Geotechnical Engineering Report CFTRL.pdf

USDA – Agricultural Research Service (ARS) Master Plan & Program of Requirements (POR) Edinburg, TX – Cattle Fever Tick Research Laboratory Revised Final Submittal – December 10, 2021

Appendix I: Geotechnical Engineering Report

REPORT C OVER PAGE

Geotechnical Engineering Report

Edinburg Drainage Improvements Edinburg, Texas December 17, 2020

Terracon Project No. 88205114

Prepared for:

Burns & McDonnell Engineering Company, Inc.

Bloomington, New Mexico

Prepared by:

1506 Mid Cities Drive Consultants, Inc.

Pharr, Texas

Edinburg Drainage Improvements ■ Edinburg, Texas December 17, 2020 ■ Terracon Project No. 88205114

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

PAVEMENTS

DETENTION POND CONSIDERATIONS

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

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INTRODUCTION

Geotechnical Engineering Report Edinburg Drainage Improvements

22675 Moorefield Rd Edinburg, Texas

Terracon Project No. 88205114 December 17, 2020

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Edinburg Drainage Improvements to be located at 22675 Moorefield Rd in Edinburg, Texas. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Foundation design and construction

■ Groundwater conditions ■ Floor slab design and construction

■ Site preparation and earthwork ■ Seismic site class per IBC

■ Excavation considerations ■ Pavement design and construction

The geotechnical engineering Scope of Services for this project included the advancement of four test borings to depths ranging from approximately 10 to 20 feet below existing site grades.

Maps showing the site and boring locations are presented in the Site Location and Exploration Plan sections, respectively. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs in the Exploration Results section.

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel Information The project site is located at 22675 Moorefield Rd in Edinburg, Texas.

Latitude/Longitude: 26.38698°, -98.34387°.

See Site Location

Existing Improvements Existing buildings and pavements at the location of the proposed building.

Undeveloped land at the location of the proposed detention ponds.

Current Ground Cover Asphaltic concrete pavement, native grass, and bare soils.

Existing Topography Relatively flat and level.

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Geology

Based on the Geologic Atlas of Texas, McAllen – Brownsville prepared by The University of Texas, the site is located on the Goliad Formation of the Pliocene period of the Tertiary Age. The Goliad formation is comprised of clay, sand, sandstone, marl, caliche, limestone, and conglomerate. The clay is commonly light shades of pink green with calcareous concretions.

The sand and sandstone are medium to very coarse grained, in part cross bedded mostly quartz, with some black and red chert. The conglomerate is composed of black chert and dark siliceous granules and pebbles in a calcareous (caliche) matrix. The sandstone and conglomerate are locally well bedded. The marl and limestone are poorly bedded or massive.

Tertiary vertebrate and reworked cretaceous invertebrate fossils are fairly common. The formation thickness is up to 600 feet.

PROJECT DESCRIPTION

Information Provided By Mr. Robert Darnell via email on November 6, 2020.

Project Description

We understand that the proposed development may include the construction of a single-story building. Development also include construction of flexible pavement for the driveway and parking areas. We also understand the on-site soils need to be evaluated for future reuse as earthen berms.

Construction Type We anticipate that the building will likely consist of pre-engineered metal structure with CMU, brick veneer or stucco exterior walls supported by a shallow foundation system.

Finished Floor Elevation, FFE About 4 feet above existing grade.

Maximum loads (assumed)

■ Columns: 30 kips

■ Walls: 1 kip per linear foot

■ Slabs: 125 pounds per square foot

Grading/Slopes Up to 1 foot of cut and 2 feet of fill may be required to develop final grade.

Pavements

We understand flexible (asphalt) pavement sections will be considered at this project. Anticipated traffic is as follows:

■ Standard Duty: 30,000 ESALs

■ Standard to Heavy Duty: 50,000 ESALs

The pavement design period is 20 years.

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GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and foundation options. Conditions encountered at each exploration point are indicated on the individual logs. The individual logs and the GeoModel can be found in the Exploration Results section of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer Layer Name General Description

1 SAND

Clayey sand (SC) Dense to very dense; moderate cementation

2 CLAY

Sandy lean clay (CL) Medium stiff to hard

Groundwater Conditions

The boreholes were observed while drilling and at the completion of drilling for the presence and level of groundwater. Groundwater was not observed during or upon completion of drilling in both conducted borings.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project. The boreholes were backfilled with on-site soil cuttings after completion of the groundwater level observations.

GEOTECHNICAL OVERVIEW

Our findings indicate the proposed building structure can be supported on a shallow foundation system. The desired foundation system may be used at this site provided the site and foundation are designed and constructed as recommended in this report.

The suitability and performance of a soil supported foundation for a structure depends on many factors including the magnitude of soil movement expected, the type of structure, the intended use of the structure, the construction methods available to stabilize the soils, and our understanding of the owner’s expectations of the completed structure's performance.

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Expansive soils are present on this site. This report provides recommendations to help mitigate the effects of soil, shrinkage and expansion. However, even if these procedures are followed, some movement in the structure should be anticipated. Eliminating the risk of movement may not be feasible, but it may be possible to further reduce the risk of movement if significantly more expensive measures are used during construction. We would be pleased to discuss other construction alternatives with you upon request.

Moreover, moderate cementation soils with caliche features were encountered at borings B-1, B- 2, and D-2. Caliche is a calcium-carbonate cemented material; it has a close resemblance to rock when it is dry. The N-values of caliches was greater than 50 below per foot of penetration. Caliche is typically difficult to excavate. Excavations in caliche materials may require heavy equipment.

Geotechnical engineering recommendations for foundation systems and other earth connected phases of the project are outlined below. The recommendations contained in this report are based upon the results of data presented herein, engineering analyses, and our current understanding of the proposed project.

The General Comments section provides an understanding of the report limitations.

Field Percolation

Two boreholes (D-1 and D-2) were drilled in the proposed leech field to approximate depths of 4 and 6 feet below existing grade, respectively. The percolation testing was conducted generally in accordance with local practice. Based on the boreholes performed within the proposed area, the soils in the boring areas consisted of sandy lean clay (CL) and clayey sand (SC). Based on the percolation tests, the percolation rate for both boreholes were about 10.5 and 12.0 inch/hour, respectively.

EARTHWORK

Earthwork will include clearing and grubbing, excavations and fill placement. The following sections provide recommendations for use in the preparation of specifications for the work.

Recommendations include critical quality criteria as necessary to render the site in the state considered in our geotechnical engineering evaluation for foundations.

Site Preparation

Construction area should be stripped of all vegetation, topsoil, pavements and other unsuitable material. Additional excavation as recommended in this report or as needed should be performed within the proposed building area. Once final subgrade elevation has been achieved, the exposed

Responsive ■ Resourceful ■ Reliable 5 subgrade should be carefully proofrolled with a 15-ton pneumatic roller or a fully loaded dump truck to detect weak zones in the subgrade. Special care should be exercised when proofrolling the fill soils to detect soft/weak areas. Weak areas detected during proofrolling, as well as zones of fill containing organic matter and/or debris should be removed and replaced with select fill in the proposed building area. Proper site drainage should be maintained during construction, so that ponding of surface runoff does not occur and cause construction delays and/or inhibit site access.

Subsequent to proofrolling, and just prior to placement of fill, the exposed subgrade within the construction area should be evaluated for moisture and density. If the moisture, density, and/or the requirements do not meet the criteria described in the table below, the subgrade should be scarified to a minimum depth of 8 inches, moisture adjusted and compacted to at least 95 percent of the Standard Effort (ASTM D-698) maximum dry density. Select fill should meet the following criteria.

Proper site drainage should be maintained during construction, so that ponding of surface runoff does not occur and cause construction delays and/or inhibit site access.

Fill Material Types

Engineered fill should consist of approved materials, free of organic material, debris and particles larger than about 2 inches. The maximum particle size criteria may be relaxed by the geotechnical engineer of record depending on construction techniques, material gradation, allowable lift thickness and observations during fill placement. Soils for use as engineered fill material should conform to the following specifications:

Fill Type 1 USCS Classification Acceptable Location for Placement

Aggregate Base Course 2

SC, GC, Caliche, Crushed Limestone, Crushed Concrete

Top 6 inches of building pad area.

Select Fill CL and/or SC

(7≤PI≤20)

Must be used to construct the pad and all grade adjustments within the construction area.

On-Site Soils SC

On-site SC soils may be suitable for use as fill within the building, pavement and landscaping areas as long as they are free from organics, cohesive and have a Plasticity Index (PI) between 7 and 20.

1. Prior to any filling operations, samples of the proposed borrow and on-site materials should be obtained for laboratory moisture-density testing. The tests will provide a basis for evaluation of fill compaction by in-place density testing. A qualified soil technician should perform sufficient in-place density tests during the filling operations to evaluate that proper levels of compaction, including dry unit weight and moisture content, are being attained.

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Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Fill Lift Thickness The fill should be placed in thin, loose lifts of about 8 inches, with compacted thickness not exceeding 6 inches.

Compaction Requirements (on-site soils, subgrade, and select fill)

The on-site soils, subgrade, and select fill should be compacted to at least 95 percent of the Standard Effort (ASTM D-698) maximum dry density within 2 percentage points of the optimum moisture content.

Utility Trench Backfill

Utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the structures should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the structures. The trench should provide an effective trench plug that extends at least 5 feet from the face of the any structure exterior. The plug material should consist of cementitious flowable fill or low permeability clay. The trench plug material should be placed to surround the utility line. If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

Care should be taken that utility trenches are properly backfilled. Backfilling should be accomplished with properly compacted select fill with loose lift thickness of generally 8 niches except for the first lift above the utility pipes that can be relaxed to 12 inches. Compaction should be accomplished with a hand-held compaction device inside utility trenches. Select fill should be competed to at least 95% Standard Proctor dry density (ASTM D-698) in the range of +/- 2 percentage points of optimum moisture for engineered fill.

Excavation

It is anticipated that excavation of the very dense and hard soils, encountered below existing site grades, may require the use of specialized heavy-duty equipment, together with ripping or jack-hammering to advance the excavation and removal. Consideration should be given to obtaining a unit price for difficult excavation in the contract documents for the project.

2. Crushed limestone and crushed concrete material should meet the requirements of 2014 TxDOT Item 247, Type A, or D, Grades 1-2 and 3. The select fill materials should be free of organic material and debris, and should not contain stones larger than 2 inches in the maximum dimension. The clayey gravel and caliche materials should meet the gradation requirements of Item 247, Type B, Grades 1-2 and 3 as specified in the 2014 TxDOT Standard Specifications Manual and a Plasticity Index between 7 and 20.

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We also note difficult excavation condition could be encountered during grading and foundation excavations. The depths of the encountered cemented soils with caliche features are shown in the individual boring logs in the Exploration Results section. We note that the soil types encountered on the project site have a high hydraulic conductivity and are susceptible to erosion. Excavations may need to be formed due to the possibility of erosion/sloughing of these soils.

All excavations must comply with the applicable Federal, State, and local safety regulations and codes, and especially with the excavation standards of the Occupational Safety and Health Administration (OSHA). Per the OSHA soil classification, the on-site materials are generally classified as Type A and B soils. Temporary slopes of 1.5H:1V may be used. Construction site safety, including excavation safety, is the sole responsibility of the Contractor as part of its overall responsibility for the mean, methods, and sequencing of construction operations.

Terracon’s recommendations for excavation support are intended for the Client’s use in planning the project and do no relieve the Contractor of its responsibility to construct, support, and maintain safe slopes. Under no circumstances should the following recommendations be interpreted to mean that Terracon is assuming responsibility for either construction site safety or the Contractor’s activities.

Wet Weather/Soft Subgrade Conditions

Construction operations may encounter difficulties due to the wet or soft surface soils becoming a general hindrance to equipment due to rutting and pumping of the soil surface, especially during and soon after periods of wet weather.

If the subgrade cannot be adequately compacted to minimum densities as described above, one of the following measures will be required: (1) removal and replacement with select fill, (2) chemical treatment of the soil to dry and increase the stability of the subgrade, or (3) drying by natural means if the schedule allows.

In our experience with similar soils in this area, chemical treatment is an efficient and effective method to increase the supporting value of wet and weak subgrade. Terracon should be contacted for additional recommendations if chemical treatment of the soils is needed.

Prior to placing any fill, all surface vegetation, topsoil, possible fill material and any otherwise unsuitable materials should be removed from the construction areas. Wet or dry material should either be removed or moisture conditioned and recompacted. After stripping and grubbing, the subgrade should be proof-rolled where possible to aid in locating loose or soft areas. Proof-rolling can be performed with a 15-ton roller or fully loaded dump truck. Soft, dry and low-density soil should be removed or compacted in place prior to placing fill.

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Grading and Drainage

Positive drainage should be provided during construction and maintained throughout the life of the development. Infiltration of water into utility trenches or foundation excavations should be prevented during construction. Planters and other surface features which could retain water in areas adjacent to the building should be sealed or eliminated. In areas where sidewalks or paving do not immediately adjoin the structure, we recommend that protective slopes be provided with a minimum grade of approximately 3 percent for at least 10 feet from perimeter walls, except in areas where ADA ramps are required, these areas should comply with state and local regulations.

Backfill against exterior walls, and in utility and sprinkler line trenches, should be well compacted and free of all construction debris to reduce the possibility of moisture infiltration.

Downspouts, roof drains or scuppers should discharge into extensions when the ground surface beneath such features is not protected by exterior slabs or paving. Consideration should be given to extending drainage piping to day light at the face of curbs then empty onto pavement surfaces.

Sprinkler systems should not be installed within 5 feet of foundation walls. Landscaped irrigation adjacent to the foundation systems should be minimized or eliminated.

Where paving or flatwork abuts the structure, effectively seal and maintain joints to prevent surface water infiltration. The joint between the sidewalk curb and building should be sealed. The sidewalk curb along the building line is recommended to prevent water from standing over the joint between the building and sidewalk should the outside edge of the slab rise due to soil swelling at the sidewalk edge.

Utility trenches are a common source of water infiltration and migration. All utility trenches that penetrate beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches that could migrate below the building.

We recommend constructing an effective clay “trench plug” that extends at least 5 feet out from the face of the building exterior. The plug material should consist of clay compacted at a water content at or above the soils optimum water content. The clay fill should be placed to completely surround the utility line and be compacted in accordance with recommendations in this report.

Earthwork Construction Considerations

Shallow excavations, for the proposed structure, are anticipated to be accomplished with heavy-duty construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of floor slabs. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over, or adjacent to construction area should be removed. If the subgrade freezes, desiccates, saturates, or is

Responsive ■ Resourceful ■ Reliable 9 disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted, prior to floor slab construction.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local, and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety, or the contractor's activities; such responsibility shall neither be implied nor inferred.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation and top soil, proof-rolling and mitigation of areas delineated by the proof-roll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of compacted fill in the building area and 5,000 square feet in pavement areas. One density and water content test for every 50 linear feet of compacted utility trench backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. In the event unanticipated conditions are encountered, the Geotechnical Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

SHALLOW FOUNDATIONS

Based upon the subsurface conditions observed during our investigation a shallow (slab-and-grade, strip/spread footings) foundation system would be appropriate to support the structural loads of the proposed structure provided the subgrade is prepared as discussed in this report.

Recommendations for this type of foundation system is provided in the following sections, along with other geotechnical considerations for this project.

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The slab-on-grade foundation may be designed using the following parameters provided the subgrade is prepared as outlined in the Earthwork and Floor Slabs sections of this report:

Slab-on-Grade Foundation - Design Parameters

Item Description

Select Fill Pad Minimum 2 feet of select fill over 6 inches of moisture conditioned and compacted on-site soils.

Allowable Bearing Pressure 1

Compacted Select Fill Net Total Load - 3,000 psf

Climatic Rating 15

Design Plasticity Index 21

Soil Support Index 0.93

Estimated PVR 2 About 1 inch or less

Approximate Total Settlement 3 About ½ inch

Estimated Differential Settlement 3 Approximately ½ of total settlement

Min. Perimeter Grade Beam Embedment 4 24 inches below finished grade

1. The net allowable bearing pressure provided above include a factor of safety of at least 2.

2. The slab-on-grade foundation system should be designed to tolerate the anticipated soil movement and provide satisfactory support to the proposed structure. The foundation should have adequate exterior and interior grade beams to provide sufficient rigidity to the foundation system such that the slab deflections that result are considered tolerable to the supported structure.

3. This estimated post-construction settlement is assuming proper construction practices are followed.

Settlement response of a select fill supported slab is influenced more by the quality of construction than by soil-structure interaction. Therefore, it is essential that the recommendations for foundation construction be strictly followed during the construction phases of the pad and foundation.

4. To bear within the select fill or moisture conditioned and recompacted on-site soils. The grade beams may be thickened and widened where necessary to support column loads.

Construction Considerations for Slab-on-grade Foundation

Excavations for grade beams should be performed with equipment capable of providing a relatively clean bearing area. The bottom 6 inches of the excavations should be completed with a smooth-mouthed bucket or by hand labor. The excavations should be neatly excavated and properly formed. Debris in the bottom of the excavation should be removed prior to reinforcing steel placement. Water should not be allowed to accumulate at the bottom of the excavation. Due to the presence of dry and sandy soils, caving of grade beam excavation may occur. Therefore, the foundation contractor should be prepared to use forms.

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To reduce the potential for groundwater seepage into the excavations and to minimize disturbance to the bearing area, we recommend that concrete and reinforcing steel be placed as soon as possible after the excavations are completed. Excavations should not be left open for more than 36 hours. The bearing surface of the grade beams should be evaluated after excavation is completed and immediately prior to placing concrete.

SEISMIC CONSIDERATIONS

The seismic design requirements for buildings and other structures are based on Seismic Design Category. Site Classification is required to determine the Seismic Design Category for a structure.

The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC).

Based on the soil properties encountered at the site and as described on the exploration logs and results, it is our professional opinion that the Seismic Site Classification is C. Subsurface explorations at this site were extended to a maximum depth of 20 feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

FLOOR SLABS

Information regarding the final grade elevation was not provided. We anticipate that Finished Floor Elevation (FFE) may be at about 4 feet above the existing grade. If significant fill or cuts are planned, Terracon should be notified to review and/or modify our recommendations given in this subsection.

The subsurface soils at this site generally exhibit low to moderate expansion potential. Based on the information developed from our field and laboratory programs and on method TEX-124-E in the Texas Department of Transportation (TxDOT) Manual of Testing Procedures, we estimate that the subgrade soils at this site exhibit a Potential Vertical Rise (PVR) of about 1 to 1½ inches in present condition.

The actual movements could be greater if poor drainage, ponded water, and/or other sources of moisture are allowed to infiltrate beneath the structure after construction. We have provided recommendations to maintain the site PVR to about 1 inch or less. In addition, positive structure perimeter drainage should be carefully observed.

After site stripping and over-excavation activities as recommended, place the select fill over a moisture conditioned and compacted fill body. The building pad should be constructed directly below the floor slab and should also extend a minimum of 3 feet beyond the edge of the proposed structure area, including any movement sensitive flatwork that abuts the structure such as

December 17, 2020 ■ Terracon Project No. 88205114

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The subgrade and select fill soils should be prepared as outlined in the Earthwork section of this report, which contains material and placement requirements for select fill, as well as other subgrade preparation recommendations. The floor slab should be designed using the following recommendations.

Floor Slab Design Parameters

Item Description Excavation Minimum 6 inches.

Floor Slab Support 1 Minimum 2 feet of select fill over 6 inches of moisture conditioned and compacted on-site soils.

Estimated Modulus of Subgrade Reaction 2

125 pounds per square inch per inch (psi/in) for point loads.

Estimated Potential Vertical Rise (PVR) About 1 inch or less

1. Floor slabs should be structurally independent of structure footings or walls (if any) to reduce the possibility of floor slab cracking caused by differential movements between the slab and foundation.

2. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in Earthwork, and the floor slab support as noted in this table. It is provided for point loads. For large area loads the modulus of subgrade reaction would be lower.

The use of a vapor retarder should be considered beneath concrete slabs on grade covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Saw-cut control joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations refer to the ACI Design Manual. Joints or cracks should be sealed with a water-proof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates differential movement between the walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the length of the structural dowels. The Structural Engineer should account for potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates differential movement between the walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the length of the structural dowels. The Structural Engineer should account for potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

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Floor Slab Construction Considerations

Finished subgrade, within and for at least 10 feet beyond the floor slab, should be protected from traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are constructed. If the subgrade should become damaged or desiccated prior to construction of floor slabs, the affected material should be removed, and structural fill should be added to replace the resulting excavation. Final conditioning of the finished subgrade should be performed immediately prior to placement of the floor slab support course.

The Geotechnical Engineer should approve the condition of the floor slab subgrades immediately prior to placement of the floor slab support course, reinforcing steel, and concrete. Attention should be paid to high traffic areas that were rutted and disturbed earlier, and to areas where backfilled trenches are located.

UNDERGROUND UTILITY

Design Recommendations and Construction Considerations

The recommendations and criteria presented in the following subsections can be used to aid in the design and analysis of buried pipes and utilities at this site.

Trench Bearing Pressures

The subsurface soils should have sufficient bearing capacity to support the proposed buried pipes. A net allowable bearing pressure of 3,000 pounds per square foot (psf) maybe used to support the buried pipes. This bearing pressure includes a factor of safety of 3. The bearing pressure also assumes that the bearing surface will be relatively free and clean of any soft or moist material and loose debris. Correct preparation of the trench bottom is essential for a satisfactory pipe installation.

Modulus of Soil Reaction

A modulus of soil reaction for the in-situ soil, Es or En, of at least 800 psi may be used in the design of the flexible pipe. Additionally, the modulus of soil reaction, Eb or sometimes referred to as E’, of the backfill material supporting the sides of the pipe is also used in the design of the flexible piping. This value is a function of several variables that include:

Soil type that comprises the backfill material supporting the pipe sides.

Degree of compaction of the backfill material supporting the pipe sides.

Lift thickness of the backfill material supporting the pipe sides.

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Values for Eb (E’) vary, depending on the pipe backfill and bedding materials. Fine-grained soils consisting of primarily clay and silt should not be used for bedding materials and backfill around the pipe. More specific information regarding this design parameter is included in ASTM D 2321 entitled “Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity Flow Applications”. The following table presents typical modulus of soil reaction values, Eb, for various backfill materials at different compaction ranges.

Type of Material

Modulus of Soil Reaction, Eb 1, psi, For Degrees of Compaction

Dumped (no compaction)

Slight <85%

Moderate 85% to 95%

High >95%

Fine Grained Soil (LL<50): CL, ML NR NR NR NR Fine Grained Soil (LL<50) with >25% Coarse-Grained Material: CL, ML or

Coarse-Grained Soil with fines: GM, GC, SM, SC

NR NR 1,000 2,000

Coarse-Grained Soil with <12% fines:

GW, GP, SW, SP NR 1000 2,000 3,000

Crushed Rock 1,000 3,000

1. These values do not include a factor of safety. A factor of safety may be needed for design purposes. These values are for use in predicting the initial deflections only. If a high degree of compaction is not achieved in the backfill adjacent to the sides of the pipe, an approximate deflection lag factor should be applied for long-term deflection estimates. It should be noted that LL refers to the Liquid Limit, and NR means that the use of these materials is not recommended by ASTM D 2321 for the backfill envelope.

Excavations

Various excavations are planned for site improvements. If groundwater seepage occurs in an excavation with a sand side slope, instability could occur, even for a relatively flat slope.

Temporary dewatering or shoring may be required to address this condition. Excavations and trenches should follow Occupational Safety and Health Administration (OSHA) Safety and Health Standards (29 CFR Part 1926 Revised, 1989), state and federal standards and guidelines. All excavation and safety/health issues are responsibility of the contractor.

Trench Backfill

Appropriate trench backfill is generally determined by several factors including the bearing capacity of the soil supporting the pipe, requirements of the pipe manufacturer regarding support

Responsive ■ Resourceful ■ Reliable 15 of the pipe, and the proposed improvements at the ground surface along the trench. Pipe manufacturers generally require a specified bedding and granular material around the pipe.

Typically, the bedding and embedment material around buried utilities is designed to support and protect the piping. The backfill material above the embedment also helps to protect the piping and to support any overlying structure, roadway, or other improvement. Inadequate compaction of this material can lead to excessive settlement of the backfill, stress in the pipe, and premature distress to any overlying improvement. Therefore, we recommend that the embedment and backfill material be properly placed, moisture conditioned, and compacted in accordance with the appropriate project documents or those requirements established by the City of Edinburg - Public Utility Standard Specifications for public works construction.

Backfill beneath roadways should attempt to match the soil type exposed in the excavation sidewalls. As a compaction guideline, we recommend that all trench backfill be placed and compacted as recommended in the Fill Material Types and Fill Compaction Requirements sections of this report.

Flowable fill can be used as an alternative to soil backfill, particularly beneath roadways. Flowable fill typically consists of a mixture of sand, portland cement, fly ash, and water and is readily available from ready-mixed concrete suppliers. This very low strength cementitious fill is placed in a slurry form and readily takes the shape of the excavation. Properly designed and placed, it can be excavated by a backhoe for future repairs or modifications as required.

As another alternate for backfill material, Cement-Stabilized Backfill may be used and should consist of a non-plastic sand or caliche as aggregate with a minimum of 2 sacks of Type I Portland cement per cubic yard based on the dry weight of the aggregate or as indicated by the City of Pharr - Public Utility Standard Specifications. No mixing will be allowed on the street surface.

Embedment backfill along the sides to the top of the pipe and possibly 12 to 24 inches above the pipe should consist of materials that are acceptable to the project civil engineer or materials meeting those requirements established by the City of Pharr - Public Utility Standard Specifications for public works construction. To avoid potential damage to the pipe, the embedment material should not contain materials exceeding 3 inches in maximum dimension.

The on-site soils meeting the applicable City of Edinburg - Public Utility Standard Specifications criteria may be used for site restoration.

Construction equipment with wheel or gross loads exceeding the pipe’s design strength should not be driven over or close to the pipeline. Additional cover placed on top of the pipe or an alternate route should be provided for machinery producing excessive loads.

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Tunnel Construction

The open trench method of installing underground utilities is the most commonly used construction process. However, interference with traffic and the resulting disruption of business and industry are some of the undesirable consequences of the open trench method. In these cases, tunneling can be a safe and practical alternative, but improper or unsafe tunnel construction can be costly.

The tunneling methods generally used for installing underground utilities include: boring and jacking, mining (or tunneling), jacking, directional drilling and micro tunneling. These means, and methods are the responsibility of the contractor and will not be discussed in this report.

Construction Observation and Testing

Each lift of compacted backfill should be tested, evaluated, and reworked as necessary until approved by the engineer prior to placement of additional lifts. Each lift of backfill should be tested for density and water content at a frequency of at least one test for every 150 linear feet of compacted utility trench backfill.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

PAVEMENTS

Flexible pavement may be considered for this project. Pavement subgrade preparations are included in this section to limit changes in soil moisture conditions to help mitigate the effects of soil movement. However, even if these recommendations are followed some pavement distress could still occur.

General Pavement Comments

Traffic conditions and pavement life conditions were not available at the time of this report. A critical aspect of pavement performance is site preparation. Pavement designs noted in this section must be applied to the site which has been prepared as recommended in the Earthwork section.

We recommend the moisture content and density of the top 6 inches of the subgrade be evaluated and the pavement subgrades be proofrolled within two days prior to commencement of actual paving operations. Areas not in compliance with the required ranges of moisture or density should be moisture conditioned and re-compacted.

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Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the materials with properly compacted fills.

If a significant precipitation event occurs after the evaluation or if the surface becomes disturbed, the subgrade should be reviewed by qualified personnel immediately prior to paving. The subgrade should be in its finished form at the time of the final review.

Based on the subsurface conditions, we anticipate that the pavement subgrade will generally consist of the on-site soils. The top 6 inches of the finished subgrade soils directly beneath the pavements may be chemically treated. Chemical treatment will increase the supporting value of the subgrade and decrease the effect of moisture on subgrade soils. These 6 inches of treatment should be considered as required part of the pavement design and is not a part of site and subgrade preparation for wet/soft subgrade conditions.

If chemical treatment of the subgrade is chosen, we anticipate that the on-site surficial soils should be treated with about 3 percent of lime/cement. This percentage is given as application by dry weight and is typically equivalent to about 15 pounds of modifier per square yard per 6-inch depth. The recommended percentage of modifier is for estimating and planning. The actual quantity of modifier required should be determined at the time of construction by laboratory tests on bulk samples of the subgrade soils. Specifications for treated subgrade are presented later in this section. An alternative pavement section with treated subgrade is also provided.

After proofrolling and repairing deep subgrade deficiencies, the entire subgrade should be scarified and developed as recommended in Earthwork section of this report to provide a uniform subgrade for pavement construction. Areas that appear severely desiccated following site stripping may require further undercutting and moisture conditioning. If a significant precipitation event occurs after the evaluation or if the surface becomes disturbed, the subgrade should be reviewed by qualified personnel immediately prior to paving. The subgrade should be in its finished form at the time of the final review.

Pavement Design Parameters

Traffic patterns and anticipated loading conditions were not available at the time that this report was prepared. However, we anticipate that traffic loads will be produced primarily by light traffic and occasional delivery and trash removal trucks. Pavement thickness can be determined using AASHTO, Asphalt Institute and/or other methods if specific wheel loads, axle configurations, frequencies, and desired pavement life are provided.

Terracon can provide thickness recommendations for pavements subjected to loads other than the above-mentioned traffic if this information is provided.

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Pavement performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of pavements:

■ Final grade adjacent to parking lots and drives should slope down from pavement edges at a minimum 2%;

■ The subgrade and the pavement surface should have a minimum ¼ inch per foot slope to promote proper surface drainage;

■ Install pavement drainage surrounding areas anticipated for frequent wetting (e.g., garden centers, wash racks);

■ Install joint sealant and seal cracks immediately;

■ Seal all landscaped areas in, or adjacent to pavements to reduce moisture migration to subgrade soils;

■ Place compacted, low permeability backfill against the exterior side of curb and gutter;

and,

■ Place curb, gutter and/or sidewalk directly on low permeability subgrade soils rather than on unbound granular base course materials.

Pavement Section Thicknesses

As a minimum, we recommend the following typical pavement sections be considered.

Pavement Area

Traffic Design Index

Description

Automobile Parking Areas DI-1

Light traffic (Few vehicles heavier than passenger cars, no regular use by heavily loaded two axle trucks).

(EAL(1) < 6)

Driveways DI-2

Light to medium traffic (Similar to DI-1 including not over 50 loaded two axle trucks or lightly loaded larger vehicles per day.

No regular use by heavily loaded trucks with three or more axles).

(EAL = 6-20)

Driveways for Truck Traffic

Areas

DI-3

Medium to heavy traffic (Including not over 300 heavily loaded two axle trucks plus lightly loaded trucks with three or more axles and no more than 30 heavily loaded trucks with more than three axles per day).

(EAL = 21-75)

1. Equivalent daily 18-kip single-axle load applications.

Listed below are pavement component thicknesses, which may be used as a guide for pavement systems at the site for the traffic classifications stated herein. These systems were derived based on general characterization of the subgrade. Specific testing (such as CBR's, resilient modulus

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Alternative Minimum Recommended Flexible Pavement Section Thickness, inches

Component DI-1 1 DI-2 1 DI-3 1

Hot Mix Asphaltic Concrete (HMAC) 2, 3 2 2½ 3

Granular Base Material 2 6 8 12

Treated Subgrade 2 6 6 6

1. See Pavements for more specifics regarding traffic classifications.

2. All materials should meet the current Department of Transportation (TxDOT) Standard Specifications for

Highway and Bridge Construction.

3. A minimum 2-inch surface course should be used on ACC pavements.

The listed pavement component thicknesses should be used as a guide for pavement systems at the site for the traffic classifications stated herein. These recommendations assume a 20-year pavement design life. If pavement frequencies or loads will be different than that specified Terracon should be contacted and allowed to review these pavement sections.

We recommend a Portland Cement Concrete (PCC) pavement be utilized in the main access lanes, parking lots, dumpster pads or other areas where extensive wheel maneuvering are expected.

We recommend that waste dumpster areas be constructed of at least 7-inches of reinforced concrete pavement. The concrete pad areas should be designed so that the vehicle wheels of the collection truck are supported on the concrete while the dumpster is being lifted to support the large wheel loading imposed during waste collection.

Minimum Recommended Flexible Pavement System, inches

Component DI-1 1 DI-2 1 DI-3 1

Hot Mix Asphaltic Concrete (HMAC) 2, 3 2 2½ 3½

Granular Base Material 2 6 8 12

Moisture Conditioned Subgrade 8 8 8

1. See Pavements for more specifics regarding traffic classifications.

2. All materials should meet the current Department of Transportation (TxDOT) Standard Specifications for

Highway and Bridge Construction.

3. A minimum 2-inch surface course should be used on ACC pavements.

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Proper joint spacing will also be required to prevent excessive slab curling and shrinkage cracking. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer.

Presented below are our recommended material requirements for the various pavement sections.

Hot Mix Asphaltic Concrete Surface Course – The…