Geotech_Report_-_Juarez-Lincoln.pdf

REVISED GEOTECHNICAL ENGINEERING

REPORT

Laredo-Bus Processing Inspection Facility Lincoln-Juarez United States Land Port of Entry Laredo, Texas

Schnabel Reference 11223002.01

August 19, 2013 (Revision 2)

July 24, 2013 Revised August 19, 2013

Ms. Stefee Knudsen, AIA, LEED® AP (BD+C) THA Architecture, Inc.

733 SW Oak Street, Suite 100 Portland, OR 97205

Subject: Project 11223002.01, Revised Geotechnical Engineering Report (10% Redesign) – Bus Processing Inspection Facility, Lincoln-Juarez United States Land Port of Entry (LPOE), Laredo, Texas

Dear Ms. Knudsen:

SCHNABEL ENGINEERING, LLC (Schnabel) is pleased to submit this revision geotechnical engineering report for the above referenced project. This report includes tables, figures, and appendices with relevant data collected for this study. This study was performed in accordance with our proposal dated March 7, 2012, as authorized by your e-mail notice to proceed received on April 30, 2012. This report has been revised based on comments received from the design team. This report contains the infiltration test results that were provided initially in our April 2, 2013 data report. The report has been revised based on design team comments received in July and August, 2013.

We appreciate the opportunity to be of service for this project. Please call us if you have any questions regarding this report.

Sincerely, SCHNABEL ENGINEERING, LLC

Christopher S. Clarke, PE Project Engineer

John O. Sturman, PE, PG, GE, CEG Senior Associate

CSC:JOS:sam K:\11223002 Laredo Bus Screening Station\WP\FINAL\11223002.01 - Laredo Bus Screening Station Redesign Revised 8-19- 13.Docx

THA Architecture Laredo-Bus Processing Inspection Facility

August 19, 2013 Page i Schnabel Engineering, LLC Project 11223002.01 ©2013 All Rights Reserved

GEOTECHNICAL ENGINEERING REPORT

LAREDO-BUS PROCESSING INSPECTION FACILITY

LAREDO, TEXAS

TABLE OF CONTENTS

1.0 EXECUTIVE SUMMARY

2.0 SCOPE OF SERVICES

3.0 DESCRIPTION OF SITE AND PROPOSED CONSTRUCTION

3.1 Site Description

3.2 Proposed Construction

3.3 Regional Geology

3.4 Regional Seismicity

4.0 SUBSURFACE EXPLORATION PROGRAM

4.1 Subsurface Exploration and Field Testing

5.0 LABORATORY TESTING

5.1 Soils Testing

6.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

6.1 Site Geology

6.2 Generalized Subsurface Stratigraphy

6.3 Groundwater

6.4 Seismic Site Classification

7.0 SITE GRADING AND EARTHWORK

7.1 Compacted Fill Subgrades

7.2 Compacted Fill

7.3 Slopes

8.0 FOUNDATION RECOMMENDATIONS

8.1 Spread Footings

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9.0 FLOOR SLAB RECOMMENDATIONS

10.0 LATERAL EARTH PRESSURE RECOMMENDATIONS

11.0 PAVEMENT RECOMMENDATIONS

12.0 CORROSION CONSIDERATIONS

13.0 CONSTRUCTION CONSIDERATIONS

13.1 Site Grading and Earthwork

13.2 Spread Footings

13.3 Floor Slabs and Pavement Subgrades

13.4 Engineering Services During Construction

14.0 GENERAL SPECIFICATION RECOMMENDATIONS

15.0 LIMITATIONS

REFERENCES

LIST OF FIGURES

Figure 1: Site Vicinity Map Figure 2: Geologic Map Figure 3: Footing Undercut Detail Figure 4: Lateral Earth Pressure Diagram for Site Retaining Walls Figure 5: Lateral Earth Pressure Diagram for Below-Grade Walls Figure 6: Subdrain Design Recommendations

APPENDICES

Appendix A: Subsurface Exploration Data Appendix B: Soil Laboratory Test Data Appendix C: Existing Subsurface Information Appendix D: Infiltration Testing Data Report

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1.0 EXECUTIVE SUMMARY

This report presents the results of subsurface exploration, laboratory testing, and geotechnical engineering analysis for the 10% Re-Design of the proposed Bus Processing and Inspection Facility at the Land Port of Entry (LPOE) in Laredo, Texas.

We are providing this executive summary solely for purposes of overview. Any party that relies on this report must read the full report. This executive summary omits several details, any one of which could be very important to the proper application of the report.

The test borings indicate that subsurface conditions consist of a mixture of fine grained and coarse grained fill soils of Stratum A, encountered to depths of up to 6.5 ft. Below the existing fill soils and ground surface were the alluvial silt and clay soils of Stratum B1, encountered to depths of up to 28.5 ft. Below and interlayered with the fine grained alluvium of Stratum B1, was the coarse grained alluvial sands and gravels of Stratum B2, encountered to a depth of up to 48.5 ft.

Below the coarse grained alluvium of Stratum B2, the fine-grained argillaceous sandstone of Stratum C2 and the residual soils of Stratum C1 were encountered up to a depth of 48.8 feet, the maximum depth encountered. The fine-grained argillaceous sandstone was observed, through SPT sampling, to be weathered to a soil consistency.

Groundwater was observed in some of the test borings performed. Groundwater, where identified, was observed at depths ranging from 28 to 39 ft below the ground surface corresponding to elevations ranging from EL 374 to 387 ft. Groundwater observations were made during drilling and generally groundwater was not encountered the following day in boreholes that were left open.

We recommend the proposed building and site canopy structures be supported by spread footing foundations bearing on the natural soils of Strata B1 and B2 with an allowable bearing pressure of 2.5 ksf) Footings should bear a minimum of 2 ft below finished exterior grades. Lowering footings and/or undercut and replacement may be required to prepare a suitable bearing grade for the proposed structures.

Slabs on-grade may be earth supported on new structural fill or suitable natural soils. Any existing fill soils should be removed in their entirety and replaced with new structural fill. High plasticity soils, if encountered, are generally not suitable for floor slab support and should be removed to a depth of 2 ft or in their entirety, whichever is less, and replaced with suitable structural fill or dense graded aggregate.

Pavements may be supported on suitable natural soils, existing fill soils without deleterious materials that pass a proofroll, or new structural fill. Any deleterious existing fill soils or high plasticity soils, if encountered, should be removed in their entirety or to a minimum a depth of 2 ft and replaced with suitable structural fill. We recommend that soils placed under paved areas have a California Bearing Ratio (CBR) value of at least 8.

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Structural fill placed within the expanded building footprints and pavement subgrades should consist of soil classifying as ML, SC, SM, SP, SW, GC, GM, GP, or GW per ASTM D-2487. The structural fill soils should generally have a liquid limit less than 45 and a plasticity index less than

20. High plasticity soils, if encountered, are not suitable for placement in a structural fill.

An allowance should be established to account for possible additional costs that may be required to construct the proposed bus screening facility as recommended in this report. Additional costs may be incurred for various reasons, including but not limited to soft or unsuitable subgrade conditions, difficulty in obtaining structural fill and backfill compaction, removal and replacement of existing fill, the presence of unidentified utilities, etc.

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2.0 SCOPE OF SERVICES

Our proposal dated March 7, 2012 defines the scope of services for this project. These services are based upon the original Statement of Work dated August 2, 2010 and our current understanding of the realignment of the building, canopy, and pavement layout at the site. Services performed for this project included the drilling of five (5) geotechnical test borings, soil laboratory testing, engineering analysis, and preparation of this geotechnical engineering report. This geotechnical engineering report includes the following:

1. A discussion of the general geologic setting, including discussion of potential geologic hazards, a description of terrain, and a geologic history based on available published maps and reports.

2. An evaluation of estimated subsurface conditions at the site based on the subsurface data collected during our exploration.

3. Foundation requirements for support of the proposed building, including a recommended allowable soil bearing pressure, bearing grades, and estimated foundation settlements.

4. Lateral earth pressure recommendations for use in the design of site retaining walls and below-grade walls.

5. Recommendations for the base floor slab support, including a modulus of subgrade reaction (k) value for design, if applicable.

6. Recommendations for pavement support, including a preliminary CBR based on the available soil information.

7. Recommendations regarding temporary handling of groundwater during construction and in design of permanent below-grade features.

8. Recommended seismic site classification per IBC 2009 based on extrapolated SPT boring data.

9. Comments concerning the potential for soil attack on buried steel and concrete.

10. Comments regarding geotechnical construction considerations for use in the design and construction plans and specifications.

11. Results of infiltration testing that was performed subsequent to the initial issuance of the geotechnical engineering report.

Services with respect to specific construction dewatering recommendations, CA services, radon testing and control, environmental matters, design of excavation sheeting, temporary slopes, erosion control, cost or quantity estimates, plans, specifications, construction observations and testing, and services not specifically identified are not included in the scope of services.

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3.0 DESCRIPTION OF SITE AND PROPOSED CONSTRUCTION

3.1 Site Description

The project site is flat, bounded to the south by the existing LPOE, to the north by Hidalgo St., to the east by existing buildings, and to the west by Santa Ursula Ave. This site area is generally concrete paved with minor landscaping in grass covered median areas. The existing Building 4 canopy structure is located at the project site and contains vehicle processing offices, mechanical lifts and screening devices, and other inspection and security features. A grass and earthen area south of Hidalgo St. is at the northern portion of the project site. This area currently contains an existing sign structure and light poles, but is mostly undeveloped. A Vicinity Map is included as Figure 1.

3.2 Proposed Construction

At the time of this proposal, we understand that specific building and canopy layouts, pavement areas, and other project specific details are not yet available. We have based our understanding of the proposed construction on project details described in the original scope of work dated August 2, 2010 and our conversations with the design team. We understand that the GSA intends to complete the design and construct a Bus Processing Facility at the Lincoln-Juarez United States Land Port of Entry (LPOE) in Laredo, Texas. The project design requirements indicate that a new 10,000 to 15,000 square foot bus and bus passenger processing facility will be added to increase the LPOE capacity. Based upon the 10% Redesign Drawings dated March 5, 2012 we understand that a combined bus processing and passenger facility will be constructed in the footprint of the existing Building 4 canopy structure. Based upon the original SOW, this facility will include a luggage x-ray and inspection area; I-94 processing area and permit counters; waiting area; detention area; areas for State and Federal inspection agencies;

restrooms; pedestrian inspection lanes; bus stalls; an inspection area; and a loading and unloading canopied area.

We understand that the proposed facility will be constructed in accordance with applicable Federal, State, and local design requirements. We assume that a single structure will be constructed for the Bus Processing Facility; however, at this time only a conceptual building footprint and preliminary estimated building loads have been provided. Based upon the square footage requirements, we have assumed that the structure will be 1 to 2 stories in height and set near to existing grade. Based upon our correspondence with the project structural engineer, kpff, we understand that column loads will be limited to about 150 kips for the canopy columns and 25 kips for the building columns. The walls supporting the proposed bus processing facility will transfer loading of approximately 2.8 kips per foot.

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3.3 Regional Geology

The site lies near the western portion of the Gulf Coastal Plain. The Gulf Coastal Plain area is characterized as being typically underlain by marine and continental Tertiary sedimentary rocks, which are typically sandstone and claystone. These sedimentary rocks were formed as a result of rapid depositional progradation across the cretaceous continental margin and into the Gulf of Mexico.

Considering its proximity to the Rio Grande River System, the surficial geology at the site consists of fluvial terrace deposit of deposited during the Pliestocene epoch. A geologic map for the Laredo area is shown as Figure 2.

3.4 Regional Seismicity

This region of southern Texas exhibits low levels of seismicity. Based on available earthquake databases, only one earthquake has occurred with a Moment Magnitude 5.0 or greater since 1973 within 500 km (310 mi) of Laredo (including Northern Mexico). In 1995 an earthquake occurred in western Texas near Alpine having a Moment Magnitude of 5.7. This earthquake is known to be the second largest earthquake in Texas recorded history according to the Texas State Historical Association. The epicenter of this earthquake was approximately 486 km (302 mi) away from Laredo.

The seismic hazard at the site is considered to be low (equivalent UBC Seismic Zone designation of 0).

Based on the seismic spectral ground motions (Ss = 0.067 and S1 = 0.017), a design maximum horizontal ground acceleration of 0.043 g has been estimated to develop geotechnical-related design recommendations for lateral loading of below-grade and site retaining walls. The Seismic Considerations Section provides recommendations for the IBC soil Site Class.

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4.0 SUBSURFACE EXPLORATION PROGRAM

We conducted a subsurface exploration and field testing program to identify the subsurface stratigraphy underlying the site and to evaluate the geotechnical properties of the materials encountered. This program included drilling test borings and collecting soil samples. Exploration methods used are discussed below. The appendices to this report contain the results of our exploration.

4.1 Subsurface Exploration and Field Testing

4.1.1 Test Borings

Our subcontractor, Alpha and Omega Drilling, drilled five (5) test borings under our observation between May 14 and 16, 2012. The Standard Penetration Test (SPT) was conducted at selected depths in the borings. Appendix A includes specific observations, remarks, and logs for the borings, classification criteria, drilling methods, and sampling protocols. Figure A1, included at the end of Appendix A, indicates the approximate test boring locations. We will retain soil samples up to 45 days beyond the issuance of this report, unless you request other disposition.

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5.0 LABORATORY TESTING

Our laboratory conducted tests on selected samples obtained during the subsurface exploration. The testing aided in the classification of materials encountered in the subsurface exploration and provided data for use in the development of recommendations for design of building and canopy foundations, earthwork, and pavements. Moisture contents are shown on the boring logs in Appendix A. Appendix B presents the results of the laboratory testing program.

5.1 Soils Testing

5.1.1 Index Testing

We conducted natural moisture content, Atterberg Limit, and gradation tests on test samples representing Strata A, B1, B2, and C2 to provide soil classifications and to provide parameters for use with published correlations with soil properties. The index property testing includes data collected during both our 2011 and 2012 subsurface exploration and testing programs. The results are presented in the Summary of Laboratory Tests in Appendix B and are summarized for each stratum in Section 6.0.

5.1.2 Compaction and CBR Testing

We conducted Standard Proctor compaction and CBR testing of soil samples representing Stratum A and a combination of Strata A and B1 to evaluate compaction characteristics and to provide soil parameters for pavement design. The test results are included in Appendix B and are summarized in Section 6.0.

5.1.3 Corrosivity Testing

We conducted tests for pH, sulfides, redox potential, and resistivity testing on four (4) samples representing Strata A and B1. The test results are presented in Appendix B and are summarized for each stratum in Section 6.0.

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6.0 SITE GEOLOGY AND SUBSURFACE CONDITIONS

Prior to our most recent subsurface exploration in May of 2012, Schnabel had previously performed a geotechnical exploration consisting of drilling eight (8) borings to varying depths in the median areas to the north of the current project site in June of 2011. Based upon our current understanding of the project site development, we understand that the proposed site improvements will be limited to the area south of Hidalgo Street. Therefore, we have included the previous boring and laboratory data collected south of Hidalgo Street in this report. The applicable borings from our previous investigation include borings B-1 through B-5. This data is included in our stratigraphy description and provided in Appendix A of this report. The approximate boring locations are identified on our Boring Location Plan, Figure A1.

6.1 Site Geology

The upper FILL soils of Stratum A, are believed to be manmade deposits that are a results of earthwork activities associated with roadway construction and construction of the existing Land Port of Entry Facilities. Below the fill soils, the alluvial deposits of Strata B1 and B2 are believed to be Pleistocene epoch fluvial terrace deposits associated with the nearby Rio Grande River System. This Alluvium typically contains gravel, sand, silt, and clay in varying proportions. Our investigation found that much of the gravel particles in the alluvium were rounded to subrounded which are typical characteristics of sedimentary deposits.

Underlying the Stratum B alluvium, is believed to be the sandstone and localized areas of clay of the Laredo Formation formed during the Eocene epoch. The sandstone found in this deposit is described as being very fine to fine grained, ferruginous, gluconitic, micaceous, crossbedded, and extensively bioturbated. The clay of the Laredo Formation is known to contain limestone concretions and some gypsum.

6.2 Generalized Subsurface Stratigraphy

We characterized the following generalized subsurface stratigraphy based on the exploration and laboratory test data included in the appendices. These stratum designations do not imply continuity of the materials described, but give the general descriptions and characteristics of the materials at the site.

Stratum A:

(Fill)

Below the ground surface to depths up to 6.5 ft.

Light to dark brown, grayish brown, medium to light gray, and black FILL, sampled as silty sand, sandy lean clay, clayey sand sandy silt, silt, and sandy silty clay with varying amounts of gravel, burnt charcoal, rock fragments, brick fragments, and roots; firm to hard consistency and loose to very dense relative density (N = 5 to 60).

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Stratum B1:

(Fine Grained Alluvium)

Below the ground surface and Stratum A to depths up to between 10 to 28.5 ft.

Light to medium brown, grayish brown, gray, and white SANDY SILT, SILT, LEAN CLAY, and SILTY CLAY with varying amounts of mica, sand, gravel, and cemented nodules; firm to hard consistency (N = 4 to 43)

Stratum B2:

(Coarse Grained Alluvium)

Below and interlayered with Stratum B1 to depths up to between 30 to

48.5 ft.

Light to medium brown and bluish gray

SILT SAND, POORLY GRADED SAND

with SILT and GRAVEL, SILTY

GRAVEL, POORLY GRADED GRAVEL

with varying amounts of gravel, sand mica, and shell fragments; very loose to very dense relative density (N=2 to 100+)

Stratum C1:

(Residual Soil - Laredo Formation)

Below Stratum C2, investigated to depths of up to 48.5 ft. Only encountered in Boring SB-1. We note that this stratum was likely weathered in place by alluvial processes and is likely a more severely weathered zone within the Laredo Formation.

Bluish gray, CLAYEY SAND; medium dense (N=11).

Stratum C2:

(Fine Argillaceous Sandstone - Laredo Formation)

Below Stratum B2 investigated to depths of up to 48.8 ft, the maximum depth investigated. Only encountered in borings SB-1, SB-4, SB-5, and B-1. We note that since this stratum was only sampled with SPT equipment, some of the aspects of the rock character could not be fully evaluated.

Bluish gray, disintegrated FINE-

GRAINED ARGILLACEOUS

SANDSTONE sampled disintegrated rock having a USCS classification of clayey sand with gravel, very dense (N=100+).

Disintegrated rock is defined as residual material with SPT N values between 60 blows per foot and refusal. Refusal is defined as an N value of 100 blows for a penetration of two inches or less.

Topsoil was encountered in Borings SB-3 to a depth of 4 inches, but not encountered in the other borings during the 2011 or 2012 investigation. Concrete pavement was observed to be between 10 and 12 inches in thickness in Borings B-2, SB-2, SB-4, and SB-5. The topsoil and pavement thicknesses reported herein should not be considered as an indication of stripping depths for planning demolition and stripping operations since pavement sections and depths of unsuitable materials should be expected to vary and the depth of stripping is dependent on other factors such as equipment used, presence of fill

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Numbers after the description of the soil strata indicate the minimum and maximum penetration resistance, or “N” value, for each stratum. The group symbols indicated by the two capital letters on the boring logs and in the subsurface stratification represent the Unified Soil Classification System (ASTM D- 2488) group symbols based on visual observation of the samples recovered from the test borings.

Explanations of “N” values and criteria for visual identification of soil samples are given in Appendix A.

There may be variations between samples that were visually classified and samples where laboratory tests have been used for classification.

6.2.1 Soil Classification Testing

Two split-spoon samples from the FILL soils of Stratum A classified as SANDY SILTY CLAY (CL-ML) and SANDY LEAN CLAY (CL) per ASTM D-2487 with 56.8 and 65.3 percent fines passing through the No.

200 sieve. The samples had liquid limits of 26 and 27 and plasticity indices of 6 and 8. Four split spoon samples from Stratum A were tested to measure natural moisture content. These soil samples had moisture contents between 4.4 and 18.5 percent.

Six split-spoon samples from the fine grained alluvium of Stratum B1 classified as SILT (ML), SILTY CLAY (CL-ML), LEAN CLAY (CL), and LEAN CLAY WITH SAND (CL) per ASTM D-2487 with between

84.0 and 92.3 percent fines passing the No. 200 sieve. Four of the samples had liquid limits between 27 and 33 and plasticity indices between 7 and 15. Two of the samples were non-plastic. A total of seven samples from Stratum B1 were tested for natural moisture content, which were between 8.9 and 14.7 percent.

One sample of the coarse grained alluvium of Stratum B2 classified as SILTY SAND per ASTM D-2487 with 41.5 percent passing the No. 200 sieve. The sample was non-plastic. Four samples of the Stratum B2 soils were tested for natural moisture content. The natural moisture contents of these samples were between 6.9 and 13.3 percent.

One sample of the weathered fine argillaceous sandstone of Stratum C2 was tested for its USCS classification. This material had the consistency of disintegrated rock and classified as CLAYEY SAND WITH GRAVEL (SC) per ASTM D-2487 with 27.1 percent fines passing the No. 200 sieve. The sample had a liquid limit of 31 and a plasticity index of 15. The natural moisture content of this sample was 11.9 percent.

6.2.2 Moisture-Density Relations

We conducted Standard Proctor Testing in accordance with ASTM D-698 and California Bearing Ratio (CBR) testing in accordance with ASTM D-1883 on two bulk samples collected from Stratum A and a combination of Strata A & B1.

One sample of Stratum A fill soil, collected during our 2011 investigation, classified as SANDY SILTY CLAY (CL-ML) per ASTM D-2487. This sample was tested for CBR at a surcharge pressure of 75 psf

August 19, 2013 Page 11 Schnabel Engineering, LLC and had a laboratory CBR value of 17.1 a swell value of 0.1 percent. Standard Proctor Testing indicated a maximum dry density of 114.6 pcf and an optimum moisture content of 13.8 percent.

One sample that was composed of a combination of Strata A and B1, collected during our 2012 investigation, classified as LEAN CLAY with SAND (CL) per ASTM D-2487. The sample was tested for CBR at a surcharge pressure of 50 psf and had a laboratory CBR value of 7.9 and swell value of 0.0 percent. Standard Proctor Testing in accordance with ASTM D-698 indicated a maximum dry density of

115.4 pcf and an optimum moisture content of 13.6 percent.

6.2.3 Soil Corrosivity Testing

Testing conducted to evaluate the corrosivity of the site soils of Strata A, B1, and B2 resulted in pH values of 6.5 to 8.5, Redox Potential values of 77 to 250 mV, Resistivity values of 1,700 to 2,800 ohm-cm and negative tests for sulfides.

Laboratory testing also indicated 63 and 350 mg/kg of water soluble sulfate present in two of the soil samples, and levels below the threshold value in the remaining two samples tested. Additionally, testing indicated that three soil samples had chloride levels between 22 and 51 mg/kg, and one additional soil sample had chloride levels below the threshold value. A discussion of these results is presented in the Corrosion Considerations section of this report.

6.3 Groundwater

Groundwater observations included on the test boring logs were made in the test borings during and after drilling. Groundwater was observed in the borings to the depths drilled at the times indicated on the logs.

Groundwater, where identified, was observed during drilling at depths ranging from 28 to 39 ft below the ground surface corresponding to elevations ranging from EL 374 to 387 ft. Groundwater was only encountered in Borings B-1, B-4, and B-7. Borings B-1, B-4, B-7, SB-2, and SB-3 were left open for 24-hour groundwater measurements. The remaining borings were backfilled for safety considerations. All borings, except SB-2 were observed to be dry following 24-hours open. In boring SB-2, we believe that the observed water level at 20 feet is significantly influenced by the mud rotary drilling technique performed at this location. Only SB-2 was drilled using the mud rotary method; water was not introduced into the other borings.

Water level observations made during the subsurface investigation indicate groundwater levels at the times indicated on the boring logs. Variation in groundwater conditions should be expected based on location at the site and on seasonal conditions and weather patterns. Additionally, perched groundwater conditions may also be present at the site.

Based on our groundwater observations, we do not expect groundwater levels to impact the proposed construction.

Infiltration characteristics of shallow strata were evaluated in 2013. The April 2, 2013 Data Report is included as Appendix D.

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6.4 Seismic Site Classification

We evaluated the Seismic Site Class and Seismic Site Coefficients for this project according to the International Building Code (IBC) Section 1615 (2009). Our analysis indicates Site Class D for this location. This Site Class was evaluated based on corrected SPT values extrapolated to a depth of 100 feet.

Furthermore, we considered the potential for liquefaction of the in situ soils at the site. Liquefaction is a phenomenon where loose, granular soils below the water table experience a sudden reduction in strength in response to strong earthquake shaking over successive cycles of ground motion. Liquefaction of granular soil layers can result in excessive settlements of foundations and floor slabs, and can result in lateral spreading of the ground surface on gently sloping sites. Based on the subsurface information collected, including the relatively deep groundwater table at the site, liquefaction of the subsurface soils at the site is not expected in response to the low design earthquake ground motions and depth to water.

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7.0 SITE GRADING AND EARTHWORK

Grading plans and site layout plans are not available at the existing site. Based upon the existing site conditions and our understanding of the proposed construction we estimate that cut and fill depths will be limited to within 3 feet. Recommendations for compacted fill subgrade preparation, fill soil requirements, placement and compaction criteria, are presented in subsequent sections.

7.1 Compacted Fill Subgrades

Subgrades to receive compacted structural fill for building or pavement support should be stripped of vegetation, topsoil, construction debris, or organics. The existing fill soils of Stratum A are unsuitable for support of foundations and floor slabs. We recommend that the existing fill soils be completely removed and replaced within the building footprints and pavement areas. Prior to placement of structural fill, dense graded aggregate, or lean concrete placement, the areas to be filled should be cleared and grubbed.

Unsuitable soft, loose, or deleterious materials should be undercut to approved subgrades as indicated by the Geotechnical Engineer.

The Geotechnical Engineer should evaluate the suitability of the fill subgrades. Subgrades should be proofrolled with a minimum of two passes, if possible, with a minimum 10 ton loaded dump truck or other suitable weight rubber-tired construction equipment. Areas that exhibit excessive pumping, weaving, or rutting should be scarified, dried and recompacted, or undercut and replaced with compacted structural fill as recommended by the Geotechnical Engineer. Alternatives to undercutting include the use of a geosynthetic and/or bridge lifts to stabilize soft subgrade areas. The Geotechnical Engineer should evaluate these alternatives during construction. Subgrade evaluation techniques complementary to proofrolling could include a combination of probing with a penetrometer, drilling hand augers, or observing test pits.

We estimate that the soils at this site are potentially susceptible to erosion due to the presence of fine sand and silt particles. The use of a geomaterial and/or vegetative cover will help limit the erosion that may be experienced in areas of slopes and berms. Additionally, water should not be allowed to collect against building walls and roof areas within the fill soil and should be removed from these areas through proper drainage design.

When excavation of unsuitable materials is required, it should be performed in a manner to limit disturbance of the underlying suitable material. The excavation should be performed under the observation of the Geotechnical Engineer to evaluate required excavation depths.

Compacted structural fill subgrades should be kept free of ponded water. If springs or other flowing water is present at the compacted structural fill subgrade level, the Contractor should direct water to discharge beyond the fill limits. Recommendations for discharging springs should be provided by the Geotechnical Engineer.

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Some existing structures present on site will need to be removed before earthwork construction.

Therefore, buried foundations and other associated debris may be encountered during grading activities.

Existing foundations should be removed from the proposed building area in their entirety or at least to a depth of one footing width below the bottom of the new footing. Existing foundations and walls in the proposed pavement areas should be removed to at least 2 ft below the design pavement subgrade level.

Existing utilities and drainage structures within the building area should be removed and replaced with compacted structural fill.

We understand that no elevation modifications that require compacted fill subgrades are planned.

7.2 Compacted Fill

New structural fill should classify as ML or more granular per ASTM D-2487 with a maximum particle size of 4 in. For footings, structural fill should extend beyond proposed foundation limits as indicated in Figure

3. For pavements, structural fill should be sloped at a minimum 1:1 slope to the ground surface from the pavement edge. The maximum recommended liquid limit and plasticity index of soil to be placed as structural fill material should be 45 and 20, respectively.

Compacted structural fill should be placed in maximum 8-inch thick horizontal, loose lifts. Fill should be compacted to at least 95 percent of the maximum dry density per ASTM D698 (Standard Proctor), except that the top 12 inches in pavement areas should be compacted to at least 100 percent of the same standard.

Soils placed as backfill adjacent to retaining and below-grade walls should classify as SC or more granular per ASTM D-2487 and should be compacted to at least 92 percent of the maximum dry density according to ASTM D-698. Soil placed as backfill behind retaining and below-grade walls should have a maximum liquid limit of 40 and a maximum plasticity index of 20.

Backfill placed in excavations, trenches, and other areas that large compaction equipment cannot access should be placed in maximum 6-inch thick lifts. Backfill should meet the material, placement, and compaction requirements outlined above.

High plasticity soils, if encountered, are not suitable for use as structural fill. High plasticity soils may be used in landscaped areas and other areas where stability and structural support are not required.

Moisture conditioning of site soils should be expected to obtain proper compaction.

The natural moisture contents of site soils are expected to vary. Moisture conditioning of some of the site soils may be required to achieve proper compaction. Moisture conditioning might include, for example scarifying or drying of we soils or adding moisture to dry soil. Careful planning of fill operations to allow moisture conditioning for individual fill lifts will be required. Some delays due to moisture condition or difficulties achieving compaction should be expected.

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7.3 Slopes

We understand that no permanent fill slopes are planned. If fill slopes are added for landscaping purposes, we recommend that permanent slopes constructed of structural fill be limited to a slope no greater than 3H:1V.

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8.0 FOUNDATION RECOMMENDATIONS

We based our geotechnical engineering analysis on the information developed from our subsurface exploration and soil laboratory testing, along with the available schematic plans, and estimated structural loading furnished to our office. We recommend shallow spread footings for support of the proposed canopy and building structures based on our analysis. The following sections of the report provide our detailed recommendations.

8.1 Spread Footings

Based upon our analysis of the subsurface data, the proposed building and canopy structures may be supported by spread footings on compacted structural fill or natural soils of Strata B1 and B2 that do not contain soft, loose, or high plasticity soil. Compacted structural fill should meet the requirements outlined in Section 7.0. We recommend footings supported on these materials be designed for a net allowable soil bearing pressure of 2,500 psf. This bearing pressure provides a factor of safety against general bearing capacity failure of at least 3.0. The above allowable soil bearing pressure may be increased by 33 percent for wind and seismic loads when used in conjunction with load combinations defined in IBC Section 1605.3.2, Alternative Basic Load Combinations for use with allowable stress design. This increase is not applicable for other allowable stress load combinations, strength design or load and resistance factor design.

The existing fill soils of Stratum A are unsuitable for direct support of foundations and floor slabs. Up to approximately 6.5 ft of existing fill was encountered below the ground surface in the area of the planned passenger inspection building. The proposed finished floor elevation for passenger inspection building is at EL 413.5 ft, which roughly corresponds to the existing grade. Across the site, we expect variable amounts of existing fill soils will need to be removed to construct the canopy structures.

Lowering of some footings to reach suitable bearing soils should be expected during construction to reach suitable bearing soils. When lowering of footings is required to reach suitable bearing material, the resulting overexcavation should be backfilled with structural fill, dense graded aggregate, or lean concrete. Such lowering or overexcavation includes footing areas with existing foundation elements. The existing foundation elements should be removed to a depth of the footing width B below the footing subgrade elevation. If unsuitable soils are encountered at that elevation, the excavation should be extended per Figure 3. As an alternative to lowering foundations, foundations can be left at planned grades and undercuts can be backfilled with structural fill, dense graded aggregate, or lean concrete placed in accordance with Figure 3.

Actual foundation grades should be observed in the field by a qualified Geotechnical Engineer.

Foundation elements should be designed to minimize the influence on the adjacent foundations. Where different elevations are required due to differences in floor slab elevations, or where lowering of footings is required for subgrade conditions encountered, a maximum slope of 1H:1V should be maintained between bottom edges of adjacent footings.

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If existing foundation elements are encountered below the planned column footings, the existing foundation elements should be removed to a depth of at least one footing width (see Figure 3) below the new footing subgrade. The excavation should then be backfilled with lean concrete.

Footings should bear a minimum of 24 in below exterior finished grades to limit the potential for water to influence the footing bearing surface. Column footings should be at least 750 mm (30 in) wide and wall footings should be at least 16 in wide for shear considerations. Total footing settlements are not expected to exceed approximately 1 in. Differential settlement between adjacent footings should not exceed about half the total settlement.

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9.0 FLOOR SLAB RECOMMENDATIONS

Earth supported floor slabs are considered feasible at the site. The floor slabs should be supported on new structural fill or suitable natural soils. Existing fill soils, if encountered beneath floor slabs, should be removed in their entirety and replaced with new structural fill. High plasticity soils are not considered suitable for direct support of floor slabs. High plasticity soils were not identified in the subsurface investigation. However, should high plasticity soils be identified during construction, these soils should be removed to a depth of 2 ft or in their entirety, whichever is less, and replaced with suitable structural fill or dense graded aggregate.

Where new structural fill or suitable Stratum B soils are present at slab subgrade elevations, we recommend a modulus of subgrade reaction, ks, of 125 pci for floor slab design.

A 4 in minimum thickness of dense graded aggregate should be provided below the floor slabs. A minimum 6-mil thick impermeable plastic membrane should be placed over the underslab stone layer to serve as a vapor barrier and to prevent infiltration of concrete into the gravel or crushed stone layer during concrete placement.

All floor slab subgrades should be proofrolled using a 10-ton loaded dump truck or other equivalent weight rubber-tired construction equipment, where possible, and should be observed and approved by a qualified Geotechnical Engineer prior to placement of dense graded aggregate. All debris and soft or loose soils near the final floor slab subgrade as a result of construction operations should be stripped and removed prior to placement of dense graded aggregate.

Based on the results of water level observations made during the field exploration program, groundwater appears to be well below expected lowest floor elevations of the proposed structures. Accordingly, under-floor subdrainage systems are not considered necessary.

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10.0 LATERAL EARTH PRESSURE RECOMMENDATIONS

Building walls, site retaining walls, and any below-grade walls that extend below the lowest floor slab elevations should be designed to resist lateral earth pressures developed from the surrounding soil, backfill, and surcharge loads. Equivalent fluid pressures for walls backfilled with soil should be calculated based on a moist unit weight of 120 pcf.

Active earth pressure coefficients should be used for site retaining wall design whereas an at-rest earth pressure coefficient should be used for braced below-grade wall design, if applicable. The following parameters, shown in Table 1, should be used for the design of retaining walls and below grade walls assuming the use SC or more granular material (per ASTM D2487) as backfill.

Table 1: Earth Pressure Coefficients Parameter Soil Backfill Value

Ka (Active Condition)

0.33

Kp (Passive Condition

3.00

Ko (At-Rest Condition)

0.50 γt (Unit Weight of Soil)

120 pcf

Drainage behind the walls must be provided to reduce the possibility of hydrostatic pressures acting on the walls. The earth pressures assume that any groundwater, surface infiltration, or perched water in the soils surrounding the walls is collected and disposed of by a subdrainage system as detailed in Figures 4 and 6. The wall pressures could be reduced by using geogrid or other reinforcing materials.

In addition to lateral earth pressures from backfill and surrounding soils, below-grade and site retaining walls should also be designed to resist surcharge loads within the area defined by a 45-degree slope from the bottom of the walls. Lateral earth pressures from surcharge loads can be estimated with a uniform lateral pressure equal to the lateral earth pressure coefficient times the vertical surcharge pressure as shown in Figures 4 and 5. If any backfill is placed adjacent to walls, the material should meet the specifications and compaction requirements for backfill against walls as detailed in the Earthwork section of this report.

Wall footings founded on new structural fill or the natural soils of Stratum B1 may be designed using a friction coefficient of 0.38. The unit weight of the natural soils of Stratum B1 and new structural fill is estimated to be approximately 120 pcf.

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11.0 PAVEMENT RECOMMENDATIONS

New travel lanes and bus parking areas will be constructed at or near existing grades for the proposed development. Existing fill soils, new structural fill, and the natural soils of Strata A, B1, and B2 may be encountered at pavement subgrades. The low plasticity and coarse grained natural soils of Strata B1 and B2 are generally considered suitable for direct support of pavements provided that they are stable during proofrolling. Additionally, the existing fill soils of Stratum A may be considered suitable for pavement support provided that it is free of organics, construction debris, or other deleterious materials and is also stable during proofrolling. The suitability of the existing fill for pavement support should be evaluated by the Geotechnical Engineer.

In the event that soft, loose, or deleterious existing fill soils or high plasticity soils are encountered, these materials should be removed in their entirety or to a depth of 0.6 m (2 ft) whichever is less and replaced with new structural fill or dense graded aggregate.

Subgrade preparation should include stripping of topsoil and any unsuitable soils, placing structural fill as necessary, and compacting the subgrades immediately below pavements. Pavement and fill subgrades should be proofrolled with a 9,100 kg (10-ton) loaded dump truck or other equivalent weight construction equipment immediately prior to placing structural fill, dense graded aggregate, or stone base course material.

Based on laboratory testing performed on bulk samples obtained during our subsurface investigation and the anticipated surcharge pressure from an estimated pavement section, we recommend a preliminary design California Bearing Ratio (CBR) value of 8 for the near surface soils of Strata A, B1, and B2.

However, representative pavement subgrade soil samples should be obtained for CBR testing during construction. If field CBR values obtained during construction vary significantly from the estimated design value presented herein, modifications to the design paving section may be necessary.

Adequate control of surface drainage should be maintained by grading the area surrounding the pavements and adjacent foundations to direct surface water away from the paved areas. Water collection below the pavement section may also be controlled by installing underdrains below the pavement sections.

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12.0 CORROSION CONSIDERATIONS

The results of the corrosion series testing were used to evaluate the corrosion potential per American Water Works Association (AWWA) Specification C105. The AWWA ranking system is widely used to evaluate corrosion potential in ferrous metals. AWWA Specification C105 includes a procedure for ranking soils on a 10-point scale to evaluate whether the soils are potentially corrosive to cast iron and recommends that cast iron pipes installed within soils with a ranking of 10 or greater have corrosion protection. Ferrous materials (i.e. cast iron and steel) behave similarly when exposed to corrosive environments. The results of the corrosion series testing resulted in soil rankings between 2 and 8.5 for the four corrosion series test samples. Based on our evaluation of the corrosion series testing and the AWWA ranking system, the site soils appear to be below the established corrosive limit with regard to cast iron piping and ferrous metals in contact with the ground and thus do not require corrosion protection measures.

The results of the sulfate content testing for water soluble sulfates in the soil from Strata A, B1, and B2 indicated sulfate contents within the range of “Negligible” sulfate exposure per ACI 318, Table 4.3.1 corresponding to a range of 0 to 1,000 mg/kg of sulfates in soil. Therefore, the use of sulfate-resistant cement is not considered necessary for buried concrete structures.

The results of the chloride content testing of the Strata A, B1, and B2 soil samples indicate chloride contents below the permissible level of 100 mg/kg per FHWA guidelines. Special protective measures for reinforcing steel in concrete do not appear to be necessary based on the results of the chloride testing.

The structural engineer should review this data to make the final evaluation concerning corrosion protection measures.

Should fill soils be required to be imported to the site, these borrow soils will also need to be tested for corrosion properties in addition to the engineering properties. All corrosion protection measures should be reviewed and approved by the structural engineer.

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13.0 CONSTRUCTION CONSIDERATIONS

13.1 Site Grading and Earthwork

The test boring indicated limited amounts of topsoil across the project site. However, the depth of stripping needed to provide a suitable base for placement and compaction of earthwork or for pavement subgrade preparation may include topsoil and other softer surficial layers, with or without organic matter.

Stripping depths in previously cultivated areas will be greater, particularly during periods of wet weather.

The depth of required stripping should be determined by the excavation Contractor prior to construction using test pits, probes, or other means that the Contractor wishes to employ, and this determination should be the excavation Contractor's responsibility.

Traffic on stripped or undercut subgrades should be limited to reduce disturbance of underlying soils.

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

13.2 Spread Footings

Footing subgrades should be observed by the Geotechnical Engineer to evaluate if the soils are…