4-131-23-203 Geotechnical Report.pdf

GEOTECHNICAL ENGINEERING STUDY

ERWIN PARK IMPROVEMENTS

MCKINNEY, TEXAS

Presented To:

Teague Nall and Perkins, Inc.

October 2023

PROJECT NO. 131-23-203

TABLE OF CONTENTS

Page

1.0 INTRODUCTION ------------------------------------------------------------------------------------------------------- 1

2.0 FIELD EXPLORATION AND LABORATORY TESTING ------------------------------------------------------ 2

3.0 SUBSURFACE CONDITIONS -------------------------------------------------------------------------------------- 3

4.0 FOUNDATION RECOMMENDATIONS --------------------------------------------------------------------------- 5

5.0 EXPANSIVE SOIL CONSIDERATIONS ------------------------------------------------------------------------- 11

6.0 EARTHWORK ---------------------------------------------------------------------------------------------------------- 13

7.0 PAVEMENTS ----------------------------------------------------------------------------------------------------------- 17

8.0 CONSTRUCTION OBSERVATIONS ----------------------------------------------------------------------------- 21

9.0 REPORT CLOSURE ------------------------------------------------------------------------------------------------- 21

APPENDIX A

Plate

Plan of Borings --------------------------------------------------------------------------------------------------------------- A.1 Unified Soil Classification System --------------------------------------------------------------------------------------- A.2 Key to Classification and Symbols -------------------------------------------------------------------------------------- A.3 Logs of Borings ------------------------------------------------------------------------------------------------------ A.4 – A.9 Particle Size Distribution Reports ----------------------------------------------------------------------------- A.10 – A.13 Free Swell Test Results -------------------------------------------------------------------------------------------------- A.14

Report No. 131-23-203 CMJ ENGINEERING, INC.

1.0 INTRODUCTION

1.1 Project Description

The project site is located at the existing Erwin Park at 4300 County Road 1006 in McKinney, Texas.

The project, as currently planned, will consist of improvements to include new concrete parking lots, a gateway entry feature, and prefabricated pavilions/restrooms. Plate A.1, Plan of Borings, presents the project vicinity and approximate locations of the exploration borings.

1.2 Purpose and Scope

The purpose of this geotechnical engineering study has been to determine subsurface conditions, evaluate the engineering characteristics of the subsurface materials encountered, develop recommendations for the type or types of foundations, and provide earthwork recommendations.

To accomplish its intended purposes, the study has been conducted in the following phases: (1) drilling sample borings to determine the general subsurface conditions and to obtain samples for testing; (2) performing laboratory tests on appropriate samples to determine pertinent engineering properties of the subsurface materials; and (3) performing engineering analyses, using the field and laboratory data to develop geotechnical recommendations for the proposed construction.

The design is currently in progress and the locations and/or elevations of the structures could change. Once the final design is near completion (80- to 90-percent stage), it is recommended that

CMJ Engineering, Inc. be retained to review those portions of the construction documents pertaining to the geotechnical recommendations, as a means to determine that our recommendations have been interpreted as intended.

1.3 Report Format

The text of the report is contained in Sections 1 through 9. All plates and large tables are contained in Appendix A. The alpha-numeric plate and table numbers identify the appendix in which they appear. Small tables of less than one page in length may appear in the body of the text and are numbered according to the section in which they occur.

Units used in the report are based on the English system and may include tons per square foot (tsf), kips (1 kip = 1,000 pounds), kips per square foot (ksf), pounds per square foot (psf), pounds per cubic foot (pcf), and pounds per square inch (psi).

2.0 FIELD EXPLORATION AND LABORATORY TESTING

2.1 Field Exploration

Subsurface materials at the project site were explored by six (6) vertical soil borings drilled to a depth of 20 feet. The borings were drilled using continuous flight augers at the approximate locations shown on the Plan of Borings, Plate A.1. The boring logs are included on Plates A.4 through A.9 and keys to classifications and symbols used on the logs are provided on Plates A.2 and A.3.

Undisturbed samples of cohesive soils were obtained with nominal 3-inch diameter thin-walled

(Shelby) tube samplers at the locations shown on the logs of borings. The Shelby tube sampler consists of a thin-walled steel tube with a sharp cutting edge connected to a head equipped with a ball valve threaded for rod connection. The tube is pushed into the soil by the hydraulic pulldown of the drilling rig. The soil specimens were extruded from the tube in the field, logged, tested for consistency with a hand penetrometer, sealed, and packaged to limit the loss of moisture.

The consistency of cohesive soil samples was evaluated in the field using a calibrated hand penetrometer. In this test, a 0.25-inch diameter piston is pushed into the relatively undisturbed sample at a constant rate to a depth of 0.25 inch. The results of these tests, in tsf, are tabulated at respective sample depths on the logs. When the capacity of the penetrometer is exceeded, the value is tabulated as 4.5+.

To evaluate the relative density and consistency of the harder formations, a modified version of the

Texas Cone Penetration test was performed at selected locations. Texas Department of

Transportation (TxDOT) Test Method Tex-132-E specifies driving a 3-inch diameter cone with a 170-pound hammer freely falling 24 inches. This results in 340 foot-pounds of energy for each blow.

This method was modified by utilizing a 140-pound hammer freely falling 30 inches. This results in

350 foot-pounds of energy for each hammer blow. In relatively soft materials, the penetrometer cone is driven 1 foot and the number of blows required for each 6-inch penetration is tabulated at respective test depths, as blows per 6 inches on the log. In hard materials (rock or rock-like), the penetrometer cone is driven with the resulting penetrations, in inches, recorded for the first and second 50 blows, a total of 100 blows. The penetration for the total 100 blows is recorded at the respective testing depths on the boring logs.

2.2 Laboratory Testing

Laboratory soil tests were performed on selected representative samples recovered from the borings. In addition to the classification tests (liquid limits, plastic limits, and particle size analyses), moisture content, unconfined compressive strength, and unit weight tests were performed. Results of the laboratory classification tests, moisture content, unconfined compressive strength, and unit weight tests conducted for this project are included on the boring logs. Results of the particle size analyses are presented on Plates A.10 through A.13.

Swell tests were performed on specimens from selected samples of the clays. These tests were performed to help in evaluating the swell potential of near-surface soils in the area of the proposed structures. The results of the swell tests are presented on Plate A.14.

The above laboratory tests were performed in general accordance with applicable ASTM procedures, or generally accepted practice.

3.0 SUBSURFACE CONDITIONS

3.1 Soil Conditions

Specific types and depths of subsurface strata encountered at the boring locations are shown on the boring logs in Appendix A. The generalized subsurface stratigraphies encountered in the borings are discussed below. Note that depths on the borings refer to the depth from the existing grade or ground surface present at the time of the investigation, and the boundaries between the various soil types are approximate.

Natural soils encountered consist of dark brown, brown, light brown, and gray silty clays, clays, and shaly clays. The various natural soils contain iron stains, calcareous seams, calcareous deposits, limestone fragments, and occasionally contain ironstone nodules, calcareous nodules, and pebbles.

The various soils encountered in the borings had tested Liquid Limits (LL) varying from 42 to 81 with

Plasticity Indices (PI) varying from 25 to 55 and are classified as CL and CH by the Unified Soil

Classification System (USCS). The various clayey soils were generally very stiff to hard in consistency (soil basis) with pocket penetrometer readings of 3.0 to over 4.5 tsf. Tested unit weight values ranged from 85 to 108 pcf and tested unconfined compressive strengths were 6,030 to 15,060 psf.

Tan limestone is next encountered beneath the overburden clays in Borings B-2 through B-5 at depths of 1 to 7 feet. The tan limestone is moderately hard (rock basis), with Texas Cone Penetration

(THD) test values of 2½ to 4⅜ inches of penetration per 100 blows.

Gray limestone is next encountered in Borings B-1 through B-4 and B-6 at depths of 6 to 14 feet and extends through boring termination at a depth of 20 feet. The gray limestone occasionally contains shale seams and is considered hard (rock basis), with Texas Cone Penetrometer (THD) test values of 1¼ to 2 inches of penetration per 100 blows.

The Atterberg Limits tests indicate the various clayey soils encountered at this site are active to highly active with respect to moisture-induced volume changes. Active clays can experience volume changes (expansion or contraction) with fluctuations in their moisture content. Results of select free swell tests indicate a very high potential for moisture-induced volume change from present, in-situ moisture conditions.

3.2 Groundwater Observations

The borings were drilled using continuous flight augers in order to observe groundwater seepage during drilling. Groundwater seepage was not encountered during drilling and the borings were dry at completion.

Fluctuations of the groundwater level can occur due to seasonal variations in the amount of rainfall;

site topography and runoff; hydraulic conductivity of soil strata; and other factors not evident at the time the borings were performed. During wet periods of the year, seepage can occur through joints in the clays, within or atop the tan limestone, or atop the gray limestone, particularly during periods of heavy or extended rainfall. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

4.0 FOUNDATION RECOMMENDATIONS

4.1 General Foundation Considerations

Two independent design criteria must be satisfied in the selection of the type of foundation to support the proposed structures. First, the ultimate bearing capacity, reduced by a sufficient factor of safety, must not be exceeded by the bearing pressure transferred to the foundation soils. Second, due to consolidation or expansion of the underlying soils during the operating life of the structure, total and differential vertical movements must be within tolerable limits. The recommended foundation alternative for the proposed structure is discussed below.

The moisture-induced volume changes associated with the active to highly active clays present at this site indicate that shallow or near surface footings could be subject to differential movements of a potentially detrimental magnitude. The most positive foundation system for the proposed structure would be situated below the zone of most significant seasonal moisture variations. A deep foundation system transferring loads to a suitable bearing stratum is considered the most positive foundation system.

However, if differential movements can be tolerated, consideration can be given to the use of a monolithic slab-on-grade. The key to success of slab-on-grade construction is proper design/construction, and providing the most optimum conditions for reduced slab movements.

Providing excellent drainage away from the structure, preventing ponding of water aside the slab, preventing excess drying of soils, and using onsite soil backfill to prevent water intrusion into utility line backfill will enhance slab performance. Recommendations for these foundation systems are presented below.

4.2 Potential Vertical Movements

The clay soils encountered at the site are highly active. Analyses indicate that the potential vertical movements of onsite soils due to their expansive characteristics may be on the order of 2 to 4 inches for slab-on-grade elements placed near present site grades. The greatest movements will occur where the greater thicknesses of dryer, more highly plastic clays are present. The actual amount of movement will depend greatly on the moisture content of the soils prior to construction. In other words, where a ground-supported floor slab is placed upon moist soils, the future expansive soil movement of these soils will be limited since these soils exist in a pre-swelled state, and additional moisture will not cause significant additional heaving of the soils. Conversely, when on-site soils are extremely dry, moisture will cause significant swelling of these soils.

4.3 Stiffened, Monolithic Slab-On-Grade – Maintenance Building, Restrooms, and Pavilions

4.3.1 General Considerations

A stiffened, monolithically placed slab-on-grade foundation, either rebar or post-tensioned, used at this site must be designed with exterior and interior grade beams to provide sufficient rigidity to tolerate the differential soil movements. These differential movements typically will occur between the periphery and interior of the slab-on-grade system. Foundation movements are anticipated to occur primarily due to post-construction heave of the underlying soils but also can occur due to shrinkage of the clays around the perimeter of the slab. It is recommended that all fill soils be properly placed and compacted in accordance with this section and Report Section 6.0 prior to foundation installation.

Reduction in potential soil movements can be achieved by methods developed in this area. A more commonly used method consists of moisture conditioning the soils and placing a 1-foot select fill cap. Excavation of tan limestone is not necessary in order to achieve the recommended depth of moisture condition. Inclusion of a horizontal moisture barrier from the foundation out for a distance of 5 feet also will greatly restrict moisture mitigation and differential moisture change below the slab.

Moisture conditioning and placement of a horizontal poly barrier as described above is required in order to use the slab design parameters presented below. The use of these methods will not eliminate the risk of unacceptable movements. Moisture conditioning is recommended to be achieved by mechanically reworking the clays as discussed below.

Consideration should be given to extending the moisture conditioning process beyond the building line to include entrances, sidewalks, flatwork, or any other on-grade areas or elements sensitive to movement. Outside the building, a poly barrier capped with a minimum 6 inches of select fill is recommended. The poly barrier should extend a minimum of 5 feet away from the foundation edge and should slope down slightly to shed excess moisture away from the structure. The use of these methods will not eliminate the risk of unacceptable movements.

Slab-on-grade construction should only be considered if slab movement can be tolerated. The owner must fully understand that if the floor slab is placed on-grade, some movement and resultant cracking within the floor and interior wall partitions may occur. This upward slab movement and cracking usually is difficult and costly to repair and may require continued maintenance expense.

Soil treatments presented in this section are referenced as an alternative to the use of a pier and structurally suspended grade beam and floor slab. The owner must fully understand that if the floor slab is placed on-grade, some movement and resultant cracking within the floor and interior wall partitions may occur. This upward slab movement and cracking usually is difficult and costly to repair and may require continued maintenance expense.

4.3.2 Design Parameters

The foundation should be designed by a structural engineer familiar with stiffened slabs-on-grade subject to differential movement. Design parameters are presented below for PVR and differential swell using the Post-Tensioning Institute’s (PTI) slab-on-grade design method, 3rd Edition.

With Moisture- Conditioned Pad(1)

Design Potential Vertical Rise Edge Moisture Variation -

1 inch(1)

Approximate Center Lift: 7.2 feet(1) Approximate Edge Lift: 3.8 feet(1)

Differential Swell -

Approximate Center Lift: 0.7 inch(1) Approximate Edge Lift: 1.2 inches(1)

(1) Valid only after 5 feet of moisture conditioning with installation of 1-foot select fill cap

It should be recognized that a post-tensioned or conventionally reinforced slab-on-grade foundation system placed at this site will be subject to differential movements as indicated above. If slab stiffness is not sufficient to resist the ground movements, these movements can cause cracking of interior sheet rock walls and exterior brick walls. Poor drainage, water leaks, free water sources, long-term percolation in recessed planter areas and/or trees can result in greater differential movements. For example, should leaks develop in underground water or sewer lines or the grades around the structures are changed and cause ponding of water, unacceptable slab movements could develop. Again, a greater risk of unsatisfactory foundation performance exists with a slab-on-grade design than for a drilled shaft design.

Beams may be designed based on an allowable soil bearing pressure of 1,800 pounds per square foot or less within the shallow soils. The beams should extend at least 12 inches into natural soils or compacted and tested fill. The beam depth is given in regard to bearing capacity and is not intended to be a structural recommendation.

A properly engineered and constructed vapor barrier should be provided beneath the slab-on-grade.

The key to the success of this foundation is proper design/construction, and providing control of the below-slab water. Providing excellent drainage away from the structure, preventing ponding water aside the slab, and using relatively impermeable backfill to prevent water intrusion via utility line backfill enhance the slab performance.

4.3.3 Mechanical Reworking of Near-Surface Clays with 2’ Select Fill Cap

In general, the procedure is performed as follows:

1. Remove all existing surface vegetation, trees and associated root mats, organic topsoil and any other deleterious material.

2. Excavate surficial clays to a uniform elevation a minimum of 5.5 feet below finished grade or to the top of tan limestone, whichever occurs first. Observation of complete clay removal should be conducted by the geotechnical engineer or their designated representative. Excavation of intact tan limestone is not necessary in order to achieve the recommended depth of moisture conditioning. Scarify the exposed clay subgrade, if present, at the base of the excavation, to a depth of 8 inches, adjust the moisture, and compact at a minimum of 4 percentage points above optimum moisture to between 93 and 98 percent of Standard Proctor density (ASTM D 698).

Over-compaction should not be allowed.

3. Fill pad to 1 foot below final grade using site excavated or similar clay soils with no rock fragments greater than 4 inches in maximum dimension. Compact in maximum 9-inch loose lifts at a minimum of 4 percentage points above optimum moisture to between 93 and 98 percent of Standard Proctor density (ASTM D 698). Field density tests should be taken as each lift of fill material is placed. Each lift should be compacted, tested, and documented prior to subsequent lift placement. Over-compaction should not be allowed.

4. Complete pad fill using a minimum of 1 foot of sandy clay/clayey sand, non-expansive select fill with a Liquid Limit less than 35 and a Plasticity Index (PI) between 5 and 16. The select fill should be compacted in maximum 9-inch loose lifts at -2 to +3 percentage points of the soil’s optimum moisture content at a minimum of 95 percent of Standard Proctor density (ASTM D 698). The select fill should be placed within 48 hours of completing the installation of the moisture conditioned soils.

The above earthwork operations should be continuously observed and tested by an experienced geotechnician working in conjunction with the project geotechnical engineer.

4.4 Straight Drilled Shafts – Gateway Entry Feature (Area of Boring B-1 only)

4.4.1 Design Parameters

Recommendations and parameters for the design of cast-in-place straight shafts are outlined below.

Specific recommendations for the construction and installation of the drilled shafts are included in the following section and shall be followed during construction.

Bearing Stratum Gray LIMESTONE

Depth of Pier Bearing Stratum: 8 feet below existing grades

Required Shaft Depth: All piers should penetrate into the bearing strata a minimum of 2 feet. Deeper penetrations may be necessary to develop the required load carrying capacity.

Allowable End Bearing Capacity: 40,000 psf

Allowable Skin Friction: Applicable below a minimum penetration of 2 feet into the gray limestone; 6,000 psf for compressive loads and 4,000 psf for tensile loads.

The above values contain a safety factor of three (3). Penetrations greater than the minimum penetration may be required to develop additional skin friction and/or uplift resistance. Settlement of properly constructed shafts should be primarily elastic and are estimated to be less than 1 inch.

In order to develop full load carrying capacity in end bearing, adjacent shafts should have a minimum center-to-center spacing of 2.5 times the diameter of the larger shaft. Closer spacing may require some reductions in skin friction and/or changes in installation sequences. Closely spaced shafts should be examined on a case-by-case basis. As a general guide, the design end bearing will vary linearly from the full value at a spacing of 2.5 diameters to 50 percent of the design value at 1 diameter.

Drilled shaft design parameters for use with Lpile based on our laboratory test results are presented in Table 4.4.1-1 together with our recommended design stratigraphy. The design depth interval is referenced from present existing grades. For the limestone, the “Strong Rock” model is suitable for use with Lpile.

TABLE 4.4.1 –1 - RECOMMENDED LATERAL LOAD DESIGN VALUES

Soil Type

Depth

Interval

Design Total Unit Weight

(pcf) Design Strength

Design k-value (pci)

Gray Limestone

8’+ 140 Uniaxial Compressive

Strength (psi) 0.0005 E=1X106 psi 1,500

4.4.2 Soil Induced Uplift Loads

The drilled shafts could experience tensile loads as a result of post construction heave in the site soils. The magnitude of these loads varies with the shaft diameter, soil parameters, and particularly the in-situ moisture levels at the time of construction. In order to aid in the structural design of the reinforcement, the reinforcement quantity should be adequate to resist tensile forces based on soil adhesion equal to 1,800 psf acting over the upper 8 feet of the pier shaft. This load must be resisted by the dead load on the shaft, continuous vertical reinforcing steel in the shaft, and a shaft adhesion developed within the bearing strata as previously discussed. In order to aid in the structural design of the reinforcement, minimum reinforcing should be equal to 0.5 percent of the shaft area.

4.4.3 Drilled Shaft Construction Considerations

Drilled pier construction should be monitored by a representative of the geotechnical engineer to observe, among other things, the following items:

Identification of bearing material

Adequate penetration of the shaft excavation into the bearing layer

The base and sides of the shaft excavation are clean of loose cuttings

If seepage is encountered, whether it is of sufficient amount to require the use of temporary steel casing. If casing is needed it is important that the field representative observe that a high head of plastic concrete is maintained within the casing at all times during their extraction to prevent the inflow of water

Precautions should be taken during the placement of reinforcing steel and concrete to prevent loose, excavated soil from falling into the excavation. Concrete should be placed as soon as practical after completion of the drilling, cleaning, and observation. Excavation for a drilled pier should be filled with concrete before the end of the workday, or sooner if required to prevent deterioration of the bearing material. Prolonged exposure or inundation of the bearing surface with water will result in changes in strength and compressibility characteristics. If delays occur, the drilled pier excavation should be deepened as necessary and cleaned, in order to provide a fresh bearing surface.

Excavations for the shafts should be maintained in the dry. The concrete should have a slump of 6 inches plus or minus 1 inch. The concrete should be placed in a manner to prevent the concrete from striking the reinforcing cage or the sides of the excavation. Concrete should be tremied to the bottom of the excavation to control the maximum free fall of the plastic concrete to less than 10 feet, or focus concrete in the middle of the reinforcing cage to prevent segregation.

A drilling rig of sufficient size and weight will be necessary for drilling and/or coring through the hard layers to reach the desired bearing stratum and achieve the required penetration. It should be anticipated that hard to very hard zones can be present in the tan limestone overlying the gray limestone. The hard to very hard layers can complicate pier drilling operations.

In addition to the above guidelines, the specifications from the Association of Drilled Shaft

Contractors Inc. "Standards and Specifications for the Foundation Drilling Industry" as Revised 1999 or other recognized specifications for proper installation of drilled shaft foundation systems should be followed.

5.0 EXPANSIVE SOIL CONSIDERATIONS

5.1 Site Drainage

An important feature of the project is to provide positive drainage away from the proposed structures.

If water is permitted to stand next to or below the structure, excessive soil movements (heave) can occur. This could result in differential floor slab or foundation movement.

A well-designed site drainage plan is of utmost importance and surface drainage should be provided during construction and maintained throughout the life of the structures. Consideration should be given to the design and location of gutter downspouts, planting areas, or other features which would produce moisture concentration adjacent to or beneath the structure or paving. Consideration should be given to the use of self-contained, watertight planters. Joints next to the structures should be sealed with a flexible joint sealer to prevent infiltration of surface water. Proper maintenance should include periodic inspection for open joints and cracks and resealing as necessary.

Rainwater collected by the gutter system should be transported by pipe to a storm drain or to a paved area. If downspouts discharge next to the structures onto flatwork or paved areas, the area should be watertight in order to eliminate infiltration next to the structures.

5.2 Additional Design Considerations

The following information has been assimilated after examination of numerous projects constructed in active soils throughout the area. It is presented here for your convenience. If these features are incorporated in the overall design of the project, the performance of the structures should be improved.

Special consideration should be given to completion items outside the building area, such as stairs, sidewalks, signs, etc. They should be adequately designed to sustain the potential vertical movements mentioned in the report.

Roof drainage should be collected by a system of gutters and downspouts and transmitted away from the structures where the water can drain away without entering the building subgrade.

Sidewalks should not be structurally connected to the structure. They should be sloped away from the building so that water will drain away from the structures.

The paving and the general ground surface should be sloped away from the building on all sides so that water will always drain away from the structures. Water should not be allowed to pond near the buildings after the slab has been placed.

Trees and deep rooted shrubs should not be used as landscaping around the structure perimeter as the root systems can lead to desiccation of the subgrade soils. Any trees should be planted at a distance from the building such that the building will not fall within the drip line of the mature plants (usually one to one-and-one-half times the mature height of the tree). If existing tree removal is not an acceptable option, a vertical root barrier, extending to a minimum depth of 4 feet, should be constructed around the perimeter of the foundation in proximity to the area described above.

Every attempt should be made to limit the extreme wetting or drying of the subsurface soils since swelling and shrinkage will result. Standard construction practices of providing good surface water drainage should be used. A positive slope of the ground away from the foundation should be provided to carry off the run-off water both during and after construction.

Backfill for utility lines or along the perimeter beams should consist of on-site material so that they will be stable. If the backfill is too dense or too dry, swelling may form a mound along the ditch line. If the backfill is too loose or too wet, settlement may form a sink along the ditch line. Either case is undesirable since several inches of movement is possible and floor cracks are likely to result. The soils should be processed using the previously discussed compaction criteria.

6.0 EARTHWORK

6.1 Site Preparation

The subgrade should be firm and able to support the construction equipment without displacement.

The subgrade should be proof rolled to detect soft spots, which if exist, should be excavated to provide a firm and otherwise suitable subgrade. Proof rolling should be performed using a heavy pneumatic tired roller, loaded dump truck, or similar piece of equipment, minimum 25 tons. The proof rolling operations should be observed by the project geotechnical engineer or his/her representative, with particular attention given to areas of existing fill.

Prior to fill placement, the subgrade should be scarified to a minimum depth of 6 inches, its moisture content adjusted, and recompacted to the moisture and density recommended for fill.

6.2 Placement and Compaction

Fill material should be placed in loose lifts not exceeding 8 inches in uncompacted thickness. The uncompacted lift thickness should be reduced to 4 inches for structure backfill zones requiring hand-operated power compactors or small self-propelled compactors. The fill material should be uniform with respect to material type and moisture content. Clods and chunks of material should be broken down and the fill material mixed by disking, blading or plowing, as necessary, so that a material of uniform moisture and density is obtained for each lift. Water required for sprinkling to bring the fill material to the proper moisture content should be applied evenly through each layer.

The on-site soils are suitable for use in general site grading. Imported fill material should be clean soil with a Liquid Limit less than 60 and no rock greater than 4 inches in maximum dimension. The fill materials should be free of vegetation and debris.

The fill material should be compacted to a minimum of 95 percent of the maximum dry density determined by the Standard Proctor test, ASTM D698. In conjunction with the compacting operation, the fill material should be brought to the proper moisture content. The moisture content for general earth fill should range from 2 percentage points below optimum to 5 percentage points above optimum (-2 to +5). These ranges of moisture contents are given as maximum recommended ranges. For some soils and under some conditions, the contractor may have to maintain a more narrow range of moisture content (within the recommended range) in order to consistently achieve the recommended density.

Field density tests should be taken as each lift of fill material is placed. As a guide, one field density test per lift for each 5,000 square feet of compacted area is recommended. For small areas or critical areas the frequency of testing may need to be increased to one test per 2,500 square feet. A minimum of 2 tests per lift should be required. The earthwork operations should be observed and tested on a continuing basis by an experienced geotechnician working in conjunction with the project geotechnical engineer.

Each lift should be compacted, tested, and approved before another lift is added. The purpose of the field density tests is to provide some indication that uniform and adequate compaction is being obtained. The actual quality of the fill, as compacted, should be the responsibility of the contractor and satisfactory results from the tests should not be considered as a guarantee of the quality of the contractor’s filling operations.

If fill is to be placed on existing slopes that are steeper than five horizontal to one vertical, then the fill materials should be benched into the existing slopes in such a manner as to provide a good contact between the two materials and allow relatively horizontal lift placement.

Permanent slopes at the site should be as flat as practical to reduce creep and occurrence of shallow slides. The following slope angles are recommended as maximums.

TABLE 6.2-1 – RECOMMENDED PERMANENT SLOPE ANGLES

Height (ft.) Horizontal to Vertical

0 – 3 1:1

3 – 6 2:1

6 – 9 3:1

> 9 4:1

The above angles refer to the total height of a slope. Site improvement should be maintained away from the top of the slope to reduce the possibility of damage due to creep or shallow slides.

6.3 Trench Backfill

Trench backfill for pipelines or other utilities should be properly placed and compacted. Overly dense or dry backfill can swell and create a mound along the completed trench line. Loose or wet backfill can settle and form a depression along the completed trench line. Distress to overlying structures, pavements, etc. is likely if heaving or settlement occurs. On-site soil fill material is recommended for trench backfill. Care should be taken not to use free-draining granular material, to prevent the backfilled trench from becoming a french drain and piping surface or subsurface water beneath structures, pipelines, or pavements. If a higher class bedding material is required for the pipelines, a lean concrete bedding will limit water intrusion into the trench and will not require compaction after placement. The soil backfill should be placed in approximately 4- to 6-inch loose lifts. The density and moisture content should be as recommended for fill in Section 6.2, Placement and Compaction, of this report. A minimum of one field density test should be taken per lift for every 150 linear feet of trench, with a minimum of 2 tests.

6.4 Excavation

Based on the exploration borings, excavations may encounter limestone in major intact units. This limestone is generally moderately hard to hard and will require heavy duty specialized equipment for excavation. In addition, overexcavation should be anticipated within the limestones. Overexcavation may result from large blocks or chunks breaking along either weathered or clay seams beyond the planned excavation.

Seasonal water seeps can occur where the limestones are approached or exposed by cuts. Subsoil drains may be required in some areas to intercept this seepage. This can be evaluated after grading has been performed.

The side slopes of excavations through the overburden soils should be made in such a manner to provide for their stability during construction. Existing structures, pipelines or other facilities, which are constructed prior to or during the currently proposed construction and which require excavation, should be protected from loss of end bearing or lateral support.

Temporary construction slopes and/or permanent embankment slopes should be protected from surface runoff water. Site grading should be designed to allow drainage at planned areas where erosion protection is provided, instead of allowing surface water to flow down unprotected slopes.

Trench safety recommendations are beyond the scope of this report. The contractor must comply with all applicable safety regulations concerning trench safety and excavations including, but not limited to, OSHA regulations.

6.5 Acceptance of Imported Fill

Any soil imported from off-site sources should be tested for compliance with the recommendations for the particular application and approved by the project geotechnical engineer prior to the materials being used. The owner should also require the contractor to obtain a written, notarized certification from the landowner of each proposed off-site soil borrow source stating that to the best of the landowner's knowledge and belief there has never been contamination of the borrow source site with hazardous or toxic materials. The certification should be furnished to the owner prior to proceeding to furnish soils to the site. Any potential off-site soil borrow on which the test results indicate the presence of contaminants above background levels should be rejected. Soil materials derived from the excavation of underground petroleum storage tanks should not be used as fill on this project.

6.6 Soil Corrosion Potential

Specific testing for soil corrosion potential was not included in the scope of this study. However, based upon past experience on other projects in the vicinity, the soils at this site may be corrosive.

Standard construction practices for protecting metal pipe and similar facilities in contact with these soils should be used.

6.7 Erosion and Sediment Control

All disturbed areas should be protected from erosion and sedimentation during construction, and all permanent slopes and other areas subject to erosion or sedimentation should be provided with permanent erosion and sediment control facilities. All applicable ordinances and codes regarding erosion and sediment control should be followed.

7.0 PAVEMENTS

7.1 Pavement Subgrade Preparation

Finished grades near present existing grades will consist of moderately to highly plastic silty clays and clays. The clay soils are subject to loss in support value with the moisture increases which occur beneath pavement sections. They react with hydrated lime, which serves to improve and maintain their support value. Treatment of these soils with hydrated lime will improve their subgrade characteristics to support area paving. Areas of cuts could expose the limestones. Stabilization of limestone is not required. Observations by qualified geotechnical personnel may be required following rough grading to determine pavement subgrade areas containing sufficient quantities of clay to warrant lime stabilization.

In lieu of a lime stabilized subgrade for pavement consisting of Portland cement concrete, the recommended PCC pavement thicknesses presented in Section 7.2 may be increased by 2 inches, and placed atop a properly compacted subgrade.

Alternatively, in lieu of a lime stabilized subgrade, a flexible base meeting TxDOT Item 247, Type A, Grade 1/2 may be utilized on an equal basis, and placed atop a properly compacted subgrade. The option of using a flexible base in lieu of lime stabilizing the subgrade presents a relatively quick, straight forward solution to preparing the subgrade prior to pavement placement.

Prior to lime stabilization or compaction, the subgrade should be proofrolled with heavy pneumatic equipment (minimum 25 tons). The proof rolling operations should be observed by the project geotechnical engineer or his/her representative. Any soft or pumping areas should be undercut to a firm subgrade and properly backfilled as described in the Earthwork section. The subgrade should be scarified to a minimum depth of 6 inches and uniformly compacted to a minimum of 95 percent of Standard Proctor density (ASTM D 698), to minus 2 to plus 4 percentage points of the optimum moisture content determined by that test. It should then be protected and maintained in a moist condition until the pavement is placed.

We recommend a minimum of 8 percent hydrated lime be used to modify the clay subgrade soils.

The estimated amount of hydrated lime required to stabilize the subgrade should be on the order of

36 pounds per square yard for a 6-inch depth, based on a soil dry unit weight of 100 pcf. The hydrated lime should meet the requirements of Item 260 (Type A) in the Texas Department of

Transportation (TxDOT) Standard Specifications for Construction of Highways, Streets and Bridges, 2014 Edition. Lime treatment should extend beyond exposed pavement edges to reduce the effects of shrinkage and associated loss of subgrade support. The presence of limestone fragments, pebbles, calcareous nodules, and ironstone nodules in the surficial soils can complicate mixing of the soil and lime.

We recommend that subgrade stabilization extend to at least one foot beyond pavement edges to aid in reducing pavement movements and cracking along the curb line due to seasonal moisture variations after construction. Each construction area should be shaped to allow drainage of surface water during earthwork operations, and surface water should be pumped immediately from each construction area after each rain and a firm subgrade condition maintained. Water should not be allowed to pond in order to prevent percolation and subgrade softening, and lime should be added to the subgrade after removal of all surface vegetation and debris. Sand should be specifically prohibited beneath pavement areas, since these more porous soils can allow water inflow, resulting in heave and strength loss of subgrade soils (lime stabilized soil will be allowed for fine grading).

After fine grading each area in preparation for paving, the subgrade surface should be lightly moistened, as needed, and recompacted to obtain a tight non-yielding subgrade.

As previously discussed, cuts may expose limestone. These limestones provide excellent support in an undisturbed condition; however, they are difficult to cut to finished grade and some fill is required. Pulverization and compaction equipment often break down the limestone to a material that also benefits from stabilization, although large rock fragments hamper conventional mixing procedures. Depending on the required grades, it may be advisable to undercut such areas and place a material suitable for stabilization, place a flexible base, or to place a lime stabilized clay.

This can best be evaluated by an on-site inspection after grading is completed.

Surface drainage is critical to the performance of this pavement. Water should be allowed to exit the pavement surface quickly. All pavement construction should be performed in accordance with the following procedures.

7.2 Pavement Sections

The project may include the construction of parking lots and/or drives. At the time of this investigation, vehicle traffic studies were not available for the proposed parking and drive areas.

Therefore, several rigid pavement sections are presented for a 20-year design life based on our experience with similar facilities for Light-Duty Parking Areas, Medium-Duty Parking Areas and

Drives, and Medium- to Heavy-Duty Drives. In general, these areas are defined as follows:

Light-Duty Parking Areas are those lots and drives subjected almost exclusively to passenger cars, with an occasional light- to medium-duty truck (2 to 3 per week)

Medium-Duty Parking Areas and Drives are those lots and drives subjected to a variety of light-duty vehicles to medium-duty vehicles and an occasional bus or heavy-duty truck, includes an 85-kip fire apparatus (1 to 2 per week).

Medium- to Heavy-Duty Drives are those drives subjected to a variety of light to heavy-duty vehicles. These pavements include areas subject to significant bus traffic or trash vehicles.

We recommend that rigid pavements be utilized at this project whenever possible, since they tend to provide better long-term performance when subjected to significant slow moving and turning traffic.

For Portland cement concrete pavement, a minimum thickness of 5 inches of concrete is recommended for light-duty parking areas, 6 inches for medium-duty parking areas and drives, and 7 inches for medium- to heavy-duty areas.

A California Bearing Ratio or other strength tests were not performed because they were not within the scope of our services on this project. A subgrade modulus of 100 psi was considered appropriate for the near-surface soils. If heavier vehicles are planned, the above cross sections can be confirmed by performing strength tests on the subgrade materials once the traffic characteristics are established. Periodic maintenance of pavement structures normally improves the durability of the overall pavement and enhances its expected life.

The above sections should be considered minimum pavement thicknesses and higher traffic volumes and heavy trucks may require thicker pavement sections. Additional recommendations can be provided after traffic volumes and loads are known. Periodic maintenance should be anticipated for minimum pavement thickness. This maintenance should consist of sealing cracks and timely repair of isolated distressed areas.

7.3 Pavement Material Requirements

Reinforced Portland Cement Concrete: Reinforced Portland cement concrete pavement should consist of Portland cement concrete having a 28-day compressive strength of at least 3,500 psi. The mix should be designed in accordance with the ACI Code 318 using 3 to 6 percent air entrainment.

The pavement should be adequately reinforced with temperature steel and all construction joints or expansion/contraction joints should be provided with load transfer dowels. The spacing of the joints will depend primarily on the type of steel used in the pavement. We recommend using No. 3 steel rebar spaced at 18 inches on center in both the longitudinal and transverse direction. Control joints formed by sawing are recommended every 12 to 15 feet in both the longitudinal and transverse direction. The cutting of the joints should be performed as soon as the concrete has “set-up” enough to allow for sawing operations.

Lime Stabilized Subgrade: Lime treatment (road mix) – Item 260, Texas Department of

Transportation Standard Specifications for Construction and Maintenance of Highways, Streets, and

Bridges, 2014 Edition.

Flexible Base: Crushed Stone Flexible Base – Item 247, Type A, Grade 1/2, Texas Department of

Transportation Standard Specifications for Construction of Maintenance of Highways, Streets, and

Bridges, 2014 Edition.

7.4 General Pavement Considerations

The design of the pavement drainage and grading should consider the potential for differential ground movement due to future soil swelling on the order of 4 inches. In order to minimize rainwater infiltration through the pavement surface, and thereby minimizing future upward movement of the pavement slabs, all cracks and joints in the pavement should be sealed on a routine basis after construction. Reduction in potential differential movement can be reduced in a similar manner as discussed in Section 4.3. Should reduction levels per Section 4.3 or an intermediate level of movement reduction be desired, contact this office for additional recommendations.

8.0 CONSTRUCTION OBSERVATIONS

In any geotechnical investigation, the design recommendations are based on a limited amount of information about the subsurface conditions. In the analysis, the geotechnical engineer must assume the subsurface conditions are similar to the conditions encountered in the borings. However, quite often during construction anomalies in the subsurface conditions are revealed. Therefore, it is recommended that CMJ Engineering, Inc. be retained to observe earthwork and foundation installation and perform materials evaluation during the construction phase of the project. This enables the geotechnical engineer to stay abreast of the project and to be readily available to evaluate unanticipated conditions, to conduct additional tests if required and, when necessary, to recommend alternative solutions to unanticipated conditions. Until these construction phase services are performed by the project geotechnical engineer, the recommendations contained in this report on such items as final foundation bearing elevations, proper soil moisture condition, and other such subsurface related recommendations should be considered as preliminary.

It is proposed that construction phase observation and materials testing commence by the project geotechnical engineer at the outset of the project. Experience has shown that the most suitable method for procuring these services is for the owner or the owner's design engineers to contract directly with the project geotechnical engineer. This results in a clear, direct line of communication between the owner and the owner's design engineers and the geotechnical engineer.

9.0 REPORT CLOSURE

The boring logs shown in this report contain information related to the types of soil encountered at specific locations and times and show lines delineating the interface between these materials. The logs also contain our field representative's interpretation of conditions that are believed to exist in those depth intervals between the actual samples taken.