S02_Attachment_Tampa VAMC Geotech Final Report 39 pages.pdf

SUMMARY REPORT OF A

GEOTECHNICAL SITE EXPLORATION

PROPOSED WATER TOWER

JAMES A. HALEY VETERANS HOSPITAL

TAMPA, HILLSBOROUGH COUNTY, FLORIDA

GSE PROJECT NO. 16564

Prepared For:

TOLAND MIZELL MOLNAR, LLC

NOVEMBER 2024

GSE Engineering & Consulting, Inc.

5590 SW 64th Street, Suite B Gainesville, Florida 32608

(352) 377-3233 Phone (352) 377-0335 Fax www.gseengineering.com

November 11, 2024

Thomas C. Steele, AIA, LEED AP BD+C Toland Mizell Molnar, LLC 590 Means Street NW, Suite 200 Atlanta, Georgia 30318

Subject: Summary Report of a Geotechnical Site Exploration and Utility Location Services Proposed Water Tower James A. Haley Veterans Hospital

Tampa, Hillsborough County, Florida GSE Project No. 16564

GSE Engineering & Consulting, Inc. (GSE) is pleased to submit this geotechnical site exploration report for the above referenced project.

Presented herein are the findings and conclusions of our exploration, including the geotechnical parameters and recommendations to assist with water tower foundation design and the construction of the piping.

GSE appreciates this opportunity to have assisted you on this project. If you have any questions or comments concerning this report, please contact us.

Sincerely, GSE Engineering & Consulting, Inc.

Kevin P. Fisher, E.I. Kenneth L. Hill, P.E.

Staff Engineer Principal Engineer Florida Registration No. 40146

KPF/KLH:tlf Q:\Projects\16564 Proposed Water Tower – James A. Haley Veterans Hospital\16564.docx

Distribution: Addressee (1 – Electronic) File (1) http://www.gseengineering.com/

Summary Report of a Geotechnical Site Exploration and Utility Location Services November 11, 2024 Proposed Water Tower James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564 ii

TABLE OF CONTENTS

1.0 INTRODUCTION ............................................................................................................ 1-1

1.1 General ......................................................................................................................... 1-1

1.2 Project Description....................................................................................................... 1-1

1.3 Purpose ......................................................................................................................... 1-1

2.0 FIELD AND LABORATORY TESTS ............................................................................ 2-1

2.1 General Description ..................................................................................................... 2-1

2.2 Standard Penetration Test Borings............................................................................... 2-1

2.3 Soil Laboratory Tests ................................................................................................... 2-1

3.0 REVIEW OF PUBLISHED DATA .................................................................................. 3-1

3.1 Review of Published Topographic Data ...................................................................... 3-1

3.2 Review of Published Hydrological Data...................................................................... 3-1

3.3 Review of Published Soil Survey Information ............................................................ 3-1

3.4 Review of Published Regional Geology ...................................................................... 3-2

3.5 Review of State Sinkhole Information and GSE In-House Geotechnical Information 3-3

4.0 FINDINGS ........................................................................................................................ 4-1

4.1 Surface Conditions ....................................................................................................... 4-1

4.2 Subsurface Conditions ................................................................................................. 4-1

4.3 Laboratory Soil Analysis ............................................................................................. 4-2

5.0 EVALUATION AND RECOMMENDATIONS ............................................................. 5-1

5.1 General ......................................................................................................................... 5-1

5.2 Groundwater ................................................................................................................ 5-1

5.3 Karst Geology Review and Sinkhole Development Potential ..................................... 5-1

5.4 Preliminary Deep Cement Grout Injection Recommendations ................................... 5-2

5.5 Water Tower Foundations............................................................................................ 5-3

5.6 Water Tower Site Preparation ...................................................................................... 5-5

5.7 Trench Excavation ....................................................................................................... 5-6

5.8 Quality Control and Construction Materials Testing ................................................... 5-7

5.9 Fill Suitability .............................................................................................................. 5-7

6.0 FIELD DATA ................................................................................................................... 6-1

6.1 Standard Penetration Test Soil Boring Logs ................................................................ 6-2

6.2 Laboratory Results ....................................................................................................... 6-3

6.3 Key to Soil Classification ............................................................................................ 6-4

7.0 LIMITATIONS ................................................................................................................. 7-1

7.1 Warranty ...................................................................................................................... 7-1

7.2 SPT Borings ................................................................................................................. 7-1

7.3 Site Figures .................................................................................................................. 7-1

7.4 Unanticipated Soil Conditions ..................................................................................... 7-1

7.5 Misinterpretation of Soil Engineering Report.............................................................. 7-1

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564 iii

LIST OF FIGURES

Figure

1. Project Site Location Map

2. Site Plan Showing Approximate Locations of Field Tests

3. Site Plan Showing Approximate Locations of Cement Grout Injection Points

APPENDIX

Utility Test Summary of Results (GeoView, Inc.)

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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1.0 INTRODUCTION

1.1 General

GSE Engineering & Consulting, Inc. (GSE) has completed this geotechnical exploration for the proposed Water Tower located in Tampa, Hillsborough County, Florida. This exploration was performed in accordance with GSE Proposal No. 2024-201 (Rev. 1) dated April 17, 2024. Mr.

Thomas C. Steele, AIA, LEED AP BD+C, Architect/Project Manager, of Toland Mizell Molnar, LLC authorized our services on April 22, 2024.

1.2 Project Description

We understand you are designing water supply improvements at the James A. Haley Veterans Hospital in Tampa, Florida. The hospital campus is located at the southwest corner of the E 131st Avenue and Bruce Downs Boulevard intersection in Tampa, Florida.

You provided information about the project and site plans illustrating the locations of the proposed improvements and requested work. The project will include a 180-feet tall water tower and new water distribution piping. Additionally, you have requested underground utilities be located at certain locations using non-intrusive methods.

The water tower will hold 1 million gallons of water. We estimate the water tower will have a total weight of about 9,000 kips. We understand the water tower structure will be a pedestal style waterspheroid tank. You have requested that one soil boring be performed at the location of the water tower, and that two additional soil borings be performed in areas of piping. You provided a map of the requested soil boring locations.

In addition to the soil borings, you have requested that underground utilities be located at seventeen locations using geophysical methods. This work was being performed by our subconsultant, GeoView, Inc. and has been partially completed. GeoView has completed their Phase 1 investigation, which consisted of determining the locations and depths of the underground utilities using GPR and electronic locators. GeoView was in the process of completing their Phase 2 investigation, which consisted of determining the exact locations and depths of the underground utilities using vacuum excavation. The Phase 2 investigation was not feasible to continue and further investigation was deemed unnecessary at this point.

A recent aerial photograph of the site was obtained. The site plan and aerial photograph were used in preparation of this exploration and report.

1.3 Purpose

The purpose of this geotechnical exploration was to determine the general subsurface conditions, evaluate these conditions with respect to the proposed construction, and prepare geotechnical parameters and recommendations to assist with water tower foundation design and the construction of the piping. Additionally, the geophysical services were intended to locate specific underground utilities at the locations that you have requested.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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2.0 FIELD AND LABORATORY TESTS

2.1 General Description

The procedures used for field sampling and testing are in general accordance with industry standards of care and established geotechnical engineering practices for this geographic region.

This exploration consisted of performing one (1) Standard Penetration Test (SPT) boring to a depth of 48.5 feet below land surface (bls) at the proposed water tower location and two (2) SPT borings to depths of 15 feet bls at the locations where new piping will be constructed.

The soil borings were performed at the approximate locations as shown on Figure 2. The borings were located at the site using the provided site plan and obvious site features as reference. The boring locations should be considered approximate. The soil borings were performed on May 9, 2024.

2.2 Standard Penetration Test Borings

The soil borings were performed with a drill rig employing mud rotary drilling techniques and Standard Penetration Testing (SPT) in accordance with ASTM D1586. The SPTs were performed continuously to 10 feet and at 5-foot intervals thereafter. Soil samples were obtained at the depths where the SPTs were performed. The soil samples were classified in the field, placed in sealed containers, and returned to our laboratory for further evaluation.

After drilling to the sampling depth and flushing the borehole, the standard two-inch O.D. split-barrel sampler was seated by driving it 6 inches into the undisturbed soil. Then the sampler was driven an additional 12 inches by blows of a 140-pound hammer falling 30 inches. The number of blows required to produce the next 12 inches of penetration were recorded as the penetration resistance (N-value). These values and the complete SPT boring logs are provided in Section 5.1.

Upon completion of the sampling, the boreholes were abandoned in accordance with Water Management District guidelines.

2.3 Soil Laboratory Tests

The soil samples recovered from the soil borings were returned to our laboratory, and examined to confirm the field descriptions. Representative samples were then selected for laboratory testing.

The laboratory tests consisted of four (4) percent soil fines passing the No. 200 sieve determinations, four (4) natural moisture content determinations, and three (3) corrosion series tests. These tests were performed in order to aid in classifying the soils and to further evaluate their engineering properties. The laboratory tests are provided in Section 5.2.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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3.0 REVIEW OF PUBLISHED DATA

The following sections provide a review of readily available published data.

3.1 Review of Published Topographic Data

The topography at the site is relatively flat. Regional topography is gently sloping. The provided Utility Plan with topographic data indicates the ground surface elevations at the site are near elevations 35 to 38 feet1.

3.2 Review of Published Hydrological Data

The Floridan aquifer in the vicinity of the site has an elevation on the order of 20 to 30 feet2 NGVD

29. This elevation is below land surface, indicating a downward hydraulic gradient occurs at the site.

3.3 Review of Published Soil Survey Information

The majority of the site is mapped as two soil series by the Soil Conservation Service (SCS) Soil Survey for Hillsborough County3. The following soil descriptions are from the Soil Survey.

Candler-Urban land complex, 0 to 5 percent slopes - This complex consists of Candler soil that is nearly level to gently sloping and excessively drained and of areas of Urban land. This complex is on the uplands.

This map unit consists of 45 to 60 percent Candler soil and 35 to 45 percent Urban land. This included soils make up 18 percent or less of this map unit. The individual areas of the soils in this map unit are too mixed or too small to map separately at the scale used for the maps in the back of this publication.

Typically, the surface layer of Candler soil is dark gray fine sand about 6 inches thick. The upper part of the subsurface layer, to a depth of 26 inches, is brownish yellow fine sand. The lower part, to a depth of 76 inches, is a very pale brown fine sand. The subsoil to a depth of about 80 inches is very pale brown fine sand that has yellowish brown loamy sand lamellae that are about one-sixteenth to one-quarter of an inch thick and 2 to 6 inches long. In places, the soil does not have lamellae. In some areas, the subsurface layer contains 5 to 10 percent silt and clay. In some of the lower parts of the landscape, the soil is well drained.

The Urban land part of this complex is covered by concrete, asphalt, buildings, or other impervious surfaces that obscure or alter the soils so that their identification is not feasible.

Included in mapping are small areas of Kendrick, Millhopper, and Tavares soils. Kendrick and Millhopper soils are on convex shoulders and upper side slopes, Kendrick soils are well drained, and Millhopper soils are moderately well drained. Tavares soils are in lower-lying concave areas on the landscape. These soils are moderately well drained.

1 Utility Plan. Toland Mizell Molnar, LLC. Drawing Numbers CU102 & CU103 2 Potentiometric Surface of the Upper Floridan Aquifer, September 2020, U.S. Geological Survey.

3 Soil Survey of Hillsborough County, Florida. Soil Conservation Service, U.S. Department of Agriculture.

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A seasonal high water table is at a depth of more than 80 inches. The permeability of Candler soil is rapid. The available water capacity is low.

Zolfo fine sand, 0 to 2 percent slopes - This soil is nearly level and somewhat poorly drained. It is on broad, low ridges on the flatwoods. The slope is 0 to 2 percent.

In 95 percent of the areas mapped Zolfo fine sand, the Zolfo soil and similar soils make up 88 to 99 percent of the mapped areas. Dissimilar soils make up 1 to 12 percent of the mapped area.

Typically, this soil has a surface layer of very dark gray fine sand about 3 inches thick. The upper part of the subsurface layer, to a depth of about 15 inches, is grayish brown, mottled fine sand. The middle part, to a depth of about 51 inches, is light gray, mottled fine sand. The lower part, to a depth of about 60 inches, is grayish brown fine sand. The subsoil to a depth of about 80 inches is dark brown fine sand. Similar soils included in mapping, in some places, have subsoil that extends to a depth of more than 80 inches. Other similar soils, in some of the higher parts of the landscape, are moderately well drained.

Dissimilar soils included in mapping are Malabar, Millhopper, Myakka, and Smyrna soils in small areas. Malabar, Myakka, and Smyrna soils are poorly drained. Millhopper soils are moderately well drained.

In most years, a seasonal high water table is at a depth of 24 to 40 inches for more than 2 to 6 months and recedes to a depth of 60 inches during prolonged dry periods. Permeability is rapid in the surface and subsurface layers and moderate in the subsoil. The available water capacity is low.

3.4 Review of Published Regional Geology

The site is located within the north-central portion of Hillsborough County. This area of Hillsborough County maps as a transition between Undifferentiated Sediments and the Arcadia Formation, Tampa Member. The following descriptions are from the Geological Survey4.

Undifferentiated Sediments - Much of Florida's surface is covered by a varying thickness of undifferentiated sediments consisting of siliciclastics, organics and freshwater carbonates.

Pleistocene sea levels reached a maximum of approximately 100 feet (30 meters) msl (Colquhoun, 1969).

The siliciclastics are light gray, tan, brown to black, unconsolidated to poorly consolidated, clean to clayey, silty, unfossiliferous, variably organic-bearing sands blue green to olive green, poorly to moderately consolidated, sandy, silty clays. Gravel is occasionally present in the panhandle.

Organics occur as plant debris, roots, disseminated organic matrix, and beds of peat.

In southern Florida, freshwater carbonates are nearly ubiquitous in the Everglades. These sediments are buff colored to tan, unconsolidated to poorly consolidated, fossiliferous carbonate muds. Sand, silt and clay may be present in limited quantities. These carbonates often contain organics. The dominant fossils in the freshwater carbonates are mollusks.

4 Scott, Thomas N., Geologic Map of the State of Florida – Northern Peninsula. Florida Geological Survey, Open- File Report No. 80, 2001.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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Arcadia Formation, Tampa Member - The Tampa Member consists of predominantly of limestone with subordinate dolostone, sand and clay (Scott, 1988). The lithology of the Tampa Member is very similar to that of the subsurface limestone part of the Arcadia Formation except that the Tampa Member contains noticeably less phosphate (Scott, 1988). The limestone in the Tampa is white to yellowish gray, fossiliferous and variably sandy and clayey mudstone, wackestone and packstone with minor to no phosphate grains. Sand and clay beds are like those in the undifferentiated Arcadia Formation. Mollusks and corals are common in the Tampa Member as molds and casts, silicified pseudomorphs and original shell material. The Tampa Member and the lower part of the Arcadia Formation form the upper part of the Floridan aquifer system (FAS) in parts of southern Florida (Miller, 1986; Scott, 1991).

3.5 Review of State Sinkhole Information and GSE In-House Geotechnical Information GSE reviewed readily available published information on the Florida Map Direct5 on-line system.

Two database layers were queried as summarized below.

The State of Florida Sinkhole Types GIS layer is an assessment as part of a 1985 cooperative effort between the US geological survey and multiple State agency partners to summarize the types of sinkholes that occur within various areas of the State. The subject site is located within an area described as having Type I characteristics. The area is characterized as typically having a “bare or thinly covered limestone” where sinkholes “are few, generally shallow and broad and develop gradually. Solution sinkholes dominate”.

The Florida Subsidence Incident Report GIS layer represents reported subsidences. The database has been compiled by the Florida Department of Environmental Protection and Florida Geological Survey. These have not always been confirmed or verified as sinkholes and may represent other landforms. Furthermore, many of the incidents have not been field verified. At least 32 subsidence incident reports were identified within a 1 ½ mile radius of the site. The reports range from a smaller subsidence (approximately 2 feet in diameter and 2 feet deep) to a larger subsidence (largest is approximately 30 feet in diameter and 25 feet deep).

GSE reviewed in-house geotechnical information for the general area. GSE has extensive geotechnical experience in this portion of Hillsborough County. Area information and experience was considered and reviewed as part of this investigation.

5 Map Direct Gallery (state.fl.us)

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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4.0 FINDINGS

4.1 Surface Conditions

Mr. Kevin P. Fisher, E.I. with GSE visited the site on April 26, 2024 to observe the site conditions and mark the boring locations.

The site consists of existing buildings, asphalt roadways, access drives, and maintenance lots. The borings are located on either side of Richard Silver Way on the hospital campus. The hospital campus is bordered by East 131st Avenue to the north and Bruce Downs Boulevard to the east.

The topography at the site is relatively flat. Regional topography is gently sloping. The provided Utility Plan with topographic data indicates the ground surface elevations at the site are near elevations 35 to 38 feet6.

4.2 Subsurface Conditions

The locations of the SPT borings are provided on Figure 2. Complete logs for the borings are provided in Section 5.1. Descriptions for the soils encountered are accompanied by the Unified Soil Classification System symbol (SM, SP-SM, etc.) and are based on visual examination of the recovered soil samples and the laboratory tests performed. Stratification boundaries between the soil types should be considered approximate, as the actual transition between soil types may be gradual.

The SPT boring at the proposed water tower location initially penetrated a 17 feet thick stratum of poorly graded sand (SP) overlying very clayey sand (SC/CL) to a depth of 32 feet bls. This was underlain by poorly graded sand (SP) to a depth of 37 feet bls. This was underlain by the limestone formation to the explored depth of 48.5 feet bls. A loss of drilling fluid circulation occurred at a depth of 30 feet bls in the very clayey sand.

The SPT borings at locations where new piping will be constructed encountered poorly graded sand (SP) to the explored depths of 15 feet bls.

The surficial layer of poorly graded sand (SP) is generally in a loose to medium dense condition with N-values ranging from 8 to 23 blows per foot. The underlying clay-rich soils (CL/CH) are generally in a firm to stiff condition with N-values ranging from 6 to 12 blows per foot. The deeper poorly graded sand (SP) is generally in a very loose condition with an N-value of 2 blows per foot.

The limestone is generally in a hard to very hard condition with N-values ranging from 33 to 50+ blows per foot.

The groundwater table was not encountered within a depth of 10 feet bls. Due to the mud rotary method of advancing the boreholes, the depth of the groundwater table was not determined.

SPT boring B-1 encountered an overall decrease in soil strength with depth accompanied by a loss of the drilling fluid circulation at a depth of 30 feet bls within the unconsolidated portion of the boring profile above the limestone formation. These conditions are considered indicators for potential sinkhole activity that should be addressed as described in Section 5.4.

6 Utility Plan. Toland Mizell Molnar, LLC. Drawing Numbers CU102 & CU103

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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4.3 Laboratory Soil Analysis

Selected soil samples recovered from the soil borings were analyzed for the percent soil fines passing the No. 200 sieve, natural moisture content, and corrosion series. Samples selected for laboratory testing were collected at depths ranging from 2 to 25 feet bls. These tests were performed to confirm visual soil classification and evaluate their engineering properties. The complete laboratory report is provided in Section 5.2.

The laboratory tests indicate the tested soils consist of poorly graded sand and very clayey sand.

The tested poorly graded sand (SP) contains approximately 2.3 to 3.4 percent soil fines passing the No. 200 sieve with natural moisture contents of about 2.3 to 6.8 percent. The tested very clayey sand (SC/CL) contains approximately 30 percent soil fines passing the No. 200 sieve with a natural moisture content of about 31 percent.

Three (3) soil samples were collected and analyzed for corrosion series testing. Soil samples were collected from SPT boring B-1 from 2 to 4 feet bls, SPT boring B-2 from 4 to 6 feet bls, and SPT boring B-3 from 4 to 6 feet bls. The test results are tabulated below.

Boring I.D. Sample Depth (ft)

Resistivity (ohm-cm)

Chloride (ppm)

Sulfate (ppm) pH

B-1 2 - 4 3900 BDL 75 7.82

B-2 4 - 6 10000 BDL BDL 8.66

B-3 4 - 6 6500 BDL BDL 8.28

BDL: Below Detectable Limits

The soils at the site are considered slightly aggressive for concrete and slightly to moderately aggressive for steel7.

7 Structures Design Guidelines, FDOT Structures Manual, Volume 1, January 2018, Table 1.3.2-1, p. 1-6.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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5.0 EVALUATION AND RECOMMENDATIONS

5.1 General

The following recommendations are made based upon our understanding of the proposed construction, a review of the attached soil borings and laboratory test data, and experience with similar projects and subsurface conditions. If plans or the location of proposed construction changes from those discussed previously, GSE requests the opportunity to review and possibly amend our recommendations with respect to those changes.

The final design of a foundation system is dependent upon adequate integration of geotechnical and structural engineering considerations. Consequently, GSE must review the final foundation design in order to evaluate the effectiveness and applicability of our initial analyses, and to determine if additional recommendations may be warranted. Without such a review, the recommendations presented herein could be misinterpreted or misapplied resulting in potentially unacceptable performance of the foundation system.

The performance of site improvements may be sensitive to their post-construction relationship to site groundwater levels, seepage zones, or soil/rock characteristics exposed at final site grades.

GSE recommends that use of boring information for final design of all site improvements be predicated on proper horizontal and vertical control of borings.

In this section of the report, we present our geotechnical parameters and recommendations to assist with water tower foundation design, the construction of the piping, as well as our general site preparation guidelines.

5.2 Groundwater

The groundwater table was not encountered within a depth of 10 feet bls at the time of our exploration. However, we estimate the seasonal high groundwater table will range from 4 to 7 feet bls after periods of heavy and seasonal rainfall. Our seasonal high groundwater estimated are indicated on the soil boring logs.

5.3 Karst Geology Review and Sinkhole Development Potential

This geotechnical exploration was not intended to include a thorough subsurface exploration for sinkhole potential or karst geology. However, based upon the findings of boring B-1, we have included this discussion of the site karst geology and sinkhole potential.

A sinkhole may be defined as a depression or hole at the ground surface caused by a collapse or subsidence of the surface layer. In Florida, sinkholes generally fit into three categories. These include solution (chimney) sinkholes, cover-subsidence sinkholes, and cover-collapse sinkholes.

Each is briefly described below.

• Solution sinkholes (chimney) usually occur where there is little or no sediment cover over the limestone.

• Cover-subsidence sinkholes occur where thick permeable sediments cover the limestone.

In this case, the void in the rock is filled by sediments raveling downward from above.

Eventually, the ground surface often shows a gentle circular depression.

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• Cover-collapse sinkholes occur where sediments overlying the void in the rock formation collapse resulting in visible surface collapse at ground surface.

Sinkhole activity refers to geological conditions that result or may be reasonably expected to result in settlement or systematic weakening of the earth supporting surface improvements due to movement or raveling of soils, sediments, or rock materials into subterranean voids created by the effect of water on a limestone or similar rock formation. The presence of sinkhole activity represents a condition indicating the presence or imminent potential development of a sinkhole.

Soil boring B-1 located at the proposed water tower location encountered subsurface conditions that may be related to sinkhole development. The loss of drilling fluid circulation followed by very weak conditions in the sandy soil overlying the limestone formation may be related to karst geology and sinkhole activity, but it may also be representative of the local geological deposition.

Considering our review of published and in-house sinkhole development data, we recommend a cautious approach to these conditions, which includes the remediation of this potential sinkhole condition.

5.4 Preliminary Deep Cement Grout Injection Recommendations

Due to the indicators of potential sinkhole activity in SPT boring B-1, GSE recommends the subsurface soils be improved to reduce the potential for sinkhole activity and subsidence damage and densify the subsurface soils. Soil improvement should be accomplished through deep cement grout injection to compact and improve the density of sandy soils beneath the proposed water tower location. Cement grout injection is also intended to seal the top of the limestone surface to reduce the potential for future raveling.

The cement grouting program should incorporate up to 36 primary injection points spaced on an approximate 12 feet on center grid across the proposed water tower location. This spacing has been selected considering subsurface conditions encountered and our experience with similar sites.

The grout points should be vertical as shown in Figure 3. The actual locations and number of grout points should be confirmed in the field and adjusted as necessary to accommodate site specific conditions.

We recommend the grout injection pipes be drilled to a depth of approximately 45 feet, or a minimum of 5 feet into limestone. A low slump redi-mix cement grout having a slump between 4 and 8 inches should be pumped through the injection pipes until high pressures are achieved or ground heave occurs. At this point, the pipes should be lifted about 3 to 5 feet and the process repeated until the pipes are withdrawn. It is common to stop grouting at about 15 feet below grade due to the potential to cause significant ground heave.

The total quantity of grout required can vary based on site conditions but is likely to be up to approximately 200 cubic yards (cy). Grout bids should consider a mobilization cost and unit rates for 1,620 linear feet of grout injection pipe installation and 200 cubic yards of grout injected. The proposals should also include the cost of grout purchased but returned to the plant and not used.

GSE recommends all grouting operations be performed under the observation of the geotechnical engineer. The contractor should submit the proposed shop drawing grouting systems and proposed installation methods to the geotechnical engineer for review.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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The proposed preliminary grout injection remediation program should not be construed to preclude the potential for future sinkhole development in the area or other areas not remediated.

5.5 Water Tower Foundations

The SPT boring at the proposed water tower location initially penetrated a 17 feet thick stratum of poorly graded sand (SP) overlying very clayey sand (SC/CL) to a depth of 32 feet bls. This was underlain by poorly graded sand (SP) to a depth of 37 feet bls. This was underlain by the limestone formation to the explored depth of 48.5 feet bls.

The water tower will hold 1 million gallons of water. We estimate the water tower will have a total weight of about 9,000 kips. This weight is too large to be supported by conventional, shallow spread foundations as settlements will be excessive. We recommend the water tower be supported by a deep foundation system.

Based upon the soil conditions encountered and our recommended site preparation approach, we recommend a deep foundation system be considered to support the silo. We recommend using augured cast-in-place (ACIP) concrete piles to support the structure. It is our opinion the structure should not be supported by driven piles due to the potential for driving vibrations disturbing the adjacent properties and existing buildings.

5.5.1 Augured Cast-In-Place Concrete Piles

Augured cast-in-place (ACIP) concrete piles should have a minimum diameter of 16 inches. We estimate a 16-inch diameter ACIP concrete pile constructed to a bearing tip depth of approximately 45 feet bls will have an allowable axial compressive capacity of at least 100 tons. We estimate uplift capacity for this type of pile will be at least 50 tons.

The above recommended pile tip elevation considers that the piles will have a minimum of 8 feet embedment into limestone. The pile lengths are anticipated to be on the order of 45 feet.

Install ACIP concrete piles according to FDOT Standard Specification, Section 455-44, January 2019 as summarized below.

ACIP concrete piles should be constructed by drilling a hollow-stem auger into the ground to the required depth. The bottom of the auger should have a plug that prevents the soil cuttings from entering and plugging up the hollow stem. After reaching the required depth, pumping of the grout should begin such that the plug is flushed out and a continuous flow of grout is achieved and a head of at least 5 feet of grout is established by pumping a volume of grout equivalent to 5 feet of pile volume.

Once the grout head has been established, lower the auger to the drilled bottom and slowly retract the auger while pumping the grout under pressure to create a continuous grouted pile. The grout should always be pumped under pressure to help assure the piles are continuous. Ensure grout starts flowing out from the hole when the auger tip is at least 5 feet below the ground surface. If this is not the case, redrill 5 feet deeper and resume grouting. A minimum actual grout volume of 125 percent of the theoretical pile volume should be achieved for each pile, unless otherwise approved by the geotechnical engineer. Actual grout quantities on average could be 200+ percent considering the piles will be tipped in limestone.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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It is common for auger cast piles drilled into limestone to lose grout as the auger is retracted. We have observed piles taking 20+ cubic yards (cy) of grout to fill the pile. The grout injection program recommended to remediate potential sinkhole conditions should reduce the amount of grout loss and overage. If grout loss occurs, it will be necessary to continue pumping grout until the pile is filled. Temporarily abandoning the pile and redrilling at a later time will likely result in ground collapse around the pile hole due to groundwater seepage from the sandy soils.

The piles should be reinforced while the grout is still fluid but no later than 1/2 hour after pulling of the auger. Steel reinforcement usually consists of a single reinforcing bar (typically a No. 8 bar) placed the full length of the pile. The bottom of the reinforcing bar should be attached to a centering device that helps place the bar within the center of the pile, and the centering device also helps to confirm the pile section is continuous. The upper portion of the pile may require a reinforcement cage to reinforce the portion of the pile having moments from lateral loads. A lateral pile analysis will be necessary to determine the amount and depth of the moments, but typically moments from lateral forces are dissipated within the upper 20 to 25 feet of most piles. The above pile reinforcement recommendations are general in nature, and the actual pile reinforcement should be determined by the structural engineer. GSE can conduct a lateral pile analysis as necessary once the structural engineer has established the pile layout and lateral loading conditions.

The construction of the piles should be in a manner that drilling of the piles does not disturb the “wet” grout in adjacent piles. We recommend adjacent piles under construction be a minimum of 6 pile diameters away from any pile having grout placed less than 24-hours prior.

Our pile capacity estimate is based upon a single, free-standing pile. Pile groups may have different (lower) capacities, and to help reduce the effects of pile groups, we recommend the piles be separated by a minimum of three pile diameters, center-to-center.

We recommend all piles be installed under engineering observation. Additionally, at least one nonproduction pile should be load tested in accordance with ASTM D1143 and meeting the requirements of the Florida Building Code. The geotechnical engineer should assist the pile contractor in selecting the pile test location.

We recommend the load test reaction frame be capable of resisting loads of at least 250 tons.

Additionally, the compression loads applied during the load test should be monitored by a minimum 250-ton load cell. We recommend the test pile be instrumented with a minimum of five

(5) pairs of vibrating wire strain gauges. Strain gauges should be installed near the top of the pile and then approximately 10 feet apart for the approximately 45 feet long piles. The intent of the strain gauges is to evaluate the load distribution of the test pile, which can be used to optimize the capacity.

The overall intent of the test pile program is to confirm the design pile capacity, and determine whether additional capacity can be considered for the design length. Furthermore, if the contractor has the ability, and at the discretion of the owner, a “follow-up” quick load test (ASTM D1143) could be conducted to further evaluate capacity and establish production pile depths. Upon completing the load tests to two times the design load (200 tons), if practical, the test piles should be loaded to failure, or the maximum capacity of the load frame, in order to further evaluate the ultimate pile capacity.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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Piles should be constructed with concrete having a minimum 28-day compressive strength of 4,000 psi. The load test piles should have a minimum 28-day compressive strength of 6,000 psi. Pile installation locations should be accurate to 3 inches, and be installed within 1 percent of vertical.

All pile load test equipment should be provided by the pile contractor, including the reaction frame, top plate, hydraulic jack, load cell with readout, dial gauges and materials to perform the load test.

Up to date calibration curves for the pile loading system shall be provided prior to initiating the test. The load test should be performed under the observation of the geotechnical engineer of record.

5.6 Water Tower Site Preparation

The following recommendations are our general guidelines for site preparation at the area of the proposed water tower.

5.6.1 Stripping

Strip the construction limits and 10 feet beyond the perimeter of all grass, roots, topsoil, pavement, and other deleterious materials. You should expect to strip to depths of 12 or more inches. Deeper stripping will likely be necessary due to major root systems present at the site.

5.6.2 Dewatering

Temporary dewatering will not likely be necessary for this project. However, if needed, we anticipate dewatering can be accomplished with sumps placed near the construction area, or with underdrains connected to a vacuum pump.

In any case, the site should always be graded to promote runoff and limit the amount of ponding.

Localized ponding of stormwater is expected without proper grading during construction, and could render previously acceptable surfaces unacceptable.

5.6.3 Proof-Rolling

Proof-roll the subgrade with heavy rubber-tired equipment, such as a loaded front-end loader or dump truck, to identify any loose or soft zones not found by the soil borings. The proof-rolling should be monitored by a geotechnical engineer or qualified technician. Undercut or otherwise treat these zones as recommended by the geotechnical engineer in this report.

5.6.4 Proof Compaction

Compact the subgrade to a density of at least 95 percent of the Modified Proctor maximum dry density (ASTM D1557). The specified compaction should be obtained to a depth of 1 foot below the bottom of the concrete pile cap and the existing grade prior to placing fill. Vibratory roller equipment should not be used within approximately 100 feet of existing structures. Lighter “walk-behind” compaction equipment may be used to achieve the degree of compaction.

5.6.5 Fill Placement

Imported fill placed to raise the site grades should consist of clean sand having less than 10 percent passing the No. 200 sieve. On-site soils meeting the requirements of Section 4.7 may also be used as structural fill. The fill should be placed in maximum 12-inch loose lifts that are compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D1557). If lighter “walk-behind” compaction equipment is used, this may require lifts of 4 inches or less to achieve the required degree of compaction.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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5.7 Trench Excavation

Based on the information provided, we understand that piping will be constructed using trench methods. The following subsections provide information for the design and construction of the piping and excavations required for the proposed installation.

5.7.1 General

We understand the piping will be constructed in trench excavations. For design, the groundwater level should be assumed to exist at the seasonal high groundwater level since these conditions may exist after a heavy rain event. Geotechnical parameters were developed for the design of pit construction as part of the proposed piping.

5.7.2 Geotechnical Parameters

Based on the soil conditions encountered by the borings, geotechnical design parameters were developed for the soils encountered across the site for the design of trench construction. These design parameters are provided in Table 1 below.

Table 1: Geotechnical Design Soil Parameters

Boring No.

Range of Depths (ft bls)

Internal Friction Angle ϕ

(degrees)

Moist Unit Weight γ (pcf)

Submerged Unit Weight γ (pcf)

Unconfined Compression qu (ksf)

Cohesion cu

(ksf)

B-2 0 - 15 32 115 65 - - B-3 0 - 15 32 115 65 - -

5.7.3 Excavation Stability

The open excavations may be shored or laid back to a stable slope or supported by some other equivalent means used to provide safety for workers and adjacent structures, if any. The excavations should be made in accordance with OSHA Standards, OSHA 2207, Subpart P, latest revision.

• Excavations less than 5 feet bls – Excavations that are less than 5 feet in depth should be effectively protected when an indication of ground movement is anticipated.

• Excavations greater than 5 feet bls – Excavations that are deeper than 5 feet should be sloped, shored, sheeted, braced, or laid back to a stable slope or supported by some other equivalent means or protection such that workers are not exposed to moving ground or cave-ins. The slopes and shoring should be in accordance with trench safety requirements as per OSHA Standards. For shoring greater than 20 feet (if needed), an engineering evaluation is required.

The excavation pits should be backfilled in accordance with the project specifications. It is likely the excavated material may be used as backfill material provided it meets the requirements of Section 5.9 of this report. We recommend that the backfill be placed in maximum 12-inch loose lifts that are compacted to at least 95 percent of the Modified Proctor maximum dry density.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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5.7.4 Fill Placement

Imported fill placed to raise the site grades or backfill the utility trenches should consist of clean sand having less than 10 percent passing the No. 200 sieve. On-site soils meeting the requirements of Section 4.7 may also be used as structural fill. The fill should be placed in maximum 12-inch loose lifts that are compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D1557). If lighter “walk-behind” compaction equipment is used, this may require lifts of 4 inches or less to achieve the required degree of compaction.

5.8 Quality Control and Construction Materials Testing

It should be noted that the geotechnical engineering design does not end with the advertisement of the construction documents. As the geotechnical engineer of record, GSE is the most qualified to perform the construction materials testing that will be required for this project. The benefits of having the geotechnical engineer of record also perform the construction materials testing are numerous. If GSE continues to be involved with the project through construction, we will be able to constantly re-evaluate and possibly alter our geotechnical recommendations in a timely and cost-effective manner once final design and construction techniques are developed. This often results in cost savings for the project.

We recommend performing compaction testing beneath the concrete pile caps for the water tower.

We recommend a compaction test be performed for each 2,500 square feet of concrete slab area per foot of fill or native material, or a minimum of three tests, whichever is greater.

GSE recommends all auger cast piles be constructed under GSE observation. GSE should also be involved in the auger cast pile load testing.

5.9 Fill Suitability

The soils encountered at this site within the explored depths range from sands (SP) to very clayey sands (SC/CL). A discussion of the suitability for reuse as structural fill for each soil classification according to the Unified Soil Classification System (USCS) designation is provided below.

SP, SP-SM – Sands (SP) and sand with silt (SP-SM) have less than 5 percent and 12 percent soil fines passing the No. 200 sieve, respectively, and are typically well draining soils that are suitable for reuse as structural fill. The sands with silt may require moisture conditioning (drying) to make the material more workable. These soils will require stockpiling and drying before they are reused if they are excavated from below the water table.

James A. Haley Veterans Hospital Tampa, Hillsborough County, Florida GSE Project No. 16564

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SM – Silty sands (SM) can have between 12 percent and 50 percent soil fines passing the No. 200 sieve. Silty sands are typically non-plastic or have low plasticity, and can be reused as structural fill with precautions. Silty sands can be moisture sensitive and difficult to work and compact and can rut if the moisture content is near or above the optimum moisture content. We recommend these soils be moisture conditioned (dried) so that the moisture content during use is at or below the optimum moisture content. Aerating and exposure to the sun is typically the most effective methods of drying these soils. It may not be practical to reuse these materials during the wet season, as frequent rain showers may not allow these soils to dry to a workable moisture content. Suitable silty sands are limited to soil having less than 30 percent soil fines passing the No. 200 sieve. Silty sands with more than 30 percent soil fines are especially moisture sensitive, and are not recommended for reuse as structural fill. These soils will behave more as sandy silt, and for this reason, very silty sands having more than 30 percent soil fines passing the No. 200 sieve have been assigned a dual classification of SM/ML. Silty sand soils that are excavated from below the water table are not recommended for reuse as structural fill due to the amount of time that will be required to dry these soils to a workable condition.

SC – Clayey sand (SC) soils can have between 12 percent and 50 percent soil fines passing the No. 200 sieve. Clayey sands can have a high range of plasticity, varying from a PI of 7 or greater and plotting above the A-line to highly plastic. Friable clayey sands are typically suitable for use as structural fill with precautions. Clayey sands will be moisture sensitive and difficult to work and compact and can rut during placement if the moisture content is near or above the natural moisture content. We recommend these soils be moisture conditioned (dried) so that the moisture content during use is at or below the optimum moisture content. Aerating and exposure to the sun is typically the most effective methods of drying these soils. It may not be practical to reuse these materials during the wet season, as frequent rain showers may not allow these soils to dry to a workable moisture content.