33 >50% base compression 50% base compression >2.0 2.0 14 10.5 1.7 1.33 >50% base compression 50% base compression >2.0 2.0 16 10.5 1.5 1.33 >50% base compression 50% base compression >2.0 2.0 4 4.5 1.9 1.1 Resultant within base Resultant within base >1.0 1.0 7 6 1.6 1.1 Resultant within base Resultant within base >1.0 1.0

10 7.5 1.5 1.1 Resultant within base Resultant within base >1.0 1.0 11 7.5 1.4 1.1 Resultant within base Resultant within base >1.0 1.0 14 10.5 1.5 1.1 Resultant within base Resultant within base >1.0 1.0 16 10.5 1.3 1.1 Resultant within base Resultant within base >1.0 1.0

Sliding FoS Overturning Bearing FoS

S ta tic

D ry

E ar th qu ak e

Load Case

S ta tic

' W at er DRAFT failure surfaces. Cases analyzed included: after construction (AC), 4 feet of water in ditch (AC- W), earthquake (EQ), and long term (LT). The stability analyses were only performed for the critical section located at Station 2+00, which is the tallest embankment section. A uniform surface stress of 250psf was applied at the ground surface to represent potential equipment or vehicle loads. The embankment soils were conservatively assumed to have an undrained shear strength of 500 psf for the AC, AC-W, and EQ load cases. A conservative drained friction angle of 28 degrees was assumed for the embankment soils for use in the LT case. The rock layer was modeled at an elevation of 67 feet as a very hard, impenetrable layer for the slope stability analyses. The gabion wall was modeled as a triangular block with a high effective shear strength assuming a cohesion of 2,000psf and a friction angle of 35 degrees for the purpose of limiting failures from occurring within the gabion block due to the steep wall face. The results are listed in the following table. The analysis results are provided in the appendix.

13.0 PAVEMENT RECOMMENDATIONS

Design information regarding the distribution and volume of vehicles that will utilize the facility and pavements were not available. In order to develop design pavement sections, we have assumed an overall design ESAL of 1,500,000 18-kip single axle loads over the recommended pavement design life of 25 years. Pavement designs have been developed for flexible and rigid pavement sections in accordance with the design procedures of UFC 3-250-01 and minimum requirements of UFC 3-201-01. The following sections present our recommendations for the proposed pavement sections.

13.1 General Pavement Recommendations

The pavement section subgrade will consist of either existing soils or compacted fill. For all pavement sections, the subgrade soils must be compacted to at least 98 percent of maximum dry density as determined in ASTM D1557 for a minimum depth of 12 inches. The subgrade soils shall meet the requirements for compacted fill as described previously. Final pavement subgrades should be proof-rolled under the observation of a geotechnical engineer or other qualified individual to evaluate their suitability to support the pavement section.

Adequate control of surface drainage will be a very important consideration for the overall performance of this pavement design. The area surrounding pavements should be graded to direct surface water away from paved areas.

13.2 Pavement Design

The pavement design charts in Appendices E and F of UFC 3-250-01 were utilized to determine the flexible and rigid pavement sections, respectively. The compacted subgrade soils were estimated to have a CBR value of 6 in design of the flexible and aggregate pavement sections.

Calculated Required

AC 3.6 1.3

AC-W 3.6 1.4

EQ 2.2 1.2

LT 3.6 1.5

Load Case

FoS

The compacted subgrade soils were estimated to have a modulus of soil reaction of 250pci for design of the rigid pavement section; however, a 6-inch aggregate base layer will be provided under the rigid pavement to mitigate potential pumping at joints which will increase the modulus of soil reaction to 300pci. The flexural strength of the rigid plain concrete pavement was assumed to be 700psi. The aggregate base course for both the flexible and rigid pavement sections should be compacted to 100% of the maximum dry density as determined in ASTM D1557. The following table list the recommended pavement sections.

Pavement Section

Surface Course Thickness (in)

Aggregate Base Course Thickness (in)

Flexible – asphalt 4 6 Rigid – concrete 6 6

14.0 CONSTRUCTION CONSIDERATIONS

14.1 Site Grading and Earthwork

Traffic on stripped or undercut subgrades should be limited to reduce disturbance of underlying soils. Also, using lightweight, track-mounted dozer equipment for stripping will limit the disturbance of underlying soils, and may reduce the undercut volume needed. The Contractor should provide site drainage to maintain subgrades free of water to mitigate saturation and disturbance of the subgrade soils before placing compacted fill, pavement base course, floor slabs, or moisture barrier material. This will be important during all phases of the construction work. The Contractor should be responsible for reworking of subgrades and compacted fill that were initially considered suitable but were later disturbed by equipment and/or weather.

Some of the on-site soils are susceptible to moisture changes, will be easily disturbed, and will be difficult to compact under wet weather conditions. Similarly, moisture conditioning may be necessary to maintain compacted fill moisture contents at or near optimum moisture. Earthwork planning and moisture control will be important to the overall success of site grading and earthwork operations.

The contractor should anticipate the need for excavation into rock materials consisting of weathered to competent rock. It is anticipated that the rock excavations can be accomplished using hydraulic jack hammers or other appropriate and approved method. Rock blasting will not be permitted.

14.2 Foundations

Foundation subgrades should be observed by a qualified geotechnical engineer to evaluate whether the soils are suitable for the recommended bearing pressure and to verify that subgrades have not become excessively disturbed. Spread footings should be concreted the same day the excavations are completed to reduce disturbance of footing subgrades by exposure to weather conditions and construction operations. Any disturbed subgrade soils should be removed prior to pouring concrete for the footings. As an alternative to placing concrete the same day in footings, a mud slab may be poured on the approved subgrades to protect subgrade surfaces from damage before final concrete placement. A mud slab may also be poured to protect the mat foundation subgrade from damage during construction activities and prior to final concrete placement.

Forming of footings may be used if necessary; however, less subgrade disturbance will occur if footings are poured directly against the soil. Therefore, it is recommended that forming of footings be avoided. If forms are used, they should be removed and the excavations backfilled as soon as possible. Water should not be permitted to pond around footing excavations.

14.3 Floor Slabs and Pavement Subgrades

Floor slab and pavement subgrades should be observed by a geotechnical engineer or other qualified representative prior to the placement of the granular base course or other pavement-related materials. Proof-rolling should be performed as previously discussed. All loose or soft soils should be removed and the excavated surface observed to evaluate if additional excavation is necessary. Where the subgrade is unsuitable or where soils have been disturbed due to inclement weather or construction activity, the disturbed or unsuitable materials should be removed and replaced with compacted fill as detailed herein.

Construction loading conditions on pavements are typically more severe than the design conditions. Construction loads are also typically placed on partially constructed pavement sections. These two factors often contribute to subgrade and pavement failures. Consideration should be given to limiting construction traffic on partially constructed pavements or to increasing the thickness of the granular base and/or asphalt concrete base course to account for the construction loads and traffic.

Appendix

39.0 24.0

Fill? Silty Rock fragments and Sand (GC), little wood fragments, loose, brown, tan, gray.

(19% < #200 sieve)

Easy drilling, some rock.

Fill? Rock fragments and Sand (GC), some clay, med. dense.

brown, gray.

(28% < #200 sieve)

Easy drilling.

Fill? Clayey Rock fragments with sand (GC), med. dense, brown, tan, reddish brown.

(22% < #200 sieve)

Moderate drilling, rock.

Weathered rock sampled as: Silty Sand with rock fragments (GM), dense, white, gray.

(18% < #200 sieve)

Hard drilling, rock.

Weathered rock sampled as: Rock fragments (GC), some sand, little clay, very dense, light brown, gray, white.

Hard drilling, rock.

Weathered rock sampled as:

Clayey Rock fragments and Sand (GC), very dense, yellowish brown, gray, red.

(29% < #200 sieve)

Moderate drilling.

Moderate drilling using bicone, rock.

Rock fragments, very dense, dark brown.

Bicone rock drilling: 6 min, good return Bicone rock drilling: 6 min, good

11-4-5-8

6-7-8-11

5-7-9-9

14-17-32-50/4"

49-50/5"

13-16-18-50/4"

25-50/1"

10-50/1"

4.4

4.9

4.4

2.1

3.0

17.2

10.9

3.4 w

N

DATE HOLE

ELEVATION TOP OF HOLE

ELEVATION GROUND WATER

NAME OF DRILLER /METHOD

BORING LOG No: 20-STT-01

DESCRIPTION

qu

20-STT-01

ON

SAMPLER

N qu wn LL

1 2 3 4 5

LOCATION

(Coordinates or Station) wn

OF SHEETS

GeoProbe/CME45 AUTO

AMELIA DISTRIBUTION CENTER, EMMA ST. 26A, GUAYNABO, PR 00968

DRILLING EQUIPMENT

N qu qu

LL

UNCONFIED COMPRESSIVE STRENGTH, TSF

WATER TABLE OR PHREATIC LEVEL

( ) PENETROMETER, TSF

PROJECT No.

STARTED

GEOTECHNICAL TESTING SERVICES

APPROVED BORING No.

Simon Ojeda/Carlos Calderon

PL

PI

WATER CONTENT IN %

BLOWS FROM S. P. T. (ASTM D-1586)

GeoProbe/CME45

VMS AT STT, , USVI

5478T

DEPTH

M FT

BLOWS

PI Symbol

GEOTECNIA Y CIMIENTOS

COMPLETED

3-9-212-25-21

LIQUID LIMIT IN %

PLASTIC LIMIT IN %

PLASTICITY INDEX IN %

10 20 30 40 50

10 20 30 40 50

N 18.324 W 64.860

>>DRAFT

return Bicone rock drilling: 8:33 min, good return Bicone rock drilling: 15:00 min, good return

END OF BORING NO. 20-STT-01

AT 21.67 FEET DEPTH.

Comments:

1- Boring started with GeoProbe and hollow stem auger (1:05 pm 1:05 pm).

2- SPT refusal @ 10'-11" bgs.

3- Auger refusal at 11 ft bgs(2:13 pm 2/25/2021).

4- 3/9/2021 @ 9:45 am Continue boring with CME45 and casing advancer with roller bit.

w

N

DATE HOLE

ELEVATION TOP OF HOLE

ELEVATION GROUND WATER

NAME OF DRILLER /METHOD

BORING LOG No: 20-STT-01

DESCRIPTION

qu

20-STT-01

ON

SAMPLER

N qu wn LL

1 2 3 4 5

LOCATION

(Coordinates or Station) wn

OF SHEETS

GeoProbe/CME45 AUTO

AMELIA DISTRIBUTION CENTER, EMMA ST. 26A, GUAYNABO, PR 00968

DRILLING EQUIPMENT

N qu qu

LL

UNCONFIED COMPRESSIVE STRENGTH, TSF

WATER TABLE OR PHREATIC LEVEL

( ) PENETROMETER, TSF

PROJECT No.

STARTED

GEOTECHNICAL TESTING SERVICES

APPROVED BORING No.

Simon Ojeda/Carlos Calderon

PL

PI

WATER CONTENT IN %

BLOWS FROM S. P. T. (ASTM D-1586)

GeoProbe/CME45

VMS AT STT, , USVI

5478T

DEPTH

M FT

BLOWS

PI Symbol

GEOTECNIA Y CIMIENTOS

COMPLETED

3-9-212-25-21

LIQUID LIMIT IN %

PLASTIC LIMIT IN %

PLASTICITY INDEX IN %

10 20 30 40 50

10 20 30 40 50

N 18.324 W 64.860

Fill?Clayey Rock fragments and Sand (GC), dense, gray, brown, reddish brown.

(25% < #200 sieve)

Easy drilling.

Fill? Clayey Rock fragments and Sand (GC), med. dense, reddish brown, brown, gray.

Easy drilling.

Fill? Clayey Rock fragments (GC), little sand, loose, reddish brown, brown, gray, light tan.

(17% < #200 sieve)

Moderate to hard drilling, rock.

Top 8"- Fill? Clayèy Sand (SC), trace rock fragments, brown, gray, white.

Bott 5"- Rock fragments (GP), gray.

Hard drilling, rock. Auger refusal (02/25/2021).

No recovery (inferred to be Rock).

END OF BORING NO. 20-STT-02

AT 10.25 FEET DEPTH.

Comments:

1- Boring started with GeoProve with hollow stem auger (10:30 am 2/25/2021).

2- Auger Refusal at 9.5 ft., abandoned hole temporarily (11:42 am 02/25/2021).

3- Hole restarted with CME45 and casing advancer with roller bit (7:00 am 03/10/2021).

4- Casing advancer refusal at 9.33 ft, switch to roller bit (7:24 am 03/10/2021).

5- Very hard drilling to reach 10 ft with roller bit after trying multiple ones (8:20 am 03/10/2021).

6- Roller bit refusal at 10 ft, boring terminated (8:45 am 03/10/2021).

7- Groundwater not encountered during drilling.

10-16-17-15

6-6-5-8

3-4-5-12

4-12-33-50/2"

50/3"

4.1

2.5

7.5 w

N

DATE HOLE

ELEVATION TOP OF HOLE

ELEVATION GROUND WATER

NAME OF DRILLER /METHOD

BORING LOG No: 20-STT-02

DESCRIPTION

qu

20-STT-02

ON

SAMPLER

N qu wn LL

1 2 3 4 5

LOCATION

(Coordinates or Station) wn

OF SHEETS

GeoProbe/CME45 AUTO

AMELIA DISTRIBUTION CENTER, EMMA ST. 26A, GUAYNABO, PR 00968

DRILLING EQUIPMENT

N qu qu

LL

UNCONFIED COMPRESSIVE STRENGTH, TSF

WATER TABLE OR PHREATIC LEVEL

( ) PENETROMETER, TSF

PROJECT No.

STARTED

GEOTECHNICAL TESTING SERVICES

APPROVED BORING No.

Simon Ojeda/Carlos Calderon

PL

PI

WATER CONTENT IN %

BLOWS FROM S. P. T. (ASTM D-1586)

GeoProbe/CME45

VMS AT STT, , USVI

5478T

DEPTH

M FT

BLOWS

PI Symbol

GEOTECNIA Y CIMIENTOS

COMPLETED

3-10-212-25-21

LIQUID LIMIT IN %

PLASTIC LIMIT IN %

PLASTICITY INDEX IN %

10 20 30 40 50

10 20 30 40 50

N 18.324 W 64.860

42.0

26.0

26.0

14.0

Fill? Sandy Clay with rock fragments (GC), little concrete fragments, loose, gray, brown.

Easy drilling.

Fill? Clayey Rock fragments and Sand (GC), some silt, little clay, med. dense, reddish brown, yellowish brown.

(26% < #200 sieve)

Easy drilling.

Clayey Sand and Rock fragments, med. dense, reddish brown, dark gray, yellowish brown.

(43% < #200 sieve)

Moderate drilling, rock.

Weathered rock sampled as:

Clayey Sand with rock fragments (SC), very dense, reddish brown, gray.

(37% < #200 sieve)

Hard drilling, rock. Auger refusal at

9.5 ft,…