T_Final Report-2018.pdf

Geotechnical Engineering Study

West Gate ID Check Area Laughlin AFB - Del Rio, Texas

Arias Job No. 2018-711

Prepared For

AECOM

January 3, 2019

ARIAS

GEOPROFESSIONALS

142 Chula Vista, San Antonio, Texas 78232 • Phone: (210) 308-5884 • Fax: (210) 308-5886

January 3, 2019 Arias Job No. 201 8-711 VIA Email: iolita.aly@aecom.com

Ms. Jolita Aly, AlA, LEED AP Project Manager-Architect, Buildings+Places

AECOM

19219 Katy Freeway, Suite 100 Houston, Texas 77094

RE: Geotechnical Engineering Study West Gate ID Check Area Laughlin AFB Del Rio, Texas

Dear Ms. Aly:

This report presents the results of a Geotechnical Engineering Study for the proposed new West Gate ID Check Area located at the Laughlin AFB in Del Rio, Texas. This study was authorized on October 30, 2018 with the Fully Executed Subconsultant Agreement No. 107657, and was performed in general accordance with Arias Proposal No. 2018-711 dated August 20, 2018.

The purpose of this geotechnical engineering study was to establish foundation engineering properties of the subsurface materials and groundwater conditions present at the site. The scope of the study is to provide geotechnical engineering criteria for use by design engineers in preparing the foundation and pavement designs. Our findings and recommendations should be incorporated into the design and construction documents for the proposed development.

The long-term success of the project will be affected by the quality of materials used for construction and the adherence of the construction to the project plans and specifications. The quality of construction can be evaluated by implementing Quality Assurance (QA) testing. As the Geotechnical Engineer of Record (GER), we recommend that the earthwork, foundations, and pavement construction be tested and observed by Arias in accordance with the report recommendations. A summary of our qualifications to provide QA testing is discussed in the “Quality Assurance Testing” section of this report. Furthermore, a message to the Owner with regard to QA testing is provided in the ASFE publication included in Appendix E.

We appreciate the opportunity to serve you during this stage of site development. If we may be of further service, please call.

Sincerely, ARIAS & ASSOCIATES, INC. ~

TBPE Registration No. F-32 ~ ~

42~~_..c f~L•.~*~ Jerry I. Shepherd, .E., D.GE ~ JERRYD. SHEpHERD~ C ristopher M. S zak, P.E.

enior Geotechnical Engineer ~ ••................. ~ Senior Geotechnical Engineer

Austin • Corpus Fort Worth • San Antonio

Arias Geoprofessionals i Arias Job No. 2018-711

REPORT FORMAT INFORMATION

To improve clarity in the intent of our geotechnical recommendations for this project, the report is organized into two separate, but equally important sections.

Section I – Synopsis is a summary of our geotechnical recommendations specific to this project.

Section II – The Main Report contains more detailed information including foundation and pavement design parameters and site work recommendations.

A study of both of the above referenced sections is recommended for the Project Team Members.

Arias & Associates, Inc. cautions that Section I, Synopsis, is a consolidated quick reference overview of the more detailed geotechnical recommendations contained in Section II and should not be used exclusively from the remainder of the report.

TABLE OF CONTENTS

Page

Arias Geoprofessionals I- Arias Job No. 2018-711

REPORT FORMAT INFORMATION ...................................................................................... i

SECTION I: SYNOPSIS ....................................................................................................... I-1

SECTION II: GEOTECHNICAL REPORT ..............................................................................II-1

PROJECT DESCRIPTION .................................................................................................II-1

SOIL BORING AND LABORATORY TESTING ..................................................................II-1

LABORATORY TESTS ......................................................................................................II-1

Soluble Sulfate Content ................................................................................................II-2

SUBSURFACE CONDITIONS ...........................................................................................II-2

Site Stratigraphic and Engineering Properties ..............................................................II-2 Groundwater.................................................................................................................II-5

MOISTURE VARIATIONS AND ESTIMATED MOVEMENT ...............................................II-5

FOUNDATION DESIGN CONSIDERATIONS ....................................................................II-5

Recommended Foundation Type ..................................................................................II-5 Recommended Building Pad Improvement for 1” PVR .................................................II-6 Building Pad Construction ............................................................................................II-6 Stiffened Beam and Slab on Grade ..............................................................................II-7

ADDITIONAL DESIGN CONSIDERATIONS ......................................................................II-9

Flatwork Considerations ...............................................................................................II-9 Design Measures to Reduce Changes in Soil Moisture .............................................. II-10 IBC Site Class Determination ..................................................................................... II-10 Utilities ........................................................................................................................ II-11 Slab-Bearing Partition Walls & Flooring ...................................................................... II-11 Control and Construction Joints .................................................................................. II-11

PAVEMENT RECOMMENDATIONS ................................................................................ II-12

Pavement Design Parameters and Assumptions .............................................................. II-12

Rigid Concrete Pavement Joints ................................................................................. II-12 Performance Considerations ...................................................................................... II-13 Pavement Subgrade and Section Materials ................................................................ II-13

CONSTRUCTION CRITERI ............................................................................................. II-16

Site Preparation .......................................................................................................... II-16 Excavation Conditions ................................................................................................ II-17 Drainage ..................................................................................................................... II-17 Earthwork and Foundation Acceptance ...................................................................... II-17 Trench Excavations .................................................................................................... II-18

TABLE OF CONTENTS

Page

Arias Geoprofessionals I-i Arias Job No. 2018-711

GENERAL COMMENTS .................................................................................................. II-18

Geotechnical Design Review ...................................................................................... II-18 Subsurface Variations ................................................................................................ II-19 Quality Assurance Testing .......................................................................................... II-19 Standard of Care ........................................................................................................ II-20

APPENDIX A: FIGURES AND SITE PHOTOGRAPHS ........................................................... A-1

APPENDIX B: BORING LOG AND KEY TO TERMS .............................................................. B-1

APPENDIX C: LABORATORY AND FIELD TEST PROCEDURES ......................................... C-1

APPENDIX D: CALIFORNIA BEARING RATIO (CBR) ............................................................ D-1

APPENDIX E: LIME SERIES .................................................................................................. E-1

APPENDIX F: ASFE INFORMATION ..................................................................................... F-1

APPENDIX G: PROJECT QUALITY ASSURANCE ................................................................. G-1

Tables

Table 1: Project Description .................................................................................................... I-1 Table 2: Existing Conditions during Geotechnical Study ......................................................... I-1 Table 3: Building Pad Recommendations ................................................................................ I-2 Table 4: Recommended Pavement Sections .......................................................................... I-3 Table 5: Project Compaction, Moisture and Testing Requirements ......................................... I-4 Table 6: Soluble Sulfate Content Test Results ........................................................................II-2 Table 7: Generalized Subsurface Conditions-Building Borings (B-1 & B-2) .............................II-3 Table 8: Generalized Subsurface Conditions-Pavement Borings (B-3 thru B-10) ....................II-4 Table 9: BRAB and WRI Foundation Design Criteria...............................................................II-8 Table 10: PTI Slab-on-Grade Soil Design Criteria (3rd Edition) ................................................II-8 Table 11: Allowable Bearing Pressure and Beam Penetration ................................................II-9 Table 12: IBC Site Classification and Seismic Design Parameters ........................................ II-11 Table 13: Pavement Design Parameters and Assumptions ................................................... II-12 Table 14: Pavement Subgrade Materials .............................................................................. II-14 Table 15: Fill Requirements and Subgrade Treatment Options ............................................. II-15 Table 16: Rigid Pavement Section Materials ......................................................................... II-16 Table 17: Site Work (Non-Structural/General Fill) Requirements .......................................... II-17

Arias Geoprofessionals I-1 Arias Job No. 2018-711

SECTION I: SYNOPSIS

This synopsis includes a brief description of the project, subsurface findings, client-preferred foundation type, and generalized earthwork requirements for building pad and foundation and pavement design, as well as specific items of concern from a geotechnical standpoint for consideration during the design, construction, and maintenance phases of this project.

Table 1: Project Description

Project New ID Check Area

Project Location West Gate for Laughlin AFB in Del Rio, Texas

Proposed Development Single-Story structure with associated roadway and parking pavements

Anticipated Foundation Type Stiffened Beam and Slab supported on grade

Table 2: Existing Conditions during Geotechnical Study

Existing Surface Conditions Some grass area and some sparse grass areas

Predominant Soil/Rock Types Residual soil layer (about 4 to 8 feet thick, but variable) at surface overlying Limestone and

Weathered Limestone

Depth to Groundwater Groundwater not encountered during our field exploration on December 5 & 6, 2018

Estimated Existing Potential Vertical Rise (PVR)

Approximately 1-inch or less

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Table 3: Building Pad Recommendations

Site Improvement Method:

Strip all surface vegetation and excavate to provide for a minimum of 2 feet of select fill. In some areas, dense to very dense/hard to very hard limestone or weathered limestone may need to be removed, while additional select fill may be required in other areas. It is important that all grade beams bear in like materials in order to minimize the potential for differential settlement.

It is anticipated that heavy duty excavating equipment will be required, particularly in the dense to very dense/hard to very hard materials.

The Contractor should be prepared for such conditions. Proof roll exposed subgrade as described in note 3 below. Site preparation operations should be observed and tested by a representative of the Geotechnical Engineer.

Recommended Foundation Type Stiffened beam and slab on grade

Improved Site Condition (PVR): 1 inch

Observe and Proof roll: Exposed Pre-fill subgrade. (See Note 3)

Select Fill Type:

Crushed Limestone Base Material:

TxDOT Item 247, Type A, Grade 1 or 2

Working Surface:

Top 6” of Building Pad:

TxDOT Item 247, Type A, Grade 1 or 2

Notes:

1. The Building at the ID Check Area will use a slab-on-grade foundation system atop a select fill pad for a PVR of approximately 1-inch.

2. Following stripping operations, proof roll exposed subgrade as shown in Note 3 and place select fill as necessary. Removal should extend laterally to provide at least a five (5)-foot overbuild beyond the perimeter of the structure and to the width of any sidewalks wider than five (5) feet.

3. The exposed subgrade should be thoroughly proof rolled with at least a 20-ton roller or heavily loaded dump truck weighing at least 20 tons. A minimum of 15 passes should be performed with passes alternating in directions perpendicular to each other and observed by the geotechnical engineer. Any area that yields under the roller loading should be undercut to the depth specified by the geotechnical engineer or his representative and replaced with compacted select fill as outlined in Table 5. If deleterious material, rubble, or debris is encountered, they should be removed to firmer materials and disposed of properly. Over-excavated areas can be brought to grade with properly compacted select fill. It is important that the site preparation operations be observed and tested by an Arias representative to confirm similar subsurface conditions encountered in the borings, and to verify that these recommendations are followed.

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4. Select fill should be placed in maximum 8-inch loose lifts and compacted as specified in SECTION I, Table 5 (Project Compaction, Moisture and Testing Requirements).

5. For construction equipment access, and to help provide a more “all-weather” working surface, we recommend that the building pad be constructed of granular select fill consisting of crushed limestone base meeting the requirements of 2004 TxDOT Item 247, Type A, Grade 1 or 2.

6. A horizontal barrier should extend at least 10 feet horizontally beyond the perimeter of the foundation of the building addition. The barrier can consist of concrete or asphalt paving, concrete flatwork or at least 24” of compacted onsite or import clay (PI between 20 and 40). All joints within the pavement, flatwork, and at pavement/flatwork interfaces should be sealed. Any landscaping located within 10 feet of the structure foundation should be placed in watertight above-grade planter boxes with drainage discharge on top of adjacent flatwork/paving. The final grade beam depth and recommended construction should be determined by the structural engineer. The slab vapor retarder plastic should be extended from beneath the slab down the inside face (building pad side) of the grade beam trench.

Table 4: Recommended Pavement Sections

Layer Material

Rigid Concrete (see Note 4)

Parking Area & Light Duty

Drive Through

Lanes

Surface PCC 6” 8”

Subgrade

Moisture conditioned

6” 6”

Notes:

1. Periodic/preventative maintenance should be planned for to reduce deterioration of the pavement structure while aiding to preserve the investment.

2. Light duty areas include parking and drive lanes that are subjected to passenger vehicle traffic only. Light duty areas exclude drive through lanes.

3. Drive through lanes include areas subjected to 18-wheel tractor trailers, trash collection vehicles, dumpster pads including loading and unloading areas, and areas where truck turning and maneuvering may occur. For these areas, at least eight (8) inches of reinforced concrete pavement is recommended.

4. The exposed subgrade should be thoroughly proof rolled with at least a 20-ton roller or heavily loaded dump truck weighing at least 20 tons. A minimum of 15 passes should be performed with passes alternating in directions perpendicular to each other and observed by the geotechnical engineer. Any area that yields under the roller loading should be undercut to the depth specified by the geotechnical engineer or his representative and replaced with compacted select fill as outlined in Table 5. If deleterious material, rubble, or debris is encountered, they should be removed to firmer materials and disposed of properly. Over-excavated areas can be brought to grade with properly compacted select fill. It is important that the site preparation operations be observed and tested by an Arias representative to confirm similar subsurface conditions encountered in the borings, and to verify that these recommendations are followed.

5. During the paving life, maintenance to seal surface cracks within concrete pavements and to reseal joints within concrete pavement should be undertaken to achieve the desired paving life. Perimeter drainage should be controlled to reduce the influx of surface water from areas surrounding the paving. Water penetration into base or subgrade materials, sometimes due to irrigation or surface water infiltration leads to pre-mature paving degradation. Curbs should be used in conjunction with paving to reduce potential for infiltration of moisture.

Curbs should extend at least 3 inches into the underlying subgrade.

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6. Material specifications, construction considerations, and section requirements are presented under “Pavement Subgrade and Section Materials” included in Section II of this report.

Table 5: Project Compaction, Moisture and Testing Requirements

Description Material

Percent Compaction

Optimum Moisture Content Testing

Requirement Compaction Test TxDOT 113-E for gravelly soils, and TxDOT 114-

E for clayey soils

Building Pad Area

Exposed subgrade at base of excavation Proof roll Observation

Select Fill:

(Material Meeting

Requirements Outlined previously in Table 3)

≥ 98% -1% to +3% 1 per 5,000 SF;

min. 3 per lift

Pavement Areas

Scarified, Moisture Conditioned On-site Soil

(Subgrade) ≥ 95% 0 to +4%

1 per 5,000 SF;

min. 3 tests

General Fill (Onsite Material)

≥ 95% 0 to +4% 1 per 5,000 SF;

min. 3 per lift

Non-Structural Areas (Outside Building Pad)

General Fill (On-site Material)

≥ 95% 0% to +4% 1 per 10,000 SF;

min. 3 per lift

Arias Geoprofessionals II-1 Arias Job No. 2018-711

SECTION II: GEOTECHNICAL REPORT

PROJECT DESCRIPTION

The proposed project consists of the construction of the West Gate ID Check Area which will consist of a single-story Gate House with new pavements at Laughlin AFB in Del Rio, Texas. A Site Vicinity Map is provided in Appendix A of this report. At the time of this report, we have not been provided with the structural loads for the structure. However, we have assumed that the building will be relatively lightly loaded and supported by a stiffened beam and slab on grade. If any of this information is incorrect, we should be contacted immediately in order to review and revise our recommendations, as required.

SOIL BORING AND LABORATORY TESTING

A total of ten (10) borings were drilled at the approximate locations shown on the Boring Location Plan provided in Appendix A. Two (2) borings (B-1 & B-2) were drilled in the area of the planned building to depths of approximately 24 feet each. The remaining borings (B-3 through B-10) were drilled in the area of the planned new pavements to depths of approximately nine (9) feet each.

The borings were drilled and sampled in accordance with ASTM D1586 procedures for Split Spoon sampling techniques as described in Appendix C. A truck mounted drill rig using continuous flight augers together with the sampling tools noted were used to secure the subsurface samples.

Material classifications and borehole logging were conducted during the exploration by one of our field-logging technicians under the supervision of our Project Geotechnical Engineer. Final material classifications, as seen on the attached boring logs (Appendix B), were determined by the Project Geotechnical Engineer based on laboratory and field test results and applicable ASTM procedures. A key to the terms and symbols used on the logs is also included in Appendix B.

LABORATORY TESTS

As a supplement to the field exploration, we provided laboratory testing to determine water content, Atterberg Limits, percent passing the No. 200 sieve, and soluble sulfate content. The laboratory results, with the exception of the soluble sulfate content test results, are reported in the attached boring logs included in Appendix B. The soluble sulfate content test results are shown below in table 6. The soil laboratory testing for this project was done in accordance with applicable ASTM procedures with the specifications and definitions for these tests listed in Appendix C.

Remaining soil samples recovered from this exploration will be routinely discarded following submittal of this report.

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Soluble Sulfate Content Laboratory testing was conducted on eight (8) selected samples recovered from the borings drilled at the site to determine the soluble sulfate content. Testing was performed in accordance with TxDOT test method Tex-145-E “Determining Sulfate Content in Soils.” The results indicate that the sulfate contents of the samples tested range from approximately 160 to 460 parts per million (ppm). The results are indicative of a range of relatively low soluble sulfate content. Based on the results of the sulfate testing, lime or cement treatment (or treatment with another calcium-based agent if required) may be considered, if desired, for this project. A summary of the test results is provided in Table 6 below.

Table 6: Soluble Sulfate Content Test Results

Boring No. Depth, (ft.) Material Description Soluble Sulfate Content Result (ppm)

B-1 2 - 4 CLAYEY SAND (SC) 180

B-2 2 - 4 CLAYEY SAND (SC) 200

B-3 4 - 6 SANDY LEAN CLAY (CL) 160

B-5 2 - 4 LIMESTONE 180

B-6 4 - 6 CLAYEY SAND (SC) 260

B-7 4 - 6 CLAYEY GRAVEL (GC) 220

B-8 4 - 6 LIMESTONE 460

B-10 2 - 4 CLAYEY GRAVEL (GC) 200

Note: Approximate sample depth is referenced from the existing ground surface at the time of the geotechnical field exploration performed on December 5th & 6th, 2018

SUBSURFACE CONDITIONS

Generalized stratigraphy and groundwater conditions are discussed in the following sections. The subsurface and groundwater conditions are based on conditions encountered at the boring locations to the depths explored.

Soil/rock conditions may vary between the sample boring locations. Transition boundaries, or contacts, noted on the boring logs to separate soil/rock types, are approximate. Actual contacts may be gradual and vary at different locations. If conditions encountered during construction indicate more variation than established as a result of this study, we should be contacted to evaluate the significance of the changed conditions relative to our recommendations.

Site Stratigraphic and Engineering Properties

In general, the subsurface materials encountered at the project site consist of a stratum of relatively low plasticity clayey sand/clayey gravel with some lean clay over formational limestone bedrock. The generalized stratigraphic conditions for the borings performed for the building are

Arias Geoprofessionals II-3 Arias Job No. 2018-711 summarized below in Table 7 and the borings performed for the pavements are summarized below in Table 8.

Table 7: Generalized Subsurface Conditions-Building Borings (B-1 & B-2)

Stratum Depth

(ft) Material Description PI range

- 200 range

N range

I to

8 - 10

Tan CLAYEY SAND with GRAVEL (SC), CLAYEY SAND (SC), dense to very dense

(Some weathered Limestone) 9 - 11 19 - 36 36 - **50/3”

II

to

Tan WEATHERED LIMESTONE, hard

(Encountered in Boring B-1 only) -- -- **50/4”*

III

10 – 13 to

Tan LIMESTONE, very hard

(Some thin seams of MARLSTONE) 9 - 15 13 - 20 **50/1” - **50/0”

Where: Depth - Stratum depth (ft.) from existing ground surface at the time of geotechnical study.

PI - Plasticity Index No. 200 - Percent passing #200 sieve, % N - Standard Penetration Test (SPT) value, blows per foot ** - Blow Counts during seating penetration -- - No test

* - Only one test

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Table 8: Generalized Subsurface Conditions-Pavement Borings (B-3 thru B-10)

Stratum Depth

(ft) Material Description PI range

- 200 range

N range

Pavement 0.0 to 0.6

3.0” Asphalt over 4.0” Base (Encountered in Boring B-4 only) -- -- --

I 0 – 0.6 to 2 - 8

Tan & Brown CLAYEY SAND with GRAVEL

(SC), CLAYEY SAND (SC), CLAYEY

GRAVEL with SAND (GC), dense to very dense

(Some thin Limestone Seams)

8 - 19 24 - 37 40 - **50/4”

IA

to

Tan CLAYEY SAND with GRAVEL (SC), very dense 8* 39* 54 – 50/6”

II

to

Tan WEATHERED LIMESTONE, hard 12* 48* 76/12”*

III

to

Tan LIMESTONE, very hard 9 - 15 3 - 43 50/1” – **50/0”

IIIA

to

Tan LIMESTONE, very hard

(Encountered in Boring B-5 only) -- -- **50/2”

IV

to

Tan SANDY LEAN CLAY (CL), very stiff (Encountered at Boring B-3 Only) 8* 66* 16*

Where: Depth - Stratum depth (ft.) from existing ground surface at the time of geotechnical study.

PI - Plasticity Index No. 200 - Percent passing #200 sieve, % N - Standard Penetration Test (SPT) value, blows per foot ** - Blow Counts during seating penetration

* - Only one test -- - No test

The dense to very dense and hard to very hard materials and limestone will likely require heavy-duty equipment to excavate and install foundation(s) at this site. A detailed evaluation of the excavatibility of these materials was beyond our authorized scope of services. However, based on our experience in this area, we anticipate that excavating in these areas will likely encounter conditions requiring heavy-duty rock excavating equipment. Heavy-duty excavation equipment is defined as equipment capable of cutting/excavating very hard marlstone/limestone bedrock. In addition, gravelly/sandy soils can lose cohesion and slough/cave, especially if groundwater is encountered. The Contractor should be familiar with and prepared for such conditions.

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Groundwater

A dry soil sampling method was used to obtain the soil samples at the project site. Groundwater was not encountered in any of the borings during the field exploration on the December 5 and 6, 2018. The open boreholes were backfilled using soil cuttings generated from the drilling process.

Groundwater levels will often change significantly over time and should be verified immediately prior to construction. Water levels in open boreholes may require several hours to several days to stabilize depending on the permeability of the soils. Groundwater levels at this site may differ during construction because fluctuations in groundwater levels can result from seasonal conditions, rainfall, drought, or temperature effects. Pockets or seams of gravels, sands, silts or open fractures and joints can store and transmit “perched” groundwater flow or seepage. Should dewatering become necessary, it is considered means and methods and is solely the responsibility of the contractor.

MOISTURE VARIATIONS AND ESTIMATED MOVEMENT

Structural damage can be caused by volume changes in expansive soils. Expansive soils can shrink when they lose water and swell (grow in volume) when they gain water. The potential for expansive soils to shrink and swell is typically related to the Plasticity Index (PI). Soils with a higher PI generally have a greater potential for soil volume changes due to moisture content variations. Surficial soils encountered at this site have a moderate potential to shrink and swell in volume depending on changing soil water content conditions during or after construction. The term swelling soils implies not only to the tendency to increase in volume when water is available, but also to decrease in volume or shrink if water is removed.

Several methods exist to evaluate swell potential of expansive clay soils. We have estimated potential heave utilizing the TXDOT method (Tex 124-E). Using the TXDOT method, we estimate that the PVR is approximately 1-inch or less considering the existing moisture conditions at the time of the sampling activities.

It has been our experience that the PVR method can sometimes underestimate the potential shrink/swell movements. Fluctuations in the soil moisture content generated from climatic conditions (i.e., droughts or floods) or as a result of development (e.g., irrigation of landscaping in the immediate vicinity of the building, poor surface drainage, leaking plumbing or water lines) may result in greater shrink/swell movements than calculated.

FOUNDATION DESIGN CONSIDERATIONS

Recommended Foundation Type

We have not been provided with column or wall loads at the time of this report. Provided that column loads are approximately 25 to 75 kips and wall loads vary from 1.0 to 2.0 kips, we would recommend that the planned building be supported on a stiffened beam and slab on grade type

Arias Geoprofessionals II-6 Arias Job No. 2018-711 foundation. Once the structural loads are known, we should be informed promptly in order to review our recommendations and revise if required.

The project team may determine that another foundation type is desired for this project during the design phase. Should an alternate foundation type be desired, we should be contacted to provide additional geotechnical design data for the alternate foundation type as a Supplement to this Geotechnical Report.

Recommended Building Pad Improvement for 1” PVR

Building pad preparation requirements on expansive clay sites are dependent upon the soil moisture condition at the time of construction. Typically, the geotechnical engineer does not know the climate conditions that will exist at the time of construction since he does not know when the structure will be built. Therefore, having the geotechnical engineer retained to review site preparation recommendations and be an active participant in Team Meetings near the time of construction can often result in project cost savings since soil moisture conditions at the time of construction could be more accurately assessed. Additionally, it has been our experience that retaining the same firm for both geotechnical engineering services and construction materials testing is prudent since the geotechnical engineer is most familiar with site conditions and can quickly respond to field challenges.

In this area, a PVR of 1-inch is typically an acceptable amount of movement for structures of this type and the recommendations provided in this report are based on this assumption. Although this is a typically acceptable magnitude of movement in this area, it should be understood that a 1-inch PVR can result in some cracking requiring periodic maintenance; but the structural integrity of the building should be maintained. If project requirements dictate a different magnitude of PVR, we should be informed so that modifications to our recommendations may be made.

Recommendations are presented in Table 3 shown in Section I and are valid only for a 1-inch design PVR.

Building Pad Construction The building pad, plus a 5-foot overbuild or greater to include adjacent flatwork, should be stripped of vegetation and excavated, as necessary, to provide the required select fill thickness beneath the slab. If any existing fill material, deleterious materials, and other debris are encountered during the excavation of the building area they should be removed to firmer materials. Stripping should be performed to a depth of at least two (2) feet to allow for the placement of at least two

(2) feet of select fill material as shown in Table 3, Section I. It is essential that, prior to the placement of select fill, the exposed subgrade area of the excavation should be proof rolled to identify any soft areas, if present. Proof rolling should be accomplished using a loaded dump truck weighing at least 20 tons. Weak or soft areas evidenced during proof rolling, should be over-excavated and replaced as outlined in Table 3 of this report.

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Dense to very dense/hard to very hard materials will likely be encountered during the excavation for the two (2) feet of crushed limestone select fill. Heavy-duty equipment will be necessary to excavate these materials. A detailed evaluation of the excavatibility of the materials encountered at this site was beyond our authorized scope of services. However, based on our experience in this area, we anticipate that excavating these materials to the required depth will likely encounter conditions requiring heavy-duty rock excavating equipment. Heavy-duty excavation equipment is defined as equipment capable of cutting/excavating very hard bedrock. In addition, gravelly/sandy soils can lose cohesion and slough/cave, especially if groundwater is encountered.

The Contractor should be familiar with and prepared for such conditions.

In some areas, limestone bedrock may be encountered and in other areas, additional select fill may be required in order to achieve the finished floor elevation. We do not recommend that the planned grade-supported foundation elements be partially supported on fill and partially supported on limestone rock. It is very important that all grade beams bear on like materials (i.e. properly compacted crushed limestone select fill). If localized high areas of limestone rock are encountered during excavation of the grade-supported foundations, we recommend that a minimum of 12 inches of crushed limestone select fill be provided beneath the grade beam elements and a minimum of 3 feet of crushed limestone select fill be provided beneath the slab. Some of the limestone rock may have to be removed to meet this design condition.

Stiffened Beam and Slab on Grade A grid type beam and slab-on-grade is generally used to support relatively lightly loaded structures upon expansive soils where soil conditions are relatively uniform, and where uplift and settlement can be tolerated. The intent of a stiffened beam and slab-on-grade foundation is to allow the structure and foundation to move up and down with soil movements while providing sufficient stiffness to limit differential movements within the superstructure to an acceptable magnitude.

A stiffened grid type beam and slab-on-grade foundation may be utilized for the proposed structure provided it is designed specifically for these soil conditions. Also, the building pad for a stiffened beam and slab on grade must be improved as outlined in Table 3 of Section I. Once the structural loads are known, we should be informed promptly in order to review and revise our recommendations as required.

There are various design methods for use by the structural engineer to select the grade beams depths and beam spacings for this project. The foundation may be designed using the Building Research Board No. 33 (BRAB Report) as a guideline. Alternatively, the foundation may be designed based on the Design of Slab-On-Ground Foundations published by the Wire Reinforcement Institute, Inc. (WRI-August 1981). Provided in the following table are design criteria for both methods.

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Table 9: BRAB and WRI Foundation Design Criteria

Design Method BRAB WRI

Design PVR 1” 1”

Climatic Rating (Cw) – Del Rio, Texas 15 15

Effective Plasticity Index 20 20

Support Index (C) 0.94 --

Soil/Climatic Rating Factor (1-C) -- 0.06

Unconfined Compressive Strength (tsf) 1.2 --

Note: The above design values assume that the building pad has been improved as outlined in this report for an approximate 1-inch design PVR.

A stiffened beam and slab type foundation may also be designed for the structure using the 3rd Edition of the Design of Post-Tensioned Slabs-on-Ground published by the Post-Tensioning Institute. These values were estimated from the “Volflo” computer program in consideration of the subsurface conditions in the area of the borings. Provided in the following table are design criteria for this method for design PVR values of 1-inch.

Table 10: PTI Slab-on-Grade Soil Design Criteria (3rd Edition)

Design PVR About 1 inch

Depth to Constant Soil Suction 15 Feet

Constant Soil Suction 3.8 pF

Edge Moisture Variation Distance Center Lift, em

Edge Lift, em

8.3 feet

4.3 feet

Differential Soil Movement Center Lift, ym Edge Lift, ym

1.2 inches

1.8 inches

Coefficient of Slab-Subgrade Friction, µ 0.75

Note: The above design values assume that the building pad has been improved as outlined in this report for an approximate 1-inch design PVR.

Arias is providing design values for BRAB, WRI, and PTI methods for the Structural Engineer’s consideration and possible use. Arias recommends the final design methodology for the planned foundation be selected by the project Structural Engineer based on his knowledge and experience with similar foundation conditions.

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Table 11: Allowable Bearing Pressure and Beam Penetration

Allowable Bearing Pressure 3,000 psf

Bearing Stratum at Bottom of Grade Beams/Footings

Compacted Crushed Limestone Select Fill

Min. Penetration of Beams/Footings Below Final Grade for Bearing Pressure Requirements 24 inches

Note: Actual beam depth should be determined by structural engineer. Minimum penetration below final grade is necessary to reduce scour potential and the potential for water penetration under the foundation

Grade beams/footings based at the recommended depth, and founded within the compacted crushed limestone select fill, should be designed for the allowable soil bearing capacity provided above. Grade beams may be thickened and widened at concentrated loads to serve as spread footings. The beams and widened columns should be a minimum of 10 and 12 inches wide, respectively, for shear resistance. The grade beams should extend at least 24 inches below final grade within the compacted select fill.

We recommend that at least a 10-mil vapor retarder be used under the slab. The vapor retarder should conform to ASTM E1745, Class C or better and shall have a maximum water vapor permeance of 0.044 perms when tested in accordance with ASTM E96. A 10 mil Stego Wrap by Stego Industries LLC or other similar products meeting these requirements would be acceptable.

ADDITIONAL DESIGN CONSIDERATIONS

Flatwork Considerations

Minor differential movements between the planned structures and abutting sidewalks should be expected if the flatwork is supported on similar building pad conditions. Thus, we recommend that the flatwork be supported entirely on the improved building pad. Flatwork supported on unimproved, natural site conditions will result in flatwork movements on the order of the magnitudes reported in the PVR section that can result in significant cracking, joint separations, and a reversal in drainage as discussed subsequently.

We recommend that the flatwork and the structure be designed to include details that permit foundation movements without resulting in vertical separations and without distressing either element. Control joints should be included that include steel reinforcing to prevent vertical shear, but to allow bending.

The flatwork and abutting sidewalks should be designed and constructed to allow for positive drainage to be maintained away from the structure foundations. The planned site grading should allow for potential future differential movements and should never be allowed to reach a level condition or negative slope that promotes drainage toward the foundation. This reversal in

Arias Geoprofessionals II-10 Arias Job No. 2018-711 drainage can direct moisture into the building envelope and can become a constant nuisance and maintenance issue. If the potential differential movements cannot be tolerated, the Owner should consider extending the foundation pad beneath the planned sidewalks and incorporate the flatwork as part of the foundation system.

As delineated in Table 3, Note 6, a horizontal barrier should be utilized to help protect the select fill overbuild zone and to minimize the potential for water infiltration into the select fill and the possible “bathtub effect”.

Design Measures to Reduce Changes in Soil Moisture

To maintain performance of the proposed structures to a 1-inch PVR, measures must be included in the design to reduce moisture fluctuations of the soils under the slab-on-ground. Movements of foundation soil can be effectively reduced by providing horizontal and/or vertical moisture barriers around the edge of the slabs. Typically, the moisture barriers would consist of concrete flatwork or asphalt or concrete pavement placed adjacent to the edge of the building. An alternate approach would be a clay cap or possibly deepening the perimeter grade beams.

Although subgrade modification through excavation and replacement is recommended to reduce potential soil related foundation movements, the design and construction of a grade-supported foundation should also include the following elements:

• Roof drainage should be controlled by gutters and carried well away from the structure.

The ground surface adjacent to the building perimeter should be sloped and maintained a minimum of 5% grade away from the building for 10 feet to result in positive surface flow or drainage away from the building perimeter.

• Hose bibs, sprinkler heads, and other external water connections should be placed well away from the foundation perimeter such that surface leakage cannot readily infiltrate into the subsurface or compacted fills placed under the slabs-on-ground.

• Trees or other vegetation over 6 feet in height should not be planted within 15 feet of the structure unless specifically accounted for in the foundation design. Our design recommendations do not account for trees within 15 feet of the structure.

• Paved areas around the structure are helpful in maintaining equilibrium within the soil water content. If possible, pavement and sidewalks should be located immediately adjacent to the building.

• Site work excavations should be protected and backfilled without delay to reduce changes in the insitu moisture conditions.

IBC Site Class Determination Section 1613 of the International Building Code (2015) requires that every structure be designed and constructed to resist the effects of earthquake motions, with the seismic design category to be determined in accordance with Section 1613 or ASCE 7. Site classification according to the

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International Building Code (2015) is based on the soil profile encountered to the 100-foot depth.

The stratigraphy at the site location was explored to a maximum 24-foot depth.

Rock materials having similar consistency were extrapolated to be present between the 24 and 100-foot depths. On the basis of the site class definitions included in the 2015 Code and the encountered generalized stratigraphy, we characterize the site as Site Class D.

Seismic design coefficients were determined using the on-line software, Seismic Hazard Curves and Uniform Response Spectra, version 5.1.0, dated February 10, 2011 accessed at (https://earthquake.usgs.gov/designmaps/us/application.php). Analyses were performed considering the 2015 International Building Code. Input included GPS coordinates and Site Class D. Seismic design parameters for the site are summarized in the following table.

Table 12: IBC Site Classification and Seismic Design Parameters

Site Classification Fa Fv Ss S1

D 1.6 2.4 0.048 g 0.021 g

Where: Fa = Site coefficient Fv = Site coefficient Ss = Mapped spectral response acceleration for short periods S1 = Mapped spectral response acceleration for a 1-second period

Utilities

Utilities which go through the slab and beams should be designed with some flexibility to allow free movement in the lines.

Slab-Bearing Partition Walls & Flooring

Slab bearing partition walls and brittle floor tiles are susceptible to various degrees of cracking due to potential slab and foundation movements. Accordingly, the potential foundation movements cited earlier should be accounted for in the overall design.

Control and Construction Joints

Concrete, mortar, grout, and concrete or clay masonry units as well as numerous other construction materials shrink and swell upon a loss or gain of moisture in much the same manner as expansive soils. Accordingly, material volume changes or potential foundation movements can cause wall or slab cracking to occur. In general, however, unsightly cracking can normally be eliminated by controlling crack locations and making them inconspicuous so that they do not detract from the appearance of the building. Crack control should typically be implemented in the overall building design by the implementation of control or contraction joints in the structure at proper intervals.

https://earthquake.usgs.gov/designmaps/us/application.php

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PAVEMENT RECOMMENDATIONS

PAVEMENT DESIGN PARAMETERS AND ASSUMPTIONS

The pavement recommendations were prepared in accordance with the 1993 AASHTO Guide for the Design of Pavement Structures for asphalt and the ACI 330R (Guide for Design and Construction of Concrete Parking Lots) for concrete. No traffic specific design information was received for this project. Therefore, the following design parameters and assumptions were used in our analysis:

Table 13: Pavement Design Parameters and Assumptions

Traffic Load for Light Duty Pavement 15,000 equivalent single axle loads (ESALs)

Traffic Load for Drive Through Lanes 50,000 equivalent single axle loads (ESALs)

Average Daily Truck Traffic vehicle with at least 6 Wheels One (1)

Concrete Compressive Strength 4,000 psi

Raw Subgrade California Bearing Ratio (CBR) 6.0 for clayey sand/clayey gravel subgrade

Raw Subgrade Modulus of Subgrade Reaction, k in pci 125 for clayey sand/clayey gravel subgrade

Options for section thickness for rigid pavements are provided in SECTION I: SYNOPSIS, Table

4. Note that the truck lane traffic sections correspond to only one (1) heavy-duty truck per day.

If more heavy-duty truck traffic is anticipated, we should be contacted to revise our pavement recommendations as necessary

Rigid Concrete Pavement Joints

Placement of expansion joints in concrete paving on potentially expansive subgrade or on granular subgrade subject to piping often results in horizontal and vertical movement at the joint.

Many times, concrete spalls adjacent to the joint and eventually a failed concrete area is the result.

This problem is primarily related to water infiltration through the joint.

One method to mitigate the problem of water infiltration through the joints is to eliminate all expansion joints that are not absolutely necessary. It is our opinion that expansion or isolation joints are needed only adjacent where the pavement abuts intersecting drive lanes and other structures. Elimination of all expansion joints within the main body of the pavement area would significantly reduce access of moisture into the subgrade. Regardless of the type of expansion joint sealant used, eventually openings in the sealant occur resulting in water infiltration into the subgrade.

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The use of sawed and sealed joints should be designed in accordance with current Portland Cement Association (PCA) or American Concrete Institute (ACI) guidelines. Research has proven that joint design and layout can have a significant effect on the overall performance of concrete pavement.

Recommendations presented herein are based on the use of reinforced concrete pavement.

Local experience has shown that the use of distributed steel placed at a distance of 1/3 slab thickness from the top is of benefit in crack control for concrete pavements. Improved crack control also reduces the potential for water infiltration.

Performance Considerations

Our pavement recommendations have been developed to provide an adequate structural thickness to support the anticipated traffic volumes shown in Table 13. Some shrink/swell movements due to moisture variations in the underlying soils, or potential movement from settling utility backfill material, should be anticipated over the life of the pavements. The owner should recognize that over a period of time, pavements may crack and undergo some deterioration and loss of serviceability. We recommend the project budgets include an allowance for maintenance such as patching of cracks or occasional overlays over the life of the pavement.

Pavement Subgrade and Section Materials

Recommendations for the planned pavement subgrade and section materials are as follows:

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Table 14: Pavement Subgrade Materials

Subgrade Preparation Prior to Paving Section Construction

Minimum undercut depth

6 inches or as needed to remove organics and accommodate pavement sections. All soft, wet and loose materials should also be removed down to firmer natural materials

Reuse excavated soils Provided they are free of roots and debris and meet the material requirements for their intended use

Horizontal extent for undercut 2 feet beyond the paving limits

Exposed subgrade treatment (before moisture conditioning or lime treatment)

Proof roll with rubber-tired vehicle weighing at least 20 tons such as a loaded dump truck with Geotechnical

Engineer’s representative present during proof…