Geotechnical_Report.pdf

GEOTECHNICAL ENGINEERING STUDY

FOR

PROPOSED VETERANS DETENTION POND PROJECT – PHASE 2

EDINBURG, HIDALGO COUNTY, TEXAS

Raba Kistner, Inc.

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

P 956.682.5332 F 956.682.5487 F-3257

O:\Active Projects\McAllen\2026\AMA26\AMA26-003-00 Prop. Veterans Detention Pond Project - Phase 2\Reporting\AMA26-003-00 (Revised).doc

Project No. AMA26-003-00 (Revised) March 13, 2026

Mr. Christopher Hinojosa, P.E.

Engineer III City of Edinburg 415 W. University Drive Edinburg, Texas 78539

RE: Revised Geotechnical Engineering Study Proposed Veterans Detention Pond Project – Phase 2 Near the Northeast Corner of the Intersection of Alberta Road and S. Veterans Boulevard

Edinburg, Hidalgo County, Texas

Dear Mr. Hinojosa:

RABA KISTNER, INC. (RKI) is pleased to submit the report of our Geotechnical Engineering Study for the above-referenced project. This study was performed in general accordance with RKI Proposal No.

PMA26-004-00 (Revised), dated January 21, 2026. Written authorization to proceed with this study was received by our office via electronic-mail attachment on Friday, January 23, 2026, by means of the executed Job Task Order Number 2 to the Agreement Between The City of Edinburg and RKI for Geotechnical Engineering Services for Veterans Detention Pond Project – Phase II, dated August 20, 2024.

The purpose of this study was to drill borings within the 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 structures.

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

GEOTECHNICAL ENGINEERING STUDY

For

PROPOSED VETERANS DETENTION POND PROJECT – PHASE 2

NEAR THE NORTHEAST CORNER OF THE INTERSECTION OF

ALBERTA ROAD AND S. VETERANS BOULEVARD

EDINBURG, HIDALGO COUNTY, TEXAS

Prepared for

CITY OF EDINBURG

Edinburg, Texas

Prepared by

RABA KISTNER, INC.

McAllen, Texas

PROJECT NO. AMA26-003-00 (REVISED)

TABLE OF CONTENTS

i

PROJECT DESCRIPTION

LIMITATIONS

BORINGS AND LABORATORY TESTS

GENERAL SITE CONDITIONS

SITE GEOLOGY

SEISMIC COEFFICIENTS

STRATIGRAPHY

GROUNDWATER

FOUNDATION RECOMMENDATIONS AND CONSIDERATIONS

SOFT SENSITIVE SOILS

EXPANSIVE, SOIL-RELATED MOVEMENTS

PVR REDUCTION RECOMMENDATIONS

SHALLOW FOUNDATIONS

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

FLATWORK AND FLOOR SLABS

FOUNDATION CONSTRUCTION CONSIDERATIONS

SITE DRAINAGE

SITE PREPARATION

SELECT FILL

TRENCH EXCAVATION SLOPING/BENCHING

EXCAVATION EQUIPMENT

UTILITIES

DESIGN RECOMMENDATIONS AND CONSIDERATIONS FOR THE PROPOSED

DETENTION POND AND STORMWATER DRAINAGE ALIGNMENT

EXCAVATION DEWATERING

TEMPORARY EXCAVATION SLOPING AND SHORING

EXCAVATION EQUIPMENT

TABLE OF CONTENTS

ii

SLOPE INCLINATION RECOMMENDATIONS

PAVEMENT RECOMMENDATIONS

SUBGRADE CONDITIONS

SWELL/HEAVE POTENTIAL

LIME TREATMENT OF SUBGRADE

DESIGN INFORMATION

FLEXIBLE PAVEMENTS

PAVEMENT CONSTRUCTION CONSIDERATIONS

SUBGRADE PREPARATION

DRAINAGE CONSIDERATIONS

ON-SITE SOIL FILL

SELECT FILL

LIME TREATMENT OF SUBGRADE

FLEXIBLE BASE COURSE

ASPHALTIC CONCRETE SURFACE COURSE

CONSTRUCTION RELATED SERVICES

CONSTRUCTION MATERIALS ENGINEERING AND TESTING SERVICES

BUDGETING FOR CONSTRUCTION TESTING

ATTACHMENTS

Boring Location Map .......................................................................................................................... Figure 1 Logs of Borings ................................................................................................................. Figures 2 through 8 Key to Terms and Symbols ................................................................................................................. Figure 9 Results of Soil Sample Analyses ....................................................................................................... Figure 10 Grain Size Distribution .................................................................................................................... Figure 11

Important Information About Your Geotechnical Engineering Report

PROJECT DESCRIPTION

RABA KISTNER, INC. (RKI) has completed the authorized subsurface exploration for the proposed structure additions, planned to be located near the northeast corner of the intersection of Alberta Road and S. Veterans Boulevard in Edinburg, Hidalgo County, Texas (Figure 1). 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. Currently, the subject site can be described as an undeveloped, heavily vegetated covered tract of land. In general, the topography at the subject site is relatively level, with an estimated vertical relief of less than 3 ft across the site. Surface drainage is estimated to be poor. The subject site is bounded to the north by an existing irrigation canal; to the east and west by residential structures; and to the south by Alberta Road.

We understand that the proposed project will consist of the design and construction of 1) an approximately 7-ft to 12-ft deep, detention pond along with its asphalt-paved, trail alignment along the perimeter embankment; 2) a one-story, about 250 ft², restroom building; 3) a parking lot; and 4) the installation of a stormwater drainage alignment. Further, based on the project plans titled “Construction Plans for City of Edinburg Veterans Blvd. Drainage Improvements,” dated December 1, 2025, we understand that about 3 ft of fill material is planned to be placed along the berm of the proposed detention pond. Foundation loads and site grading plans for the proposed structures have not been provided at this time. The proposed restroom building is expected to create relatively light to moderate loads to be carried by the foundation system, which is anticipated to consist of a shallow foundation. The pavement systems are anticipated to consist of flexible (asphalt) pavements.

For purposes of this geotechnical engineering report, the finished grade elevation (FGE) of the proposed restroom building 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.

LIMITATIONS

This engineering report has been prepared in accordance with accepted Geotechnical Engineering practices in the region of South Texas for the use of 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 seven borings drilled within the subject site and 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 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 site. No environmental opinions are presented in this report. RKI’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 those discussed in the section titled Project Description, 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 seven borings drilled within the site, as shown in the following table.

Proposed Structure Number of Borings Depth (ft) * Boring Identification

Detention Pond and Trail 3 25 B-1 through B-3

Restroom Building 1 20 B-4

Stormwater Drainage Alignment 2 15 B-5 through B-6

Parking Lot 1 5 P-1

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

The borings (designated as “B-” and “P-”) were drilled on January 28, 2026, at the locations shown on the Boring Location Map, Figure 1. The boring locations are approximate and were located in the field by an RKI representative based on the site plan provided to our office via electronic-mail attachment by the CLIENT on Thursday, January 15, 2026. The borings were drilled to the depths indicated in the previous table 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 (ST) 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 field and 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 (plasticity) tests, hydrometers, and grain size analyses.

The results of the field and laboratory tests are presented in graphical or numerical form on the boring logs illustrated on Figures 2 through 8. A key to the classification of terms and symbols used on the logs is presented on Figure 9. The results of the laboratory and field testing are also tabulated on Figure 10 for ease of reference. The results of the hydrometers are tabulated on Figure 11.

SPT results (N-values) are noted as “blows per ft” on the boring logs and on Figure 10, 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.

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 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 Beaumont Formation consisting of clays, silts, sands, and gravel 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 association and the Raymondville-Hidalgo Association. The Hidalgo association consists of deep, moderately permeable soils that typically have a dark-grayish brown sandy clay loam surface layer, while the Raymondville-Hidalgo Association consists of deep, slowly and moderately permeable soils that typically have a gray or dark grayish brown clay loam or sandy clay loam surface layer. The corresponding soil symbol appears to be 28, Hidalgo sandy clay loam, 0 to 1 percent slopes and 52, Raymondville clay loam, 0 to 1 percent slopes.

SEISMIC COEFFICIENTS

Based upon a review of Section 1613 Earthquake Loads 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 and our experience in the area, the upper 100 feet of soil may be may be characterized as a stiff soil profile.

• Risk-Targeted Maximum Considered Earthquake Ground Motion Response Accelerations for the Conterminous United Stated of a 0.2-Second, Spectral Response Acceleration (5% of Critical Damping): Ss = 0.042g.

• Risk-Targeted Maximum Considered Earthquake Ground Motion Response Accelerations for the Conterminous United States of a 1-Second, Spectral Response Acceleration (5% of Critical Damping): S1 = 0.014g.

• Value of Site Coefficient: Fa = 1.6.

• Value of Site Coefficient: Fv = 2.4.

The Maximum Considered Earthquake Spectral Response Accelerations are as follows:

• 0.2 sec., adjusted Sms = 0.068g.

• 1 sec., adjusted Sm1 = 0.035g.

The Design Spectral Response Acceleration Parameters are as follows:

• 0.2 sec.: SDS = 0.045g.

• 1 sec.: SD1 = 0.023g.

STRATIGRAPHY

On the basis of the borings drilled for this site, the majority of the subsurface stratigraphy can be described as moderate plastic to plastic, fine-grained soils with various amounts of sand. An about 2-1/2 ft of coarse-grained soil was observed in Boring B-6. Each stratum has been designated by grouping materials that possess similar physical and engineering characteristics. The boring logs should be consulted for more specific stratigraphic information. Unless noted on the boring logs, the lines designating the changes between various strata represent approximate boundaries. The transition between materials may be gradual or may occur between recovered samples. The stratification given on the boring logs, or described herein, is for use by RKI in its analyses and should not be used as the basis of design or construction cost estimates without realizing that there can be variation from that shown or described.

The boring logs and related information depict subsurface conditions only at the specific locations and times where sampling was conducted. The passage of time may result in changes in conditions, interpreted to exist, at or between the locations where sampling was conducted.

GROUNDWATER

Groundwater was not observed in the borings either during or immediately upon completion of the field drilling activities. The boreholes were left open for the duration of the field exploration phase to allow monitoring of water levels and remain dry. The groundwater level in the borings may not have stabilized, particularly in less permeable cohesive soil, prior to backfilling. Consequently, the indicated groundwater levels, or lack thereof, may not represent present or future levels. Groundwater levels may vary significantly over time due to the effects of seasonal variation in precipitation, recharge, or other factors not evident at the time of exploration. The construction process itself may also cause variations in the groundwater levels. Groundwater may become perched at the planned fill/soil interface, or within permeable soils or backfill.

FOUNDATION RECOMMENDATIONS AND CONSIDERATIONS

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 elevation existing at the time of our study and the stratigraphic conditions encountered in the borings at the time of our study. If site grading plans differ from the assumed finished grades, we must be retained to review the site grading plans prior to bidding the project for construction. If needed and/or if desired, we will reexamine our analyses and make supplemental recommendations.

Site features that will influence the geotechnical approach to the proposed building include:

• Potential to encounter shallow groundwater seepage during excavation and site grading operations;

• Potential for sensitive soils that are easily disturbed to construction traffic;

• Presence of expansive soil/fill and potential for soil-related movements;

• Depth of planned fill for site improvements and potential for soil-related movements; and

• Potential for light to moderate foundation loads.

Please note that the foundation capacities presented herein are based on the Allowable Stress Design methodology.

GROUNDWATER SEEPAGE AND DEWATERING

As discussed herein, groundwater was not observed in the borings either during or immediately upon completion of the field drilling activities. However, it is possible for groundwater to exist beneath this site on a transient basis following periods of precipitation (see section titled Groundwater). Fluctuations in groundwater levels and groundwater seepage should be anticipated during construction. The contractor should be made aware and ready to handle/intercept potential water for anticipated excavations.

Where excavations extend into the underlying soil layers groundwater seepage should be anticipated.

Raising the finished grade and performing the excavations during the drier season (such as summertime) will aid in reducing the potential for groundwater seepage, but will not eliminate the risk.

The General Contractor should be prepared to control excess water encountered in the excavations due to perched water, seepage from natural or constructed interfaces (such as but not limited to fill and natural soil interface, utility backfills, other), and/or rainfall. Proper construction procedures and equipment will be critical for proper performance of the dewatered excavations. Additionally, protection of personnel entering the excavations and providing a dry, stable subgrade upon which to construct foundations will be crucial.

SOFT SENSITIVE SOILS

Site grading may potentially expose soft, wet, subgrade soils that require a special grading approach to establish a stable subgrade. When these sensitive soils are encountered, the geotechnical engineer should be contacted to observe the exposed subgrade. Proof-rolling and moisture conditioning of exposed subgrades may be waived if, in the opinion of the geotechnical engineer, it could result in disturbance to an otherwise stable subgrade. When these sensitive soils are encountered, we recommend excavating the subgrade areas using a trackhoe equipped with a toothless bucket working above the proposed subgrade.

Grading/construction equipment or foot traffic should be prohibited from trafficking on the potentially sensitive subgrade. If the exposed subgrade is found to be overly soft, the subgrade can be improved by placing an 18-inch thick layer of compacted, crushed rock to provide a stable working platform.

For the crushed rock working platform, the initial lift of backfill should consist of an 18-inch thick loose lift of 2-inch-minus crushed rock. This procedure may be further enhanced by placing a geogrid on the subgrade before placing the crushed rock, provided that the geogrid will not interfere with foundation or utility construction. The crushed rock should be pushed into the excavation with the equipment working on top of the rock platform. After this initial layer is placed, the crushed rock should be thoroughly surface-compacted with a self-propelled vibratory roller. Subsequent lifts of finer-gradation crushed rock or select structural fill can be placed conventionally. As an alternative, consideration can be given to pushing “bull rock” into the soft subgrade until subgrade yielding stops; however, this approach may be restricted in areas that will not interfere with foundation or utility construction. Furthermore, deep soil mixing or other ground improvements may be used to improve the exposed subgrades.

EXPANSIVE, SOIL-RELATED MOVEMENTS

The anticipated ground movements due to swelling of the underlying soils at this 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 2 inches 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 (estimated active zone of 8 ft).

For reworked on-site materials or for imported materials used for site grading, if any, the PVR values could vary and will depend on the quality and characteristics of the materials used. Recommendations for building pad select fill are provided herein.

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....) or if water seeps into the soils to greater depths than the assumed active zone depth due to deep trenching or excavations.

PVR REDUCTION RECOMMENDATIONS

As mentioned previously, for purposes of this geotechnical engineering report, the FGE of the proposed restroom building was assumed to be 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.

To reduce expansive, soil-related movements in at-grade construction beneath the building’s footprint area to about 1 inch, we recommend to remove the upper 24 inches (2 ft) of the existing subgrade soils, and replace them with properly-compacted, suitable, select fill materials within the proposed building’s footprint area up to its FGE, which was assumed to be 12 inches (1 ft) above the ground surface elevation existing at the time of our study. Keep in mind that the estimated PVR values are computed based on the recommendations for the selection and placement of suitable, select fill materials which are addressed in the Foundation Construction Considerations section of the report.

Drainage Considerations When overexcavation and select fill replacement is selected as a method to reduce the potential for expansive, soil-related movements at any site, considerations of surface and subsurface drainage may be crucial to construction and adequate foundation performance of the soil-supported building. Filling an excavation in relatively impervious clay soils with relatively pervious select fill material creates “bathtub” beneath the building, 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 building 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 area during construction;

• Sloping of the top of the subgrade with a minimum downward slope of 1.5 percent out to the base of a dewatering trench located beyond the building perimeter;

• 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 building) over the select fill material and any perimeter drain extending beyond the buildings 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 building’s perimeter;

• 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 slab.

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.

SHALLOW FOUNDATIONS

The proposed restroom building may be founded on rigid-engineered beam and slab-on-fill foundation and/or on conventional spread and/or continuous footing foundations, provided that the shallow foundation type(s) can be designed to withstand the estimated soil-related movements, as discussed herein, without impairing either the structural or the operational performance of the buildings.

Allowable Soil-Bearing Capacity

Shallow foundations bearing on new, properly-compacted, suitable, select fill materials may be proportioned using the design parameters shown in the following table:

Shallow Foundation Design Parameters

Minimum depth below FGE: 24 in.

Minimum beam width: 12 in.

Maximum allowable soil-bearing pressure for continuous footings or grade beams: 1,900 psf

Maximum allowable soil-bearing pressure for spread footings or widened beams: 2,300 psf

Where psf = pounds per square feet

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, and provided that the subgrade is prepared in accordance with the recommendations outlined in the Site Preparation subsection of the Foundation Construction Considerations section of this report, as well the ground improvement procedure presented in the PVR Reduction Recommendations subsection of the Foundation Recommendations and Considerations section of this report is implemented. It is anticipated that the total settlements will be in the order of about 1 inch. Differential settlements typically are estimated to be about one-half the total estimated 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, RKI should be informed of the deviations in order to reevaluate our recommendations and design criteria.

Wire Reinforcement Institute (WRI) Criteria

The slab-on-fill or on-grade shallow foundation may also be designed using WRI design criteria. On the basis of the subsurface stratigraphy encountered, a general effective plasticity index for the proposed building’s of 31 percent and a climatic rating (Cw) of 15 should be utilized for the design of the building’s foundation.

Construction Considerations

Shallow foundation excavations should be observed by the Geotechnical Engineer or their 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/loose materials and water are not present in the excavations. If soft soils 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 elevations.

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 excavations 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.

FLATWORK AND FLOOR SLABS

It should be noted that ground-supported flatwork such as walkways, driveways, courtyards, sidewalks, etc., will be subject to the same magnitude of potential soil-related movements as discussed previously (see Expansive, Soil-Related Movements subsection of the Foundation Recommendations and Considerations section of this report) for this site. 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 building’s foundation, and to facilitate rapid drainage away from the building’s foundation. Failure to provide positive drainage away from the building can result in localized differential vertical movements in the soil-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 buildings. These slope requirements can result in drainage problems for building supported on expansive soils. We recommend that, on all sides of the building, the maximum permissible slope be provided away from the building.

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

Where a select fill overbuild is provided outside of the floor slab/foundation footprint, 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.

Leaks should be immediately repaired.

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

SITE PREPARATION

The building’s area 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 building’s footprint area. Further, we recommend that the site improvement procedure presented in the PVR Reduction Recommendations section of this report be implemented in order to reduce expansive, soil-related movements in at-grade construction to about 1 inch.

The exposed subgrade should be thoroughly proofrolled to locate weak and yielding soils. 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 their representative to document subgrade conditions and preparation. Weak or soft areas identified during proofrolling should be removed and replaced with a suitable, compacted select fill or treated soil in accordance with the recommendations presented under the Select Fill subsection of this section of the report. If the soil 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 to aid in drying the soils and develop a firm working surface. Proofrolling operations and any excavation/backfill activities should be observed by RKI representatives to document subgrade preparation.

Upon completion of the proofrolling operations and just prior to fill placement, the exposed subgrade should be moisture-conditioned by scarifying to a minimum depth of 8 in. and recompacting to a minimum of 98 percent of the maximum dry density as determined from the American Society for Testing and Materials (ASTM) D698, Compaction Test. The moisture content of the subgrade should be maintained within the 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. Alternative select fill materials shall have a maximum liquid limit of 40 percent, a plasticity index between 7 and 20 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.

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 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 RKI personnel for compaction as specified.

TRENCH EXCAVATION SLOPING/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 development of the trench safety plan, which may require the collection of specific geotechnical data and could include designs for sloping and benching of various types of shoring, is beyond the scope of this study. Any such designs and safety plans shall be developed and prepared in accordance with current Occupational Safety and Health Administration (OSHA) guidelines and other applicable industry standards.

EXCAVATION EQUIPMENT

The boring logs are not intended for use in determining construction means and methods and may therefore be misleading if used for that purpose. We recommend that General Contractors and their subcontractors interested in bidding on the work perform their own tests in the form of test pits to determine the quantities of the different materials to be excavated, as well as the preferred excavation methods and equipment for this site.

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 Recommendations and Considerations 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.

DESIGN RECOMMENDATIONS AND CONSIDERATIONS FOR THE PROPOSED

DETENTION POND AND STORMWATER DRAINAGE ALIGNMENT

Earthen embankments may be considered around the perimeter of the proposed detention pond.

Drainage is an important key to the successful performance of any structure. Good surface drainage should be established prior to and maintained after construction to help prevent water from ponding within or adjacent to the structure and to facilitate rapid drainage away from the structure.

Site features that will influence the geotechnical approach to the proposed detention pond project include:

• Relatively shallow groundwater encountered within the site;

• Excavations that will extend at to several feet below the ground surface elevation;

EXCAVATION DEWATERING

As discussed herein, groundwater was not observed in the borings either during or immediately upon completion of the field drilling activities. It is possible for groundwater to exist beneath this site at shallower depths on a transient basis following periods of precipitation. Hence, the observed groundwater levels may not represent the conditions at the time of construction and may be encountered shallower than that observed in our boings. Typically, the Contractor is responsible for designing, installing and maintaining a dewatering system for groundwater control and taking precautions to avoid distress to nearby existing structures, as a result of dewatering. We recommend the Contractor consider retaining a dewatering expert to assist in identifying, implementing and monitoring the most suitable and cost-effective method to control groundwater.

Excavations below the groundwater table generally require lowering the piezometric level to permit construction in a relatively dry state. This should be performed to control seepage into the excavations and to reduce artesian water pressures below the bottom of the excavations.

In cohesive soils where seepage is usually low, groundwater is generally managed by collection in trench bottom sumps for pumped disposal. Care should be taken to have a redundant pumping system that allows for overnight pumping. Water must not be allowed to pond in the trench bottoms. The softening of soils can lead to instability and sloughing of trench sidewalls. In addition, if cohesive soils contain lenses/layers of water-bearing granular or cohesionless soils, they may have to be dewatered using techniques for cohesionless soils. Deep wells and/or well point systems, as well as sumps and pumps after completion of the excavations are commonly used. The implementation of one and/or more of these methods should be anticipated for the construction of the proposed structures.

Generally, the groundwater depth should be lowered to a depth of at least 5 ft below the planned excavation bottom to provide a firm working surface. Extended and/or extensive dewatering can result in settlement of existing structures/utilities in the vicinity; the Contractor is to take necessary precautions to minimize the effects on these structures. We recommend that a pre-construction survey of nearby structures/utilities be performed prior to construction to document existing conditions / distress prior to construction commencement.

Seasonal variations and/or unforeseen environmental conditions may cause elevated groundwater to be encountered during excavation and construction activities. We suggest the Contractor provide a line item for dewatering in the bid package in the event that dewatering is required.

The design of dewatering systems is beyond the scope of this study. The General Contractor should be prepared to control excess water encountered in the excavations due to perched water pockets, seepage, and/or rainfall. Proper construction procedures and equipment will be critical for proper performance of the dewatered excavations. Additionally, protection of personnel entering the excavations and providing a dry, stable subgrade upon which to construct foundations will be crucial.

Alternative methods such as jet grouting, grout injection, deep soil mixing, or other ground improvement techniques may be considered to reduce the groundwater seepage and improve/maintain exposed subgrades for the proposed improvements.

TEMPORARY EXCAVATION SLOPING AND SHORING

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 development of the trench safety plan, which may require the collection of specific geotechnical data and could include designs for sloping and benching of various types of shoring, is beyond the scope of this study. Any such designs and safety plans shall be developed and prepared in accordance with current Occupational Safety and Health Administration (OSHA) guidelines and other applicable industry standards.

To assist in preparing an excavation safety plan, we have classified the soils encountered at this site based on the data collected during this study. The on-site clay soils encountered within this site are classified as Type “B” soils under current OSHA regulations pertaining to excavations. This classification is based on the observed cohesive nature of the soil and the anticipated vibration from nearby traffic.

In excavations penetrating these soils, the sloping and benching schemes specified for Type “B” soils under the OSHA regulations require that the excavation sidewalls be sloped no steeper than 1:1 (horizontal:vertical). The sand soils encountered within this site and all the soils below the groundwater levels are classified as Type “C” soils under current OSHA regulations pertaining to excavations. In excavations penetrating these soils, the sloping and benching schemes specified for Type “C” soils under the OSHA regulations require that the excavation sidewalls be sloped no steeper than 1-1/2:1 (horizontal:vertical).

The contractor should be aware that excavation depths and inclinations (including adjacent existing slopes) should not exceed those specified in local, state or federal safety regulations, e.g., OSHA Health and Safety Standards for Excavations, 29 CFR Part 1926, or successor regulations. Such regulations are strictly enforced and, if not followed, the contractor, or earthwork or utility subcontractors could be subjected to substantial penalties. Construction site safety is the sole responsibility of the contractor, who shall also be solely responsible for the means, methods and sequencing of construction operations.

Temporary slopes left open may undergo sloughing and result in an unstable situation. The contractor should evaluate stability and failure consequences before open cut slopes are made. Minor sloughing of open face slopes may occur. If the slope is expected to remain open for an extended time, an impermeable membrane covering the slopes could be considered as a means to reduce the potential for slope degradation and instability.

It is important to note that soils encountered in the construction excavations may vary across the site and that even if the OSHA criteria are used, there is a potential for slope failure. If different subsurface conditions are encountered at the time of construction, RKI should be contacted to evaluate the conditions encountered.

An excavated temporary slope may not be feasible at all locations, and a temporary retention system may be required. While many different types and configurations of retention systems can be used, the more common include trench boxes. The design of the system should be performed by the contractor that performs the work. The design should account for the possibility of overexcavating unsuitable or disturbed subgrades. The contractor should also be responsible for monitoring the performance of the retention system. OSHA regulations should be followed with respect to bracing requirements. Worker safety and classification of soil type is the responsibility of the contractor. Presented in the following sections are considerations for the retention system.

EXCAVATION EQUIPMENT

The boring logs are not intended for use in determining construction means and methods and may therefore be misleading if used for that purpose. We recommend that earthwork and utility contractors interested in bidding on the work perform their own tests in the form of test pits to determine the quantities of the different materials to be excavated, as well as the preferred excavation methods and equipment for this site.

SLOPE INCLINATION RECOMMENDATIONS

Based on the subsurface stratigraphy encountered in the borings, we recommend that the side slopes of the proposed detention pond structure not be any steeper than of 3:1 (Horizontal : Vertical [H:V]). If the 3:1 (H:V) slope is not feasible due to property restrictions, we should be retained to review and modify our recommendations.

PAVEMENT RECOMMENDATIONS

Flexible pavement recommendations for a 20-year design period are presented in this report. 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.

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 the moderately plastic to plastic, clay soils.

On the basis of our experience with similar subsurface conditions in this area, a design California Bearing Ratio (CBR) value of 3 was assigned to evaluate the pavement components.