Geotechnical Report.pdf

Final Report of Subsurface Investigation and Geotechnical Engineering Evaluation

P-286 AHTS Maintenance Hangar

N.A.S. Whiting Field, FL

Contract N69450-17-D-0101-X031

Task Order N6945018F1037

23 July 2019

Performed By:

Universal Engineering Sciences, Inc.

1985 Cope Lane Pensacola, FL 32526

Submitted By:

Bullock Tice Associates, Inc.

909 East Cervantes Street

Pensacola, FL 32501

23 July 2019

Naval Facilities Engineering Command, Southeast ATTN: Ms. Tracy D. Cunningham, Senior Project Manager NAVFAC SE IPT Gulf Coast Building 903 Yorktown Ave.

Jacksonville, FL 32212-0030

RE: Architect-Engineer Contract Number N69450-17-D-0101-X031 (Delivery Order No. N6945018F1037) Final Geotechnical Investigation for P-286 AHTS Maintenance Hangar

BTA 144915.31

Tracy - This letter transmits the Final Report of Subsurface Investigation and Geotechnical Engineering Evaluation for the referenced portion of the Task Order consisting of the following documents:

• One hardcopy and one electronic copy (CD-ROM)

One hardcopy and one Electronic copy (CD-ROM) are being transmitted to the Activity (Tim Gleason).

Please advise if there are any questions in regard these documents.

Jon Molloy, AIA Vice President cc: Tim Gleason with enclosures Wally Throneberry/BTA Shelley Churukian/BTA File (SF) (PL); Accounting

REPORT OF GEOTECHNICAL EXPLORATION

P286 AHTS AIRCRAFT MAINTENANCE HANGAR

NAS WHITING FIELD

SANTA ROSA COUNTY, FLORIDA

UES PROJECT NO. 1730.1800117.0000

UES DOCS REPORT NO. 1686987

JULY 3, 2019

Prepared For:

909 East Cervantes Street Pensacola, Florida 32501

Prepared By:

Universal Engineering Sciences

1985 Cope Lane Pensacola, Florida 32526

(850) 944-5555

UNIVERSAL

ENGINEERING SCIENCES,

Consultants in: Geotechnical Engineering • Environmental Sciences • Construction Materials Testing • Threshold Inspection Offices in: Orlando • Daytona Beach • Fort Myers • Gainesville • Jacksonville • Ocala • Palm Coast • Rockledge • Sarasota • Miami

St. Augustine • Pensacola • Panama City • Fort Pierce • Leesburg • Tampa • West Palm Beach • Atlanta, GA • Tifton

1985 Cope Lane • Pensacola, Florida 32526 • (850) 944-5555 • Fax (850) 944-5885 www.universalengineering.com

LOCATIONS:

� Atlanta � Daytona Beach � Fort Myers � Fort Pierce � Gainesville � Jacksonville � Kissimmee � Leesburg � Miami � Ocala � Orlando (Headquarters) � Palm Coast � Panama City � Pensacola � Rockledge � Sarasota � Tampa � West Palm Beach

July 3, 2019

909 East Cervantes Street Pensacola, Florida 32501

Attention: Mr. Jon Molloy, AIA, NCARB j.molloy@bulltice.com

Reference: Report of Geotechnical Exploration P286 AHTS Aircraft Maintenance Building NAS Whiting Field Santa Rosa County, Florida UES Project No. 1730.1800117.0000

UES Report No. 1686987

Mr. Molloy:

Universal Engineering Sciences, Inc. (UES) has completed a geotechnical exploration at the above referenced site on NAS Whiting Field, in Santa Rosa County, Florida. The scope of our exploration was planned in conjunction with and authorized by you. This exploration was performed in accordance with generally accepted geotechnical engineering practices. No other warranty, express or implied, is made.

The following report presents the results of our field exploration and a geotechnical engineering interpretation of those results with respect to the project characteristics provided to us. We have included geotechnical recommendations for foundation design, seismic site classification, and site preparation.

We appreciate the opportunity to have worked with you on this project and look forward to a continued association. Please contact us if you have any questions, or if we may further assist you as your plans proceed.

Respectfully Submitted, UNIVERSAL ENGINEERING SCIENCES, INC.

Certificate of Authorization No. 549

Michael A. Johnson, P.E Guy H. Rabens, M.S., P.E.

Senior Geotechnical Engineer Principal Engineer Florida P.E. No. 35974 Florida P.E. No. 60917

This item has been electronically signed and sealed by Michael A. Johnson, P.E. using a digital signature. Printed copies of this document are not considered signed and sealed, and the signature must be verified on any electronic copies.

Digitally signed by Michael A.

Johnson Date:

2019.07.03 14:52:21 -05'00'

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 GENERAL

2.0 SCOPE OF SERVICE

2.1 PROJECT DESCRIPTION

2.2 PURPOSE

2.3 GEOTECHNICAL EXPLORATION

2.3.1 Field Procedures

2.4 LABORATORY TESTING PROGRAM

2.4.1 Visual Classification

2.4.2 Laboratory Index Testing

3.0 FINDINGS

3.1 REGIONAL GEOLOGY

3.2 USDA NRCS SOIL SURVEY

3.3 SURFACE CONDITIONS

3.4 SUBSURFACE CONDITIONS

3.5 NOTABLE FINDINGS – VERY DENSE SOILS

3.6 CALIFORNIA BEARING RATIO (CBR) TESTING

4.0 RECOMMENDATIONS

4.1 GEOTECHNICAL ASSESSMENT

4.2 GROUNDWATER CONSIDERATIONS

4.2.1 Transient Perched Groundwater

4.3 SEISMIC SITE CLASSIFICATION

4.4 FOUNDATION DESIGN

4.4.1 General

4.4.2 Allowable Net Soil Bearing Pressure

4.4.3 Foundation Size

4.4.4 Bearing Depth

4.4.5 Bearing Material

4.4.6 Settlement Estimates

4.4.7 Lateral Loads

4.4.8 Foundation Evaluations

4.5 FLOOR SLAB/PAVEMENT

4.5.1 Floor Slab

4.5.2 General Concrete Requirements for Slab/Pavement System

4.5.3 Control Joints for Slab/Pavement System

4.5.4 Concrete Placement for Slab/Pavement System

4.5.5 Groundwater Considerations

4.6 SITE PREPARATION

4.6.1 Temporary Groundwater Control

4.6.2 Nearby Structures and Vibrations

4.6.3 Existing Underground Utilities

4.6.4 Site Preparation and Grading

4.6.5 Fill Placement

4.6.6 Earth Fill Materials

4.6.7 Compaction Recommendations

4.6.8 Test Criteria to Evaluate Fill and Compaction

4.7 CONSTRUCTION RELATED SERVICES

4.7.1 Excavation and Safety

5.0 LIMITATIONS

LIST OF TABLES

TABLE 1: SUMMARY OF SOIL SURVEY INFORMATION

TABLE 2: GENERAL SOIL PROFILE

TABLE 3: SUMMARY OF CBR TEST RESULTS

LIST OF APPENDICES

SITE VICINITY MAP .................................................................................................................. A USDA NRCS SOIL SURVEY MAP ............................................................................................. A

BORING LOCATION PLAN ....................................................................................................... B BORING LOGS .......................................................................................................................... B KEY TO BORING LOGS ............................................................................................................ B

LABORATORY TESTING PROCEDURES ................................................................................ C GRAIN SIZE DISTRIBUTION CURVES ..................................................................................... C REPORT OF PROCTOR TEST RESULTS ................................................................................ C

GEOPROFESSIONAL BUSINESS ASSOCIATION (GBA) DOCUMENTS ................................. D CONSTRAINTS AND RESTRICTIONS...................................................................................... D

P286 AHTS Aircraft Maintenance Building UES Project No. 1730.1800117.0000 NAS Whiting Field, Santa Rosa County, Florida UES Docs Report No. 1686987

1.0 INTRODUCTION

1.1 GENERAL

In this report, we present the results of the subsurface exploration of the site for the proposed project. We have divided this report into the following sections:

� SCOPE OF SERVICES - Defines what we did � FINDINGS - Describes what we encountered � RECOMMENDATIONS - Describes what we encourage you to do � LIMITATIONS - Describes the restrictions inherent in this report � APPENDICES - Presents support materials referenced in this report

2.0 SCOPE OF SERVICE

2.1 PROJECT DESCRIPTION

Project information was provided to us via email correspondence with Mr. Jon Molloy on July 27, 2018. The project is located on NAS Whiting Field in Milton, Santa Rosa County, Florida. We were provided with the following documents for our use in preparation of the geotechnical engineering scope of work:

� Engineering Services SOW, dated July 2, 2017 � Survey Limits for the proposed Temporary Hangars and P286 AHTS Aircraft Maintenance

Hangar (sheet C-001), dated July 13, 2018

We understand that the project will include design and construction of a hangar building with approximate plan dimensions of 630 feet by 200 feet (approximate plan area of 126,000± square feet). At the time of this report, the site plan had not been finalized, and the final hanger location may be subject to change.

Preliminary loading information was not available at the time of this report. Therefore, we have assumed maximum column loads of 250 kips/column, and wall loads not to exceed 6 kips per linear foot.

Preliminary site grading information was not available at the time of this report. We have assumed that less than 2 feet of structural fill will be necessary to achieve finished grades.

Our preliminary recommendations are based upon the previously discussed supplied or assumed information. If any of this information is incorrect, or changes, please inform Universal Engineering Sciences so that we may review our recommendations. Without such a review, the preliminary recommendations herein may not be valid. No other site or project facilities should be designed or constructed using the soil information contained herein. As such, UES will not be responsible for the performance of any other site improvement designed using the data in this report.

UES understands that both the design and construction of the facility will be executed under the design-build contract awarded by the Government (U.S. Navy). UES further understands that the successful design-build contractor will be required to conduct its own geotechnical engineering exploration and evaluation of the project site, including subsurface testing, laboratory analyses, and the development of recommendations to be used for final design of the facility by the contractor’s Designers-of-Record (D.O.R.’s).

UES understands that its services, findings, and preliminary recommendations contained within this report are furnished for the Government’s use in preparing a contract solicitation for the design and construction of the referenced facility. The findings and recommendations presented within this report are only intended to be used for bidding purposes and will not be relied upon for final design purposes.

UES acknowledges that it cannot and will not provide any services of the types performed for the exploration and preliminary recommendations contained in this report for any bidder, contractor, subcontractor, or affiliate of the design-build contractor for this facility, as outlined in FAC 5252.209-9300 (Organizational Conflicts of Interests – June 1994) and as stipulated in Architect- Engineer Contract N69450-D-0101 between the Government and Bullock Tice Associates, Inc.

2.2 PURPOSE

The purposes of this exploration program were:

� To explore the general subsurface conditions in the proposed building area;

� To interpret and review the subsurface conditions with respect to the proposed construction;

� To perform a series of laboratory tests on selected subsurface soil samples to assist with engineering soil classification, and to establish relevant soil engineering characteristics;

� To provide preliminary geotechnical engineering recommendations for groundwater control, foundation design, seismic site classification, and site preparation to be used by prospective design-build contractors and their team members in preparing bidding documents (proposals) for the design and construction of the facility addressed in this report;

� Prepare a report which documents the results of our exploration and analysis with preliminary geotechnical engineering recommendations.

This report presents an evaluation of site conditions on the basis of traditional geotechnical engineering procedures for site characterization. The recovered samples were not examined, either visually or analytically, for chemical composition or environmental hazards. Universal Engineering Sciences would be pleased to perform these services, if you desire.

Our exploration was confined to the zone of soil likely to be stressed by the proposed construction.

Our work did not address the potential for surface expression of deep geological conditions. This evaluation requires a more extensive range of field services than performed in this study.

2.3 GEOTECHNICAL EXPLORATION

The field exploration program was initiated on May 2, 2019, and completed on June 3, 2019. The approximate test boring locations are shown on the attached Boring Location Plan in Appendix B. The approximate test locations were determined in the field by our personnel using the Site Plan (survey) provided, a hand-held GPS, Google Earth aerial imagery, existing field reference points on and adjacent to the site, and a tape measure, and should be considered accurate only to the degree implied by the method of measurement used.

Upon completion of the field tests and sampling, recovered soil samples were place in labeled plastic containers, sealed, and transported to our laboratory where the samples were visually and physically examined by a member of our geotechnical engineering staff. Select samples of the soils were then chosen for specific laboratory tests. Samples of the soils will be held in our laboratory for your inspection for 60 days following the issue date of this report, and then discarded unless we are notified and other arrangements are made.

2.3.1 Field Procedures

The field exploration for this project consisted of performing the following procedures/tests in general accordance with the methods listed and at the quantities specified.

� Performing one (1), 55 feet deep and ten (10), 30 feet deep Standard Penetration Test (SPT) borings within the proposed aircraft maintenance building footprint.

Detailed explanations of the field procedures performed are presented on an attachment in Appendix B.

2.4 LABORATORY TESTING PROGRAM

2.4.1 Visual Classification

The soil samples collected on site were visually classified in general accordance with the USCS Soil Classification System (ASTM D2487). A summary of the resulting soil descriptions are shown on the Boring Logs presented in Appendix B.

2.4.2 Laboratory Index Testing

Laboratory soil tests were performed on selected soil samples obtained from the test borings to aid in the classification of the soils, and to help in the evaluation of pertinent engineering characteristics of the soils. The classifications and laboratory testing completed for this project consisted of performing the following procedures/tests in general accordance with the methods listed.

� Soil Classification per the Unified Soil Classification System – ASTM D 2487

� Natural Moisture Content Tests – ASTM D 2216

� Sieve Analysis of Fine and Coarse Aggregates – ASTM C136

� Percent -200 Soil Fines Content Tests – ASTM D 1140

� California Bearing Ratio (CBR) – ASTM D1883

� Atterberg Limits – Standard Test Method for Liquid Limits, Plastic Limits, and Plasticity Index of Soils – ASTM D 4318

The results of the tests are presented within this report, summarized on the boring logs presented in Appendix B, and/or presented on attachments in Appendix C, as appropriate.

3.0 FINDINGS

3.1 REGIONAL GEOLOGY

Santa Rosa County is located in the Coastal Lowlands physiographic province of the Florida Panhandle region. The general geology of the Coastal Lowlands province consists of unconsolidated sands, limestones, silts, and clays ranging in age from Cretaceous to recent (Pratt, et al, 1966). The Sand and Gravel Aquifer, which ranges in thickness from approximately 250 feet to 500 feet, is the most important water-bearing zone in Santa Rosa County. The aquifer is comprised of three major zones: the surficial zone, the intermediate low permeability zone, and the main producing zone (Pratt, et. al., 1966). The Sand and Gravel aquifer is recharged by infiltration of local rainfall and, due to the high permeability of local soils, the entire area of the aquifer is considered a recharge area.

The surficial zone (which contains the unconfined water table surface) generally averages less than 100 feet in thickness and is composed primarily of inter-bedded fines sands, silts, and clays (Pratt, et al, 1966). Underlying the surficial zone is an intermediate zone of low permeability that averages approximately 50 to 100 feet in thickness (Pratt, et al, 1966). The intermediate zone acts as a leaky confining layer that separates the water table aquifer from the more productive main producing zone of the Sand and Gravel Aquifer.

The Floridian aquifer is also present is Santa Rosa County and underlies the Sand and Gravel Aquifer; however, water from the Floridian in this region is highly mineralized and is not considered a source of potable water in Santa Rosa County (Pratt, et. al, 1966).

3.2 USDA NRCS SOIL SURVEY

Based on the Web Soil Survey for Santa Rosa County, Florida, as prepared by the USDA NRCS, the predominant, pre-development soil type mapped at the site is #44 Troup loamy sand, 0 to 5 percent slopes. A summary of the characteristics of this soil series was obtained from the Soil Survey and is included in Table 1.

Table 1 – Summary of Soil Survey Information

Soil Type Constituents Internal Drainage

Hydrologic Soil Group

Soil Permeability Seasonal High

Water Table

(ft)

Corrosion Potential

Shrink- Swell

Potential Depth (in)

Perm (in/hr)

Steel Concrete

44 – Troup Loamy

Sand, 0 to 5% Slopes

SM, SP-SM,

SC, SC-SM,

CL, CL-ML

Well drained A 0-55

55-80 6.0-20 0.6-2.0

> 6 Low Moderate

Very low to low

3.3 SURFACE CONDITIONS

UES personnel visited the project site during the performance of the field portion of this geotechnical study. At the time of UES field exploration program, the subject site generally consisted of a cleared grassed area, with a wooded area located in the northwest corner of the proposed hangar building area. The proposed hangar building area was bounded on the west, south, and east sides by pavement areas. An existing building was present along the east edge and in the southern portion of the proposed hangar building area. Surface water was not observed on the property at the time of our field exploration.

Topographical information was not provided by the client. Based on estimates gathered from Google Earth, the site was relatively flat, with approximate elevations ranging from 180 to 185 feet MSL.

3.4 SUBSURFACE CONDITIONS

The general subsurface conditions encountered during the subsurface exploration are described in Table 2. For more detailed soil descriptions and stratifications at the boring locations, the Boring Logs presented in Appendix B should be reviewed. Also, see the Key to Boring Logs in Appendix B for further explanation of the symbols and placement of data on the Boring Logs.

The Boring Logs represent our interpretation of the subsurface conditions based on a review of the field logs, an engineering examination of the samples, and a limited number of laboratory tests. The horizontal stratification lines designating the interface between various strata represent approximate boundaries. Transition between different strata in the field may be gradual in both the horizontal and vertical directions. Groundwater, or lack thereof, encountered in the borings, and noted on the Boring Logs, represents conditions only at the time of the exploration.

Table 2 – General Soil Profile

Stratum No.

Typical depth (ft) Soil Descriptions Range of SPT “N”

Blow Counts From To

1 0 0.2 to 0.5

With the exception of Boring B-4, predominantly 2 to 6 inches of topsoil with roots and organics; at B-4, approximately 4 inches of pavement section materials were encountered.

N/A

2 0.2 to 0.5 55*

Predominantly loose to very dense silty sand [SM], silty clayey sand [SC-SM], and clayey sand [SC] with intermittent zones of stiff to hard clays [CL, CH, and CL/CH], and medium dense to very dense relatively clean sands [SP, SP-SM, and SP-SC].

4 to 50/0”

* Termination depth of the deepest test boring [ ] Brackets indicate Unified Soil Classification System (ASTM D 2487)

At the time of our field exploration, a stabilized groundwater table was not found within a depth of 30 feet below existing grade (BEG) at the test boring locations.

3.5 NOTABLE FINDINGS – VERY DENSE SOILS

A notable finding during the exploration program was the presence of dense to very dense and hard soil conditions across the generally starting at relatively shallow depths within the upper approximately 10 to 15 feet BEG. At the location of Boring B-11, these high consistency soils were encountered at the ground surface, and were generally prevalent throughout the depth of the boring. These soils had SPT “N” values greater than 30 blows per foot (bpf) ranging up to 50 blows with no measurable penetration (50/0”) or practical refusal.

It has been our experience that soils with SPT “N” blow counts in excess of about 30 bpf may prove to be difficult to excavate through with smaller sized equipment. Based on the boring data, it would appear that these soils could pose general construction problems at shallow depths in the area of Boring B-11. In the remaining areas of the site, it would appear that these higher consistency soils would not likely pose problems with construction operations above approximate depths of 10 to 15 feet BEG.

We recommend the contract documents stipulate that the site contractor is solely responsible for selecting their equipment appropriately for these anticipated site conditions without recourse for a change order after the project has been awarded.

3.6 CALIFORNIA BEARING RATIO (CBR) TESTING

Two CBR tests were performed on representative soils in general accordance with ASTM D1883.

A summary of the CBR test results and the moisture-density relationships of the soil and CBR values are presented in the following Table 3.

Table 3 - Summary of CBR Test Results

Sample Location

Sample Depth (feet)

Material Dry Density of Test Specimen

(pcf)

Compaction Moisture

Content (%)

Corrected CBR at

0.1 in

Percent Compaction

B-6 0.5 to 1 Brown silty sand

[SM]* 123.4 9.6 20 100

B-11 0.5 to 1

Brown red orange silty clayey sand

[SC-SM]*

124.6 9.6 31 100

B-11 0.5 to 1

Brown red orange silty clayey sand

[SC-SM]*

118.1 10.4 8 95

* Percentages passing the number 200 sieve for the soils tested were 31 and 42 percent by dry weight for borings B-6 and B-11, respectively.

** Percentages of compaction are based on modified Proctor maximum dry densities of 122.8 and 124.4 pcf with optimum moisture contents of 9.5 and 10 percent for the soils tested from borings B-6 and B-11, respectively.

4.0 RECOMMENDATIONS

4.1 GEOTECHNICAL ASSESSMENT

In this section of the report, we present recommendations for foundation design, seismic site classification, and site preparation. The following geotechnical design recommendations have been developed on the basis of the previously described project characteristics and subsurface conditions encountered. If there are any changes in these project criteria, a review should be made by UES to determine if modifications to the recommendations are warranted.

4.2 GROUNDWATER CONSIDERATIONS

The groundwater table will fluctuate seasonally depending upon local rainfall. The typical wet season groundwater level is defined as the highest groundwater level sustained for a period of 2 to 4 weeks during the "wet" season of the year, for existing site conditions, in a year with average normal rainfall amounts. Based on historical data, the rainy season in Northwest Florida is typically between June and September of any given year.

At the time of our field exploration, a stabilized groundwater table was not found within a depth of 30 feet BEG at the test boring locations. Based upon our review of U.S.G.S. data, Santa Rosa

County Soils Survey, and regional hydrogeology, our best estimate for the stabilized seasonal high groundwater table would be below a depth of approximately 30 feet BEG at the test boring locations. However, we believe that, in some instances, subsurface conditions found on site are conducive to the formation of a transient, perched groundwater condition at a depth of about 4 feet BEG across the site. This condition will be discussed in more detail in the following section.

Please note that groundwater levels could temporarily exceed these estimated levels during any given year in the future. Should impediments to surface water drainage exist on the site, or should rainfall intensity and duration, or total rainfall quantities exceed the normally anticipated rainfall quantities, the groundwater level may be shallower than the previously discussed estimated conditions.

We recommend positive drainage be established and maintained on the site during construction.

We further recommend permanent measures be constructed to maintain positive drainage throughout the life of the project. All site improvement designs should incorporate the seasonal high groundwater levels as appropriate.

4.2.1 Transient Perched Groundwater

It should be noted that relatively shallow deposits of hydraulically restrictive silty and clayey soils [CL, CH, CL/CH, and SC] were found on site at the test boring locations. During periods of above normal rainfall or for short periods following unusually intense rainfall (most especially tropical storm and hurricane events), there may be temporary water seepage zones (a.k.a., perched groundwater) present immediately above these soils that could adversely affect the performance of the site improvements including foundations, slabs, and underground utility installations. This transient groundwater atop and within these soils needs to be considered when setting foundation embedment depths and the potential need for underdrains to keep pavement and foundation subgrades dry.

Perched groundwater levels can generally be expected to occur about 6 inches to 1 foot above the restrictive soils, where present, if the groundwater table is unable to drain and/or percolate into a more pervious layer. It should be noted that undercutting of these materials will impact the depth of the hydraulically restrictive layer and thus the depth of the perched water table. The potential for groundwater to perch will be directly related to rainfall and irrigation amounts, as well as site grading.

4.3 SEISMIC SITE CLASSIFICATION

Practical refusal of the drilling equipment mobilized for the field exploration occurred at an approximate depth of 55 feet on the project site in very dense sands. Because of the inability to advance a boring to the required depth of 100 feet below existing grade, calculations to determine the seismic site class were performed by extrapolating the SPT “N” value encountered at 55 feet to a depth of 100 feet. Using this extrapolation and the calculation procedure presented in ASCE 7-10, it is our opinion that the subsurface conditions within the site will be consistent with the characteristics of Site Class D. A Site Class D is consistent with our experience on other sites on NAS Whiting Field, as well other sites throughout the Northwest Florida area.

4.4 FOUNDATION DESIGN

4.4.1 General

Based on the results of our field exploration, we consider the subsurface conditions at the site adaptable for support of the proposed structure when constructed on properly designed conventional shallow foundation systems. Provided the site preparation and earthwork construction recommendations outlined in Section 4.6 of this report are strictly followed, the following parameters may be used for the foundation design.

As noted previously, the building foundation recommendations provided in this report are based on our assumption of minimal (i.e., approximately 2 feet or less) structural fill being necessary to achieve the desired finished grade elevation in the proposed building area, single-story building construction, and our assumed maximum structural loadings of 6 kips per linear feet (klf) for continuous walls and 250 kips per column. Once the actual structural loads are known, new settlement estimates should be performed. If they exceed the structural loading estimates provided above, then the recommendations presented herein are not considered valid.

4.4.2 Allowable Net Soil Bearing Pressure

The maximum allowable net soil bearing pressure for use in the shallow foundation design should not exceed 2,500 pounds per square foot for continuous wall/strip foundations, and 2,000 pounds per square foot for column foundations. These bearing pressures are suitable for code dead and live loads plus any short duration loadings, and assume that the surficial soils to a depth of 1 foot below the base of foundations are densified to at least 95 percent of the modified Proctor maximum dry density (ASTM D 1557) prior to foundation construction.

Net bearing pressure is defined as the soil bearing pressure at the base of the foundation in excess of the natural overburden pressure. The foundations should be designed based upon the maximum load that could be imposed by all loading conditions.

4.4.3 Foundation Size

The minimum widths recommended for any isolated column footings and continuous wall footings are 24 inches and 18 inches, respectively. Even though the maximum allowable net soil bearing pressure may not be achieved, these width recommendations should control the minimum size of the foundations to prevent “shear punch” deformations.

4.4.4 Bearing Depth

The exterior foundations should bear at a depth of at least 24 inches below the finished exterior grades and the interior foundations should bear at a depth of at least 18 inches below the finish floor elevation to provide suitable confinement to the bearing level soils. Stormwater should be diverted away from the building exteriors to reduce the possibility of erosion beneath the exterior footings.

4.4.5 Bearing Material

The foundations may bear in either the compacted suitable native soils or compacted structural fill. The foundation excavation bottoms should be level or suitably benched, and free of any loose soils that have been disturbed by seepage or the construction process. Furthermore, the foundation excavation bottoms should be free of standing water. The bearing level soils, after compaction, should exhibit densities equivalent to at least 95 percent of the modified Proctor maximum dry density (ASTM D 1557) to a depth of at least 1 foot below the foundation bearing level. It is recommended that foundation bearing areas be probed to a depth of 3 feet below bearing subgrade elevations to verify the suitability of the subgrade soils.

4.4.6 Settlement Estimates

Post-construction settlement of the structure will be influenced by several interrelated factors, such as the following: subsurface stratification and strength/compressibility characteristics;

foundation sizes, bearing levels, applied loads, and resulting bearing pressures beneath the foundations; and site preparation and earthwork construction techniques, as well as building construction operations used by the contractor. Our settlement estimates for the building are based on the assumed structural loading information and the site preparation/earthwork recommendations in Section 4.6 of this report. Any deviation from these recommendations could result in an increase in the estimated post-construction settlement of the structure.

Based on the subsurface conditions found in the test borings and the recommended earthwork operations, we expect the majority of settlement to occur fairly rapidly during construction. Using the recommended maximum bearing pressures, the assumed maximum structural loads, and the field data which we have correlated to geotechnical strength and compressibility characteristics of the subsurface soils, we estimate that total post-construction settlement of the structure could be on the order of about 1-inch or less.

Differential settlements result from differences in applied bearing pressures and variations in the compressibility characteristics of the subsurface soils. Because of the general uniformity of the subsurface conditions and the recommended site preparation and earthwork construction techniques outlined in Section 4.6, we anticipate that post-construction differential settlement of the structure should be within tolerable magnitudes of about ½-inch or less over a 40 feet long portion of a continuous footing, or between similarly spaced footings.

4.4.7 Lateral Loads

Lateral loads applied to the proposed shallow foundations will be primarily resisted by resistance to sliding on the bottom of the foundations as well as lateral resistance against the sides of the foundations. We recommend an active earth pressure coefficient (Ka) of 0.33, passive earth pressure coefficient (Kp) of 3.0, at-rest earth pressure coefficient (Ko) of 0.5, total soil unit weight of 130 pcf, and a coefficient of sliding friction of 0.35 be used for this purpose, assuming site preparation is performed in accordance with the recommendations in this report.

4.4.8 Foundation Evaluations

All footings excavations should be evaluated by the contractor’s Geotechnical Engineer prior to placement of steel reinforcement and/or concrete. It should be anticipated that undercutting of select areas may be required because of variations in the soil matrix, fill quality, and/or contractor means and methods. If undercut, the unsuitable material may be replaced with No. 57 crushed stone, over-poured with concrete or placed back with compacted, clean structural fill.

4.5 FLOOR SLAB/PAVEMENT

Due to the nature of the proposed structure and its use, the floor slab system for the building will likely also function as a pavement for the vehicles and aircraft that will move in and out of the hangar. Due to the preliminary nature of the project information provided to us, and the lack of any information concerning the type of vehicles, the traffic volume, and/or the traffic loads, design recommendations for the slab as a pavement system cannot be presented or reasonably discussed in this report. Rather, the recommendations presented in this section will address the slab with regard to its function as a floor system, and present general information with regard to the function/construction of the slab as a pavement.

4.5.1 Floor Slab

The floor slab can be constructed as a slab-on-grade member using a coefficient of subgrade reaction (K) of 150 pci provided the backfill and the subgrade materials are compacted as outlined in Section 4.6 of this report. For a floor slab system, we recommend that the bearing soils be covered with an impervious membrane to reduce moisture entry and floor dampness in accordance with current Florida Building Code Requirements. In addition, stormwater should be diverted away from all floor slab areas to prevent the infiltration of water into the slab subgrade soils, and the associated deterioration of the slab subgrade(s).

4.5.2 General Concrete Requirements for Slab/Pavement System

The Portland Cement Concrete (PCC) used for a rigid slab/pavement system should be a minimum of 4,000 psi at 28 days, 4-inch maximum slump, and less than 6 percent air-entrained 6-sack minimum mix. The Portland cement should be Type I.

4.5.3 Control Joints for Slab/Pavement System

Control joints, for crack control for the slab/pavement, should be spaced closely, at about 8 to 12 feet apart, and should provide a uniform square or a compact rectangular pattern. The joint pattern, including placement of utility access facilities (manholes, junction boxes, fill ports, etc.)

should be submitted for review and approval prior to construction. Depth of the joints should be at least one-third (⅓) of the concrete slab thickness. Joints should be sawed as soon as the concrete can withstand traffic, while not so soon as to cause raveling of the concrete surface and aggregate during sawing.

Construction joints and expansion joints are the pavement features most susceptible to damage, and for that reason, their use should be minimized. Placement of construction joints should be approved prior to commencement of concrete placement. Construction joint placement should be planned to occur at narrow sections of pavements, such as driveways. In the event expansion joints are provided, they should be thoroughly cleaned of debris, on completion, and then properly sealed with an appropriate preformed or self-leveling petroleum resistant joint sealer.

4.5.4 Concrete Placement for Slab/Pavement System

Placement and curing of concrete pavement should conform with all applicable American Concrete Institute (ACI) standards and in particular with recommended procedures for hot weather concrete work. Cure the concrete pavement either with moist curing (burlap or plastic sheeting) or with a liquid curing compound. A fugitive dye should be considered for the curing compound as a means of verification that the curing compound is applied properly and remains in place for a sufficient period of time.

4.5.5 Groundwater Considerations

One of the most critical influences on pavement performance in Northwest Florida is the relationship between the pavement subgrade and the seasonal high groundwater level. Typically, as a minimum, it would be recommended that the seasonal high groundwater and the bottom of the slab/pavement be separated by at least 12 inches. However, considering the site and subsurface conditions encountered by the borings, it is anticipated that groundwater should not be present unless a transient perched condition associated with construction occurs. Therefore, it is important that precautions be taken during construction to avoid the creation of conditions conducive to the occurrence of perched groundwater under all pavement/slab areas. In addition, to protect slab/pavement subgrades from water infiltration and associated subgrade deterioration, positive drainage measures for slab/pavement areas should be implemented. These measures should promote rapid drainage of stormwater off of and away from the slab/pavement areas, and not allow ponding of water either on the pavement surface(s) or around or along all pavement edges.

4.6 SITE PREPARATION

We recommend normal, good practice site preparation procedures. These procedures include stripping the proposed construction areas of surficial vegetation, trees, roots, stumps, and other deleterious materials present; compacting the exposed subgrade, verifying subgrade compaction, and placing engineered fill to the desired grades. An expanded and more detailed synopsis of this work is provided in the following sections.

4.6.1 Temporary Groundwater Control

If encountered, we recommend that the groundwater table be lowered and maintained at a depth of at least 2 feet below bearing levels and excavation bottoms during construction. Dewatering may consist of ditching, sumps with pumps, or other means. However, groundwater control means and methods are the sole responsibility of the contractor. Furthermore, we recommend that the Contractor determine the actual groundwater levels at the time of construction to determine the groundwater impact on the construction procedures. If groundwater is encountered during trenching or foundation installation, the Geotechnical Engineer of Record should be notified so that they can determine whether there is a need for underslab drainage, perimeter drains, or other recommendations for dewatering.

4.6.2 Nearby Structures and Vibrations

Care should be exercised to avoid damaging any nearby structures while the site preparation and earthwork operations are underway. Prior to commencing site work operations in areas of this site that will be constructed near adjacent structures and/or developments, we recommend that occupants of adjacent structures should be notified, and the existing conditions of the structures be documented with photographs and survey. Compaction should cease if deemed detrimental to adjacent structures.

Pre-construction building surveys of all off-site adjacent structures are also recommended, but absent these surveys we recommend that the vibratory function of the compaction equipment be turned off when operating within 50 feet of any adjacent structures.

4.6.3 Existing Underground Utilities

The location of any existing underground utility lines within the proposed construction areas should be established prior to initiating construction. Provisions should then be made to relocate or abandon interfering utilities. It should be noted that if underground pipes are not properly removed or plugged, they may serve as conduits for subsurface erosion which may subsequently lead to excessive settlement of overlying pavements and structures.

4.6.4 Site Preparation and Grading

Prior to performing earthwork operations, all vegetation, topsoil, and other unsuitable materials and/or debris should be removed from the construction areas, and hauled offsite. Stripping will also include the demolition and removal of any existing structures, foundations, underground utilities, tanks, and construction debris that may be present within the stripping limits. Care should be taken with the removal of trees to verify removal of stumps and any associated root systems.

Any excavations performed for tree removal or for the removal of other underground appurtenances (e.g., foundations, utilities, etc.) should be extended down to undisturbed native soils, and the resulting excavations properly backfilled with suitable structural fill placed and compacted in accordance with recommendations presented in subsequent sections of this report.

The initial stripping operations should extend a minimum of 5 feet beyond the outside edges of the building and associated foundations. Based on the boring data obtained, it is anticipated that up to approximately 6 inches of topsoil or pavement materials will have to be removed, in general, in conjunction with the stripping operations for the project site. However, expect typical stripping at this site to a depth of 6 to 12 inches.

After stripping, removal of unsuitable surface soils, and rough excavation grading, we recommend that areas to provide support for structural fill be evaluated carefully for the presence of soft surficial soils, and/or plastic soils. Such evaluation should include proofrolling with observation by the Geotechnical Engineer of Record or his representative. Proofrolling should be accomplished by using a heavily-loaded 20 to 30 ton dump truck or other pneumatic tired construction vehicle of similar size and weight. A minimum of 2 overlapping passes, in each of 2 perpendicular directions, should be made over all areas of the site at or below the finished grade. In addition, finished subgrade elevations in cut areas should be proofrolled after excavation operations. It is further recommend that the proofrolled subgrades be moisture conditioned and compacted to at least 95 percent of the materials’ modified Proctor (ASTM D1557) maximum dry densities. This proofrolling and compaction process will help provide a stable base for the compaction of new structural fill, and delineate low density, loose, or disturbed areas that may exist below subgrade level. Areas of soft or loose subgrade soils should be undercut, moisture conditioned, and compacted or replaced with approved structural fill.

Care should be exercised during the site preparation activities due to the presence of near surface clayey soils. Excessive vibration could result in pumping of the clayey site subgrade soils, which may result in the need for over excavation and replacement.

4.6.5 Fill Placement

Once the site has been stripped and prepared, place fill material as required to meet finished grades. The recommended criteria for soil fill characteristics (both on-site and imported materials) and compaction procedures are listed in the following sections. The project design documents should include the following recommendations to address proper placement and compaction of project fill materials. Earthwork operations should not begin until representative samples are collected and tested (allow 3 to 4 days for sampling and testing). The maximum dry density and optimum moisture content should be determined.

4.6.6 Earth Fill Materials

Engineered structural fill should meet the following material properties.

� Material satisfactory for structural fill should include silty and/or clayey soils with USCS classifications of SM, SC-SM, or SC. The fill material should have a modified Proctor (ASTM D1557) maximum dry density of at least 100 pcf, 15 to 30 percent fines passing the No. 200 sieve, a maximum Liquid Limit of 25 and a Plasticity Index of 10 or less. Silty and clayey materials that exceed the recommended fines content, Liquid Limit, and Plasticity Index values should not be used as structural fill material within 5 feet of finished site grades. We note these soils will be sensitive to even slight changes in moisture content. Strict moisture control will be required to properly compact these soils.

� Organic content or other foreign matter (debris) should be no greater than 3 percent by weight, and no large roots (greater than ¼ inch in diameter) should be allowed.

� Material utilized as fill should not contain rocks greater than 3 inches in diameter or greater than 30 percent retained on the ¾-inch sieve.

Clean sandy soils (SP, SP-SM, and SP-SC) should not be used as structural fill and placed on top of native clayey soils (SC, SC-SM, and CL/CH) due to the potential for a trapped perched groundwater level to form. The potential for a “perched” groundwater level to occur above the clayey soils should be avoided as this could result in unstable and pumping subgrade conditions.

We note that clean sandy soils (SP, SP-SM, and SP-SC) were not found on or near the groundsurface at the test locations. Therefore, this item should not be a potential issue unless such soils are imported to the subject site.

4.6.7 Compaction Recommendations

The following recommendations are presented for fill placement and compaction. The recommendations are also applicable for the compaction of existing soil materials on the project site.

� Maximum loose lift thickness – 10 inches, mass fill. Loose lifts of 4 to 6 inches in trenches and other confined spaces where hand operated equipment is used.

� Compaction requirements – 95 percent of the maximum dry density as determined by the modified Proctor (ASTM D 1557) compaction test.

� Soil moisture content at time of compaction should be within ±2 percent of the optimum moisture content. Fill materials with greater than about 10% passing the No. 200 sieve will generally be sensitive to even slight changes in moisture. The moisture content of these soils should be maintained slightly below the optimum moisture content in order to help mitigate the potential for moisture related instability during placement and compaction.

� The use of heavy vibratory compaction equipment is not recommended due to the potential for disturbance and pumping of near surface clayey soils.

4.6.8 Test Criteria to Evaluate Fill and Compaction

The following minimum criteria for the evaluation of fill materials, and the compaction of the fill materials are recommended. The recommendations are also applicable for the evaluation and compaction of existing soil materials on the project site.

� One modified Proctor compaction test and one number 200 sieve analysis test for each soil type used as project fill. Atterberg limits tests may be necessary and should be performed at the geotechnical engineer’s discretion.

� Structure area – One density test for every 5,000 square feet of building area for each lift or two tests per lift, whichever is greater.

� Foundation areas – Test all foundation bearing subgrades for compaction to a depth of 1 foot below bearing subgrade elevation prior to the placement of reinforcing steel and concrete. We recommend testing every 1 to 3 column foundations, and one test for every 75 linear feet of wall foundation. Additionally, using the same testing frequency, we recommend the performance of Dynamic Cone Penetrometer (DCP) or Static Cone Penetrometer in the foundation excavations to assess the suitability of the bearing level soils. Recompaction of the foundation excavation bearing level soils, if loosened by the excavation process, can typically be achieved by making several passes with a walk-behind vibratory sled or jumping jack compactor, or by undercutting to more firm underlying soils and backfilling with compacted structural fill, flowable fill, lean concrete, or compacted No.

57 stone.

� Trench fill areas – One density test for every 75 to 100 linear feet of trench per lift or two tests per lift, whichever is greater.

4.7 CONSTRUCTION RELATED SERVICES

It is recommended that the Contractor utilize the services of an experienced engineering testing laboratory to perform construction materials tests and observations on this project. Field tests and observations should include: verification of embankment, stabilized subgrade, and base courses in pavement areas by performing quality assurance tests on the placement of compacted structural fill courses; concrete testing; structural steel inspections; proofrolling monitoring; and general construction observation services.

4.7.1 Excavation and Safety

In Federal Register, Volume 54, No. 209 (October 1989), the United States Department of Labor, Occupational Safety and Health Administration (OSHA) amended its “Construction Standards for Excavations, 29 CFR, Part 1926, Subpart P”. This document was issued to better allow for the safety of workers entering trenches or excavations. It is mandated by this federal regulation that excavations, whether they be utility trenches, basement excavations or footing excavations, be constructed in accordance with the new OSHA guidelines.

The Contractor is solely responsible for designing and constructing stable, temporary excavations and should shore, slope, or bench the sides of the excavations as required to maintain stability of both the excavation sides and bottom. The Contractor's “responsible person”, as defined in 29 CFR Part 1926, should evaluate the soil exposed in the excavations as part of the Contractor’s safety procedures.