De_Zavala_Park_Geotechnical_Engineering_Report.pdf

GEOTECHNICAL ENGINEERING STUDY

FOR

PROPOSED DE ZAVALA PARK

EDINBURG, HIDALGO COUNTY, TEXAS

Raba Kistner, Inc.

800 East Hackberry McAllen, TX 78501 www.rkci.com

P 956.682.5332 F 956.682.5487

TBPE Firm F‐3257

TBAE Firm BR 3427

CONSULTANTS • ENVIRONMENTAL • PROGRAM MANAGEMENT • INFRASTRUCTURE

O:\Active Projects\McAllen\2022\AMA22\AMA22-027-00 Prop. De Zavala Park-City of Edinburg\Reporting\AMA22-027-00.doc

Project No. AMA22-027-00 July 8, 2022

Mr. Mardoqueo Hinojosa, P.E., CFM, CPM City Engineer City of Edinburg – Department of Engineering 415 W. University Drive Edinburg, Texas 78539

Re: Geotechnical Engineering Study

Proposed De Zavala Park 3615 W. Rogers Road

Edinburg, Hidalgo County, Texas

Dear Mr. Hinojosa:

RABA KISTNER Consultants, Inc. (RKCI) is pleased to submit the report of our Geotechnical Engineering Study for the above-referenced project. This study was performed in accordance with RKCI Proposal No. PMA22-022-00, dated April 20, 2022. Written authorization to proceed with this study was received by our office via electronic-mail attachment on Monday, May 23, 2023, by means of the Job Task Order No. 25 to the Agreement Between City of Edinburg and RKCI for Geo-Technical Engineering Services for the Zavala Park, dated May 17, 2022. The purpose of this study was to drill borings within the subject site, to perform laboratory testing on selected samples to classify and characterize subsurface conditions, and to prepare an engineering report presenting foundation and pavement recommendations and construction guidelines for the proposed park.

The following report contains our foundation and pavement recommendations and considerations based on our current understanding of the finished floor elevations, design tolerances and structural loads. If any of these parameters change, then there may be alternatives for value engineering of the foundation and pavement systems, and RKCI recommends that a meeting be held with City of Edinburg (CLIENT) and the design team to evaluate these alternatives.

Project No. AMA22-027-00 2

We appreciate the opportunity to be of professional service to you on this project. Should you have any questions about the information presented in this report, please call. We look forward to assisting the City of Edinburg during the construction of the project by conducting the construction materials engineering and testing services (quality assurance program).

Very truly yours, RABA KISTNER CONSULTANTS, INC.

Adamari Davila, E.I.T. Katrin M. Leonard, P.E.

Graduate Engineer Vice President

Attachments

AD/KML

Copies Submitted: Above (1)

GEOTECHNICAL ENGINEERING STUDY

For

PROPOSED DE ZAVALA PARK

3615 W. ROGERS ROAD

EDINBURG, HIDALGO COUNTY, TEXAS

Prepared for

CITY OF EDINBURG

Edinburg, Texas

Prepared by

RABA KISTNER CONSULTANTS, INC.

McAllen, Texas

PROJECT NO. AMA22-027-00

TABLE OF CONTENTS

i

INTRODUCTION

PROJECT DESCRIPTION

LIMITATIONS

BORINGS AND LABORATORY TESTS

GENERAL SITE CONDITIONS

SITE DESCRIPTION

SITE GEOLOGY

SEISMIC COEFFICIENTS

STRATIGRAPHY

GROUNDWATER

FOUNDATION ANALYSIS

EXPANSIVE, SOIL-RELATED MOVEMENTS

SETTLEMENTS

SETTLEMENT REDUCTION RECOMMENDATIONS

FOUNDATION RECOMMENDATIONS

SITE GRADING

SHALLOW FOUNDATIONS

Allowable Soil-Bearing Capacity Wire Reinforcement Institute (WRI) Criteria

AREA FLATWORK

FOUNDATION CONSTRUCTION CONSIDERATIONS

SITE DRAINAGE

SITE PREPARATION

SELECT FILL

SHALLOW FOUNDATION EXCAVATIONS

CRUSHED CALICHE MATERIAL

WOVEN GEOTEXTILE

EXCAVATION SLOPING AND BENCHING

TABLE OF CONTENTS

ii

EXCAVATION EQUIPMENT

WET WEATHER CONDITIONS

UTILITIES

PAVEMENT RECOMMENDATIONS

SUBGRADE CONDITIONS

SULFATE CORROSION POTENTIAL

DESIGN INFORMATION

FLEXIBLE PAVEMENTS

Garbage Dumpsters

RIGID PAVEMENTS

PAVEMENT CONSTRUCTION CONSIDERATIONS

SUBGRADE PREPARATION

DRAINAGE CONSIDERATIONS

ON-SITE FILL

SELECT FILL

FLEXIBLE BASE COURSE

ASPHALTIC CONCRETE SURFACE COURSE

PORTLAND CEMENT CONCRETE

CONSTRUCTION RELATED SERVICES

CONSTRUCTION MATERIALS ENGINEERING AND TESTING SERVICES

BUDGETING FOR CONSTRUCTION TESTING

ATTACHMENTS

Boring Location Map Logs of Borings Key to Terms and Symbols Results of Soil Sample Analyses Important Information About Your Geotechnical Engineering Report

INTRODUCTION

RABA KISTNER Consultants, Inc. (RKCI) has completed the authorized subsurface exploration and foundation and pavement recommendations for the proposed structures to be part of the De Zavala Park, to be located within the north side of the existing De Zavala Elementary School campus, situated at 3615 W. Rogers Road in Edinburg, Hidalgo County, Texas. This report briefly describes the procedures utilized during this study and presents our findings along with our recommendations for foundation and pavement design and construction considerations for the proposed park.

PROJECT DESCRIPTION

We understand that the proposed project consists of the design and construction of the following:

1) a square-shaped, approximately 1,444 ft² in footprint area, fitness court structure;

2) a rectangle-shaped, approximately 3,360 ft² in footprint area, splash pad structure;

3) a rectangle-shaped, restroom structure;

4) two basketball court structures; and

5) their associated parking and driveway areas.

The proposed park is planned to be located within an undeveloped tract of land, located within the north side of the existing De Zavala Elementary School campus, situated at 3615 W. Rogers Road in Edinburg, Hidalgo County, Texas. The proposed structures are expected to create relatively light to moderate loads to be carried by the foundation systems, which are anticipated to consist of shallow foundation systems.

The pavement systems are anticipated to consist of flexible (asphalt) and/or rigid (concrete) pavements.

For purposes of this geotechnical engineering report, the finished grade elevation (FGE) of the proposed structures was assumed to be about 12 inches (1 ft) above ground surface elevation existing at the time of our study, since no site grading information was provided to us at the time of the preparation of this report.

LIMITATIONS

This engineering report has been prepared in accordance with accepted Geotechnical Engineering practices in the region of South Texas for the use of the City of Edinburg (CLIENT) and its representatives for design purposes. This report may not contain sufficient information for purposes of other parties or other uses and is not intended for use in determining construction means and methods.

The recommendations submitted in this report are based on the data obtained from four borings drilled within the subject site, our understanding of the project information provided to us by the CLIENT, and the assumption that site grading will result in only minor changes in the topography existing at the time of our study. If the project information described in this report is incorrect, is altered, or if new information is available, we should be retained to review and modify our recommendations.

This report may not reflect the actual variations of the subsurface conditions across the subject site. The nature and extent of variations across the subject site may not become evident until construction commences. The construction process itself may also alter subsurface conditions. If variations appear evident at the time of construction, it may be necessary to reevaluate our recommendations after performing on-site observations and tests to establish the engineering impact of the variations.

The scope of our Geotechnical Engineering Study does not include an environmental assessment of the air, soil, rock, or water conditions either on or adjacent to the subject site. No environmental opinions are presented in this report. RKCI’s scope of work does not include the investigation, detection, or design related to the prevention of any biological pollutants. The term “biological pollutants” includes, but is not limited to, mold, fungi, spores, bacteria, and viruses, and the byproduct of any such biological organisms.

If final grade elevations are significantly different from the grades existing at the time of our study (more than plus or minus 1 ft), our office should be informed about these changes. If needed and/or desired, we will reexamine our analyses and make supplemental recommendations.

BORINGS AND LABORATORY TESTS

Subsurface conditions at the subject site were evaluated by conducting four borings as shown in the following table:

Proposed Structure Number of Borings Depth, ft. *

Fitness Court 1 25

Splash Pad

Restrooms 1 25

Basketball Courts 1 25

Parking and Driveway Areas 1 5

* below the existing ground surface elevation, or auger refusal, whichever occurs first.

The borings (designated as “B-” and “P-“) were drilled on June 3, 2022 and June 4, 2022 at the locations shown on the Boring Location Map, Figure 1. The boring locations are approximate and were located in the field by an RKCI representative based on the site plan titled “De Zavala Park Improvements & New Restroom at Skate Park”, dated May 16, 2022, and provided to us by the CLIENT via electronic-mail attachment on Wednesday, June 1, 2022. The borings were drilled to the depths shown in the previous table, below the ground surface elevations existing at the time of our study using a truck-mounted, rotary-drilling rig. The borings were drilled utilizing straight flight augers and were backfilled with the auger cuttings following completion of the drilling operations. During the drilling operations, Split-Spoon (with Standard Penetration Test, SPT) and Shelby-tube samples were collected.

The SPT and ST samples were obtained in accordance with accepted standard practices and the penetration test results are presented as “blows per foot” on the boring logs. Representative portions of the samples were sealed in containers to reduce moisture loss, labeled, packaged, and transported to our laboratory for subsequent testing and classification.

In the laboratory, each sample was evaluated and visually classified by a member of our Geotechnical Engineering staff in general accordance with the Unified Soil Classification System (USCS). The geotechnical engineering properties of the strata were evaluated by the following laboratory tests: natural moisture content, Atterberg limits, sulfate content determinations, and percent passing a No. 200 sieve determinations.

The laboratory tests are presented in graphical or numerical form on the boring logs illustrated on Figures 2 through 5. A key to the classification of terms and symbols used on the logs is presented on Figure 6. The results of the laboratory and field testing are also tabulated on Figure 7 for ease of reference.

SPT results are noted as “blows per ft” on the boring logs and on Figure 7, where “blows per ft” refers to the number of blows by a falling 140-lb (pound) hammer required for 1 ft of penetration into the subsurface materials. Where hard materials were encountered, the tests were terminated at 50 blows even if one foot of penetration had not been achieved.

Samples will be retained in our laboratory for 30 days after submittal of this report. Other arrangements may be provided at the written request of the CLIENT.

GENERAL SITE CONDITIONS

SITE DESCRIPTION

The subject site for the proposed park is planned to be located within the north side of the existing De Zavala Elementary School campus, situated at 3615 W. Rogers Road in Edinburg, Hidalgo County,Texas. At the time of our field activities, the project site can be described as an undeveloped tract of land. In general, the topography at the subject site is relatively flat, with a visually estimated vertical relief of about 3 ft across the site. Surface drainage is estimated to be fair. The subject site is bounded to the north and west by existing residential structures; to the east by Mon Mack Road; and to the south by the existing De Zavala Elementary School campus.

SITE GEOLOGY

A cursory review of the Geologic Atlas of Texas (McAllen-Brownsville Sheet, dated 1976), published by the Bureau of Economic Geology at the University of Texas at Austin, indicates that the subject site appears to be located within the Lissie Formation consisting of clays, silts, sands, gravel, and caliche deposits of the Quaternary epoch (Pleistocene period).

According to the Soil Survey of Hidalgo County, Texas, published by the United States Department of Agriculture - Soil Conservation Service, in cooperation with the Texas Agricultural Experiment Station, the project site appears to be located within the Hidalgo soil association consisting of deep, moderately permeable soils that typically have a dark grayish brown sandy clay loam surface layer. The corresponding soil symbol appears to be 28, Hidalgo sandy clay loam.

SEISMIC COEFFICIENTS

Based upon a review of Section 1613 Earthquake Loads – Site Ground Motion of the 2015 International Building Code (IBC), the following information has been summarized for seismic considerations associated with this site.

Site Class Definition (Chapter 20 of the American Society of Civil Engineers [ASCE] 7): Class D. Based on the soil borings conducted for this investigation, the upper 100 feet of soil may be characterized as a very dense soil and soft rock.

Risk-Targeted Maximum Considered Earthquake Ground Motion Response Accelerations for the Conterminous United States of 0.2-Second Spectral Response Acceleration (5% Of Critical Damping) (Figure 1613.3.1(1)): Ss = 0.044g. Note that the value taken from Figure 1613.3.1(1) is based on Site Class B and is adjusted per 1613.3.3 below.

Risk-Targeted Maximum Considered Earthquake Ground Motion Response Accelerations for the Conterminous United States of 1-Second Spectral Response Acceleration (5% Of Critical Damping) (Figure 1613.3.1(2)): S1 = 0.015g. Note that the value taken from Figure 1613.3.1(2) is based on Site Class B and is adjusted per 1613.3.3 below.

Values of Site Coefficient (Table 1613.3.3(1)): Fa = 1.6

Values of Site Coefficient (Table 1613.3.3(2)): Fv = 2.4

The Maximum Considered Earthquake Spectral Response Accelerations are as follows:

0.2 sec, adjusted based on equation 16-37: Sms = 0.070g.

1 sec, adjusted based on equation 16-38: Sm1 = 0.036g.

The Design Spectral Response Acceleration Parameters are as follows:

0.2 sec, based on equation 16-39: SDS = 0.047g.

1 sec, based on equation 16-40: SD1 = 0.024g.

Based on the parameters listed above, the critical nature of the structures, Tables 1613.3.5(1) and 1613.3.5(2), and calculations performed using a Java program titled, “Seismic Hazard Curves and Uniform Hazard Response Spectra” published by the United States Geological Survey (USGS) website, the Seismic Design Category for both short period and 1 second response accelerations is A. As part of the assumptions required to complete the calculations, a Risk Category of II was selected.

STRATIGRAPHY

The subsurface stratigraphy at this site can be described by two generalized strata. Each stratum has been designated by grouping soils that possess similar physical and engineering characteristics. For purposes of this report, we have designated the subsurface strata as Strata I and II. The lines designating the interfaces between strata on the boring logs represent approximate boundaries. Transitions between strata may be gradual.

Stratum I consists of brown, loose to very loose, clayey sand soils. This layer in the borings from the ground surface elevation existing at the time of our study, extending down to depths ranging from about 3 ft to 5 ft. Boring P-1 is comprised entirely of Stratum I soils to a termination depth of about 5 ft Moisture contents were measured to range from about 7 to 24 percent for this layer.

This stratum is classified as moderately plastic, with measured plasticity indices of about 15 to 16 percent. A single percent passing a No. 200 sieve test demonstrate a percent fine of about 49 percent for this layer. SPT N-values ranging from 3 blows to 6 blows per foot of penetration were measured for this stratum. These soils are classified as SC soils in general accordance with the

USCS.

Stratum II consists of brown, soft to hard, lean clay soils with sand, sandy lean clay soils, and fat clay soils with sand. This layer was noted in Borings B-1 through B-3 from beneath the Stratum I soils, extending down to at least the termination depth of the borings. Moisture contents were measured to range from about 16 to 27 percent for this layer. This stratum is classified as moderately plastic to plastic, with measured plasticity indices of about 15 to 26 percent. Percent passing a No. 200 sieve tests demonstrate percent fines ranging from about 60 to 83 percent for this layer. SPT N-values ranging from 3 blow to more than 50 blows per foot of penetration were measured for this stratum. These soils are classified as CL and CH soils in general accordance with the USCS.

GROUNDWATER

Groundwater was observed during our drilling operations in Borings B-1 through B-3 at depths ranging from about 14 ft to 18 ft below the ground surface elevations existing at the time of our study. The boreholes were left open for the duration of the field exploration phase to allow monitoring of water level. It is possible for groundwater to exist beneath this site at shallower depths on a transient basis following periods of precipitation. Fluctuations in groundwater levels occur due to variations in rainfall and surface water run-off. The construction process itself may also cause variations in the groundwater level.

Based on the findings in the borings and on our experience in this region, we believe that groundwater seepage encountered during site earthwork activities and shallow foundation construction may be controlled using temporary earthen berm and conventional sump-and-pump dewatering methods.

FOUNDATION ANALYSIS

EXPANSIVE, SOIL-RELATED MOVEMENTS

The anticipated ground movements due to swelling of the underlying soils at the site were estimated for slab-on-grade construction using the empirical procedure, Texas Department of Transportation (TxDOT) Tex-124-E, Method for Determining the Potential Vertical Rise (PVR). PVR values on the order of about 1 inch were estimated for the stratigraphic conditions encountered in the borings. The PVR values were estimated using a surcharge load of 1 pound per square inch (psi) for the concrete slab and dry moisture conditions within the regional zone of seasonal moisture variation.

The TxDOT method of estimating expansive, soil-related movements is based on empirical correlations utilizing the measured plasticity indices and assuming typical seasonal fluctuations in moisture content.

If desired, other methods of estimating expansive, soil-related movements are available, such as estimations based on swell tests and/or soil-suction analyses. However, the performance of these tests and the detailed analysis of expansive, soil-related movements were beyond the scope of the current study. It should also be noted that actual movements can exceed the estimated PVR values due to isolated changes in moisture content (such as due to leaks, landscape watering, etc.) or if water seeps into the soils to greater depths than the assumed active zone depth due to deep trenching or excavations.

SETTLEMENTS

The subject site for the proposed park is underlain by very loose, clayey sand soils, extending down to a depth of about 5 ft below the ground surface elevation existing at the time of our study. Based on the low shear strengths of these soils, the on-site soils have the potential for settlements under the applied structural loads. The potential settlements can only be estimated once the site grading plans, foundation dimensions, and structural loads have been established for this project.

SETTLEMENT REDUCTION RECOMMENDATIONS

As stated previously, for purposes of this geotechnical engineering report, the FGE of the proposed structures was assumed to be about 12 inches (1 ft) above the ground surface elevation existing at the time of our study, since no site grading information was provided to us at the time of the preparation of this report.

In consideration of the subsurface conditions encountered in the borings, we recommend the following site improvement procedure to be implemented within the structures to be supported on shallow foundations:

Remove a minimum of 8 inches of the existing subgrades soils in order to clear the areas of all vegetation and/or organic topsoil. The excavations shall extend a minimum of 5 ft beyond the structures’ perimeters.

Further, remove a minimum of 4 ft of the subgrades soils and stockpile the excavated materials on site. The excavations shall extend a minimum of 5 ft beyond the structures’ perimeters.

Place a layer of MIRAFI HP 270 woven geotextile or approved equivalent over the exposed subgrades soils.

Place compacted, layer of crushed caliche material over the geotextile layer, in 6-inch compacted lifts up to the structures’ FGE, which is assumed to be about 12 inches (1 ft) above the ground surface elevation existing at the time of our study. The crushed caliche material shall be compacted, tested, and documented as indicated in the Crushed Caliche Material subsection presented in this report.

Please note that no construction equipment traffic should be allowed directly over the geotextile fabric. Direct equipment traffic will cause irreversible damage to this material. Construction traffic should only be allowed after a sufficiently thick layer of caliche base material has been laid over the geosynthetic product. Please refer to the manufacturer’s construction recommendations for the proper installation of the geotextile fabric.

Drainage Considerations Considerations of surface and subsurface drainage may be crucial to construction and adequate foundation performance of the soil-supported structures. Filling excavations in relatively impervious clay soils with relatively pervious select fill material creates a “bathtub” beneath the structures, which can result in ponding or trapped water within the fill unless good surface and subsurface drainage is provided.

Water entering the fill surface during construction or entering the fill exposed beyond the structures’ lines after construction may create problems with fill moisture control during compaction and increased access for moisture to the underlying expansive clays both during and after construction.

Several surface and subsurface drainage design features and construction precautions can be used to limit problems associated with fill moisture. These features and precautions may include, but are not limited to, the following:

Installing berms or swales on the uphill side of the construction areas to divert surface runoff away from the excavation/fill areas during construction;

Sloping of the top of the subgrades with a minimum downward slope of 1.5 percent out to the base of a dewatering trench located beyond the structures’ perimeters;

Sloping the surface of the fill during construction to promote runoff of rain water to drainage features until the final lift is placed;

Sloping of a final, well-maintained, impervious clay or pavement surface (downward away from the proposed structures) over the select fill material and any perimeter drain extending beyond the structures’ lines, with a minimum gradient of 6 in. in 5 ft;

Constructing final surface drainage patterns to prevent ponding and limit surface water infiltration at and around the structures’ perimeters;

Locating the water-bearing utilities, roof drainage outlets, and irrigation spray heads outside of the select fill and perimeter drain boundaries; and

Raising the elevation of the ground level floor slabs.

Details relative to the extent and implementation of these considerations must be evaluated on a project-specific basis by all members of the project design team. Many variables that influence fill drainage considerations may depend on factors that are not fully developed in the early stages of design. For this reason, drainage of the fill should be given consideration at the earliest possible stages of the project.

FOUNDATION RECOMMENDATIONS

SITE GRADING

Site grading plans can result in changes in almost all aspects of foundation recommendations. We have prepared the foundation recommendations based on the ground surface elevations and the stratigraphic conditions encountered in the borings at the time of our study. If site grading plans differ from the grades existing at the time of our study by more than plus or minus 1 ft, we must be retained to review the site grading plans prior to bidding the project for construction. This will enable us to provide input for any changes in our original recommendations, which may be required as a result of site grading operations or other considerations.

SHALLOW FOUNDATIONS

The proposed structures may be founded on conventional spread and/or continuous footing foundations in conjunction with a fill-supported concrete floor slabs, provided that the shallow foundation system can be designed to withstand the anticipated soil-related movements (see the Foundation Analyses section of this report) without impairing either the structural or the operational performance of the proposed structures.

Allowable Soil-Bearing Capacity

Shallow foundations founded on native soils or compacted, crushed caliche material in conjunction with the site improvement procedure presented in the Settlement Reduction Recommendations subsection of the Foundation Analyses section of this report may be proportioned using the design parameters tabulated in the following table:

Shallow Foundations Founded on Native Soils

Shallow Foundations Founded on Compacted, Crushed Caliche Material

Minimum depth below final grade 24 in. 24 in.

Minimum beam width 12 in. 12 in.

Maximum allowable bearing pressure for continuous footings - grade beams

1,000 psf 2,000 psf

Maximum allowable bearing pressure for spread footings - widened beams

1,250 psf 2,400 psf

*below the ground surface elevations at the time of our study

The maximum allowable soil-bearing pressures presented previously will provide a factor of safety of about 3 with respect to the measured soil shear strengths, provided that the subgrades are prepared in accordance with the recommendations outlined in the Site Preparation subsection of the Foundation Construction Considerations section of this report, and that the site improvement procedure included in the Settlement Reduction Recommendations subsection of the Foundation Analyses section of this report is implemented. Provided that the site improvement procedure recommended in this report is properly-implemented, then it is anticipated that total settlements will be in the order of about 1 inch. Differential settlements typically are estimated to be about one-half the total estimated settlement for most subsurface conditions.

Furthermore, the design parameters presented on the previous table are contingent upon the fill materials being selected and placed in accordance with the recommendations presented in the Select Fill subsection of the Foundation Construction Considerations section of this report. Should select fill selection and placement differ from the recommendations presented herein, RKCI should be informed of the deviations in order to reevaluate our recommendations and design criteria.

Wire Reinforcement Institute (WRI) Criteria

The slab-on-fill shallow foundations may also be designed using WRI design criteria. On the basis of the subsurface stratigraphy encountered, a general effective plasticity index for the proposed structures of 22 percent and a climatic rating (Cw) of 15 should be utilized for the design of the structures’ foundations.

AREA FLATWORK

It should be noted that ground-supported flatwork such as walkways, courtyards, sidewalks, etc., will be subject to the same magnitude of potential soil-related movements as discussed previously (see the Foundation Analyses section of this report). Thus, where these types of elements abut rigid building foundations or isolated structures, differential movements should be anticipated. As a minimum, we recommend that flexible joints be provided where such elements abut the main structures to allow for differential movement at these locations. Where the potential for differential movement is objectionable, it may be beneficial to consider methods of reducing anticipated movements to match the adjacent structures’ performance.

FOUNDATION CONSTRUCTION CONSIDERATIONS

SITE DRAINAGE

Drainage is an important key to the successful performance of any foundation. Good surface drainage should be established prior to and maintained after construction to help prevent water from ponding within or adjacent to the structures’ foundations and to facilitate rapid drainage away from the foundations. Failure to provide positive drainage away from the structures can result in localized differential vertical movements in soil the supported foundation and floor slab.

Current ordinances, in compliance with the Americans with Disabilities Act (ADA), may dictate maximum slopes for walks and drives around and into new structures. These slope requirements can result in drainage problems for ground-supported structures. We recommend that, on all sides of the proposed structures’ foundations, the maximum permissible slope be provided away from the proposed structures.

Also to help control drainage in the vicinity of the structures, we recommend that roof/gutter downspouts and landscaping irrigation systems not be located adjacent to the structures’ foundations.

Where a select fill overbuild is provided outside of the floor slab/foundation footprints, the surface should be sealed with an impermeable layer (pavement or clay cap) to reduce infiltration of both irrigation and surface waters. Careful consideration should also be given to the location of water bearing utilities, as well as to provisions for drainage in the event of leaks in water bearing utilities. All leaks should be immediately repaired.

Other drainage and subsurface drainage issues are discussed in the Foundation Analysis section of this report.

SITE PREPARATION

The structures areas and all areas to support select fill should be stripped of all vegetation and/or organic topsoil down to a minimum depth of 8 inches and extending a minimum of 5 ft beyond the structures’ footprint areas. Further, we recommend that the site improvement procedures presented in the Settlement Reduction Recommendations section of this report be implemented in order to strengthen and densify the surficial soils beneath the proposed structures’ footprint areas.

Exposed subgrades should be thoroughly proofrolled in order to locate and densify any weak, compressible zones. A minimum of 5 passes of a fully-loaded dump truck or a similar heavily-loaded piece of construction equipment should be used for planning purposes. Proofrolling operations should be observed by the Geotechnical Engineer or his/her representative to document subgrade conditions and preparation. Weak or soft areas identified during proofrolling should be treated with hydrated lime or Portland cement, or removed and replaced with a suitable, compacted select fill in accordance with the recommendations presented under the Select Fill subsection of this section of the report. If the treatment option is selected, the weak or soft areas may be mixed with hydrated lime or Portland cement down to a minimum depth of 8 inches in order to aid in drying the soils and develop a firm working surface.

Proofrolling operations and any excavation/backfill activities should be observed by RKCI representatives to document subgrade preparation.

Upon completion of the proofrolling operations and just prior to fill placement or slab construction, the exposed subgrade should be moisture conditioned by scarifying to a minimum depth of 6 in. and recompacting to a minimum of 98 percent of the maximum density determined from the American Society for Testing and Materials (ASTM) D698, Compaction Test. The moisture content of the subgrade should be maintained within the range of optimum moisture content to three percentage points above the optimum moisture content until permanently covered.

SELECT FILL

Materials used as select fill for final site grading preferably should be crushed stone or gravel aggregate.

We recommend that materials specified for use as select fill meet the TxDOT 2014 Standard Specification for Construction and Maintenance of Highways, Streets, and Bridges, Item 247, Flexible Base, Type A through Type E, Grades 1, 2, 3, and 5.

Alternatively, the following soils, as classified according to the USCS, may be considered satisfactory for use as select fill materials at this site: SC, GC, CL, and combinations of these soils. In addition to the USCS classification, alternative select fill materials shall have a maximum liquid limit of 40 percent, a plasticity index between 7 and 18 percent, and a maximum particle size not exceeding 4 inches or one-half the loose lift thickness, whichever is smaller. In addition, if these materials are utilized, grain size analyses and Atterberg Limits must be performed during placement at a minimum rate of one test each per 5,000 cubic yards of material due to the high degree of variability associated with pit-run materials.

If the above listed alternative materials are being considered for bidding purposes, the materials should be submitted to the Geotechnical Engineer for pre-approval a minimum of 10 working days or more prior to the bid date. Failure to do so will be the responsibility of the General Contractor. The General Contractor will also be responsible for ensuring that the properties of all delivered alternate select fill materials are similar to those of the pre-approved submittal. It should also be noted that when using alternative fill materials, difficulties may be experienced with respect to moisture control during and subsequent to fill placement, as well as with erosion, particularly when exposed to inclement weather. This may result in sloughing of beam trenches and/or pumping of the fill materials.

Soils classified as CH, MH, ML, SM, GM, OH, OL, and Pt under the USCS and not meeting the alternative select fill material requirements, are not considered suitable for use as select fill materials at this site. The upper 5 ft of subgrade soils at this site are considered suitable for use as select fill materials.

Select fill should be placed in loose lifts not exceeding 8 in. in thickness and compacted to at least 98 percent of the maximum dry density as determined by ASTM D698. The moisture content of the fill material should be maintained within the range of two percentage points below the optimum moisture content to two percentage points above the optimum moisture content until the final lift of fill is permanently covered.

The select fill should be properly compacted in accordance with these recommendations and tested by RKCI personnel for compaction as specified.

SHALLOW FOUNDATION EXCAVATIONS

Shallow foundation excavations should be observed by the Geotechnical Engineer or his/her representative prior to placement of reinforcing steel and concrete. This is necessary to document that the bearing soils at the bottom of the excavations are similar to those encountered in the borings and that excessive soft materials and water are not present in the excavations. If soft soil pockets are encountered in the foundation excavations, they should be removed and replaced with a compacted non-expansive fill material or lean concrete up to the design foundation bearing elevation.

Disturbance from foot traffic and from the accumulation of excess water can result in losses in bearing capacity and increased settlement. If inclement weather is anticipated at the time construction, consideration should be given to protecting the bottoms of beam trenches by placing a thin mud mat (layer of flowable fill or lean concrete) at the bottom of trenches immediately following excavation.

This will reduce disturbance from foot traffic and will impede the infiltration of surface water. All necessary precautions should be implemented to protect open excavations from the accumulation of surface water runoff and rain.

CRUSHED CALICHE MATERIAL

The crushed caliche flexible base material shall meet the requirements of the 2014 TxDOT Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges, Item 247, Flexible Base, Type E, Grade 4 specifications (after lime treatment). Prior to treatment with hydrated lime, the flexible base material may be composed of caliche (argillaceous limestone, calcareous or calcareous clay particles) and may contain stone, conglomerate, gravel, sand or granular materials when these materials are in situ with the caliche. Further, prior to lime treatment, the flexible base (Type E, Grade 4) shall conform to the requirements presented on the following table:

Before Hydrated Lime Is Added

Retained on Sq. Sieve Percent Retained

2” 0

1/2” 20-60

No. 4 40-75

No. 40 70-90

Max. PI (%): 15

Max. Wet Ball PI (%): 15

Wet Ball Mill Max. Amount (%): 50

Min. Comp. Strength (psi): 150 at 15 psi lateral pressure

Triaxial Test Tex-117-E

Where PI = Plasticity Index psi = pounds per square inch

The Wet Ball Test (Tex-116-E) shall be run and the plasticity index of the material passing the No. 40 sieve shall be determined (Wet Ball PI).

After A Sufficient Quantity Of Hydrated Lime Is Added To Unlimed Material

Max. PI (%): 12

Min. Comp. Strength (psi): 180 at 15 psi lateral pressure

Triaxial Test (lime treated): Tex-121-F

The base material should be placed in compacted lifts with a maximum thickness of 8 inches and compacted to a minimum of 95 percent of the maximum density as determined by the American Society for Testing and Materials (ASTM) D1557. The moisture content of the flexible base material should be maintained within the range of three percentage points below to three percentage points above the optimum moisture content until permanently cove

WOVEN GEOTEXTILE

The woven geotextile should be MIRAFI HP 270 or approved equivalent, consisting of a polypropylene yarns, which are woven into a network such that the yarns retain their relative position. The woven geotextile shall be inert to biological degradation and resistant to naturally encountered chemicals, alkalis, acids, and ultraviolet light exposure.

EXCAVATION SLOPING AND BENCHING

Excavations that extend to or below a depth of 5 ft below construction grade shall require the General Contractor to develop a trench safety plan to protect personnel entering the trench or trench vicinity. The collection of specific geotechnical data and the development of such a plan, which could include designs for sloping and benching or various types of temporary shoring, are beyond the scope of the current study.

Any such designs and safety plans shall be developed in accordance with current Occupational Safety and Health Administration (OSHA) guidelines and other applicable industry standards.

EXCAVATION EQUIPMENT

Excavations that extend to or below a depth of 5 ft below construction grade shall require the General Contractor to develop a trench safety plan to protect personnel entering the trench or trench vicinity. The collection of specific geotechnical data and the development of such a plan, which could include designs for sloping and benching or various types of temporary shoring, are beyond the scope of the current study.

Any such designs and safety plans shall be developed in accordance with current Occupational Safety and Health Administration (OSHA) guidelines and other applicable industry standards.

WET WEATHER CONDITIONS

Earthwork contractors should be made aware of the moisture sensitivity of the near surface soils and potential compaction difficulties. If construction is undertaken during wet weather conditions, the surficial soils may become saturated, soft, and unworkable. Drainage trenches within the soils to be excavated, reworked and/or recompacted may be required. Additionally, subgrade stabilization techniques, such as chemical (cement, fly ash or hydrated lime) treatment, may be required to provide a more weather-resistant working surface during pad construction. Therefore, we recommend that consideration be given to construction during the dryer months. Alternatively, the contractor should protect all exposed areas once topsoil has been stripped, as well as provide positive drainage during earthwork operations.

UTILITIES

Utilities which project through slab-on-grade, slab-on-fill, “floating” floor slabs, or any other rigid unit should be designed with either some degree of flexibility or with sleeves. Such design features will help reduce the risk of damage to the utility lines.

Our experience indicates that significant settlement of backfill can occur in utility trenches, particularly when trenches are deep, when backfill materials are placed in thick lifts with insufficient compaction, and when water can access and infiltrate the trench backfill materials. The potential for water to access the backfill is increased where water can infiltrate flexible base materials due to insufficient penetration of curbs, and at sites where geological features can influence water migration into utility trenches. It is our belief that another factor which can significantly impact settlement is the migration of fines within the backfill into the open voids in the underlying free-draining bedding material.

To reduce the potential for settlement in utility trenches, we recommend that consideration be given to the following:

Backfill materials should be placed and compacted in controlled lifts appropriate for the type of backfill and the type of compaction equipment being utilized and backfilling procedures should be tested and documented.

Curbs should be installed to a sufficient depth to reduce water infiltration beneath the curbs into the pavement flexible base materials (see also the Foundation Analyses section of this report).

Consideration should be given to wrapping free-draining bedding gravels with a geotextile fabric (similar to Mirafi 140N or CONTECH C-Drain Geocomposite) to reduce the infiltration and loss of fines from backfill material into the interstitial voids in bedding materials.

PAVEMENT RECOMMENDATIONS

Both flexible and rigid pavement recommendations for a 20-year design period are presented in this report. The CLIENT and/or design team may select either pavement type depending on the performance criteria established for the project. In general, flexible pavement systems have a lower initial construction cost as compared to rigid pavements. However, maintenance requirements over the life of the pavement are typically much greater for flexible pavements. This typically requires regularly-scheduled observation and repair, as well as overlays and/or other pavement rehabilitation at approximately one-half to two-thirds of the design life. Rigid pavements are generally more "forgiving", and therefore tend to be more durable and require less maintenance after construction.

For either pavement type, drainage conditions will have a significant impact on long-term performance, particularly where permeable flexible base materials are utilized in the pavement section. Drainage considerations are discussed in more detail in a subsequent section of this report.

SUBGRADE CONDITIONS

A single generalized subgrade condition has been assumed for this site. The predominant subgrade soils used in developing the pavement sections for this project are moderately plastic soils. On the basis of our past experience with similar subsurface conditions in this area, a design California Bearing Ratio (CBR) value of 6 was assigned to evaluate the pavement components. This design CBR value assumes that the subgrade soils will be prepared in accordance with the recommendations stated in the Subgrade Preparation subsection of the Pavement Construction Guidelines section of this report.

SULFATE CORROSION POTENTIAL

The potential concentration of soluble sulfates along the subject site was preliminarily evaluated by conducting a laboratory sulfate content determination. The result of this laboratory test is as follows:

Boring Identification

Approximate Depth Below the Ground Surface Elevation

Existing at the Time of our Study (ft)

Sulfate Content (ppm)

P-1 2 120

Where ppm = parts per million

On the basis of these sulfate content test results, the tested on-site subgrade soils do not appear to have a potential to cause sulfate-induced heave. Typically, the concentration of soluble sulfate on soils becomes a concern when the concentration reaches about 3,000 ppm and higher. The sulfate concentration in soils may vary over short distances, and as such, additional testing is recommended at the time of construction to confirm the concentration of sulfates in the exposed subgrade soils within the subject pavement areas.

DESIGN INFORMATION

The following recommendations for the pavement sections are based on our past experience with similar subgrade soils; assumed traffic loadings; an assumed CBR test value for the subgrade soils; and design procedures published by the American Association of State Highway and Transportation Officials (AASHTO). The pavement design and analyses performed are based directly on the 1993 and 1997 editions of the “Guide for the Design of Pavement Structure” by AASHTO.

For a 20-year design period, Equivalent Single Axle Loads (ESAL's) were estimated for an assumed traffic loading of 1 tractor-trailer truck per day and two garbage trucks per week for the proposed parking lot and driveway areas. This corresponds to about 27,000 ESAL's. It is recommended that the project Civil Engineer review the above-mentioned levels of traffic and design period to ensure that they are appropriate for the intended use of the proposed park.

FLEXIBLE PAVEMENTS

The flexible pavement sections shown on the following table are available for this site.

Pavement Area

PS

(in.)

FBM

(in.)

HMAC

(in.)

Automobile Drives and Parking Lots 8 8 2

Where: PS = Prepared Subgrade FBM = Flexible Base Material HMAC = Hot-Mix Asphaltic Concrete Surface Course

Garbage Dumpsters

Where flexible pavements are constructed at any site, it is recommended that reinforced concrete pads be provided in front of and beneath trash receptacles. The dumpster trucks should be parked on the concrete pads when the receptacles are lifted. It is suggested that such pads also be provided in drives where the dumpster trucks make turns with small radii to access the receptacles. The concrete pads at this site should be a minimum of 5-1/2 inches thick and reinforced with conventional steel reinforcing bars, and underlain by 8 inches of prepared subgrade.

RIGID PAVEMENTS

The following rigid pavement sections are available for this site:

Pavement Area Prepared Treated Subgrade (in.)

Reinforced Concrete (in.)

Automobile Drives and Parking Lots 8 5-1/2

We recommend that the concrete pavements be reinforced with welded wire mats or bar mats. As a minimum, the welded wire mats should be 6 x 6 inches, W4.0 x W4.0, and the bar mats should be No. 3 reinforcing bars spaced 18 inches on center in both directions. The concrete reinforcing should be placed approximately 1/3 the slab thickness below the surface of the slab, but not less than 2 inches.

The reinforcing should not extend across expansion joints.

Joints in concrete pavements aid in the construction and control the location and magnitude of cracks.

Where practical, lay out the construction, expansion, control and sawed joints to form square panels, but not to exceed American Concrete Institute (ACI) Code recommendations. The ratio of slab length-to-width should not exceed 1.25. Recommended joint spacings are 15 ft longitudinal and 15 ft transverse.

All control joints should be formed or sawed to a depth of at least 1/4 the thickness of the concrete slab. Sawing of control joints should begin as soon as the concrete will not ravel, generally the day after placement. Control joints may be hand formed or formed by using a premolded filler. We recommend that all longitudinal and transverse construction joints be dowelled to promote load transfer. Expansion joints are needed to separate the concrete slab from fixed objects such as drop inlets, light standards and buildings. Expansion joint spacings are not to exceed a maximum of 75 ft and no expansion or construction joints should be located in a swale or drainage collection locations.

If possible, the pavement should develop a minimum slope of 0.015 ft/ft to provide surface drainage.

Reinforced concrete pavement should cure a minimum of 7 days before allowing any traffic.

PAVEMENT CONSTRUCTION CONSIDERATIONS

SUBGRADE PREPARATION

Areas to support pavements should be stripped of all vegetation and/or organic topsoil down to a minimum depth of 8 inches and extend a minimum of 2 ft beyond the pavement perimeters. Upon completion of site stripping activities, the exposed subgrade should be thoroughly proofrolled in accordance with the Site Preparation subsection recommendations provided in the Foundation Construction Considerations section of this report. Likewise, upon completion of the proofrolling activities and just prior to select fill or flexible base placement, the exposed subgrade should be scarified and recompacted as recommended in such subsection.

DRAINAGE CONSIDERATIONS

As with any soil-supported structure, the satisfactory performance of a pavement system is contingent on the provision of adequate surface and subsurface drainage. Insufficient drainage which allows saturation of the pavement subgrade and/or the supporting granular pavement materials will greatly reduce the performance and service life of the pavement systems.

Surface and subsurface drainage considerations crucial to the performance of pavements at this site include (but are not limited to) the following:

1) Any known natural or man-made subsurface seepage at the site which may occur at sufficiently shallow depths as to influence moisture contents within the subgrade should be intercepted by drainage ditches or below grade French drains.

2) Final site grading should eliminate isolated…