2024.3.29 FINAL Geotech Report_NASA Engineering Consolidation Phase 1A.pdf

Report Cover Page

NASA Engineering

Consolidation Phase 1A Geotechnical Engineering Report

March 29, 2024 | Terracon Project No. 91235100

Prepared for:

RS&H Architects-Engineers-Planners, Inc.

10748 Deerwood Park Boulevard Boulevard South

Jacksonville, Florida 33256

551 League City Parkway, Suite F

League City, Texas 77573

P (281) 557-2900

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

March 29, 2024

RS&H Architects-Engineers-Planners, Inc.

10748 Deerwood Park Boulevard Boulevard South

Jacksonville, Florida 33256

Attn: Mr. Scott Coleman, AIA, DBIA – Senior Architect/ Project Manager

P: (904) 307-2103

E: scott.coleman@rsandh.com

Re: Geotechnical Engineering Report

NASA Engineering Consolidation Phase 1A

2101 NASA Road 1

Houston, Texas

Terracon Project No. 91235100

Dear Mr. Coleman:

We have completed the scope of geotechnical engineering services for the above referenced project in general accordance with Terracon Proposal No.

P91235100.Revision1 dated August 14, 2023 and authorized on October 04, 2023. Due to NASA permits and protocols, we were delayed in performing our field exploration until

January 3, 2024. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and pavements for the proposed 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 Consultants, Inc.

(Texas Firm Registration No.: F-3272)

Daniel B. Mabirizi, E.I.T. Joshua C. Miles, P.E.

Project Manager Department Manager

NASA Engineering Consolidation Phase 1A | Houston, Texas

Facilities | Environmental | Geotechnical | Materials i

Table of Contents

Report Summary .............................................................................................. i

Introduction

Project Description

Site Conditions

Geotechnical Characterization

Geology

Subsurface Profile

Groundwater Conditions

Geotechnical Overview

Earthwork

Site Preparation

Subgrade Preparation

Fill Material Types

Fill Placement and Compaction Requirements

Grading and Drainage

Earthwork Construction Considerations

Construction Observation and Testing

Deep Foundations

Drilled Shaft Design Parameters

Drilled Shaft Construction Considerations

Lateral Loading

Lateral Group Effects

Floor Slabs

Floor Slab Design Parameters

Floor Slab Construction Considerations

Pavements

General Pavement Comments

Pavement Section Thicknesses

Pavement Maintenance

General Comments

Figures GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans

Exploration and Laboratory Results

Facilities | Environmental | Geotechnical | Materials ii

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.

http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials i

Report Summary

Topic 1 Overview Statement 2

Project

Description

This project includes construction of a new multi-story engineering building within an approximate footprint area of 300 feet by 120 feet and a maximum height of 60 feet.

Geotechnical

Characterization

The subsurface materials generally consisted of fat clay and lean clay with varying amounts of silt and gravel extending to the termination depth of the borings. Sandy soils were encountered at approximately 33 to 43 feet and 60 to 65 feet.

Earthwork

Prior to placing fill, debris/unsuitable surface material should be removed.

We recommend that the soils within the footprint of the proposed building be removed and replaced to a minimum depth of 3 feet below the bottom of floor slabs. Structural fill placed beneath the entire footprint of the foundations should extend horizontally a minimum distance of 5 feet beyond the outside edge of footings.

Deep

Foundations

It is recommended to use drilled shafts to support the proposed structure loads.

Pavements With subgrade prepared as noted in Earthwork, a concrete or asphalt pavement system may be considered for this project.

General

Comments This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report for design purposes.

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed engineering building to be located at

2101 NASA Road 1 in Houston, Texas. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Site preparation and earthwork

■ Foundation design and construction

■ Estimated settlement of foundations

■ LPILE parameters

■ Pavement design guidelines

The geotechnical engineering Scope of Services for this project included the advancement of test borings, Cone Penetrometer Tests (CPTs), laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and

Exploration Plan, respectively. 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 the Exploration and Laboratory Results section.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. Our final understanding of the project conditions is as follows:

Item Description

Information

Provided

Project details site plan and information were provided by RS&H

Architects-Engineers-Planners, Inc. (RS&H) on August 8, 2023.

Project

Description

This project includes construction of a new engineering building within an approximate footprint area of 300 feet by 120 feet and a maximum height of 60 feet.

In addition, two driveways to the proposed building are planned for this project.

Finished Floor

Elevation

Finished floor elevation for the building is anticipated to be within 1 to 2 feet of existing grade.

Building

Construction Tilt-up building

Facilities | Environmental | Geotechnical | Materials 2

Item Description

Maximum Loads

■ Columns: 250 to 350 kips

■ Walls: 8 kips per linear foot (klf)

■ Slabs: 300 pounds per square foot (psf)

Planned foundation systems

Drilled straight shafts

Pavements

Information regarding anticipated traffic and preferred pavement surfacing has not been provided. For concrete pavement, the anticipated traffic categories and daily truck traffic will be assumed to consist of:

■ Category A: Car parking areas and access lanes, 1 truck per day

■ Category B: Entrance and truck service lanes, 10 trucks per day

■ Category E: Garbage or fire truck lanes

For asphalt pavement, we assume that the asphalt pavement traffic classification will consist of:

■ Class I: Parking stalls for autos and pickup trucks

■ Class II: Traffic consisting of home delivery trucks, trash pickup

The pavement design period is 20 years.

We anticipate the fire lane are to be designed to support a

90,000-pound (lb) wheel load, up to two times annually.

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 is located at 2101 NASA Road 1 in Houston, Texas.

Project GPS: 29.553926° N 95.091116° W (approximate)

See Site Location

Existing

Improvements The project site is situated between two existing parking lots.

Facilities | Environmental | Geotechnical | Materials 3

Current Ground

Cover Grass, weeds, and scattered trees

Existing

Topography Relatively level

Geotechnical Characterization

Geology

Based on the geologic maps published by the Bureau of Economic Geology, the site for the proposed construction is located on the Beaumont formation, a deltaic nonmarine

Pleistocene deposit. The Beaumont formation is heterogeneous containing thick interbedded layers of clay, fine sand, and silt.

The clay fraction is primarily composed of montmorillonite, illite, kaolinite, and finely ground quartz. The clay present in the formation has been preconsolidated by a process of desiccation. Numerous wetting and drying cycles have produced a network of small randomly oriented, closely-spaced joints within some depth zones. These small joints frequently have a shiny appearance and the clays are called slickensided in these cases.

The joint pattern may have an influence on the construction and engineering behavior of the soil.

The coastal plain in this region has a complex tectonic geology, several major features of which are: Gulf Coastal geosyncline, salt domes, and major sea level fluctuations during the glacial stages, subsidence and geologic faulting activities. Most of these geologic faulting activities have ceased for millions of years, but some are still active. A detailed geologic fault investigation and study of the site geology are beyond the scope of this report.

Subsurface Profile

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 the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration Results and the GeoModel can be found in the Figures attachment of this report.

Facilities | Environmental | Geotechnical | Materials 4

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

Lean Clay and

Lean Clay with

Sand dark gray, tan, reddish brown, and gray, stiff to hard, with scattered roots, calcareous and ferrous nodules, sand pockets, silt pockets and seams

Fat Clay and

Fat Clay with

Sand reddish brown, tan, gray, very stiff to hard, with scattered roots, calcareous and ferrous nodules, slickensides, and silt pockets

3 Clayey Sand reddish brown, tan, and gray, medium dense, with clay and silt pockets

Groundwater Conditions

Borings B-01 through B-03 were advanced using dry drilling techniques to depths of approximately 30 feet in an effort to evaluate groundwater conditions at the time of our field program. Wet rotary techniques were used thereafter to the termination depth of the boring

(about 50 feet). Groundwater was initially observed at depths that ranged from approximately

26 to 28 feet during dry drilling. After a 15-minute monitoring period, groundwater was observed at depths that ranged from about 12 to 26 feet.

The water levels observed in the boreholes can be found on the boring logs in Exploration and Laboratory Results. Mapping by the Natural Resources Conservation Service

(NRCS) indicates a seasonal high groundwater level within 6 feet of ground surface.

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 and should be evaluated prior to construction.

Geotechnical Overview

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the test borings and CPTs, provided that the recommendations provided in this report are implemented in the design and construction phases of this project.

Facilities | Environmental | Geotechnical | Materials 5

The subsurface materials generally consisted of fat clay and lean clay extending to the termination depth of the borings and CPTs. Clayey sand material was encountered at about 33 to 43 feet and again at 60 to 65 feet.

The near surface soils could become unstable with typical earthwork and construction traffic, especially after precipitation events. Effective drainage should be established early in the construction sequence and maintained after construction to avoid potential issues. If possible, the grading should be performed during the warmer and drier times of the year. If grading is performed during the winter months, an increased risk for possible undercutting and replacement of unstable subgrade will persist. Additional site preparation recommendations, including subgrade improvement and fill placement, are provided in the Earthwork section.

Based on the conditions encountered and estimated load-settlement relationships, the proposed structures can be supported on drilled straight shafts.

Our laboratory program includes consolidation testing to help evaluate the load-settlement relationship of shallow foundations. The test is currently in progress at the time of this draft report, however the sample specimen at lower-end loads preliminarily indicates that shallow foundation support of the loads noted in the project description will result in settlement that either exceeds 1 inch or will require extensive ground improvement to reduce the settlement to 1 inch. This report does not include a shallow foundation alternate. Once testing and our analysis is complete, supplemental information will be provided and a shallow foundation alternate presented in the final report if appropriate. Based on the lower strength and higher compressibility soils in the upper portion of the profile and the improved strengths with depths indicated by CPT, we believe that drilled shaft support is appropriate for the structure.

Expansive soils are present on this site. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion by partial removal and replacement of expansive soils. However, even if these procedures are followed, some movement and

(at least minor) cracking in the structure should be anticipated. The severity of cracking and other damage such as uneven floor slabs will probably increase if modification of the site results in excessive wetting or drying of the expansive soils. Eliminating the risk of movement and 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.

The Deep Foundations section addresses support of the building on drilled straight shafts. The Floor Slabs section addresses slab-on-grade support of the building on approved select fill.

Our opinion of pavement section thickness design has been developed based on our understanding of the intended use, assumed traffic, and subgrade preparation recommended herein using methodology contained in ACI 330 “Guide to Design and

Construction of Concrete Parking Lots” and NAPA IS-109 “Design of Hot Mix Asphalt

Facilities | Environmental | Geotechnical | Materials 6

Pavements” and adjusted with consideration to local practice. The Pavements section includes minimum pavement component thickness.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration and Laboratory Results), engineering analyses, and our current understanding of the proposed project. The

General Comments section provides an understanding of the report limitations.

Earthwork

Earthwork is anticipated to include stripping, excavations, and engineered 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 and floor slabs.

Site Preparation

Prior to placing fill, debris/unsuitable surface material should be removed. Complete stripping of the topsoil should be performed in the proposed building.

Although no evidence of fill or underground facilities (such as septic tanks, cesspools, basements, and utilities) was observed during the exploration and site reconnaissance, such features could be encountered during construction. If unexpected fills or underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction.

Subgrade Preparation

We recommend that the soils within the footprint of the proposed building be removed to a minimum depth of 3 feet below the bottom of floor slabs. Select fill placed beneath the entire footprint of the foundations should extend horizontally a minimum distance of 5 feet beyond the outside edge of footings.

The subgrade should be proofrolled with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck. The proofrolling should be performed under the observation of the Geotechnical Engineer or representative. Areas excessively deflecting under the proofroll should be delineated and subsequently addressed by the

Geotechnical Engineer. Such areas should either be removed or modified by treating with lime. Excessively wet or dry material should either be removed or moisture conditioned and recompacted.

Facilities | Environmental | Geotechnical | Materials 7

All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of 10 inches, moisture conditioned as necessary, and compacted per the compaction requirements in this report. Compacted structural fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation or slab construction.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill. Structural fill is material used below, or within 5 feet of structures.

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.

Soil Type 1 USCS Classification and Parameters Acceptable Placement Location

Select Fill

Lean Clay (CL) or

Clayey Sand (SC)

10≤PI≤20

Must be used to construct the structural fill building pad beneath the grade-supported slab foundations. Select fill should also be considered below exterior flatwork to reduce potential movements.

1. Select fill should consist of approved materials 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.

Reuse of On-Site Soil: Excavated on-site near surface soil is not expected to be suitable for reuse as Select Fill and should not be placed beneath settlement sensitive structures and within foundation bearing zones. The near surface on-site soils 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.

Fill Placement and Compaction Requirements

Select fill should meet the following compaction requirements.

Facilities | Environmental | Geotechnical | Materials 8

Item Select Fill Fill

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

95% of maximum

Water Content

Range 1

-3% to +3% of optimum

Existing Fat Clays: 0 to +4%

1. Maximum density and optimum water content as determined by the standard

Proctor test (ASTM D 698).

2. High plasticity cohesive fill should not be compacted to more than 100% of standard Proctor maximum dry density.

Grading and Drainage

All grades must provide effective drainage away from the building during and after construction and should be maintained throughout the life of the structure. Water retained next to the building can 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. The roof should have gutters/drains with downspouts that discharge onto splash blocks at a distance of at least 10 feet from the building.

Exposed ground should be sloped and maintained at a minimum 5% away from the building for at least 10 feet beyond the perimeter of the building. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork. 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

Shallow excavations for the proposed structure are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of grade-supported improvements such as floor slabs. Construction traffic over the completed

Facilities | Environmental | Geotechnical | Materials 9 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 areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

The groundwater table could affect overexcavation efforts, especially for overexcavation and replacement of lower strength soils. A temporary dewatering system consisting of sumps with pumps may be necessary to achieve the recommended depth of overexcavation depending on groundwater conditions at the time of 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.

Excavations or other activities resulting in ground disturbance have the potential to affect adjoining properties and structures. Our scope of services does not include review of available final grading information or consider potential temporary grading performed by the contractor for potential effects such as ground movement beyond the project limits. A preconstruction/ precondition survey should be conducted to document nearby property/infrastructure prior to any site development activity. Excavation or ground disturbance activities adjacent or near property lines should be monitored or instrumented for potential ground movements that could negatively affect adjoining property and/or structures.

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, and pavements), evaluation and remediation of 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, as recommended by the Geotechnical Engineer prior to placement of additional lifts.

Facilities | Environmental | Geotechnical | Materials 10

In areas of foundation excavations, the bearing subgrade should be evaluated by the

Geotechnical Engineer. If unanticipated conditions are observed, 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.

Deep Foundations

Based on site conditions and the expected loadings, we are providing recommendations for drilled straight shafts.

Vertical downward forces can be resisted by the allowable end bearing pressure of the soils at the bottom of the deep foundation coupled with skin friction along the sides of the shaft. Vertical uplift forces can be resisted by the dead weight of the foundation.

Deep foundations will also provide resistance to vertical forces through the mobilization of the skin friction acting at the interface of the deep foundation sidewall and adjacent soils. The allowable skin friction values provided in the following tables may be used to calculate the uplift resistance for the deep foundation.

Drilled Shaft Design Parameters

Allowable skin friction and end bearing values for drilled, straight-shaft foundations are presented in the following table. These design parameters were computed based on a generalized soil profile and engineering properties of the subsurface soils observed within the depths explored at this site.

Drilled Shaft Design Summary

Below Existing Grade1

(feet)

Allowable Skin

Friction

(psf)

Allowable End Bearing

Pressure

(psf)

0 to 4 -- --

4 to 10 200 --

10 to 33 270 3,000

33 to 43 300 5,600

43 to 60 400 4,500

Facilities | Environmental | Geotechnical | Materials 11

Drilled Shaft Design Summary

Below Existing Grade1

(feet)

Allowable Skin

Friction

(psf)

Allowable End Bearing

Pressure

(psf)

1. Below existing grade at the time of our field program.

2. The allowable end bearing and skin friction values include a factor of safety of 2 for skin friction and a factor of safety of 3 for end bearing.

Drilled, straight-shaft foundations will provide resistance to structural uplift loads through the mobilization of the skin friction acting at the interface of the shaft sidewall and the adjacent soils. The allowable skin friction values provided in the previous table with a reduction of 30% may be used to calculate the uplift resistance for the shafts.

The upper 4 feet of pile skin friction and end bearing values have been ignored to account for surface effects, the presence of expansive soils, and anticipated disturbance during foundation installation. A minimum penetration of 4 feet into the desired bearing strata with a minimum of 4 feet of the selected bearing stratum below the bottom of the shaft is required to achieve the recommended allowable end bearing values provided in the above table. The drilled, straight-shaft foundations should extend through new fill soils and be placed to bear within the native soils at a minimum depth of 14 feet below existing grade.

There are numerous factors which contribute to the behavior of groups subjected to axial load. Several of these factors are foundation type, size and length, spacing, overall group size, loading conditions, installation procedures and soil type and strength. We recommend a minimum spacing of three diameters, center-to-center, for shafts placed in groups beneath square or rectangular caps. However, for shafts placed in a linear pattern beneath load bearing walls, a minimum spacing of two diameters, center-to-center, would generally be acceptable. Closer spacing than three diameters in groups or two diameters in rows could result in increased group settlement and a reduction of load-carrying capacity of individual foundation elements.

Settlement of a single, isolated shaft will depend on the elastic properties of the foundation, the applied load, and the interaction of the soil and foundation. Settlement is anticipated to be primarily elastic and will occur relatively soon as load is applied.

Significant consolidation settlement due to applied load is not anticipated for the allowable capacities. Our experience indicates that a single, isolated foundation loaded to about one-half of its ultimate capacity will result in settlements of about 1 inch or less. Groups generally undergo more settlement than single, isolated foundation elements for the same applied load. Based on the above recommended spacing, we

Facilities | Environmental | Geotechnical | Materials 12 anticipate that settlement of a group will be on the order of 1 inch under working loads with differential settlement between foundations to be about ½ inch.

Drilled Shaft Construction Considerations

The drilling contractor should be experienced in the subsurface conditions observed at the site, and the excavations should be performed with equipment capable of providing a clean bearing area. The drilled straight-shaft foundation should be installed in general accordance with the procedures presented in "Standard Specification for the

Construction of Drilled Piers", ACI Publication No. 336.1-01.

The successful completion of the drilled straight-shaft will depend to a large extent on the suitability of the equipment and the operator's skills. The operation sequence should be scheduled so that the shaft excavation can be completed, reinforcing steel placed, and the concrete poured in a continuous, rapid, and orderly manner to minimize the time the excavation is open. Concrete should be placed as soon as practical and in all instances should be placed within the same day in order to use the side friction values recommended in this letter report.

Based on the subsurface conditions observed, the installation of drilled straight-shafts may require the use of the Slurry Displacement Method and/or temporary steel casing due to the presence of sandier/siltier zones. If drilled shaft installation is attempted without utilizing Slurry Displacement Method or temporary casing, zones of sloughing soils and/or groundwater inflow may occur during construction. Therefore, we recommend that provisions be incorporated into the plans and specifications to utilize slurry or casing to control sloughing and/or groundwater seepage during shaft construction.

The need for casing or slurry will depend on the depth of the drilled shaft and the groundwater conditions at the time of construction. If casing is used and seepage persists, the water accumulating in the foundation excavation should be pumped out.

The condition of the bearing surface should be evaluated immediately prior to placing concrete, if casing is used in lieu of slurry. If groundwater inflow is too severe to be controlled by the use of casing and pumping or significant sloughing of the sidewalls occurs, the slurry method of construction should be utilized to complete the foundation installation.

Where casing is used, removal of the casing should be performed with extreme care and under proper supervision to minimize mixing of the surrounding soil and water with the fresh concrete. Rapid withdrawal of the casing may develop a suction that could cause the soil and water to flow into the excavation. An insufficient head of concrete in the casing during withdrawal could also allow the water to intrude into the wet concrete.

Under no circumstances should loose soil be placed in the annulus between the casing

Facilities | Environmental | Geotechnical | Materials 13 and the drilled shaft sidewalls. The casing must be removed in order to utilize the skin friction values previously provided.

During slurry displacement, the foundation excavation is filled with a slurry mixture. The level of slurry should be maintained above the groundwater level to maintain a positive head in the foundation excavation. Therefore, the slurry tends to seep out of the excavation, rather than the groundwater seeping into the open excavation. The slurry must be maintained in the foundation excavation until design termination depth is achieved and should be removed only as concreting proceeds. The properties of the slurry including the density, viscosity, and pH must be carefully controlled and should be in accordance with Item 416 of Texas Department of Transportation (TXDOT) Standard

Specifications for Construction of Highways, Streets, and Bridges.

Slurry left in place for long periods of time will build up on the sides of the shaft causing a reduction in skin friction.

The following procedures and equipment are recommended for installation of drilled shafts by the Slurry Displacement Method:

■ The bottom of the drilled straight-shaft should be cleaned as well as practical just prior to concreting to remove cuttings.

■ The concrete should be placed by means of a tremie with a one-way valve to prevent slurry from entering the pipe. The tremie should extend to the bottom of the drilled shaft to allow displacement of the slurry during concrete placement.

■ During concrete placement, the end of the tremie should remain several feet within the concrete mass to reduce the entrapment of slurry. A tremie embedment of 5 to 10 feet is generally considered acceptable.

■ The concrete should be relatively fluid to reduce the entrapment of slurry. We recommend that concrete with a slump of 6 to 8 inches be used.

■ The upper few feet of concrete should be expunged from the shaft excavation if found to be contaminated with slurry or soil.

Production shaft installation should be closely monitored by a qualified technician experienced in drilled shaft installation techniques. At a minimum, the technician should observe shaft excavation, note any unusual installation occurrences, observe slurry properties and/or casing installation and removal, observe concrete placement and generally evaluate if shaft installation is being performed in accordance with project specifications.

Lateral Loading

The following table lists input values for use in LPILE analyses. Such analysis should be considered if lateral loads exceeds 10 kips. Modern versions of LPILE provide estimated

Facilities | Environmental | Geotechnical | Materials 14 default values of kh and E50 based on strength and are recommended for the project.

Since deflection or a service limit criterion will most likely control lateral capacity design, no safety/resistance factor is included with the parameters.

Stratigraphy1

L-Pile Soil Model Su

(psf)2

(pcf)2 ε50

K (pci)

Below Existing

Grade 1 (feet)

Static Cyclic

0 to 6 Stiff Clay w/o Free

Water 750 -- 115 Use Default Value

6 to 33 Stiff Clay w/o Free

Water 1,000 -- 55 Use Default Value

33 to 43 Sand (Reese) -- 29 55 Use Default Value

43 to 60 Stiff Clay w/o Free

Water 1,500 -- 55 Use Default Value

60 to 65 Sand (Reese) -- 29 60 Use Default Value

1. See Subsurface Profile in Geotechnical Characterization for more details on

Stratigraphy.

2. Definition of Terms:

Su: Undrained shear strength

: Internal friction angle

’: Effective unit weight

Lateral Group Effects

When shafts or piles are used in groups, the lateral capacities of the shafts or piles in the second, third, and subsequent rows of the group should be reduced as compared to the capacity of a single, independent shaft. Guidance for applying p-multiplier factors to the p values in the p-y curves for each row of pile foundations within a pile group are as follows:

Center to Center Pile

Spacing 1,2

P-Multiplier, Pm

Front Row Second Row

Third and

Subsequent

Rows

3B 0.8 0.4 0.3

4B 0.9 0.65 0.5

5B 1.0 0.85 0.7

6B 1.0 1.0 1.0

Facilities | Environmental | Geotechnical | Materials 15

Center to Center Pile

Spacing 1,2

P-Multiplier, Pm

Front Row Second Row

Third and

Subsequent

Rows

1. Spacing in the direction of loading. B = pile diameter

2. For the case of a single row of piles supporting a laterally loaded grade beam, group action for lateral resistance of piles would need be considered when spacing is less than three pile diameters (measured center-to-center).

3. See adjacent figure for definition of front, second and third rows.

Spacing closer than 3D (where D is the diameter of the shaft or piles) is not recommended without additional geotechnical consultation due to potential for the installation of a new shaft disturbing an adjacent installed shaft likely resulting in axial capacity reduction.

Floor Slabs

Planned finished grade for the proposed building was not available at the time of this report. We anticipate that the finished floor elevation of the proposed building is planned to be within about 1 to 2 feet above the existing grade. If the grading is planned to be altered from what has been previously described, Terracon should be notified to review and/or modify our recommendations.

Design parameters for floor slabs assume the requirements for Earthwork have been followed. Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab.

The near-surface soils observed at this site generally exhibit a moderate to high expansion potential. These soils can subject the interior floor slab of the building to significant movements (due to shrinking and swelling) with fluctuations in their moisture content. This movement potential is influenced primarily by the properties of the subgrade soils, as well as the moisture content of the subgrade at the time of construction, overburden pressures, and the stability of the moisture contents throughout the life of the building. 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 up to approximately 1¾ inches. Therefore, we recommend that the near-surface soils be prepared as stated below to reduce the potential for slab movement associated with volumetric changes of the near-surface clay soils due to

Facilities | Environmental | Geotechnical | Materials 16 moisture variations to a more acceptable level. 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.

The most common method of subgrade preparation to reduce potential expansion of the subgrade would be to provide a pad of properly placed and compacted select fill beneath the grade-supported floor slabs. The corresponding decrease in the potential soil movements is primarily a function of the fill pad thickness and the moisture levels of the underlying clay subgrade. While the indicated preparations do not eliminate the potential for soil movement, the magnitude of such movements should be reduced to more acceptable levels. To provide uniform support to the floor slab and to reduce the estimated PVR to approximately 1 inch or less, we recommend that a minimum 36 inches of properly placed and compacted select fill material be constructed immediately beneath the floor slab. The select fill pad should extend a minimum of 5 feet beyond the edge of the building area. The final exterior grade adjacent to the structure should be sloped to promote effective drainage away from the structure.

Select fill should be utilized for all grade adjustments within the proposed building area. The subgrade and select fill soils should be prepared as outlined in the Fill Placement and

Compaction Requirements section of this report, which contains material and placement requirements for select fill, as well as other subgrade preparation recommendations.

The subgrade soils for flatwork outside of the structure which will be sensitive to movement should be prepared as discussed previously. This preparation will be important on surrounding sidewalks and paving immediately adjacent to the structure. If these adjacent flatwork areas are not prepared as stated above for the building area, the estimated PVR for these areas could approach those indicated previously for in-situ conditions. If the soils swell in these areas, this movement could result in significant distress to the adjacent sidewalks and paving and possibly result in reversed drainage (flow of runoff toward the structure) around the perimeter of the structure.

Floor Slab Design Parameters

Floor Slab Support1 Subgrade compacted to recommendations in Earthwork

Estimated Modulus of

Subgrade Reaction 2

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

1. Floor slabs should be structurally independent of building footings or walls 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

Facilities | Environmental | Geotechnical | Materials 17 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, when the project includes humidity-controlled areas, 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 contraction 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 waterproof, 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.

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 observe 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.

Facilities | Environmental | Geotechnical | Materials 18

Pavements

General Pavement Comments

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.

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.

Our opinion of pavement section thickness design has been developed based on our understanding of the intended use, assumed traffic, and subgrade preparation recommended herein using methodology contained in ACI 330 “Guide to Design and

Construction of Concrete Parking Lots” and NAPA IS-109 “Design of Hot Mix Asphalt

Pavements” and adjusted with consideration to local practice. Our pavement design has considered the following traffic levels in association with these design methods:

Asphalt (NAPA IS-109)

■ Class I: Parking stalls for autos and pickup trucks

■ Class II Traffic consisting of home delivery trucks and trash pickup

Portland Cement Concrete (ACI 330-21)

■ Category A: Car parking areas and access lanes, 1 truck per day

■ Category B: Entrance and truck service lanes, 10 trucks per day

■ Category E: Garbage and fire truck lanes

The top 6 inches of the finished subgrade soils directly beneath the pavements should be chemically treated with lime. The decision about the type and proper amount of additive should be made after the subgrade is open for inspection. Chemical treatment will increase the supporting value of the subgrade and decrease the effect of moisture on subgrade soils. This 6 inches of treatment is a required part of the pavement design and is not a part of the site and subgrade preparation for wet/soft subgrade conditions.

Facilities | Environmental | Geotechnical | Materials 19

Pavement Section Thicknesses

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 tests, etc.) was not performed for this project to evaluate the support characteristics of the subgrade.

Asphaltic Concrete Design

Layer Thickness (inches)

Traffic Class I 1 Traffic Class II 1

Asphaltic Concrete 2 2.5

Aggregate Base 8 10

Treated Subgrade 6 6

1. See Project Description for more specifics regarding traffic assumptions.

The asphaltic concrete sections above should not be used in locations where emergency vehicles, which are permitted to exceed roadway weight limits, may travel.

Portland Cement Concrete Design

Layer Thickness (inches)

Traffic Category A 1 Traffic Category B 1 Traffic Category E 1

Concrete 5 6 8

Treated

Subgrade 6 6 6

1. See Project Description for more specifics regarding traffic classifications.

The concrete pad in waste dumpster 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.

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

Concrete Pavement – The materials and properties of concrete pavement including joint requirements should meet applicable requirements in ACI 330-21 Commercial Concrete

Parking Lots and Site Paving Design and Construction - Guide. The thickness of concrete

Facilities | Environmental | Geotechnical | Materials 20 has been developed based on a minimum modulus of rupture of 550 psi which typically correlates to a portland cement concrete mix design with a minimum 28-day compressive strength of 3,500 psi. If submitted concrete mix designs indicate a varying modulus of rupture and compressive strength will be used, Terracon should be contacted to revise the concrete thicknesses.

If river gravel is planned to be utilized in the portland cement concrete mix, Terracon should be contacted for additional services. The presence of river gravel in the portland cement concrete mix can result in excessive cracking and distress to the concrete pavement as a result of differing thermal expansion properties between the river gravel and cement paste. Special care should be taken in developing the project’s portland cement concrete mix design, joint layout, and placement to help reduce the potential for excessive cracking and distress if river gravel is planned to be utilized for the project.

Reinforcing Steel – ACI 330-21 indicates that distributed steel reinforcement is not necessary when the pavement is properly jointed to form short panel lengths that will help reduce intermediate cracking. Use of distributed steel is common in the area, mostly as continuation of historical practice. In shrink/swell-prone areas, distributed steel can limit some abrupt differential movement of adjacent panels subjected to differing soil moisture conditions (such as near pavement openings susceptible to infiltration or near the root system of trees).