8-08 Geotechnical Report.pdf

Geotechnical Evaluation Report

Proposed Concession/Restroom Building Grady-Littlejohn Sports Complex Wilson Creek Parkway McKinney, Texas

Prepared for

LJA Engineering

Douglas P. Ziolkowski, P.E.

Senior Engineer License Number: 57574 July 10, 2024

Project B2404002

Braun Intertec Corporation TBPELS Firm Registration No. F-12228

AA/EOE

Braun Intertec Corporation 1160 Mustang Drive, Ste. 300 Dallas, TX 75261

Phone: 817.786.5999 Web: braunintertec.com

Send USPS mail to: P.O. Box 1685 Grapevine, TX 76099

July 10, 2024 Project B2404002

Mr. Billy Vicic Associate Principal LJA Engineering 2150 South Central Expressway, Suite 300 McKinney, Texas 75070

Re: Geotechnical Evaluation Proposed Restroom/Concession Building Grady-Littlejohn Sports Complex Wilson Creek Parkway McKinney, Texas

Dear Mr. Vicic:

Braun Intertec Corporation is pleased to present this Geotechnical Evaluation study for the proposed restroom/concession building planned at Grady-Littlejohn Sports Complex in McKinney, Texas. The work was performed in general accordance with Braun Intertec Proposal No. QTB193882 dated March 21, 2024. This report contains a summary of the soil, rock, and groundwater conditions observed within one test boring drilled and completed at the subject property.

Thank you for making Braun Intertec Corporation your geotechnical consultant for this project. If you have questions about this report or if there are other services that we can provide in support of our work to date, please contact us.

Sincerely, BRAUN INTERTEC CORPORATION

TBPELS Firm Registration No. F-12228

Douglas P. Ziolkowski, P.E.

Senior Engineer

Randy Deatherage, P.E.

Senior Manager | Senior Engineer

LBoren Randy Deatherage

Table of Contents Description Page

A. Introduction

A.1. Project Description A.2. Site Conditions, Topography and History A.3. Purpose A.4. Background Information and Reference Documents A.5. Scope of Services

B. Results B.1. Geologic Overview B.2. Subsurface Conditions B.3. Depth to Rock B.4. Free Water B.5. Laboratory Test Results

C. Recommendations C.1. Design and Construction Discussion

C.1.a. Expansive Soil Conditions C.1.b. Foundation-Type Structure Support and Floor Slab Types C.1.c. Existing Fill and Existing Utilities C.1.d. Reuse of On-Site Soils C.1.e. Groundwater C.1.f. Weather C.1.g. Existing Plaza Flatwork

C.2. Site Grading and Subgrade Preparation C.2.a. Site Grading C.2.b. Excavation Oversizing C.2.c. Excavated Slopes C.2.d. Excavation Dewatering C.2.e. Building and Pavement Subgrade Proof Roll C.2.f. Fill Materials and Compaction C.2.g. Inspections of Soils C.2.h. Moisture Density Relations Testing C.2.i. Mixing of Fill Lifts and Benching C.2.j. Rock Fragments

C.3. Straight Drilled Shafts C.3.a. Design Parameters for Drilled Shaft Foundations C.3.b. Group Effects for Axial Loads C.3.c. Drilled Shaft Support C.3.d. Adhesion Uplift C.3.e. Lateral Loading Considerations C.3.f. Grade Beams and Pier Caps C.3.g. Concrete Placement C.3.h. Drilled Shaft Construction Considerations

Table of Contents (continued)

C.3.i. Special Inspections of Drilled Shafts C.4. Drilled and Underreamed (Belled) Shafts

C.4.a. Soil Parameters for the Design of Drilled Piers C.4.b. Adhesion Uplift C.4.c. Lateral Load Design Considerations C.4.d. Drilled and Underreamed Shaft Construction Considerations

C.5. Slab-on-Grade Systems with Subgrade Modifications C.5.a. Slab-on-Grade Subgrade Preparation Discussion C.5.b. Slab-on-Grade Subgrade Modification- Method 3 C.5.c. Additional Discussion Regarding Building Pad Preparation C.5.d. Alternative to Special Fill C.5.e. Excavation Observations C.5.f. Confirmation Testing (Test Boring) Program for Method 3

C.6. Additional Floor Slab Considerations C.6.a. Membrane under Slab C.6.b. Utilities through Slab

C.7. Stiffened Slab or Mat Design Parameters C.8. Flatwork C.9. Drainage Considerations C.10. Landscaping and Trees C.11. Seismic Site Classification C.12. Equipment Support

D. Procedures D.1. Test Borings D.2. Exploration Logs

D.2.a. Log of Boring Sheets D.2.b. Geologic Origins

D.3. Material Classification and Testing D.3.a. Visual and Manual Classification D.3.b. Laboratory Testing

D.4. Groundwater Measurements E. Qualifications

E.1. Variations in Subsurface Conditions E.1.a. Material Strata E.1.b. Groundwater Level

E.2. Continuity of Professional Responsibility E.2.a. Plan Review E.2.b. Construction Observations and Testing

E.3. Use of Report E.4. Standard of Care

Table of Contents (continued)

Appendix A – Site Figures Figure 1- Site Vicinity Map Figure 2- Site Topographical Map Figure 3- Site Geologic Map Figure 4- Boring Location Plan

Appendix B- Test Boring Logs Log of Boring: Sheet ST-01 Descriptive Terminology of Soil Descriptive Terminology of Rock

Appendix C- Laboratory Test Results Table C.1- Summary of Free Swell Test Results

Appendix D- Construction Specifications Guideline Specifications for Chemical Injection

A. Introduction

A.1. Project Description

This Geotechnical Evaluation Report addresses the design and construction of a new concession/restroom building and new site flatwork improvements at the existing Grady-Littlejohn

Sports Complex located on the south side of Wilson Creek Parkway in McKinney, Texas. The proposed building will replace a former restroom/concession building that was destroyed by fire earlier in 2024.

The new building will be roughly 2,500 square feet in size and will be located in the approximate location of the former structure. In addition to the new building, there will be handicap modifications made throughout the entire sports complex.

The following tables provide additional project details.

Table 1. Building Description

Aspect Description

Below grade levels None

Above grade levels One

Finished floor elevation New Building will have a Slab at Elevation 553.5 feet*

Column loads- Dead plus Live Load (kips)

25 to 50 Kips (estimated)

Nature of construction Masonry or Concrete Construction supported on drilled shafts with floor slab on modified subgrade or possibly with shallow stiffened mat foundation with slab on modified subgrade.

Cuts or fills for building to achieve finish subgrade* Cuts and fills of less than 6 inches are anticipated.

Tolerable foundation movement Less than 1 inch total and ½ inch differential

* Based on topographic plan by LJA Engineering.

An illustration of the site with the test boring is included as Figure 4 within Appendix A.

A.2. Site Conditions, Topography and History

The Grady-Littlejohn Sports complex is located on the south side of Wilson Creek Parkway approximately ¾ mile east of US Highway 75 in the southeast portion of McKinney, Texas (refer to Figure 1- Site Vicinity Map included within Appendix A). The proposed concession/restroom building will be

Grady-Littlejohn Sports Complex July 10, 2024 located within the center of the sports complex. The building area and surrounding flatwork is situated in a plaza area that has been raised up above the flood plain for the nearby Wilson Creek. The proposed concession/restroom building will be reconstructed within the plaza area which is covered by the concrete foundation slab for the previous structure, concrete flatwork and an open landscape area with manicured grass and a few trees. There are some open square cutouts in the concrete plaza slab which are currently devoid of vegetation. Some of the flatwork surrounding the area of the proposed concession/restroom building is experiencing distress. Further discussion about the distress is provided within Section C.1 of this report.

Based on the Site Topographical Map (refer to Figure 2 in Appendix A), the regional topography of the Grady-Littlejohn Sports complex formerly sloped from the northwest to the southeast toward a small tributary branch of Wilson Creek, which is located approximately ¼ mile south of the site. The plaza area where the new building will be constructed is generally flat with little relief, but it is raised up approximately 5 to 7 feet above the surrounding baseball/softball fields located to the north and south of the plaza.

A.3. Purpose

The purpose of our geotechnical evaluation was to provide recommendations for use in the design and construction of the new building and site improvements. In support of that purpose, we characterized subsurface geologic conditions at a selected exploration location and evaluated the impact of the observed conditions on the planned improvements.

A.4. Background Information and Reference Documents

We reviewed the following information:

Aerial images of the site viewed in Google Earth™, imagery dates from January 1995 to January 2024.

Site Vicinity and Site Topographical Maps- US Dept. of the Interior, Geological Survey, McKinney West Quadrangle, dated 2022- Refer to Figures 1 and 2 in Appendix A.

Site Geology Map- Geologic Atlas of Texas; Sherman Sheet, Revised 1987- Refer to Figure 3 in Appendix A.

Site KMZ file (used for Boring Location Plan - Figure 4 in Appendix A.)

We have described our understanding of the proposed construction and site to the extent others reported it to us. Depending on the extent of available information, we may have made assumptions based on our experience with similar projects. If we have not correctly recorded or interpreted the project details, the project team should notify us. New or changed information could require additional evaluation, analyses, and/or recommendations.

A.5. Scope of Services

We performed our scope of work in general accordance with our proposal to Mr. Billy Vicic with LJA Engineering as described within Braun Intertec Proposal No. QTB193882 dated March 21, 2024. The following list describes the geotechnical tasks completed following our authorized scope of services.

Reviewed the background information and reference documents previously cited.

Coordinated the staking and clearing the exploration locations of underground utilities. We selected and staked the exploration location for one (1) test boring. The Boring Location Plan (Figure 4) included in Appendix A show the approximate location of the test boring.

Performed a total of one (1) test boring. Boring ST-01 was drilled in the general limits of the proposed new building and was drilled to a depth of 45 feet beneath the existing ground surface.

Performed laboratory testing on select samples to aid in soil classification and engineering analysis.

Summarized the observed subsurface profile and observed groundwater conditions.

Discussed the site conditions that will impact structure design and performance, qualifying the nature of their impact, and outlined alternatives for mitigating their impact.

Discussed the reuse of on-site materials during construction and the potential impact of groundwater on construction.

Provided discussion on potential vertical movements (soil heave) based on the site conditions and laboratory test results. Provided recommendations to reduce total heave related design movements to a level of 1-inch or less.

Provided recommendations for preparing structure subgrades, including excavation support, if applicable, and the selection, placement and compaction of excavation backfill and other structural fill.

Provided recommendations for deep foundation design parameters for straight drilled shafts.

Provided alternate recommendations for relatively shallow, drilled and underreamed shaft foundations. Also, provided recommendations for shallow foundation design parameters for stiffened or mat slab foundation.

Our scope of services did not include environmental services or testing, and the persons performing this evaluation were not trained to provide environmental services or testing. We can provide these services or testing at your request.

B. Results

B.1. Geologic Overview

The site is situated within an area underlain by Alluvium Deposits associated with the nearby Wilson Creek. The Alluvium deposits generally consist of clay, silt, sand or gravel deposits. Underlying the Alluvium deposits are soils and rock of the Austin Chalk geologic formation (refer to Qal and Kau on Figure 3- Site Geologic Map within Appendix A). This Austin Chalk formation is typically composed of residual fat and lean clay soils that are weathered from the underlying limestone formation. Soils developed on the Austin Chalk Formation are typically composed of highly plastic fat clays and less plastic lean clays with weathered rock seams. The plastic soils observed exhibit expansive characteristics. The soils transition into tan, weathered rock, which generally becomes less weathered and denser with depth, and extends to unweathered rock, which at this site is gray in color. The intact, unweathered rock materials are relatively strong and can support significant loads.

The geology maps used as part of this study typically did not include ground verification of the boundaries between geologic formations even though the maps were originally developed by others using aerial photography. As a result, the mapped boundaries should be considered approximate. The soils and rock observed at the site are generally consistent with the anticipated geology. No apparent fill materials were observed but may be encountered due to the past site grading.

B.2. Subsurface Conditions

Table 2 below provides a subsoil strata summary of the material observed in the one (1) soil boring drilled at the site. Please refer to the Log of Boring sheet provided in Appendix B for additional details. The Descriptive Terminology sheets in Appendix B include definitions of abbreviations used in Table 2. Please note that local variations should be expected in the field.

Table 2: Subsoil Strata Summary

B.3. Depth to Rock

Tan weathered limestone was encountered at a depth of approximately 38 feet below the existing ground surface. Gray unweathered limestone was encountered at a depth of approximately 40 feet below existing grade.

B.4. Free Water

Free water was observed during drilling in test boring ST-01 at a depth of approximately 28 feet below the existing grade. At the end of drilling, free water was observed at a depth of approximately 20 feet. A

Strata Soil Type -

ASTM

Classification

Relative Density/

Consistency

Approximate Depth to

Bottom of Stratum

Commentary and Details

Natural- Fat

Clay CH 1 to 4½+ tsf 38 feet

Brown to light brown, sometimes mottled.

Stiff to hard in consistency Contains varying amounts of calcareous material and silt.

Weathered Limestone

SPT-

50/2” BPF

40 feet Tan

Unweathered

Limestone

SPT-

50/2” BPF

Termination

Gray Extends to beyond 45 feet depth groundwater study was not included in our scope of work. Details regarding the observed free water levels are included in the Log of Boring included in Appendix B.

It is difficult to accurately predict the magnitude of subsurface water fluctuations that may occur following periods of inclement weather. Free water can be present above any of the less permeable soils or rock and can flow through fissures and sandier soils, creating a temporary perched water condition, particularly during wetter seasons. Therefore, water levels should be expected to fluctuate throughout the year with variations in weather, precipitation runoff, irrigation, site topography, utilities, and water levels from nearby surface water features and other factors that are unknown or not evident at the time of this study.

Long-term observations would be required to provide an accurate evaluation of the water levels and their fluctuations. If these services are desired, Braun Intertec would be pleased to provide water level monitoring as an additional scope of services.

B.5. Laboratory Test Results

Laboratory testing was performed on selected samples recovered from the boring to confirm visual classification and estimate the pertinent engineering properties of the observed soils. Below is a summary of the selected data. Additional laboratory results are presented on the corresponding Log of Boring included within Appendix B.

Atterberg limit tests, moisture content tests and percent passing the No. 200 sieve tests were performed on selected soil samples. The individual test results can also be found on the Log of Boring Sheet.

The measured in-situ moisture content of the soils ranged from approximately 22 to 25 percent. The observed moisture contents indicated the soils were generally in a moist condition, which is expected for soils covered by a slab for a long period of time.

Liquid limits of the tested samples ranged from 57 to 71 with corresponding plasticity indices between 38 to 51, indicating a high to very high soil plasticity. A high plasticity index is generally associated with a high potential for active clay soils to shrink and swell in response to changes in the soil moisture content.

In addition to the index testing outlined above, a total of one (1), one-dimensional free swell test was performed. The test result was 0.9% swell. The test result is presented on Table C.1 in Appendix C.

Additionally, we performed two (2) unconfined compressive strength tests on cohesive soils collected in the one test boring for the proposed new structure. The test results varied from 2.1 to 3.1 tsf and are included on the test boring log provided within Appendix B. The test results are also presented in graphic form within Appendix C.

C. Recommendations

C.1. Design and Construction Discussion

The following conclusions and recommendations are based on our site observations, our interpretation of the field and laboratory data obtained during this exploration, our discussions with the project team, and our experience with similar subsurface conditions. Soil and rock penetration data were considered in developing our estimate of allowable bearing pressures. When developing these estimates, we also considered previous correlations of penetration data and allowable foundation bearing pressures.

Subsurface conditions in unexplored locations may vary from those observed in the one test boring. If anything changed from the above understanding such as building finished floor elevation, Braun Intertec must be advised so that we may reevaluate and possibly revise our recommendations. If these characteristics or the layout of the proposed project changes, we should be contacted to review the changes and provide further recommendations as needed.

C.1.a. Expansive Soil Conditions The current site stratigraphy beneath the proposed new concession/restroom building consists of fat clays extending to depths of approximately 38 feet below the existing grade. These soils typically provide sufficient support when maintained in a moist condition. However, our analysis showed that the native clay subgrade soils have expansive properties and will tend to shrink and swell in response to changes in moisture. These shrinking and swelling movements can cause the unsatisfactory performance of the foundation and slab-on-grade systems and reducing the magnitude of these movements, through either mitigation and/or moisture control, will be paramount to the success of structures bearing on them.

The potential for soil heave was estimated using the Texas Department of Transportation Potential Vertical Rise (PVR) method (Test Procedure TEX-124-E) and free swell test results. Based on the laboratory data and our experience performing geotechnical explorations within the site area, we estimate that the potential vertical rise (PVR) beneath the new structure and flatwork could vary from 2 inches to approximately 3 inches. These estimated movements apply to the conditions where the proposed slab elevation is constructed at or very near existing grades and construction occurs following an extended dry period. If drainage is not properly controlled and the soils beneath the new structure become saturated, the estimated potential vertical movement may exceed 3½ inches in localized areas.

The estimated shrink/swell movements are based on the soil moisture variations from a dry to a wet condition. The actual soil movements that will occur depending on various factors. The soil movements could be less than the calculated PVR if the moisture remains fairly consistent. However, extreme moisture fluctuations resulting from extended droughts, flooding, shallow groundwater, poor site drainage, and/or leaking irrigation lines may result in shrinking or swelling values in excess of the calculated PVR.

C.1.b. Foundation-Type Structure Support and Floor Slab Types As indicated in Section C.1.a, the estimated potential heave beneath the new concession/restroom building was estimated to be within 2 to 3 inches after grading has occurred. The allowable design total movement related to heave for slabs on grade is typically considered by local practicing structural engineers to be one inch or less. During our evaluation, we considered several soil modification methods for the site slab on grade as well as the possible use of a structural slab system. The soil modification methods included:

Method 1 - Remove a specific depth of the surficial, high-plasticity, clay soils and replace with imported select fill;

Method 2 - Remove a specified depth of the surficial, high-plasticity, clay soils, moisture condition the soils and place the moisture-conditioned materials back into the excavation to a specified depth and complete the balance with imported select fill or flexible base to achieve the desired final grade;

Method 3 - Electrochemically pressure inject and in-situ stabilize the surficial clays and install a surface layer of special fill or flexible base; or, Utilize some combination of the above three methods.

The select fill referenced in Methods 1 and 2 consists of low plasticity silty clay, sandy clay, or clayey sand soils with a plasticity index between 7 and 18. Historically, these soils were normally imported from borrow pits located near existing or former river and/or stream channels, however, presently, these soils are often manufactured and imported to the project site. Select fill materials would not be expected on this site.

Select fill materials will need to be imported from an approved off-site source.

In Braun Intertec’s opinion, Method 3 of subgrade modification is the preferred method due to site constraints and the grades surrounding the plaza. Method 1- undercutting and replacement with select fill would result in relatively deep cuts and thicknesses of select fill beneath the structure and thus be very costly. Method 2 could be implemented but is considered impractical again due to the site constraints and grading of the plaza. Braun Intertec recommends using Method 3, as described above, for subgrade modification beneath the slab-on-grade floor system for new concession/restroom building. Method 3 of subgrade modification would also be beneficial in controlling future movements below critical flatwork areas within the plaza as discussed further in Section C.8. Our specific recommendations utilizing Method 3 below the new building are provided in detail within Section C.5 of this report.

Foundations We recommend using straight-sided, drilled shafts socketed into gray, unweathered rock (limestone) to support the new building. The drilled shafts will also be used to resist uplift pressures from the expansive clays. Our recommendations for drilled straight shaft foundation systems are presented in Section C.3 of this report.

As an alternative foundation system to using straight shaft piers, we recommend considering using drilled and underreamed shafts bearing at relative shallow depths (15 to 18 feet below existing grade) on clay soils to support the new building. Our recommendations for drilled and underreamed shaft foundation systems are presented in Section C.4 of this report.

As a final alternative foundation system, the building could possibly be constructed on a stiffened or mat slab foundation system provided subgrade modifications are made below the slab. Recommendations for stiffened or mat slab foundations are provided within Section C.7.

Structural Floor Slab The two most common floor slab systems associated with a pier and grade beam foundation consist of either a suspended structural floor slab system or ground supported floor slab constructed over a modified subgrade. A suspended floor slab structurally connects the floor slab and grade beams directly beneath the floor slab to the drilled shafts and provides separation of the floor slab from the underlying expansive soils by either a formed void system or a crawl space. A suspended floor slab system is not in contact with the underlying expansive clays, therefore, eliminating the effects of post-construction slab movement due to the swelling and shrinking of the underlying soils. The former building on the site was constructed as a slab-on grade system. As such, we have not provided recommendations for a suspended slab system, but we can provide such recommendations if requested.

Slab-on Grade Floor System

An alternative to a structurally suspended floor slab is to support the floor slab systems directly on a modified subgrade. When installing a floor slab on a modified subgrade in expansive clays, the owner must accept the risk of soil-related movement beneath the slab. Subgrade modifications must be performed beneath any floor slab area supported on-grade to reduce the swell potential of properly installed clay fill soils beneath the proposed new building. General discussion regarding proposed subgrade modification below the building was provided above. Additional recommendations for subgrade modifications beneath the slab-on-grade system for the new building are provided in Section C.5.

The recommendations we provide in this report have been prepared to reflect the current site grades known to us and as referenced within this report. If designed and constructed properly, the subgrade modification methods we recommend beneath the new building are intended to reduce the total potential vertical movements to 1-inch or less. The estimated differential movement should be limited to 50 percent or less of the total vertical movement. The resulting soil-related movements are dependent on strict implementation of our recommendations for grading, backfill, and drainage. If our recommendations are not followed, then the risk that greater than predicted movements and the associated distress will be experienced increases significantly.

C.1.c. Existing Fill and Existing Utilities No apparent fill or possible fill was observed within the test boring but may be present within the limits of the proposed building. Undocumented fill materials, whose purpose and method of compaction are unknown, cannot be relied upon for structural support due to the risk of differential strength and compressibility of the fills. The principal risks associated with existing fill materials are settlement of the fill under the proposed loads and the presence of unsuitable materials within the fill. Refer to discussion within Section C.2 and Section C.5 regarding proof rolling any existing fill left in place prior to performing electrochemical injection if this method of subgrade modification is utilized.

It is imperative that any existing underground utilities that are located beneath the new building area be removed and relocated elsewhere. The utility trenches from these existing utilities must be excavated and properly compacted with clayey backfill materials prior to beginning excavation for subgrade improvements or prior to constructing new foundations.

C.1.d. Reuse of On-Site Soils It is our understanding that a portion of the new building will be constructed where the former concession/restroom building was located. After the existing slab and foundations are removed, it is unknown what soil conditions may be encountered. It is possible that some select fill materials were placed below the foundations and slab, but the quality and thickness of such material is unknown. If apparent select fill is encountered, it may be possible that some portions can be reused for the new building provided the material is properly tested and approved for reuse. We recommend for initial budget purposes that all select fill planned below the new building be new select fill. The new select fill must be imported from an approved off-site source and must be tested to ensure compliance with the material specifications.

On-site clayey soils can be used as grade raise fill beneath the building provided they are processed and installed per the requirements for common fill soils as described in Section C.2 and C.5. We do not recommend reusing existing fill that contains debris or organic material as common fill or moisture-conditioned fill.

C.1.e. Groundwater Free water seepage was observed in the test boring at a depth of approximately 20 feet after the boring was completed. We do anticipate subsurface water impacting earthwork operations, however free water should be anticipated during the installation of all deep drilled shafts bearing into limestone based on our experience in this area of McKinney. Free water should not be encountered if drilled and underreamed shafts are used to support the new structure, but timely placement or rebar and pouring concrete is recommended.

During construction, some of the soils will collect water from precipitation or surface runoff. We recommend the contractor remove any water that collects in work areas before performing further work. Groundwater conditions may be different at the time of construction. Groundwater conditions typically vary because of seasonal variations in rainfall, landscape irrigation, site drainage, and runoff.

Groundwater can also be present within fractures in the unweathered rock layer.

C.1.f. Weather To account for potential rainfall during construction, we recommend maintaining construction grades to intercept surface water flow into the area and drain water from the areas to an appropriate collection point. After grading, the contractor should compact the soil surface with a smooth drum roller in an effort to lower infiltration rates. After rain events, the contractor should limit construction traffic until the surface is dry enough that traffic will not mix accumulated surface water into the soil.

C.1.g. Existing Plaza Flatwork As part of our scope of work on this project, we were asked to observe and evaluate the condition of the flatwork surrounding the proposed new concession/restroom building and elsewhere within the plaza between the baseball/softball fields. The plaza flatwork is in generally fair condition with some minor to moderate random cracking and some minor to moderate undulations. Based on the Braun Intertec’s senior engineer’s observations and experience, there are several areas of concern which need to be addressed.

First, the close proximity of existing trees to the former building area and flatwork areas is a concern.

Tree roots can be seen within open planter areas which are extending under the flatwork slab. The tree roots not only draw moisture from beneath the slab causing drying shrinkage movements but also, the roots can physically lift the flatwork slab when they are close to the surface. It is not known whether the planters within the plaza have vertical root barriers installed but all future planters should contain vertical root barriers to keep tree roots from spreading beneath new or remediated flatwork areas.

Second, the types of trees themselves are a concern. One of the trees within the plaza was observed to be a coniferous tree, which has shallow roots and requires a high amount of water to satisfy its needs.

The removal of this type of tree should be strongly considered.

Lastly, there were some open squares within the flatwork which were devoid of plants and concrete.

These open areas are allowing free water to pond in them before the water evaporates. Consideration should be given to covering over these open areas with additional new flatwork.

Within Section C.5 of this report, we provide recommendations for subgrade modifications below the new building slab utilizing electrochemical stabilization to mitigate future movements. The stabilization is extended a minimum 10 feet outside the structure limits. As discussed late in Section C.8, we recommend that additional critical flatwork areas within the plaza section of the sports complex also be treated with electrochemical injection before designing and constructing new planter areas within the flatwork.

C.2. Site Grading and Subgrade Preparation

C.2.a. Site Grading Before proceeding with construction, all vegetation, root systems, and other deleterious, non-soil materials must be stripped from proposed construction areas. Braun recommends that all tree roots greater than 2 inches in diameter be removed from the site and not incorporated into the structural fill soils. Some hand labor may be necessary to adequately remove the tree roots from the soil matrix.

Additionally, organic material must not comprise more than 5 percent of the soil matrix used as structural fill.

Proper subgrade preparation and placement and construction of the grade raise fill materials will be very critical to the performance of building foundations, floor slabs, and new flatwork constructed above or near these soft wet areas and elsewhere on-site. Care should be exercised during the grading operations at the site. The traffic of heavy equipment, including heavy compaction equipment, may create a general deterioration of the shallower, clayey soils. Therefore, it should be anticipated that some construction difficulties could be observed during periods when these soils are saturated and that it may be necessary to improve, remove or simply stay off of the saturated soils.

C.2.b. Excavation Oversizing When removing materials below structures or pavements, we recommend the excavation extend outward and downward at a slope of 1H:1V (horizontal: vertical) or flatter. When using Method 3 for subgrade modification as described in Section C.5, the base of the excavation should extend to only the outside face of the building lines. Further discussion is provided within Section C.5.

C.2.c. Excavated Slopes Based on the borings, we anticipate on-site soils in excavations will consist of fat clay. Table 3 provides OSHA (Occupational Safety and Health Administration) guidelines in reference to soil type.

Table 3. Maximum Allowable Slopes

Slopes constructed in this manner may still exhibit surface sloughing. OSHA requires an engineer to evaluate slopes or excavations over 20 feet in depth. An OSHA-approved qualified person should review the soil classification in the field. Excavations must comply with the requirements of OSHA 29 CFR, Part 1926, Subpart P, “Excavations and Trenches.” This document states excavation safety is the responsibility of the contractor. The project specifications should reference these OSHA requirements.

Soil Classification Soil Type Slopes (H:V)

Fat Clay Type B 1:1

Fat Clay (with seepage) Type C 1 ½:1

C.2.d. Excavation Dewatering We recommend removing any accumulation of free water that may develop within the excavation using sumps and pumps.

C.2.e. Building and Pavement Subgrade Proof Roll After excavating the building pad and other areas to the depths indicated within Section C.5 and before the placement of special fill or flexible base materials, we recommend proof rolling the subgrade soils per TxDOT Item 216 provided the exposed materials are not intact rock. Proof rolling is commonly performed with a partial to fully loaded dump truck, water truck or similar equipment. We also recommend having a geotechnical representative observe the subgrade response during the proof roll.

Areas that fail the proof roll likely indicate soft or weak areas that will require additional soil correction work to support building foundations and slabs as well as pavements.

The contractor should correct areas that display yielding or rutting. Possible options for subgrade correction include moisture conditioning (ripping and drying or wetting) and re-compaction, excavation (undercutting) and replacement with re-compacted soil or crushed aggregate, chemical stabilization, and/or geotextiles. We recommend performing a second proof roll after the aggregate flexible base material is in place, and before constructing the foundations or pavements.

C.2.f. Fill Materials and Compaction Table 4 contains our recommendations for fill materials.

Table 4. Fill Materials*

Locations to Be Used

Fill Classification

Possible Soil Type

Descriptions Gradation Additional Requirements

Below Foundations, floor slabs, utilities

Select fill SC, CL

1. 100% passing 3-inch sieve

2. 60% maximum passing

No. 200 sieve

1. Liquid Limit <35

2. Plasticity Index between 7 and 18

3. < 2% Organic Content (OC)

Common Fill CH, CL 100% passing 3-inch sieve 4. < 2% Organic Content (OC)

Special Fill Cap -- See Table 5 Below Plasticity Index between 2 and 10

Flexible Base -- Meet the Requirements of TxDOT Item 247, Grade 1-2, Type A or D, no wet ball testing required

*Abbreviations are defined in the attached Descriptive Terminology sheets.

Table 5. Special Fill Gradation Requirement

Sieve Size Cumulative Percent Retained (%)

3/8” < 5%

No. 4 15-35

No. 10 25-45

No. 40 40-65

No. 80 50-80

No. 200 >80

All fill soils should be installed in loose lifts approximately eight inches thick. We recommend compacting fill per the criteria presented below in Table 6. The project documents should specify the relative compaction of fill, based on the structure located above the fill, and vertical proximity to that structure.

Table 6. Compaction Recommendations Summary

Reference Recommended Compaction, percent

(ASTM D698 – Standard Proctor) Moisture Content Variance from

Optimum, percentage points Select fill soils 95 plus -2 to +3

Special Fill Soils 95 plus

Top Lift 100+ -2 to +3

Injected Clay Subgrade below building-refer to Section C.6.b

94 to 98 +2 to +5

Common fill, below structures, pavements, and utilities

93 to 98 +2 to +7

We recommend performing density tests in the fill to evaluate if the contractors are effectively compacting the soil and meeting project requirements. Table 7 contains our recommended frequency of testing for various aspects of the project.

Table 7. Fill Testing Frequency

Zone Designation Fill Testing Frequency Minimum Tests per Soil Lift

Building Pad 1 test per every 1,500 square feet 2

Flatwork Areas 1 test every 2,500 square feet 2

Zone Designation Fill Testing Frequency Minimum Tests per Soil Lift

Utility Lines 1 test every 150 linear feet 1 Test per every 1 foot of fill

Grade Beams 1 test every 100-150 linear feet 1 Test per every 6” compacted lift

C.2.g. Inspections of Soils The purpose of soil inspections is to evaluate whether the work is per the recommendations contained in the Geotechnical Evaluation Report for the project. Inspections should include evaluation of the subgrade, observing the preparation of the subgrade (surface compaction or dewatering, excavation oversizing, placement procedures and materials used for fill, etc.), and compaction testing of the fill.

C.2.h. Moisture Density Relations Testing Moisture density relations testing (field densities) should be performed on each lift by the Geotechnical Engineer or his/her qualified representative to document that the proper moisture content and compaction requirements have been achieved. If the compacted materials fail to meet the moisture and density requirements, the lift should be reprocessed as necessary to obtain the required results.

C.2.i. Mixing of Fill Lifts and Benching All fill materials should be placed in level, uniform lifts with each lift properly moisture treated and compacted as recommended above. Each lift should be thoroughly mixed to help insure the uniformity of the layer. Fills should be benched into adjacent slopes as applicable.

C.2.j. Rock Fragments Excavated rock materials or rock fragments to be placed as fill, should be completely broken down, distributed as widely as practical across the site, and placed with no nested voids. Placing soil clods or rock fragments larger than a three-inch diameter increases the risk of nested voids and may lead to an unexpected localized settlement that will likely damage site improvements. Rock fragments larger than three inches in size should be removed from the excavation.

C.3. Straight Drilled Shafts

C.3.a. Design Parameters for Drilled Shaft Foundations The bearing stratum at this site is gray, unweathered rock (limestone) which was observed at approximately 40 feet depth below the existing grade within the area of the proposed building. We recommend the straight, drilled shafts (also known as drilled piers or caissons) be designed to have at least two feet of penetration into the intact, gray rock (or below any temporary casing, whichever is deeper) to achieve the allowable end bearing and skin friction values. We also recommend allowable skin friction only be considered for that portion of the shaft embedded more than two feet in the intact, gray rock and below any temporary casing, if required. However, variations in the rock surface should be anticipated. The final depth of penetration will be determined by a representative of the geotechnical engineer in the field. Due to the difficulty in observing and confirming the cleanliness of the shaft excavations prior to concrete placement, we recommend that the minimum shaft diameter be at least

24 inches for piers extending below a depth of 30 feet. The minimum diameter shaft is recommended to be at least 30 inches for drilled shafts extending beyond 50 feet in depth. Table 8 below contains our recommended design parameters for the straight, drilled shafts.

Table 8. Recommended Drilled Shaft Design Parameters

Bearing Stratum Approximate Depth Range*

Allowable End Bearing Resistance

Allowable Skin Friction -

Compression Allowable Skin

Friction – Tension

Gray Rock (Limestone)

40 feet or deeper 50,000 psf 7,500 psf 6,000 psf

Note: *See individual boring logs for depth to limestone below existing grade.

Settlement of a properly constructed drilled shaft founded in gray rock is expected to occur as the drilled shaft is loaded. Total and differential settlements are estimated to be less than 1/4-inch.

C.3.b. Group Effects for Axial Loads To develop allowable bearing resistance given in Table 8, we recommend that adjacent shafts maintain a minimum center-to-center spacing of three times the diameter of the larger shaft. Closer spacing will require reductions in the skin friction values presented above, and possibly special installation sequences.

Groups of three or more shafts, or groups of shafts with uplift loads, should be evaluated on a case-by-case basis by this office. Alternative installation sequences should be implemented during group shaft installation to allow for a minimum of 48 hours of curing time for concreted shafts, before installation of adjacent shafts.

C.3.c. Drilled Shaft Support Based on our experience in this portion of McKinney, we anticipate that all drilled shafts will require temporary casing to prevent the infiltration of groundwater and maintain the integrity of the shaft excavation. Project planning and budgeting should anticipate the need for casing for 100 percent of the piers.

C.3.d. Adhesion Uplift Based on the structural loading conditions and the expansive soil conditions encountered at this site, the drilled shafts must be designed to accommodate uplift forces. Swelling clay soils in contact with the shaft perimeter will cause such uplift pressures to develop in upward skin friction. Consideration should be given to potential uplift forces generated through soil-to-shaft adhesion of expansive clay soils within the active zone. Although these conditions may vary with location and soil conditions at the time of placement, it may be assumed for design purposes that the active zone extends to 12 feet below the final ground surface. If the subgrade modification method described in Section C.6 of this report are completed beneath the new building area, then an uplift pressure of 750 pounds per square foot may be applied in the design of those drilled shaft acting over a depth of 12 feet.

Care must be taken to prevent desiccation of the soils. If the area will be left open for greater than 48 hours, the moisture conditioned pad or electrochemically injected pad should be protected with special fill material of at least 2 feet in thickness. Uplift resistance for wind loads will be provided by side friction developed within the rock and the deadweight of the drilled shaft element.

C.3.e. Lateral Loading Considerations Our recommended lateral load design parameters for use in the L-Pile computer program are provided in Tables 9 and 10. Table 9 presents design values for the soil and weathered rock (limestone) materials observed in the upper 0 to 40 feet. Table 10 presents design values for the gray unweathered rock (limestone). Due to possible soil shrinkage, the upper five feet should not be considered for lateral loading conditions in shaft design.

Table 9. Recommended L-Pile Soil Design Parameters

Stratum Soil Type

Depth Range

(ft.) p-y Model

Effective Unit

Weight (pcf)

Undrained Shear

Strength (ksf)

Strain Factor ε50

Friction Angle

(degrees) ks value

(pci)

Natural Fat Clay (CH) 0-5 Neglect 125 Neglect Neglect Neglect Neglect

1 and 2

Fat Clay (CH) and weathered Rock

5 - 40 Stiff clay w/out free water

115 2 0.005 0 1,000

Table 10. Recommended L-Pile Rock Design Parameters

Stratum Type Depth Range

(ft)

Unit Weight

(pcf)

Uniaxial Compressive

Strength (psi)

Young’s Modulus, Er (psi)

Rock Quality

Designation, RQD, (%)

Strain Factor, krm

Unweathered Rock

(Limestone) – Weak Rock

(Reese)

Below 40 140 2,500 100,000 70 0.0004

The program models the shaft behavior using a finite difference method and determines the non-linear response of the soil using various soil resistance-pile deflection (p-y) criteria. The program accommodates the analysis of various shaft types subjected to axial load, lateral load, and bending moments. Braun Intertec recommends the designers size the drilled shafts and select appropriate reinforcing steel to resist the anticipated forces.

C.3.f. Grade Beams and Pier Caps Any pier caps constructed over expansive clays should be constructed over the appropriate specified void space depending on whether or not subgrade modification is performed. Grade beams constructed over the clays modified as outlined in Section C.5 should be formed over a void height of at least six inches where the required soil preparation has been completed to reduce the potential vertical rise movement to 1 inch or less beneath the structure. The recommended void is typically formed on a rigid cardboard form placed beneath the grade beam concrete. Pre-fit void forms must be installed at the drilled shafts. The pre-fit forms must conform to the actual installed drilled shaft diameter (for both cased and uncased shafts) such that a tight fit results between the void form and pier surface preventing concrete from migrating between the void form and shaft during concrete placement.

Rigid soil retainers must be installed along the outside faces of the grade beam and void form after the concrete forms are removed to protect the void forms and maintain the void height during backfill placement. The soil retainers must be of sufficient rigidity to resist bowing or deflection during placement and compaction of the grade beam backfill. It is recommended that trapezoidal void boxes not be installed on this project. We also recommend that provisions be made for observing and confirming the integrity of the void system before installing the soil retainers and backfill placement.

The composition of the grade beam backfill required for the project is dependent upon the location of the grade beam and the type of slab system selected for installation. All exterior faces of perimeter grade beams must be backfilled with clay soils the PI of which must be between 25 and 60 shortly after removing the concrete forms and placement of the rigid retainer panels. In those areas of the site where the subgrade modifications described in Section C.5 are applied, the backfill of the interior grade beams and interior faces of exterior grade beams must consist of chemically injected clay soils and select/special fill or flex base materials meeting the requirements specified in Section C.2 and C.5.

The composition of the backfill material for the interior grade beams or the interior face of exterior grade beams for those conditions described in Section C.5 must be similar to the subgrade modifications beneath the slab on grade in thickness, location, and required compaction. We recommend that any perimeter grade beam extend at least 6 inches below the bottom of the special fill or select fill to provide additional protection against lateral migration of surface water from the building exterior into the special fill or select fill once construction is complete. All grade beam backfill materials must be compacted to the moisture and compaction criteria presented in Sections C.2 and C.5 to reduce the potential for water to enter the void space during or after construction and induce additional swelling of the underlying soils. Any rain or surface water, which accumulates within the grade beam excavations, must not be allowed to pond under or around the grade beams and must be removed as soon as possible by pumping or other methods.

The grade beams should be formed rather than cast against earth trenches. Backfill against the exterior face of grade beams should be properly compacted on-site clays. Compaction and moisture should be in accordance with Tables 4 through 7 for chemically injected on-site soils.

C.3.g. Concrete Placement Prior to placing concrete in drilled shaft excavations, we recommend the use of a cleanout bucket to remove any soft sediments, disturbed soil, or debris from the bottom of the excavation. Proper equipment and procedures for providing a clean base should be utilized during construction; otherwise, end bearing should be neglected.

Concrete should be placed with a bottom discharge bucket, flexible drop chute, elephant trunk hopper, or tremie.