13-Appendix H-Geotechnical Engineering Report.pdf

ECS Southwest, LLP Geotechnical Engineering Report

Fort Worth Convention Center Expansion Phase 1

1201 Houston St Fort Worth, Texas 76102

ECS Project Number 63:1834

May 4, 2023

May 4, 2023

Ms. Debbie Fulwiler President Elements of Architecture, Inc.

1201 6th Ave, Suite 100 Fort Worth, Texas 76104

ECS Project No. 63:1834

Reference: Geotechnical Engineering Report

Fort Worth Convention Center Expansion Phase 1 1201 Houston St Fort Worth, Texas 76102

Dear Ms. Fulwiler:

ECS Southwest, LLP (ECS) has completed the subsurface exploration, laboratory testing, and geotechnical engineering analyses for the referenced project. Our services were performed in general accordance with our agreed scope of work. This report presents our understanding of the geotechnical aspects of the project along with the results of the field exploration and laboratory testing conducted, and our design and construction recommendations.

It has been our pleasure to be of service to Elements of Architecture, Inc. during the design phase of this project. We would appreciate the opportunity to remain involved during the continuation of the design phase, and we would like to provide our services during the construction phase operations as well to verify the assumptions of subsurface conditions made for this report. Should you have any questions concerning the information contained in this report, or if we can be of further assistance to you, please contact us.

Respectfully submitted, Ishtiaque Hossain, PhD, P.E. Ranasinghege (Jay) Jayatilaka, Ph.D., P.E.

Geotechnical Department Manager Chief Engineer

IHossain@ecslimited.com JJayatilaka@ecslimited.com

Asif Akhtar, PhD, E.I.T.

Geotechnical Staff Project Manager AAkhtar@ecslimited.com

The electronic seal on this document was authorized by Jay Jayatilaka, PhD, P.E. No. 90187, on May 4, 2023 mailto:IHossain@ecslimited.com mailto:JJayatilaka@ecslimited.com

Fort Worth Convention Center Expansion Phase 1 May 4, 2023 ECS Project No. 63:1834 Page i

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Project Location/Current Site Use

2.2 Proposed Construction

3.0 FIELD EXPLORATION AND LABORATORY TESTING

3.1 Subsurface Characterization

3.2 Groundwater Observations

3.3 Laboratory Testing

4.0 DESIGN RECOMMENDATIONS

4.1 Existing Fill Materials

4.2 Potential Vertical Movements

4.3 Subgrade Improvements

4.4 Foundations

4.4.1 Straight Drilled Shafts- Axial Design Parameters

4.4.2 Straight Drilled Shafts- Lateral Design Parameters

4.4.3 Straight Drilled Shafts- Construction Considerations

4.4.4 Grade Beams/ Pier Caps

4.5 Floor Slab Systems

4.5.1 Structural Floor Slabs

4.5.2 Slab-On-Grade/ Flatwork on Prepared Subgrade

4.6 Building Perimeter Conditions

4.7 Seismic Design Considerations

4.8 Pavement Sections

4.8.1 Pavement Sections

4.8.2 Pavement Materials

4.8.3 Pavement Joints

4.9 Site Retaining Walls

4.9.1 Design Parameters for Bearing and Sliding

4.9.2 Lateral Earth Pressure

4.9.3 Wall Drainage

4.9.4 Backfill Settlement

5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 Subgrade Preparation

5.1.1 Stripping and Grubbing

5.1.2 Proofrolling

5.2 Earthwork Operations

5.3 Material Specifications

5.3.1 Select Fill

5.3.2 Granular Fill

5.4 Foundation and Slab Observations

5.5 Utility Installations

6.0 CLOSING

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APPENDICES

Appendix A – Drawings & Reports

• Site Location Diagram

• Boring Location Diagram

• Generalized Subsurface Section Line A-A’

• Regional Geology

Appendix B – Field Operations

• Reference Notes for Boring Logs

• Subsurface Exploration Procedure

• Boring Logs B-01, B-02, P-01 and P-02

Appendix C – Laboratory Testing

• Laboratory Testing Summary

Appendix D – Supplemental Report Documents

• Clay Plug at Utility Trench

Fort Worth Convention Center Expansion Phase 1 May 4, 2023 ECS Project No. 63:1834 Page 1

EXECUTIVE SUMMARY

The following summarizes the main findings of the exploration, particularly those that may have a cost impact on the planned development. Further, our principal foundation recommendations are summarized. This Executive Summary is intended as a very brief overview of the primary geotechnical conditions that are expected to affect design and construction. Information gleaned from the executive summary should not be utilized in lieu of reading the entire geotechnical report.

• The borings encountered Clayey Sand, Sand and Gravel, and Fat Clay/Sandy Lean Clay Fill followed by weathered tan Limestone. Below weathered tan Limestone, gray Limestone with shale layers were encountered until the termination depths of 50 feet below existing grades. Groundwater was not observed within borings during the drilling operations.

• Fill materials are present at the site. The soils in the building area were relatively soft. We recommend excavating a portion of fill materials and replace with moisture and density control if slab-on-grade is used for the building expansion.

• The planned building expansion may be supported by straight drilled shafts bearing in gray limestone with shale layers. Floor slabs can be placed on grade if some movement can be tolerated. If movements cannot be tolerated, a structural slab should be used.

• It is recommended that ECS conduct a geotechnical review of the project plans (prior to issuance for construction) to check to see that ECS’ geotechnical recommendations have been properly interpreted and implemented.

• To prevent misinterpretation of ECS recommendations, ECS should be retained to perform quality control testing and documentation during construction of the earthwork and foundations for the project.

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1.0 INTRODUCTION

The purpose of this study was to provide geotechnical information for the proposed building addition which will be located on the southeast corner of the existing Fort Worth Conventional Center. In addition to building expansion, the existing Commerce Street will be realigned. The new pavement will be about 1,000 linear feet long. The recommendations developed for this report are based on project information supplied by the client.

Our services were provided in accordance with our Proposal No. 63:2661-GP (Rev. 2), dated February 13, 2023, as authorized by the client on March 1, 2023, which includes our Terms and Conditions of Service.

This report contains the results of our subsurface exploration and geotechnical laboratory testing program, site characterization, engineering analyses, and recommendations for the design and construction of the planned development.

The report includes the following items.

• A brief review and description of our field and laboratory test procedures and the results of testing conducted.

• A review of surface topographical features and site conditions.

• A review of area and site geologic conditions.

• A review of subsurface soil stratigraphy with pertinent available physical properties.

• A final copy of our soil test borings.

• Recommendations for foundations.

• Recommendations for floor slabs.

• Recommendations for pavement subgrades and pavement sections.

• Recommendations for site preparation and construction of compacted fills, including an evaluation of on-site soils for use as compacted fills.

Fort Worth Convention Center Expansion Phase 1 May 4, 2023

2.0 PROJECT INFORMATION

2.1 PROJECT LOCATION/CURRENT SITE USE

The project site is located within the existing Fort Worth Convention Center, west of Commerce Street and E 12th Street in Fort Worth, Texas (GPS: 32.7495 N, 97.3269 W). Existing buildings and concrete pavements currently occupy the site. The site slopes down from the northwest to southeast with a relief of about 6 feet. The location is depicted in Figure 2.1.1 as shown below.

Figure 2.1.1 Site Location

2.2 PROPOSED CONSTRUCTION

We understand that this project consists of addition to the existing Fort Worth Convention Center on the southeast corner. The addition will consist of a steel framed construction and will have a total area of 6,000 sf. We understand that the existing pavement will be demolished prior to construction of the new addition. We further understand that the existing conventional center building is supported by straight drilled shafts in conjunction with structurally supported floor slab.

In addition to building expansion, the existing Commerce Street will be realigned. The new pavement will be about 1,000 linear feet long.

Fort Worth Convention Center Expansion Phase 1 May 4, 2023

3.0 FIELD EXPLORATION AND LABORATORY TESTING

Our exploration procedures are explained in greater detail in Appendix B including the insert titled Subsurface Exploration Procedures. Our scope of work included drilling four (4) borings. Our borings were located with a handheld GPS unit and their approximate locations are shown on the Boring Location Diagram in Appendix A.

3.1 SUBSURFACE CHARACTERIZATION

The regional parent geologic mapping indicates that the site is underlain by the Fort Worth Limestone and Duck Creek (Kfd) geologic formation. In the Fort Worth Limestone and Duck Creek Formation, the parent rock consists of alternating layers of limestone and shale while the Duck Creek formation consists predominately of hard limestone with marl layers. Generally, the more intact un-weathered limestone is grayish in color and weathers into a tan limestone or into highly plastic clay soils. These clays typically exhibit high to very high shrink/swell with change in moisture contents. The clays can typically range from Tan directly above the rock to darker colors near the ground surface and will have higher shrink/swell tendencies near the surface. Groundwater in these formations is mostly encountered at the contacts and limited in quantity (perched).

The subsurface conditions encountered were generally consistent with published geological mapping. The following sections provide generalized characterizations of the soil and rock strata.

Please refer to the boring logs in Appendix B.

Subsurface Stratigraphy

Approximate Depth to Bottom of Strata (ft)

Elevation of Bottom of Strata (1)

(ft) 0Bstratum 1Bdescription Consistency

2 to 62 EL. +602.0 to 606.0 I

FILL, CLAYEY SAND/ SAND AND

GRAVEL, light brown, light gray

Stiff to very stiff

8 to 93 EL. +597.0 to 600.0 II

FILL, FAT CLAY/ SANDY LEAN

CLAY, dark brown, brown, sandy Very stiff to hard

10 to 164 EL. +592.0 to 598.0 III LIMESTONE, weathered, tan, with clay layers

505 EL. +558.0 IV

LIMESTONE, gray, with shale layers

Notes:

(1) Please note that the ground surface elevations were not surveyed by a licensed surveyor; these elevations are approximate based on dfwmaps.com. Elevation ranges are approximate +/- several feet.

(2) Encountered in all borings except B-02.

(3) Encountered in borings B-01 and B-02.

(4) Encountered in all borings. All borings except B-01 were terminated in this stratum at a depth of 10 feet from the existing ground.

(5) Encountered in boring B-01. This boring was terminated in this stratum at a depth of 50 feet from the existing ground surface.

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3.2 GROUNDWATER OBSERVATIONS

Groundwater level observations were made in the borings during drilling operations. In auger drilling operations, water is not introduced into the borehole and the groundwater position can often be determined by observing water flowing into the excavation. Furthermore, visual observation of soil samples retrieved can often be used in evaluating the groundwater conditions.

Groundwater was not observed within all borings during the drilling operations.

Variations in groundwater levels can occur as a result of changes in precipitation, evaporation, surface water runoff, construction activities, and other factors not immediately apparent at the time of this exploration. The highest groundwater observations are normally observed in the late winter and early spring. Therefore, the groundwater conditions at this site could be different at the time of construction. The possibility of groundwater level fluctuation should be considered when developing the design and construction plans for the project.

3.3 LABORATORY TESTING

The laboratory testing consisted of selected tests performed on samples obtained during our field exploration operations. Classification and index property tests were performed on representative soil samples. The soil samples were tested for moisture content, Atterberg Limits, overburden swell, sulfate, unconfined compressive strength of rock, and gradations (passing #200) of which the results are presented in Appendix C.

Soil samples were visually classified on the basis of texture and plasticity in accordance with ASTM D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedures) and including USCS classification symbols, and ASTM D2487 Standard Practice for Classification for Engineering Purposes (Unified Soil Classification System (USCS). After classification, the samples were grouped in the major zones noted on the boring logs in Appendix B. The group symbols for each soil type are indicated in parentheses along with the soil descriptions. The stratification lines between strata on the logs are approximate; in situ, the transitions may be gradual.

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4.0 DESIGN RECOMMENDATIONS

The following recommendations have been developed on the basis of the previously described project characteristics and subsurface conditions. If there are any changes to the project characteristics or if different subsurface conditions are encountered during construction, ECS should be consulted so that the recommendations of this report can be reviewed. Site grading information was not available at the time of preparing this report; however, we have assumed that the building finished floor will be within 2 feet from the existing site grades. If the finished floor elevations deviate from these assumed grades, the recommendations provided below should be evaluated by our office.

4.1 EXISTING FILL MATERIALS

Fill was encountered in the borings in the building area up to a depth of about 9 feet. The existing fill consisted of sandy lean clay, fat clay and clayey sand. The soils were relatively soft. We recommend the subgrade be prepared as described in Section 4.3 Subgrade Improvements if slab-on-grade is used for the expansion.

4.2 POTENTIAL VERTICAL MOVEMENTS

Based on Borings B-01 and B-02 located in the area of the proposed building, on-site subgrade generally consists of sandy lean clay, fat clay and clayey sand fill to depths of about 8 to 9 feet followed by tan weathered limestone.

Based on test method TEX-124-E in the Texas Department of Transportation (TxDOT) Manual of Testing Procedures and our experience with similar soils, we estimate up to about 3 inches of potential vertical movements (PVM) of soils if the soils are at dry moisture levels at the time of construction.

Swell tests performed on selected samples from borings indicated low potential for swell when permitted free access to water at the current moisture levels and under the approximate existing overburden pressure. Typically, moisture levels under a pavement increase with time. Therefore, the moisture levels beneath the concrete pavement could have been increased and reduced swell potential. Based on the current soil moisture conditions, the future swell potential is estimated to be about one inch.

4.3 SUBGRADE IMPROVEMENTS

Because of the presence of relatively soft fill materials near the surface, we recommend excavating 3 feet of soil below the existing grade if slab-on-grade is used for the expansion. The exposed subgrade should then be proofrolled with construction equipment having a minimum axle load of 10 tons [e.g. fully loaded tandem-axle dump truck]. Proofrolling should be traversed in two perpendicular directions with overlapping passes of the vehicle under the observation of an ECS technician. This procedure is intended to assist in identifying any localized yielding materials.

Where proofrolling identifies areas that are yielding or “pumping” subgrade those areas should be repaired. The subgrade should then be scarified. The excavated soil should then be placed at a moisture content at or above optimum moisture content and compacted to at least 95% of the

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Maximum Dry Density as obtained using the Standard Proctor Method (ASTM D-698). If additional fill materials are required to establish finished grades, they should be select fill. Properties of select fill are provided in Section 5.3 Material Specifications. The prepared subgrade should not be allowed to dry and should be moist cured until floor slab is placed.

The subgrade preparation should extend beyond the building lines to include building entrances, abutting sidewalks, and flatwork areas sensitive to movement and 5 feet beyond those elements.

4.4 FOUNDATIONS

Based on the conditions encountered in the borings, the planned additions may be supported on straight drilled shaft bearing in gray limestone with shale layers.

4.4.1 Straight Drilled Shafts- Axial Design Parameters

Axial design parameters for straight drilled shafts are presented in the following table.

Axial Design Parameters for Straight Drilled Shafts

Parameter Recommendations

Bearing stratum Gray Limestone with shale layers

Net allowable end bearing capacity (psf)1

75,000

Allowable skin friction in compression (psf)2

10,000

Allowable skin friction in tension (psf)2

7,000

Reduction in skin friction due to two closely located shafts

No reduction is required for straight drilled shafts with center-to-center spacing of 2.5 times diameter of larger shaft. For closely spaced shafts, the design skin friction varies linearly from the full value at 2.5 times diameters to 50% of the design value at 1.0 times shaft diameter.

Groups of 3 or more shafts spaced closer than 2.5 times shaft diameter

Should be evaluated by ECS. Alternative installation sequences will be required to allow for a minimum of 48 hours of concrete curing time, prior to installation of adjacent shafts.

Soil induced uplift3 1,000 psf acting over the shaft perimeter to a depth of 8 feet.

Settlement4 Less than ½ inch.

Minimum shaft diameter5 18 inches.

Notes:

1. A minimum penetration of 2 feet or one shaft diameter, whichever is greater, into bearing stratum is required to develop the end bearing.

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Parameter Recommendations

2. The skin friction should be applied to that portion of the drilled shafts in direct contact with the bedrock below any temporary casing. The design penetration should be measured from the top of gray limestone, or below the bottom of temporary casing, whichever is deeper.

3. The drilled shafts will be subject to uplift due to swelling of the expansive clays in contact with the drilled shafts. The drilled shafts must be designed with adequate embedment depth resist uplift forces and should be reinforced with sufficient, full-depth, vertical reinforcing steel to resist uplift forces.

4. Settlement will primarily be within the elastic range with a portion of settlement occurring during construction.

5. The actual shaft diameter and penetration into gray limestone must be determined by the structural engineer based on the load applied on the drilled shaft.

4.4.2 Straight Drilled Shafts- Lateral Design Parameters

The drilled shafts may be subject to lateral loads. Preliminary Lateral design parameters in overburden soils and rock are presented in the following table for use in LPILE 2016 computer program, developed by Ensoft, Inc.

LPILE Design Parameters for Soil

Soil Description

LPILE

Material Type

Effective Unit Weight, (pcf)

Undrained Shear strength, (psf)

Friction Angle, (degrees)

K Value (pcf)

E50

Clay Soil (0’ to top of limestone)

Soft Clay 120 750 - - 0.01

LPILE Design Parameters for Limestone

Soil Description LPile

Material Type

Unit Weight, (pcf)

Uniaxial Compressive

Strength, (psi)

Elastic Modulus, Er

(psi)

RQD

Krm

Gray Limestone Weak Rock 135 700 - 80 0.0005

4.4.3 Straight Drilled Shafts- Construction Considerations

The drilled shafts should be installed in accordance with American Concrete Institute’s “Standard Specification for the Construction of Drilled Piers” (ACI 336). Recommendations provided in this report are based on proper construction procedures including maintaining a dry shaft excavation.

We recommend that all drilled shafts be observed by qualified geotechnical personnel, to verify proper shaft installation. Observations should include:

Fort Worth Convention Center Expansion Phase 1 May 4, 2023 ECS Project No. 63:1834 Page 6

1. identification of the bearing stratum.

2. minimum penetration depth.

3. removal of all smear zones and cuttings.

4. correct handling of groundwater seepage.

5. shafts are within acceptable vertical tolerance; and

6. other related items

Groundwater was not observed in the borings during the drilling operations but could be encountered during the installation of straight drilled shafts, particularly if construction proceeds during a wet period of the year. Rapid placement of steel and concrete may permit shaft installation to proceed; however, if significant seepage is encountered, the use of temporary casing for installation of the straight shafts may be required. The casing must be installed to a sufficient depth to ensure that an adequate seal is obtained. Typically, a casing penetration of 1 to 2 feet into the gray limestone with shale layers will provide a satisfactory seal.

After the satisfactory installation of the temporary casing, water and loose material should be removed prior to beginning the design penetration. The required penetration into the bearing material can then be excavated through the casing. The design penetration should be measured from the bottom of temporary casing or the top of gray limestone, whichever is deeper. Reinforcing steel and concrete should be placed immediately after the excavation has been completed, cleaned and observed.

The concrete should have a slump between 5 and 7 inches and should be placed in a manner that prevents it from striking the reinforcing steel and sides of the excavation. Concrete placed in an excavation in excess of 10 feet should be placed in such a manner (using a tremie, centralizing chute, or by similar means) to prevent segregation of aggregates or to prevent concrete from striking the reinforcing steel. The concrete in the upper five feet of the shaft should be mechanically consolidated. Straight drilled shafts should be completed within 8 hours after design penetration into gray limestone with shale layers has begun.

Care should be taken to avoid creating an oversized cap ("mushroom") near the ground surface. A "mushroom" at the top of the drilled shaft could be lifted by expansive soils. Pier caps extending outside the nominal pier diameter (if used) should be constructed over void forms to reduce the potential for additional uplift forces.

Gray limestone with shale layers is relatively hard. We recommend the drilling equipment be equipped with suitable rock drilling teeth and it should have sufficient torque and weight to drill through the rock strata. A contractor experienced with drilling hard bedrock should be retained for this project.

4.4.4 Grade Beams/ Pier Caps

All grade beams should be supported by the drilled shafts and formed with a nominal 8-inch void beneath the beam if structural slab is used. This void is provided to isolate the grade beams from the underlying active clays. Cardboard carton forms can be used to create this void. A soil retainer should be provided to help prevent “in fill” of this void.

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Cardboard void forms must have sufficient strength to support the weight of the grade beam during construction. The excavation in which the void box lays must remain dry. Care must be exercised during construction to prevent collapse of these cartons. Backfill material must not be allowed to enter the void carton area below the grade beams, since this reduces the void space in which the underlying soils need to swell.

Soils placed along the exterior of the grade beams should be on-site clay soils placed and compacted to at least 95% of the Maximum Dry Density at a minimum moisture content at or above optimum moisture content as obtained using the Standard Proctor Method (ASTM D-698). The purpose of this clay backfill is to reduce the opportunity for surface or subsurface water infiltration beneath the structure.

4.5 FLOOR SLAB SYSTEMS

A structural (suspended) floor system is recommended if floor slab movement of about one (1) inch cannot be tolerated. If the floor slab can tolerate movements of about one (1) inch, it can be supported on grade provided the subgrade is prepared as discussed in Section 4.3 Subgrade Improvements.

4.5.1 Structural Floor Slabs

Two methods are available for constructing a suspended floor slab system:

1. cardboard carton forms to create a void; and,

2. raising the floor slab above the underlying soils with a crawl space.

Cardboard carton forms should be at least 12 inches thick. If these forms are used, care must be taken to preserve their structural integrity and ability to create a consistent void. A rigid material layer (such as Masonite) should be placed directly on the forms to prevent puncture by personnel during placement of concrete. This rigid layer would also help reduce the potential for concrete to leak down between the cardboard forms.

If crawl space is utilized, we recommend that the floor slab be suspended at least 12 inches above final subgrade elevations. If utility lines are suspended beneath the slab, the crawl space clearance should be increased to a minimum of 2 feet to provide access to these lines.

The subgrade beneath the crawl space must be graded to remove water from beneath the structure. If gravity drainage cannot adequately remove the water from beneath the structure, it may be necessary to direct the underfloor drainage ditches to a sump pump. Construction must also contain sufficient ventilation to limit corrosion of the metal components.

Future movements of soil supported utility lines must be considered when designing connections, especially where these lines approach or enter the stationary structure. In addition, isolating plumbing lines from the soil can be considered to eliminate plumbing line movements. The commercially available Mudskipper system or similar methods can be used to isolate plumbing lines from soil.

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4.5.2 Slab-On-Grade/ Flatwork on Prepared Subgrade

In conjunction with drilled shafts, the floor slabs can be supported on an improved subgrade if movements of about one (1) inch can be tolerated in the buildings. We recommend preparing the building subgrade as discussed in Section 4.2 Subgrade Improvements.

We recommend that a modulus of subgrade reaction (ks) of 100 pci be used for the design of the slab-on-grade. Adequate construction joints, contraction joints and isolation joints should also be provided in the slab to reduce the impacts of cracking and shrinkage. Please refer to ACI 302.1R96 Guide for Concrete Floor and Slab Construction for additional information regarding concrete slab joint design.

If floor treatments that are sensitive to moisture will be used, a vapor retarder of polyethylene sheeting or similar material should be placed beneath the slab to reduce moisture migration through the slab. Please refer to ACI 302.1R96 Guide for Concrete Floor and Slab Construction and ASTM E 1643 Standard Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs for additional guidance on this issue.

Some of the risks associated with placing slabs or foundations on grade may include uneven floors, floor and wall cracking and sticking doors or windows. Even at low level of post construction movement values, these differential movements cause distress throughout the structure because the movements are seasonal and occur over the life of the structures.

4.6 BUILDING PERIMETER CONDITIONS

Soils placed along the exterior of the building should be on-site clay soils placed and compacted at least 95% of the Maximum Dry Density at or above optimum moisture content as obtained using the Standard Proctor Method (ASTM D-698). The purpose of this clay backfill is to reduce the opportunity for surface or subsurface water infiltration beneath the structure. Additionally, where penetrations into the structure occur, a clay plug (or suitable synthetic alternative) should be placed at the building line to reduce the opportunity for infiltrating water, regardless of the backfill material. A typical clay plug at utility trench detail is provided in Appendix D of the report.

Positive drainage away from the structures should also be provided. Additionally, Irrigation of lawn and landscaped areas should be moderate, with no excessive wetting or drying of soils around the perimeter of the structures allowed. Trees and bushes/shrubs planted near the perimeter of the structures can withdraw large amounts of water from the soils and should be planted at least their anticipated mature height away from the buildings.

Where flatwork is placed against or near the structure, a positive seal must be installed and adequately maintained to reduce water intrusion. Down spouts and gutters should be used to collect and distribute water away from the structure.

Routine maintenance is required to ensure that the recommendations contained in this report are followed and maintained. Greater potential movements could occur with extreme wetting or drying of the soils due to poor drainage, ponding of water, plumbing leaks, lack of irrigation, and/or lack of routine maintenance, etc.

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4.7 SEISMIC DESIGN CONSIDERATIONS

Seismic Site Classification: The International Building Code (IBC) requires site classification for seismic design based on the upper 100 feet of a soil profile. The methods are utilized in classifying sites, namely the shear wave velocity (vs) method; the undrained shear strength (su) method; and the Standard Penetration Resistance (N-value) method. The undrained shear strength (su) method was used in classifying this site.

Seismic Site Classification

SEISMIC SITE CLASSIFICATION

Site Class

Soil Profile Name Shear Wave Velocity, Vs, (ft./s) N value (bpf) Su (psf)

A Hard Rock Vs > 5,000 fps N/A N/A

B Rock 2,500 < Vs ≤ 5,000 fps N/A N/A

C Very dense soil and soft rock 1,200 < Vs ≤ 2,500 fps >50 su ≥ 2,000

D Stiff Soil Profile 600 ≤ Vs ≤ 1,200 fps 15 to 60 1,000 ≤ su ≤ 2000

E Soft Soil Profile Vs < 600 fps <15 su < 1000

Based upon our interpretation of the subsurface conditions, the appropriate Seismic Site Classification is “C” as shown in the preceding table.

Ground Motion Parameters: In addition to the seismic site classification, ECS has determined the design spectral response acceleration parameters following the IBC methodology. The Mapped Reponses were estimated from the USGS website https://earthquake.usgs.gov/ws/designmaps/.

The design responses for the short (0.2 sec, SDS) and 1-second period (SD1) are noted in bold at the far right end of the following table.

GROUND MOTION PARAMETERS [IBC Method]

Period (sec)

Mapped Spectral Response

Accelerations (g)

Values of Site Coefficient for Site Class

Maximum Spectral Response Acceleration

Adjusted for Site Class (g)

Design Spectral Response

Acceleration (g)

Reference Figures 1613.3.1

(1) & (2) Tables 1613.3.3

(1) & (2) Eqs. 16-37 &

16-38 Eqs. 16-39 &

16-40

0.2 SS 0.088 Fa 1.2 SMS=FaSs 0.106

SDS=2/3

SMS

0.07

1.0 S1 0.049 Fv 1.7 SM1=FvS1 0.082

SD1=2/3

SM1

0.055

The Site Class definition should not be confused with the Seismic Design Category designation which the Structural Engineer typically assesses. If a higher site classification is beneficial to the project, we can provide additional testing methods that may yield more favorable results.

4.8 PAVEMENT SECTIONS

The streets may be designed and constructed as per City of Fort Worth 2015 Pavement Design Manual, dated January 29, 2015 (Revised December 14, 2015). Based on the Master Thoroughfare Plan of City of Fort Worth we understand the pavement is classified as Commercial Mixed Use https://earthquake.usgs.gov/ws/designmaps/

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(CMU) street. Design parameters used for the pavement design as collector are summarized in the table below.

Pavement Design Inputs

Design Parameters Design Values

Street Classifications Commercial Collector

Design Life 25 years

Annual ESAL’s 100,000

Total ESAL’s for the design period 3,006,000

Growth Rate 1.5

Reliability (percentage) 85

Initial Pavement Serviceability for Concrete 4.5

Terminal Pavement Serviceability 2.25

Subgrade CBR 3.0

CBR for lime stabilized subgrade 15

Lime Stabilized Layer Thickness 8 inches

Effective Modulus of Subgrade Reaction, k (per manual) 221 pci

Overall Standard Deviation for rigid pavements 0.39

Load Transfer Coefficient 3.0

Drainage Coefficient, Cd 1

Loss of Support 0.0

Concrete Modulus of Elasticity 4,000,000 psi

Concrete Modulus of Rupture 620 psi

Design Software WinPAS

4.8.1 Pavement Sections

Based on the results of our analysis and City of Fort Worth Pavement Design Manual, recommended concrete pavement sections over lime stabilized subgrade are provided below:

Pavement Sections

Street Classification PCC Section (inches) Lime Treated Subgrade (inches)

Collector 8.0 8.0

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An important consideration with the design and construction of pavements is surface and subsurface drainage. Where standing water develops, either on the pavement surface or within the base course layer, softening of the subgrade and other problems related to the deterioration of the pavement can be expected. Furthermore, good drainage should reduce the possibility of the subgrade materials becoming saturated during the normal service period of the pavement.

4.8.2 Pavement Materials

Pavement materials should meet the following requirements of City of Fort Worth 2015 Pavement Design Manual, dated January 29, 2015 (Revised December 14, 2015).

1. Lime Stabilized Subgrade: For lime stabilization, a preliminary application rate of 8% lime by dry weight of clay can be used. The actual amount of lime required should be confirmed by additional laboratory tests (lime series) during the construction phase.

The lime stabilization should conform TxDOT Item 260. The stabilized soil should be compacted to at least 95% of the Maximum Dry Density at workable moisture contents of about 3 percentage points above the optimum moisture content as obtained using the Standard Proctor Method (ASTM D-698). Stabilization should extend at least 2 feet beyond the pavement edges. Soluble sulfates should be tested for subgrade soils to determine the appropriate procedure for lime stabilization.

2. Portland Cement Concrete: Minimum compressive strength of 3,600 lbs per sq inch at 28 days. Concrete should be designed with 3 to 6 percent entrained air.

3. Reinforcing Steel: #3 bars at 18” centers each way.

4.8.3 Pavement Joints

Pavement joints should meet the following requirements of City of Fort Worth 2015 Pavement Design Manual, dated January 29, 2015 (Revised December 14, 2015).

1. Transverse Contraction Joint spacing should not exceed five times the slab thickness in inches.

2. Longitudinal Joints shall be used if width in feet is greater than five times the pavement slab thickness in inches.

3. Expansion Joints to be constructed a maximum of 300’ apart on straight paving. The reinforcement steel requirements depend on the pavement slab thickness.

4.9 SITE RETAINING WALLS

Site retaining walls may be required. Retaining walls associated with the structure should be supported on straight drilled shafts as discussed in Section 4.4 Foundations of this report. Cast-in-place concrete cantilever walls can be used for site retaining walls. Recommendations are provided below.

4.9.1 Design Parameters for Bearing and Sliding

The design parameters for bearing and sliding calculations are provided below.

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Bearing and Sliding Design Parameters

Parameter Recommendation

Bearing stratum 1 On site clay or properly placed and compacted fill

Net allowable end bearing capacity 2 2,500 psf

Minimum embedment 2 feet below lowest adjacent final grade

Minimum dimension 18 inches

Passive pressure (triangular distribution)3, 4 265 psf/ ft

Coefficient of sliding4 0.40

Notes:

1. Retaining walls should be placed on a slope no steeper than 3H:1V and no higher than 5 feet, as defined from the exterior lower footing edge, down to the limit of the slope upon which the retaining wall is built.

2. The net allowable bearing pressure is the pressure in excess of the surrounding overburden pressure at the footing base elevation.

3. The side of the excavation for footings must be nearly vertical and concrete should be placed against these vertical faces. The upper 1-foot of the passive earth pressure should be neglected. In addition, the passive pressure should be ignored if the material in front of the wall will be excavated at any time in the future.

4. A factor of safety of 1.5 is recommended against sliding.

4.9.2 Lateral Earth Pressure

The lateral pressure acting on the walls will depend on the backfill material type, the amount of wall movement and drainage conditions behind the walls. Recommended lateral design parameters are provided below. The values in the table that follows under “Active Conditions” pertain to retaining walls free to tilt outward as a result of lateral earth pressures. For rigid, non-yielding walls (such as below grade walls) which are not allowed to rotate, the values under “At-Rest Conditions” should be used.

Lateral Earth Pressure Design Values

Backfill Type (Level Backfill)

Total Unit

Weight

(pcf)

Active Condition At Rest Condition

Earth Pressure Coefficient, ka

Equivalent Fluid Pressure (psf/ ft)

Earth Pressure Coefficient, ko

Equivalent Fluid Pressure (psf/ft)

On Site Soil/ Imported Soil

125 0.46 57 0.63 79

Select Fill 125 0.36 45 0.53 67

Granular Fill 125 0.28 35 0.44 55

The lateral pressure design values presented above are for a drained condition behind the wall.

Drainage should be provided behind the walls as discussed in Section 4.9.3 Wall Drainage.

Properties of backfill materials are provided in Section 5.3 Material Specifications. The Select fill or granular backfill limits should extend outward at least 1 foot from the base of the heel and then upward on a 1H:1V slope. For narrower backfill widths of select or granular fill, the equivalent fluid pressures for on-site soils should be used.

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The values presented above assume the surface of the backfill materials to be level. Sloping the surface of the backfill materials will increase the earth pressures acting on the retaining wall and can be evaluated if required. The above values also do not include the effect of surcharge loads such as construction equipment, vehicular loads, or future buildings or paving near the walls.

Surcharge loads should be considered if they apply at the surface above the wall within an angle of 45° extending up from the base of the wall.

4.9.3 Wall Drainage

The lateral pressure design values presented above assume a drained condition behind the wall.

Hydrostatic pressures resulting from groundwater seepage entering and ponding within the backfill materials should be considered in the design if proper drainage is not provided.

For walls with a height of 4 feet or less, weep holes can be used for drainage. For walls with a height greater than 4 feet, a vertical wall drain consisting of a composite geosynthetic drainage medium is recommended if select fill or on-site soil is chosen as backfill. The vertical drain should be located immediately behind the wall system and extend from the level of longitudinal drains, upward to not higher than 2 feet below the top of the wall. The vertical drains should transport water to the longitudinal drains and then to a storm water line. Composite geosynthetic drainage systems are typically proprietary systems. They are available in different sizes and with different flow rates. The manufacturer should be consulted for installation and spacing guidelines.

If free-draining granular backfill is used, a vertical wall drain would not be necessary. The granular backfill should transport water to longitudinal drains and then to a storm water line. However, in this case, we recommend that a 2-foot thickness of well-compacted, impervious clay cover be placed over the backfill surface to reduce infiltration in areas that are not covered by pavement. A geotextile filter fabric should be placed between the aggregate backfill and the clay cover materials and between the aggregate backfill and the backslope of the native material to reduce infiltration of fines into the backfill.

4.9.4 Backfill Settlement

Backfill placed behind the walls should be compacted. Special care must be exercised to “tie in” the backfill with adjacent undisturbed, firm, natural soils by providing deep benches into the firm natural soil during placement of each fill lift. All loose materials and “slope wash” that may accumulate in the wall excavation during construction should be completely removed prior to placement of the backfill materials.

Some post-construction settlement of the backfill surface should be anticipated. This is typically on the order of one percent of the backfill height, even if satisfactory compaction of the backfill materials is achieved. This will lead to potential differential settlement. Therefore, it is recommended that special consideration be given to the design of any foundation elements, floor slabs, and pavements that may extend over this backfill as a result of the potential for differential settlements introduced by this condition.

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5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 SUBGRADE PREPARATION

In a dry and undisturbed state, the soil at the site will provide good subgrade support for fill placement and construction operations. However, the soils at the site contain fines which are considered moderately erodible, moisture and disturbance sensitive when wet and degrade quickly with disturbance from contractor operations. Therefore, good site drainage should be maintained during earthwork operations in order to keep the surface water away from the project area during the construction phase. We recommend that an attempt be made to enhance the natural drainage without interrupting its pattern. The erosion and sedimentation shall be controlled in accordance with sound engineering practice and current jurisdictional requirements.

5.1.1 Stripping and Grubbing

The subgrade preparation should consist of stripping vegetation, rootmat, topsoil, existing pavements, and soft or yielding materials from the 5-foot expanded pavement limits. In grassy areas of the site may have about 6 inches of topsoil. Deeper topsoil or organic laden soils may be present in flower beds and other landscaping areas. The root balls in large trees may extend deep and will require additional localized stripping depth to completely remove the organics.

The site preparation may involve demolition of a part of the existing pavement and utilities currently occupying the site. Underground utilities which will be abandoned should be removed or at least filled with flowable concrete. Existing foundation elements, if present, should be removed or cut off at least 2 feet below the new structural elements and utilities.

ECS should be retained to verify that topsoil and yielding surficial materials have been removed prior to the placement of new fill or construction of pavements.

5.1.2 Proofrolling

Prior to fill placement or other construction on subgrades, the subgrades should be evaluated by an ECS field technician. The exposed subgrade outside the moisture conditioned area should be proofrolled with construction equipment having a minimum axle load of 10 tons [e.g. fully loaded tandem-axle dump truck]. Proofrolling should be traversed in two perpendicular directions with overlapping passes of the vehicle under the observation of an ECS technician. This procedure is intended to assist in identifying any localized yielding materials.

Where proofrolling identifies areas that are yielding or “pumping” subgrade those areas should be repaired prior to the placement of subsequent fill or other construction materials. Methods of stabilization include undercutting, moisture conditioning, or chemical stabilization. The situation should be discussed with ECS to determine the appropriate procedure. Test pits may be excavated to explore the shallow subsurface materials to help in identifying the cause of the observed yielding materials, and to assist in the evaluation of appropriate actions to prepare the subgrade.

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5.2 EARTHWORK OPERATIONS

Prior to placement of any new general fill, all subgrades should be scarified to a depth of 6 inches, compacted to at least 95% of Maximum Dry Density as obtained by the Standard Proctor Method (ASTM D-698) and moisture conditioned above the optimum value. Fills should be benched into the existing soils.

Onsite soils can be used as fill materials. Imported soil used in the building area should be select fill.

Imported soil used for general fill outside of the building subgrade improvements should not have a Plasticity Index (PI) of greater than 30. Fill soils should be placed in 8-inch loose lifts for mass grading operations and 4-inch lifts for trench type excavations where walk behind or “jumping jack” compaction equipment is used. Fill materials should be placed at or above optimum moisture content and compacted to at least 95% of the Maximum Dry Density as obtained by the Standard Proctor Method (ASTM D-698).

Upon completion of the filling operations, care should be taken to maintain the soil moisture content prior to construction of floor slabs and pavements. Soil moisture levels can be preserved by various methods that can include covering with plastic, watering, etc. If the soil becomes desiccated, the affected material should be removed and replaced, or these materials should be scarified, moisture conditioned and recompacted.

Utility cuts should not be left open for extended periods of time and should be properly backfilled.

Backfilling should be accomplished with properly compacted on-site soils, rather than granular materials. The clay plug detail provided in Appendix D is an acceptable method for the utility trench cut-off.

Field density and moisture tests should be performed on each lift as necessary to verify that adequate compaction is achieved. As a guide, one test per 2,500 square feet per lift is recommended in the building and paving areas (two tests minimum per lift). Utility trench backfill should be tested at a rate of one test per lift per each 150 linear feet of trench (two tests minimum per lift). Certain jurisdictional requirements may require testing in addition to that noted previously.

Therefore, these specifications should be reviewed, and the more stringent specifications should be followed.

5.3 MATERIAL SPECIFICATIONS

Material specifications recommended for this project are provided below.

5.3.1 Select Fill

For the purposes of this report, Select Fill may consist of imported material that is free of debris and organic matter and have a Plasticity Index (PI) of 5 to 15, and contain 40 to 70 percent passing the No. 200 sieve.

This material should be placed and compacted at workable moisture contents above the optimum moisture content and compacted to at least 95% of the Maximum Dry Density as obtain using the Standard Proctor Method (ASTM D-698).

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5.3.2 Granular Fill

The granular fill can be used as backfill materials behind retaining walls and below grade walls.

Granular fill should consist of crushed limestone with less than 3% passing N0.200 Sieve and less than 30% passing No.40 sieve. The fine materials in the granular fill should be non-plastic. The granular fill should be compacted to 95% of maximum dry density at or above the optimum moisture content as obtained using the Standard Proctor Method (ASTM D-698).

5.4 FOUNDATION AND SLAB OBSERVATIONS

Protection of Foundation Excavations: Exposure to the environment may weaken the soils in foundations if the foundation excavations remain open for too long a time. Therefore, foundation concrete should be placed immediately after the excavation has been completed, cleaned, and observed. If the bearing soils are softened by surface water intrusion or exposure, the softened soils must be removed from the foundation excavation immediately prior to placement of concrete.

5.5 UTILITY INSTALLATIONS

Utility Subgrades: The soils encountered in our exploration are expected to be generally acceptable for support of utility pipes. The pipe subgrades should be observed and probed for stability by ECS.

Any loose or yielding materials encountered should be removed and replaced with acceptable material.

Utility Backfilling: The granular bedding material (often AASHTO #57 stone) should be at least 4 inches thick, but not less than that specified by the civil engineer’s project drawings and specifications. We recommend that the bedding materials be placed up to the springline of the pipe.

Fill placed for support of the…