S-1. Geotech Report.pdf

Geotechnical Study

Replace Overruns on Center Runway

Laughlin AFB, Texas

Arias Job No. 2014-525

Prepared For URS Group, Inc.

October 31, 2014

ARIAS

GEOPROFESSIONALS

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

October 31, 2014 Arias Job No. 201 4-525

Mr. Bill Griffin, P.E.

URS Group, Inc.

9400 Amberglen Boulevard Austin, Texas 78729

RE: Geotechnical Study Replace Overruns on Center Runway Laughlin AFB, Texas

Dear Mr. Griffin:

The results of a Geotechnical Study are presented herein for the proposed upgrades and modifications to the runway overruns at Laughlin AFB, Texas. This project was authorized on September 5, 2014 by the signed acceptance of Subcontract # 314592.US by Ms.

Rebecca Lopez of the URS Group, Inc..

The purpose of this geotechnical engineering study was to establish the geotechnical properties of the subsurface soil and groundwater conditions present at the site. The scope of the study is to provide geotechnical criteria for use by design engineers in preparing the pavement design for the project. 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 and foundation 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 F.

Thank you for the opportunity to be of service to you.

Sincerely, Arias & Associates, Inc.

TBPE Registration No: F-32 ~

~&4LA 1L

Rene P. Gonzales, p1E~ .~ 8625 Christopher M. Szy ~zak, P.E.

Senior Geotechnical Em Senior Geotechnical Engineer

Austin • Corpus Christi • Eagle Pass • Fort Worth • San Antonio

Arias & Associates, Inc. i Arias Job No. 2014-525

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 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 is a consolidated quick reference overview of the more detailed geotechnical recommendations contained in Section II and should not be utilized exclusively from the remainder of the report.

TABLE OF CONTENTS

Page

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INTRODUCTION LETTER

REPORT FORMAT INFORMATION ………………………………………………………………i

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

SECTION II: MAIN REPORT .............................................................................................. II-1

PROJECT AND SITE DESCRIPTION ............................................................................ II-1

SOIL BORINGS AND PAVEMENT SECTION DETERMINATION .................................. II-1

Sample Locations ...................................................................................................... II-1

Drilling Methods ......................................................................................................... II-1

Bulk Samples ............................................................................................................. II-2

Pavement Thickness Observations ............................................................................ II-2

LABORATORY TESTS ................................................................................................... II-3

General ...................................................................................................................... II-3

Bulk Sample Testing .................................................................................................. II-3

Sulfate Content Testing ............................................................................................. II-3

SUBSURFACE CONDITIONS ........................................................................................ II-4

Geology ..................................................................................................................... II-4

Site Stratigraphy and Engineering Properties ........................................................... II-5

Groundwater .............................................................................................................. II-6

Bulk Sample Test Results ......................................................................................... II-6

Soil Design Parameters ............................................................................................. II-7

General Comments Regarding Lime-Treatment ....................................................... II-7

ENGINEERING ANALYSIS AND RECOMMENDATIONS .............................................. II-7

Potential Pavement Heaving and Distress due to Expansive Clay Soils ................... II-7

RECOMMENDATIONS FOR PAVEMENT RECONSTRUCTION ................................... II-8

Subgrade Preparation in Pavement Areas ................................................................ II-8

General Site Earthwork Recommendations .............................................................. II-9

CONSTRUCTION CRITERIA .......................................................................................... II-9

Site Preparation ......................................................................................................... II-9

Drainage .................................................................................................................. II-10

Earthwork and Subgrade Acceptance ..................................................................... II-10

Trench Excavations ................................................................................................. II-10

QUALITY CONTROL .................................................................................................... II-11

GENERAL COMMENTS ............................................................................................... II-11

Geotechnical Design Review ................................................................................... II-11

Subsurface Variations ............................................................................................. II-12

Quality Assurance Testing ....................................................................................... II-12

Standard of Care ..................................................................................................... II-13

TABLE OF CONTENTS

Page

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APPENDIX A: FIGURES ....................................................................................................... A-1

APPENDIX B: BORING LOGS AND KEY TO CLASSIFICATION SYMBOLS ...................... B-1

APPENDIX C: LABORATORY TEST RESULTS .................................................................. C-1

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

APPENDIX E: ASFE INFORMATION – GEOTECHNICAL REPORT ................................... E-1

APPENDIX F: QUALITY ASSURANCE TESTING ............................................................... F-1

Tables

Table 1: Project Description .................................................................................................. I-1

Table 2: Existing Conditions at Time of Geotechnical Study ................................................. I-1

Table 3: Replacement of Existing Pavement Section ........................................................... I-2

Table 4: Project Compaction, Moisture and Testing Requirements ...................................... I-3

Table 5: Pavement Section Thickness Observations ........................................................... II-2

Table 6: Sulfate Test Results ............................................................................................... II-4

Table 7: Generalized Soil Conditions (B-1 thru B-5) ............................................................ II-5

Table 8: Generalized Soil Conditions (B-6 thru B-12) .......................................................... II-6

Table 9: Summary of CBR Test Results .............................................................................. II-6

Table 10: Geotechnical Parameters for Pavement Design .................................................. II-7

Table 11: Replacement of Existing Pavement Section ........................................................ II-8

Table 12: Site Work (Non Structural/General Fill) Requirements ......................................... II-9

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SECTION I: SYNOPSIS

This synopsis includes a brief description of the project, subsurface findings, recommended earthwork requirements for pavement construction, and 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: Replace Overruns on Center Runway

Project Location:

Runway 13C – 31C

Laughlin AFB, Texas

Proposed Development: Replace Pavements on Overrun Areas

Civil Engineer: URS Group, Inc.

Table 2: Existing Conditions at Time of Geotechnical Study

Ground Cover: Asphalt surfaced aircraft runway

Geologic Formation: Uvalde Gravel over Buda Limestone

Pavement Section and Soil Types: Asphaltic Concrete Pavement

Aggregate Base Material

Fill: Sandy Lean Clay (CL)

Clayey Sand (SC), Lean Clay (CL), and Limestone

Plasticity Index (PI) of FILL Soils: Average = 20 (Range = 13 to 25)

Plasticity Index (PI) of Sand/Clay Soils

(NATIVE):

Average = 16 (Range = 8 to 33)

Groundwater Depth Measured: Not encountered during drilling

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Table 3: Replacement of Existing Pavement Section

Anticipated Pavement Type: Asphalt Concrete

Aggregate Base Material

Site Improvement Method: Undercut & Replace existing pavement section

Minimum Undercut Depth: Remove existing pavement materials and additional material, if needed, to accommodate proposed pavement section

Proofrolling: Use a heavily loaded dump truck or pneumatic tired roller of at least 20 tons.

Any areas which excessively yield or pump under the wheel loading should be undercut to the depth specified by the Geotechnical Engineer’s representative.

Replace with material of similar type and compact to subgrade requirements.

Scarify, Moisten & Compact Subgrade 9 inches

Select Fill Type for General Site Grading LEAN CLAY (CL):

PI = 7 to 20

LL < 40

-200 > 50%

Maximum Particle Size = 3”

Notes:

1. Remove existing asphaltic concrete pavement and underlying aggregate base material in runway and taxiway areas. Remove existing vegetation, organic material, and any debris in area of proposed new shoulders.

2. Following stripping and undercutting operations, the exposed subgrade should be proofrolled and any unstable areas remediated as noted above. The subgrade should be thoroughly scarified to a minimum depth of 6 inches, moisture conditioned, and compacted as specified in Table 4 presented subsequently.

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Table 4: Project Compaction, Moisture and Testing Requirements

Description Material

Percent Compaction

Optimum Moisture Content Testing

Requirement According to Standard

Proctor ASTM D 698

Pavements for Runway, Taxiway, and Shoulders

Subgrade soil at base of excavation 95% 0 to +4%

1 per 5,000 SF, min. 3 tests per lift

Select Fill – LEAN CLAY (CL) 95% -1 to +3% 1 per 5,000 SF, min. 3 tests per lift

Non-Structural Areas

(Outside Pavement

Areas)

General Fill (On-site Material) 95% 0 to +4%

1 per 5,000 SF, min. 3 tests per lift

Arias & Associates, Inc. II-1 Arias Job No. 2014-525

SECTION II: MAIN REPORT

PROJECT AND SITE DESCRIPTION

The proposed project will consist of reconstructing the overrun pavement areas of the

Runway 13C-31C at Laughlin AFB, Texas. The site is located in Del Rio, Val Verde County, Texas as depicted on the Site Vicinity Map (Figure 1 in Appendix A). We understand preliminary plans are to replace the existing overrun areas on each end of the center runway.

The overrun areas are each about 1000-feet long by 150-feet wide.

The project is located along the center runway at the existing airfield. The condition of the existing pavements varied with location. Reflective cracking was observed in some areas.

No apparent pavement failures or asphalt patch areas were observed. A detailed evaluation or engineering analysis of the existing pavement section was not included as part of our scope of services. Photographs taken at the time of our site visit are included in Appendix A.

SOIL BORINGS AND PAVEMENT SECTION DETERMINATION

Sample Locations

Twelve (12) soil borings designated B-1 through B-12 were each drilled to a depth of about

10 feet at the approximate locations shown on the Boring Location Plan (Figure 2 provided in

Appendix A). The borings were taken on October 4, 2014 and boring depths were measured from below the existing pavement surface. Prior to drilling the borings, the pavement was cored with a 6-inch core barrel to provide samples and measure the asphalt pavement thickness. The underlying aggregate base material was removed, placed in plastic zip-lock bags, and the thickness was measured in the hole.

The sides of the holes where the aggregate base material was present, and the bottom of the holes where the clay subgrade was present, were sprayed with phenolphthalein to check for the presence of calcium-based stabilizing agents. No reaction was observed (i.e. material did not change to pink in color) in the base material on the side of the holes nor in the clay subgrade.

Drilling Methods

A truck-mounted drill rig using continuous flight augers together with the sampling tools was used to secure the subsurface soil samples. Drilling was performed in accordance with

ASTM D 1452. Sampling was performed in accordance with ASTM D1586 procedures for performing the Standard Penetration test and ASTM D1587 for thin-walled tube sampling as described in Appendix D. The Arias & Associates, Inc. (Arias) field representative recorded the number of blows required to drive the split-barrel sampler through three consecutive 6-inch intervals. The sum of the blows required to penetrate the final 12 inches is the Standard

Penetration Test (SPT) N value.

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Bulk Samples

Two (2) bulk samples of the subgrade soils were obtained from areas adjacent to the runway.

The approximate sample locations are indicated on the boring location plan. The bulk samples were collected to determine: (1) the relationship of maximum dry density as a function of moisture content, and (2) California Bearing Ratio (CBR). The test results are plotted and tabulated in Appendix C.

Pavement Thickness Observations

The apparent pavement thickness of the pavement layers encountered in the soil borings was measured. The measured thickness of the asphalt and base material at the 12 boring locations are provided subsequently in Table 5.

Table 5: Pavement Section Thickness Observations

Boring Number

PAVEMENT SECTION THICKNESS, INCHES Estimated Structural Number

SN

Asphalt Aggregate Base

Total Pavement Section

B-1 <1 18 18 1.80

B-2 <1 18 18 1.80

B-3 <1 12 12 1.20

B-4 <1 18 18 1.80

B-5 2 10 12 1.88

B-6 3.5 2 5.5 1.74

B-7 3 9 12 2.22

B-8 12 1 13 5.38

B-9 12” concrete 1 13 6.10

B-10 3.5 8.5 12 2.39

B-11 5.5 4 9.5 2.98

B-12 5.5 7.5 13 3.47

Notes:

1. Pavement section determined by using 6-inch core barrel to obtain samples of asphalt pavement, and aggregate base material was removed and the thickness measured.

2. Pavement surface at locations B-1 thru B-4 consisted of an aggregate surface treatment wearing course.

3. Boring B-9 drilled in concrete taxiway located perpendicular to the asphalt surface runway overrun.

4. Aggregate Base Course at locations B-1 thru B-10 appeared to consist of a clayey gravel aggregate material likely obtained from an on-site borrow source. The flexible base at Borings B-11 and B-12 consisted of crushed limestone aggregate.

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5. Structural Numbers, SN, shown in the table were estimated using the following structural layer coefficients: 0.44 for the asphalt pavement, 0.10 for clayey gravel aggregate fill, and 0.14 for crushed limestone aggregate. The values are provided for comparison purposes only and should not be utilized as a basis for design, construction, or to develop potential remedial measures.

Soil classifications and borehole logging were conducted during the exploration by our engineering technician under the supervision of our Geotechnical Engineer. Final soil classifications, as seen on the attached boring logs (Appendix B), were determined in the laboratory based on laboratory and field test results and applicable ASTM procedures.

LABORATORY TESTS

General

As a supplement to the field investigation, laboratory testing was conducted to determine soil water content, Atterberg Limits, percent passing the No. 200 sieve, and sieve analysis of the aggregate base. The laboratory results are reported in the attached boring logs included in

Appendix B, and sieve analysis results for the base material are plotted as Grain Size

Distribution curves given in Appendix C.

The soil laboratory testing for this project was done in accordance with applicable ASTM or

TxDOT procedures with the specifications and definitions for these tests listed in the

Appendix D.

Bulk Sample Testing

A Modified Proctor test was performed on the bulk sample of the subgrade soils to determine the relationship of maximum dry density as a function of moisture content in accordance with

ASTM D 1557. The results are depicted in Appendix C. Samples were then compacted in accordance with ASTM D 1883, the samples were soaked for 96 hours, and then the California

Bearing Ratio (CBR) was determined. The results are presented graphically in Appendix C and are summarized in Table 8.

Sulfate Content Testing

The sulfate content was determined for select samples of the aggregate base material and clay soils (fill and native) in accordance with the procedures noted in Appendix D. The results of the sulfate tests are presented in Table 6.

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Table 6: Sulfate Test Results

Boring No.

Approx. Sample

Depth (ft) Material Description

Sulfate Result (ppm)

B-1 1½ to 2 Brown and Tan Sandy Lean Clay (CL) 240

B-2 1½ to 2 Tan Clayey Sand (SC) 120

B-4 2 to 4 Tan Clayey Sand (SC) 120

B-5 0 to 2 FILL: Light Brown Clayey Gravel (GC) 180

B-7 6 to 8 Tan Lean Clay (CL) 140

B-8 1 to 2 FILL: Brown and Tan Sandy Lean Clay

(CL) 120

B-8 8 to 10 Tan Lean Clay (CL) 4,800

B-9 4 to 6 Light Brown and Tan Lean Clay (CL) 160

B-10 6 to 8 Tan Lean Clay (CL) 160

B-11 1 to 2 Light Brown Lean Clay (CL) 140

B-12 1 to 2 Brown and Tan Lean Clay (CL) 120

B-12 2 to 4 Tan Lean Clay (CL) 120

Bulk Sample at Runway 13C 0 to 2 Brown and Tan Clayey Sand (SC) 120

Bulk Sample at Runway 31C 0 to 2 Light Brown Clayey Sand (SC) 120

Note:

1. Approximate sample depth is referenced from the existing ground surface at the time of the geotechnical field exploration performed on October 4, 2014.

The base material and subgrade soils (fill and native) were sprayed with phenolphthalein to observe for the presence of calcium-rich material. None of the recovered subgrade samples changed colors. This would suggest that the site soils have not been treated with lime and/or cement additives.

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

SUBSURFACE CONDITIONS

Site geology, generalized stratigraphy below the pavement, 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.

Geology

The earth materials underlying the project site have been regionally mapped as older residual soils of the Uvalde Gravel Formation of the Plio-Pleistocene Epochs of the Tertiary and Quaternary Periods of the Geological Time Scale. The Uvalde Gravel Formation is in

Arias & Associates, Inc. II-5 Arias Job No. 2014-525 turn underlain by Buda Limestone. The Uvalde Gravel consists primarily of gravel and cobble-sized particles of chert, quartz, limestone, and igneous rock. The material is often cemented with calcium deposits and is typically quite dense. The Buda is a dense, hard, fine-grained, buff or light gray limestone, tinged with blue or yellow, and on weathering, is locally blotched with red. It has a smooth conchoidal fracture, and is generally distinctly nodular.

Site Stratigraphy and Engineering Properties

The subsurface conditions encountered in the soil borings varied with location. In general, Borings B-1 thru B-5 encountered clay soils over limestone bedrock, while the Borings B-6 thru B-12 encountered clay fill soils over relatively low plasticity clay soils.

The general stratigraphic conditions at the boring locations for each of the soil profiles are provided in Tables 7 and 8. The presence and thickness of the various subsurface materials can be expected to vary away from and between the exploration locations. The descriptions generally conform to the Unified Soils Classification System.

Table 7: Generalized Soil Conditions (B-1 thru B-5)

Stratum Depth, ft Material Type

PI

range

No.

range

PP

range

N range

PAVEMENT

SECTION

to

(1 - 1.5)

Surface Treatment over

10 to 18 inches of Clayey Gravel 12-18 25-48 -- 11 - 28

FILL

1.5 to

SANDY LEAN CLAY (CL), CLAYEY

SAND (SC), brown and tan, stiff, medium dense with gravel

(Boring B-1 only)

13-20 24-52 1.8 17 - 22

I (1 - 6) to (6 -10)

CLAYEY SAND (SC), LEAN CLAY (CL),

SANDY FAT CLAY (CH), tan, light tan, brown, medium dense to very dense, very stiff to hard, with calcareous deposits

11-33 32-52 4.5+ 11 - 89

II

(6 - 8) to

LIMESTONE, light tan, very dense -- -- -- 80 -

**50/5”

Where: Depth - Depth from existing ground surface during geotechnical study, feet PI - Plasticity Index, % No. 200 - Percent passing #200 sieve, % N - Standard Penetration Test (SPT) value, blows per foot -- - No test ** - Blow counts During Seating Penetration PP - Pocket Penetrometer, (tsf)

Borings B-2 thru B-5 encountered limestone stratum beginning about 6 to 8 feet below the ground surface. Based on our experience at Laughlin AFB, localized areas of bedrock could occur at shallower depths at locations away from our boring locations.

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Table 8: Generalized Soil Conditions (B-6 thru B-12)

Stratum Depth, ft Material Type

PI

range

No.

range

PP

range

N range

PAVEMENT

SECTION

to

(0.5 - 1.1)

3” to 12” of Asphalt over

1 to 9 inches of Clayey Gravel and Crushed Limestone Base

8-15 14-40 -- 11-28

FILL

(0.5 - 1.1) to (3 - 8)

SANDY LEAN CLAY (CL), brown, tan, light brown, firm to very stiff, with gravel

14-25 51-74 2.8-4.5+ 6-23

I (3 - 8) to

LEAN CLAY (CL), CLAYEY SAND (SC),

tan, firm to hard, very dense, with calcareous deposits

8-16 37-84 3.8-4.5+ 6-90

Groundwater

A dry soil sampling method was used to obtain the soil samples at the project site.

Groundwater was not encountered in the 12 soil borings drilled as part of this study. Water levels in open boreholes may require several hours to several days to stabilize depending on the permeability of the soils. Groundwater levels will often change significantly over time and should be verified immediately prior to construction.

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, and silts can store and transmit “perched” groundwater flow or seepage. Groundwater seepage can occur at fill/native soil, sand/clay, and soil/limestone interfaces.

Bulk Sample Test Results

Two (2) bulk samples were taken at various locations across the site to determine the

California Bearing Ratio (CBR) value of the subgrade soils. The results of the CBR testing are included in Appendix C and are summarized below:

Table 9: Summary of CBR Test Results

Sample Sample

Location Sample Description PI

Maximum Unit Dry

Weight, pcf

Optimum Moisture

Content, %

Corrected

CBR

14-1421 Runway 13C Brown and Tan Clayey SAND (SC) with Gravel

17 121.1 11.8 31

14-1422 Runway 31C Light Brown Clayey

SAND (SC) with Gravel 16 114.1 15.3 14.5

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Soil Design Parameters

The input design parameters used in the airfield pavement design methods typically include

CBR values for the subgrade and subbase materials in addition to the gross weights of the design aircraft, and the number of annual departures for the design aircraft. The testing provided on the subgrade samples indicated CBR values ranging from 14.5 to 31. We recommend that the design CBR of 10 be used for the site soils. The modulus of subgrade reaction for the subgrade soils was then estimated using published correlations. The geotechnical parameters for pavement design are summarized in Table 10.

Table 10: Geotechnical Parameters for Pavement Design

Subgrade California Bearing Ratio (CBR) 10 for Clayey SAND (SC) subgrade

Soil Subgrade Modulus of Subgrade Reaction, k in pci

200 pci for Clayey SAND (SC) subgrade

General Comments Regarding Lime-Treatment

The subgrade soils encountered as part of this study consisted of variable conditions that ranged from sandy clay to clayey sands and gravels. In our opinion, lime-treatment will not provide effective strength improvements to the clayey sand subgrade soils encountered in most of the borings drilled as part of this study. Due to the variable soils and the relatively low to moderate shrink/swell potential, we do not recommend that lime-treated subgrade be included as part of the pavement structure.

ENGINEERING ANALYSIS AND RECOMMENDATIONS

It was beyond the scope of this study to perform a pavement condition assessment or evaluate surface water drainage conditions. However, some general comments will be made in regard to our cursory observations of the pavement and information gathered during this study. Furthermore, it was not within our scope to design the pavement section for the runway reconstruction. However, we have provided pavement design considerations and subgrade preparation recommendations.

Potential Pavement Heaving and Distress due to Expansive Clay Soils

Pavement damage can be caused by volume changes in clay soils. Clays can shrink when they lose water and swell (grow in volume) when they gain water. The potential of expansive clays to shrink and swell is typically related to the Plasticity Index (PI). Clays with a higher PI generally have a greater potential for soil volume changes due to moisture content variations.

The soils found at this site are capable of swelling and shrinking in volume dependent on potentially changing soil water content conditions during or after construction.

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Several methods exist to evaluate swell potential of expansive clay soils. We have estimated potential heave for this site utilizing the TXDOT method (Tex 124-E). Using this method, we estimate that the potential vertical rise (PVR) ranged from about 1 to 2 inches based on the soil conditions encountered in our soil borings.

RECOMMENDATIONS FOR PAVEMENT RECONSTRUCTION

Subgrade Preparation in Pavement Areas

Table 11 presents our recommended subgrade preparation requirements for the new pavement areas:

Table 11: Replacement of Existing Pavement Section

Recommended Pavement Type: Asphalt Concrete

Aggregate Base Material

Free-Draining Gravel with Edge Drains

Filter Fabric wrapped around Gravel at Edge Drain only

Site Improvement Method: Undercut & Replace existing pavement section

Minimum Undercut Depth: Remove existing pavement materials and additional material, if needed, to accommodate proposed pavement section

Proofrolling: Use a heavily loaded dump truck or pneumatic tired roller of at least 20 tons.

Any areas which excessively yield or pump under the wheel loading should be undercut to the depth specified by the Geotechnical Engineer’s representative.

Replace with material of similar type and compact to subgrade requirements.

Scarify, Moisten & Compact Subgrade 9 inches

Select Fill Type for General Site Grading LEAN CLAY (CL):

PI = 7 to 20

LL < 40

-200 > 50%

Maximum Particle Size = 3”

Notes:

1. Remove existing asphaltic concrete pavement and underlying aggregate base material in runway and taxiway areas. Remove existing vegetation, organic material, and any debris in area of proposed new shoulders.

2. Following stripping and undercutting operations, the exposed subgrade should be proofrolled and any unstable areas remediated as noted above. The subgrade should be thoroughly scarified to a minimum depth of 6 inches, moisture conditioned, and compacted as specified in Table 4.

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It should be noted that 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. 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.

General Site Earthwork Recommendations

If fill is needed to raise site grade outside of the runway reconstruction area, general fill obtained from on-site excavations may be used. Requirements for compacted general fill are outlined in the following table.

Table 12: Site Work (Non Structural/General Fill) Requirements

Stripping Depth 6 inch minimum or as needed to remove existing asphalt, concrete, and vegetation (if any)

Non Structural/General Fill Type On-site material free of roots, debris and other deleterious material with a maximum particle size of 4 inches

Maximum Non Structural/General Fill Loose Lift Thickness

9 inches

Positive drainage is very important to reducing soil volume changes that can detrimentally affect the performance of the planned pavements. Proper attention to surface and subsurface drainage details during the design and construction phase of development can prevent many potential soil shrink-swell related problems during and following the completion of the project.

CONSTRUCTION CRITERIA

Site Preparation

Remove the existing pavement and aggregate base material. Strip away existing topsoil, grass, organics, and deleterious debris, as needed, within the pavement areas. Undercut to the required depth and extent as noted previously in Table 10. Additional excavation may also be necessary due to encountering deleterious materials such as buried debris and/or rubble, or undesirable soft and wet subgrade conditions. The site representative of the

Geotechnical Engineer should observe undercutting operations.

After the surface materials are removed, proofrolling of the exposed surface should be performed with a heavily loaded dump truck or pneumatic tired roller of at least 20 tons as previously noted in Table 11. Any areas which excessively yield or pump under the wheel loading should be undercut to the depth specified by the Geotechnical Engineer’s representative and replaced with compacted select fill to existing grade as specified. The

Arias & Associates, Inc. II-10 Arias Job No. 2014-525 backfill should be placed and compacted in accordance with the requirements for select fill given in Table 4.

At least one density test should be conducted per 5,000 square feet of the runway and shoulders pad per lift of prepared fill and subgrade as noted in Table 4.

Drainage

Good positive drainage during and after construction is very important to reduce expansive soil volume changes that can detrimentally affect the performance of the planned development. Proper attention to surface and subsurface drainage details during the design and construction phase of development can prevent many potential soil shrink-swell related problems during and following the completion of the project.

Earthwork and Subgrade Acceptance

Exposure to the environment may weaken the pavement subgrade and/or fill soils, or result in excessive drying out if there is a significant delay of subsequent earthwork. Therefore, it is recommended fill be extended to final grade as soon as possible. If the subgrade or lifts of fill soils are exposed to severe drying or wetting, the unsuitable soil must be re-conditioned or removed as appropriate and replaced with compacted fill. The final pavement subgrade should be free of loose soil, ponded water or debris and should be observed prior to constructing the underdrain system by the Geotechnical Engineer or his representative.

Subgrade preparation and fill placement operations should be monitored by the Geotechnical

Engineer or his representative. As a guideline, at least one in-place density test should be performed for each 5,000 sq. ft. of compacted surface per lift. Any areas not meeting the required compaction should be recompacted and retested until compliance is met.

Trench Excavations

Excavations should comply with OSHA Standard 29CFR, Part 1926, Subpart P and all State of Texas and local requirements. Trenches 20 feet deep or greater require that the protective system be designed by a registered professional engineer. A trench is defined as a narrow excavation in relation to its depth. In general, the depth is greater than the width, but the bottom width of the trench is not greater than 15 feet. Trenches greater than 5 feet in depth require a protective system such as trench shields, trench shoring, or sloping back the excavation side slopes.

The Contractor’s “Competent Person” shall perform daily inspections of the trench to verify that: (1) the trench is properly constructed and that surcharge and vibratory loads are not excessive; (2) excavation spoils are sufficiently away from the edge of the trench; (3) proper ingress and egress into the trench is provided; and (4) all other items are performed as outlined in these OSHA regulations. It is especially important for the inspector to observe the effects of changed weather conditions, surcharge loadings, and cuts into adjacent backfills of

Arias & Associates, Inc. II-11 Arias Job No. 2014-525 existing utilities. The flow of water into the base and sides of the excavation and the presence of any surface slope cracks should also be carefully monitored.

Although the geotechnical report provides an indication of soil types to be anticipated, actual soil and groundwater conditions will vary along the trench route. The “Competent Person” must evaluate the soil and groundwater in the trench excavation at the time of construction to verify that proper sloping or shoring measures are performed.

Appendix B to the regulations has sloping and benching requirements for short-term trench exposure for various soil types up to the maximum allowable 20-foot depth requirement.

QUALITY CONTROL

As Geotechnical Engineer of record, we should be engaged to: (1) observe and evaluate the pavement and earthwork for site subgrade improvement activities; (2) determine that the actual bearing materials are consistent with those encountered during the field exploration;

and (3) monitor and test the subgrade preparation and select fill placement. It is also important that we be given the opportunity to review the design and construction documents.

The purpose of this review is to check to see if our recommendations are properly interpreted into the project plans and specifications.

GENERAL COMMENTS

The scope of this study is to provide geotechnical criteria for use by design engineers in preparing the pavement design for reconstruction of the pavements. Environmental studies of any kind, evaluation of the condition of existing pavements, and design of new pavements were not a part of our scope of work or services even though we are capable of providing such services.

This report was prepared for this project exclusively for the use of the URS Group, Inc. and their design team. If the development plans change relative to pavement layout, size or anticipated loads, or if different subsurface conditions are encountered, we should be informed and retained to ascertain the impact of these changes on our recommendations.

We cannot be responsible for the potential impact of these changes if we are not informed.

Geotechnical Design Review

Arias should be given the opportunity to review the design and construction documents. The purpose of this review is to check to see if our geotechnical recommendations are properly interpreted into the project plans and specifications. Please note that design review was not included in the authorized scope and additional fees may apply.

Arias & Associates, Inc. II-12 Arias Job No. 2014-525

Subsurface Variations

Soil and groundwater conditions may vary away from the sample boring location. Transition boundaries or contacts, noted on the boring logs to separate soil types, are approximate.

Actual contacts may be gradual and vary at different locations. The Contractor should verify that similar conditions exist throughout the proposed area of excavation. If different subsurface conditions or highly variable subsurface conditions are encountered during construction, we should be contacted to evaluate the significance of the changed conditions relative to our recommendations.

Quality Assurance Testing

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.

As Geotechnical Engineer of Record (GER), we should be engaged by the Owner to provide

Quality Assurance (QA) testing. Our services will be to evaluate the degree to which constructors are achieving the specified conditions they’re contractually obligated to achieve, and observe that the encountered materials during earthwork for foundation installation are consistent with those encountered during this study. In the event that Arias is not retained to provide QA testing, we should be immediately contacted if differing subsurface conditions are encountered during construction. Differing materials may require modification to the recommendations that we provided herein. A message to the Owner with regard to the project QA is provided in the ASFE publication included in Appendix F.

Arias has an established in-house laboratory that meets the standards of the American

Standard Testing Materials (ASTM) specifications of ASTM E-329 defining requirements for

Inspection and Testing Agencies for soil, concrete, steel and bituminous materials as used in construction. We maintain soils, concrete, asphalt, and aggregate testing equipment to provide the testing needs required by the project specifications. All of our equipment is calibrated by an independent testing agency in accordance with the National Bureau of

Standards. In addition, Arias is accredited by the American Association of State Highway &

Transportation Officials (AASHTO), the United States Army Corps of Engineers (USACE) and the Texas Department of Transportation (TxDOT), and also maintains AASHTO

Materials Reference Laboratory (AMRL) and Cement and Concrete Reference Laboratory

(CCRL) proficiency sampling, assessments and inspections.

Furthermore, Arias employs a technical staff certified through the following agencies: the

National Institute for Certification in Engineering Technologies (NICET), the American

Concrete Institute (ACI), the American Welding Society (AWS), the Precast/Prestressed

Concrete Institute (PCI), the Mine & Safety Health Administration (MSHA), the Texas Asphalt

Pavement Association (TXAPA), and the Texas Board of Professional Engineers (TBPE).

Our services are conducted under the guidance and direction of a Professional Engineer

(P.E.) licensed to work in the State of Texas, as required by law.

Arias & Associates, Inc. II-13 Arias Job No. 2014-525

Standard of Care

Subject to the limitations inherent in the agreed scope of services as to the degree of care and amount of time and expenses to be incurred, and subject to any other limitations contained in the agreement for this work, Arias has performed its services consistent with that level of care and skill ordinarily exercised by other professional engineers practicing in the same locale and under similar circumstances at the time the services were performed.

Information about this geotechnical report is provided in the ASFE publication included in

Appendix E.

Arias & Associates, Inc. A-1 Arias Job No. 2014-525

APPENDIX A: FIGURES

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

VICINITY MAP

Laughlin AFB Runway Overruns Runway 13 C and 31 C

Del Rio, Texas

Date: October 23, 2014 Job No.: 2014-525 Figure 1

Drawn By: TAS Checked By: RPG

Approved By: SAH Scale: N.T.S.

Approximate Site Location

Note: Drawing provided by URS

BORING LOCATION PLAN

Runway 13 C

Del Rio, Texas

Date: October 31, 2014 Job No.: 2014-525 Figure 2

Drawn By: TAS Checked By: RPG

Approved By: SAH Scale: N.T.S.

B-2

B-1

B-3

B-4

B-5

CBR

Note: Drawing provided by URS

BORING LOCATION PLAN

Runway 13 C

Del Rio, Texas

Date: October 23, 2014 Job No.: 2014-525 Figure 2

Drawn By: TAS Checked By: RPG

Approved By: SAH Scale: N.T.S.

B-12

B-11

B-10

B-9

B-8

B-7

B-6

CBR

Photo 1 – View looking towards the north at the drilling operations of Boring B-2 on Runway 13 C.

Photo 2 – View looking towards the east/northeast at the drilling operations of Boring B-4 on Runway 13 C.

SITE PHOTOS

Del Rio, Texas

Date: October 31, 2014 Job No.: 2014-525 Appendix A

Drawn By: TAS Checked By: RPG

Photo 3 – View looking towards the south at the drilling operations of Boring B-6 on Runway 31 C.

Photo 4 – View looking towards the north/northwest at the drilling operations of Boring B-10 on Runway 31 C.

SITE PHOTOS

Del Rio, Texas

Date: October 31, 2014 Job No.: 2014-525 Appendix A

Drawn By: TAS Checked By: RPG

Arias & Associates, Inc. B-1 Arias Job No. 2014-525

APPENDIX B: BORING LOGS AND KEY TO CLASSIFICATION

SYMBOLS

2-Course Surface Treatment FILL: Tan Clayey Sand (SC) with Gravel

FILL: SANDY LEAN CLAY (CL), stiff, brown and tan, with trace gravel

-tan and brown, Clayey Sand (SC) with gravel below 4'

SANDY FAT CLAY (CH), hard, light brown and tan

-very stiff, lean clay (CL), below 8'

Borehole terminated at 10 feet

SS

SS

SS

SS

SS

Location: See Boring Location Plan

Coordinates: N29o22'8.8'' W100o47'23.9''

Boring Log No. B-1

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index N = SPT Blow Count

-200 = % Passing #200 Sieve

Single flight auger: 0 - 10 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Split Spoon (SS)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

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A R

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1.

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-200NPL LL PIWCSNDepth (ft)

FILL: Light Brown Clayey Gravel (GC) with sand

-Clayey Sand (SC) with Gravel below 1'

CLAYEY SAND (SC), medium dense, tan

-light tan below 4'

LIMESTONE, dense, light tan

Borehole terminated at 9.25 feet

50/3"

SS

SS

SS

SS

SS

Location: See Boring Location Plan

Coordinates: N29o22'7.1'' W100o47'21.1''

Boring Log No. B-2

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index N = SPT Blow Count

-200 = % Passing #200 Sieve

Single flight auger: 0 - 9.25 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Split Spoon (SS)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

.G P

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-200NPL LL PIWCSNDepth (ft)

FILL: Brown Clayey Gravel (GC) with sand

CLAYEY SAND (SC), medium dense, light tan

-dense below 3'

LIMESTONE, dense, light tan

Borehole terminated at 8.92 feet

**50/6"

**50/5"

4.5+

T

SS

SS

SS

SS

Location: See Boring Location Plan

Coordinates: N29o22'6.7'' W100o47'19.7''

Boring Log No. B-3

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index

PP = Pocket Penetrometer (tsf)

N = SPT Blow Count ** = Blow Counts During Seating

Penetration -200 = % Passing #200 Sieve

Single flight auger: 0 - 8.92 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Thin-walled tube (T) Split Spoon (SS)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

.G P

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(B O

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-200NPPPL LL PIWCSNDepth (ft)

FILL: Light Brown Clayey Sand (SC) with Gravel -brown and tan below 0.5'

CLAYEY SAND (SC), dense to very dense, tan

LIMESTONE, dense, light tan

Borehole terminated at 8.83 feet

**50/4"

SS

SS

SS

SS

SS

Location: See Boring Location Plan

Coordinates: N29o22'4.9'' W100o47'18.8''

Boring Log No. B-4

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index N = SPT Blow Count

** = Blow Counts During Seating Penetration

-200 = % Passing #200 Sieve

Single flight auger: 0 - 8.83 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Split Spoon (SS)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

.G P

J

/3

/1

(B O

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IN

G L

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S A

-0

2, A

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-0 1.

G D

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-0

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-200NPL LL PIWCSNDepth (ft)

2" Asphalt FILL: Light Brown Clayey Gravel (GC) with sand -brown and tan with less gravel below 0.5'

CLAYEY SAND (SC), medium dense, tan, with calcareous deposits

LIMESTONE, dense, light tan

Borehole terminated at 9 feet

50/6"

**50/6"

1.75

T

SS

SS

SS

SS

Location: See Boring Location Plan

Coordinates: N29o22'3.1'' W100o47'17.6''

Boring Log No. B-5

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index

PP = Pocket Penetrometer (tsf)

N = SPT Blow Count ** = Blow Counts During Seating

Penetration -200 = % Passing #200 Sieve

Single flight auger: 0 - 9 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Thin-walled tube (T) Split Spoon (SS)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

.G P

J

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/1

(B O

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IN

G L

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S A

-0

2, A

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S S

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G D

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A R

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-0

1.

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-200NPPPL LL PIWCSNDepth (ft)

3.5" Asphalt 2" Tan Clayey Sand (SC) with Gravel FILL: SANDY LEAN CLAY (CL), firm, brown, with calcareous deposits -with gravel to 2'

-light brown, very stiff, 2' to 4'

-brown and tan, hard, below 4'

LEAN CLAY (CL), firm, tan, with calcareous deposits

Borehole terminated at 10 feet

2.87 L/D

(UW)

4.5+

4.5+

SS

SS

T

T

SS

Location: See Boring Location Plan

Coordinates: N29o20'53.1'' W100o45'59.2''

Boring Log No. B-6

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index

PP = Pocket Penetrometer (tsf)

N = SPT Blow Count -200 = % Passing #200 Sieve DD = Dry Density (pcf) Uc = Compressive Strength (tsf)

UW = Unit Weight (pcf)Single flight auger: 0 - 10 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Split Spoon (SS) Thin-walled tube (T)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

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(B O

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-0

2, A

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S S

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G D

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-0

1.

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LB

UcDD-200NPPPL LL PIWCSNDepth (ft)

3" Asphalt FILL: Light Tan Clayey Gravel (GC) with sand

FILL: SANDY LEAN CLAY (CL), very stiff, brown and tan, with calcareous deposits

-hard below 2'

LEAN CLAY (CL), very stiff, tan, with calcareous deposits and trace gravel

-gravelly, with sand, below 8'

Borehole terminated at 10 feet

2.75

4.5+

4.5+

T

T

T

T

SS

Location: See Boring Location Plan

Coordinates: N29o20'54.7'' W100o46'0''

Boring Log No. B-7

Groundwater Data:

During drilling: Not encountered

Field Drilling Data:

Coordinates: Hand-held GPS Unit Logged By: W. Persyn Driller: Accu Drilling Equipment: Truck-mounted drill rig

WC = Water Content (%) PL = Plastic Limit LL = Liquid Limit PI = Plasticity Index

PP = Pocket Penetrometer (tsf)

N = SPT Blow Count -200 = % Passing #200 Sieve

Single flight auger: 0 - 10 ft

Soil Description

Nomenclature Used on Boring Log

Arias & Associates, Inc.

Backfill: Cuttings

Thin-walled tube (T) Split Spoon (SS)

Job No.: 2014-525

Project: Replace Overruns on Center Runway Laughlin AFB, Texas

Sampling Date: 10/4/14

-5

.G P

J

/3

/1

(B O

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IN

G L

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S A

-0

2, A

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S S

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-0

1.

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LB

-200NPPPL LL PIWCSNDepth (ft)

12" Asphalt

1" BASE

FILL: SANDY LEAN CLAY (CL), stiff, brown and tan, with gravel

-hard below 3'

-tan and dark brown…