B08_Attachment_11_BITH_244484_Final_Geotech_Report.pdf

GEOTECHNICAL INVESTIGATION

BITH 244484 PEDESTRIAN BRIDGE REPAIRS

KOUNTZE, TEXAS

REPORT NO. 1140267701

Reported to:

HDR ENGINEERING, INC.

Denver, Colorado

Submitted by:

GEOTEST ENGINEERING, INC.

TBPE REGISTRATION NO. F-410

Houston, Texas

TABLE OF CONTENTS

Page

1.0 EXECUTIVE SUMMARY

2.0 INTRODUCTION

2.1 Authorization

2.2 Project Description

2.3 Purpose and Scope of Work

3.0 SITE EXPLORATION

3.1 Physical Description

3.2 Geology

3.3 Faults Review

4.0 FIELD WORK

4.1 Soil Borings and Sampling

4.2 Water Level Observation

4.3 Piezometer Installation

4.4 Borehole Completion

4.5 Environmental Issues

5.0 LABORATORY TESTING

5.1 Geotechnical Testing

5.1.1 Tests Performed

5.1.2 Table of Test Results

6.0 SUBSURFACE SOIL AND GROUNDWATER CONDITIONS

6.1 Soil Stratigraphy

6.2 Water Level Conditions

7.0 GEOTECHNICAL RECOMMENDATIONS

7.1 Observations from Site Visit

7.2 Evaluations and Recommendations

7.3 Abutment Slope Stability

7.3.1 Method of Analyses

7.3.2 Water Level and Soil Parameters

7.3.3 Loading Conditions

7.3.4 Factors of Safety (F.S.)

7.4 Select Fill Requirements

7.5 Recommendations for Helical Pile Foundations

TABLE OF CONTENTS (cont'd)

Page

7.5.1 Minimum Embedment Requirement

7.5.2 Axial Capacity

7.5.3 Corrosion

7.6 Recommendations for Geotextile Fabric and Stone for Gabion Mattress

8.0 PROVISIONS

ILLUSTRATIONS

Figure

Vicinity Map

Plan of Borings ................................................................................................................... 2.1 and 2.2

Boring Log Profiles ............................................................................................................ 3.1 and 3.2

Results of Slope Stability Analyses .............................................................................. 4.1 thru 4.3

TABLES

Table

Summary of Boring Information

Summary of Soil Parameters Used for Slope Stability Analyses

Summary of Soil Parameters for Lpile Input

APPENDIX A

Log of Borings ....................................................................................................... A-1 thru A-4

Terms Used on Boring Logs .................................................................................. A-5

Classification of Soils Used for Engineering Purposes ......................................... A-6

APPENDIX B

Summary of Laboratory Testing Results ............................................................... B-1 thru B-4

Grain Size Distribution Curves .............................................................................. B-5 thru B-14

Consolidated Undrained Triaxial Test Results ...................................................... B-15

Double Hydrometer Test Results ........................................................................... B-16

APPENDIX C

Site Pictures .......................................................................................................................... C-1 and C-2

APPENDIX D

Drawings Provided by Halff Associates, Inc.

APPENDIX E

Slope Stability Analyses Backup

Geotest Engineering, Inc. Report No. 1140267701

BITH 244484 Pedestrian Bridge Repairs May 30, 2023

Kountze, Texas

1.0 EXECUTIVE SUMMARY

A geotechnical investigation was conducted by Geotest Engineering, Inc. for the proposed Pedestrian Bridge Abutment Repairs at Big Thicket National Preserve in Kountze, Texas.

The project includes rehabilitation/repair of the abutments supporting two (2) pedestrian bridges; the Kirby Bridge and Turkey Bridges. The detail project description is given Section

1.2 of this report.

The purpose of this investigation is to perform a geotechnical investigation and to develop geotechnical recommendations for the proposed abutment repairs of the pedestrian bridges. This study included drilling and sampling four (4) soil borings (designated as GB-1 through GB-4), each to a depth of 50 feet, performing appropriate laboratory tests, performing an engineering analysis and preparing a geotechnical report.

The principal findings and conclusions developed from this study are summarized below:

• The project alignment lies in the Fluviatile Terrace Deposits and Lissie Formation.

Fluviatile terrace deposits include sand, gravel, silt, clay, or mud of recent origin.

Generally associated with remnants of ancient floodplains, this geology unit is found on terraces. A small area containing these deposits is found in the central portion of the project area, in association with alluvium. The upper zones of the Lissie formation consist of clay, silt and minor amounts of siliceous in the areas to the northwest. The

Lissie formation is characterized by featureless flat to gently rolling surface and fluviatile depositions. The calcareous deposits and concentrations of calcium carbonate, iron oxide, iron-manganese oxides are common in the zone of weathering.

• Based on the available information, no surface fault was found near the project alignment.

• The subsurface conditions as encountered in borings GB-1 through GB-4 are given below.

Kirby Bridge (GB-1 and GB-2). As revealed by the borings GB-1 and GB-2 drilled near the

Kirby Bridge at north abutment and south abutment, respectively, the subsurface soils beneath the existing ground surface consist of cohesionless soils to the depths ranging from

18 feet to 32 feet and underlain by cohesive soils to termination depth of 50 feet. The cohesionless soils consist of very loose to medium dense brown and gray poorly graded sand, silty sand and clayey sand. The cohesive soils consist of medium stiff to very stiff gray, reddish brown, yellowish brown, gray and brown fat clay, lean clay with sand and sandy lean clay.

Turkey Bridge (GB-3 and GB-4). As revealed by the borings GB-3 and GB-4 drilled near

Turkey Bridge at east abutment, the subsurface soils beneath the existing ground surface mainly consist of cohesionless soils to the termination depths of 50 feet. The cohesionless soils consist of loose to very dense gray, brown, brown and gray and yellowish brown poorly graded sand, silty sand and clayey sand. A stratum of sandy lean clay was encountered at depth of 28 to 30 feet in boring GB-3.

• At Kirby Bridge (GB-1 and GB-2), groundwater was first encountered during drilling at a depth of 8 feet in boring GB-1 and at 1 foot in boring GB-2. The water level measured

15 minutes after first encountered was at a depth of 0 feet in boring GB-2 and at 8 feet in boring GB-1. The water level measured 24 hours after drilling was at a depth of 6.3 feet in boring GB-1. At Turkey Bridge (GB-3 and GB-4), groundwater was first encountered during drilling at depths ranging from 8 feet (GB-4) to 10 feet (GB-3). The water level measured 15 minutes after first encountered was at depth ranging from 8 feet (GB-4) to

9.6 feet (GB-3). The water level measured 24 hours after drilling was at depth ranging from 7.5 feet (GB-4) to 8.9 feet (GB-3).

• The recommendations pertaining to bridge abutment repairs are presented in Section 7.3 of this report.

• The abutment slope stability analysis is presented in Section 7.4 of this report.

• The recommendations for helical pile foundations are discussed in Section 7.6 of this report.

2.0 INTRODUCTION

2.1 Authorization

The Big Thicket National Preserve, the owner, selected HDR Engineering, Inc. to provide engineering services for the proposed Pedestrian Bridge Abutment Repairs at Big Thicket

National Preserve in Kountze, Texas. HDR Engineering, Inc., retained the service of Geotest

Engineering, Inc. to provide geotechnical support for the aforementioned project. This study was authorized by Standard Subcontract for Subsurface/Underground Services Agreement on

September 15, 2021, by accepting Geotest Proposal No. 1140530799 dated June 16, 2021.

2.2 Project Description

The project includes rehabilitation/repair of the abutments supporting two (2) pedestrian bridges; the Kirby Bridge and Turkey Bridges. The pedestrian bridges consist of prefabricated steel truss superstructures approximately 120 feet in length supported on precast concrete sills that are founded directly on existing ground. The bridges are located on natural surface trails with widths of approximately 5 feet. These bridges were damaged in recent hurricanes and the high water flows of the underlying creeks have eroded away the soils supporting the bridge sills, creating an unsafe environment. The project location map is shown on Figure 1.

2.3 Purpose and Scope of Work

The purpose of this investigation was to explore the subsurface conditions and to develop geotechnical recommendations pertaining to the design and construction of proposed Pedestrian

Bridge Abutment Repairs at Big Thicket National Preserve in Kountze, Texas.

The scope of the geotechnical investigation consists of the following tasks:

• drilled and sampled four (4) soil borings, each to a depth of 50 feet, to determine site soil stratigraphy, soil properties, and water levels during drilling;

• performed appropriate laboratory tests on selected recovered soil samples to evaluate pertinent geotechnical engineering properties of the soils;

• performed engineering analyses to develop geotechnical recommendations for the proposed rehabilitation/repair of the damaged abutments of pedestrian bridges.

• prepared a geotechnical report summarizing the results of our field investigation, laboratory testing, geotechnical analyses, and geotechnical recommendations for the rehabilitation/repair of the abutments.

3.0 SITE EXPLORATION

3.1 Physical Description

The two (2) pedestrian bridges; the Kirby Bridge and Turkey Bridge were damaged in recent hurricanes and the high water flows of the underlying creeks have eroded away the soils supporting the bridge sills, creating an unsafe environment.

3.2 Geology

The geology of the site is characterized by two formations. The Fluviatile Terrace

Deposits formation located near the Turkey Bridge and the Lissie formation located near Kirby

Bridge.

Based on the Beaumont Sheet, Texas, Geologic Atlas of Texas (Bureau of Economic

Geology, University of Texas, 1982) the location of Big Thicket National Preserve in Kountze, Texas, lies within the boundaries of the Fluviatile Terrace Deposits Formation and Lissie

Formation’s surface exposure. Fluviatile terrace deposits include sand, gravel, silt, clay, or mud of recent origin. Generally associated with remnants of ancient floodplains, this geology unit is found on terraces. A small area containing these deposits is found in the central portion of the project area, in association with alluvium. The upper zones of the Lissie formation consist of clay, silt and minor amounts of siliceous in the areas to the northwest. The Lissie formation is characterized by featureless flat to gently rolling surface and fluviatile depositions. The calcareous deposits and concentrations of calcium carbonate, iron oxide, iron-manganese oxides are common in the zone of weathering.

3.3 Faults Review

A review of information in the Geotest Library relating to known surface and subsurface geologic faults in the general area of the project site was undertaken. The available information consisted of U. S. Geological Survey and NASA maps, open file reports, and information contained in our files relating to geologic faults in this area. Based on this available information, no fault was identified near the project alignment.

4.0 FIELD WORK

4.1 Soil Borings and Sampling

Subsurface conditions were explored by drilling a total of four (4) borings to depths of 50 feet. All borings were drilled using a tractor amount rig. The location of each of the borings is shown on the plan of borings on Figure 2.1 and Figure 2.2.

Samples were obtained continuously to a 50-foot depth. Cohesive samples were obtained with a 3-inch diameter thin-walled tube sampler in general accordance with ASTM Method D 1587.

Cohesionless or semi cohesive samples were obtained with a 2-inch split spoon barrel in general accordance with ASTM Method D 1586. At each of the boring locations, samples were removed from the sampler in the field and carefully examined and logged by an experienced soils technician.

Suitable portions of each sample were then sealed and packaged for transportation to Geotest's laboratory. Undrained shear strengths of cohesive soil samples were estimated using a calibrated hand penetrometer in the field.

Detailed description of the soils encountered in the borings drilled for the project are presented on the boring logs on Figures A-1 through A-4 in Appendix A. The depth at which water was encountered during drilling and 24-hour water level is also noted on the boring logs. The terms used on borings logs and classification of soils for engineering purposes are presented following the logs of borings on Figures A-5 and A-6, respectively in Appendix A. Survey information

(Northing, Easting and ground surface elevation) of each boring is presented on Table 1.

4.2 Water Level Observation

Water level measurements were made in all open boreholes at the time of drilling. Twenty-four (24) hours water level measurements were also made after the completion of drilling of most of the borings, except for the boring drilled on the last day as drilling crew demobilized from the site.

4.3 Piezometer Installation

No piezometer was installed for this project.

4.4 Borehole Completion

After taking final measurements of the depths to water at the boring locations, all boreholes were backfilled with cement bentonite grout.

4.5 Environmental Issues

No environmental concerns were observed or detected during our field investigation.

5.0 LABORATORY TESTING

5.1 Geotechnical Testing

The laboratory testing program was designed to evaluate the pertinent physical properties and shear strength characteristics of the subsurface soils. Classification tests were performed on selected samples to aid in soil classification. All the tests were performed in accordance with

ASTM procedures.

5.1.1 Tests Performed

Undrained shear strengths of selected cohesive samples were measured by unconsolidated undrained (UU) triaxial compression tests (ASTM D2850). The results of the

UU triaxial compression tests are plotted on the boring logs as soil squares. The shear strength of cohesive samples was measured in the field with a calibrated hand pocket penetrometer and also in the laboratory with a Torvane. The shear strength values obtained from the penetrometer and Torvane are plotted on the boring logs as open circles and triangles, respectively.

Measurements of moisture content and dry unit weight were taken for each UU triaxial test sample. Moisture content measurements (ASTM D2216) were also made on other samples to define the moisture profile at each boring. The liquid and plastic limit tests (ASTM D4318) were performed on appropriate samples. Sieve analysis (ASTM D6913), percent passing No.

200 sieve tests (ASTM D1140) and hydrometer test (ASTM D7928) were performed on selected samples. The results of all tests are plotted or summarized on the boring logs presented on

Figures A-1 through A-4 in Appendix A. The summary of laboratory test results are also summarized in tabular format presented on Figures B-1 through B-4 in Appendix B. Grain size distribution curves are presented on Figures B-5 and B-14 in Appendix B.

One (1) multi stage Consolidated Undrained (CU) triaxial compression tests (ASTM

D4767) were performed on three (3) undisturbed soil samples. Three (3) stages of consolidation

(with pore pressure measurements) were carried out on three (3) samples following saturation of the samples and consolidation to approximately 50%, 100% and 200% of estimated insitu over burden pressure. Results of the consolidated undrained (CU) triaxial compression tests with pore water measurements are presented on Figures B-15 in Appendix B.

One (1) double hydrometer test (ASTM D4221) was performed to determine the dispersion of the cohesive soils. The double hydrometer test results are presented on Figure B-

16 in Appendix B.

5.1.2 Table of Test Results

The summary of D50 values, CU triaxial compression test results and double hydrometer test results are tabulated below.

Summary of D50 and D90 (where applicable) Values

Boring No.

Soil Description

Depth

(feet)

D90, mm

D50, mm

GB-1 Clayey sand 2.5-4.0 0.3533 0.0822

GB-1 Poorly Graded Sand 10.5-12.0 0.3972 0.2683

GB-1 Poorly Graded Sand 14.5-16.0 0.6566 0.3137

GB-2 Silty sand 2.5-4.0 0.3503 0.1869

GB-2 Silty sand 6.5-8.0 0.3668 0.1940

GB-2 Poorly Graded Sand 12.5-14.0 0.3981 0.2750

GB-2 Poorly Graded Sand 18.5-20.0 0.7367 0.4011

GB-2 Poorly Graded Sand 24.5-26.0 0.7439 0.3564

GB-2 Poorly Graded Sand 30.5-32.0 0.7180 0.3548

GB-2 Fat Clay 36.5-38.0 0.0069 <0.0011

GB-3 Silty sand 2.5-4.0 0.6366 0.2685

GB-3 Silty sand 8.5-10.0 0.2227 0.1076

GB-3 Poorly Graded Sand 14.5-16.0 1.3967 0.4902

GB-3 Poorly Graded Sand 20.5-22.0 1.5000 0.6241

GB-3 Poorly Graded Sand 24.5-26.0 1.2381 0.5785

GB-3 Sandy Lean Clay 28.5-30.0 0.2643 0.0550

Summary of D50 and D90 (where applicable) Values

Boring No.

Soil Description

Depth

(feet)

D90, mm

D50, mm

GB-3 Poorly Graded Sand with Silt 32.5-34.0 1.8091 1.0115

GB-3 Silty Sand 38.5-40.0 1.4731 0.1496

GB-3 Silty Sand 42.5-44.0 0.2465 0.1464

GB-3 Silty Sand 48.5-50.0 1.9561 0.2521

GB-4 Silty Sand 0.0-1.5 0.5785 0.2566

GB-4 Silty Sand 4.5-6.0 0.1979 0.0925

GB-4 Poorly Graded Sand with Silt 10.5-12.0 0.3029 0.1701

GB-4 Silty Sand 16.5-18.0 0.3842 0.1220

GB-4 Poorly Graded Sand with Silt 22.5-24.0 0.7536 0.4653

GB-4 Poorly Graded Sand 30.5-32.0 4.0937 0.8310

GB-4 Poorly Graded Sand 36.5-38.0 4.2870 0.8603

GB-4 Silty Sand 42.5-44.0 0.2405 0.1603

GB-4 Silty Sand 48.5-50.0 1.6177 0.1111

Summary of C-U Triaxial Compression Test Results

Sample ID

Total Stress Effective Stress

Ccu

(psf) cu

(deg)

C'(psf) ' (deg)

GB-1, 34-36, Fat Clay (CH) 139 16.7 258 10.0

Summary of Double Hydrometer Test Results

Boring

No.

Depth

(feet)

Soil Description Double Hydrometer Test

Results (ASTM D4221)

GB-1 20.0-22.0 Lean Clay with Sand (CL) Dispersive

(Dispersion = 54%)

6.0 SUBSURFACE SOIL AND GROUNDWATER CONDITIONS

6.1 Soil Stratigraphy

Based on the laboratory test results and the reoccurrence of generally similar elevations within the discrete boreholes advanced over the site, two boring log profiles were developed and are presented on Figures 3.1 and 3.2. To the right of each boring shown on the profile, is the overall classification of the soil contained within each stratum. The classification is based on ASTM

D2487. The interpreted soil stratigraphy is given below.

Kirby Bridge (GB-1 and GB-2)

As revealed by the borings GB-1 and GB-2 drilled near the Kirby Bridge at north abutment and south abutment, respectively and as shown on boring log profile presented on

Figure 3.1, the subsurface conditions below the existing grade are described below:

Depth, feet Elevation, feet

From To From To Soil Description

18 ~ 32 106.9

~ 99.2

82.1 ~

74.9

Cohesionless soils consist of very loose to medium dense brown and gray poorly graded sand (SP), Poorly graded sand with silt (SP-SM), silty sand

(SM) and clayey sand (SC). Fill consisting of brown silty sand with gravel and pieces of glass and wires were encountered between 0 and 2 feet in boring

GB-1.

18 ~

50 82.1 ~

74.91

56.9 ~

49.2

Cohesive soils consist of medium stiff to very stiff gray, brown and gray, reddish brown and yellowish brown fat clay

(CH), lean clay with sand (CL) and sandy lean clay (CL).

The fat clay soils are of very high plasticity with liquid limits ranging from 72 to 94 and plasticity indices ranging from 44 to 59. The sandy lean clay and lean clay with sand are of medium plasticity with a liquid limit of about 35 and a plasticity index of about 17. The fines content (percent passing No. 200 sieve) of fat clay ranges from 92.8 to 97.8 percent. The fines content of lean clay with sand is about 74.8 percent and the fines content of sandy lean clay is about 52.4 percent. The fines content of poorly graded sand ranges from 1.9 to 3.9 percent. The fines content of poorly graded sand with silt is about 7.7 percent. The fines content of silty sand ranges from 13.4 to 32.0 percent. The fines content of clayey sand is about 48.5 percent.

Turkey Bridge (GB-3 and GB-4)

As revealed by the borings GB-3 and GB-4 drilled near the Turkey Bridge at east abutment and as shown on boring log profile presented on Figures 3.2, the subsurface conditions below existing grade are described below:

Depth, feet Elevation, feet

From To From To Soil Description

50 94.6 ~

93.0

44.6 ~

43.0

Cohesionless soils consist of loose to medium dense gray, brown and gray, brown, and yellowish brown poorly graded sand (SP), Poorly graded sand with silt (SP-SM), silty sand

(SM) and clayey sand (SC).

Gray sandy lean clay (CL) was encountered between the depths of 28 and 30 feet in boring GB-

3.

The sandy lean clay is of medium plasticity with a liquid limit of about 36 and a plasticity index of about 18. The fines content (percent passing No. 200 sieve) of sandy lean clay is about

56.6 percent. The fines content of poorly graded sand ranges from 1.3 to 3.7 percent. The fines content of poorly graded sand with silt ranges from 5.1 to 6.7 percent. The fines content of silty sand ranges from 12.3 to 45.1 percent. The fines content of clayey sand ranges from 40.6 to 43.6 percent.

6.2 Water Level Conditions

At Kirby Bridge (GB-1 and GB-2), groundwater was first encountered during drilling at a depth of 8 feet in boring GB-1 and at 1 foot in boring GB-2. The water level measured 15 minutes after first encountered was at a depth of 0 feet in boring GB-2 and at 8 feet in boring

GB-1. The water level measured 24 hours after drilling was at a depth of 6.3 feet in boring GB-

1. At Turkey Bridge (GB-3 and GB-4), groundwater was first encountered during drilling at depths ranging from 8 feet (GB-4) to 10 feet (GB-3). The water level measured 15 minutes after first encountered was at depth ranging from 8 feet (GB-4) to 9.6 feet (GB-3). The water level measured 24 hours after drilling was at depth ranging from 7.5 feet (GB-4) to 8.9 feet (GB-3).

7.0 GEOTECHNICAL RECOMMENDATIONS

The project is to provide geotechnical support for the rehabilitation/repair of the abutments supporting two (2) pedestrian bridges, the Kirby Bridge and Turkey Bridge. The bridges are located on natural surface trails with width of approximately 5 feet. These bridges were damaged in recent hurricanes and the high water flows of the underlying creeks have eroded away the soils supporting the bridge sills, creating an unsafe environment.

7.1 Observations from Site Visit

A site visit was performed on November 18, 2021 by Geotest representatives along with representatives from HDR Engineering Inc. and Big Thicket National Preserve, to assess the conditions of abutment erosion and the dispersive characteristics of site soils at the abutments. The pictures are shown in Appendix C.

The following observations were noted during the site visit.

Location Situation

Kirby Bridge Upper portion slope of Kirby Bridge south and north abutments were protected by timber walls and the soils inside the walls was partially eroded and the maximum erosion depth is about 12 inches. The minor erosion also found outside of the timber wall.

Turkey Bridge No erosion was found in west abutment of Turkey Bridge. However, approximate 8-foot-deep erosion was encountered on the east abutment.

7.2 Evaluations and Recommendations

Based on site observations, it is our opinion that abutment erosion has occurred on south and north Kirby Bridge and east Turkey Bridge. Several factors may have contributed to the slope erosion as mentioned below.

• Due to the sheet flow over the abutment slope face causing rills.

• Presence of dispersive soils along the slope face, which might have washed away with the high flow of water.

• Lack of vegetation cover.

The existing soils along the slope face indicates cohesionless soils extending to depths of 18 to 26 feet which are susceptive to erosion.

Based on the site observations and review of existing and original sections, the following recommended alternatives can be considered for the slope repair.

Abutment Repair Method 1 – Gabion Mattress Protection

This repair method is applied for Kirby Bridge south and north abutments. The existing vegetation need to be removed and abutment should be regraded or backfilled with selected fill, then 18-inch gabion mattress with geotextile fabric is applied for full slope after re-grading the slope and provided 3' x 3' key at the bottom of slope. The details of this repair method is illustrated in cross sections provided by HDR Engineering, Inc. (shown in Appendix D, Sub Sheet No. S8).

Abutment Repair Method 2- Helical Piles with Stone Riprap Protection

This repair method is applied for Turkey Bridge east abutment. Helical Piles should be installed and support the east bridge end before the backfill of the abutment. The existing vegetation need to be removed and abutment should be regraded or backfilled with selected fill, then 18-inch gabion mattress with geotextile fabric is applied for full slope after re-grading the slope and provide

3' x3' key at the bottom of slope. The details of this repair methods are illustrated in cross sections provided by HDR Engineering, Inc. (shown in Appendix D, Sub Sheet No. S11).

7.3 Abutment Slope Stability

The slope stability analysis was performed using the Simplified Bishop Method by using a computer program GEOSTASE for Turkey Bridge east abutment. Based on the bridge layout drawings provided to us, the abutment slope will be a 2(H):1(V) slope inclination. The depth of the existing tributary crossing at the Turkey Bridge is about 20 feet. Slope stability for the existing abutment slope was analyzed for the end of construction (EOC), rapid drawdown (RD) and long term (LT) conditions.

7.3.1 Method of Analyses

The GEOSTASE computer program performs a search of circular failure surfaces based on user-input search limits and computes factors of safety for each surface generated based on a two-dimensional limiting equilibrium approach. The critical failure surface is a surface that gives the lowest factor of safety for the input soil parameters, groundwater levels and external conditions.

7.3.2 Water Level and Soil Parameters

The water level conditions and selected soil parameters (total and saturated unit weight, cohesion and friction angle) used in the slope stability analyses were developed based on the field and laboratory test data of corresponding soil. The developed soil parameters for each soil case (as given in Table 2) and water level for EOC, RD and LT conditions are discussed below.

• End of Construction: The end of construction case models the initial undrained condition of the soil at the end of construction after the completion of the slope excavation. For the analysis of this case, the water level in the existing tributary crossing was assumed to be at El. 77 feet and along the slope to the top of slope. The soil parameter of angle of internal friction for granular/cohesionless soils was based on the Standard Penetration Test (SPT) data obtained in the field. For cohesive soil, unconsolidated-undrained shear strength parameters were used for the analysis. The selected unconsolidated-undrained shear strength parameters were based on a lower bound value of the undrained shear strength profile developed from the laboratory unconsolidated-undrained triaxial compression tests, torvanes and pocket penetrometers. The selected soil parameters used for the analysis of end of construction case are also presented on the Table 2.

• Rapid Drawdown: The rapid drawdown case models the condition where high floodwater saturates and piezometerically "loads" the slope and then quickly recedes leaving a large unbalanced piezometric head in the bank slope. This unbalanced force increases the shear stresses in the soils behind the slope. For this case, a completely saturated slope from the bottom of the creek to the top of slope (El. 94 ft) was considered and the water level within the existing creek was assumed to instantaneously drop from top of bank slope to normal water level (El. 77 feet) in the creek, subsequent to the saturation of the bank soils.

The rapid drawdown condition was analyzed for 3-stage rapid drawdown analyses with Duncan, Wright and Wong (1990) procedure. In the 3-stage rapid drawdown analyses, both total stress and effective stress strength parameters were utilized for the analyses. The total stress strength parameters include undrained cohesion (ccu) and undrained angle of internal friction (cu) and effective strength parameters include drained cohesion (c') and drained angle of internal friction ('). The soil parameters used for the analyses of rapid drawdown are presented on Table 2.

• Long Term Conditions: The long term design case represents steady state piezometric and stress conditions. When a slope is excavated, regarded or backfilled, altered stress conditions create pore pressure changes within the slope and the undrained strength of the bank soils is mobilized. With time, the soil pore pressures adjust to the imposed stress and piezometric conditions and the bank soils rely on their available strength for long term stability. In this analysis, the static water level within the bank soils and within the existing tributary was assumed to be the water level at El. 77 feet. The effective strength parameters include drained cohesion (c') and drained angle of internal friction ()w were used for the analysis of long term condition. The soil parameters used for the analysis of long term condition is presented on Table 2.

7.3.3 Loading Conditions

The surcharge load for helical piles which is located at the top of existing abutment is about 5,700 psf, this loading is based on the exposed abutment cap dimensions to be conservative since the foundation is below ground and existing bridge plans are not available to provide the actual foundation dimensions. The surcharge for other location at the top of slope is assumed to be 250 psf.

7.3.4 Factors of Safety (F.S.)

Based on the soil parameters and water level conditions discussed previously and taking into the considerations of the resistance from the proposed helical piles, slope stability analyses were performed for the proposed embankment slope inclination at bridge location. The results of these analyses are presented on Figures 4.1 through 4.3. The computed minimum factors of safety are also summarized in the table below.

Bridge Borings Abutment Slope EOC RD LT Figure Nos.

Turkey

Bridge

GB-3 and

GB-4

2H:1V

East Bank

With Helical Piles and

18-ich gabion mattress

Protection

1.59 1.34 1.50 4.1, 4.2, 4.3

The analysis is assuming the helical piles should extent at least 18 feet below the top of bank. Based on the results presented above, it was noted that factors of safety for the existing abutment slope configuration under all analyzed cases meet the HCFCD minimum required factors of safety of 1.3 for end of construction, 1.25 for rapid drawdown and 1.5 for long term conditions.

7.4 Select Fill Requirements

The select fill required for the abutments should consist of nondispersive sandy clay or lean clay with a liquid limit less than 45 and a plasticity index between 12 and 25. The select fill should be compacted at moisture content within three percent above optimum to reduce swelling potential of the compacted fill. If on-site cohesionless soils are used as backfill, then gabion mattress and

Class 2 geotextile (such as Tensar US 160NW or similar products) is required to prevent future erosion.

7.5 Recommendations for Helical Pile Foundations

Based on the information provided to us by DHR, we understand that east abutment of

Turkey Bridge will be supported by battered helical piles. The helical piles should be installed before the backfill of the abutment.

7.5.1 Minimum Embedment Requirement

We recommend that the design of the helical pile foundation system consider the following minimum embedment requirements:

• The helical piles should have a depth of embedment adequate to support the imposed axial and lateral loads and not less than 18 feet based on the abutment global stability analysis.

• Computation of design capacities of the helical piles should provide factor of safety of 2.0 for reductions in capacities due to construction-related disturbance, shrink-swell characteristics of surficial soils with changes in moisture and erosion or scour.

7.5.2 Axial Capacity

Axial capacities of battered helical piles including pile capacity, pile spacing, shaft size, shaft length, helix size, helix spacing and bracket attachment should be designed by an experienced structural engineer or by a contractor that specializes in the design and installation of helical piles.

It is recommended that the helical pile foundation system bear in the natural soils below the fill soils. The individual bearing capacity of the helix is a function of the shape and size of the helix and the properties of the bearing stratum.

7.5.3 Corrosion

The helical pile system and devices should be protected from corrosion. Loss in steel due to corrosion should be accounted for in determining structural capacities by reducing the thickness of all helical pile components by the sacrificial thickness over a period of 50 years. Any requirement for soil corrosivity will be decided by helical pile manufacturer.

7.6 Recommendations for Geotextile Fabric and Stone for Gabion Mattress

Geotextile fabric is required to reduce soil migration where the soils are cohesionless soils before the stone for gabion mattress is installed. Design procedures in Hydraulic

Engineering Circular No. 23, September 2099, Design Guideline 16 (Publication No. FHWA-

NHI-09-112, Volume 2) are recommended for design of the fabric and developing a selection criterion for the use of the geotextile fabric (such as Tensar US 160NW or similar products). The finish and installation of geotextile should follow HCFCD Standard Specification Section 02364,

2.5 Geotexile Separation Fabric.

The stone used in gabion mattress should follow HCFCD Standard Specification Section

02378, 2.1 Riprap.

8.0 PROVISIONS

The description of subsurface conditions and the recommendations in this report are based on the test borings made at the time of drilling at specific locations. However, some variation in soil conditions may occur between test borings. Should any subsurface conditions other than those described in the boring logs be encountered, Geotest should be immediately notified so that further investigation and supplemental recommendations can be provided. The depth of the groundwater level may vary with changes in environmental conditions such as frequency and magnitude of rainfall as well as the water level change in the channel. The stratification lines on the logs of borings represent the approximate boundaries between soil types, however, the transition between soil types may be more gradual than depicted.

This report has been prepared for the exclusive use of HDR Engineering, Inc. and Big

Thicket National Preserve for the design and construction of the proposed Pedestrian Bridge

Abutment Repairs at Big Thicket National Preserve in Kountze, Texas.

This report cannot be reproduced without the permission of the Geotest Engineering, Inc. or

HDR Engineering, Inc., or Big Thicket National Preserve.

Geotest Engineering, Inc. �������

PLAN OF BORINGS

GB-1

GB-2

FIGURE 2.1

LEGEND

BORING

Ι

Ι

Jo b

N o.

FIGURE 2.2

GB-3

GB-4

PLAN OF BORINGS

LEGEND

BORING

ΙΙ

ΙΙ

Jo b

N o.

Distance Along Section

Ι − Ι (feet)

Ι − Ι (feet)

ΙΙ − ΙΙ (feet)

ΙΙ − ΙΙ (feet)

BITH 244484 Pedestrian Bridge_Turkey Creek 2(H):1(V) Slope_with 18" Gabion Mattress_18 ft Deep Helical Pile _EOC

Geotest Engineering, Inc. GEI Job No. 1140267701 \Turky Creek_EOC2.gsd

Simplified Bishop Method

Figure 4.1

0 20 40 60 80 100 120 140 160

GEOSTASE® by GREGORY GEOTECHNICAL SOFTWARE

GEOSTASE FS = 1.59

GEOSTASE® by GREGORY GEOTECHNICAL SOFTWARE

1 1

XL 1

XL 2

DL 1

DL 2 DL 3 DL 4

P 1 P 2

0 20 40 60 80 100 120 140 160

140No. FS 1 1.59 2 1.62 3 1.66 4 1.69 5 1.81 6 1.83 7 1.90 8 1.91 9 1.91 10 1.94

Soil Moist Wt Sat Wt c Phi ru Pconst Piez Surf Soil No. (pcf) (pcf) (psf) (deg) (ratio) (psf) No. Options

1 SM 110.0 110.0 0.0 28.0 0.000 0.0 1

2 SM/SP 115.0 115.0 0.0 30.0 0.000 0.0 1

3 CL 120.0 120.0 2000.0 0.0 0.000 0.0 1

4 SM/SP 120.0 120.0 0.0 30.0 0.000 0.0 1

5 Stone RPP 140.0 140.0 0.0 40.0 0.000 0.0 1

EL

EV

AT

IO

N , F

EE

T

DISTANCE, FEET

SURCHARGE

DL1 = 5,700 psf DL2 ~ DL4 = 250 psf

2(H):1(V) Slope_with 18" Gabion Mattres_18 ft Deep Helical Pile _RD

Geotest Engineering, Inc. GEI Job No. 1140267701 \Turky Creek_RD2.gsd

Simplified Bishop Method

Figure 4.2

0 20 40 60 80 100 120 140 160

GEOSTASE® by GREGORY GEOTECHNICAL SOFTWARE

GEOSTASE FS = 1.34

GEOSTASE® by GREGORY GEOTECHNICAL SOFTWARE

1 1

2 2

XL 1

XL 2

DL 1

P 1 P 2

0 20 40 60 80 100 120 140 160

140No. FS 1 1.34 2 1.39 3 1.40 4 1.45 5 1.46 6 1.48 7 1.50 8 1.51 9 1.51 10 1.53

Soil Moist Wt Sat Wt c Phi ru Pconst Piez Surf Soil No. (pcf) (pcf) (psf) (deg) (ratio) (psf) No. Options

1 SM 110.0 110.0 0.0 28.0 0.000 0.0 2 R

2 SM/SP 115.0 115.0 0.0 30.0 0.000 0.0 2 R

3 CL 120.0 120.0 150.0 26.0 0.000 0.0 2 R

4 SM/SP 120.0 120.0 0.0 30.0 0.000 0.0 2 R

5 Stone RPP 140.0 140.0 0.0 40.0 0.000 0.0 2 R

EL

EV

AT

IO

N , F

EE

T

DISTANCE, FEET

SURCHARGE

2(H):1(V) Slope_with 18" Gabion Mattress_18 ft Deep Helical Pile _LT

Geotest Engineering, Inc. GEI Job No. 1140267701 \Turky Creek_LT2.gsd

Simplified Bishop Method

Figure 4.3

0 20 40 60 80 100 120 140 160

GEOSTASE® by GREGORY GEOTECHNICAL SOFTWARE

GEOSTASE FS = 1.50

GEOSTASE® by GREGORY GEOTECHNICAL SOFTWARE

1 1

XL 1

XL 2

DL 1

DL 2 DL 3 DL 4

P 1 P 2

0 20 40 60 80 100 120 140 160

140No. FS 1 1.50 2 1.60 3 1.62 4 1.65 5 1.68 6 1.71 7 1.72 8 1.74 9 1.79 10 1.79

Soil Moist Wt Sat Wt c Phi ru Pconst Piez Surf Soil No. (pcf) (pcf) (psf) (deg) (ratio) (psf) No. Options

1 SM 110.0 110.0 0.0 28.0 0.000 0.0 1

2 SM/SP 115.0 115.0 0.0 30.0 0.000 0.0 1

3 CL 120.0 120.0 150.0 26.0 0.000 0.0 1

4 SM/SP 120.0 120.0 0.0 30.0 0.000 0.0 1

5 Stone RPP 140.0 140.0 0.0 40.0 0.000 0.0 1

EL

EV

AT

IO

N , F

EE

T

DISTANCE, FEET

SURCHARGE

DL2 ~ DL4 = 250 psf

TABLES

Table

Summary of Boring Information

Summary of Soil Parameters Used for Slope Stability Analyses

Summary of Soil Parameters for Lpile Input

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TABLE 3 1 of 1

Boring

Submerged Unit Weight

Undrained Cohesion

Internal Friction Angle

No. From To From To (pcf) (psf) (degree) GB-3 and GB-4 94.6 85.6 0 9 Sand 48 28

85.6 66.6 9 28 Sand 53 30

66.6 64.6 28 30 Stiff Clay without free water 58 1000 0.010

64.6 44.6 30 50 Sand 58 30

Depth (feet) ���

SUMMARY OF SOIL PARAMETERS FOR LPILE INPUT

BITH 244484 Pedestrian Bridge Repairs

Elevation (feet) Lpile Program Soil Type

Notes: 1. Use groundwater level at ground surface (flood condition)

2. Use Internal defult p-y subgrade modulus k computed by Lpile (input k as 0)

APPENDIX A

Log of Borings ....................................................................................................... A-1 thru A-4

Terms Used on Boring Logs .................................................................................. A-5

Classification of Soils Used for Engineering Purposes ......................................... A-6

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% DISPERSION = 54

APPENDIX C

Site Pictures .......................................................................................................................... C-1 and C-2

Job No. 1140267701

FIGURE C-1

Photo 1: Kirby Bridge

Photo 2: North Abutment of Kirby Bridge

Photo 3: South Abutment of Kirby Bridge

Photo 4: South Abutment of Kirby Bridge

Job No. 1140267701

FIGURE C-2

Photo 5: Turkey Bridge

Photo 6: West Abutment of Turkey Bridge

Photo 7: East Abutment of Turkey Bridge

Photo 8: East Abutment of Turkey Bridge

APPENDIX D

Drawings Provided by Halff Associates, Inc.

APPENDIX E

Slope Stability Analyses Backup

*** GEOSTASE(R) ***

** GEOSTASE(R) (c)Copyright by Garry H. Gregory, Ph.D., P.E.,D.GE **

** Current Version 4.30.31-Double Precision, August 2019 ** (All Rights Reserved-Unauthorized Use Prohibited)

SLOPE STABILITY ANALYSIS SOFTWARE

Simplified Bishop, Simplified Janbu, or General Equilibrium (GE) Options.

(Spencer, Morgenstern-Price, USACE, and Lowe & Karafiath) Including Pier/Pile, Planar Reinf, Nail, Tieback, Line Loads Applied Forces, Fiber-Reinforced Soil (FRS), Distributed Loads Nonlinear Undrained Shear Strength, Curved Strength Envelope, Anisotropic Strengths, Water Surfaces, 3-Stage Rapid Drawdown 2- or 3-Stage Pseudo-Static & Simplified Newmark Seismic Analyses.

Analysis Date: 10/ 27/ 2022 Analysis Time:

Analysis By: Geotest Engineering, Inc. GEI Job No. 1140267701 Input File Name: J:\1140260001-1140269901\1140267701-BITH 244484 Pedestrian Bridge Abutment Repairs_HDR Engineering\Slope Stability Analysis\Turky Creek_EOC2.gsd Output File Name: J:\1140260001-1140269901\1140267701-BITH 244484 Pedestrian Bridge Abutment Repairs_HDR Engineering\Slope Stability Analysis\Turky Creek_EOC2.OUT Unit System: English

PROJECT: BITH 244484 Pedestrian Bridge_Turkey Creek

DESCRIPTION: 2(H):1(V) Slope_with 18" Gabion Mattress_18 ft Deep Helical Pile _EOC

BOUNDARY DATA

7 Surface Boundaries 16 Total Boundaries

Boundary X - 1 Y - 1 X - 2 Y - 2 Soil Type No. (ft) (ft) (ft) (ft) Below Bnd

1 0.000 73.600 15.000 73.600 2 2 15.000 73.600 24.000 77.000 2 3 24.000 77.000 56.000 93.000 5 4 56.000 93.000 64.000 93.000 1 5 64.000 93.000 74.000 94.000 1 6 74.000 94.000 84.000 93.000 1 7 84.000 93.000 160.000 93.000 1 8 43.000 85.000 55.900 91.500 1 9 55.900 91.500 56.000 93.000 1 10 24.000 77.000 24.020 74.000 2 11 24.020 74.000 28.000 74.000 2 12 28.000 74.000 28.020 77.500 2 13 28.020 77.500 43.000 85.000 2 14 43.000 85.000 160.000 85.000 2 15 0.000 66.400 160.000 66.400 3 16 0.000 64.400 160.000 64.400 4

User Specified X-Origin = 0.000(ft)

User Specified Y-Origin = 40.000(ft)

MOHR-COULOMB SOIL PARAMETERS

5 Type(s) of Soil Defined

Soil Number Moist Saturated Cohesion Friction Pore Pressure Water Water and Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface Option Description (pcf) (pcf) (psf) (deg) Ratio(ru) (psf) No.

1 SM 110.0 110.0 0.00 28.00 0.000 0.0 1

2 SM/SP 115.0 115.0 0.00 30.00 0.000 0.0 1

3 CL 120.0 120.0 2000.00 0.00 0.000 0.0 1

4 SM/SP 120.0 120.0 0.00 30.00 0.000 0.0 1

5 Stone RPP 140.0 140.0 0.00 40.00 0.000 0.0 1

WATER SURFACE DATA

2 Water Surface(s) Defined

Unit Weight of Water = 62.400 (pcf)

Water Surface No. 1 Specified by 2 Coordinate Points Pore Pressure Inclination Factor = 0.50

Point X-Water Y-Water No. (ft) (ft)

1 0.00 77.00 2 160.00 77.00

Water Surface No. 2 Specified by 2 Coordinate Points Pore Pressure Inclination Factor = 1.00

Point X-Water Y-Water No. (ft) (ft)

1 0.00 0.00 2 0.00 0.00

Drained Shear Strength Reduction Factor applied after first stage = 1.0000

DISTRIBUTED LOAD(S)

4 Load(s) Specified

Load BND No. X - 1 Y - 1 Stress X - 2 Y - 2 Stress Deflection No. (ft) (ft) (psf) (ft) (ft) (psf) (deg from Vert)

1 4 60.000 93.000 5700.000 64.000 93.000

5700.000 0.00 2 5 64.000 93.000 250.000 74.000 94.000

250.000 0.00 3 6 74.000 94.000 250.000 84.000 93.000

250.000 0.00 4 7 84.000 93.000 250.000 160.000 93.000

250.000 0.00

NOTE - Load Stress Varies Linearly Within Specified Range.

For Multi-Stage Analysis, Refer to Detailed Output for Distributed Loads Applied to Each Stage.

Slip Surfaces Have Been Limited To An Area Defined By 2 XCLUDE Lines The First 0 XCLUDE Lines Deflect Slip Surfaces Upward

Boundary X - 1 Y - 1 X - 2 Y - 2 No. (ft) (ft) (ft) (ft)

1 60.00 75.00 64.00 75.00 2 63.90 75.00 64.00 93.00

PIER/PILE LOAD(S)

2 Pier/Pile Load(s) Specified

Pier/Pile X-Pos Y-Pos Load Spacing Inclination Length Force Incl.

No. (ft) (ft) (lbs) (ft) (deg) (ft) Factor 1 60.50 93.00 1000.0 5.0 90.00 18.0 0.00 2 63.50 93.00 1000.0 5.0 90.00 18.0 0.00

METHOD A Selected: Pier/Pile capacity subtracted from Driving Forces/Moments.

NOTE - An Equivalent Line Load Is Calculated For Each Row Of Piers/Piles Assuming A Uniform Distribution Of Load Horizontally Between Individual Piers/Piles.

TRIAL FAILURE SURFACE DATA

Circular Trial Failure Surfaces Have Been Generated Using A Random Procedure.

200 Trial Surfaces Have Been Generated.

200 Surfaces Generated at Increments of 2.4121(in) Equally Spaced Within the Start Range

Along The Specified Surface Between X = 0.00(ft) and X = 40.00(ft)

Each Surface Enters within a Range Between X = 65.00(ft) and X = 160.00(ft)

Unless XCLUDE Lines Were Specified, The Minimum Elevation To Which A Surface Extends Is Y = 40.00(ft)

Specified Maximum Radius = 300.000(ft)

3.000(ft) Line Segments Were Used For Each Trial Failure Surface.

The Simplified Bishop Method Was Selected for FS Analysis.

Total Number of Trial Surfaces Attempted = 200

Number of Trial Surfaces With Valid FS = 200

Statistical Data On All Valid FS Values:

FS Max = 73.918 FS Min = 1.585 FS Ave = 8.238 Standard Deviation = 10.850 Coefficient of Variation = 131.70 %

Critical Surface is Sequence Number 72 of Those Analyzed.

*****BEGINNING OF DETAILED GEOSTASE OUTPUT FOR CRITICAL SURFACE FROM A SEARCH*****

BACK-CALCULATED CIRCULAR SURFACE PARAMETERS:

Circle Center At X = 38.489213(ft) ; Y = 111.107015(ft); and Radius = 44.646173(ft)

Circular Trial Failure Surface Generated With 27 Coordinate Points

Point X-Coord. Y-Coord.

No. (ft) (ft)

1 14.271 73.600 2 16.845 72.058 3 19.516 70.693 4 22.273 69.510 5 25.103 68.515 6 27.994 67.712 7 30.932 67.105 8 33.904 66.697 9 36.897 66.489 10 39.897 66.483 11 42.890 66.678 12 45.864 67.074 13 48.805 67.669 14 51.698 68.460 15 54.533 69.443 16 57.295 70.615 17 59.971 71.969 18 62.551 73.500 19 65.023 75.201 20 67.374 77.064 21 69.595 79.080 22 71.676 81.242 23 73.606 83.538 24 75.379 85.958 25 76.984 88.493 26 78.416 91.129 27 79.482 93.452

COORDINATES OF INTERSECTION OF PIER/PILE(S) WITH FAILURE SURFACE

Pier/Pile No. X-Int. Y-Int.

Factor Of Safety For The Critical or Specified Surface = 1.585

***Table 1 - Geometry Data on the 40 Slices***

Slice Width Height X-Cntr Y-Cntr-Base Y-Cntr-Top Alpha Beta Base Length No. (ft) (ft) (ft) (ft) (ft) (deg) (deg) (ft)

1 0.73 0.22 14.64 73.38 73.60 -30.92 0.00 0.85 2 1.84 1.34 15.92 72.61 73.95 -30.92 20.70 2.15 3 2.67 3.43 18.18 71.38 74.80 -27.07 20.70 3.00 4 2.76 5.73 20.89 70.10 75.83 -23.22 20.70 3.00 5 1.73 7.47 23.14 69.21 76.67 -19.37 20.70 1.83 6 0.02 8.11 24.01 68.90 77.00 -19.37 26.57 0.02 7 1.08 8.58 24.56 68.71 77.28 -19.37 26.57 1.15 8 2.89 10.16 26.55 68.11 78.27 -15.52 26.57 3.00 9 0.01 11.29 28.00 67.71 79.00 -11.67 26.57 0.01 10 0.02 11.30 28.01 67.71 79.00 -11.67 26.57 0.02 11 0.00 11.30 28.02 67.71 79.01 -11.67 26.57 0.00 12 2.91 12.33 29.48 67.41 79.74 -11.67 26.57 2.97 13 2.97 14.31 32.42 66.90 81.21 -7.82 26.57 3.00 14 2.99 16.11 35.40 66.59 82.70 -3.97 26.57 3.00 15 3.00 17.71 38.40 66.49 84.20 -0.12 26.57 3.00 16 2.99 19.12 41.39 66.58 85.70 3.73 26.57 3.00 17 0.11 19.79 42.95 66.69 86.47 7.58 26.57 0.11 18 2.86 20.33 44.43 66.88 87.22 7.58 26.57 2.89 19 2.94 21.30 47.33 67.37 88.67 11.43 26.57 3.00 20 2.89 22.06 50.25 68.06 90.13 15.28 26.57 3.00 21 2.83 22.61 53.12 68.95 91.56 19.13 26.57 3.00 22 1.37 22.88 55.22 69.73 92.61 22.99 26.57 1.49 23 0.10 22.93 55.95 70.04 92.97 22.99 26.57…