Geotechnical_Report.pdf

Geotechnical Engineering Study

Proposed Administration Building Falcon Dam

Falcon Village, Texas

Arias Job No. 2011-650

Prepared For ALS 88 Design Build LLC

November 30, 2011

ARIAS & ASSOCIATES

Geotechnical • Environmental • Testing

November 30, 2011 Arias Job No. 2011-650

Ms. Annastacia L. Sequoyah ALS 88 Design Build LLC 18249 FM 471 South Natalia, Texas 78059

RE: Geotechnical Engineering Study Proposed Administration Building Falcon Dam Falcon Village, Texas

Dear Ms. Sequoyah:

The results of a Geotechnical Engineering Study for a proposed Administration Building at Falcon Dam in Falcon Village, Texas are presented in this report. This project was authorized on October 24, 2011 by signed acceptance of Arias Proposal No. 2011-650, dated October 19, 2011.

The purpose of this geotechnical engineering study was to establish foundation and pavement engineering properties of the subsurface soil 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. Slope stability and/or global stability analyses of the site slopes/retaining walls was beyond our authorized service scope. We can assist in these analyses if desired.

In order to help contribute to the success of this project, we recommend that the site work, building, and pavement construction be tested and observed by one of our representatives in accordance with the report recommendations. Furthermore, the geotechnical engineer of record should be employed during construction to observe that the site preparation and foundation construction are performed in accordance with the recommendations presented in this report.

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

RENEp:GONZA Rene P. Gonzales, P.E. ~ .# Dexter Bacon, P.E.

Senior. Geotechnical Eng~~r 86259 ~ Senior Vice President

1295 Thompson Rd 142 Chula Vista 5233 IH 37, Suite B-12 Eagle Pass, Texas 78852 Falcon Village, Texas 78232 Corpus Ch~sti, Texas 78408

(830) 757-8891 (210) 308-5884 (361) 288-2670

(830) 757-8899 Fax (210) 308-5886 Fax (361) 288-4672 Fax

Sincerely, Arias & Associates, Inc.

TBPE Registration No: F-32

Arias & Associates, Inc. i Arias Job No. 2011-650

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

Arias & Associates, Inc. ii Arias Job No. 2011-650

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 LABORATORY TESTS................................................................ II-1 SUBSURFACE CONDITIONS ........................................................................................ II-2

Site Stratigraphy and Engineering Properties ........................................................... II-2 Groundwater.............................................................................................................. II-2

MOISTURE VARIATIONS AND ESTIMATED MOVEMENT........................................... II-2 FOUNDATION DESIGN CONSIDERATIONS ................................................................ II-3

Building Foundation Types ........................................................................................ II-3 Recommended Building Pad Improvement for 1” PVR ............................................. II-4 Stiffened Beam and Slab-on-Grade Foundation ....................................................... II-4 Design Measures to Reduce Changes in Soil Moisture ............................................ II-6 Flatwork Considerations ............................................................................................ II-7 IBC Site Classification and Seismic Design Coefficients........................................... II-8

PAVEMENT RECOMMENDATIONS .............................................................................. II-9 Performance Considerations ................................................................................... II-10 Pavement Subgrade and Section Materials ............................................................ II-11

ADDITIONAL DESIGN CONSIDERATIONS................................................................. II-12 Utilities ..................................................................................................................... II-12 Slab-Bearing Partition Walls & Flooring .................................................................. II-12 Control and Construction Joints .............................................................................. II-12

CONSTRUCTION CRITERIA........................................................................................ II-12 Site Preparation....................................................................................................... II-12 Drainage.................................................................................................................. II-13 Earthwork and Foundation Acceptance................................................................... II-13 Trench Excavations ................................................................................................. II-14

QUALITY CONTROL .................................................................................................... II-15 GENERAL COMMENTS ............................................................................................... II-15

TABLE OF CONTENTS

Page

Arias & Associates, Inc. iii Arias Job No. 2011-650

APPENDIX A: SITE VICINITY MAP...................................................................................... A-1

APPENDIX B: SITE PHOTOGRAPHS.................................................................................. B-1

APPENDIX C: BORING LOCATION PLAN AND BORING LOGS ........................................C-1

APPENDIX D: KEY TO CLASSIFICATION SYMBOLS.........................................................D-1

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

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

Tables

Table 1: Project Description .................................................................................................. I-1 Table 2: Existing Conditions at Time of Geotechnical Study................................................. I-1 Table 3: Hybrid Method – Building Pad Recommendations for 1” PVR ................................ I-2 Table 4: Project Compaction, Moisture and Testing Requirements ...................................... I-3 Table 5: Recommended Pavement Sections ........................................................................ I-4 Table 6: Generalized Soil Conditions................................................................................... II-2 Table 7: BRAB and WRI Foundation Design Criteria........................................................... II-5 Table 8: PTI Slab-on-Grade Soil Design Criteria (3rd Edition) .............................................. II-5 Table 9: Allowable Bearing Pressure and Beam Penetration .............................................. II-6 Table 10: Seismic Design Parameters ................................................................................. II-8 Table 11: Pavement Design Assumptions ........................................................................... II-9 Table 12: Concrete Paving Requirements ......................................................................... II-10 Table 13: Pavement Subgrade and Section Materials ....................................................... II-11 Table 14: Cement Treatment Considerations .................................................................... II-12 Table 15: Site Work (Non Structural/General Fill) Requirements....................................... II-13

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SECTION I: SYNOPSIS

This synopsis includes a brief description of the project, subsurface findings, recommended foundation types, generalized earthwork requirements for building pad 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: Proposed Administration Building

Project Location: Falcon Village, Texas

Proposed Development: New single-story, 5,500 square foot building

Preferred Foundation Type: Stiffened beam and slab-on-grade

Desired Improved Site Condition (PVR):

1” for a stiffened beam and slab-on-grade foundation

Table 2: Existing Conditions at Time of Geotechnical Study

Ground Cover: Existing wood frame building, mature trees, and grass landscaping

Predominant Soil Types:

Clayey, Silty Sand (SC-SM) over Moderately

Plastic Clays (CL,CH) and Formational Sandstone

Average Plasticity Index (PI) of Upper Clayey Sand:

15 (Range 4 - 42)

Groundwater Depth Measured: Not Observed

Estimated Potential Vertical Rise (PVR): <1 inch

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Table 3: Building Pad Recommendations for 1” PVR

Recommended Foundation Type: Stiffened Beam and Slab-on-Grade

Site Improvement Method: Remove organics and existing foundations and re-compact near-surface sands

Desired Improved Site Condition (PVR): 1 inch

Minimum Undercut Depth: 6 inches

Scarify, Moisten & Compact Exposed Subgrade 6 inches

Minimum Select Fill Thickness: 1 foot

Select Fill Type Liquid Limit <40%, PI 8-17, max. 3” maximum particle size

Notes:

1. The building pad improvements will be used with a stiffened slab-on-grade foundation system.

2. Following stripping operations, undercut at least 6 inches of the existing soils from beneath all slab areas. Undercutting should extend laterally to provide at least a 5-foot overbuild beyond the building perimeter and to the width of any adjacent sidewalks wider than five (5) feet.

3. The exposed subgrade should be scarified to a depth of 6 inches, moisture conditioned and compacted as specified in SECTION I, Table 4 (Project Compaction, Moisture and Testing Requirements).

4. After moisture conditioning and compacting the subgrade, clean onsite soil may be placed back in the foundation excavation to raise site grades. The reused soil should be reconditioned as specified in SECTION I, Table 4 (Project Compaction, Moisture and Testing Requirements).

Reconditioning should be performed to provide a homogenous mixture of soil with no dry clods or clumps.

5. The final approximate 12 inches, or as required to achieve final design grade, of the building pad should be constructed using imported select fill. The select fill should be placed within 48 hours of completion of the subgrade compaction and should be placed in maximum 8-inch loose lifts as specified in SECTION I, Table 4 (Project Compaction, Moisture and Testing Requirements).

6. Based on the information provided by the client, we understand that paving and/or concrete flatwork will not be constructed adjacent to the proposed building foundation; therefore, we recommend that a perimeter grade beam having a depth of at least 18 inches below final grade be utilized. The final grade beam depth and recommended construction should be determined by the structural engineer.

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Table 4: Project Compaction, Moisture and Testing Requirements

Percent Compaction

Optimum Moisture Content Description Material

According to Standard Proctor

ASTM D 698

Testing Requirement

Subgrade soil at base of excavation 93% to 98% At least 1%

1 per 5,000 SF;

min. 3 tests Building Pad

Area Select Fill ≥ 98% -2% to +3% 1 per 5,000 SF;

min. 3 per lift

Scarified On-site Soil (Subgrade) ≥ 95% -2% to +3% 1 per 5,000 SF;

min. 3 tests

General Fill (Onsite Material) ≥ 95% -2% to +3% 1 per 5,000 SF;

min. 3 per lift Pavement

Areas

Base Material ≥ 95%

(ASTM D 1557)

+3% 1 per 5,000 SF;

min. 3 per lift

Non-Structural Areas (Outside Building Pad)

General Fill (On-site Material) ≥ 95% -2% to +3% 1 per 5,000 SF;

min. 3 per lift

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Table 5: Recommended Pavement Sections

Concrete Paver Stones, inches Section Option 1 Section Option 2

Layer Material Light traffic

Moderate traffic

Light traffic

Moderate traffic

Surface Concrete Paver Stone 3⅛ 3⅛ 3⅛ 3⅛

Bedding Course 1 to 1½ 1 to 1½ 1 to 1½ 1 to 1½ Base

Flexible Base -- -- 6 10 Cement Treated 6 12 -- --

Subgrade Moisture Conditioned -- -- 6 6

Reinforced Concrete, inches

Layer Material Light traffic Moderate traffic Heavy traffic

Surface Portland cement concrete 5 6 7

Subgrade Cement Treated 6 6 6

Notes:

1. New pavements over granular soils may be subject to erosion and undermining during severe rain events and flooding. Potential pavement distress from erosion would be expected to be most probable along the pavement edges. The use of deep pavement curbs can be considered to reduce the potential for pavements to be undermined as a result of erosion. The implementation of adequate erosion control materials and methods should be determined by the project civil engineer.

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

3. Moderate traffic areas include entrance aprons and drives into the site, single access route drive lanes to parking areas, and areas where paving will be subjected to truck traffic (5 trucks per day, with no 18-wheeled, tractor trailer traffic).

4. Heavy traffic areas include areas subjected to 18-wheel tractor trailers, trash collection vehicles, and dumpster pads including loading and unloading areas, and areas where truck turning and maneuvering may occur. Concrete pavement is recommended for heavy traffic areas. The recommended pavement thicknesses are valid provided fewer than 25 trucks per day are anticipated. If higher traffic volumes are anticipated, Arias should be consulted to provide alternate recommendations.

5. During the paving life, maintenance to seal surface cracks within concrete or asphalt paving and to reseal joints within concrete pavement should be undertaken to achieve the desired paving life. Perimeter drainage should be controlled to prevent or retard influx of surface water from areas surrounding the paving. Water penetration leads to paving degradation. 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 asphalt paving to reduce potential for infiltration of moisture into the base course. Curbs should extend the full depth of the base course and should extend at least 3 inches into the underlying subgrade. The base layer should be tied into the area inlets to drain water that may collect in the base.

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6. The intent of the 6 inches of cement treated subgrade beneath the concrete pavements is to provide improved subgrade support conditions to assist with the construction of the site pavements. It is acceptable to replace the cement treated subgrade beneath the concrete pavement section with 4 inches of flexible base material over 6 inches of moisture conditioned subgrade.

7. Material specifications, construction considerations, and section requirements are presented in the Pavement Subgrade and Section Materials included in Section II of this report.

Arias & Associates, Inc. II-1 Arias Job No. 2011-650

SECTION II: MAIN REPORT

PROJECT AND SITE DESCRIPTION

The proposed project will include upgrades and site improvements to the existing administration and maintenance areas at Falcon Dam. The project will include a new 5,500 square foot, single-story building and associated site parking. A Site Vicinity Map is provided in Appendix A. The site is currently occupied by several existing wood frame buildings that will be demolished as part of the site improvements. Representative site photographs are provided in Appendix B of this report.

We understand the new building will have relatively light structural loads and preliminary plans are to support the structure on a stiffened beam foundation. For the purpose of this geotechnical engineering study, we are assuming that the acceptable PVR for the slab-on-grade foundation is on the order of 1 inch.

SOIL BORINGS AND LABORATORY TESTS

Five (5) soil test borings were drilled at the approximate locations shown on the Boring Location Plan provided in Appendix C. The borings were drilled within the area of the proposed building and parking areas to depths of 5 to 30 feet. The boring depths were measured from below the existing ground surface elevation on November 11, 2011. The test borings were sampled in accordance with ASTM D1586 for Split Spoon sampling techniques as described in Appendix E. A truck-mounted drill rig using continuous flight augers together with the sampling tool noted was used to secure the subsurface soil samples.

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

As a supplement to the field exploration, laboratory testing to determine soil water content, Atterberg Limits, and percent passing the US Standard No. 200 sieve, was conducted. The laboratory results are reported in the attached boring logs included in Appendix C. A key to the terms and symbols used on the logs is also included in Appendix D. The soil laboratory testing for this project was done in accordance applicable ASTM procedures with the specifications and definitions for these tests listed in the Appendix E.

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

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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.

Site Stratigraphy and Engineering Properties The generalized subsurface stratigraphy encountered at this site is summarized in the table below.

Table 6: Generalized Soil Conditions

Stratum Depth

(ft) Material Type PI range No. 200 Range

N range

I 0 to (8-13)

Tan, Brown to Light Brown, Clayey, Silty SAND (SC-SM), loose to very dense 4 - 42 16 - 42 4 - 75

II 8 to 21 Very Dense SANDSTONE (only in Boring B-2) -- -- > 50

III (13-21) to

Light Gray and Brown Lean (CL) to Fat (CH) CLAY, very stiff to hard, with sand 42 70 - 96 26 - >50

Where: Depth - Depth from existing ground surface at the time of geotechnical study, feet PI - Plasticity Index, % No. 200 - Percent passing #200 sieve, % N - Standard Penetration Test (SPT) value, blows per foot

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

Groundwater was not observed within the soil borings during the soil sampling activities which were performed on November 11, 2011. 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.

After obtaining samples and final groundwater measurements, the bore holes were backfilled with excavated soil.

MOISTURE VARIATIONS AND ESTIMATED MOVEMENT

Structural 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.

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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. The term swelling soils implies not only 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 for this site utilizing the TXDOT method (Tex 124-E). Using the TXDOT method, we estimate that the PVR is approximately ½ to 1 inches at this site considering the existing dry soil moisture conditions at the time of the sampling activities.

FOUNDATION DESIGN CONSIDERATIONS

Both shallow and deep foundation types are utilized in this area. Deep drilled piers are suited to buildings with moderate to heavy loading conditions, or for more movement– sensitive structures. The piers, when properly founded, can reduce foundation movement of the superstructure. Grade beams, isolated from the soil, typically span between the piers and either a structurally suspended slab or soil supported slab-on-grade is used at the ground floor level. The structurally suspended slab option is used when excellent performance is expected from the structure in terms of minimal aesthetic distress, such as floor tile, foundation and wall cracking.

A shallow foundation type consisting of a stiffened beam and slab-on-grade “waffle slab” is a common alternate approach for small to moderate size buildings. This foundation type is typically used for light to moderate loading conditions and can be more cost-effective than a deep foundation system. When founded within expansive soils, subgrade improvement is recommended in order to reduce potential soil and foundation movement to a magnitude acceptable to the owner and design team. Some aesthetic distress, as noted above, is normally acceptable to the owner and design team with this foundation alternative.

Each approach has its advantages and disadvantages in terms of cost and overall performance.

Building Foundation Types We understand that a stiffened beam and slab-on-grade foundation is the client-preferred foundation type for the proposed Administration Building. Criteria for this foundation type are provided in this report. 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.

It is our opinion that the building may be supported on a stiffened beam and slab-on-grade foundation.

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Recommended Building Pad Improvement for 1” PVR Stiffened beam and slab-on-grade foundations for this site will require minor site improvements to provide a construction platform to assist with the placement of reinforcing steel and concrete. 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.

Recommendations presented herein are valid only for a 1-inch PVR.

The near surface clayey, silty sands (SC-SM) encountered in our soil borings would be expected to have a relatively low shrink/swell potential. Substantial site improvements will not be required to achieve the design PVR site conditions for this project. However, we anticipate earthwork will be required to repair disturbed areas resulting from the demolition of the existing foundations, removal of large trees, and relocation of site utilities. We recommend that extensive proofrolling of the subgrades be provided upon removal of the existing foundations, vegetation, and site utilities. Rubble and/or soft subgrade conditions observed during proofrolling should be replaced and corrected as recommended in this report.

We recommend the final floor elevations be selected to provide positive drainage away from the planned foundations. The final approximate 12 inches, or as required to achieve final grade, of the building pad should be constructed using import select fill. In fill areas where site grades will be raised by more than 1 foot, we recommend that select fill be used beneath the foundation areas to achieve design grades.

Based on the information provided by the client, we understand that pavement and/or concrete flatwork will not be constructed around the perimeter of the building. Therefore, we recommend that the perimeter grade beam be constructed to a depth of at least 18 inches below final adjacent grade to aid in reducing the potential for moisture fluctuation beneath the building pad. The final grade beam depths and locations should be determined by the structural engineer.

Stiffened Beam and Slab-on-Grade Foundation A grid type beam and slab-on-grade foundation is generally used to support relatively light structures 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.

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A stiffened grid type beam and slab-on-grade foundation may be utilized for the proposed building provided it is designed specifically for these soil conditions and the building pad and/or site is improved as outlined in the previous report section.

There are various design methods for use by the structural engineer to select the grade beams depths and beam spacings for the 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. (August 1981). Provided in the following table are design criteria for both methods.

Table 7: BRAB and WRI Foundation Design Criteria

Design Method BRAB WRI Design PVR 1” 1” Climatic Rating (Cw) – Falcon Village, Texas 15 15 Effective Plasticity Index 20 20 Support Index (C) 0.95 -- Soil/Climatic Rating Factor (1-C) -- 0.05 Unconfined Compressive Strength (tsf) 1.5 --

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

A stiffened beam and slab type foundation may also be designed 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 soil conditions in the building area. Provided in the following table are design criteria for this method.

Table 8: PTI Slab-on-Grade Soil Design Criteria (3rd Edition)

Design PVR 1” Depth to Constant Soil Suction 8 Feet Constant Soil Suction 3.8 pF Edge Moisture Variation Distance Center Lift, em

Edge Lift, em

9.0 feet

5.2 feet

Differential Soil Movement Center Lift, ym Edge Lift, ym

0.7 inch

1.1 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 a 1” PVR respectively.

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Table 9: Allowable Bearing Pressure and Beam Penetration

Allowable Bearing Pressure 1,800 psf

Bearing Stratum at Bottom of Grade Beams Compacted Select Fill or Onsite

Reconditioned Soils Min. Penetration of Beams Below Final Grade for Bearing Pressure Requirements

18 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.

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 foundations be selected by the project Structural Engineer based on his knowledge and experience with similar foundation conditions.

Grade beams based at the recommended depth and founded within the existing fill soils or compacted 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 18 inches below final grade within the existing fill soils or 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.

Design Measures to Reduce Changes in Soil Moisture Measures to reduce future moisture fluctuations of the soils under the floor slab must be considered. Movements of foundation soil can be effectively reduced by providing horizontal and/or vertical moisture barriers around the edge of the slab. Typically the moisture barriers would consist of concrete flatwork or asphalt or concrete pavement placed adjacent to the edge of the building, or a deepened perimeter grade beam as previously discussed in this report.

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:

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• 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 proposed foundations and slabs.

• No trees or other vegetation over 6 feet in height shall be planted within 15 feet of the structure unless specifically accounted for in the foundation design.

• Utility bedding should not include gravel within 4 feet of the perimeter of the foundation.

Compacted clay or flowable fill trench backfill should be used in lieu of permeable bedding materials between 2 feet inside the building to a distance of 4 feet beyond the exterior of the building edge to reduce the potential for water to infiltrate within utility bedding and backfill material.

• 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.

• Flower beds and planter boxes should be piped or water tight to prevent water infiltration under the building. Experience indicates that landscape irrigation is a common source of foundation movement problems and pavement distress.

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

See SECTION II: ADDITIONAL DESIGN CONSIDERATIONS for further discussion of utilities and slab bearing partition walls.

Flatwork Considerations Minor differential movements between the planned structure 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 buildings 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.

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The flatwork and abutting sidewalks should be designed and constructed to allow for positive drainage to be maintained away from the building foundation. The planned site grading should allow for potential future differential movements and should never be allowed to reach a level or negative slope that promotes drainage toward the foundation. This reversal in 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 may wish to consider extending the foundation pad beneath the planned sidewalks and incorporating the flatwork as part of the foundation system.

See SECTION II: ADDITIONAL DESIGN CONSIDERATIONS for further discussion of utilities and slab bearing partition walls.

IBC Site Classification and Seismic Design Coefficients Section 1613 of the International Building Code (2009) 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 International Building Code (2009) is based on the soil profile encountered to 100-foot depth. The stratigraphy at the site location was explored to a maximum 30-foot depth.

Clay soils and limestone having similar consistency were extrapolated to be present between 15 and 100-foot depths. On the basis of the site class definitions included in Table 1613.5.2 and 1613.5.5 of the 2009 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 (http://earthquake.usgs.gov/hazards/designmaps/javacalc.php). Analyses were performed considering the 2009 International Building Code. Input included zip code 78545 and Site Class C. Seismic design parameters for the site are summarized in the following table.

Table 10: Seismic Design Parameters

Site Classification Fa Fv Ss S1 C 1.6 2.4 0.054g 0.014g

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

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PAVEMENT RECOMMENDATIONS

Accumulation of water beneath the site pavements can cause progressive and rapid deterioration of the pavement section. Similarly, pavement surfaces should be well drained to eliminate ponding with a two-percent minimum slope, as possible. The pavement recommendations were prepared in accordance with the 1993 AASHTO Guide for the Design of Pavement Structures and the ACI Design Guide SCM-28 (95). No traffic specific design information was received for this project. Therefore, the following design parameters and assumptions were used in our analysis:

Table 11: Pavement Design Assumptions

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

Traffic Load for Heavy Duty Pavement 50,000 equivalent single axle loads (ESALs)

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

Raw Subgrade California Bearing Ratio (CBR) 3 for compacted clayey SAND (SC) subgrade

Raw Subgrade Modulus of Subgrade Reaction, k in pci 125 for compacted clayey SAND (SC) subgrade

Options for section thickness for the proposed pavements are provided in SECTION I, Table 5 “Recommended Pavement Design Sections”. Note that the truck lane traffic sections correspond to only one heavy-duty truck per day. If more heavy-duty truck traffic is anticipated, we should be contacted to provide additional recommendations. A truck traffic section is recommended for use at loading docks, entrances, driveways, dumpsters pads and channeled traffic areas. Areas subjected to truck traffic stopping, starting, loading, unloading or turning should not utilize asphalt pavement. For these areas, a 7” concrete section should be used.

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Table 12: Concrete Paving Requirements

Minimum compressive strength at 28 days 4,000 psi Desired slump during placement 5 ± 1 inch Reinforced Steel #4 @ 18” each way placed D/3 from top of slab Construction Joint Dowels 1” diameter, 18” long @ 12” oc lubricated both sides Expansion Joints May be eliminated except at tie-ins with existing concrete and structures

Contraction Joints – transverse and longitudinal

Light traffic – 12 feet spacing Moderate and heavy traffic – 15 feet spacing

Placement In accordance with ACI 304R (guide for measuring, mixing, transporting, and placing), ACI 305R (hot weather concreting, and ACI 306R (cold weather concreting)

Performance Considerations Our pavement recommendations have been developed to provide an adequate structural thickness to support the anticipated traffic volumes. Some soil related 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 repairs over the life of the pavement.

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Pavement Subgrade and Section Materials Recommendations for subgrade preparation in the planned pavement areas are as follows.

Table 13: Pavement Subgrade and Section Materials

Stripping Depth 6 inches or as needed to remove roots and organics

Reuse Excavated Soils Provided they are free of roots and debris and meet the general fill material requirements.

Undercut Extent 2 feet beyond the paving limits

Exposed Subgrade Treatment (before cement treatment or moisture conditioning)

Proof roll with rubber tired vehicle weighting at least 20 tons such as a loaded dump truck with Geotechnical Engineer’s representative present during proof rolling

Pumping/Rutting Areas Discovered During Proofrolling

Remove to firmer materials and replace with compacted general or select fill under direction of geotechnical engineer representative

General Fill Type On-site material free of roots, debris and other deleterious material with a maximum particle size of 3 inches

Reuse of Recycled Asphalt/Concrete

Demolished asphalt and concrete from project site may be used as general fill provided the materials are processed to a maximum size of 3 inches. The asphalt and concrete should be broken down and then mixed with existing base material and/or subgrade to be used as fill.

Maximum General Fill Loose Lift Thickness 9 inches

To prevent degradation of the prepared subgrade, paving preferably should be placed within 14 days. If pavement placement is delayed, protection of the subgrade surface with an emulsion-based sealer should be considered. Alternately, the paving section could be slightly overbuilt so blading performed to remove distressed sections does not reduce the treated subgrade thickness.

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Table 14: Cement Treatment Considerations

Treatment depth 6 inches Cement type Type 1 or 2 Treatment application rate (estimated) 4 - 6% by dry weight Soil dry unit weight (estimated) 105 pcf but may be variable Determination of Cement application rate The actual application rate should be determined by laboratory testing of soil samples taken after the pavement subgrade elevation has been achieved.

The quantity of cement should be sufficient to result in a compressive strength of 300 psi when tested at 7 days.

Treatment procedure TxDOT Item 275 Treated layer compaction and moisture criteria

ASTM D 698

≥ 98% compaction at -1 to +3 from optimum

ADDITIONAL DESIGN CONSIDERATIONS

Utilities Utilities which go through the slab and beams should be designed with some flexibility to allow free movement in the lines as a result of potential soil shrinkage or swelling.

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.

CONSTRUCTION CRITERIA

Site Preparation Strip away any existing asphalt, concrete, topsoil, grass, organics, and deleterious debris as needed and dispose outside of the building, pavement and other structural areas. Undercut to the required depth and extent as noted in the main report. Additional excavation may be

Arias & Associates, Inc. II-13 Arias Job No. 2011-650 required to accommodate the required select fill thickness, or as required, to remove existing utilities or foundations. 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. Unless passing density reports are provided for a specific area, existing fill soils found during the excavation should be considered as uncertified and removed to suitable natural soils.

After the surface materials are removed, the exposed subgrade surface should be proofrolled with a heavily loaded dump truck weighing 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 and replaced with compacted select fill to existing grade as specified. The voids in undercut areas can be backfilled and compacted with on-site general fill materials.

Table 15: Site Work (Non Structural/General Fill) Requirements

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

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

The backfill should be placed and compacted in accordance with the General Fill requirements in Table 4 in Section I.

At least one density test should be conducted per 5,000 square feet of building pad per lift of prepared fill and subgrade or a minimum of three density tests should be taken per lift within the building pad area.

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 aid in preventing many potential soil shrink-swell related problems during and following the completion of the project.

Earthwork and Foundation Acceptance Exposure to the environment may weaken the soils at the foundation bearing level if the excavation remains open for long periods of time. Therefore, it is recommended that all foundation excavations be extended to final grade and constructed as soon as possible in

Arias & Associates, Inc. II-14 Arias Job No. 2011-650 order to reduce potential damage to the bearing soils. If bearing soils are exposed to severe drying or wetting, the unsuitable soil must be re-conditioned or removed as appropriate and replaced with compacted fill, prior to concreting. The foundation bearing level should be free of loose soil, ponded water or debris and should be observed prior to concreting by the geotechnical engineer or his representative.

Foundation concrete should not be placed on soils that have been disturbed by rainfall or seepage. If the bearing soils are softened by surface water intrusion during exposure or by desiccation, the unsuitable soils must be removed from the foundation excavation and replaced with compacted select fill prior to placement of concrete.

Subgrade preparation and fill placement operations should be monitored by the soil 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 or a minimum of three tests 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 the trench is properly constructed and that surcharge and vibratory loads are not excessive, that excavation spoils are sufficiently away from the edge of the trench, proper ingress and egress into the trench is provided and 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 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 by the Trench Safety Engineer.

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 soils and groundwater in the trench excavation at the time of construction to verify that proper sloping or shoring measures are performed.

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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 observe and evaluate the foundation installation and earthwork for site subgrade improvement activities to determine that the actual bearing materials are consistent with those encountered during the field exploration and to observe 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 engineering criteria for use by design engineers in preparing the foundation design.