Attachment 20 - Geotechnical Report .pdf

Proposal Cover Page Report Cover Page

LRAFB Arnold Gate Improvements Geotechnical Engineering Report

January 26, 2024 | Terracon Project No. 35235133

Prepared for:

Garver, LLC.

Little Rock, AR 72118

25809 I30 South Bryant, AR 72022

(501) 847-9292

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

January 26, 2024

Garver, LLC.

4701 Northshore Drive Little Rock, AR 72118

Attn: Thomas Graham E: TCGraham@GarverUSA.com

Re: Geotechnical Engineering Report LRAFB Arnold Gate Improvements Arnold Drive Little Rock Air Force Base, Jacksonville, Arkansas Terracon Project No. 35235133

Dear Mr. Graham:

We have completed a subsurface exploration and geotechnical engineering evaluation for the referenced project in general accordance with Terracon Proposal No. P35235133 dated September 14, 2023. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork, lateral earth pressure and pavement recommendations for the project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Certificate of Authorization No. 223, expires 12/31/2025

Gabrielle E. Whitesides Christopher S. Handley, P.E.

Field Engineer Geotechnical Department Manager

Geotechnical Engineering Report LRAFB Arnold Gate Improvements | Little Rock Air Force Base, Jacksonville, Arkansas January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials i

Table of Contents

Introduction Project Description Site Conditions Geotechnical Characterization Geotechnical Overview Earthwork

Site Preparation Excavation Fill Material Types Fill Placement and Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Lateral Earth Pressures Lateral Earth Pressure Design Parameters Subsurface Drainage for Below-Grade Walls

General Comments

Figures GeoModel Pile Capacity Charts

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans Exploration and Laboratory Results Supporting Information

Note: This report was originally delivered in a web-based format. Blue 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 logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

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Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed stairwell additions to be located at Arnold Drive in Little Rock Air Force Base, Jacksonville, Arkansas. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil (and rock) conditions

■ Groundwater conditions

■ IBC seismic site class

■ Site preparation and earthwork

■ Lateral earth pressure parameters and drainage recommendations

■ Pavement thickness design and construction

Drawings showing the site and boring locations are shown on the attached Site Location and Exploration Plan. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs in Exploration Results.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information Provided

An email containing the request for proposal from Thomas Graham was received by Terracon on September 12, 2023.

The email contained project information as well as an attached kmz titles “LRAFB Arnold Gate Improvements” showing the proposed improvements and planned borings.

Traffic counts were provided via email on January 18, 2024.

A draft grading plan was provided via email on January 24, 2024.

Project Description We understand the Little Rock Air Force Base is looking to complete roadway improvements near the security gate along Arnold Drive.

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Item Description

Grading

A final grading plan was not provided to Terracon, and undulating hills exist along the planned alignment. We also understand that a retaining wall may be planned as part of the project. We considered that no more than 5 feet of cut and fill will be required to develop the project.

Retaining Walls We understand that a retaining wall may be necessary based on the final grading of the roadway. No information regarding the retaining wall was available at the time of this report.

Pavements

Traffic counts from ArDOT were provided. The pavements will be utilized primarily by passenger vehicles (cars, pickup trucks, SUV’s) with occasional busses, single-unit trucks, and articulated trucks.

Terracon should be notified if any of the above information is inconsistent with the planned construction, as modifications to our recommendations may be necessary.

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

Project Location

The project is located at the security gate at the Little Rock Air Force Base near the intersection of Highway 107 and Arnold Drive in Jacksonville, Arkansas.

Latitude/Longitude 34.8979, -92.1704 (approximate) See Site Location

Existing Improvements

The project is near the existing security gate near Arnold Drive at the Little Rock Air Force Base. Existing structures and roadways surround the proposed project. From the concept layout provided, it appears that the new roadway alignment is planned on currently undeveloped land. The northern portion of the alignment is within heavy tree vegetation.

Existing Topography

There are undulating hills along the planned roadway alignment.

Elevations along the alignment range from approximately 370 to 391 feet.

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Item Description

Geology The subsurface conditions at the project site consist of variable layers of sandy lean to fat clay with varying amounts of sandstone gravels and clayey sand overlying sandstone bedrock.

Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based on the subsurface exploration, laboratory data, geologic setting, and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical evaluation. Conditions observed at each boring location are indicated on the individual logs. The individual logs are in the Exploration Results and the GeoModel is in the Figures attachment 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 Fill Clayey gravel fill observed in boring B-1

Lean to Fat Clay Soils

Soft to very stiff lean to fat clay soils with varying amounts of gravel and sand

Clayey Sand

Soils Medium dense to very dense clayey sand soils with varying amounts of gravel

Weathered Sandstone

Weak, weathered sandstone

The borings were observed during drilling and shortly after completion of drilling for the presence and level of water. Groundwater was not encountered in the other borings at these times. A longer period of time may be required for groundwater to develop and stabilize in a borehole. Longer term observations in piezometers or observation wells, sealed from the influence of surface water, are often required to define groundwater levels.

Groundwater levels may fluctuate due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the borings were performed. “Perched” water could occur above lower permeability soil layers and/or near the soil/bedrock interface, and “trapped” water could be present within existing fill materials. Therefore, groundwater conditions at other times may be different than the conditions encountered in our exploratory borings. The potential for water level fluctuations and perched water

Proposal for Geotechnical Engineering Services

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SITE LOCATION

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY GOOGLE EARTH

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EXPLORATION PLAN

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

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Facilities | Environmental | Geotechnical | Materials 4 should be considered when developing design and construction plans and specifications for the project.

Geotechnical Overview

Clayey gravel fill was encountered in boring B-1. We are not privy to information regarding the construction of the existing fill. There is an inherent risk to the owner that unsuitable material within or buried by the fill will not be discovered that could result in unpredictable post-construction performance of the pavements supported on the existing fill. Soft to very stiff lean to fat clay soils with varying amounts of gravel and sand, and medium dense to very dense clayey sand soils, underlain by weathered sandstone were encountered in all borings.

Surficial low-strength soils were observed in Boring B-2 to depths ranging from 0.5 to 2 feet below the existing ground surface. Expansive fat clay soils were encountered at the site. These materials have the potential to shrink and swell with seasonal fluctuations in the soil moisture content.

This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. However, even if these procedures are followed, some movement and at least minor cracking in the structure could still occur. The severity of cracking and other cosmetic damage caused by movement of the pavements will probably increase if any modification of the site results in excessive wetting or drying of the expansive soils.

Eliminating the risk of movement and cosmetic distress 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.

The surficial clay soils encountered in the borings are moisture-sensitive and are susceptible to strength loss with moisture content increases and when exposed to repetitive construction traffic.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration Results), engineering analyses, and our current understanding of the proposed project. Recommended earthwork procedures are presented in the Earthwork section of the report. Recommended pavement sections can be found in the Pavements section of the report. The General Comments section provides an understanding of the report limitations.

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Earthwork

Site preparation, excavation, subgrade preparation and placement of engineered fill should follow the recommendations presented in this section. The recommendations presented for design and construction of earth-supported elements including pavements are contingent upon the recommendations outlined in this section being followed. We recommend earthwork on this project be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of subgrade preparation, engineered fill, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project.

Site Preparation

Areas within the limits of construction should be stripped and cleared of any pavement and debris. Tree stumps and major root systems should be removed full-depth. Also, surface and subsurface features from past site use should be removed and replaced full-depth.

Depressions and excavations created during demolition and from tree stump and root removal should be cleaned of loose material, water, and debris and properly backfilled with tested and approved, engineered fill.

Following initial stripping and any necessary undercutting, the exposed soils should be proofrolled. A Terracon representative should observe the proofrolling. Proofrolling can be accomplished using a loaded tandem-axle dump truck with a gross weight of at least 20 tons, or similarly loaded equipment. Areas that display excessive deflection (pumping) or rutting during proofroll operations should be improved by scarification/compaction or by removal and replacement with engineered fill.

Excavation

We anticipate that excavations in the overburden soils for the proposed roadway construction can be accomplished with conventional earthmoving equipment.

The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of pavements or constructed slopes. General fill is material used to achieve grade outside of these areas.

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Reuse of On-Site Soil: Excavated on-site soil may be selectively reused as fill below pavement and landscaping areas if they meet the requirements for structural full outlined below. Portions of the on-site soil have an elevated fines content and will be sensitive to moisture conditions (particularly during seasonally wet periods) and may not be suitable for reuse when above optimum moisture content.

Material property requirements for on-site soil for use as general fill and engineered fill are noted in the table below:

Fill Type

USCS

Classification Acceptable Location for Placement

Native Clayey Sands, Native Fat Clays and/or

Lean to Fat Clays (LL≥45 and/or PI≥25)

CH, CL/CH, SC General fill – These soils should not be used in pavement areas

Native Lean Clays (LL<45 and PI<23)

CL

Structural fill - All locations and elevations, except where free-draining material is required

Imported Fill Materials: Imported fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

Fill Type 1 USCS Classification

Acceptable Location for Placement

Low Volume Change (LVC) material

GM

or

CL, GC, SC

(LL≤45 and

10≤PI≤20) 2

Structural fill - All locations and elevations, except where free-draining material is required

Drainage Fill 3 GW, SW, SP Free-draining granular fill

Aggregate Base ArDOT Class 7

Aggregate Base Pavement subgrade

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Fill Type 1 USCS Classification

Acceptable Location for Placement

1. Structural fill should consist of approved materials that are relatively free of organic matter and debris. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site.

2. LL=Liquid Limit. PI=Plasticity Index. Fill meeting a PI of 10 to 20 is preferred but may be difficult to find. Utilizing lean clay soils with a liquid limit of less than 45 percent and a plasticity index between 20 and 25 percent is generally accepted in the area, although this will somewhat increase the risk of shrink-swell movement.

3. Well-graded, free-draining granular material such as ASTM No. 57 or 67 stone.

Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Description

Maximum Lift Thickness

■ 8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

■ 4 to 6 inches in loose thickness when hand-guided equipment (i.e., jumping jack or plate compactor) is used

Minimum Compaction Requirements 1,2,3

■ ≥95% of maximum density in utility trenches, beneath pavements

Water Content Range

Low plasticity cohesive: -2% to +2% of optimum Granular: Workable moisture levels4

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Item Description

1. Maximum density and optimum water content as determined by the standard-energy moisture-density relationship (Proctor test, ASTM D 698).

2. In this case, granular materials should be compacted to at least 65% relative density (ASTM D 4253 and D 4254).

3. Consideration can be given to compacting all fill below proposed roadways to 95% during mass grading. Immediately prior to construction, we recommend that the subgrade below roadways be rough-graded and then scarified and recompacted. We recommend this process include scarifying the subgrade to a depth of about 8 inches, moisture conditioning the scarified soil to within the recommended range and compacting the scarified soil to at least 98%. Scarified soils which cannot be recompacted to this degree should be undercut and replaced with stable material.

4. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proofrolled or containing excess water (ponding). Materials not amenable to density testing should be placed and compacted to a stable condition observed by the Geotechnical Engineer or representative.

Utility Trench Backfill

Any soft or unsuitable materials encountered at the bottom of utility trench excavations should be removed and replaced with structural fill or bedding material in accordance with public works specifications for the utility be supported. This recommendation is particularly applicable to utility work requiring grade control and/or in areas where subsequent grade raising could cause settlement in the subgrade supporting the utility.

Trench excavation should not be conducted below a downward 1:1 projection from existing foundations without engineering review of shoring requirements and geotechnical observation during construction.

On-site materials are considered suitable for backfill of utility and pipe trenches from 1 foot above the top of the pipe to the final ground surface, provided the material is free of organic matter and deleterious substances.

Trench backfill should be mechanically placed and compacted as discussed earlier in this report. Compaction of initial lifts should be accomplished with hand-operated tampers or other lightweight compactors. Where trenches are placed beneath pavements, the backfill should satisfy the gradation and expansion index requirements of engineered fill discussed in this report. Flooding or jetting for placement and compaction of backfill is not recommended.

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Grading and Drainage

The site should be graded to provide effective drainage away from the building during and after construction, and these conditions should be maintained throughout the life of the structure. Accumulation of water adjacent to the structure could contribute to significant moisture increases in the subgrade soils and subsequent softening/settlement or expansion/heave, which could result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential floor slab and/or foundation movements, cracked slabs and walls, and roof leaks.

After building construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance program. Where paving or flatwork abuts the structure, a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Earthwork Construction Considerations

Terracon should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation, proofrolling, placement and compaction of engineered fill, backfilling of excavations into completed subgrades, and just prior to construction of pavements.

Care should be taken to avoid disturbance of prepared subgrades. Unstable subgrade conditions can develop during general construction operations, particularly if the soils are wetted and/or subjected to repetitive construction traffic. If unstable subgrade conditions develop, stabilization measures will need to be employed. Construction traffic over the completed subgrade should be avoided to the extent practical. If the subgrade becomes frozen, desiccated, saturated, or disturbed, the affected materials should be removed or these materials should be scarified, moisture conditioned, and compacted prior to pavement construction.

Based on conditions encountered in the borings, significant seepage is generally not expected in excavations for this project. If seepage is encountered in excavations during construction, the contractor is responsible for designing, implementing, and maintaining appropriate dewatering methods to control seepage and facilitate construction. In our experience, dewatering of excavations in clay soils can typically be accomplished using sump pits and pumps. If seepage occurs where sand seams or sand layers are encountered in excavations, a more extensive dewatering system may be required.

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, state, and federal safety regulations. The contractor should be aware that slope

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials 10 height, slope inclination, and excavation depth should in no instance exceed those specified by these safety regulations. Flatter slopes than those dictated by these regulations may be required depending upon the soil conditions encountered and other external factors. These regulations are strictly enforced and if they are not followed, the owner, contractor, and/or earthwork and utility subcontractor could be liable and subject to substantial penalties. Under no circumstances should the information provided in this report be interpreted to mean that Terracon is responsible for construction site safety or the contractor’s activities. Construction site safety is the sole responsibility of the contractor who shall also be solely responsible for the means, methods, and sequencing of the construction operations.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (vegetation, topsoil, trees and any existing pavements), evaluation and remediation of any existing fill materials, as well as proofrolling and mitigation of unsuitable areas delineated by the proofroll.

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 as required by ArDOT Construction Standards. One density and water content test should be performed for every 50 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.

Lateral Earth Pressures

Lateral Earth Pressure Design Parameters

Structures with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to values indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction, methods and degree of compaction, and the strength of the materials being restrained. Two wall restraint conditions are shown in the diagram below. Active earth pressure is commonly used for design of free-standing cantilever retaining walls where wall movement is acceptable. The “at-rest” condition assumes no wall movement and is commonly used for design of basement walls, loading dock walls, or other walls

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Facilities | Environmental | Geotechnical | Materials 11 restrained at the top. The recommended design lateral earth pressures do not include a factor of safety. The drained parameters do not provide for possible hydrostatic pressure on the walls.

Lateral Earth Pressure Design Parameters

Earth Pressure

Condition 1

Coefficient for Backfill Type 2,3

Surcharge Pressure 4 p1 (psf)

Equivalent Fluid Unit Weight

(pcf) 2,5

Drained 5 Undrained 5

Active (Ka) Granular - 0.3

Clay - 0.42 (0.31)S (0.42)S

At-Rest (Ko) Granular - 0.47

Fine Grained - 0.58 (0.47)S (0.58)S

Passive (Kp) Granular - 3.3

Clay - 2.4

1. For active earth pressure, wall must rotate about base, with top lateral movements 0.002 H to 0.004 H, where H is wall height. For passive earth pressure, wall must move horizontally to mobilize resistance.

2. Uniform, horizontal backfill, with a maximum unit weight of 120 pcf for clay soils and 130 pcf for granular soils.

3. Granular material backfill phi = 32 degrees (minimum); Clay soil phi = 24 degrees (minimum)

4. Uniform surcharge, where S is surcharge pressure.

5. Loading from heavy compaction equipment is not included.

6. To achieve “Drained” conditions, follow guidelines in Subsurface Drainage for

Below-Grade Walls below. “Undrained” conditions are recommended when drainage behind walls is not incorporated into the design.

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils. For the granular values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 degrees from vertical for the active case.

The lateral earth pressure recommendations given in this section are applicable to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity type concrete walls. These recommendations are not applicable to the design of modular block - geogrid reinforced backfill walls (also termed MSE walls). Recommendations covering these types of wall systems are beyond the scope of services for this assignment. However, we would be pleased to develop a proposal for evaluation and design of such wall systems upon request.

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Subsurface Drainage for Below-Grade Walls

A perforated rigid plastic drain line installed behind the base of walls and extends below adjacent grade is recommended to prevent hydrostatic loading on the walls. The invert of a drain line around a below-grade building area or exterior retaining wall should be placed near foundation bearing level. The drain line should be sloped to provide positive gravity drainage to daylight or to a sump pit and pump. The drain line should be surrounded by clean, free-draining granular material having less than 5% passing the No. 200 sieve, such as No. 57 aggregate. The free-draining aggregate should be encapsulated in a filter fabric. The granular fill should extend to within 2 feet of final grade, where it should be capped with compacted cohesive fill to reduce infiltration of surface water into the drain system.

As an alternative to free-draining granular fill, a prefabricated drainage structure may be used. A prefabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion and is fastened to the wall prior to placing backfill.

Pavements

Pavement Subgrade Preparation

Pavement designs are provided for the traffic conditions and pavement life conditions as noted in Project Description and in the following sections 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.

Grading and paving are commonly performed by separate contractors and there is often a time lapse between the end of grading operations and the commencement of paving.

Subgrades prepared early in the construction process may become disturbed by

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Facilities | Environmental | Geotechnical | Materials 13 construction traffic. Non-uniform subgrades often result in poor pavement performance and local failures relatively soon after pavements are constructed. Depending on the paving equipment used by the contractor, measures may be required to improve subgrade strength to greater depths for support of heavily loaded concrete/asphalt trucks.

We recommend the moisture content and density of the subgrade be evaluated and the pavement subgrades be proofrolled (using a loaded tandem-axle dump truck with a minimum gross weight of 20 tons or similarly loaded rubber-tire equipment) within two days prior to commencement of actual paving operations. Areas not in compliance with the required ranges of moisture or density should be scarified, moisture conditioned, and compacted. 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. The subgrade should be in its finished form at the time of the final review.

Support characteristics of subgrade for pavement design do not account for shrink/swell movements of an expansive clay subgrade, such as soils observed on this project. Thus, the pavement may be adequate from a structural standpoint, yet still experience cracking and deformation due to shrink/swell related movement of the subgrade.

Pavement Design Parameters

A minimum California Bearing Ratio (CBR) of 0.8 was used for the low volume change select fill for the asphaltic concrete (AC) pavement designs. The value was obtained by CBR testing results, shown in the Exploration and Laboratory Results section of the Attachments.

Pavement Section Thicknesses

Pavement thickness depends upon many factors including but not limited to:

■ applied wheel/axle loads and number of repetitions

■ subgrade and pavement material characteristics

■ climate conditions

■ site and pavement drainage

Recommended minimum pavement sections are provided below. These pavement thickness recommendations are based on the 1993 AASHTO Guide for Design of Pavement Structures. Other pavement sections could also be considered.

We used the following traffic data information and design parameters for the subject project:

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Facilities | Environmental | Geotechnical | Materials 14 n Design ESALs for flexible pavement section: 400,000 n Design CBR:0.8

If these assumptions for design traffic loading are inconsistent with those desired by the client, the updated traffic information should be submitted for our review regarding any potential changes to our design recommendations. Periodic maintenance should be expected to realize the anticipated design life.

The following table provides recommendations for an asphalt pavement section:

Minimum Pavement Recommendations

Flexible Pavement

Asphaltic Concrete

2 inches Type 12.5 mm HMAC 1

4 inches Type 25 mm HMAC 1

Aggregate Base 12 inches Class 7 Aggregate Base 1

1. Arkansas Department of Transportation Standard Specifications

Pavements and subgrades will be subject to freeze-thaw cycles and seasonal fluctuations in moisture content. Pavement thickness design methods are intended to provide adequate thickness of structural materials over a particular subgrade such that wheel loads are reduced to a level that the subgrade can support. The subgrade support parameters for pavement thickness design do not account for shrink/swell movements of a subgrade constructed of expansive clay soils. Therefore, the pavement may be adequate from a structural standpoint, yet still experience cracking and deformation due to shrink/swell related movement of the subgrade.

The pavement sections provided above consider that the subgrade soils will not experience significant increases in moisture content. Paved areas should be sloped to provide rapid drainage of surface water and to drain water away from the pavement edges. Pavements should be designed so water does not accumulate on or adjacent to the pavement, since this could saturate and soften the subgrade soils and subsequently accelerate pavement deterioration.

Periodic maintenance of the pavements will be required. Cracks should be sealed, and areas exhibiting distress should be repaired promptly to help prevent further deterioration. Even with periodic maintenance, some movement and related cracking may still occur, and repairs may be required.

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Pavement Drainage

Pavements should be sloped to provide rapid drainage of surface water. Water allowed to pond on or adjacent to the pavements could saturate the subgrade and contribute to premature pavement deterioration. In addition, the pavement subgrade should be graded to provide positive drainage within the granular base section. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the granular subbase.

Pavement Maintenance

The pavement sections represent minimum recommended thicknesses, and periodic maintenance and repairs should be anticipated. Preventive maintenance should be planned and provided for through an on-going pavement management program.

Maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment. Pavement care consists of both localized (e.g., crack sealing, joint sealing, and patching) and global maintenance (e.g., surface sealing).

Additional engineering consultation is recommended to determine the type and extent of a cost-effective program. Even with periodic maintenance, some movements and related cracking may still occur, and repairs may be required.

Pavement performance is affected by the pavement’s 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 paved areas should slope down from the edges at a minimum 2%.

■ Subgrade and pavement surfaces should have a minimum 2% slope to promote proper surface drainage.

■ Install pavement drainage systems surrounding areas anticipated for frequent wetting.

■ 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.

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

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General Comments

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration.

Variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly impact excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety, cost estimating, excavation support, and dewatering requirements/design are the responsibility of others.

Construction and site development have the potential to affect adjacent properties. Such impacts can include damages due to vibration, modification of groundwater/surface water flow during construction, foundation movement due to undermining or subsidence from excavation, as well as noise or air quality concerns. Evaluation of these items on nearby properties are commonly associated with contractor means and methods and are not addressed in this report. The owner and contractor should consider a preconstruction/precondition survey of surrounding development. If changes in the nature, design, or location of the project are planned, our conclusions and

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials 17 recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials

Figures

Contents:

GeoModel

E L

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A T

IO

N

M

S L

(f ee t)

LRAFB Arnold Gate Improvements Little Rock Air Force Base, AR Terracon Project No. 35235133

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

B-1

B-2

B-3

B-4

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

GEOMODEL

3 Medium dense to very dense clayey sand soils with varying amounts of gravel

4 Weak, weathered sandstone

LEGEND

Fill

Lean Clay with Gravel

Clayey Sand with Gravel

Sandstone

Lean Clay with Sand

Sandy Lean Clay with Gravel

Sandy Fat Clay

Sandy Lean Clay

Model Layer General DescriptionLayer Name

Clayey gravel fill observed in boring B-1

Soft to very stiff lean to fat clay soils with varying amounts of gravel and sand2

Clayey Sand Soils

Weathered Sandstone

Fill

Lean to Fat Clay Soils

0.8

3.5

8.5

13.8

8.5

13.9

8.5

3.5

8.5

13.9

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials

Attachments

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials

Exploration and Testing Procedures

Field Exploration

Exploration Type and Quantity

Approximate Boring Depth (feet)

Location

Soil Borings - 4 15 or auger refusal Locations provided by GarverPercolation Tests - 2 1

Boring Layout and Elevations: Terracon personnel provided the boring layout using handheld GPS equipment (estimated horizontal accuracy of about ±10 feet) and referencing existing site features. Approximate ground surface elevations were estimated using Google Earth. If elevations and a more precise boring layout are desired, we recommend borings be surveyed.

Subsurface Exploration Procedures: We advanced the borings with a truck-mounted, track-mounted, ATV-mounted rotary drill rig using continuous flight augers (solid stem and/or hollow stem, as necessary, depending on soil conditions). Five samples were obtained in the upper 10 feet of each boring and at intervals of 5 feet thereafter. In the thin-walled tube sampling procedure, a thin-walled, seamless steel tube with a sharp cutting edge was pushed hydraulically into the soil to obtain a relatively undisturbed sample. In the split-barrel sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon was driven into the ground by a 140-pound automatic hammer falling a distance of 30 inches. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths. For safety purposes, all borings were backfilled with auger cuttings after their completion.

Pavements were patched with cold-mix asphalt and/or pre-mixed concrete, as appropriate.

We also observed the boreholes while drilling and at the completion of drilling for the presence of groundwater. Groundwater was not observed at these times in the boreholes.

The sampling depths, penetration distances, and other sampling information was recorded on the field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory for testing and classification by a geotechnical engineer. Our exploration team prepared field boring logs as part of the drilling operations. These field logs included visual classifications of the materials observed during drilling and our interpretation of the subsurface conditions between samples. Final boring logs were prepared from the field logs. The final boring logs represent the Geotechnical Engineer's

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials interpretation of the field logs and include modifications based on observations and tests of the samples in our laboratory.

Laboratory Testing

The project engineer reviewed the field data and assigned laboratory tests. The laboratory testing program included the following tests on selected samples:

■ Moisture Content

■ Percent Fines

■ Atterberg Limits

■ Standard Proctor

■ California Bearing Ratio

The laboratory testing program included examination of soil samples by an engineer.

Based on the results of our field and laboratory programs, we described and classified the soil samples in accordance with the Unified Soil Classification System.

Percolation testing has not been completed at the time of this report. An addendum with percolation test results will be issued.

Rock classification was conducted using locally accepted practices for engineering purposes; petrographic analysis may reveal other rock types. Boring log rock classification was determined using the attached Description of Rock Properties.

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials

Site Location and Exploration Plans

Contents:

Site Location Plan Exploration Plan

Note: All attachments are one page unless noted above.

January 26, 2024 | Terracon Project No. 35235133

Facilities | Environmental | Geotechnical | Materials

Note to Preparer: This is a large table with outside borders. Just click inside the table above this text box, then paste your GIS Toolbox image.

When paragraph markers are turned on you may notice a line of hidden text above and outside the table – please leave that alone. Limit editing to inside the table.

Site Location

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSE MAP PROVIDED BY GOOGLE EARTH

Note to Preparer: This is a large table with outside borders. Just click inside the table above this text box, then paste your GIS Toolbox image.

When paragraph markers are turned on you may notice a line of hidden text above and outside the table – please leave that alone. Limit editing to inside the table.

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

Exploration and Laboratory Results

Boring Logs (B-1 through B-4) Proctor Results CBR Results

5-7-9 N=16

6-7-7 N=14

6-22-33 N=55

16-25-40 N=65

30-50/4"

50/4"

17.9

14.8

9.7

9.1

10.4

7.9

57-20-37

FILL - CLAYEY GRAVEL

LEAN CLAY WITH GRAVEL (CL), with sandstone gravels, gray and light brown, stiff

CLAYEY SAND WITH GRAVEL (SC), gray and light brown, very dense

WEATHERED SANDSTONE, gray and light brown, weak rock

Boring Terminated at 13.8 Feet

0.8

3.5

8.5

13.8

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

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ATTERBERG

LIMITS

LL-PL-PI

LOCATION See Exploration Plan

Latitude: 34.8987° Longitude: -92.1718°

G R

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DEPTH

Advancement Method:

Solid-Stem Auger

Abandonment Method:

Notes:

Project No.: 35235133

Drill Rig: 840

BORING LOG NO. B-1

Garver LLCCLIENT:

North Little Rock, AR

Driller: JC

Boring Completed: 12-14-2023

PROJECT: LRAFB Arnold Gate Improvements

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Arnold Drive Little Rock Air Force Base, AR

SITE:

Boring Started: 12-14-2023

25809 I 30 Bryant, AR

WATER LEVEL OBSERVATIONS

Groundwater not encountered

P E

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T F

IN

E

S

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LE

T

Y P

E

3.5

8.5

13.9

1-1-1 N=2

3-5-8 N=13

5-10-20 N=30

20-50/6"

50/5"

50/4"

20.3

23.2

15.9

9.2

7.3

6.4

46-20-26

34-19-15

LEAN CLAY WITH SAND (CL), brown, soft

SANDY LEAN CLAY WITH GRAVEL (CL), grayish brown and reddish brown, stiff to very stiff

WEATHERED SANDSTONE, light brown and gray, weak rock

Boring Terminated at 13.9 Feet

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

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M O

D E

L

LA

Y E

R

DEPTH

Advancement Method:

Solid-Stem Auger

Abandonment Method:

Notes:

Project No.: 35235133

Drill Rig: 840

BORING LOG NO. B-2

Garver LLCCLIENT:

North Little Rock, AR

Driller: JC

Boring Completed: 12-14-2023

PROJECT: LRAFB Arnold Gate Improvements

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Arnold Drive Little Rock Air Force Base, AR

SITE:

Boring Started: 12-14-2023

25809 I 30 Bryant, AR

W A

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ATTERBERG

LIMITS

LL-PL-PI

LOCATION See Exploration Plan

Latitude: 34.8987° Longitude: -92.1708°

G R

A P

H

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L O

G

WATER LEVEL OBSERVATIONS

Groundwater not encountered

P E

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M P

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T

Y

9-7-12 N=19

13-13-19 N=32

10-14-18 N=32

18-32-50/4"

35-50/4"

50/6"

9.4

9.5

11.7

8.1

9.2

7.7

55-22-33

70-24-46

SANDY FAT CLAY (CH), light brown and grayish brown, very stiff to hard

CLAYEY SAND WITH GRAVEL (SC), light brown and grayish brown, very dense

WEATHERED SANDSTONE, light brown and grayish brown, weak rock

Boring Terminated at 14 Feet

5.0

8.5

14.0

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

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