AMEND_0003_Attachment K - Final Geotechnical Report and Soil Sampling Report.pdf

Base San Juan Hurricane Rebuild West and Central Locations

Project No. 10878158 USCG Base San Juan, PR

Attachment K Sector San Juan Final Geotechnical Report April 12, 2019

USCG Sector San Juan and Comunidad Rio Bayamón

San Juan, PR

Sector San Juan & Comunidad Rio Bayamón, PR DD1391 PP/PPR Alternative Development Report

U.S. DEPARTMENT OF HOMELAND SECURITY

U.S. COAST GUARD

ORDER NUMBER 70Z04718FPSJPAE00

CONTRACT NUMBER 70Z05018DAECOMT06

Sector San Juan Final Geotechnical Report April 12, 2019

ARCHITECTURAL/ENGINEERING SERVICES

FOR

DD1391 PLANNING PROPOSAL/PROJECT PROPOSAL REPORT

FOR

HURRICANE EXECUTION PLAN - SHORE

AT

U.S. COAST GUARD SECTOR SAN JUAN

SAN JUAN, PUERTO RICO

CG SFRL P/N 07-11062507

DESPIAU ASSOCIATES

CONSULTING GEOTECHNICAL ENGINEERS

Preliminary Report Geotechnical Engineering and Subsoil Exploration for USCG San Juan Station Facilities, at Old San Juan Ward of the Municipality of San Juan, Puerto Rico - Project No. 60588321

Reference No. DA/18O3786

Prepared for:

AECOM TECHNICAL SERVICES, INC.

4840 Cox Road

Glen Allen, VA 230060

Jose R. Despiau, P.E., License #17343 Geotechnical Engineer, Despiau Associates – Consulting Geotechnical Engineers.

Table of Contents Page

I. INTRODUCTION

II. SITE DESCRIPTION

III. SUBSURFACE IINVESTIGATION AND SAMPLING PROGRAM

IV. SURFACE SOIL DESCRIOTION AND GEOLOGICAL MAPPING

4.1 Surface Soils

4.2 Geological Notes

4.3 Stratigraphic Units

4.3.1 Fill Deposits

4.3.2 Swamp Deposits

4.3.3 Silica Sands and Older Alluvial Deposits

4.4 Groundwater Levels

V. SEISMIC ANALYSIS

5.1 Liquefaction Hazards

5.2. Soil Grading and Density

5.3 Groundwater

5.4 Seismic Design Parameters

5.5 Liquefaction Potential Analysis

5.5.1 Earthquake‐Induced Settlement

5.5.2 Seismic Strength Loss

5.5.4 Earthquake‐Induced Lateral Spreading and Flow Failures

5.6 Liquefaction Assessments

VI. PRELIMINARY ENGINEERING RECOMMENDATIONS

6.1 Engineering Assessments

6.2 Deep Foundation Alternative Using Drilled Pier Foundations

6.2.1 Pile Types and Capacities

6.2.2 Additional Drilled Shaft Recommendations

6.2.3 Lateral Load Design Considerations

6.2.4 Negative Skin Friction and Filling Considerations

6.2.5 Building Floor Slab Using Pile Foundation Solution

6.2.6 Pile Installation Monitoring Program

6.3 Rammed Aggregate Piers (RAP) – Impact Geopier System

Table of Contents - Continue

Page

6.3.1 Rammed Aggregate Piers Foundation Recommendations

6.3.2 Settlement Considerations for Shallow Foundations

6.3.3 Additional Rammed Aggregate Pier Considerations

6.4 Additional Foundations Considerations

6.5 Groundwater Considerations

6.6 Deep Excavation Supporting Systems

6.6.1 Additional Considerations for Deep Excavation Supporting Systems

6.7 Pavements

6.8 Nearby Structures

6.8.1 Additional Considerations for control of Vibrations for Nearby Structures

6.8.2 Settlement Monitoring

6.9 General Earthwork Recommendations

6.9.1 Excavations

4.9.2 Excavation Dewatering

6.9.3 Temporary Cut Sections

6.9.4 Backfill Material

6.9.5 Demolition

6.10 Proposed Storm Water Run-off Control

6.11 Additional Recommendations

V. LIMITATIONS OF THIS REPORT

Appendix (A) – Figures

1. US Geological Survey Service Topographical plan at a scale 1:20,000 1A. Geological Map

2. Boring Location Plan

Appendix (B) - Boring Logs

Appendix (C) - Special Laboratory Tests

Appendix (D) - Fill Specifications

Appendix (E) – Liquefaction Analysis

Appendix (F) – Borings Subsurface Utility Survey Daily Report

Appendix (G) – Photographs

I. INTRODUCTION

This report covers the Preliminary Subsoil Exploration and Geotechnical Engineering Services for the Proposed Hurricane Execution Plan for U.S. Coast Guard (USCG) Station Facilities, at San Juan

Antiguo Ward of the Municipality of San Juan, Puerto Rico.

The work was undertaken at the request of Mr. Patrick Price of AECOM Technical Services, Inc., Project Consultants for Project No. 60588321 of Prime Contract: 70Z501AECOMT06, between

AECOM Technical Services and Despiau Associates. The work was made in accordance to

Proposal No. DA/07-09-18RR for the subsurface exploration dated October11, 2018. The work was commenced after the Contract Acceptance Sheet and order to proceed for the work was received on November 29, 2018.

This report presents the results of the field exploratory drilling, laboratory tests performed on secured soil samples, engineering analyses, summary of findings, and preliminary foundation recommendations to assist the A/E design team in the conceptual design, preparation of cost estimates, environmental site assessment, to be used as part of the Hurricane Execution Plan for the USCG San Juan Station.

Reportedly, as part of this planning state it is required to analyze the need of any new construction, major renovations, and critical utilities to include increased resiliency in the site’s ability to remain operational during an event, or unscheduled outage, and the ability to return to full operation, independent of any local utility disruption for extended periods of time, or until the outage is over.

Among the requirements to be consider on the Hurricane Execution Plan is the evaluation of the following facilities:

1. New Health Services Building (Medical, Admin, CGIS)

2. New Engineering Support/Shops Building (Medical, Admin, CGIS)

3. New Operations Building (Command Staff, Sector Command Center, Sector Staff)

Sector San Juan & Comunidad Rio Bayamón, PR Page 2

The selected boring locations were used to establish the general profile data of the Site for the present preliminary geotechnical engineering review. This report has been prepared for the exclusive use of the Owner and the A/E Consultant Firm involved in the preparation of the site engineering design plans and specifications.

Originally, the herein geotechnical service included the performance of one (1) water boring to assess the subsoil conditions near the easternmost shore facilities. However, this was later eliminated not to disturb the ongoing activities of Navigation Team (ANT) San Juan. The reason being that at this preliminary planning stage it was better-off not affecting the ANT activities.

Nevertheless, should the proposed design scheme require new structures and/or any improvement to the shore facilities (i.e. piers), then a thorough investigation shall be performed during the final complementary geotechnical investigation to be performed for the final design.

It shall be noted the herein geotechnical assessment and recommendations are preliminary which are based on a limited number of exploratory borings. Once the final design scheme is determined, a final complementary geotechnical exploration which shall include additional exploratory borings, special laboratories and further evaluations, shall be performed for the finally selected structures to be developed at the Site.

II. SITE DESCRIPTION

The existing USCG San Juan Station Facilities are located southwest sector of Old San Juan island at the reclaimed lands of La Puntilla Headland at Old San Juan Ward, of the Municipality of San

Juan, Puerto Rico as identified in the submitted plans. Figure No. 1 of Appendix A show a portion of the USGS topographical map.

The site most prominent topographical feature of La Puntilla Headland is the Port of San Juan adjacent to San Juan Bay and west of San Antonio Channel. The project site is found inland and south of the U.S. Custom Office Facilities.

The site is on relatively flat lands which were originally reclaimed from the mangrove swamp area, Sector San Juan & Comunidad Rio Bayamón, PR Page 3 located between the San Antonio Channel and adjacent Isla Grande Airport and Old US Coast Guard

Military Reservations and Facilities, which comprise the lowlands south and eastern inland sectors of the southeast of La Puntilla Headland. The area was filled with mixture of sand, clay marl, and gravel and is identified as artificial fill (af) in published US Geological Survey Map of the San Juan

Quadrangle.

III. SUBSURFACE IINVESTIGATION AND SAMPLING PROGRAM

The subsurface soil conditions at the site were investigated seven (7) standard penetration test borings performed to assess the existing subsoil conditions at the site. Also, two (2) additional borings [E1 & E2] were performed for environmental purposes to 10 feet below the existing ground surface. However, NO environmental laboratories to chemically characterize the presence of any hazardous substances and/or petroleum products (i.e. VOCs, PCBs, PAHs, BTEX, and RCRA, etc..)

were performed. In lieu, all gathered samples were furnished to AECOM’s environmental personnel at the Site following all Change of Custody Protocols. The location of borings is shown in the accompanying Boring Location Plans, in Appendix A, Figure No. 2 at the end of this report.

The borings were staked out at the field using handheld GPS (3.0 mts. accuracy), then a Subsurface

Utility Clearance Survey was performed at all nine (9) boring locations. A quality level B was used for this project. Quality B level, identifies underground assets by means of diverse forms of induction, including but not limited to sound and electromagnetic induction, and ground penetration radar. The

Borings Subsurface Utility Survey Daily Reports are included in Appendix (F) of this report.

Sampling of soils was performed continuously in the upper 10 ft. and thereafter, at approximately five-foot intervals. All soil samples were taken with a 2"-O.D. split barrel sampler following the standard penetration test procedures in ASTM D-1586, D-1552, & D-2113. Penetration resistance values from the standard penetration tests are recorded in the "N" column of the boring logs. Also, during drilling operations, visual inspection for sheen or discoloring and test for vapors using photoionization detection (PID) was performed. However, no detection by the PID was detected.

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The procedures used for the laboratory tests, as well as the routine and special laboratory procedures used, for the determination of the index soil properties are contained in the Appendix (B) to this report.

IV. SURFACE SOIL DESCRIOTION AND GEOLOGICAL MAPPING

4.1 Surface Soils

The US Soil Conservation Service Manual – Soil Survey of San Juan Area of Puerto Rico, Sheet #4, prepared by the Soil Conservation Service identifies the surface soils of the area as follows:

• Made Land (Md) – These consist of areas where the soil profile has been covered or destroyed by earthmoving operations. The areas generally have been graded for engineering purposes. In some areas the hazards that affect engineering uses have been overcome and the land type has been used as sites for dwelling and light industries.

4.2 Geological Notes

Based on available US Geological Survey Map I-1010, of the San Juan Quadrangle prepared by

Messrs. Maurice H. Pease, Jr. and Watson H. Monroe (1977), the units that outcrop at and in the site’s, vicinity are as follows:

• Artificial Fill (Holocene) (af) - Identified as sand, limestone, and volcanic rock as fill over valleys, and swamps.

• Alluvium (Holocene) (Qa) - Identified as sand, clay and sandy clay.

• Swamp deposits (Holocene) (Qs) - described as sandy muck and clayey sand, generally underlain by peat formed in mangrove swamps. Most of the areas now covered by artificial fills are underlain by swamp deposits.

• Eolianite (Holocene and Pleistocene) (Qe) - Identified as calcareous sandstone, well-cemented, crossbedded, composed of fine to coarse grains of shell fragments and quartz.

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• Beach Deposits (Holocene) (Qb) - Identified as sand composed of grains of quartz, volcanic rock and shell. It is found to the east at Escambrón Headland.

• Silica Sand Holocene (Qss) – Described quartz sand, very pure, derived from ferruginous sand by leaching. The deposits grade downward into older alluvial deposits (map unit QTt)

Silica sand and underlying parent material called Santurce Sand by Kaye (1959).

• Older Alluvial Fan Deposits (QTt) – Described as clay, silt and sand, mainly red or mottled red and light-.

4.3 Stratigraphic Units

4.3.1 Fill Deposits

The surface layers were described as fill layers of red, yellow, olive gray, dark grayish brown, mixture of silty clay and sandy silty clay with variable amounts of subangular gravel fragments with occasional few roots and peat with debris (i.e. brick and glass fragments). The upper fill layers extend to an average depth of 4.0 to 8.0 ft. The layers were found in a very loose to dense compacted state, with Standard Resistance to Penetration (N-values) varying from 2 to 47 blows/foot, where higher values correspond to the gravellier material. The natural moisture content varies from 5 to 38 percent.

Underneath the prominently silty sand and gravelly fill section, the lower fill section was found in a very loose to medium silty sand and silty clay with disseminated fibrous peat of old dredged material, used to reclaimed land at the site, as part of the dredging of the San Juan Harbor. These were found to extend to depths varying from 20 of 33 ft, at an average of 26.5 ft. The layers were found in a very loose to dense compacted state, with Standard Resistance to Penetration (N-values) varying from 2 to 25 blows/foot, where higher values correspond to the gravellier material. The natural moisture content varies from 5 to 38 percent.

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4.3.2 Swamp Deposits

Beneath and intercalated the above described layer, the swamp deposits were found in the dredged sandy muck compressible material, layers of silty clay, with some sand and with many shells and coral fragments with few peat inclusions was found varying in depth between 10 to 40.0 ft. in depth

[Borings 1, 2, 4, 5, & 7]. The standard penetration resistance values range from 0 (wh-weight of hammer was enough to drive sampler) to 13 blows/foot. The natural moisture content values range from 23 to 85 percent, where the higher values correspond to greater organic content values.

4.3.3 Silica Sands and Older Alluvial Deposits

It is followed by the virgin deposits of very pure quartz sand, deposits graded downward into Older

Alluvial Deposits described as silty clay with traces of sand in a very stiff to hard state of consistency.

It also includes calcareous sandstone, well-cemented, crossbedded, composed of fine to coarse grains of shell fragments and cemented quartz sand. The standard penetration resistance values range from 19 blows/foot to practical refusal to penetration with N-values in excess of 75 blows for a few inches of penetration [Boring 3 & 7]. The natural moisture content values range from 19 to 39 percent. The graphical representation of the soil profiles is found in the boring logs included as

Appendix (B) to this Report.

4.4 Groundwater Levels

At the Borings of exploration, the ground water level was initially found varying from 5.0 to 7.0 ft., upon completion of the borings, it was measured at an average of 6.0 ft.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. It is logical to expect variation of the groundwater level as they will be influenced by the adjacent bodies of water, San Juan Bay to the east and south. Consequently, groundwater levels during construction or at other times in the lifespan of the structures may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

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Therefore, dewatering might be necessary during the excavation phase of the project depending on the water levels of the adjacent body of water. All the depths were established after the boring were completed and were measured from the existing ground surface prevailing during the period of the field work.

V. SEISMIC ANALYSIS

5.1 Liquefaction Hazards

When cyclic loading occurs during an earthquake, loose non-cohesive materials (gravels, sands, silty-sands) tend to decrease in volume. This tendency to decrease in volume, is much greater in loose than dense soils. When loose non-cohesive soils are saturated and rapid loading occurs under undrained conditions, the soil densification causes excess pore water pressure to increase. The increase in pore water pressure results in a loss of soil strength due to a decrease in effective stress and eventually liquefaction occurs, once the effective stress drops to zero.

Liquefaction of loose sands can lead to large displacements of foundations, flow failures of slopes, ground surface settlement, sand boils, and post-earthquake stability failures.

For the present Liquefaction Potential Assessment three primary factors exist at the site.

These three factors identified below contribute to liquefaction potential.

1. Loose, uniformly graded soils.

2. High groundwater table (i.e. 6.0 ft.) and saturated soils.

3. Sufficiently high, earthquake induced ground acceleration and sustained shaking.

5.2. Soil Grading and Density

Liquefiable soils generally have a Coefficient of Uniformity of less than 5 and a low proportion of soil finer than 75 microns in size (typically less than 5% to 10% but up to 30%). Samples obtained from the performed exploration disclosed layers and lenses of loose sandy silt and silty sand beneath the upper surface layers to varying depth of 7 .0 to 25.0 ft. Laboratory Tests performed on samples from this horizon were assessed as being a uniformly graded fine sand or silty sand

Sector San Juan & Comunidad Rio Bayamón, PR Page 8 material with no or little apparent cohesion. Thus, based on our analysis, several layers between 7 and 30 ft. liquefiable.

5.3 Groundwater

At the Borings of exploration, the ground water level was initially found varying from 5.0 to 7.0 ft., upon completion of the borings, it was measured at an average of 6.0 ft. Although, it is likely that the groundwater levels will vary in elevation depending in the seasonal variations of the adjacent

San Juan Bay, for the liquefaction potential analyses the ground water level was established at 6.0

ft. as the water level observed during our site explorations.

5.4 Seismic Design Parameters

Based on our experience with the geology of the area, it is our opinion that the subsurface characteristics reflect those of Site Class E as described in International Building Code 2018 and the Puerto Rico Building Code 2016. The “Site Class” is a designation used by the 2018

International Building Code (IBC) (ICC 2018) to quantify ground motion amplification. The classification is based on the stiffness in the upper 100 feet of soil and bedrock materials at a site.

We performed a SPT Borings up to 80 feet in depth. Based on our exploratory borings and experiences at the Site’s vicinity analysis, we can assume the profile will be constant within the upper

100 feet. This information, without regard for liquefaction potential, leads us to classify the site as

Site Class E.

Our analyses have identified that a liquefaction hazard is present at the site. The IBC indicates that sites classified as Site Class D or E with S1 greater than 0.2 a site‐specific ground response analysis be completed to determine the response spectrum for design as per Section 11.4.8 of ASCE 7. We anticipate seismic design parameters may change if a site‐specific ground response analysis is completed; therefore, the parameters provided in the following Table, which presents the parameters obtained from the building code and the resulting values for SDS and SD1, should be considered preliminary.

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Preliminary Seismic Design Parameters

Parameter MCER Return Period 2,475 years

Site Class E Risk Category IV

Spectral Response Acceleration (Short Period), Ss 0.997 g Spectral Response Acceleration (1-Second Period), S1 0.398 g

Site Coefficient, Fa 1.3 Site Coefficient, Fv Null *

Modified Spectral Response Acceleration (Short Period), SMS 1.296 Modified Spectral Response Acceleration (1-Second Period), SM1 Null *

Spectral Response Acceleration (Short Period), SDS 1.864 g Spectral Response Acceleration (1-Second Period), SD1 Null *

NOTE: * Null – Refer to Section 11.4.8 of ASCE 7 for specific requirements.

5.5 Liquefaction Potential Analysis

We performed site‐specific liquefaction potential analysis on the soils underlying the site. The analysis was conducted using the data from the seven (7) SPT Borings performed. The ability of the subsoil to resist the effect of ground shaking associated for an earthquake of Magnitude 7.5 has been assessed. Several methods were used to assess the liquefaction potential using

NovoTech Software, Ltd. NOVO-LIQ computer program. The following methods are assessed in the program:

NCEER Workshop (1197) Boulanger & Idriss (2004) Vancouver Task Force (2007) Cetin el al (2004) Chinese Code Seed el al (1983) Tokimatsu & Yoshimi (1983) Kokusho el al (1983)

Based on Section 1613 – Earthquake Loads of the 2016 Puerto Rico Building Code, the liquefaction potential of the loose silty sand material within the profile was studied. The Peak Ground

Acceleration value of PGA = 0.31 was used, considering the distance to the Puerto Rico Trench

Fault alignment is approximately 171 km to the site. The engineering analysis and evaluations

Sector San Juan & Comunidad Rio Bayamón, PR Page 10 disclosed that the underlying sandy layers extending to about 25 ft. in depth [representative borings

1, 2, 3 & 5] show a low safety factor [<1.0] against liquefaction. “Liquefaction” is more apt to have effect on loose silty sands which are found beneath the groundwater level.

Also, liquefaction induced lateral spreading or flow failures can occur when the shear stresses required to maintain static equilibrium are greater than the shear strength of the liquefied soil.

Structures built on ground that experiences lateral spreading can be expected to sustain significant damage relative to the damage that would be expected from ground shaking alone.

5.5.1 Earthquake‐Induced Settlement

Post‐liquefaction settlement results from densification of liquefiable sandy soils and remolding of cyclically softened clay‐like soils following an earthquake. The permanent ground surface settlement is not typically uniform across the area and can result in significant differential settlement. Differential settlement will have the most significant effect on structures supported by shallow foundations.

We evaluated liquefaction with the SPT data collected. The deepest SPT Boring was 80 feet. Based on our evaluation, between 8 to 10.5 inches of settlement can be expected considering the subsurface profile.

5.5.2 Seismic Strength Loss

Our analyses indicate the soils at the site will weaken and exhibit significantly reduced shear strength during and after a major earthquake due to liquefaction and/or cyclic shear strength reduction. This will could potentially cause problems for structures at the site as the bearing capacity of shallow foundations could be significantly reduced during a major earthquake.

5.5.4 Earthquake‐Induced Lateral Spreading and Flow Failures

Lateral spreading occurs when large blocks of ground are displaced down gentle slopes or towards the free face of channels as a result of earthquake‐induced inertial forces acting on the soil mass.

Initiation of lateral spreading is often made worse when the soils within and beneath the soil mass liquefy or soften as a result of the shaking.

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Lateral spreading deformations can be experienced relatively far from a free face. Similar to lateral spread, flow failures result when large volumes of soil near the free face of channels, shores or ocean (i.e. San Juan Bay) bottoms displace vertically and laterally during or after earthquakes. As the ground begins to shake and the shearing resistance of liquefied soils decreases, ground displacement occurs in response to mainly static shear forces present within the soil mass and to a lesser extent earthquake‐induced inertial force. Flow failures typically manifest larger deformations than lateral spreading. Both lateral spreading and flow failures are destructive and pose a significant risk to the structures in their vicinity.

Preliminary evaluation reveals the predicted lateral spread deformations may be in excess of 9 feet.

It should be acknowledged that the methods used to predict the lateral displacements are empirical and therefore, the magnitude of lateral spreading may vary from that provided above.

5.6 Liquefaction Assessments

It is considered that the site is susceptible to varying degrees of seismically induced liquefaction in an earthquake event. The liquefaction potential of the loose sandy silty material beneath the existing modified fill section (4 ft. approximately) within the profile was studied. The engineering analysis and evaluations disclosed that the underlying silty sand with organic clay layers extending to about an average depth of 30 ft. in depth show a low (FS< 1) safety factor against liquefaction.

“Liquefaction” is more apt to have effect on loose silty sands which are found beneath the groundwater level. When the loose sandy silt material is subjected to sustained vibrations during an earthquake, these tend to lose the capacity. As the soil grain are separated and a “boiling effect”, under the progressive buildup of water pressure is produced by the seismic ground shaking.

This liquefaction potential is greatest when the loose silty sand layers are overlain by loose material as in this case.

Our liquefaction assessment and site observations indicate that the site is susceptible to liquefaction.

Therefore, liquefaction hazard mitigation will be required as part of the site development.

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VI. PRELIMINARY ENGINEERING RECOMMENDATIONS

6.1 Engineering Assessments

The present exploration disclosed an upper fill section mainly composed of silty clay and sandy silty clay with variable amounts of subangular gravel fragments with occasional few roots and peat and debris (i.e. bricks and glass fragments). The upper fill layers extend to an average depth of 4.0 to

9.0 ft.

Beneath and intercalated with the above described layer, the swamp deposits were found in the dredged sandy muck material, layers of silty clay, with some sand with many shells and coral fragments with few peat inclusions was found varying in depth between 10 to 40.0 ft.

Analysis made on the swampy sandy muck revealed it is highly compressible which can cause substantial total and differential settlements. Thus, to avoid a new consolidation cycle of the compressible layer found at the site NO ADDITIONAL FILL SECTION SHALL BE ALLOWED.

Neglecting this important factor, the of the Site engineering design would cause detrimental effects

(i.e. differential settlements) to existing structures to remain. Therefore, the use of shallow spread footings shall be avoided, unless they are constructed over deep foundations or over a soil improved soil by means of Rammed Aggregate Impact Piers or similar solution.

Deeper into the profile, the virgin deposits of very pure quartz sand, deposits graded downward into

Older Alluvial Deposits which indlude calcareous sandstone, well-cemented, crossbedded, composed of fine to coarse grains of shell fragments and cemented quartz sand.

As previously mentioned, the liquefaction potential of the loose silty sand material beneath the existing modified fill section within the profile was evaluated. The engineering analysis and evaluations disclosed that the underlying sandy layers extending from about 4.0 to 30 ft. in depth show a low safety factor against liquefaction. “Liquefaction” is more apt to have effect on loose silty sands which are found beneath the groundwater level. When the loose silty sand material is subjected to sustained vibrations during an earthquake, these tend to lose the capacity. As the soil grain are separated and a “boiling effect”, under the progressive buildup of water pressure is

Sector San Juan & Comunidad Rio Bayamón, PR Page 13 produced by the seismic ground shaking. This liquefaction potential is greatest when the loose silty sand layers are overlain by loose material as in this case.

Thus, any future structure planned (i.e. Health Service Building, Engineering Support/Shops

Building, Operations Building, etc..) at the project site shall consider the use of a deep or intermediate foundation solution to transmit the loads the loads of the structure to the underlying competent layers.

However, although it is likely that liquefaction will occur, there are engineering options that will minimize the potential for liquefaction induced ground damage such as intermediate or deep foundations. Therefore, any future structure planned (i.e. Health Service Building, Engineering

Support/Shops Building, Operations Building, etc..) at the project site shall consider the use of a deep or intermediate foundation solution to transmit the loads the loads of the structure to the underlying competent layers. Based on the preliminary subsoil exploration and geotechnical assessment performed, two (2) foundation alternatives can be considered for the new development.

These are the following:

1. Drilled Shafts (deep foundations), or

2. Spread Footings over Rammed Aggregate Impact Piers (intermediate foundation)

Thus, Drilled Shafts or Rammed Aggregate Piers shall be considered as the foundation type to be used for the proposed structures. These are required, to transmit the loads of the structures to the underlying very stiff to hard Older Alluvial Deposits.

Pre-cast driven piles SHALL NOT be considered for the project due to the nearby structures with unknown foundations. Moreover, induced vibration during pile driving operations may cause the same effects as earthquakes (liquefaction), therefore Pre-cast Piles shall be discarded.

In the following sections of this report, the preliminary foundation recommendations for the previously described foundation alternatives will be further discussed.

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6.2 Deep Foundation Alternative Using Drilled Pier Foundations

6.2.1 Pile Types and Capacities

Preliminarily, the use of 18-inch or 24-inch diameter Drilled Shafts may satisfactorily transmit the loads of the structure to the underlying competent layers. The following Tables presents a summary of the recommended pile types and minimum depth of embedment which shall be considered in the present evaluation. It shall be noted that the herein foundation recommendation are for evaluation and cost estimate purposes. Actual design capacities (Carrying and Tension) shall be provided in the final geotechnical evaluation once the final design scheme is determined.

SUMMARY OF DRILLED SHAFT FOUNDATION DESIGN PARAMETERS

(SECTOR COVERED BY BORINGS NO. 1 through 7)

Shaft Diameter (inches) * Length in ft., from existing surface

* Predicted Range of Capacities

18” inch diameter 50 to 60 ft. 30 - 60 tons 24” inch diameter 50 to 60 ft. 40 - 80 tons

*NOTE: Final Design Parameters (i.e. lengths and capacities) shall be provided once the final geotechnical evaluation is performed.

Since at this stage the final grading plans are not available, the predicted lengths of foundation units have been given from existing surface elevation, prevailing during the period of the field work. The actual lengths of deep foundation units shall be determined once the final design scheme is determined.

6.2.2 Additional Drilled Shaft Recommendations

The following recommendation shall also be considered.

1. It is predicted caving will occurred considered the subsurface profile and groundwater steel casing will be required to properly drill the piers prior to concrete placement.

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2. Groundwater should be removed from each pier hole prior to concrete placement. A dewatering system shall be installed which will permit proper excavation, inspection and concreting of each pier unit.

3. Pier concrete should be placed immediately after completion of drilling and cleaning. A tremie should be used for concrete placement. Free-fall concrete placement in piers will only be acceptable if the concrete is placed in a dry hole and provisions are taken to avoid striking the concrete on the sides of the hole or reinforcing steel. The use of a bottom-dump hopper, or an elephant's trunk discharging near the bottom of the hole where concrete segregation will be minimized, is recommended. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. The free unobstructed fall of concrete with a minimum slump of 2.5 in. produces adequate compaction up to the top 5 ft. of depth. Additional details are presented in ACI 336.3R-

72.

4. Casing should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent infiltration of water or caving soils or the creation of voids in pier concrete. Pier concrete should have a relatively high fluidity when placed in cased pier holes or through a tremie. Pier concrete with slump in the range of 5 to 7 inches is recommended.

5. If the center-to-center spacing of drilled shafts is less than 4 diameters, the interaction effects between adjacent shafts shall be evaluated. Adjacent shafts should bear at the same elevation. The capacity of individual piers must be reduced when considering the effects of group action. Capacity reduction is a function of pier spacing and the number of piers within a group.

6. If the center-to-center spacing of drilled shafts is less than 6 diameters, the sequence of construction should be specified in the contract documents. Larger spacing may be required to preserve shaft excavation stability or to prevent communication between shafts during excavation and concrete placement.

7. The project’s geotechnical engineer or approved representative shall observe the bearing

Sector San Juan & Comunidad Rio Bayamón, PR Page 16 surface and shaft configuration during construction.

6.2.3 Lateral Load Design Considerations

The following design model and in-situ soil parameters shall be used for lateral load evaluations of the drilled shafts sections being proposed.

Lateral load evaluations depend on the specific requirements of the structure. However, often, a 1/4-inch allowable lateral deflection is used as a limit. In no case, the lateral load shall exceed 0.33 the ultimate load capacity. The normally consolidated to slightly over consolidated cohesive as well as for granular soils, the pile deformation can be estimated assuming that the coefficient of sub grade reaction Kh, increases linearly with depth in accordance with the expression:

Kh = f * z / D

Where, Kh = coefficient of lateral subgrade reaction (tons/ft3) f = coefficient of variation of lateral subgrade reaction (tons/ft3) z = depth (ft.)

D = width/diameter of loaded area

The soil parameters to be used in the lateral pile design shall be provided in the final geotechnical report once the final design scheme is determined.

6.2.4 Negative Skin Friction and Filling Considerations

Since additional fill at the site is not predicted, the negative skin friction, if any, should be very small and an adequate allowance for residual settlements shall be considered in the design analyses. The final grading plans shall be submitted to this office to permit reevaluations of such important parameter in the pile foundation design.

Sector San Juan & Comunidad Rio Bayamón, PR Page 17

6.2.5 Building Floor Slab Using Pile Foundation Solution

The only way to provide a ground floor slab not affected by total and differential settlement is to structurally support it. Thus, considering the potential of future erosion due to tidal fluctuation and the expected wave surge at the project site, any ground floor slab shall be structurally design and supported with the previously recommended pile units.

6.2.6 Pile Installation Monitoring Program

Although the construction of the Drilled shafts may not induce greater vibration, considering the proximity to existing structures, the shaft installation shall assure minimum effects from vibrations caused by the installation method. The foundation contractor shall be solely and completely responsible for all injury, loss or damage resulting from foundation installation at the site. He should implement a vibration monitoring program to verify, at the start of and during installation operations, that no harmful vibrations reach nearby structures

6.3 Rammed Aggregate Piers (RAP) – Impact Geopier System

Another foundation solution to cope with the subsoil conditions at the Site is the use of rammed aggregate piers (i.e. Geopier System) is a ground-improvement process; these piers can provide a cost-effective alternative which has been substantially used for the last decade on projects where deep foundations or significant excavation and material replacement would previously have been required.

Although conventional, shallow foundations are often most cost-effective solution; in this project, the expected foundation loads coupled with weak soil conditions presents difficulties to cope with liquefiable soils and expected settlements.

Deep foundations provide an effective way to address the settlement issue but add significant cost to the project. On the other hand, the presented Impact Geopier alternative approach, is used to improve the subsurface soil conditions and allow the use of a shallow foundation solution for the

Sector San Juan & Comunidad Rio Bayamón, PR Page 18 proposed structures. The Impact System is an efficient and cost-effective intermediate foundation solution for the support of settlement-sensitive structures. The Impact Geopier System creates stiff

Rammed Aggregate Pier (RAP) elements using a patented vertical ramming process using a patented displacement mandrel. It can replace massive over excavation and replacement, and deep foundations piles.

Impact Geopier System uses a specially designed mandrel and tamper foot is driven into the ground using a strong static force augmented by dynamic vertical impact energy. Depths normally range from about 10 to 40 feet, depending on design requirements. A sacrificial cap prevents soil from entering the tamper foot and mandrel during driving. The process eliminates spoils (possibly contaminated) and displaces soils laterally, densifying, and reinforcing the existing soils.

After driving to design depth, the hollow mandrel serves as a conduit for aggregate placement.

Aggregate is placed inside the mandrel. The mandrel is then lifted approximately three feet and then driven back down two feet, forming a one-foot thick compacted lift. Compaction is achieved through static down force and dynamic vertical ramming from the hammer. The process densifies aggregate vertically and the patented beveled tamper foot forces aggregate laterally into cavity sidewalls. This results in soil improvement in excellent coupling with surrounding soils and reliable settlement control with superior strength and stiffness.

Following installation, the Rammed Aggregate Pier (RAP) elements support shallow foundations, floor slabs and reduce liquefaction potential and improve stability support of structures

(i.e. embankments, walls and power generation pads, etc..). The footing stresses are attracted to the stiff RAP elements, resulting in engineered settlement control.

Also, RAP elements with the addition of specially designed structural steel anchors, can resist uplift loads generated by earthquakes and wind.

6.3.1 Rammed Aggregate Piers Foundation Recommendations

The loads of the proposed structures shall be designed over 24” or 30”-inch diameter Impact Geopier elements. The number of RAP elements shall be a function of the design load required and shall

Sector San Juan & Comunidad Rio Bayamón, PR Page 19 consider the actual backfill thickness to establish the project final grading elevations and the expected loadings conditions.

Thus, the proposed structures can be founded over RAP elements, using a mat foundations or over spread footing, braced with a grade beam, following the herein recommendations.

The plan dimensions footings must be selected to develop full coverage of the RAP elements and to have a RAP area replacement ratio of at least 30%. The top level of the RAP units shall correspond to the bottom level of foundation. The design of the foundations for the proposed structure shall consider an allowable soil bearing pressures and stiffness modulus given in the following Table.

SUMMARY OF PRELIMINARY FOUNDATION RECOMMENDATIONS

(Final Design Parameters shall be provided once the final geotechnical evaluation is performed.)

Boring Numbers

Allowable Soil Bearing Pressure

(ksf.)

Stiffness

Modulus (pci.)

In-situ Soils Modulus of Subgrade

Reaction (lbs./sq-in./in) 1 through 7 3.0 ksf. 125 50

Note: The above parameters are valid, provided the underlying bearing soils are improved using Impact Pier (Geopier) foundation elements, which shall be drilled to a minimum depth indicated in the following section of this report.

Even though Geopier RAP elements are required for the structures planned, the effects of settlements on any ground floor slabs must be considered. The use of structurally supported ground floor slab shall be considered in the design.

However, in lieu to the structurally support the ground slabs, the same improvement approach of using RAP elements can be considered for which additional amount of RAP elements shall be required. RAP slab support is classified as either slab-on-grade or structural and depends on the actual fill thickness and RAP elements. A structural slab design is required when the slab must span the clear distance between RAP elements.

The RAP element length to be considered for the Proposed New Marine Facilities is being presented in the following Table. These depths correspond to the depth at which the residual and weathered rock material was found, measured from the existing surface elevation prevailing during the field

Sector San Juan & Comunidad Rio Bayamón, PR Page 20 work.

PRELIMNARY PREDICTED LENGTHS OF RAP ELEMENTS

Boring No. Structure Minimum Depth of RAP Foundation (ft.)

1 & 6 U.S.C.G. San Juan Station Buildings & Facilities 55 to 60 ft.

2 to 5 U.S.C.G. San Juan Station Buildings & Facilities 45 to 50 ft.

7 U.S.C.G. San Juan Station Buildings & Facilities 50 to 55 ft.

6.3.2 Settlement Considerations for Shallow Foundations

Under the soil improvement scheme using RAP elements presented in the previous section of this report, the expected settlements can be tolerated by the proposed structures. As required by the

RAP unit’s supplier’s the installation process shall be monitored by inspecting Soils Engineer or approved representative. The estimated and predictions of differential considering the Geopier support elements do not exceed 0.15 of an inch between adjacent supports of the structure.

6.3.3 Additional Rammed Aggregate Pier Considerations

To examine the performance of the Geopier system and ensure quality control, at least one (1) test

Geopier element shall be performed. Considering the subsoil data up-to-date, preliminary the location of Boring No. 1 may be used for the testing. The test pier shall be provided with a replicate of a footing. The modulus load test shall be performed to a stress not less than 150% of the maximum stress top of pier stress to obtain the maximum deflection and yielding at site-specific stiffness of greater than the design stiffness of the RAP element. The deflection at the bottom of the pier shall be recorded as a function of the design stress. At all loading stages, the total deflection, which shall not exceed a total deflection of 1 inch, shall be recorded. These results test on the installed Geopier system shall fully satisfy the performance requirements.

In accordance with the design, the Full-Time Quality Control (QC) representative shall be provided

Sector San Juan & Comunidad Rio Bayamón, PR Page 21 by the installer who shall report all the RAP foundation construction activities and details. The installer of the Geopier elements shall certify the units were installed at the required subgrade level, at approximately the top of footing elevation. The material type (i.e. clean crushed stone (3/4” minus diameter) and procedures used for each Geopier element installation for both the bottom bulb and the shaft shall be recorded by the installer. For the test RAP element, each 1-foot lift shall be tamped with a specialized tamper for approximately 60 seconds. This specialized tamper is flat on the bottom with beveled edges shall be used for compaction in lifts vertically, as well as for pushing the aggregate laterally into the surrounding soil inside the pre-drilled section.

6.4 Additional Foundations Considerations

Any new ground floor slab, shall be founded over a well-engineered fill material obviously, following the removal and replacement of the any unsuitable loose fill section to a minimum of 1.2 meters (4.0 ft.) and providing a high-density geotextile Terratex HD or equivalent prior to the backfilling process.

Also, a uniform fill section is required, for which the expected fill section may increase even more.

This is to assure the differential settlements are maintained within tolerable limits for the structural building units. In addition, The earth fill material shall be of A-2-4 or better AASHTO type, compacted to a minimum 95 % of its maximum dry density. A-1-a fill type is shall be deposited at the flood susceptible zones or under water, if any, compacted to a minimum 83 % of its maximum Bulk Density.

In addition, any new structure addition shall be provided with structural joints to cope with the differential settlement that may be experienced at the junction between existing and the new structure. Thus, the proposed steel-frame building shall be completely structurally independent from any existing structure.

Sector San Juan & Comunidad Rio Bayamón, PR Page 22

6.5 Groundwater Considerations

The permanent groundwater level was found varying from 5.0 to 7.0 ft., upon completion of the borings, it was measured at an average of 6.0 ft. Dewatering should be expected and implemented during any excavation and foundation procedures during construction, due to the high permeability of surface soils.

However, dewatering may cause the lowering of groundwater in the area around the excavation, which will result in an increase in effective stress of soil and hence settlement of the ground.

Nonetheless, dewatering may have adverse effects of ground settlement near the excavation adjoining sensitive structures, an assessment of the possible adverse effects of the dewatering shall me performed considering the dewatering technique selected.

Also, the construction of any underground structure shall consider special dewatering techniques

(i.e. well points, among others), if the proposed invert elevation of the proposed excavation is greater

(deeper) than the ground water levels. Dewatering can be accomplished by pumping through a system of well points installed adjacent to the excavation to sump pits near the excavations. The adequacy of the control of the dewatering process should be maintained during the excavation process to prevent the bottom of the excavation to heave or boil. Also, casting of concrete shall be made in dry conditions.

Special care shall be taken not to affect adjacent structures while dewatering procedures are implemented (i.e. Draw Down). Thus, any dewatering techniques shall be properly designed to cope with these circumstances.

Also, in the case underground structures (i.e. basement(s) or Cisterns) are considered, an effective drain blanket shall be provided to allow drainage of water continuously throughout the structure that will dispose of the relatively large flows through the upper loose sands which are highly permeable.

The basis of this solution is to account for the groundwater levels found close or above the foundation level.

Thus, the final solution requires an estimate to be made of the quantity of water that will be collected

Sector San Juan & Comunidad Rio Bayamón, PR Page 23 for which the pumps (permanent) must be designed. A final design volume determination will require additional evaluations and possibly a pumping test. Such evaluations are beyond the scope of the present work. Furthermore, during the period of the foundation and construction sequence a temporary dewatering system to maintain the excavation dry shall also be required in this project.

The selection and design of any dewatering system is beyond the scope of the present work. Also, proper control of the surface water is necessary, so that excavations are maintained dry during foundation casting and back filling operations.

6.6 Deep Excavation Supporting Systems

A variety of excavation methods and lateral supporting systems are to be practiced based on subsoil, and ground water, allowable construction period, budget and machinery. Excavation methods include full open cut methods, braced excavation methods, anchored excavation methods, and zoned excavation methods. Types of deep vertical soil support systems that are commonly used in metropolitan areas include conventional retaining walls, Soldier pile with wooden lagging walls, Sheet pile walls, and Pile walls-Contiguous, Secant or Tangent.

However, the major disadvantages of soldier pile and lagging systems are that they are primarily limited to temporary construction and they cannot be used in high water table conditions without extensive dewatering therefore their use shall be discarded considering the high-water table and tidal fluctuations at the site. Also, taking into consideration the induced vibration to install a Sheet pile system that would in turn be detrimental to adjacent structures its use shall also be discarded.

Thus, the other supporting system to be considered are Pile Retaining Walls. There are three distinct bored pile wall options in current use: Contiguous wall, Tangent wall and Secant wall.

Contiguous…