B.08 USACE Camp Santiago GER - 09-11-2020.pdf

GEOTECHNICAL FINDINGS AND RECOMMENDATIONS REPORT

for

Camp Santiago Joint Training Center Facility Restoration

Puerto Rico

September 2020

U.S. Army Corps of Engineers

Transatlantic Middle East District, Winchester, VA

Contract No. W912QR-18-0014

Task Order W912ER20F0138

Camp Santiago Facility Restoration i

TABLE OF CONTENTS

1.0 INTRODUCTION AND PROJECT OVERVIEW

1.1 Introduction

1.2 Site

1.3 Proposed Structures and Structural Loads

1.4 Scope of Work

2.0 LITERATURE REVIEW

2.1 Soils

2.2 Geology

2.3 Landslides

2.4 Seismicity

3.0 FIELD INVESTIGATION

3.1 Site Reconnaissance

3.2 Drilling Equipment and Methods

3.3 Soils

3.4 Groundwater

3.5 Test Pits

3.6 Soil Percolation Field Tests

3.7 Soil Resistivity Field Tests

4.0 LABORATORY TESTING

4.1 Soil Classification and Moisture Content

4.2 Modified Proctor

4.3 California Bearing Ratio

4.4 Unit Weights

4.5 Soil Chemistry

4.6 Organic Content

4.7 Carbonate Content

4.8 Soil Collapse Potential

5.0 ANALYSES

5.1 Development of Soil Parameters

5.2 Collapsible Soils

5.3 Shallow Foundation Analysis

5.3.1 Bearing Capacity

5.3.2 Settlement

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5.4 Deep Foundation Analysis

5.4.1 Axial Pile Capacity

5.4.2 Lateral Pile Capacity

5.5 Liquefaction Susceptibility Analysis

6.0 RECOMMENDATIONS

6.1 Parameters

6.1.1 Soil Design Parameters

6.1.2 Corrosion Potential

6.1.3 Seismic Parameters

6.2 Collapsible Soils

6.3 Shallow Foundations

6.3.1 Barracks Structures

6.3.2 HQ Structures

6.3.3 DFAC Structures

6.3.4 Canopy Structure at HQ6

6.4 Deep Foundations

6.5 Liquefaction Mitigation

6.5.1 Ground Improvement

6.5.2 Alternative Shallow Foundations

6.6 Earthwork

6.6.1 Subgrade Preparation

6.6.2 Fill Placement

6.6.3 General

6.7 Floor System

6.8 Pavement Design

6.9 Sewage Lines

7.0 LIMITATIONS

8.0 REFERENCES

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List of Tables

TABLE 1 - TEST BORING & TEST PIT SUMMARY TABLE

TABLE 2 - GROUNDWATER SUMMARY TABLE

TABLE 3 - FIELD SOIL RESISTIVITY TEST RESULTS

TABLE 4 - USCS SOIL CLASSIFICATION TEST RESULTS

TABLE 5 - MODIFIED PROCTOR TEST RESULTS(MOISTURE DENSITY RELATIONSHIP FOR COMPACTION)

TABLE 6 - CALIFORNIA BEARING RATIO (CBR) TEST RESULTS

TABLE 7 - SOIL CHEMISTRY TEST RESULTS

TABLE 8 - ORGANIC CONTENT TEST RESULTS

TABLE 9 - CARBONATE CONTENT TEST RESULTS

TABLE 10 - COLLAPSIBLE POTENTIAL OF SOIL TEST RESULTS

TABLE 11 - UNIT WEIGHT TEST RESULTS

TABLE 12 - STRUCTURE INFORMATION SUMMARY TABLE

TABLE 13 - SHALLOW FOUNDATION RECOMMENDATIONS SUMMARY TABLE

TABLE 14- DEEP FOUNDATION RECOMMENDATIONS SUMMARY TABLE

TABLE 15 - LIQUEFACTION ANALYSES SUMMARY TABLE

Attachments

Attachment 1- CLIENT PROVIDED INFORMATION

Proposed Building Layout Foundation Loads Design Drawings

Attachment 2- GEOLOGIC BACKGROUND INFORMATION

Figure 1 – Project Location Topographic Map Figure 2 – Historical Topographic Map Figure 3 – Aerial Photo Figure 4 – General Soils Map Figure 5 – Alluvium Thickness in Southern Puerto Rico Figure 6 – Landslide Susceptibility Map

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Attachments (cont.)

Attachment 3- SITE RECONNAISSANCE PHOTOGRAPHS

Attachment 4- FIELD INVESTIGATION RESULTS

As-Drilled Geotechnical Test Borings and Test Pits Plan Subsurface Cross Section Test Boring Logs Test Pits Logs Field Soil Resistivity Test Results Field Soil Percolation Tests Results

Attachment 5- Laboratory Testing Results

Soil Classification and Moisture Content Test Results Modified Proctor Test Results California Bearing Ratio (CBR) Test Results Unit Weight Test Results Soil Chemistry Test Results Organic Content Test Results Carbonate Content Tests Results Soil Collapse Potential Tests Results

Attachment 6- Soil Design Parameters

Soil Strength Parameters Subgrade Modulus Correlation Collapsible Soils Correlation (UFC 3-220-10N, Figure 6)

Attachment 7- Shallow Foundation Analyses

Bearing Capacity Certification Bearing Capacity Calculations Settlement Calculations

Attachment 8- Deep Foundation Analyses

Axial Capacity Calculations Lateral Capacity Analyses

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Attachments (cont.)

Attachment 9- Liquefaction Analysis

Seismic Site Class Calculations Seismic Coefficient Liquefaction Analyses

Attachment 10- Response to Review Comments

Camp Santiago Facility Restoration

1.0 INTRODUCTION AND PROJECT OVERVIEW

1.1 Introduction

This Geotechnical Report by Michael Baker International, Inc. (Michael Baker) presents the results of a geotechnical investigation to support the United States Army Corps of Engineers (USACE) in the proposed design and construction of the Facility Restoration at Camp Santiago Joint Training Center (Camp Santiago) in Puerto Rico. The geotechnical investigation was performed in accordance with the scope of services described in Michael Baker’s Geotechnical Work Plan to USACE dated January 2020.

The Proposed Restoration at Camp Santiago includes design and construction of barracks, battalion and brigade headquarter buildings, dining facilities, supply buildings, new pavements, and new sewage and water lines. The purpose of this geotechnical investigation is to determine subsurface conditions at the project site and provide recommendations in support of the design and construction of the facility of the proposed buildings and pavement areas.

1.2 Site

Camp Santiago is a joint military training installation located in the foothills of the Cordillera Central Mountains; the site is approximately 2.5 miles west-northwest of Coco, Salinas County, Puerto Rico and approximately 3 miles southeast of Mariano Colón, Coamo County, Puerto Rico. Relief at the project site is gentle with a maximum elevation of approximately 190 feet above mean sea-level (feet-msl) (57.9 meters-msl) and minimum elevation of approximately 150 feet-msl (45.7 meters-msl) (Figure 1). The project site is situated adjacent to an isolated mountain in the north, whereas a larger range exists to the west, with plains located to the south and east. The site drains to the south into a tributary of the Rio Nigua.

1.3 Proposed Structures and Structural Loads

The Facility Restoration included the following proposed buildings:

10 two-story Barracks Buildings (Barracks), 2 one-story Dining Facilities (DFAC), 13 one-story Headquarters, Administrative and Supply Buildings (HQ), 3 one-story Headquarters, Administrative and Supply Buildings (HQ5) and 1 one-story Headquarters, Administrative and Supply Building (HQ6).

Attachment 1 of this report presents the layout of the proposed structures.

The foundation analyses and recommended foundation design criteria are based on unfactored foundation loading information (e.g. Allowable Stress Design) provided by USACE; see Attachment 1 for the detailed load information for each proposed structure and Table 12 for the summary of structural information for the proposed buildings

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1.4 Scope of Work

This work has been performed in general accordance with the Geotechnical Work Plan prepared by Michael Baker for USACE for Camp Santiago, Puerto Rico, dated January 2020. The geotechnical scope of services has been performed as Task Order W912ER20F0138 of the overall Contract #W912-QR-18- D0014.

Michael Baker’s geotechnical scope of work consisted of a geotechnical literature review, geotechnical field investigation, foundation analysis, and geotechnical engineering report development.

The following tasks were completed for the preparation of this report:

Conducted a geological background review of site conditions.

Performed a site reconnaissance.

Performed a geotechnical subsurface investigation consisting of 49 test borings and 10 test pits.

Performed field soil resistivity and percolation tests.

Conducted laboratory testing of selected soil samples.

Performed geotechnical analyses.

Provided geotechnical recommendations for design and construction

Review comments on the draft Geotechnical Findings and Recommendations Report submission, dated August 2020 were received from USACE on August 28, 2020. Responses to these comments are provided in Attachment 10, and the report was revised as necessary.

2.0 LITERATURE REVIEW

Refer to the Geologic Background Information provided in Attachment 2 of this report. All figures referenced in this section are located in this attachment.

2.1 Soils

According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Web Soil Survey, the soils at the project site are not public information. However, the General Soil Map of Puerto Rico (Figure 4) indicates that the soils in the area are of the NRCS identified Coamo Series, Guamani Series, or the Vives Series.

The Coamo clay loam (ClB) is a gently sloping mixed loamy alluvium derived from volcanic and sedimentary rock over mixed gravelly alluvium derived from volcanic and sedimentary rock, having a depth to bedrock greater than 80 inches. Generally, it has a liquid limit of approximately 31 percent and a plasticity index of 16 percent, indicating a medium plasticity soil, with a low shrink-swell potential. The soil is identified as well drained, with a depth to the water table of more than 80 inches, and typically classifies as Unified Soil Classification System (USCS) lean clay (CL).

The Guamini silty clay loam (Gm) is a gently sloping medium textured sediment over sand, pebbles, and cobbles at foot of slopes with a depth to bedrock greater than 80 inches. Generally, it has a liquid limit of approximately 17 percent and a plasticity index of 8 percent, indicating a low plasticity soil, with no shrink-swell potential information available. The soil is identified as well drained with a depth to the water table more than 80 inches. No information regarding the USCS classification could be found in the NRCS data, however based on the Atterberg limits, the soil likely classifies as a USCS inelastic silt (ML).

The Vives silty clay loam (Vs) is gently sloping fine and moderately fine textured sediments on foot-slopes with a depth to bedrock greater than 80 inches. Generally, it has a liquid limit of approximately 40 percent and a plasticity index of 19 percent, indicating a medium to high plasticity soil, with a low shrink-swell potential. The soil is identified as moderately well drained with a depth to the water table more than 80 inches. No information regarding the USCS classification could be found in the NRCS data;

however, based on the Atterberg limits, the soil likely classifies as a USCS lean clay (CL).

In addition to the three soil types listed, a generally unmapped soil series known as the Camp Santiago Series exists within the NRCS archives and is located within the vicinity of the site. Per the NRCS description the Camp Santiago Series soil consisted of gently to moderately sloping well drained, moderately permeable soils on foot slopes and toe slopes of volcanic mountains from material that weathered from extrusive volcanic residuum. The NRCS also identifies the Coamo and Guamani series as geographically associated soils.

Based on the geographic and geomorphological features identified in Figure 1, the project site is located on a piedmont plain. Piedmont plains are found in arid climates which are dissected by incised stream channels and dotted with residual bedrock knobs. The project site exists on the both a piedmont and alluvial plain. As previously discussed, the project site is located at the foot of an isolated mountain to

Camp Santiago Facility Restoration 2 the north and is in the drainage path of the large continuous mountain range to the west. A unique situation has developed where the project site is situated on the old alluvial plain formed by the mountains to the west, which is likely covered with the piedmont materials from the mountain to the north.

As it relates to soils, the northern and northeastern extent of the project site is likely composed of Camp Santiago soils formed in the piedmont, which is likely overlaying alluvial plain material from the western plain outwash which thickens to the south. The southern and southeastern portion of the site are likely Coamo series soils which is based on the distance from the range to the west; it is not likely that large proportions of boulders and cobbles (Guamani Series) were transported several miles. If any exist, it is likely from construction or a result of sedimentation from the northern mountain. Vives soils, which are identified as fine, excellent farming material, likely exist further to the south and the east at a maximum extent from the mountains.

2.2 Geology

According to the Preliminary Report on the Geology of the Coamo Quadrangle, Puerto Rico, bedrock at the site is of the Santonian and Campanian aged, Guayama series, Cariblanco Formation, the Maestrichtian and Campanian aged, Guayama series, Coamo Formation, a Tertiary aged porphyritic diorite dike, and Quaternary colluvium (alluvium per new GIS based mapping).

The Cariblanco Formation is composed of volcaniclastic conglomerate, sandstone, and siltstone.

Volcaniclastic rock is sedimentary rock that is composed of volcanic clasts and sediments as opposed to the traditional siliciclastic sedimentary rocks, which are largely composed of quartz and lithics.

The Coamo Formation is mapped as the primary bedrock at the project site, it is composed of tuff-breccia, tuffaceous conglomerate, tuff, siltstone, limestone, as well as tuffaceous and calcareous sandstone. Specifically, in the northwestern portion of the project site the rock is partly tuffaceous calcareous sandstone and siltstone. In the southeastern portion of the project site bedrock is identified primarily as tuff-breccia, and tuffaceous conglomerate. Tuff is a volcanic rock that is formed by the lithification of the ash and debris distributed by pyroclastic flows during volcanic eruptions.

The porphyritic diorite dike is located at the northwestern extent of the project site and the alluvium/colluvium is in the west-northwestern corner of the project site. The alluvium/colluvium is up to 60 feet thick near the project site (Rodriguez-Martinez). The anticipated composition of the alluvium and colluvium is as discussed in Section 2.1.

The Rio Jeuyes Fault, a normal fault (Glover III), intersects the site longitudinally. The upthrown rock unit is of the Cariblanco Formation in the northeast and the downthrown unit is of the Coamo Formation in the southwest. The Rio Jeuyes Fault is not believed to have been active since the Maestrichtian age, however, Puerto Rico still exists within an active tectonic zone.

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2.3 Landslides

According to available landslide susceptibility mapping in Puerto Rico (Figure 6), the project site is in an area moderately susceptible to landslides. However due to the low relief of the project site, potential for landslides as a result of construction is not anticipated to be an issue.

2.4 Seismicity

Seismic design for the project location considers the regional seismicity of the area. The project site is in one of the most seismically active zones in the world. Puerto Rico is located at the convergence between two tectonic plates, the North American plate and the Caribbean plate, which is accompanied by a complex fault system.

In the past century, the four largest earthquakes to occur within 150 miles (250 km) of the site include:

July 29, 1943 a Magnitude 7.7 earthquake occurred approximately 85 miles (135 km) northwest of Camp Santiago.

January 07, 2020 a Magnitude 6.4 earthquake occurred approximately 35 miles (55 km) southwest of Camp Santiago.

January 13, 2014 a Magnitude 6.4 earthquake occurred approximately 80 miles (130 km) northwest of Camp Santiago.

October 11, 2009 a Magnitude 6.1 earthquake occurred approximately 125 miles (200 km) northeast of Camp Santiago.

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3.0 FIELD INVESTIGATION

The field investigation program completed by Michael Baker consisted of 49 test borings, 10 test pits, 1 percolation test, and 16 field soil resistivity tests. Detailed discussion of the field investigation program is presented in the following sections. A Plan of as-drilled test borings and test pits is presented in Attachment 4 of this report.

3.1 Site Reconnaissance

Site reconnaissance was conducted prior to the drilling of the test borings. Site Reconnaissance Photographs are presented in Attachment 3 of this report.

The site is former barracks and administration buildings that were not in use. There were a few buildings being used for storage and administrative activities, but the vast majority of the building were vacant.

Some of the buildings showed hurricane damage and were without roofs and/or door. The buildings were one story concrete block or concrete buildings. The land was general level with no large slopes or embankments. No signs of structural distress or foundation disturbance due to subsurface conditions was observed among the existing structures at the site.

The borings were located by a surveyor with utility clearance provided by Jaca & Sierra Engineering, PSC. Minor relocation of a few borings resulted from the utility clearance. Once the borings were cleared of utilities, drilling of the borings commenced.

3.2 Drilling Equipment and Methods

The test borings were drilled by Jaca & Sierra Engineering, PSC (Jaca & Sierra) of San Juan, Puerto Rico.

Drilling operations took place across two mobilizations; the first being in February 2020 and the second being in May 2020.

A total of 49 borings were drilled for the proposed buildings included:

Three borings for each of the proposed barracks (total of 30 barracks borings);

One boring for each of the proposed Dining Facilities (total of 2 Dining Facilities borings);

One boring for each of the Headquarters, Administrative and Supply buildings (total of 17

Headquarters, Administrative and Supply Buildings borings).

Each boring was advanced approximately 20 feet (6 meters) through the soil overburden, except for test boring 306B1 which was terminated at approximately 60 feet (18 meters).

Michael Baker provided an on-site representative to monitor drilling and sampling on a fulltime basis, log each borehole, field classify soil samples, and select representative samples for subsequent laboratory testing.

The borings were drilled using a track-mount drill rig. Each boring was advanced through the soil overburden with hollow stem augers to the specified termination depth. Standard penetration tests (SPTs) were completed with a split-barrel sampler. After completing the drilling program, borings were backfilled with cuttings.

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The detailed boring logs prepared by Michael Baker and a general subsurface profile are presented in Attachment 4. A summary of the test borings is presented in Table 1.

3.3 Soils

The soil encountered at the test borings and test pits generally consisted of fill and native soil. Minor amounts of topsoil were identified in only ten of the borings at a thickness equal to or less than 2 feet (0.61 meters). The fill was encountered either beneath the topsoil or at the ground surface in approximately one third of the borings and varied in thickness from approximately 1.1 feet (0.34 meters) to 9 feet (2.74 meters). Beneath the topsoil and fill, native soil was encountered throughout the remaining sampled intervals. The native soils were visually classified as brown silty sand with varying amounts of clay and gravel-size rock fragments and described as moist to dry and medium dense to very dense. Bedrock was not encountered in any of the borings. However, one test boring, 310B3, did encounter weathered bedrock (brecchia) at a depth of 4.0 feet (1.22 meters).

3.4 Groundwater

Water levels were typically recorded immediately after drilling “0-hour” and after one-day “24-hour”.

Groundwater was generally encountered at depths greater than 11.5 feet (3.5 meters). Groundwater elevations generally ranged from 134 feet (41 meters) msl to 164 feet (50 meters) msl.

Two test borings (304B2 and 304B3) encountered groundwater at a depth less than one meter from the ground surface; however, these measurements are believed to have been affected by a nearby leaking water line and are not considered indicative of the groundwater table.

Water level measurements have been made in the test borings at the times and under the conditions indicated herein. It should be noted that ground water levels might fluctuate due to variations in season, rainfall, temperature, site grading and other factors not evident at the times these measurements were made.

Refer to the test boring logs (Attachment 4) and the groundwater summary table (Table 2) for detailed information on the groundwater measurements recorded in the test borings during the subsurface investigation program.

3.5 Test Pits

Ten test pits, including 5 tests pits to investigate new pavement areas and 5 test pits to investigate new sewer lines, were competed during this field exploration program. One additional test pit was excavated to perform percolation testing. Test pits were excavated in general accordance with applicable portions of ASTM D 2488 and ASTM D 5434. Test pits were generally advanced to a depth of 4.5 to 5 feet (1.37 to

1.52 meters) below existing ground surface for the pavement areas and the proposed sewage system. A Michael Baker representative was present during the test pit excavations to observe and log each test pit and monitor bulk soil sample collection for subsequent laboratory testing. Visual classifications of the test pit soils included a 1.0 to 2.5 foot (0.30 to 0.76 meters) thick layer of fill described as brown silty sand and silty gravel underlain by native soil described as silty sand, sandy silt, and sandy clay. No

Camp Santiago Facility Restoration 6 groundwater was observed in any of the test pits. The detailed pits logs prepared by Michael Baker are presented in Attachment 4 A summary of the test borings is presented in Table 1.

3.6 Soil Percolation Field Tests

The percolation test was performed in accordance with Regulations for the Control of Underground Injection, Appendix A, Section E, Puerto Rico Environmental Quality Board (“Reglamento para el Control de la Inyección Subterránea, Apéndice A, Sección E, Junta de Calidad Ambiental de Puerto Rico” in Spanish), September 14, 1983. The procedure requires an excavation of 1-foot-wide by 1-foot-long by 2-feet-deep. Testing is started by filling the excavation with water; after allowing for the soil to saturate, the test is made by refilling the hole with a column of water of 1-foot depth. The rate of water level drop is measured by keeping a record of elapsed time and the corresponding relative water level from fixed reference for the last 6 inches of water in the test hole. The result of the percolation test is presented as the average time of the column of water to drop 1 inch (average of the last 6 inches). The recorded percolation at the site is 60 minutes per inch. The results of field percolation tests are presented in Attachment 4.

3.7 Soil Resistivity Field Tests

Soil resistivity is a measure of how much the soil resists or conducts electric current. Four (4) resistivity tests with four (4) different pin spacings were conducted on four unique samples at the site. Total resistivity measurements ranged from 16,844 to 61,253 ohm-cm. The results of field resistivity tests are presented in Attachment 4 and a summary of the test results are presented in Table 3.

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4.0 LABORATORY TESTING

Laboratory testing was performed by Jaca & Sierra Testing Laboratories, a USACE validated geotechnical testing laboratory. The laboratory tests were performed on representative samples collected from the test borings and test pits; the type and number of tests selected were dependent upon field conditions and materials encountered during the field investigation. The laboratory testing was performed in general accordance with the test methods listed below. Detailed laboratory test results from Jaca & Sierra are included in Attachment 5. Summary tables of the laboratory test results are included in Tables 4 through 11.

Testing included the following:

103 moisture content and soil classifications - ASTM D 2216, ASTM D422 & D4318 30 visual manual description of soil - ASTM D 2488 10 modified Proctors - ASTM D 1557 Procedure C 10 California bearing ratio tests - ASTM D 1883/1557 10 organic content tests - ASTM D 2974 6 unit weights - ASTM D 2216 10 chloride and sulfate tests - USEPA SW-846 6010B 6 carbonate content of soil tests - ASTM D4373 6 collapsible potential of soil tests - ASTM D 5333 5 soil pH tests - SW846 9045C 5 soil tests for the parameters Boron, Calcium, Copper, Iron, Magnesium, Manganese, Phosphorus, Potassium and Zinc - SW846 6010/3051 5 total solids test - S2540G

Testing of rock was not performed because rock was not encountered during execution of the geotechnical test boring drilling program.

4.1 Soil Classification and Moisture Content

Moisture contents of the selected soil samples ranged from 2% to 21%; however, the moisture content was generally 12% or less. Laboratory soil classification were provided in general accordance with USCS;

descriptions of the selected soil samples were predominately silty sand (SM). The remaining soil sample classifications (at a much lower frequency of occurrence) included silty, clayey sand (SC-SM), clayey sand (SC), sandy lean clay (CL), and sandy silt (ML). The visual classifications provided by Jaca & Sierra were predominately silty sand (SM). See Table 4 for the soil classification and moisture content testing results.

4.2 Modified Proctor

The Modified Proctor test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density for a given energy departed to the soil. Maximum dry density ranged from 105.9 pound per cubic foot (pcf) to

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131.0 pcf. Optimum moisture content of the site soils ranged from 8.7% to 16.3%. See Table 5 for the Modified Proctor testing results.

4.3 California Bearing Ratio

The California Bearing Ratio (CBR) test is a penetration test for evaluation of the mechanical strength of natural ground, subgrades and base courses. A three-point CBR test was performed on bulk samples that were collected from test pits at Camp Santiago. Compaction efforts are reported for 95% and 100% compaction for each sample. For the 95% compaction effort, CBR values ranged from 2 to 18; for the 100% compaction effort, CBR values ranged from 3 to 30. See Table 6 for the CBR test results.

4.4 Unit Weights

Dry densities for the laboratory tested bulk samples ranged from 82.3 to 95.5 pcf. See Table 11 for the unit weight test results.

4.5 Soil Chemistry

Soil chemistry testing was performed in accordance with the Work Plan dated January 2020. Results are as follows:

Total solids ranged from 87.6% to 93.1%;

Total Phosphorus ranged from 59.6% to 314%;

Boron ranged from 82.7 milligrams per kilogram (mg/kg) to 110 mg/kg;

Calcium ranged from 17,418 mg/kg to 91,902 mg/kg;

Copper ranged from 33.1 mg/kg to 109 mg/kg;

Iron ranged from 26,317 mg/kg to 38,505 mg/kg;

Magnesium ranged from 9,168 mg/kg to 41,829 mg/kg;

Manganese ranged from 449 mg/kg to 663 mg/kg;

Potassium ranged from 722 mg/kg to 2,649 mg/kg;

Zinc ranged from 46.2 mg/kg to 73.7 mg/kg;

Chloride ranged from 24.6 mg/kg to 1,300 mg/kg;

Sulfate ranged from 12.3 mg/kg to 581 mg/kg;

pH (in water) ranged from 7.3 to 7.9; and pH (in calcium chloride) ranged from 7.1 to 7.8.

See Table 7 for the soil chemistry test results.

4.6 Organic Content

The Organic content in the site soils ranged from 3.5% to 8.3%. See Table 8 for the organic content test results.

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4.7 Carbonate Content

Carbonate content was reported as calcite equivalents ranging from 1% to 31%. See Table 9 for the carbonate content test results.

4.8 Soil Collapse Potential

Collapsible potential of soil testing presented the strain and void ratios of the soil samples versus the applied stress trials. Collapse potential of the site soils was considered as the change in void ratio upon wetting per UFC 3-220-10 Figure 6; this change in void ratio was observed at an applied stress of 2 tons per square foot (tsf) in all the soil samples. The collapse potential of the laboratory tested soils ranged from 0.1 to 3.3 percent. See Table 10 for the collapsible potential of soil test results.

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5.0 ANALYSES

5.1 Development of Soil Parameters

Soil parameters used in the analyses, including moist and saturated unit weight, effective friction angle, and effective cohesion, were developed for the native soils based on the laboratory testing and published correlations with test boring SPT blow counts from the EM 1110-2-2504, 1994.

The subgrade modulus was estimated based on guidance provided by the US Army Corps of Engineers Manual TM 5-809-12, Concrete Floor Slabs on Grade Subjected to Heavy Loads dated August 1987.

Lateral earth pressures coefficients (Ka, Ko, Kp) were estimated from Rankine's theory. These values are estimated for horizontal soil surfaces only. Deviations from horizontal will change the earth pressure coefficients.

The soil design parameter development calculations are provided in Attachment 6.

5.2 Collapsible Soils

Based on the laboratory tests performed, the severity of the potential issues in regard to collapsible soils ranges from “no problem” to moderate trouble” based on UFC 3-220-10N Figure 6 presented in Attachment 6.

According to UFC 3-220-10N, collapsing soils are distinguished by their potential to undergo large decrease in volume upon increase in moisture content even without increase in external loads. Examples of soils exhibiting this behavior are loess, weakly cemented sands and silts where cementing agent is soluble (e.g., soluble gypsum, halite, etc.) and certain granite residual soils; a common feature of collapsible soils is the loose bulky grains held together by capillary stresses. Deposits of collapsible soils are usually associated with regions of moisture deficiency. The site soils were not visually described as cemented and were generally medium dense to dense; therefore, the collapse potential of the site soils is assumed to be low.

5.3 Shallow Foundation Analysis

Shallow foundation analyses were conducted for:

strip footings for the DFAC and HQ structures, square footings for the Barracks Structures, and mat foundation for the canopy structure at HQ6.

Footing sizes for each structure type were based on the preferred footing shape, the provided loadings, the available bearing capacity of the site soils, and a maximum allowable settlement of 1.0 inch. See Table 13 for a summary of the shallow foundation calculations.

Depth to groundwater was conservatively assumed as the highest water level recorded across the borings drilled for each structure type.

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5.3.1 Bearing Capacity

As described in Section 3.2, shallow foundations at Camp Santiago will be founded on medium dense to dense silty sand. The soil parameters derived in the parameter development analysis (Section 5.1) were used to calculate allowable bearing capacity for each structure type. Ultimate bearing capacity was computed using the general bearing capacity equation and bearing capacity factors presented in the AASHTO LRFD Bridge Design Specifications, 9th Edition, 2020. A Factor of Safety of 3.0 was used to compute an allowable bearing capacity in accordance with UFC 3-220-01 Table 2-3. For load cases where extreme limit states were considered (i.e. seismic loading), a Factor of Safety of 2.0 was used to compute an allowable bearing capacity. This was based on general guidance in UFC 3-220-01 Table 2-3.

The detailed bearing capacity calculations are presented in Attachment 7. Please note that allowable bearing capacity is based on an equivalent uniform bearing pressure applied over the effective footing width. Where moments are imposed on a footing, foundation pressures are higher at one end of the footing and lower at the opposite end; it is permissible from a design standpoint to have foundation contact pressures at the footing toe that exceed the allowable bearing capacity determined as described above. Therefore, the maximum allowable foundation contact pressure at the toe of the footing was also calculated, where applicable, to provide additional design guidance.

Foundations were also checked for sliding resistance, using AASHTO (2020) Section 10.6.3.4 criteria and a minimum Factor of Safety of 1.5.

5.3.2 Settlement

The site soils are generally medium dense to dense silty sand; therefore, settlement is estimated to be primarily elastic. The elastic settlement for each structure was calculated using the Hough Method in accordance with AASHTO (2020). A representative soil boring for each structure type was considered in the analysis to determine a maximum estimated foundation settlement for the calculated bearing pressure imposed by the provided loadings, based on a minimum required footing size determined from the analyses. Design footing sizes were increased, if necessary, to maintain estimated foundation settlements within the 1.0-inch threshold. The detailed settlement calculations can be found in Attachment 7.

5.4 Deep Foundation Analysis

Due to the 23.4-kip net uplift load at the HQ5 structures, shallow foundations are not feasible; therefore, 12-inch outside diameter pipe piles were considered for the HQ5 foundations. Pile axial and lateral capacity calculations are provided in Attachment 8. See Table 13 for a summary of the deep foundation calculations.

5.4.1 Axial Pile Capacity

Axial capacity of the pipe piles was calculated using AASHTO (2020) methodology. A Factor of Safety of

3.0 was applied, assuming that load testing would not be performed for construction control, in accordance with UFC 3-220-01 Table 2-3.

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Per AASHTO (1995) for driven piles subject to uplift load, the nominal uplift capacity was taken as 70% of the total side friction calculated for axial compression. A Factor of Safety of 2.0 was used to calculate allowable uplift capacity, considering the uplift loading is due to wind, in accordance with IBC (2012) Section 1810.3.3.1.5.

5.4.2 Lateral Pile Capacity

A laterally loaded pile analysis was performed using LPile 2018 to the determine maximum pile head deflection of the proposed pipe pile. The analysis was based on available subsurface data, including subsurface conditions encountered in the HQ5 borings and the following design assumptions:

• Top of Pile is at El. 50 meters-msl;

• Soil overburden above the water table can be modeled as Reese Sand with an average unit weight of 120 pcf, a friction angle of 30 degrees, and a k value of 90 pounds per cubic inch (pci);

• Soil overburden below the water table can be modeled as Reese Sand with an average unit weight of 62.6 pcf, a friction angle of 30 degrees, and a k value of 60 pci;

• Groundwater table is at El. 36 meters-msl;

• Cyclic loading with 5000 cycles of loading;

• Maximum service loading considered;

• Loading evenly distributed across 4 piles;

• Minimum pile spacing of 3 pile diameters;

• P-Multiplier of 0.4 applied to account for lateral group effects;

• Pinned head condition (conservative).

Pushover Analysis

To provide further design flexibility, a laterally loaded pile pushover analysis was completed to estimate the maximum lateral capacity per pile using LPile 2018, based on a maximum allowable pile head deflection of 0.50 inches. The pushover analysis was performed considering the maximum axial loading and lateral group effects; two separate analyses were conducted, considering configurations with 5 pile diameter spacing and with 3 pile diameter spacing.

5.5 Liquefaction Susceptibility Analysis

Liquefaction susceptibility analyses were completed for all of the test borings to account for the variability in the SPT N-Values and groundwater readings. Sands above the water-table or with SPT N- Values greater than 30 are classified as non-liquefiable per Youd et. al (2001); therefore, the initial screening process to identify potentially liquefiable soils at the site was completed by selecting all test borings with SPT N-Values less than 30 blows per foot (bpf) below the design groundwater table.

Design groundwater tables to be used in liquefaction susceptibility analyses were developed for each of the northwest, central, and southeast portions of the site and were determined based on the shallowest groundwater reading recorded in the test borings drilled for each designated area. See Table 15 for the groundwater depths considered in the liquefaction analyses.

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Peak ground acceleration design parameters to be used in liquefaction susceptibility analyses, presented in Section 6.1.3, were developed in accordance with ASCE 7-16 based on earthquake ground motions that correlate to a probability of ground motion exceedance equal to 2% in 50 years. A site adjusted peak ground surface acceleration (PGAM) of 0.489g was used in the liquefaction susceptibility analysis. Due to the lack of Deaggregation data for Puerto Rico, the design earthquake magnitude (Mw) considered in the analysis was selected to be in the range of 7.7 (the maximum recorded earthquake in the past century within 250 km of the site) and 6.5 (an estimated mean design earthquake magnitude).

Please note that the mean design earthquake magnitude was estimated based on historical earthquake mapping from the USGS Earthquake Catalog tool as presented in Attachment 9.

The liquefaction analysis was performed in accordance with the simplified procedure established in Youd et. al. 2001 and complemented by Cetin et al 2009. Liquefaction potential at the site is considered low when the capacity to demand ratio is calculated higher than 1.3, medium when calculated between 1.1 and 1.3, and high when calculated at 1.1 or lower. Shear wave velocity in the soil was assumed to be 175 m/s (575 feet per second) based on typical shear wave velocity considered for site class D in the AASHTO table 3.10.3.1-1 for this analysis.

The liquefaction susceptibility analysis indicated that liquefaction potential is high in three isolated areas at the project site;

HQ Building 444 (boring 444B1) from 13.5 to 19.5 feet below ground surface (ft-bgs);

DFAC Building 302 (boring 302B1) from 13.5 to 19.5 feet-bgs; and Barracks Building 454 (boring 454B3) from 13.5 to 16.5 feet-bgs.

The soil settlements due to seismic-induced liquefaction calculated considering the maximum design earthquake, Magnitude 7.7, were estimated to be approximately 1.3 inches at Building 444, 1.1 inches at Building 302, and 0.5 inches at Building 454. The soil settlements due to seismic-induced liquefaction calculated considering the estimated mean design earthquake, Magnitude 6.5, were estimated to be approximately 1.3 inches at Building 444, 0.6 inches at Building 302, and 0.0 inches at Building 454.

Building 458 (boring 458B3) was considered to have a medium liquefaction potential considering the maximum design earthquake; potential liquefaction induced settlements at this building were minimal at less than 0.4 inches. All other buildings at the site were determined to have low potential for liquefaction (considering the maximum design earthquake) based on the available filed data and are not subject to liquefaction induced settlements.

Due to the limited depth of the borings, liquefaction potential was only able to be analyzed to an approximate depth of 19.5 feet-bgs. Since the liquefiable layers identified in borings 302B1 and 444B1 were located at the bottom of the sampling interval, it is possible that the potential liquefaction induced settlements could be greater than what the analysis suggests. In general, blow counts did increase with depth across the site. Deeper site soils (deeper than 20 feet) were encountered at test boring 306B1;

however, the subsurface condition at test boring 306B1 was generally more dense (i.e. less susceptible to liquefaction) than borings 302B1 and 444B1 and may not be indicative of the subsurface conditions below 19.5 feet at borings 302B1 and 444B1.

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See Table 15 for a summary of the liquefaction analyses. See Attachment 9 for the detailed liquefaction calculations.

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6.0 RECOMMENDATIONS

Based on the subsurface conditions encountered at the time of the field investigation, Michael Baker provides the following recommendations for the proposed buildings and pavement areas.

6.1 Parameters

6.1.1 Soil Design Parameters

Barracks Structures, HQ Structures, and HQ5 Structures

• Cohesionless Soils (silty SAND)

• Effective Friction Angle (ɸ) = 30 degrees

• Moist Unit Weight = 120 pcf

• Effective Cohesion = 0 psf

• Active Earth Pressure coefficient, Ka = 0.33

• At-Rest Earth Pressure coefficient, K0 = 0.50

• Passive Earth Pressure coefficient, Kp = 3.00

DFAC Structures and Canopy Structure at HQ6

• Cohesionless Soils (silty SAND)

• Effective Friction Angle (ɸ) = 32 degrees

• Moist Unit Weight = 120 pcf

• Effective Cohesion = 0 psf

• Ka = 0.31

• K0 = 0.47

• Kp = 3.25

6.1.2 Corrosion Potential

The following criteria, obtained from AASHTO (2020) (Article 10.7.5), is considered as indicative of potential pile deterioration or a corrosive environment.

Resistivity less than 2,000 ohm-cm, pH less than 5.5, pH between 5.5 and 8.5 in soils with high organic content, Sulfate concentrations greater than 1,000 ppm, Landfills and cinder fills, Soils subject to mine or industrial drainage, The chemical analysis and field resistivity test results indicate that the site does not present a corrosive environment.

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6.1.3 Seismic Parameters

Using the OSHPD Seismic Design Maps web application, detailed summary reports were generated that provide earthquake ground motion parameters for designing structures in accordance with ASCE 7-16.

The short term and one second spectral response accelerations obtained from OSHPD were confirmed using ASCE 7-16 Figure 22-6, which is based on a target risk of structural collapse equal to 1% in 50 years.

The Maximum Considered Earthquake Geometric Mean (MCEG) PGA was confirmed using ASCE 7-16 Figure 22-12, which is based on a probability of ground motion exceedance equal to 2% in 50 years.

Based on the test boring data, the depth to the top of rock is generally greater than 60 feet at the site.

The site is classified as Site Class D by its soil stiffness as identified by the SPT blow counts in accordance ASCE 7-16.

The mapped acceleration parameters for the project, according to standard, ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, are presented below:

Site Class D – Stiff Soil (based on a weighted average of the N values of the upper 100 feet of soil at 444B1 - see Attachment 9 for the full calculation)

Risk Category IV (based on IBC 2018 Table 1604.5) Maximum Considered Earthquake Geometric Mean (MCEG) Spectral Response Acceleration for peak ground acceleration, PGAM, for a probability of ground motion exceedance equal to 2% in 50 years:

o Peak ground acceleration (PGA) is 0.375g (ASCE 7-16 Figure 22-12) o Site coefficient based on site class for peak ground acceleration (FPGA) = 1.225 (ASCE 7-

16 Table 11.8-1) o PGAM = 0.459g (ASCE 7-16 Eqn 11.8-1)

Maximum Considered Earthquake (MCER) Spectral Response Acceleration for short periods, SMS, for a target risk of structural collapse equal to 1% in 50 years based upon a generic structural fragility:

o Mapped spectral acceleration (short period, 0.2 seconds), SS, is 0.937g (ASCE 7-16 Figure 22-6) o Site coefficient based on site class for short periods (Fa) = 1.125 (ASCE 7-16 Table 11.4-1) o SMS = 1.054g (ASCE 7-16 Eqn 11.4-1) o SDS = 0.703g (design spectral response acceleration parameter) (ASCE 7-16 Equation

11.4-3) MCER Spectral Response Acceleration for 1-second periods, SM1, for a target risk of structural collapse equal to 1% in 50 years based upon a generic structural fragility:

o Mapped spectral acceleration (1-second period), S1, is 0.353g (ASCE 7-16 Figure 22-6) o Since S1 is greater than 0.2g, the parameters provided below are only valid if the seismic response coefficient (Cs) is determined in accordance with ASCE 7-16 Section 11.4.8, otherwise a ground motion hazard analysis will need to be performed.

Site coefficient based on site class for 1-second periods (Fv) = 1.95 (ASCE 7-16

Table 11.4-2) SM1 = 0.690 (ASCE 7-16 Eqn 11.4-2)

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SD1 = 0.459 (design spectral response acceleration parameter) (ASCE 7-16 Eqn 11.4-4)

6.2 Collapsible Soils

Based on the laboratory tests performed, the severity of the potential issues in regard to collapsible soils at the site ranges from “no problem” to “moderate trouble” based on UFC 3-220-10N Figure 6. In general, the collapse potential of the site soils is considered to be low.

6.3 Shallow Foundations

A Declaration of Soil Bearing Capacity certification is provided in Attachment 7; however, it needs to be emphasized that the allowable soil bearing capacities calculated for each proposed structure type (i.e.

Barracks, DFAC HQ, HQ5, and the Canopy at HQ6) at this site is a function of, among other things, the recommended minimum shallow foundation dimensions, which varies across the proposed structures.

Accordingly, the Shallow Foundation Recommendations Summary Table (Table 13) is to be considered the most accurate information with respect to allowable soil bearing capacity and shallow foundation design guidance for this project.

A summary of the shallow foundation recommendations for each structure is provided in Table 13 and discussed below.

6.3.1 Barracks Structures

Spread footings bearing on soil are recommended to support the Barracks structures. Based on the provided loading, the recommended minimum footing size for the Barracks structures are 8 feet by 8 feet; with the exception of Barracks Buildings 458 and 460, where minimum footing sizes of 9 feet by 9 feet are recommended to maintain estimated foundation settlements at 1 inch maximum. All footings should be placed a minimum of 36 inches below finished grade to provide adequate bearing capacity and sliding resistance. Maximum settlement is estimated at 1.0 inch for Barracks Buildings 458 and 460, and

0.8 inches at all other Barracks buildings.

6.3.2 HQ Structures

HQ Buildings 306 to 330

Strip footings bearing on medium dense to dense silty sand are recommended to support the HQ structure Buildings 306 to 330. Based on the provided loading, the minimum recommended footing width is 5.5 feet. All footings should be placed a minimum of 36 inches below finished grade to provide adequate bearing capacity and sliding resistance. Maximum settlement is estimated at 0.8 inches.

HQ Buildings 440 to 446

Strip footings bearing on medium dense to dense silty sand are recommended to support the HQ structure Buildings 440 to 446. Due to lower average blow count soils (N<25) and increased settlement susceptibility at the location of these HQ structures, wider/deeper strip footings are recommended to

Camp Santiago Facility Restoration 18 maintain estimated foundation settlements at 1 inch maximum. Based on the provided loading, the minimum recommended footing width is 9 feet for a footing embedment of 48 inches, or 8 feet for a footing embedment of 60 inches. As indicated, maximum settlement is estimated at 1.0 inch for these strip footing options.

As an alternative to the large strip footing sizes indicated above, 12” diameter pipe piles, similar to those recommended for foundation support at the HQ5 structures (refer to Section 6.4, below), could be considered for bearing support of the foundations at HQ Buildings 440 to 446. However, for HQ Building 444, where liquefaction potential is high, additional analyses would need to be performed as part of the deep foundation design to assess the strength loss due to liquefaction and the ability of the piles to resist the settlement and potential downdrag forces caused by liquefaction.

6.3.3 DFAC Structures

Strip footings bearing on medium dense to dense silty sand are recommended to support the DFAC Structures. Based on the provided loading, the minimum recommended footing width is 4.5 feet. All footings at these structures should be placed a minimum of 36 inches below finished grade to provide adequate bearing capacity and sliding resistance. Maximum settlement is expected to be 0.9 inches.

6.3.4 Canopy Structure at HQ6

A mat foundation bearing on medium dense to dense silty sand is recommended to support the Canopy Structures at HQ6. Based on the provided drawings, the size of the mat is approximately 13.5 feet wide by 37 feet long. The proposed mat should be placed a minimum of 36 inches below finished grade.

Maximum settlement is estimated to be negligible (less than o.1 inches) for the proposed mat foundation at this structure.

6.4 Deep Foundations

Referring to the discussion in Section 5.4, the recommended foundation type for the HQ5 structures is driven pipe piles. Based on the provided loading, Michael Baker recommends a minimum of four (4) 12-inch outside diameter steel pipe piles for the most heavily loaded foundations, spaced at a minimum of 3 pile diameters (36 inches) center to center. Minimum pile lengths of 20 feet are recommended. The recommended minimum steel pipe wall thickness is 0.375 inches.

Different pile configurations can be considered at these structures, using the following criteria:

Minimum 12-inch outside diameter, 0.375-inch wall thickness steel pipe piles Minimum pile length of 20 feet Allowable geotechnical axial compressive capacity of 40 kips per pile.

Allowable uplift capacity of 12 kips per pile.

Based on a maximum pile head deflection of 0.5 inches, the maximum allowable shear loads are as follows:

o 11 kips per pile, based on a minimum spacing of 5 pile diameters (60 inches) o 6.7 kips per pile, based on a minimum spacing of 3 pile diameters (36 inches)

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A drivability analysis was not performed for the proposed deep foundations; however,…