16-Job 25.0235 Geotechnical Report - Additional Specifications.pdf

GEOTECHNICAL ENGINEERING STUDY

Proposed Retaining Wall Modification and SH 99 Frontage Roads Construction

SH 99 – Between Cumberland Ridge Dr and Schiel Rd Harris County Precinct 3, Texas

TxDOT CSJ No. 3510-06-028

Reported to:

Harris County Toll Road Authority Harris County, Texas

Prepared by:

QC Laboratories, Inc.

10810 Northwest Freeway Houston, Texas 77092

(713) 695-1133

PROJECT NO.: 19G19722.Revision1 May 2023

10810 Northwest Freeway ● Houston TX 77092 ● Tel: 713-695-1133 ● Fax: 713-695-0808

May 4, 2022

Harris County Toll Road Authority

7701 Wilshire Place

Houston, Texas 77040

Attn: Mr. Kaleb Sterling, P.E. – Project Manager

Re: Geotechnical Engineering Study

Proposed Retaining Wall Modification and SH 99 Frontage Roads Construction

SH 99 – Between Cumberland Ridge Drive and Schiel Road

Harris County, Texas, Precinct 3

QCL Project No. 19G19722.Revision1

Dear Mr. Sterling:

We are pleased to submit our geotechnical engineering report for the above referenced project.

This study was authorized through the issuance of the Addendum to Harris County Purchase

Order (PO) Number HCNTY-0000045698, dated December 20, 2022, and by acceptance of QC

Laboratories, Inc. (QCL) Proposal No. 40831.Revision1, dated December 9, 2022.

We appreciate the opportunity to be of service to you on this phase of the project. If we may be of additional assistance, please contact us.

Sincerely, QC LABORATORIES, INC.

(Texas Registered Engineering Firm F-3601)

Peng Sia Tang, M.S.C.E., P.E. 5/4/23

Senior Geotechnical Engineer

Copies Submitted: Addressee - (1) Electronic

Mr. Dale Hilliard / HCTRA - (1) Electronic

Geotechnical Engineering Report Page i Proposed Retaining Wall Modification and SH 99 Frontage Roads Construction May 4, 2023 SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

QCL Project No. 22G19722.Revision1

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Project Description and Scope of Services

2.0 INVESTIGATION TECHNIQUES

2.1 Field Exploration

2.2 Texas Cone Penetrometer Tests

2.3 Laboratory Tests

3.0 GENERAL SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology and Faulting in the Project Area

3.2 Pavement Cores

3.3 Site Conditions

3.4 Subsurface Soil Conditions

3.5 WATER-LEVEL MEASUREMENTS

4.0 FINDINGS AND RECOMMENDATIONS

4.1 MSE Retaining Walls

4.1.1 Structural and Local Stability of the MSE Wall

4.1.2 Local and Global Stability Analyses of the Modified Existing Embankments and MSE Wall

Conclusion: Based on the results of the above local and global slope stability analyses, all the modified embankment slopes have short term and long term loading conditions factors of safety above the TxDOT target value of 1.5. Thus, these modified embankment slopes are theoretically stable in terms of short term undrained and long term effective stress loading conditions

4.1.3 Settlement of the Modified Embankments and the Proposed MSE Wall 16

4.2 Site Preparation and Earthwork

4.3 Constructability Considerations

4.3.1 Open Excavation and Shored and Braced Excavation

4.4 Continuously Reinforced Concrete Pavements (CRCP)

5.0 BASIS FOR RECOMMENDATIONS

6.0 OBSERVATIONS DURING CONSTRUCTION

6.1 Construction Materials Testing

7.0 LIMITATIONS

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Appendix A

Vicinity Map ........................................................................................................................ Plate A-1 Plan of Borings .................................................................................................................... Plate A-2 Logs of Boring (gINT) ................................................................................... Plates A-3 through A-17 Logs of Borings (Wincore) ................................................................................... A-18 through A-32 Boring Log Profiles ........................................................................................... Plates A-33 and A-34 Key to Symbols and Terms ............................................................................... Plates A-35 and A-36 A General Local MSE Wall Stability Analysis (Total and Effective Stress) ........ Plates A-37 and A-38

Appendix B

Summary of Test Results............................................................................... Plates B-1 through B-6

Appendix C

Global Stability Analysis Results for Existing Embankment Slopes Modified – Short Term and Long Term Loading Conditions Analyses:

NB Frontage Road: Station 30+00............................................................ Plates C-1 and C-2

NB Frontage Road: Station 32+00............................................................ Plates C-3 and C-4

NB Frontage Road: Station 34+00............................................................ Plates C-5 and C-6

NB Frontage Road: Station 36+00............................................................ Plates C-7 and C-8

NB Frontage Road at Schiel Road – Retaining Wall Modification ......... Plates C-9 and C-10

SB Frontage Road: Station 18+39 ........................................................ Plates C-11 and C-12

SB Frontage Road: Station 20+00 ........................................................ Plates C-13 and C-14

SB Frontage Road: Station 22+00 ........................................................ Plates C-15 and C-16

SB Frontage Road: Station 23+00 ........................................................ Plates C-17 and C-18

SB Frontage Road: Station 24+00 ........................................................ Plates C-19 and C-20

SB Frontage Road: Station 25+00 ........................................................ Plates C-21 and C-22

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

EXECUTIVE SUMMARY

A Geotechnical Engineering Report has been prepared for the proposed retaining wall modification and the SH 99 frontage roads upgrade between Cumberland Ridge Drive and

Schiel Road in Harris County Precinct 3, Texas.

For this project, a total of fourteen (14) soil borings were drilled and sampled by QCL to depths that ranged from about 10 to 52 feet below the existing grade along the project alignments.

A summary of our findings and recommendations are listed below.

Groundwater and/or caving soils were generally observed at depths that ranged from about 6 to 35 feet below existing grade.

In general, the existing SH 99 main lane embankment at the locations of borings drilled consisted of up to about 16 to 23 feet of embankment fill consisting of firm to hard Lean

Clays (CL) with slight to high plasticity, and some stiff Fat Clays (CH) with very high plasticity. Sand seams/layers/pockets and partings were generally found within this embankment fill.

In general, the natural soils found at the project site generally consist of firm to hard

Lean Clays (CL) with slight to high plasticity, and stiff to hard Fat Clays (CH) with high to very high plasticity.

The subsurface soils found in the soil borings drilled along the project alignment consisted mostly of firm to hard Lean Clays (CL) and Fat Clays (CH), with occasional strata of Silty or Silty-Sandy Lean Clays (CL-ML). Cohesionless soils including Sand (SP), Sand with Silt (SP-SM), Silty Sand (SM) and Clayey Sand (SC), and Silts (ML), ranging in very loose to very dense in consistency, were found in most of the borings within depth zones presented in Table E of this report.

As part of the proposed NBFR reconstruction/construction, the eastern corner of the existing south retaining wall at Schiel Road crossing is proposed to be modified and

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas reconstructed. The design parameters and construction recommendations for the proposed MSE wall are presented in Section 4.1 of this report.

Engineering analyses were performed to evaluate the local and global slope stability for existing SH 99 embankment earth slopes at select locations that will be modified during the proposed NBFR and SBFR and entrance/exit ramps construction/reconstruction, and the proposed retaining wall modification. Based on the results of the above local and global slope stability analyses, all the modified embankment slopes have short term and long term loading conditions factors of safety above the TxDOT target value of 1.5. Thus, these modified embankment slopes are theoretically stable in terms of short term undrained and long term effective stress loading conditions.

The settlements at the locations of the proposed modifications to existing SH 99 embankment, and at the proposed MSE wall location, are addressed in Section 4.1.3 of this report.

Site preparation and earthwork recommendations for the proposed improvements in this project are provided in Section 4.2 of this report.

Constructability issues and considerations for this project are discussed in Section 4.3 of this report.

Open excavation and Braced/Shored excavations recommendations are provided in

Section 4.3.1 of this report.

Pavement subgrade preparation and stabilization, reinforcement requirements, material specifications and construction standards for the proposed continuously reinforced concrete pavements (CRCP) are provided and discussed in Section 4.4 of this report.

Geotechnical Engineering Report Page 1

SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

QCL Project No. 22G19722

1.0 INTRODUCTION

1.1 Project Description and Scope of Services

The general vicinity of this project site is shown in Plate A-1 in Appendix A. This project consists of the proposed retaining wall modification and the SH 99 frontage roads upgrade between

Cumberland Ridge Drive and Schiel Road in Harris County Precinct 3, Texas.

The improvements proposed in this project are shown in Plate A-2a. An overlay of the outline of the proposed improvements over the aerial photography of the project area is shown on Plate A-

2b.

Based on the project information provide by you and Cobb, Fendley & Associates, Inc., we understand that additional geotechnical investigations and analyses are required for the following proposed improvements along SH 99 between Cumberland Ridge Drive and Schiel Road:

Proposed SH 99 NB Frontage Road Construction: As can be seen from Plate A-2b, the southern portion of the SH 99 northbound frontage road (NBFR) and the NB entrance ramp to SH 99 main lanes have been constructed.

o Only a small segment close to the Cumberland Ridge intersection is portland concrete cement (PCC) pavement, and the remaining pavements are asphaltic concrete (AC) pavements.

o The existing AC pavements are proposed to be removed and reconstructed into

PCC pavements.

o In addition, new PCC pavements are proposed to be constructed within the within the existing grassy right-of-way (ROW) along the remainder of the proposed NBFR alignment.

o As part of the proposed reconstruction/construction, the existing east slope of the SH 99 earth embankment will be modified, with some portions of the existing earth slope (typically at approximately 4H:1V) trimmed to approximately

3H:1V along some segments.

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Additionally, as part of the existing SH 99 NBFR proposed reconstruction/construction, the eastern corner of the existing south retaining wall at Schiel Road crossing is proposed to be modified and reconstructed. We understand the proposed modified retaining wall will be a Mechanically Stabilized Earth (MSE) type wall.

Proposed SH 99 SB Frontage Road and Exit Ramp Construction: As can be seen from

Plate A-2b, the southern portion of the SH 99 southbound frontage road (SBFR) and the

SB exit ramp from SH 99 main lanes have been constructed.

o Only the portion close to the Cumberland Ridge Drive intersection is portland concrete cement (PCC) pavement, and the remaining pavements are asphaltic concrete (AC) pavements.

o The existing AC pavements are proposed to be removed and reconstructed into

PCC pavements.

o In addition, new PCC pavements are proposed to be constructed within the existing grassy right-of-way (ROW) along the remainder of the proposed SBFR alignment.

o As part of the proposed construction, the existing west slope of the SH 99 earth embankment will be modified, with some portions of the existing earth slope

(typically at approximately 4H:1V) trimmed to approximately 3H:1V along some segments.

We understand that the PCC pavements are proposed to consist of 9.5 inches of continuously reinforced concrete pavement (CRCP), over 1” of asphaltic concrete (AC), then 6 inches of cement-treated base (CTB), over 6 inches of stabilized subgrade.

This project is funded by Harris County Toll Road Authority (HCTRA). This project will be designed in accordance with Harris County Toll Road Authority (HCTRA) and Texas Department of Transportation (TxDOT) guidelines and requirements.

Our scope of services included evaluating the subsurface conditions by drilling and sampling soil fourteen (14) borings at locations shown on Plate A-2a, perform laboratory tests of selected soil

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas samples, engineering analysis, and preparing a geotechnical engineering report for the project that addresses the following:

Logs of Borings (both in gINT and Wincore format), Plan of Borings, groundwater observations, and laboratory test results.

Discussion of subsurface soils’ properties and stratigraphy found along the project alignment.

Discussion of groundwater conditions found along the project alignments.

Site and subgrade preparation.

MSE retaining wall design guidelines, including discussion and applicable design parameters for the structural design of reinforced earth zone, and local stability evaluation (bearing capacity, overturning, sliding, and settlement), as well as global stability analyses, etc. Recommendations for foundation soils preparation and improvements, and construction of the MSE wall.

Pavement construction recommendations including recommendations for pavement subgrade preparation and stabilization, and construction of the proposed CRCP pavements.

2.0 INVESTIGATION TECHNIQUES

2.1 Field Exploration

In this study, the subsurface conditions along the project alignments were evaluated by drilling and sampling fourteen (14) soil borings to depths ranging from about 5 to 52 feet below the existing grade. The field investigation program was conducted following criteria from both

HCTRA and TxDOT Geotechnical Investigation guidelines.

TABLE A. SUMMARY OF BORINGS CONDUCTED IN THIS PROJECT

Boring

No.

Depth, ft.

Remarks

B-1 52 On existing outside shoulder on SH 99 NB main lane

B-2 20 At proposed retaining wall modification

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Boring

No.

Depth, ft.

Remarks

B-3 40 On shoulder on SH NB main lane, just south of intersection of NB SH main lane and NB frontage road

B-4 10 On existing outside shoulder on SH 99 NB frontage road

B-5 10 On existing outside shoulder on SH 99 NB frontage road

B-6 10 On exiting open grassy area

B-7 45 On existing outside shoulder on SH 99 SB main lane

B-8 40 On existing outside shoulder on SH 99 SB main lane

B-9 40 On existing outside shoulder on SH 99 SB main lane exit ramp

B-10 52 On existing outside shoulder on SH 99 SB main lane

B-11 10 On existing inside shoulder of existing SH SB feeder road

B-12 10 On existing inside shoulder of existing SH SB feeder road

B-13 10 On exiting open grassy area

B-14 10 On exiting open grassy area

Total 349

The boring locations are shown on the Plan of Borings, Plates A-2a in Appendix A of this report.

Some of the borings are located within the existing pavements; at these locations, the pavements were cored through using a pavement coring machine to facilitate the soil borings.

Soil samples were taken continuously to 20 feet and at 5‐foot intervals thereafter to the termination depths of the borings using both a truck- or an ATV-mounted drilling equipment.

Cohesive soils were generally obtained with a 3‐inch diameter tube sampler. Pocket penetrometer tests were performed in the field on extruded tube samples to serve as a general measure of consistency.

Cohesionless soils and soils for which good quality tube samples could not be obtained were sampled using a split‐spoon sampler by means of the Standard Penetration Test (SPT). The SPT test consists of measuring the number of blows required for a 140‐pound hammer (falling 30 inches) to drive the split spoon sampler 12 inches into the subsurface soils, after being seated 6

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas inches. This blow count is used to evaluate the stratum. For this project, an automatic hammer was used to perform the Standard Penetration Test.

Each soil sample was removed/extruded from the sampler in the field, examined, and visually classified by an experienced technician. Upon completion of drilling operations, the boreholes were backfilled with grout. Boreholes located within existing pavement areas were patched at the surface with a lean concrete product.

Following completion of our field services, samples were transported to our laboratory in

Houston. Samples not consumed by testing will be retained in our laboratory for at least 60 days and then discarded unless the Client requests otherwise.

2.2 Texas Cone Penetrometer Tests

In addition to the standard Shelby tube and split spoon sampling with SPT tests, we also performed TxDOT Cone Penetrometer (TCP) Test to evaluate the in-situ strength of the subsurface soils.

The TCP Test was performed in general accordance with TEX 132-E Texas Cone Penetration Test at 5-foot intervals. The TCP test is an in-situ soil displacement test whereby a 170-pound hammer is allowed to fall 24 inches to drive a three-inch cone into undisturbed soils. After initially seating the cone into the soil stratum to be tested, the number of hammer blows is recorded to drive the cone in two sets of 6-inch increments into the soils. Where very hard or dense soils are encountered, the distance the cone penetrates after a series of 50 hammer blows is recorded. This is repeated for two intervals of 50 blows each (a total of 100 hammer blows) for a total penetration of 12 inches or less.

2.3 Laboratory Tests

In the laboratory, a qualified engineer classified each sample. Laboratory tests were performed on selected soil samples to evaluate the physical properties of the soils. The geotechnical engineering properties of the soils were evaluated by performing the following tests:

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

TABLE C. SUMMARY OF LABORATORY TESTS CONDUCTED

Laboratory Tests

Moisture Content (ASTM D2235)

Dry Density (ASTM D2937)

Atterberg Limits (ASTM D4318 - Method B)

Unconfined Compression (ASTM D2166)

Percent Passing the No. 200 Sieve (ASTM D1140)

Detailed soil descriptions and results of the tests are provided on the giNT format logs of boring on Plates A-3 through A-17 in Appendix A of this report, and on the Wincore logs of boring on Plate A-18 through A-32 in Appendix A. Individual test results are presented either on the boring log sheets or on the Summary of Test Results on Plate B‐1 through B-6 in Appendix B of this report.

3.0 GENERAL SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology and Faulting in the Project Area

The geological setting along the SH 99 – Segment F1 alignment was addressed in Corsair Report

No. 1200502 (dated August 26, 2013) Section 4.1. Our project area is located within the Willis

Formations.

The geological faulting in the SH 99 – Segment F-1 area was addressed in Corsair Report No.

1200502 (dated August 26, 2013) Section 4.2. Accordingly, the project site will not be impacted by any documented geological fault.

3.2 Pavement Cores

As mentioned previously, cores were obtained at borings located within existing pavements to facilitate the drilling and sampling of the underlying soils. At the completion of coring and soil sampling, the core locations were backfilled and patched with a lean concrete product. Outlined in the table below is a summary of the cores obtained during our field exploration.

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

TABLE D. PAVEMENT CORE INFORMATION

Boring No.

Pavement Description

B-1 12-½” Portland Cement Concrete (PCC) / 1” Asphaltic Concrete (AC) /

5” Stabilized Aggregate / 7-¼” Stabilized Sand with Gravel

B-3 11-¾” Portland Cement Concrete (PCC) / 1” Asphaltic Concrete (AC) / 7-½” Stabilized Aggregate /

6-¾” Stabilized Sand with Gravel

B-4 4-5/8” Asphaltic Concrete (AC) / 5-¼” Stabilized Aggregate /

8” Stabilized Sand with Gravel

B-5 4-7/8” Asphaltic Concrete (AC) / 6” Stabilized Aggregate /

7-½” Stabilized Sand with Gravel

B-7 12-½” Portland Cement Concrete (PCC) / 1” Asphaltic Concrete (AC) / 7-½” Stabilized Aggregate /

7-½” Stabilized Soil with Gravel

B-8 12-½” Portland Cement Concrete (PCC) / 1-1/8” Asphaltic Concrete (AC) /

5” Stabilized Aggregate / 8-7/8” Stabilized Sand with Gravel

B-9 12” Portland Cement Concrete (PCC) / 2” Asphaltic Concrete (AC) /

13” Stabilized Soil with Gravel

B-10 14” Portland Cement Concrete (PCC) / 1-¼” Asphaltic Concrete (AC) /

5” Stabilized Aggregate / 3” Stabilized Sand with Gravel /

4” Stabilized Soil with Gravel

B-11 10-5/8“ Portland Cement Concrete (PCC) / 1-5/8” Asphaltic Concrete (AC) /

10” Stabilized Aggregate / 2” Stabilized Soil with Gravel

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Boring No.

Pavement Description

B-12 4-½” Asphaltic Concrete (AC) / 7” Stabilized Aggregate /

8” Stabilized Sand with Gravel / 11-½” Stabilized Soil

3.3 Site Conditions

The general area of the project site is located in a mixed residential-commercial-agricultural area.

The land within the proposed SH 99 NBFR and SBFR areas are open grassy lots.

3.4 Subsurface Soil Conditions

The borings were drilled along the proposed NBFR and SBFR and the entrance and exit ramps, at boring locations shown on Plate A-2a.

For the gINT logs, consistency of cohesive soils (clays) were classified based on the shear strength parameters including the hand penetrometer readings and the unconfined compression test results. The relative density of the cohesionless soils (sands and silts) were classified based on the

SPT test blow counts.

For the Wincore logs, consistency of cohesive soils (clays) were classified based on the shear strength parameters including the hand penetrometer readings and the unconfined compression test results. The relative density of the cohesionless soils (sands and silts) were classified based on the TCP test blow counts.

The soils as found various boring locations drilled on existing main lane shoulders, entrance and exit ramps, existing NBFR and SBFR, and within the existing grassy areas of the proposed new

NBFR and SBFR alignments, are shown on the individual boring logs on Plates A-3 through A-32, and in the Boring Log Profiles shown on Plates A-33 and A-34.

Existing SH 99 Main Lane Embankments: The existing SH 99 main lane embankment at the locations of borings drilled consisted of up to about 16 to 23 feet of embankment fill consisting of firm to hard Lean Clays (CL) with slight to high plasticity, and some stiff Fat Clays (CH) with very

Geotechnical Engineering Report Page 9

SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas high plasticity. Sand seams/layers/pockets and partings were generally found within this embankment fill.

A Clayey Sand (SC) (SC) stratum is found within this embankment fill between depths of about 12 and 14 feet at Boring B-9.

Natural Soils at This Project Site: The natural soils found at the project site generally consist of firm to hard Lean Clays (CL) with slight to high plasticity, and stiff to hard Fat Clays (CH) with high to very high plasticity.

Clayey Sand (SC) strata were found at the following locations: B-2 (between depths of about 2 and 4 feet); and, B-7 (between depths of about 21 and 25 feet.

A 2-ft stratum of Sandy Silt (ML) was found at the ground surface.

More detailed soils and stratigraphic information is presented on the Logs of Borings (Plates A-3 through A-32) and on the Boring Log Profiles (Plates A-33 and A-34) in Appendix A of this report.

The boring logs contain our field and laboratory test results, as well as our Field Technician's and

Engineer's interpretation of conditions believed to exist between actual samples retrieved.

Therefore, the boring logs contain both factual and interpretive information. Lines delineating subsurface strata on the boring logs are intended to group soils having similar engineering properties and characteristics; they should be considered approximate as the actual transition between soil types (strata) may be gradual. A key to the soil symbols and terms used on the boring logs is provided on Plate A5, in Appendix A of this report.

3.5 WATER-LEVEL MEASUREMENTS

The borings at this site were drilled using dry auger drilling technique. Dry drilling was used to the depth of groundwater or caving soils. Upon reaching groundwater, drilling was suspended to facilitate observation of groundwater levels prior to switching to wet rotary.

No free water was encountered at any of the fourteen (14) soil borings during and at completion of drilling. It should be noted, however, that fluctuations in the groundwater levels will occur corresponding to variations in rainfall and surface water run-off. The actual groundwater condition should be evaluated prior to construction.

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

4.0 FINDINGS AND RECOMMENDATIONS

The findings and recommendations contained in this report are prepared based on conditions encountered in the boring drilled at this site, our field and laboratory test results, our experience with geotechnical conditions similar to those at this site, and our engineering analyses. In the event that any changes in the nature, location and configurations and design of the proposed structures are made and are materially different from those made available to QCL to date, the findings and recommendations contained in this report shall not be considered valid until the changes are reviewed and the findings are verified in writing.

4.1 MSE Retaining Walls

As part of the SH 99 NBFR proposed reconstruction/construction, the eastern corner of the existing south retaining wall at Schiel Road crossing is proposed to be modified and reconstructed. The plan view of the proposed retaining wall modification is shown on Plate A-

2a.

We understand the proposed modified retaining wall will be a Mechanically Stabilized Earth

(MSE) type wall. Some pertaining information of the proposed retaining wall modification that entails partial removal of the existing northeast corner of the retaining wall and embankment fill, and constructing a new MSE wall are summarized in the table below.

TABLE K. SUMMARY OF PROPOSED MSE WALL

MSE Wall Section Approx.

Length

(feet)

Approx. Width

(feet)

Approximate Wall Height

(feet)

Minimum Maximum

Retaining Wall

Modification at NE Corner of SH 99 and Schiel Road

47 Assuming 0.7*H.

Say 9 feet at highest wall section

3 12.5

Considering TxDOT Houston District criteria, we assumed the following MSE wall design and construction conditions:

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

The MSE wall shall be designed and constructed in general accordance with the latest

TXDOT-Houston District Standard Details Drawing STDB-6 “Cement Stabilized Backfill

Embankment at Bridge Abutments (CSBE - RW)”.

The minimum width of the reinforced earth zone of the MSE wall shall be 0.7 times the height of the wall, but not less than 8 feet.

The MSE wall section with a height of 8 feet or greater should be embedded at least two feet below the final lowest exterior grade; the MSE wall section lower than 8 feet in height should be embedded at least one foot below the final lowest exterior grade.

The MSE wall should be provided with adequate surface insulation and drainage such that surface runoff intrusion is minimal, and adequate back-wall drainage is provided such that the embankment soils will be well drained that full saturation of the embankment soils does not occur.

A uniform 250 psf surcharge load is imposed at the embankment surface subjected to traffic.

Based on the above information and assumptions and the subsurface soil conditions observed at the boring locations, the following MSE retaining wall design recommendations are provided.

4.1.1 Structural and Local Stability of the MSE Wall

The MSE wall shall be designed and constructed in accordance with the latest TXDOT-Houston

District Standard Details Drawing STDB-6 “Cement Stabilized Backfill Embankment at Bridge

Abutments (CSBE - RW)”.

Lateral Earth Pressures: The backfill soils contained within the MSE walls will impose a lateral earth pressure between active and at-rest earth pressures against the MSE wall, depending on the degree of rotation/deflection the imposed loading would incur on the retaining wall structure. For practical design purposes, the approach of imposing an active lateral earth pressure and applying adequate factors of safety in the structural design and local stability analyses is employed in typical retaining wall structure design.

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

For the proposed MSE wall, cement stabilized sand backfill will be used in both the reinforced soil zone and the designated cement stabilized sand backfill area. The following design soil parameters are provided for the structural design and local stability analyses of the MSE wall.

TABLE L. SOIL PARAMETERS FOR MSE WALL DESIGN

Backfill Type Estimated Unit Weight (pcf)

Total and Effective Stress Soil Parameters

Total Effective C (psf) φ (degrees) C’ (psf) φ’ (degrees)

Cement Stabilized Sand

Backfill

For MSE Zone

(TxDOT SSCMHSB Item

423, Subsection 2.4.4)

125 63 0 35 0 35

Foundation Soils

(see Boring B-2)

125 63 1,200 0 200 24

The values presented in the above table do not include either a hydrostatic component or a surcharge component. The effect of surcharge loads, where applicable, should be incorporated into pressure diagrams by adding a pressure component equal to the appropriate lateral earth pressure coefficient multiplied by the surcharge load to the full height of the structure.

Adequate backwall drainage should be provided for the MSE wall system to ensure that no full saturation of the retained backfill occurs. In unpaved areas, the final 12-inches of backfill behind the walls should consist of cohesive soils (clay), to help reduce percolation of surface water into the backfill.

Structural Design: A detailed structural design and analysis of the MSE wall include the structural design of the reinforced earth zone, including the pullout and rupture resistance of the reinforcements. The detailed MSE wall structural and local stability design should be conducted by a structural engineer working in conjunction with the soil reinforcement manufacturer.

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Local MSE Stability Analyses: The local stability analyses of the MSE wall, in terms of foundation soil bearing capacity, and against sliding and overturning should be checked to ensure that the minimum factors of safety are provided.

A general local stability analysis of the proposed MSE wall, using estimated dimensions, was conducted and is presented on Plates A-36 and A-37.

A detailed sliding and overturning analysis of the MSE wall should be conducted by the structural engineer designing the MSE walls, based on the final MSE dimensions and configuration, and working in conjunction with the structural information provided by the MSE reinforcement manufacturer.

The allowable soil bearing capacity of the foundation soils found at these retaining walls, with the recommended foundation soil improvements, are provided in the table below:

TABLE M. RECOMMENDED FOUNDATION SOILS IMPROVEMENT AND

ALLOWABLE SOIL BEARING CAPACITY

MSE Wall

Section

Applic-able

Borings

Foundation Soil Types and

Recommended Foundation Soil

Improvements

Estimated MSE Wall

Height (feet)

Allowable Soil

Bearing Capacity of

Improvement

Subgrade, psf (FS=2)

Minimum Maximum

Retaining

Wall

Modification with New

MSE Wall at

NE corner of

SH 99 and

Schiel Road

B-2 2’ of stiff sandy clay / 2’ of Clayey Sand / stiff Sandy Lean Clay

Recommended Foundation Soils

Improvement:

Remove top 2 feet of sandy clay subgrade soils (top 1 feet if height of wall is less than 8 feet, providing gradual transition in design).

Inspect excavated subgrade for soft/weak and deleterious material;

remove such material and replace with clean similar stable onsite soils.

Proofroll and compact (see Section

4.2 “Earthwork”), and place

12.5

3,000

[based on short term, total stress condition]

3,500

(based on long term, effective stress condition)

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

MSE Wall

Section

Applic-able

Borings

Foundation Soil Types and

Recommended Foundation Soil

Improvements

Estimated MSE Wall

Height (feet)

Allowable Soil

Bearing Capacity of

Improvement

Subgrade, psf (FS=2)

Minimum Maximum compacted cement stabilized sand to:

o At least 2-feet thick below the leveling pad for walls above 8 feet in height o At least one-foot thick below leveling pad for walls less than8 feet in height

4.1.2 Local and Global Stability Analyses of the Modified Existing Embankments and MSE

Wall

Slope stability analyses were performed utilizing a commercial slope stability software program, SLIDE. This software calculates the factor of safety against slope failure using a two-dimensional limit equilibrium method. Slope stability analyses were performed considering both short-term and long-term loading conditions as critical cases for the MSE retaining wall.

For the slope stability analyses:

Local and global slope stability analyses were performed for existing SH 99 embankment earth slopes at select locations that will be modified during the proposed NBFR and

SBFR and entrance/exit ramps construction/reconstruction, and the proposed retaining wall modification.

The design recommendations for the proposed MSE wall modification presented in

Section 4.1 apply. In the global stability analyses, we assumed that the structural and local (sliding, overturning and bearing) stability of the MSE wall are adequately evaluated and designed and constructed, and the MSE wall acts as a structural unit with adequate structural and local stability, such that the global slip circles will not extend within the reinforced earth zone.

The construction of the modified MSE wall section, and the modification of the existing embankment slopes conducted in conjunction with the proposed NBFR and SBFR and the entrance/exit ramps, are carried out as recommended in Section 4.2 of this report.

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Short term undrained and long term effective shear strengths of the embankment soils and subsurface soils at various location evaluated were selected based on field and laboratory test results, available existing soil and laboratory data, and our past experience working with similar soils, as well as referencing published literatures regarding strength characteristics of the similar soils in the region.

The slope configurations at selected slope modification and at the proposed MSE wall modification locations, and the soil strength and other parameters used in our stability analyses, are presented on the Plates C-1 through C-22 in Appendix C of this report. A summary of the global stability analyses for the proposed MSE walls are presented in the table below.

TABLE N. RESULTS OF LOCAL AND GLOBAL SLOPE STABILITY ANALYSES

Modified Slope Location Overall Slope Height

(feet)

Computed Factors of Safety

Short Term Long Term

Modified Slope at NBFR at Station 30+00

16-¾ 4.295 (Local)

4.619 (Global) *see Plate C-1

2.599 (Local)

4.207 (Global) *see Plate C-2

Modified Slope at NBFR Station 32+00

20-¼ 2.717 (Local)

2.618 (Global) *see Plate C-3

2.112 (Local)

2.234 (Global) *see Plate C-4

Modified Slope at NBFR Station 34+00

22-¾ 2.149 (Local)

2.001 (Global) *see Plate C-5

1.693 (Local)

2.037 (Global) *see Plate C-6

Modified Slope at NBFR Station 36+00

25-¾ 2.070 (Local)

1.582 (Global) *see Plate C-7

1.893 (Local)

1.848 (Global) *see Plate C-8

Modified Slope at NBFR At Modified MSE Wall at Schiel Road

15-½

2.762 (Local)

2.487 (Global) *see Plate C-9

1.572 (Local)

1.710 (Global)

*see Plate C-10

Modified Slope at SBFR Station 18+39

13 8.297 (Upper Slope)

9.478 (Lower Slope)

*see Plate C-11

3.458 (Upper Slope)

4.082 (Lower Slope)

*see Plate C-12

Modified Slope at SBFR Station 20+00

9 10.124 (Lolca)

9.293 (Global)

*see Plate C-13

4.533 (Upper Slope)

7.573 (Middle Slope)

4.446 (Lower Slope)

*see Plate C-14

Modified Slope at SBFR Station 22+00

11- ¾

4.759 (Local)

4.360 (Global)

*see Plate C-15

2.570 (Local)

3.168 (Global)

*see Plate C-16

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas

Modified Slope Location Overall Slope Height

(feet)

Computed Factors of Safety

Short Term Long Term

Modified Slope at SBFR Station 23+00

14-½ 3.881 (Local)

3.786 (Global)

*see Plate C-17

2.435 (Local)

3.735 (Global)

*see Plate C-18

Modified Slope at SBFR Station 24+00

16- ¾ 4.344 (Local)

3.469 (Global)

*see Plate C-19

2.522 (Local)

2.668 (Global)

*see Plate C-20

Modified Slope at SBFR Station 25+00

19- ¾ >2.572 (Local)

2.572 (Global)

*see Plate C-21

2.457 (Local)

2.538 (Global)

*see Plate C-22

Minimum Factors of Safety Required by TxDOT 1.5 1.5

1. Total height of the overall embankment slope above the surrounding finish grade.

2. TxDOT recommends a minimum factor of safety of 1.3 for general structures, and 1.5 for critical structures with low tolerance to failure.

Conclusion: Based on the results of the above local and global slope stability analyses, all the modified embankment slopes have short term and long term loading conditions factors of safety above the TxDOT target value of 1.5. Thus, these modified embankment slopes are theoretically stable in terms of short term undrained and long term effective stress loading conditions.

4.1.3 Settlement of the Modified Embankments and the Proposed MSE Wall

The existing SH 99 embankment has probably been constructed since about 2014 or 2015. We anticipate that all elastic settlement and a significant portion of the long term consolidation settlement, as estimated in Corsair’s Geotechnical Report No. 1200502, has materialized. Thus, the proposed modifications to the existing SH 99 embankment at various locations are not anticipated to incur any significant additional settlements to the existing embankment.

The proposed MSE wall, designed and constructed as recommended in this report, is estimated to have a total settlement about 3-¼ inches on the higher side of the MSE wall, and about 2 inches on the lower side of the MSE wall.

The settlements were estimated using soil properties and consolidation parameters estimated based on laboratory test results and assuming good quality construction planning, technique

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas and workmanship. The accuracy of the settlement estimates are dependent on how well the analysis models simulate the behavior of the embankment fill and subsurface soils, the fill material used and the degree of compaction of embankment fill, and the construction time and sequence, etc.

4.2 Site Preparation and Earthwork

The majority of the surface soils found along the alignments of the proposed NBFR and SBFR construction/reconstruction consist mostly of Lean Clays (CL) with medium to high plasticity.

Sandy silts were found at Boring B-4A, Clayey Sands (SC) were found at Boring B-7, and Sandy-

Silty Clays (CL-ML) were found at Boring B-13, in the top 2 feet of the surface.

The construction areas shall be cleared and prepared in accordance with TxDOT Standard

Specifications for Construction and Maintenance of Highways, Streets and Bridges (SSCMHSB)

Items 100, 104, 105, 110, 112 and 132.

Proposed NBFR and SBFR Construction in Existing Grassy Area: The proposed construction areas should be stripped of vegetation, topsoil, soft and weak soils, and debris/unsuitable surface material. Roots of trees should be grubbed to full depths. In retaining wall areas, stripping should extend at least 5 feet horizontally beyond the edge of the proposed roadway embankment construction area. The inspected subgrade should then be excavated to the design grade.

Proposed NBFR and SBFR Reconstruction in Existing Pavement Area: The existing pavement structure and its base of the NBFR and SBFR reconstruction areas should be excavated and removed. The exposed surface should then be inspected and stripped of vegetation, topsoil, soft and weak soils, and debris/unsuitable surface material. The inspected subgrade should then be excavated to the design grade.

Proposed Retaining Wall Modification and MSE Wall Area: The existing retaining wall section and the embankment fill to be modified should be excavated and removed. Temporary shoring should be provided to provide lateral support for the excavated retaining wall/embankment.

The exposed surface should then be inspected and stripped of vegetation, topsoil, soft and

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas weak soils, and debris/unsuitable surface material. The inspected subgrade should then be excavated to the design grade.

In retaining wall and other structural areas, stripping should extend at least 5 feet horizontally beyond the edge of the proposed roadway embankment construction area; in pavement embankment and other general fill areas, stripping should extend at least 3 feet beyond the pavement limits. Existing utilities and structures that are designated to be removed, should be excavated and removed, and the holes should be backfilled with compacted select fill (in structural area) or compacted clean onsite similar soils (in roadway embankment and general fill area).

Once final subgrade elevations have been achieved, the subgrade should be proof-rolled with a

20-ton pneumatic roller or equivalent equipment to detect soft or weak areas. Special care should be exercised when proofrolling areas containing fill soils in an attempt to observe soft and weak zones within the fill soils. Weak areas detected during proofrolling, as well as zones of fill containing organic matter and/or debris, should be removed and replaced with soils exhibiting similar classification, moisture content, and density as the adjacent in-situ soils.

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

Constructability issues due to wet/weak soil conditions should be addressed as outlined in

Section 4.3 of this report.

Subsequent to proofrolling, the exposed subgrade within the construction areas should be evaluated for moisture and density. The subgrade should have an in-place dry density of at least 95 percent of the maximum dry density as determined by Tex-114-E and moisture adjusted to within 3 percent of the optimum moisture content. If the moisture or density does not meet the above criteria, the subgrade should be scarified to a minimum depth of 8 inches;

moisture adjusted to within 3 percent of the optimum moisture content and compacted to at least 95 percent of the maximum dry density (Tex-114-E).

Samples of the subgrade soils and backfill materials should be obtained prior to compaction operations for laboratory moisture/density testing (Proctor tests). These tests will then provide a basis for evaluating the in-place density of fill soils during compaction operations. A qualified soil

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas technician should perform sufficient in-place density tests during the filling operations to verify that proper levels of compaction are being attained.

4.3 Constructability Considerations

As mentioned previously, the surface soils found along the project alignments consist mostly of

Lean Clays (CL) with medium to high plasticity. Sandy silts were found at Boring B-4A, Clayey

Sands (SC) were found at Boring B-7, and Sandy-Silty Clays (CL-ML) were found at Boring B-13, in the top 2 feet of the surface. Based on the nature of these soils, construction difficulties should be anticipated, especially during the wet season or immediately after rain events.

Although these surface soils are typical of this geologic region, our experience suggests that local contractors find these materials troublesome and can often be the source of change orders, construction delays, and budget overruns.

We recommend that the project team (namely the Contractor) should have a contingency plan in-place to mitigate the adverse effects of the above- mentioned conditions, should the grounds become wet/weak during construction. The following are typical mitigating measures implemented at sites where weak and wet surface/near surface soils are present due to poor surface drainage and/or shallow perched water or groundwater table. Under more extreme site conditions, a combination of these mitigating measures may have to be carried out. Ultimately, it is the responsibility of the Contractor to select the proper surface and groundwater control equipment and techniques to properly grade and drain the site and to dry wet surface soils to a point that allows for the drying of the ground surface and maintaining a dry and stable site.

Promote good site drainage to dry the site and the surface soils. Good site drainage is of prime importance for a site to pass the proofrolling criteria and to provide a firm and stable platform to support the construction activities and traffic. The objectives are to cut off offsite flow into the construction area, drain excess free water and dry the soils within the construction area, and maintain the groundwater level at least 3 feet below the subgrade preparation depth or the excavation bottom elevation.

Soft/loose soils that are too wet should be scarified to sufficient depth to dry the soils to a moisture content that allows for successful compaction, and recompacted to pass proofrolling and the subsequent compaction. Increase the excavation depth, scarify and

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas compact the subgrade to necessary depth to pass the proofroll and allow for successful compaction of the subgrade and subsequent fill to meet the moisture and density requirements.

Alternatively, soft/weak/wet soils may be removed and replaced with clean similar onsite soils at moisture contents that can be successfully compacted to pass the proofrolling and allow for successful compaction of the subgrade and subsequent fill to meet the moisture and density requirements.

Alternatively, chemical treatment of the onsite soils with lime can be carried out to sufficient depth to aid in drying and stability/compaction of the subgrade soils and to form the foundation pad, or to provide a working surface for subsequent placement of recommended compacted fill.

4.3.1 Open Excavation and Shored and Braced Excavation

OSHA regulations require that excavation 5 feet or deeper be laid back to stable slopes or protected by shoring or bracing. Additionally, excavation next into existing embankments will also require shoring and bracing to protect the excavated slope soils.

For excavations on level grounds, either excavated side slopes or vertical cut excavations are feasible. Excavations must be performed and evaluated under the supervision of a contractor designated Competent Person. The Competent Person, as defined by OSHA (29 CFR, Standard

Number 1926.650 (b), Subpart P), “must be capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.”

Occupational Safety and Health Administration (OSHA) standards provide recommendations for the design of temporary sloped excavations with a depth less than 20 feet. The OSHA standards provide maximum allowable slopes contingent on three designated soil types: Type A, Type B, or

Type C. According to OSHA standards, temporary sloped excavations should be no steeper than

0.75-horizontal on 1-vertical (0.75H:1V) for Type A soils, 1H:1V for Type B soils, and 1.5H:1V for

Type C soils. The surface slopes should be protected from deterioration and weathering if they

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SH 99 – Between Cumberland Ridge Drive and Schiel Road Harris County Precinct 3, Texas are left open for significant periods of time. The onsite clay soils within the anticipated construction excavations in this project should be classified at OSHA Soil Type “C”.

Bracing for vertical excavation walls should be designed to resist a lateral earth pressure (in psf) resulted from a liquid with a unit weight of 70 pcf in clay soils (and 50 pcf in sandy soils), where H is the depth of the excavation in feet.