S06 VADAHerzogLot-Geotechnical Report.pdf

ECS Southwest, LLP Geotechnical Engineering Report

Herzog MRCC Canopy Addition

SWQ of East Ledbetter Drive and 52nd Street

Dallas, Texas

ECS Project Number 19:8778

January 24, 2023 (revised)

January 24, 2023 (revised)

Mr. Jim Lyles, PE

Federal Project Manager/ Sr. Civil Engineer

O’Brien Engineering, Inc.

2340 E Trinity Mills Rd #220

Carrolton, Texas 75006

ECS Project No. 19:8778

Reference: Geotechnical Engineering Report

Herzog MRCC Canopy Addition

SWQ of East Ledbetter Drive and 52nd Street

Dallas, Texas

Dear Mr. Lyles:

ECS Southwest, LLP (ECS) has completed the subsurface exploration, laboratory testing, and geotechnical engineering analyses for the above-referenced project. Our services were performed in general accordance with our agreed to scope of work. This report presents our understanding of the geotechnical aspects of the project along with the results of the field exploration and laboratory testing conducted, and our design and construction recommendations.

It has been our pleasure to be of service to O’Brien Engineering, Inc. during the design phase of this project. We would appreciate the opportunity to remain involved during the continuation of the design phase, and we would like to provide our services during construction phase operations as well to verify the assumptions of subsurface conditions made for this report. Should you have any questions concerning the information contained in this report, or if we can be of further assistance to you, please contact us.

Respectfully submitted, ECS Southwest, LLP

Mohammad Faysal, Ph.D., P.E. S. Brent McNeme, P.E.

Geotechnical Team Manager Group Manager mfaysal@ecslimited.com bmcneme@ecslimited.com

Michael P. Batuna, P.E.

Principal Engineer

Mbatuna@ecslimited.com

Herzog MRCC Canopy Addition January 24, 2023

ECS Project No. 19:8778 Page i

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Project Location

2.2 Proposed Construction

3.0 FIELD EXPLORATION AND LABORATORY TESTING

3.1 Subsurface Characterization

3.2 Groundwater Observations

3.3 Laboratory Testing

4.0 DESIGN RECOMMENDATIONS

4.1 Potential Vertical Movements

4.2 Subgrade Improvements

4.3 Foundations

4.3.1 Straight Drilled Shafts – Axial Design Parameters

4.3.2 Straight Drilled Shafts – Soil Induced Uplift Loads

4.3.3 Straight Drilled Shafts – Lateral Design Parameters

4.3.4 Straight Drilled Shafts – Construction Considerations

4.3.5 Grade Beams / Pier Caps

4.3.6 Shallow Footings

4.3.7 Shallow Footings - Construction Considerations

4.3.8 Slab on Grade

4.4 Perimeter conditions

4.5 Seismic Design Considerations

4.6 Pavement Sections – Private Drives and Parking

5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 Subgrade Preparation

5.1.1 Stripping and Grubbing

5.1.2 Proofrolling

5.1.3 Rock Excavation Considerations

5.2 Earthwork Operations

5.3 Material Specifications

5.3.1 Moisture Conditioned Clay Fill

5.3.2 Select Fill

5.3.3 Flexible Base

5.3.4 Lime Stabilized On-Site Clay

5.4 Foundation and Slab Observations

5.5 Utility Installations

6.0 CLOSING

ECS Project No. 19:8778 Page ii

APPENDICES

Appendix A – Figures

• Site Location Diagram

• Boring Location Diagram

• Regional Geology

Appendix B – Field Operations

• Reference Notes for Boring Log

• Subsurface Exploration Procedure

• Boring Log B-01

Appendix C – Laboratory Testing

• Laboratory Testing Summary

Appendix D – Supplemental Report Documents

• Clay Plug at Utility Trench

ECS Project No. 19:8778 Page 1

EXECUTIVE SUMMARY

The following summarizes the main findings of the exploration, particularly those that may have a cost impact on the planned development. Further, our principal foundation recommendations are summarized. Information gleaned from the executive summary should not be utilized in lieu of reading the entire geotechnical report.

• The project will consist of adding a canopy to the site. We assume that the final site grades will be within 2 feet of the existing grades. We understand that the canopy has been moved since the boring was completed, therefore, if subsurface conditions differ than what is provided in this report, ECS should be contacted to review the provided recommendations.

• The boring encountered 4 inches of concrete pavement underlain by 3 inches gravel base.

The subsurface stratigraphy consists of high plasticity clay underlain by weathered tan limestone and gray limestone. Gray limestone was encountered at an approximate depth of 21 feet and extended until the termination depth of 25 feet.

• Groundwater seepage was not observed in the boring during drilling and at the completion of drilling operations.

• The proposed canopy structure can be supported on straight drilled shafts bearing in gray limestone. The structure may also be supported on shallow footings bearing in improved clay soil. Floor slabs can be placed on an improved subgrade.

• It is recommended that ECS conduct a geotechnical review of the project plans (prior to issuance for construction) to check to see that ECS’ geotechnical recommendations have been properly interpreted and implemented.

• To prevent misinterpretation of ECS recommendations, ECS should be retained to perform quality control testing and documentation during construction of the earthwork and foundations for the project.

ECS Project No. 19:8778 Page 2

1.0 INTRODUCTION

The purpose of this study was to provide geotechnical information for the design and construction of a large canopy as a cover for emergency generators on the site. The canopy will be an open-air pre-engineered metal structure with a footprint of approximately 75 feet by 55 feet. We understand that the canopy has been moved approximately 100 feet to the southeast since the boring was completed, therefore, if subsurface conditions differ than what is provided in this report, ECS should be contacted to review the provided recommendations.

The project report will include the results of our subsurface explorations and geotechnical laboratory testing programs, site characterization, engineering analyses, and recommendations for the design and construction of the planned development. The recommendations developed for this report are based on project information provided by the client.

Our services were performed in general accordance with ECS Proposal No. 19:12186-GP, dated April

19, 2022, as authorized by O’Brien Engineering, Inc. on April 20, 2022, which includes the purchase order (PO No: 000281, Project No: 0461024.021) and O’Brien Engineering, Inc. terms and conditions.

The report includes the following items.

• A brief review and description of our field and laboratory test procedures and the results of testing conducted.

• A review of surface topographical features and site conditions.

• A review of area and site geologic conditions.

• A review of subsurface soil stratigraphy with pertinent available physical properties.

• A final copy of our soil test boring.

• Recommended foundation types.

• Recommendations for pavement design.

• Recommendations for site preparation and construction of compacted fills, including an evaluation of on-site soils for use as compacted fills.

ECS Project No. 19:8778 Page 3

2.0 PROJECT INFORMATION

2.1 PROJECT LOCATION

The project site is located south of the main Dallas Veterans Affairs campus, more specifically at the southwest quadrant of East Ledbetter Drive and 52nd Street, east of the Veterans Resource

Center in Dallas, Texas. The location is depicted in Figure 2.1.1 as shown below.

Figure 2.1.1 Site Location

The project site is currently a developed area with several storage trailers and small buildings on-site, as well as surface parking, and pavement. According to the NCTCOG (www.dfwmaps.com), which provided elevation contours in 2-foot intervals, the site is relatively flat.

2.2 PROPOSED CONSTRUCTION

The following information explains our understanding of the planned development including the proposed building and related structure.

Summary of Design Information

SUBJECT DESIGN INFORMATION / ASSUMPTIONS

Project Footprint Approximately 4,125 square feet in plan view

Usage Canopy addition

Framing Open-air pre-engineered metal structure

Foundation Loads Assumed less than 25 kips

Finish Floor Elevation Assumed within 2 feet from the existing grades

If ECS’ understanding of the project is not correct, please contact ECS so that we may review these changes and revise our recommendations, as appropriate.

ECS Project No. 19:8778 Page 4

3.0 FIELD EXPLORATION AND LABORATORY TESTING

Our exploration procedures are explained in greater detail in Appendix B in Subsurface Exploration

Procedures. Our scope of work included drilling one soil boring to a depth of 25 feet below the existing grades. Boring was located with a handheld GPS unit and the approximate boring location is shown on the Boring Location Diagram in Appendix A.

3.1 SUBSURFACE CHARACTERIZATION

The subsurface conditions encountered were generally consistent with published geological mapping. The following sections provide generalized characterizations of the soil strata encountered during our subsurface exploration. For specific subsurface information refer to the boring log in Appendix B.

The regional parent geologic mapping indicates that the site is underlain by the Austin Chalk (Kau) geologic formation. The parent rock of the Austin Chalk Formation is a chalky massive limestone. In the Dallas area, this rock varies from 300 to 500 feet thick in full section. It can commonly be seen in the bottoms of creeks, and in some cliff-like outcrops as a bluish-gray rock. Upper portions of this limestone typically weather becoming tan in color with more frequent fractures, joints, and clay layers.

Through chemical and mechanical weathering, the Austin Chalk forms highly plastic residual clay soils. These clays typically exhibit moderate to high shrink/swell with changes in moisture. The clays directly above the rock are typically tan in color and limy (calcareous). Clays progressively closer to the ground surface take on a darker brown appearance, have higher plasticity, and contain less calcareous deposits and limestone fragments. A summary of subsurface stratigraphy encountered in the boring is shown in Table below.

Subsurface Stratigraphy

Approximate Depth to

Bottom of Strata (ft)

Elevation of Bottom of

Strata (1) (ft) Stratum

No.

Material Description Consistency

0.6 - - Gravel (3”) -

6 EL.+490.0 I

FAT CLAY (CH), dark brown, with calcareous nodules

Very Stiff to

Hard

11 EL.+485.0 II

FAT CLAY (CH), dark brown, with calcareous deposits Hard

21 EL.+475.0 III LIMESTONE, tan, weathered -

25(2) EL.+471.0 IV LIMESTONE, gray -

Notes:

(1) Please note that the ground surface elevations were or were not surveyed by a licensed surveyor; these elevations are approximate based on dfwmaps.com. Elevation ranges are approximate +/- several feet.

(2) Boring termination depth.

ECS Project No. 19:8778 Page 5

3.2 GROUNDWATER OBSERVATIONS

Groundwater level observations were made in the boring during drilling operations. In auger drilling operations, water is not introduced into the borehole and the groundwater position can often be determined by observing water flowing into the excavation. Furthermore, visual observation of soil samples retrieved can often be used in evaluating the groundwater conditions. Groundwater seepage was not observed during drilling and upon drilling completion.

Variations in groundwater levels can occur as a result of changes in precipitation, evaporation, surface water runoff, construction activities, and other factors not immediately apparent at the time of this exploration. The highest groundwater observations are normally observed in the late winter and early spring. Therefore, the groundwater conditions at this site could be different at the time of construction. The possibility of groundwater level fluctuation should be considered when developing the design and construction plans for the project.

3.3 LABORATORY TESTING

The laboratory testing consisted of selected tests performed on samples obtained during our field exploration operations. Classification and index property tests were performed on representative soil samples. The tests included moisture content, Atterberg limits, and swell tests.

Soil samples were visually classified on the basis of texture and plasticity in accordance with ASTM

D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedures) and including USCS classification symbols, and ASTM D2487 Standard Practice for Classification for

Engineering Purposes (Unified Soil Classification System (USCS). After classification, the samples were grouped in the major zones noted on the boring log in Appendix B. The group symbols for each soil type are indicated in parentheses along with the soil descriptions. The stratification lines between strata on the logs are approximate; in situ, the transitions may be gradual.

ECS Project No. 19:8778 Page 6

4.0 DESIGN RECOMMENDATIONS

The following recommendations have been developed on the basis of the previously described project characteristics and subsurface conditions. If there are any changes to the project characteristics or if different subsurface conditions are encountered during construction, ECS should be consulted so that the recommendations of this report can be reviewed. Additionally, we understand that the canopy has been moved since the boring was completed, therefore, if subsurface conditions differ at the new offset location than what is provided in this report, ECS should be contacted to review the provided recommendations.

Site grading information was not provided during this report; however, we have assumed that the finished elevation will be within 2 feet from the existing site elevations. If the finished elevations deviate from this assumed grade, the recommendations provided below should be evaluated by our office.

Based on the conditions encountered in the boring, the proposed structure may be supported on

Straight drilled shafts bearing in gray limestone or shallow footings bearing in clay soil.

4.1 POTENTIAL VERTICAL MOVEMENTS

The soils encountered at this site are highly expansive. These soils are susceptible to shrink swell tendencies, occurring seasonally, throughout the life of the structure with the changes in moisture content. Based on test method TEX-124-E in the Texas Department of Transportation (TxDOT)

Manual of Testing Procedures and our experience with similar soils, we estimate Potential Vertical

Soil Movements (PVM) will be about 5 inches in a dry moisture condition. The actual movements could be greater if poor drainage, ponded water, and/or other unusual sources of moisture are allowed to saturate the soils beneath the structure after construction.

4.2 SUBGRADE IMPROVEMENTS

We recommend subgrade improvements below the building pad in order to reduce movements to about one inch. The recommended depths of subgrade modification to achieve post-construction movements of 1 inch are provided below.

Subgrade Improvements to Achieve Movements of 1 inch

Depth of Select

Fill/Flexible Base (foot)

Depth of Moisture

Conditioning (feet)

Total Depth of

Improvement (feet) PVM (Inches)

1 9 10 1.0

The subgrade improvements should extend beyond the building lines to include building entrances, abutting sidewalks, flatwork areas sensitive movement and 5 feet beyond those elements. Select fill or flexible base should not be used in exposed areas outside the building. Soils placed along the exterior of the grade beams should be on-site clay soils placed and compacted to at least 93% of the Maximum Dry Density at a minimum of 5 percentage points above optimum moisture content as obtained using the Standard Proctor Method (ASTM D698). Properties of moisture conditioned soil, select fill, and flexible base are provided in Section 5.3 Material Specifications.

ECS Project No. 19:8778 Page 7

4.3 FOUNDATIONS

Based on the conditions encountered in the boring, the planned structure can be supported on straight drilled shafts bearing in gray limestone. Also, the structure may be supported on shallow footings bearing on improved subgrade. Design parameters for these systems are presented below.

4.3.1 Straight Drilled Shafts – Axial Design Parameters

Axial design parameters for straight drilled shafts are presented in the following table:

Axial Design Parameters for Straight Shafts

Parameter Recommendations

Bearing stratum Gray Limestone

Minimum penetration into gray Limestone 2 feet

Net allowable end bearing capacity1 60,000 psf

Allowable skin friction in compression2 8,000 psf

Allowable skin friction in tension2 6,000 psf

Reduction in skin friction due to two closely located shafts

No reduction is required for straight drilled shafts with center-to-center spacing of 2.5 times diameter of larger shaft. For closely spaced shafts, the design skin friction varies linearly from the full value at 2.5 times diameters to 50% of the design value at 1.0 times shaft diameter.

Groups of 3 or more shafts spaced closer than

2.5 times shaft diameter

Should be evaluated by ECS. Alternative installation sequences will be required to allow for a minimum of

48 hours of concrete curing time, prior to installation of adjacent shafts.

Soil induced uplift3 Refer Section 4.3.2 Straight Drilled Shafts – Soil

Induced Uplift Loads.

Settlement4 Less than ½ inch.

Minimum shaft diameter 18 inches.

Notes:

1. A minimum penetration of 2 feet or one shaft diameter, whichever is greater, into bearing stratum is required to develop the end bearing.

2. The skin friction should be applied to that portion of the drilled shafts in direct contact with the bedrock below any temporary casing or the top of gray limestone, whichever is deeper.

3. The drilled shafts will be subject to uplift due to swelling of the expansive clays in contact with the drilled shafts. The drilled shafts must be designed with adequate embedment depth resist uplift forces and should be reinforced with sufficient, full-depth, vertical reinforcing steel to resist uplift forces.

4. Settlement will primarily be within the elastic range with a portion of settlement occurring during construction.

ECS Project No. 19:8778 Page 8

4.3.2 Straight Drilled Shafts – Soil Induced Uplift Loads

The shafts situated in the expansive clays will be subject to uplift as a result of heave in the expansive clay soils. The magnitude of these loads varies with the elevation of the top of drilled shaft. For the conditions encountered at this site, soil induced uplift of 1,800 psf over the shaft perimeter for a depth of 10 feet or to the top of limestone, whichever is shallower. For subgrade soil that have been moisture conditioned or where moisture contents have been maintained in accordance with our recommendations, the uplift can be reduced to 900 psf.

4.3.3 Straight Drilled Shafts – Lateral Design Parameters

Drilled shafts may be subject to lateral loads. Lateral design parameters for drilled shafts are presented in the following tables for use in LPILE 2016 computer program, developed by Ensoft, Inc.

LPILE Design Parameters for Soil

Soil Description LPile Material Type Unit Weight, (pcf)

Undrained Shear

Strength, (psf)

Friction Angle, (degrees) E50

Clay soils (0’ to top of tan limestone) Soft Clay 120 750 - 0.01

LPILE Design Parameters for Rock

Soil Description LPile Material

Type

Unit Weight, (pcf)

Uniaxial

Compressive

Strength, (psi)

Elastic

Modulus, Er

(psi)

RQD

Krm

Tan Limestone Weak Rock

(Reese) 130 200 20,000 50 0.0005

Gray Limestone Weak Rock

(Reese) 135 500 100,000 80 0.0005

4.3.4 Straight Drilled Shafts – Construction Considerations

The drilled shafts should be installed in accordance with American Concrete Institute’s “Standard

Specification for the Construction of Drilled Piers” (ACI 336). Recommendations provided in this report are based on proper construction procedures including maintaining a dry shaft excavation.

We recommend that all drilled and underreamed shafts be observed by qualified geotechnical personnel, to verify proper shaft installation. Observations should include:

1. identification of the recommended belling depth

2. removal of all smear zones and cuttings

3. correct handling of groundwater seepage

4. shafts are within acceptable vertical tolerance and

5. other related items

Groundwater was not observed in the boring; however, could be observed during installation of the straight drilled shafts, particularly if construction proceeds during a wet period of the year.

ECS Project No. 19:8778 Page 9

Rapid placement of steel and concrete will most probably permit shaft installation to proceed without casing. However, the seepage rates could be sufficient enough to require the use of temporary casing for proper installation of some of the shafts. If casing is used, it must be installed to a sufficient depth to ensure that an adequate seal is obtained. Typically, a casing penetration of

1 to 2 feet into the gray limestone will provide a satisfactory seal.

After the satisfactory installation of the temporary casing, water and loose material should be removed prior to beginning the design penetration. The required penetration into the bearing material may be excavated through the casing. The design penetration should be measured from the top of gray limestone, or below the bottom of temporary casing, whichever is deeper.

Reinforcing steel and concrete should be placed immediately after the excavation has been completed, cleaned and observed.

The concrete should have a slump between 5 and 7 inches and should be placed in a manner that prevents it from striking the reinforcing steel and sides of the excavation. Concrete placed in an excavation in excess of 10 feet should be placed in such a manner (using a tremie, centralizing chute, or by similar means) to prevent segregation of aggregates or to prevent concrete from striking the reinforcing steel. The concrete in the upper five feet of the shaft should be mechanically consolidated. Straight drilled shafts should be completed within 12 hours after design penetration into gray limestone has begun.

Care should be taken to avoid creating an oversized cap ("mushroom") near the ground surface. A

"mushroom" at the top of the drilled shaft could be lifted by expansive soils. Pier caps extending outside the nominal pier diameter (if used) should be constructed over void forms to reduce the potential for additional uplift forces.

Limestone is relatively hard. We recommend the drilling equipment be equipped with suitable rock drilling teeth and it should have sufficient torque and weight to drill through the rock strata. A contractor experienced with drilling hard bedrock should be retained for this project.

4.3.5 Grade Beams / Pier Caps

All grade beams/ pier caps should be supported by the drilled shafts and formed with a nominal 10-inch void beneath the beam if structural slab is used. If slab on grade with moisture conditioning is used, the void space can be reduced to 4 inches. This void is provided to isolate the grade beams from the underlying active clays. This void is provided to isolate the grade beams from the underlying active clays. Cardboard carton forms can be used to create this void. A soil retainer should be provided to help prevent “in fill” of this void.

Cardboard void forms must have sufficient strength to support the weight of the grade beam during construction. The excavation in which the void box lays must remain dry. Care must be exercised during construction to prevent collapse of these cartons. Backfill material must not be allowed to enter the void carton area below the grade beams, since this reduces the void space in which the underlying soils need to swell.

Soils placed along the exterior of the grade beams should be on-site clay soils placed and compacted to at least 93% of the Maximum Dry Density at a minimum of 5 percentage points above optimum moisture content as obtained using the Standard Proctor Method (ASTM D698). The purpose of this

ECS Project No. 19:8778 Page 10 clay backfill is to reduce the opportunity for surface or subsurface water infiltration beneath the structure.

4.3.6 Shallow Footings

The structure can be supported on a shallow footing foundation system on improved subgrade if some movement can be tolerated in the foundation system. The design parameters for shallow footings are presented in the following table.

Shallow Footing Design Parameters

Design Parameter Spread Footing Continuous Footing

Net Allowable Bearing Pressure (1) 2,500 psf 2,000 psf

Acceptable Bearing Soil Material Improved Clay Subgrade

Minimum Width 36 inches 24 inches

Minimum Footing Embedment

Depth 2 feet below lowest adjacent final grade

Ultimate passive pressure

(triangular distribution) (2, 3) 245 psf/ft

Ultimate coefficient of sliding (3) 0.36

Estimated Total Settlement Less than 1- inch

Estimated Differential Settlement Less than ½ to ¾ inches between footings

Less than ½ to ¾ inches over 40 feet length

Notes:

(1) The net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. No footing should be founded within a 45 degree plane from the base of the adjacent footing or excavation.

(2) The side of the excavation for footings must be nearly vertical and concrete should be placed against these vertical faces.

The upper 1-foot of the passive earth pressure should be neglected. In addition, the passive pressure should be ignored if the material in front of the wall will be excavated at any time in the future.

(3) A minimum factor of safety of 1.5 is recommended against sliding.

4.3.7 Shallow Footings - Construction Considerations

Footing excavations should be protected from standing water or desiccation. The base of all foundation excavations should be free of water and loose soil and rock prior to placing concrete.

Complete construction of a spread footing or a section of wall footing, including excavation, placement of steel and concrete, and backfilling should be completed in a reasonably continuous manner, preferably within 72 hours of excavation to reduce the disturbance to foundation bearing material. A seal slab of footing strength concrete should be provided at the bottom of any footing which will remain open for more than 72 hours or if rain events are expected before footings are constructed.

Backfilling of footings should be accomplished using excavated material for footings and as soon as possible to reduce disturbance of foundation soils. Backfill should be placed at a minimum of 5 percentage points above optimum moisture content and compacted to at least 93% of the

Maximum Dry Density as obtained using the Standard Proctor Method (ASTM D-698). Construction of footings should be inspected by a qualified geotechnical engineer to verify the bearing materials and to perform related observations and testing.

ECS Project No. 19:8778 Page 11

4.3.8 Slab on Grade

A slab on grade can be used for the canopy. In order to use a slab on grade, the building pad subgrade must be prepared for a maximum PVM of 1.0 inch.

The following graphic depicts our soil-supported slab recommendations:

1.

2.

Concrete Slab Thickness: 4 inches minimum

Concrete Slab Strength: 3,000 psi minimum

Subgrade Modulus: Provided subgrades are prepared as, discussed herein, we recommend that a modulus of subgrade reaction (ks) of 125 pci be used, as applicable, for the design of the slab on grade.

Vapor Retarder: If floor treatments that are sensitive to moisture will be used, a vapor retarder of polyethylene sheeting or similar material should be placed beneath the slab to minimize moisture migration through the slab. If a vapor retarder is considered to provide moisture protection, special attention should be given to the surface curing of the slabs to minimize uneven drying of the slabs and associated cracking and/or slab curling. The use of a blotter or cushion layer above the vapor retarder can also be considered for project-specific reasons. Please refer to ACI 302.1R96 Guide for

Concrete Floor and Slab Construction and ASTM E 1643 Standard Practice for Installation of Water

Vapor Retarders Used in Contact with Earth or Granular Fill under Concrete Slabs for additional guidance on this issue.

Slab Isolation: If a slab on grade is used, we recommend that it be isolated from the foundations so differential movements of the structure will not induce shear stresses on the floor slab. For maximum effectiveness, temperature, and shrinkage reinforcements in slabs on ground should be positioned in the upper third of the slab thickness. The Wire Reinforcement Institute recommends the mesh reinforcement be placed 2 inches below the slab surface or upper one-third of slab thickness, whichever is closer to the surface. Adequate construction joints, contraction joints, and isolation joints should also be provided in the slab to reduce the impacts of cracking and shrinkage. Please refer to ACI

302.1R96 Guide for Concrete Floor and Slab Construction for additional information regarding concrete slab joint design.

4.4 PERIMETER CONDITIONS

Soils placed along the exterior of the structure should be on-site clay soils placed and compacted to at least 95% of the Maximum Dry Density at or above optimum moisture content as obtained using the Standard Proctor Method (ASTM D-698). The purpose of this clay backfill is to reduce the opportunity for surface or subsurface water infiltration beneath the structure. Additionally, where penetrations into the structure occur, a clay plug (or suitable synthetic alternative) should be placed

Concrete Slab Vapor Barrier (if required)

Improved Subgrade

ECS Project No. 19:8778 Page 12 at the building line to reduce the opportunity for infiltrating water, regardless of the backfill material. A typical clay plug detail is provided in Appendix D of the report.

Positive drainage away from the structure should also be provided. Additionally, Irrigation of lawn and landscaped areas should be moderate, with no excessive wetting or drying of soils around the perimeter of the structure allowed. Trees and bushes/shrubs planted near the perimeter of the structure can withdraw large amounts of water from the soils and should be planted at least their anticipated mature height away from the buildings.

Where flatwork is placed against or near the structure, a positive seal must be installed and adequately maintained to minimize water intrusion. Down spouts and gutters should be used to collect and distribute water at least 10 feet away from the structure.

Routine maintenance is required to ensure that the recommendations contained in this report are followed and maintained. Greater potential movements could occur with extreme wetting or drying of the soils due to poor drainage, ponding of water, plumbing leaks, lack of irrigation, and/or lack of routine maintenance, etc.

4.5 SEISMIC DESIGN CONSIDERATIONS

Seismic Site Classification: The International Building Code (IBC) 2015 requires site classification for seismic design based on the upper 100 feet of a soil profile. The methods are utilized in classifying sites, namely the shear wave velocity (vs) method; the undrained shear strength (su) method; and the Standard Penetration Resistance (N-value) method. The undrained shear strength

(su) method was used in classifying this site.

The seismic site class definitions for the weighted average of shear wave velocity, SPT N-value or unconfined compressive strength (su) in the upper 100 feet of the soil profile are shown in the following table:

Seismic Site Classification

Site

Class Soil Profile Name

Shear Wave

Velocity, Vs, (ft./s)

Standard

Penetration

Resistance, N

Soil Undrained Shear

Strength, su (psf)

A Hard Rock Vs > 5,000 fps N/A N/A

B Rock 2,500 < Vs ≤ 5,000 N/A N/A

C Very dense soil and soft rock 1,200 < Vs ≤ 2,500 N >50 su ≥ 2,000

D Stiff Soil Profile 600 ≤ Vs ≤ 1,200 15 ≤ N ≤ 50 1,000 ≤ su ≤ 2000

E Soft Soil Profile Vs < 600 N <15 su < 1000

Based on the 2015 International Building Code (IBC) Site Class Definitions, in our opinion the site soil and rock can be characterized as Site Class C.

Ground Motion Parameters: In addition to the seismic site classification, ECS has determined the design spectral response acceleration parameters following the IBC methodology. The Mapped

Reponses were estimated from the USGS website https://earthquake.usgs.gov/ws/designmaps/.

The design responses for the short (0.2 sec, SDS) and 1-second period (SD1) are noted in bold at the far-right end of the following table.

ECS Project No. 19:8778 Page 13

4.6 PAVEMENT SECTIONS – PRIVATE DRIVES AND PARKING

As previously mentioned, the Potential Vertical Movement (PVM) at this site is approximately 5 inches when in a dry moisture condition and all pavements are subjected to this movement. Should these movements be unacceptable for the pavements, the recommendations included in this report to achieve more desirable future movements, should be followed.

Both asphalt pavement and Portland cement concrete pavement can be used for parking lots and drives. The pavements can be placed on tan limestone. If additional fill is required to establish finished grade, flexible base should be used between the bottom of pavement and the top of tan limestone.

Typical pavement sections are provided below. The Standard Duty and Medium Duty asphalt pavements are suitable for design life of 50,000 and 100,000 ESAL, respectively. The Standard Duty and Medium Duty concrete pavements are suitable for design life of 80,000 and 200,000 ESAL, respectively.

Please note that the recommended pavement sections provided below are considered the minimum necessary to provide satisfactory performance. In some cases, jurisdictional minimum standards for pavement section construction may exceed those provided below.

Recommended Pavement Sections

Material

Description

Asphaltic Concrete Pavement Portland Cement Concrete (PCC) Pavement

Standard Duty Medium Duty Standard Duty Medium Duty Dumpster Area

Asphalt Surface

Course 2 inches 2 inches -- -- --

Asphalt Binder

Course1 3 inches 4 inches -- -- --

Portland Cement

Concrete -- -- 5 inches 6 inches 7 inches

Subgrade2

6 inches

Lime Stabilized

Soil

6 inches

Lime Stabilized

Soil

6 inches

Lime

Stabilized Soil

6 inches

Lime Stabilized

Soil

6 inches

Lime Stabilized

Soil

Notes:

1. Flexible base material may be substituted for the asphalt binder using a substitute ratio of three inches of flexible base for each inch of asphalt binder.

2. Flexible base materials may be substituted with the lime stabilization at an equivalent thickness substitution.

3. In lieu of lime stabilization, the Portland cement concrete thickness should be increased by one inch.

Pavement sections were designed using the “AASHTO Guide for Design of Pavement Structures

1993”.

An important consideration with the design and construction of pavements is surface and subsurface drainage. Where standing water develops, either on the pavement surface or within the base course layer, softening of the subgrade and other problems related to the deterioration of the pavement can be expected. Furthermore, good drainage should reduce the possibility of the subgrade materials becoming saturated during the normal service period of the pavement.

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Please note, the recommended pavement sections provided above are considered the minimum necessary to provide satisfactory performance based on the provided traffic loading. In some cases, jurisdictional minimum standards for pavement section construction may exceed those provided above.

Pavement should be specified, constructed and tested to meet the following requirements:

1. Reinforcing steel may consist of #3 reinforcing steel bars placed at 18 inches on center each way. The reinforcing steel should be placed at mid-point of the pavement section.

2. Hot Mix Asphaltic Concrete: Item 340 of the TxDOT Standard Specifications, Type D

Surface Course. The coarse aggregate in the surface course should be crushed limestone rather than gravel.

3. Portland cement Concrete: Minimum compressive strength of 3,600 psi (28 Days).

Concrete should be designed with 3 to 6 percent entrained air.

4. Crushed Limestone Base Material: Item 247 of the TxDOT Standard Specifications, Type

A or B, Grade 2 or better. The material should be compacted to a minimum 95 percent of standard Proctor maximum dry density (ASTM D 698) and within three percentage points of the material's optimum moisture content.

Proper joint placement and design is critical to pavement performance. Load transfer at joints and maintenance of watertight joints should be accomplished by use of proper joint seals and dowels.

Control joints in new pavement should be sawed as soon as practical and preferably within 5 to 12 hours after placing concrete in order to control the location of cracks which form as the concrete cures. Longitudinal and transverse control joints should be sawed at about 15-foot spacing. Joints should be properly cleaned and sealed as soon as possible to avoid infiltration of water, small gravel, etc.

Ground Motion Parameters

GROUND MOTION PARAMETERS [IBC 2015 Method]

Period

(sec)

Mapped Spectral

Response

Accelerations

(g)

Values of Site

Coefficient for Site Class

Maximum Spectral

Response Acceleration

Adjusted for Site Class (g)

Design Spectral

Response

Acceleration

(g)

Reference Figures 1613.3.1

(1) & (2)

Tables 1613.3.3

(1) & (2)

Eqs. 16-37 &

16-38

Eqs. 16-39 &

16-40

0.2 SS 0.092 Fa 1.2 SMS=FaSs 0.110

SDS=2/3

SMS

0.074

1.0 S1 0.051 Fv 1.7 SM1=FvS1 0.087

SD1=2/3

SM1

0.058

The Site Class definition should not be confused with the Seismic Design Category designation which the Structural Engineer typically assesses. If a higher site classification is beneficial to the project, we can provide additional testing methods that may yield more favorable results.

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5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 SUBGRADE PREPARATION

In a dry and undisturbed state, the soil at the site will provide good subgrade support for fill placement and construction operations. However, these soils contain fines that are considered moderately erodible and are moisture and disturbance sensitive. Therefore, good site drainage should be maintained during earthwork operations, which would help maintain the integrity of the soil. We recommend that an attempt be made to enhance the natural drainage without interrupting its pattern. All erosion and sedimentation should be controlled in accordance with sound engineering practice and current jurisdictional requirements.

5.1.1 Stripping and Grubbing

The subgrade preparation should consist of stripping vegetation, root mat, topsoil, existing pavements and foundations, and soft or unsuitable materials from the 5-foot expanded building and pavement limits. Grassy areas of the site may have about 6 inches of topsoil. Deeper topsoil or organic laden soils may be present in flower beds and other landscaping areas. The root balls in large trees may extend deep and will require additional localized stripping depth to completely remove the organics.

The site preparation will involve demolition of the existing building, pavement, and utilities currently occupying the site. Underground utilities which will be abandoned should be removed or at least filled with flowable concrete. Existing foundation elements, if present, should be removed or cut off at least 2 feet below the new structural elements and utilities.

ECS should be retained to verify that topsoil and unsuitable surficial materials have been removed prior to the placement of new fill or construction of structure.

5.1.2 Proofrolling

Prior to fill placement or other construction on subgrades, the subgrades should be evaluated by an ECS field technician. The exposed subgrade should be thoroughly proofrolled with construction equipment having a minimum axle load of 25 tons [e.g. fully loaded tandem-axle dump truck].

Proofrolling should be traversed in two perpendicular directions with overlapping passes of the vehicle under the observation of an ECS technician. This procedure is intended to assist in identifying any localized yielding materials.

Where proofrolling identifies areas that are unstable or “pumping” subgrade those areas should be repaired prior to the placement of any subsequent Structural Fill or other construction materials.

Methods of stabilization include undercutting, moisture conditioning, or chemical stabilization. The situation should be discussed with ECS to determine the appropriate procedure. Test pits may be excavated to explore the shallow subsurface materials to help in determining the cause of the observed unstable materials, and to assist in the evaluation of appropriate remedial actions to stabilize the subgrade.

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5.1.3 Rock Excavation Considerations

Shallow rock was encountered during our subsurface exploration and rock excavation techniques may be necessary for this project. It has been our experience that single-tooth rippers can usually rip to depths on the order of two (2) to three (3) feet below the top of the tan limestone in large, open, excavations. Below that, or in small excavations, more extensive efforts are required. If excavations are advanced deeper than 1 to 2 feet below the top of the tan limestone, excavation or ripping can be achieved only with great difficulty, and other means are normally required to facilitate the removal of the rock.

For purposes of contract terms, we recommend that “rock” be defined as follows:

“Rock shall be defined as those natural materials which cannot be excavated in an open excavation with a Caterpillar Model No. D-8, heavy-duty tract type-tractor, weighted at not less than 285 hp

(flywheel power) and equipped with a single-shank hydraulic ripper, capable of exerting not less than 45,000 lbs. breakout force, or equivalent machinery. For footings, utility trenches, and pits, the rock shall be defined as those materials that cannot be excavated with a Caterpillar Model No.

215D LC track-type hydraulic excavator, equipped with a 42-inch wide short-tip radius rock bucket, rated at not less than 120 hp flywheel power with the bucket-curling force of not less than 25,000 lbs. and stick-crowd force of not less than 18,000 lbs.”

Depending on the excavation methods, the rock at this site will typically excavate in relatively large, blocky, and platy pieces, which are difficult to compact for suitable long-term performance. Also, these materials experience rapid degradation due to weathering over relatively short periods, once exposed to air and water conditions. Therefore, these larger pieces, which break up as rock-like fragments in the initial excavation, must be compacted with sufficient compaction energy to substantially break them down into soil size particles during construction.

Excavated tan limestone may be suitable for fill within the building and paving limits. For this report, all rock materials excavated at the site will be considered nondurable. Nondurable rock materials removed during excavations may be used as fill if suitably decomposed by mechanical effort.

Durability is the term used to describe the ability of a rock or rock-like material to withstand long-term chemical and mechanical weathering without size degradation. Any rock excavated from the site and used as earthwork fill should have a well-graded grain size distribution with rock and soil particles ranging from clay or silt size particles to a maximum size of 4 inches in diameter with 2 inches thick plates. Particles larger than this should be decomposed by mechanical compaction equipment to achieve the desired grain size distribution.

Once appropriately broken down, this material may then be placed and compacted at workable moisture contents above the optimum moisture content and compacted to at least 95% of the

Maximum Dry Density as obtained using the Standard Proctor Method (ASTM D698).

5.2 EARTHWORK OPERATIONS

Prior to placement of any new fill, all subgrades should be scarified to a minimum depth of 6 inches, compacted to at least 95% of Maximum Dry Density as obtained by the Standard Proctor Method

(ASTM D698) and moisture conditioned above the optimum value. All fills should be benched into the existing soils.

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On-site soils are suitable for fill materials. Imported soil used for general fill should not have a

Plasticity Index (PI) of greater than the material encountered onsite. General fill materials, outside of the building subgrade improvements, should be placed at or above optimum moisture content and compacted to at least 95% of the Maximum Dry Density as obtained by the Standard Proctor

Method (ASTM D698). Fill soils should be placed in 8 inches loose lifts for mass grading operations and 4 inches for trench type excavations where walk behind or “jumping jack” compaction equipment is used.

Upon completion of the filling operations, care should be taken to maintain the soil moisture content prior to construction of floor slabs and pavements. Soil moisture levels can be preserved by various methods that can include covering with plastic, watering, etc. If the soil becomes desiccated, the affected material should be removed and replaced, or these materials should be scarified, moisture conditioned and recompacted.

Utility cuts should not be left open for extended periods of time and should be properly backfilled.

Backfilling should be accomplished with properly compacted on-site soils, rather than granular materials. A utility trench cut-off at the building line is recommended to help prevent water from migrating through the utility trench backfill to beneath the proposed structure. The clay plug detail provided in Appendix D is a suitable method for the utility trench cut-off.

Field density and moisture tests should be performed on each lift as necessary to verify that adequate compaction is achieved. As a guide, one test per 2,500 square feet per lift is recommended in the building and paving areas (two tests minimum per lift). Utility trench backfill should be tested at a rate of one test per lift per each 150 linear feet of trench (two tests minimum per lift). Certain jurisdictional requirements may require testing in addition to that noted previously. Therefore, these specifications should be reviewed, and the more stringent specifications should be followed.

5.3 MATERIAL SPECIFICATIONS

Material specifications recommended for this project are provided below.

5.3.1 Moisture Conditioned Clay Fill

Moisture conditioning may be performed within the building and flatwork areas sensitive to movements. Moisture conditioning of the existing clays, and all new clayey fill is performed to increase the moisture of the clays to a level that reduces their ability to absorb additional water that could result in post-construction heave in these soils.

The moisture conditioning should consist of undercutting, scarifying and/or reworking, as required to achieve the required subgrade improvement. During this process, the clay should receive adequate amounts of water to ensure uniform moisture content of at 5 percentage points above the optimum moisture content. During the addition of water, the soils should be adequately mixed, and re-mixed, to ensure a uniform distribution of the moisture throughout the soil mass. Once appropriately mixed, the material should be compacted to 93% of the Maximum Dry Density as obtained using the Standard Proctor Method (ASTM D698).

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Outside of the moisture conditioned zone and where clay is used to establish site grades, we recommend that the clay material be placed and compacted to at least 95% of the Maximum Dry

Density at or above the optimum moisture content as obtained using the Standard Proctor Method

(ASTM D-698). These soils should be free of deleterious materials and be reworked to ensure a uniform distribution of water in order to achieve a uniform moisture content above the optimum moisture content.

Care should be taken to verify and preserve the specified moisture levels in the reworked clays prior to placement of floor slabs and pavements.

5.3.2 Select Fill

For the purposes of this report, Select Fill may consist of onsite or imported material that is free of debris and organic matter and have a Plasticity Index (PI) of 5 to 15, and contain 40 to 70 percent passing the No. 200 sieve.

This material should be placed and compacted at workable moisture contents at or above the optimum moisture content and compacted to at least 95% of the Maximum Dry Density as obtained using the Standard Proctor Method (ASTM D698).

5.3.3 Flexible Base

Flexible base should meet the requirements of TxDOT Item 247, Type A, Grade 1 or 2. Recycled concrete meeting the gradation requirements of flexible base is also acceptable for use. The flexible base and recycled concrete should be compacted to 95% of maximum dry density at or above the optimum moisture content as obtained using the Standard Proctor Method (ASTM D-698).

5.3.4 Lime Stabilized On-Site Clay

In lieu of importing select fill, as defined above, the on-site clay soils may be lime stabilized. The advantage to lime stabilization over untreated fill is the nearly “weatherproof” nature of the soil and once placed and compacted the material essentially retains the virtually impermeable nature of the parent clay, limiting water infiltration beneath the building.

A preliminary lime application rate of 8% hydrated lime by dry weight of clay should be used for budgeting purposes. The lime stabilized clay should be thoroughly mixed and appropriately mellowed for at least 48 hours and tested for gradation and lime reactivity (pH) prior to final placement and compaction.

Once appropriately mixed and mellowed, this material may then be placed and compacted at workable moisture contents at least +3% above the optimum moisture content and compacted to at least 95% of the Maximum Dry Density as obtain using the Standard Proctor Method (ASTM D-

698).

5.4 FOUNDATION AND SLAB OBSERVATIONS

Protection of Foundation Excavations: Exposure to the environment may weaken the soils in foundations if the foundation excavations remain open for too long a time. Therefore, foundation

ECS Project No. 19:8778 Page 19 concrete should be placed immediately after the excavation has been completed, cleaned, and observed.