21-Attachment LL - Report Files.pdf

HARRIS COUNTY

FLOOD CONTROL DISTRICT

GEOTECHNICAL REPORT

GEOTECHNICAL STUDY

U520 Detention Basin Improvements

Harris county, Texas

SUBMITTED TO

FREESE AND NICHOLS, INC.

10497 TOWN AND COUNTRY WAY, SUITE 600

HOUSTON, TEXAS 77024

BY

HVJ ASSOCIATES, INC.

HOUSTON, TEXAS

JANUARY 10, 2019

REPORT NO. HG1610135

January 10, 2019

Mr. Marc Miller, PE Water Resources Freese and Nichols, Inc.

10497 Town and Country Way, Suite 600 Houston, Texas 77024

Re: Geotechnical Investigation U520 Basin Improvements Harris County, Texas Owner: Harris County Flood Control District (HCFCD) HVJ Proposal No. HG1610135

Dear Mr. Miller:

Submitted herein is the draft report of our geotechnical investigation for the above referenced project. The study was conducted in general accordance with our proposal number HG1610135 dated June 14, 2016 (Revised July 27, 2016) and is subject to the limitations presented in this report.

It has been a pleasure working for you on this project and we appreciate the opportunity to be of service. Please notify us if there are questions or if we may be of further assistance.

Sincerely, HVJ ASSOCIATES, INC.

Texas Firm Registration No. F-000646

Selvaratnam Sanjeevan, PE Nitharsan Kanapathippillai, EIT Project Manager 1/10/2019 Staff Engineer

Copies submitted: 1

This document was released for the purpose of interim review under the authority of Selvaratnam Sanjeevan, PE 125078 on January 10, 2019. It is not to be used for construction, bidding or permit purposes.

TABLE OF CONTENTS

Page

1 EXECUTIVE SUMMARY ..................................................................................................................... I

2 INTRODUCTION

2.1 Project Description

2.2 Scope of Work

3 FIELD INVESTIGATION

3.1 Geotechnical Borings

3.2 Water Level Measurements

3.3 Survey Data

3.4 Sampling Methods

4 LABORATORY TESTING

4.1 Dispersive Tests for Cohesive Soils

4.2 Sieve and Hydrometer Test Results

4.3 Consolidated Undrained Test Results

4.4 Direct Shear Test Results

5 SITE CHARACTERIZATION

5.1 General Geology

5.2 Geologic Faulting

5.3 Soil Stratigraphy

5.4 Groundwater Conditions

6 DETENTION BASIN PRELIMINARY DESIGN RECOMMENDATIONS

6.1 General

6.2 Method of Analysis and Required Factor of Safety

6.3 Soil Parameters and Water Level

6.4 Results

6.5 Dispersive Soils and Erosion Protection Measures

6.6 Groundwater Seepage Control/Dewatering

7 DESIGN REVIEW

8 LIMITATIONS

9 REFERENCES

PLATES

Plate

SITE VICINITY MAP

PLAN OF BORINGS

GEOLOGIC MAP

FAULT MAP

APPENDICES

Appendix

BORING LOGS AND KEY TO TERMS & SYMBOLS ........................................................................ A

SUMMARY OF LABORATORY TEST RESULTS .................................................................................. B

PIEZOMETER INSTALLATION RECORDS ........................................................................................ C SOIL PROFILE ............................................................................................................................................... D

CRUMB TEST RESULTS .............................................................................................................................. E

DOUBLE HYDROMETER TEST RESULTS ........................................................................................... F

SEIVE AND HYDROMETER TEST RESULTS .................................................................................... G

CONSOLIDATED UNDRAINED TRIAXIAL TEST RESULTS ....................................................... H

DIRECT SHEAR TEST RESULTS ............................................................................................................... I

SLOPE STABILITY ANALYSES-PROPOSED 4H:1V SLOPES........................................................... J

SOIL PARAMETERS CALCULATIONS .................................................................................................. K

POND CROSS SECTION ............................................................................................................................. L i

1 EXECUTIVE SUMMARY

The purpose of this study is to provide geotechnical recommendations for the proposed U520 Detention Ponds located at the southeast corner of FM 529 and Greenhouse Road in Harris County, Texas. The proposed improvements will include expansion of three existing basins to provide additional storage volume and construction of one new basin.

Based on the detention basin cross section and information provided by Freese and Nichols, Inc., the top of berm is at El. 128 for Pond 1 and 4 and at El. 130 for Pond 2 and 3. Based on the information provided by Freese and Nichols, Inc., we understand that 4H:1V slopes are considered for the proposed ponds. The normal storage is at El. 113.25. The purpose of this study is to assess the feasibility of the detention pond cross section based on the generalized subsurface conditions in the project area.

Based on the subsurface conditions revealed by the soil borings, the findings and recommendations of this report are summarized below:

1. Stiff to hard cohesive soils were generally encountered at surface to an elevation of 117 to 108 feet underlain by medium dense to very dense water-bearing cohesionless soils.

Cemented sand seams were encountered at borings B-11, B-12, B-13, B-21, B-22 and B-23 near the pond bottom elevation and this may cause difficulty for the pond excavation. The locations and depth of cemented sand seams encountered are shown in Table 5-2. Boring B-3 was performed on top of an existing stockpile. The existing stockpile fill consisted of lean clay with sand.

2. The water level readings in the piezometers were recorded between El. 113 and El. 91.

Based on the piezometer readings, we expect the groundwater may be encountered during excavation for the ponds.

3. Sand layer was encountered at an elevation of 117 to 108 feet and hence the normal storage elevation will not be able to maintain at El. 111 whenever the groundwater level is below the normal storage elevation. We recommend installing clay liner of thickness of about 2 feet along the slopes below the normal storage elevation and throughout the pond bottom to retain water.

4. Stability analysis was performed for the proposed detention pond sections considering end of construction, rapid drawdown and long term loading conditions. The results of our analyses indicates that the proposed pond section meet the HCFCD required factor of safety values.

5. Dispersive soils, sands and silts are highly susceptible to erosion and piping and are a major cause of slope distress in the Houston area. The results of crumb and double hydrometer tests revealed the presence of intermediate to dispersive cohesive soils at all the pond locations. We also encountered sand and silt below El. 117 at all the pond locations.

Rainfall and runoff on exposed slopes containing potential dispersive clays, sands and silts may result in surficial erosion which often results in rilling and gullying on the slopes. In other cases, standing water at top of the slopes may result in a distinctive erosion pattern ii referred to as “tunnel and jug hole”. Cohesionless soils were encountered at the bottom level of the ponds, which is susceptible to piping.

We recommend that erosion protection measures are required for the slopes and toe of the ponds. We also recommend that water should not be allowed to accumulate at top of the pond slopes. Hence, we recommend backslope interceptors/swale system at top of the pond slopes. The surrounding site-finish grading should be established so that surface water runoff may be collected at areas of the site where it may be captured into a drainage structure.

6. If the pond slopes will be concrete lined, soils will not be exposed to shrink/swell cycles and hence there will be no reduction in shear strength. If the pond slopes will be concrete lined, there is a possibility of steepening the pond slopes during final design.

7. Water bearing sands may be encountered during excavation for the ponds. We recommend that eductors may be used for the dewatering. The residences located near the east bank of detention ponds 1 and 2 and west bank of detention pond 4 are close enough that dewatering for an extended period could potentially impact the structure. If the structure is supported on deep foundations and the wells are properly constructed to avoid migration of fines, the risk to the structure should be limited. The structure foundation should be determined prior to starting dewatering and a risk assessment should be performed.

8. The cohesive soils encountered in the project area generally consisted of lean clay. The plasticity index of lean clays generally ranges between 15 and 30. Hence, the lean cohesive soils that will be obtained during pond excavation generally meet the imported select fill plasticity criteria per HCFCD Standard Specifications, Section 02921. The high plasticity clays encountered in the project area may be blended with lower plasticity material or treated with lime to be used as select fill.

Please note that this executive summary does not fully relate our findings and opinions. Those findings and opinions are only presented through our full report.

2 INTRODUCTION

2.1 Project Description

HVJ Associates, Inc. was retained by Freese and Nichols, Inc. to perform a geotechnical study for the proposed U520 Detention Ponds located at the southeast corner of FM 529 and Greenhouse Road in Harris County, Texas (Key Map No. 406R, 406V, 407N & 407S). The proposed improvements will include expansion of three existing basins to provide additional storage volume and construction of one new basin. We understand that the total area of the basin is about 95 acres and the proposed depth of the basin will be about 23 to 25 feet. A site vicinity map showing the approximate project location is presented on Plate 1 of the report.

Based on the detention basin cross section and information provided by Freese and Nichols, Inc., the top of berm is at El. 128 for Pond 1 and 4 and at El. 130 for Pond 2 and 3. Based on the information provided by Freese and Nichols, Inc., we understand that 4H:1V slopes are considered for the proposed ponds. The normal storage is at El. 113.25.

The purpose of this study is to assess the feasibility of the detention pond cross section based on the generalized subsurface conditions in the project area.

2.2 Scope of Work

The objectives of this study were to gather information on subsurface conditions at the site and to provide preliminary recommendations for the proposed detention basins. The objectives were accomplished by:

1. Drilling and field testing 23 soil borings to determine soil stratigraphy and to obtain samples for laboratory test;

2. Installing 5 piezometers to gain an understanding of the groundwater conditions at the site;

3. Performing laboratory tests to determine physical and engineering characteristics of the soils; and

4. Performing engineering analyses to develop preliminary recommendations for the proposed detention basins.

Subsequent sections of this report contain descriptions of the field exploration, laboratory testing program, general subsurface conditions, and preliminary detention pond recommendations.

3 FIELD INVESTIGATION

3.1 Geotechnical Borings

The subsurface stratigraphy at the project site was determined by drilling and sampling 23 soil borings. Borings were drilled using an ATV (Mayhew 200) mounted drilling equipment in accordance with Part 3 of HCFCD “Geotechnical Investigation Guidelines” dated December 2010.

Drilling was performed using dry auger and wet rotary techniques. The depths at the dry auguring and wet rotary techniques performed are presented in Table 3.1. All the borings with the exception of borings converted to piezometers were backfilled with soil cuttings. Borings B-1 (PZ-1), B-11

(PZ-2), B-14 (PZ-3), B-18 (PZ-4), and B-23 (PZ-5) were converted into piezometers to monitor long term groundwater readings. The approximate boring locations are shown on Plate 2.

Table 3-1 – Drilling Techniques Depths

Boring Dry Auguring, Feet Wet Rotary, Feet From To From To

B-1 0 25 25 45 B-2 0 27 27 35 B-3 0 30 30 45 B-4 0 25 25 45 B-5 0 25 25 35 B-6 0 35 35 35 B-7 0 25 25 35 B-8 0 25 25 35 B-9 0 15 N/A N/A B-10 0 25 25 35 B-11 0 20 20 35 B-12 0 25 25 35 B-13 0 25 25 35 B-14 0 35 N/A N/A B-15 0 35 N/A N/A B-16 0 25 25 35 B-17 0 35 N/A N/A B-18 0 35 N/A N/A B-19 0 25 25 35 B-20 0 15 N/A N/A B-21 0 25 25 35 B-22 0 25 25 35 B-23 0 25 25 35

N/A – Wet rotary technique was not performed.

3.2 Water Level Measurements

Groundwater level was measured in the borings during drilling, and after 24 hours of drilling operations. Borings B-1 (PZ-1), B-11 (PZ-2), B-14 (PZ-3), B-18 (PZ-4), and B-23 (PZ-5) were converted into piezometers to monitor long term groundwater readings. Groundwater measurements are presented in Section 5.4. Piezometer installation records are presented in Appendix C.

3.3 Survey Data

The coordinates and elevations of borings provided to us by Freese and Nichols, Inc. via Gorrondona and Associates, Inc. are summarized in the table below.

Table 3-2 – Borehole Survey Data Detention Pond No. Boring Northing

(feet) Easting

(feet) Elevation

(feet)

Pond-1

B-7 13880196.1 3015054.8 130.3 B-8 13879704.7 3014091.1 130.7 B-9 13879747.8 3014596.7 118.1 B-10 13879621.1 3015088.4 129.2 B-11 13879210.3 3014132.0 129.6 B-12 13879124.7 3014585.6 128.8 B-13 13879126.6 3015098.6 127.9

Pond-2

B-1 13881201.2 3014015.1 133.6 B-2 13881272.6 3014586.4 133.1 B-3 13880891.3 3014349.3 137.0 B-4 13880767.9 3014039.1 132.3 B-5 13880256.9 3014084.5 131.4 B-6 13880375.6 3014608.6 133.6 B-15 13881235.4 3015077.2 133.1

Pond-3

B-14 13881649.1 3015139.8 132.5 B-16 13881244.2 3015443.5 131.1 B-17 13880691.0 3015188.5 131.3 B-18 13880852.5 3015685.4 131.0

Pond-4

B-19 13880161.7 3015763.8 129.7 B-20 13879843.1 3015447.8 119.0 B-21 13880325.0 3016033.3 129.3 B-22 13879931.9 3016060.8 128.7 B-23 13879353.1 3015685.0 127.7

Coordinates shown are in U.S. Feet and are referenced to U.S. State Plane Texas South Central Zone, North American Datum 83. Elevations are in feet and are referenced to North American Vertical Datum (NAVD) 88.

3.4 Sampling Methods

Soil samples were obtained continuously to a depth of 20 feet and at 5-foot intervals thereafter to the termination depth of borings. Cohesive soil samples were generally obtained with a three-inch thin-walled (Shelby) tube sampler in general accordance with ASTM D-1587 standard. Each sample was extruded in the field, visually classified, and strength estimate obtained with a pocket penetrometer. Cohesionless soils were generally sampled with the split spoon sampler in accordance with ASTM D 1586 standard. Suitable portions of each sample were sealed and packaged for transportation to our laboratory.

4 LABORATORY TESTING

Selected soil samples were tested in the laboratory to determine applicable physical and engineering properties applicable to the site. All tests were performed according to the relevant ASTM Standards. These tests consisted of moisture content measurement, percent passing No. 200 sieve, Atterberg limits, unconfined compression (UC), unconsolidated undrained (UU) compression at insitu moisture content, sieve and hydrometer, crumb, double hydrometer, consolidated undrained (CU) triaxial compression, direct shear, and permeability tests.

The Atterberg Limits and percent passing number 200 sieve tests were utilized to verify field classification by the Unified Soils Classification System (ASTM D2487), the UC and UU tests were performed to obtain the undrained shear strength of the soil, crumb and double hydrometer tests were conducted to identify the presence of dispersive soils, the CU and direct shear tests were performed to obtained the drained shear strength of the soil and permeability tests were conducted to estimate the permeability of soil. The type and number of tests performed for this investigation are summarized below:

Table 4-1 – Type and Number of Laboratory Tests

Laboratory Test Name Number of Tests

Moisture Content (ASTM D2216) 264 Atterberg Limits (ASTM D4318) 64

Percent Finer than No. 200 Sieve (ASTM D1140) 116 Unconfined Compression (ASTM D2166) 24 Unconsolidated Undrained (ASTM D2850) 16

Sieve Analysis with Hydrometer (ASTM D422) 13 Crumb Test (ASTM D6572) 29

Double Hydrometer Test (ASTM D4221) 9 Consolidated Undrained Triaxial (ASTM D4767) 4

Direct Shear (ASTM D3080) 3

The laboratory test results are presented on the boring logs in Appendix A. A summary of laboratory test results, except for the sieve analysis, hydrometer, crumb, double hydrometer, consolidated undrained triaxial, and direct shear tests, is provided in Appendix B. The project scope also involves permeability tests. The HCFCD suggested that they will assign the permeability tests after reviewing the pond cross sections and soil profile. Permeability test assignments were not provided to us at the time of writing this draft report. The HCFCD Geotechnical Manual recommends to perform crumb and pinhole tests to identify the presence of dispersive soils.

However, double hydrometer tests were performed instead of pinhole tests as requested by the HCFCD Geotechnical Engineer.

4.1 Dispersive Tests for Cohesive Soils

Crumb and double hydrometer tests were conducted to identify the presence of dispersive soils at the project location. Crumb tests were initially assigned on selected soil samples and some of the soils that showed dispersive nature were then re-assigned for double hydrometer tests which are more reliable than crumb tests. The test results are summarized in Table 4-2 below. The results of crumb and double hydrometer tests indicate that the cohesive soils at the site are generally non-dispersive. However, intermediate to dispersive cohesive soils were observed at all the pond locations. Laboratory test results of crumb and double hydrometer tests are presented in the Appendices E and F, respectively.

Table 4-2 – Crumb and Double Hydrometer Test Results

Pond Boring Depth, Feet

Sample Description Crumb Test Double Hydrometer Test

Pond-1

B-7 10-12 Lean Clay Intermediate Dispersion = 56% B-8 4-6 Fat Clay Non-Dispersive Not Performed B-8 18-20 Lean Clay Dispersive Non-Dispersive B-9 2-4 Fat Clay Non-Dispersive Not Performed B-10 6-8 Lean Clay Intermediate Non-Dispersive B-11 8-10 Lean Clay Non-Dispersive Not Performed B-12 4-6 Lean Clay Intermediate Non-Dispersive B-13 10-12 Lean Clay Intermediate Non-Dispersive

Pond-2

B-1 4-6 Silty Clay Non-Dispersive Not Performed B-1 16-18 Lean Clay Intermediate Non-Dispersive B-2 2-4 Fat Clay Non-Dispersive Not Performed B-3 4-6 Fill Non-Dispersive Not Performed B-3 14-16 Lean Clay Intermediate Non-Dispersive B-4 10-12 Lean Clay Non-Dispersive Not Performed B-5 8-10 Lean Clay Non-Dispersive Not Performed B-6 2-4 Lean Clay Non-Dispersive Not Performed B-6 14-16 Lean Clay Non-Dispersive Not Performed B-15 8-10 Lean Clay Non-Dispersive Not Performed

Pond-3

B-14 12-14 Lean Clay Intermediate Not Performed B-16 6-8 Lean Clay Non-Dispersive Not Performed B-17 8-10 Lean Clay Non-Dispersive Not Performed B-18 4-6 Lean Clay Non-Dispersive Not Performed B-18 12-14 Lean Clay Non-Dispersive Not Performed

Pond-4

B-19 10-12 Lean Clay Non-Dispersive Not Performed B-20 2-4 Fat Clay Dispersive Non-Dispersive B-21 6-8 Lean Clay Intermediate Dispersion = 47% B-22 2-4 Lean Clay Non-Dispersive Not Performed B-22 12-14 Fat Clay Non-Dispersive Not Performed B-23 8-10 Lean Clay Non-Dispersive Not Performed

4.2 Sieve and Hydrometer Test Results

We performed sieve analysis and hydrometer tests in accordance with ASTM D422 on select samples to obtain the diameter of 10 percent (D10) passing that may be used to estimate the permeability of soil. The test results are presented in Appendix G and summarized in Table 4-3.

Table 4-3 – Sieve and Hydrometer Test Results

N/A- Cu and Cc values were unable to be calculated due to the high fraction of fine particles.

4.3 Consolidated Undrained Test Results

We performed four consolidated undrained (CU) triaxial compression tests to estimate the drained shear strength of the soil. The effective stress and total stress parameters obtained from the CU tests are presented in the table 4-4 below. The test results are presented in Appendix H.

Table 4-4 – Consolidated Undrained Test Results

Boring No.

(Depth)

Plasticity Index

(PI)

Soil Description

Total Stress Parameters

Effective Stress Parameters

Cohesion (ccu)

Friction Angle (φcu)

Cohesion (c’)

Friction Angle (φ’)

B-6 (10’-12’) 31 Lean Clay 1410 psf 11.8o 378 psf 23.0o B-8 (6’-8’)* 38 Fat Clay 75 psf 32.9o 252 psf 26.0o

B-14 (8’-10’) 26 Lean Clay 263 psf 33.6o 309 psf 24.0o B-22 (10’-12’)* 30 Lean Clay 87 psf 26.1o 237 psf 23.0o

* Three samples were unable to be obtained and hence multi-stage CU tests were performed.

4.4 Direct Shear Test Results

Three direct shear tests were performed to estimate the drained shear strength of the soil. The peak shear strength parameters obtained from the direct shear tests are presented in the table 4-5 below.

The test results are also presented in Appendix I.

Pond No.

Boring No.

Depth, Feet

Soil Description

Coefficient of Uniformity, CU

Coefficient of Curvature, CC

D10, mm

Pond-1 B-10 14-16 Sandy Lean Clay N/A N/A <0.001 B-12 12-14 Lean Clay 95.0 5.6 <0.001

Pond-2

B-1 18-20 Clayey Sand 110 59.6 <0.001 B-2 23-25 Clayey Sand 5.5 2.3 0.015 B-3 14-16 Lean Clay N/A N/A <0.001 B-3 28-30 Sandy Silt 2.3 1.4 0.09 B-4 16-18 Silty Sand 100 13 <0.001 B-5 16-18 Silty Sand 160 41 <0.001 B-5 18-20 Silty Sand 3.4 1.4 0.041 B-15 18-20 Silty Sand 4.1 1.3 0.022

Pond-3 B-18 8-10 Sandy Lean Clay N/A N/A <0.001

Pond-4 B-20 6-8 Sandy Silt 150 1.9 <0.001 B-23 16-18 Silty Sand 4.3 2.1 0.03

Table 4-5 – Direct Shear Test Results

Boring (Depth)

Plasticity Index

(PI)

Soil Description

Peak Shear Strength Parameters

Residual Shear Strength Parameters (at 0.5” strain)

Cohesion (c’)

Friction Angle (φ’)

Cohesion (c’)

Friction Angle (φ’)

B-8 (4’- 6’) 38 Fat Clay 1100 psf 28.9o 168 psf 33.8 o

B-17 (6’-8’) 28 Sandy Lean

Clay 840 psf 42.0o 293 psf 28.6 o

B-19 (8’-10’) 27 Lean Clay 850 psf 38.7o 396 psf 16.7 o

5 SITE CHARACTERIZATION

5.1 General Geology

There are two major surface geological formations that exist in the Houston area: the Beaumont formation and the Lissie formation. The Beaumont formation is a relatively younger formation generally found to the southeast of the Lissie formation. The Beaumont formation dips southeastward and extends beneath beach sand and waters of the Gulf of Mexico as far as the continental shelf. The project site is located in an area where the Lissie formation is typically encountered. A geologic map is presented on Plate 3.

The upper Lissie formation is sometimes denoted as the Montgomery formation. The upper Lissie formation is heterogeneous, containing interbedded layers of clay, sand and silt. It was deposited in mid-Pleistocene times in shallow coastal river channels and flood plains.

The clay present in the formation has been preconsolidated by a process of desiccation. Numerous wetting and drying cycles have produced a network of randomly oriented and closely spaced joints, which are sometimes slickensided, that is, have a shiny appearance when exposed. The joint pattern strongly influences the engineering behavior of the soil.

The sand layers vary in compactness from loose to very dense, and in thickness from a fraction of an inch to many feet due to an irregular depositional environment. Sands are generally subrounded to subangular and vary from coarse to very fine, are poorly graded, and often contain significant amounts of silt-sized particles in the sand matrix.

5.2 Geologic Faulting

The tectonic history of the Texas Gulf Coast includes a relatively stable depositional cycle since the Cretaceous Period (about 65 million years). During this period the area was subjected to deposition of clays, silts, and sands resulting in over 30 thousand feet of sedimentary rocks. Underlying this clastic sequence are salt formations, which have migrated upwards to produce the typical salt dome features associated with the Texas Gulf Coast. In conjunction with salt movement, dewatering and compaction of some of the deeper sediments in the basin have resulted in the development of growth faults.

A literature review was conducted to identify the documented faults in the project area (Sachin D.

Shah and Jennifer Lanning-Rush, 2005). The primary objective of this review was to evaluate available information from published and open file reports. Based on our review, we believe that faulting may not affect the project; however, it should be noted that unmapped faults that could impact the project may exist within the project area. A detailed fault study is beyond the scope of work for this project. A fault map is presented on Plate 4.

5.3 Soil Stratigraphy

Our interpretation of soil and groundwater conditions at the project site is based on information obtained at the boring locations only. This information has been used as the basis for our conclusions and recommendations. Significant variations at areas not explored by the project boring may require re-evaluation of our findings and conclusions.

Stiff to hard cohesive soils were generally encountered at surface to an elevation of 117 to 108 feet underlain by medium dense to very dense water-bearing cohesionless soils with occasional cemented sand seams.

A generalized summary of the soil profile encountered in the project area is presented in Table 5-1.

The generalized profile is intended to provide a conceptual framework for considering the site and is not intended as a basis of any particular analysis. Substantial deviations from the summarized conditions exist at several of the boring locations and should be accounted for in design and construction. Details of the subsurface stratigraphy at specific depths encountered in the borings are shown on the boring logs presented in Appendix A. A boring log soil profile is presented in Appendix D.

Table 5-1 – Generalized Soil Stratigraphy

Stratum Approx. Elevation, Feet Soil Description From To

I Surface 117 to 108 Stiff to Hard Cohesive Soils

(CL, CH)

II 117 to 108 104 to 89 Medium Dense to Very Dense Cohesionless Soils

(SC, ML, SM, SP-SM)

Notes:

1. Fill material was observed in Boring B-3 from El. 137 to El. 131.

2. A Cohesive soil (CL) layer was observed in Boring B-4 between El. 89 and El. 87.

3. A cohesionless soil (ML) layer was observed in Boring B-13 from El. 128 to El. 122.

4. A cohesionless soil (ML) layer was observed in Boring B-16 from El. 131 to El. 127.

It should be noted that cemented sand seams were encountered at borings B-11, B-12, B-13, B-21, B-22 and B-23 near the pond bottom elevation and this may cause difficulty for the pond excavation. The locations and depth of cemented sand seams encountered are shown in Table 5-2.

Table 5-2 – Location and Elevation of Cemented Sand Layer

Pond Boring

No.

Approx. Elevation, Feet

From To

Pond-1 B-11 103 102 B-12 119 117

Pond

Boring No.

Approx. Elevation, Feet From To

B-13 100 98

Pond-4

B-21 104 101 B-22 102 101

B-23 101 98 95 93

Boring B-3 was performed on top of an existing stockpile. The existing stockpile in the vicinity of boring B-3 consisted of lean clay with sand.

Permeability of soils For fairly uniform sand, Hazen (1930) proposed an empirical relationship for the permeability (k) in the form, k (cm/sec) = c(D10)2 where, C = 1.0 to 1.5, D10 = Diameter of 10 percent passing.

Based on the above correlation, permeability of sand encountered in the project area ranges between 10-6 and 10-2 cm/sec.

According to Kozeny Carman empirical relationship for sandy soils modified by Carrier (2003), the permeability of sand encountered in the project area ranges between 10-2 and 3x10-1 cm/sec. The permeability equation by Carrier (2003) is as follows, k (cm/sec)= 1.99x104[100%/�(fi/Dli 0.404x Dsi

0.595)]2[1/SF]2[e3/(1+e)] where, fi = fraction of particles between two sieve sizes, in percent (Note: larger sieve, l; smaller sieve, s) D = Diameter SF = Shape Factor e= Void Ratio

Permeability of cohesive soils were estimated from an empirical relationship proposed by Tavenas, et al. (1983). The estimated permeability of soils encountered in the project area is presented in table below. We will perform permeability tests on clay soils after reviewing the pond cross sections and soil profile.

Table 5-3 – Generalized Permeability of Soils

Pond Soil Description

Permeability, cm/s

Pond-1, 2 and 3 Fat Clay 5x10-9

Lean Clay 1x10-8

Pond Soil Description

Permeability, cm/s

Sand 2x10-2

Pond-4 Lean Clay 1x10-8 Fat Clay 5x10-9

Sand 3x10-1

Plasticity of Cohesive Soils The cohesive soils encountered in the project area generally consisted of lean clay. The plasticity index of lean clays generally ranges between 15 and 30. Hence, the lean cohesive soils that will be obtained during pond excavation generally meet the imported select fill plasticity criteria per HCFCD Standard Specifications, Section 02921. The high plasticity clays encountered in the project area may be blended with lower plasticity material or treated with lime to be used as select fill. The Casagrande’s Plasticity Chart presented in Figure 5-1 illustrates the range of plasticity of the cohesive soils.

Figure 5-1 Casagrande’s Plasticity Chart

Undrained Shear Strength of Cohesive Soils The undrained shear strength values obtained from our laboratory test results are presented in Figure 5-2. The undrained shear strength values generally ranges between 1500 and 6000 psf.

Figure 5-2 UC/UU Test Results

5.4 Groundwater Conditions

Groundwater level was measured in the borings during drilling, and after 24 hours of drilling operations. Borings B-1 (PZ-1), B-11 (PZ-2), B-14 (PZ-3), B-18 (PZ-4), and B-23 (PZ-5) were converted into piezometers to monitor long term groundwater readings. The table below summarizes the water readings.

Table 5-3 – Groundwater Measurements

Pond Boring

Groundwater Depth During

Drilling, Feet

Groundwater Depth

After 24 hours, Feet

Groundwater Depth in Piezometer, Feet

10/20/16 to

10/21/16 11/3/16 11/18/16 2/13/17

Pond-1

B-7 N/A Dry -- -- -- -- B-8 N/A Dry -- -- -- -- B-9 Dry Dry -- -- -- -- B-10 N/A Dry -- -- -- --

B-11 (PZ-2) N/A 21.5 (El. 108.1) 16.7 (El. 107.1) Dry Dry Dry B-12 N/A 28.5 (El. 100.3) -- -- -- -- B-13 N/A Dry -- -- -- --

Pond-2

B-1 (PZ-1) N/A 26.5 (El. 107.1) 42.5 (El. 91.1) Dry Dry Dry B-2 N/A 30.0 (El. 103.1) -- -- -- -- B-3 N/A 29.7 (El. 107.3) -- -- -- -- B-4 N/A 30.5 (El. 101.8) -- -- -- -- B-5 N/A 26.8 (El. 104.6) -- -- -- -- B-6 Dry Dry -- -- -- -- B-15 Dry Dry -- -- -- --

Pond-3

B-14 (PZ-3) Dry Dry 19.2 (El. 113.3) Dry Dry Dry B-16 N/A Dry -- -- -- -- B-17 Dry Dry -- -- -- --

B-18 (PZ-4) Dry Dry 20.5 (El. 110.5) Dry Dry Dry

Pond-4 B-19 N/A 23.4 (El. 106.3) -- -- -- -- B-20 Dry Dry -- -- -- --

Pond Boring

Groundwater Depth During

Drilling, Feet

Groundwater Depth

After 24 hours, Feet

Groundwater Depth in Piezometer, Feet

10/20/16 to

10/21/16 11/3/16 11/18/16 2/13/17

B-21 N/A Dry -- -- -- -- B-22 N/A Dry -- -- -- --

B-23 (PZ-5) N/A Dry 27.4 (El. 100.3) Dry Dry Dry N/A- Wet rotary has started before we encountered groundwater due to difficult drilling conditions.

The water level readings in the piezometers were recorded between El. 113 and El. 91. Based on the piezometer readings, we expect the groundwater may be encountered during excavation for pond. It should be noted that groundwater levels determined during drilling may not accurately reflect the true groundwater conditions, and therefore should only be considered as approximate.

Groundwater levels measured in open standpipe piezometer are more accurate; however, these readings will fluctuate seasonally and in response to rainfall.

6 DETENTION BASIN PRELIMINARY DESIGN RECOMMENDATIONS

6.1 General

The project scope involves expansion of three existing basins to provide additional storage volume and construction of one new basin. We understand that the depth of the proposed basins will be about 23 to 25 feet.

Based on the detention basin cross section and information provided by Freese and Nichols, Inc., the top of berm is at El. 128 for Pond 1 and 4 and at El. 130 for Pond 2 and 3. Based on the information provided by Freese and Nichols, Inc., we understand that 4H:1V slopes are considered for the proposed ponds. The normal storage is at El. 113.25.

The purpose of this study is to assess the feasibility of the typical cross section shown above. We have performed slope stability analyses using four conservative subsurface profiles employed based on the plasticity indices of the subsurface soils at the site. The details are provided in the subsequent sections of this report.

It should be noted that a sand layer was encountered at an elevation of 117 to 108 feet and hence the normal storage elevation will not be able to maintain at El. 113.25 whenever the groundwater level is below the normal storage elevation. We recommend installing clay liner of thickness of about 2 feet along the slopes below the normal storage elevation and throughout the pond bottom to retain water.

6.2 Method of Analysis and Required Factor of Safety

Slope stability analyses were conducted using the 2016 version of slope stability program SLOPE/W by the Morgenstern-Price method for circular rotational failure. The program calculates the factor of safety against slope failure using a two-dimensional limiting equilibrium method. Tension cracks and optimization of critical failure surface are included in the analysis.

The HCFCD requires that slope stability analyses be performed for the short term (end of construction), rapid drawdown and long term loading conditions. The slope should have safety factors of 1.3, 1.25 and 1.5 for short term, rapid drawdown and long term loading conditions, respectively.

The factor of safety represents the calculated resisting forces and moments divided by the calculated driving forces and moments of the various potential failure surfaces analyzed. These forces and moments are based on the estimated unit weights and shear strengths of the various soils in the slope profile. Accordingly, a factor of safety of 1.0 indicates impending failure. The larger the factor of safety is above 1.0, the lower the risk is that the slope will fail. As a practical matter, and in consideration of the variables and unknowns involved, the risk cannot be reduced to zero. The goal is to reduce the risk of slope failure to a reasonable and acceptable level, with due consideration of the consequences of failure.

6.3 Soil Parameters and Water Level

The soil parameters used in each case are discussed below and were estimated based on the field and laboratory data developed for this study, and also our experience with similar soils. Unconfined Compression (UC), Unconsolidated Undrained (UU), Consolidated Undrained (CU), and Direct Shear (DS) tests were conducted to estimate the shear strength parameters. The UC and UU tests were utilized to estimate the end of construction soil strength parameters. For long term and rapid drawdown analyses, effective shear strength parameters from the CU and DS tests were used.

End of Construction: The end of construction case models the initial undrained condition of the soil. The piezometric level was assumed at toe of the slope. A surcharge of 250 psf was assumed along the bank for construction equipment loading.

Long Term: The long-term design case represents steady state piezometric and stress conditions.

When a slope is excavated, 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 piezometric level was taken at the normal storage elevation of the proposed pond (El. 113.25). A surcharge of 250 psf was assumed along the bank to account for the maintenance traffic.

Rapid Drawdown: The rapid drawdown case models the condition where high floodwater saturates and piezometrically “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 bank soils. For this analysis, the maximum flood level was taken at El. 125 as recommended by the pond designer for Ponds 1, 2 and 4 and at El. 129.5 for Pond 3. We analyzed two scenarios for the drawdown elevation. The water level in the basin was “drawn down” to the bottom of the slope and to the normal storage elevation. Surcharge was not considered for rapid drawdown analyses per HCFCD guidelines.

Weathered Soil Parameters The shear strength for long term and rapid drawdown was reduced as per the HCFCD’s guidelines for the top 8 feet from the surface of the slope for the cohesive soils with Plasticity Index greater than 20. The weathered soil (or mobilized) parameter calculations are presented in Appendix J. The shear strength was reduced based on the corresponding maximum plasticity indices (PI) (Figure 13, Mesri and Ghaffar, 1993). Table 6-1 presents the soil parameters used for slope stability analyses.

Table 6-1 – Soil Parameters for Slope Stability Analyses

(Location)

Boring Used For

Analysis

Elevation, Feet

Soil Description γt, pcf

EOC

Cu, psf

Plasticity Index

(PI)

RD/LT

φ'peak, deg c’peak, psf φ'weathered, deg c’ weathered, psf

Pond-1 B-8

128-121 Fat Clay 125 2,000 49 26 252 17 25 121-108 Lean Clay 125 2,000 27 24 309 24 83 108-90 Sand 120 0 - 36 - - -

Pond-2 B-6 130-116 Lean Clay 125 2,000 31 23 378 23 49 116-90 Sand 120 0 - 34 - - -

Pond-3 B-17 130-117 Lean Clay 125 1,600 31 23 378 23 49 117-113 Sandy Clay 125 2,000 16 24 309 - - 113-90 Sand 120 0 - 34 - - -

Pond-4 B-10 & B-13

128-116 Lean Clay 125 1,800 23 24 309 24 218 116-112 Fat Clay 125 1,800 38 26 252 20 25 112-90 Sand 120 0 - 34 - - -

Where:

γt: Moist Unit Weight of Soil EOC: End of Construction cu: Unconsolidated Undrained Cohesion RD: Rapid Drawdown c’peak: Peak Consolidated Drained Cohesion LT: Long Term φ’peak: Peak Consolidated Drained Friction Angle c’weathered: Consolidated Drained Cohesion Reduced for Weathering φ’weathered: Consolidated Drained Friction Angle Reduced for Weathering

6.4 Results

Based on the soil parameters and water levels discussed above, we analyzed the stability of the proposed pond cross section. The results of our analyses indicates that the proposed pond sections meet the HCFCD required factor of safety values. The slope stability outputs are presented in Appendix J. The estimated factor of safety values are summarized in Table 6-2.

Table 6-2 – Slope Stability Results – Proposed 4H:1V Slope

(Location)

Factor of Safety

End of Construction Long Term

Rapid Drawdown Maximum Water Level to El. 105

Maximum Water Level to El. 113.25

Pond-1 4.0 1.7 1.3 1.3 Pond-2 3.5 2.1 1.3 1.3 Pond-3 3.4 2.0 1.25 1.3 Pond-4 3.6 2.1 1.4 1.4

6.5 Dispersive Soils and Erosion Protection Measures

Dispersive soils, sands and silts are highly susceptible to erosion and piping and are a major cause of slope distress in Houston area. Dispersive soils are clays that disintegrate in the presence of relatively pure water as a result of their chemical composition. The results of crumb and double hydrometer tests revealed the presence of intermediate to dispersive cohesive soils at all the pond locations. We also encountered sand and silt below El. 117 at all the pond locations. Cohesionless soils were encountered at the bottom level of the ponds, which is susceptible to piping.

Rainfall and runoff on exposed slopes containing potential dispersive clays, sands and silts may result in surficial erosion which often results in rilling and gullying on the slopes. In other cases, standing water at top of the slopes may result in a distinctive erosion pattern referred to as “tunnel and jug hole”. The typical slope distress due to dispersive soils is depicted in the Figure 6-2 below.

Figure 6-2 Typical Slope Failures due to Dispersive Soils

We recommend erosion protection measures for the slopes and toe of the ponds. We also recommend that water should not be allowed to accumulate at crest of the pond slopes since it may result in rilling and gullying on the slopes. Hence, we recommend backslope interceptors/swale system at top of the pond slopes. The surrounding site-finish grading should be established so that surface water runoff may be collected at areas of the site where it may be captured into a drainage structure.

Following is a discussion of various erosion protection measures that can be considered for this project.

Turf establishment: Turf establishment following HCFCD Standard Specifications, Section 02921 and HCFCD Policy Criteria & Procedure Manual, Section 10.3 may be used as an erosion protection measure for the pond slopes. Turf establishment is not a good alternative for pond bottom as a piping protection measure, where either concrete liner or stone riprap should be used. Turf establishment must be performed as quickly as practical after slope construction.

Stone Riprap: Stone riprap following HCFCD Standard Specifications, Section 02378 may be used as erosion and piping protection measure for pond slopes and toe. We recommend that a geotextile filter conforming to the requirements of HCFCD Standard Specification, Section 02379 should be installed as a filter beneath stone riprap to reduce erosion of soils from beneath the riprap. Stone riprap should be used for the slopes from about 5 feet above the sand layer and extended for a horizontal distance of at least 10 feet at toe of the slopes. Stone riprap should also be used in areas where high flow velocities are anticipated such as near inlets, outlets and spillways.

Concrete Liner: Concrete liner following HCFCD Standard Specifications, Section 02376 and HCFCD Policy Criteria & Procedure Manual, Section 10.4 may be used as erosion and piping protection measure for pond slopes and bottom. We recommend that a geotextile filter conforming to the requirements of HCFCD Standard Specification, Section 02379 should be installed as a filter beneath concrete liner to reduce erosion of soils from beneath the liner. Concrete liner should be used for the slopes from about 5 feet above the sand layer and extended for a horizontal distance of at least 10 feet at toe of the slopes. Concrete liner should also be used in areas where high flow velocities are anticipated such as near inlets, outlets and spillways.

Note: Concrete lined slopes will significantly reduce the exposure of soils to shrink/swell cycles and hence the reduction in shear strength may not be required. If the pond slopes will be concrete lined, there is a possibility of steepening the pond slopes during final design.

6.6 Groundwater Seepage Control/Dewatering

Based on our water level measurements, groundwater seepage may be encountered during excavation for the detention ponds. Assessment of the need for groundwater control and installation of appropriate dewatering equipment is the contractor's responsibility at the time of construction. The following comments are intended to represent common solutions to groundwater control problems encountered in similar soil conditions in the Houston area, and may not be construed as dewatering system design recommendations.

A conventional pump and sump arrangement may be adequate where water bearing cohesive soils are encountered during pond excavations. Well points or eductors may be utilized to lower the groundwater level to at least three feet below the excavation level where water bearing cohesionless soils are encountered. Well points are generally not effective below about 15 feet beneath the top of the well point, and deeper dewatering requires deep wells with submersible pumps and eductors.

We expect water bearing sands during excavation for the ponds. We recommend that eductors may be used for the dewatering. The residences located near the east bank of detention ponds 1 and 2 and west bank of detention pond 4 are close enough that dewatering for an extended period could potentially impact the structure. If the structure is supported on deep foundations and the wells are properly constructed to avoid migration of fines, the risk to the structure should be limited. The structure foundation should be determined prior to starting dewatering and a risk assessment should be performed. If necessary, control of groundwater should be accomplished in a manner that will preserve the strength of the foundation soils, will not cause instability of the excavation, and will not result in damage to existing structures.

7 DESIGN REVIEW

HVJ Associates, Inc. should review the design and construction plans and specifications prior to release to assess if they are in general conformance with the geotechnical recommendations and design criteria presented herein.

8 LIMITATIONS

This investigation was performed for the exclusive use of Freese and Nichols, Inc. to provide geotechnical recommendations for the design of U520 Detention Basins in Houston, Texas. HVJ has endeavored to comply with generally accepted geotechnical engineering practice common in the local area. HVJ makes no warranty, express or implied. The analyses and recommendations contained in this report are based on data obtained from subsurface exploration, laboratory testing, the project information provided to us and our experience with similar soils and area conditions.

The methods used indicate subsurface conditions only at the specific locations where samples were obtained, only at the time they were obtained, and only to the depths penetrated. Samples cannot be relied on to accurately reflect the strata variations that usually exist between sampling locations.

Should any subsurface conditions other than those described in our boring logs be encountered, HVJ should be immediately notified so that further investigation and supplemental recommendations can be provided.

9 REFERENCES

1. Mesri, G., and Abdel-Ghaffar, M. E. M. 1993. “Cohesion intercept in effective stress-stability analysis.’’ Journal of Geotechnical Engineering, Vol. 119, No.8, pp. 1229-1249.

2. United States Department of Agriculture, Soil Mechanics Note No. 13, February 21, 1991.

PLATES

APPROVED BY:

6120 S. Dairy Ashford Road Houston, Texas 77072-1010

281.933.7388 Ph

281.933.7293 Fax

PROJECT NO.:

PREPARED BY:

DRAWING NO.:

DATE: 2/3/2017 SV NK

HG1610135 PLATE 1

PROJECT AREA

SITE VICINITY MAP

U520 BASIN IMPROVEMENTS

PROJECT NO.:

PREPARED BY:

DRAWING NO.:

APPROVED BY:

6120 S. Dairy Ashford Road Houston, Texas 77072-1010

281.933.7388 Ph

281.933.7293 Fax

APPROXIMATE BORING LOCATIONS

DATE: 02/01/17

PLAN OF BORINGS

U520 DETENTION BASIN IMPROVEMENTS

SS AH

HG1610135 PLATE 2

A B

C D

B-1 (PZ-1)

B-2

B-3

B-4

B-5

B-6

B-7

B-8 B-9

B-10

B-11 (PZ-2)

B-12 B-13

B-14 (PZ-3)

B-15 B-16

B-17

B-18 (PZ-4)

B-19

B-20

B-21

B-22

B-23 (PZ-5)

A B C D

E

F F

E

Detention Pond-1

Detention Pond-2

Detention Pond-3

Detention Pond-4

N

Note: See Appendix D for Section Details

DRAWING NO.:

APPROVED BY:

6120 S. Dairy Ashford Road Houston, Texas 77072-1010

DATE: 6/30/2018

GEOLOGIC MAP

U520 BASIN IMPROVEMENTS

SV NK

HG1610135 PLATE 3

Project Area

Lissie Formation -- Upper part, clay, silt, sand, and very minor siliceous gravel of granule and small pebble size gravel more abundant northwestward, locally calcareous, concretions of calcium carbonate, iron oxide, and iron-manganese oxides common in zone of weathering; fluviatile; surface fairly flat and featureless except for numerous rounded shallow depressions and pimple mounds, bower part, clay, silt, sand, and minor amount of gravel; gravel slightly coarser than in upper part, noncalcareous, iron oxide concretions mare abundant than in upper part; fluviatile; very gently rolling; thickness ± 200 feet

DRAWING NO.:

APPROVED BY:

6120 S. Dairy Ashford Road Houston, Texas 77072-1010

DATE: 2/3/2017

FAULT MAP

U520 BASIN IMPROVEMENTS

SV NK

HG1610135 PLATE 4

LONG POINT FAULT

PINEY POINT WEST FAULT

PINEY POINT EAST FAULT

Project Area BRITTMORE FAULT

ADDICKS SOUTH FAULT

WHITE OAK FAULT

WOODLAND TRAILS FAULT

BREEN FAULT

UNNAMED FAULT

EUREKA HEIGHTS FAULT

APPENDIX A

BORING LOGS AND KEYS TO TERMS & SYMBOLS

CL

ML

CL

SC

ML

SM

Crumb (4'-6'):

Non-Dispersive

Crumb (16'-18'):

Intermediate

Double Hydrometer

(16'-18'):

Non-Dispersive D10 (18'-20')=

<0.001 mm

SANDY SILTY CLAY (CL-ML), very stiff, low plasticity, brown and gray, w/ gravel at 1', moist

LEAN CLAY WITH SAND (CL), very stiff to hard, moderate plasticity, brown and gray, sandy below 12', moist

CLAYEY SAND (SC), medium dense, reddish brown, w/ clay layer at 23'-25', wet

SANDY SILT (ML), dense to very dense, reddish brown, w/ gravel at 33'-35', wet

SILTY SAND (SM), very dense, brown, wet

3.74

66.1

71.7

65.6

25.0

57.0

16.0

P=4.5

P=4.5

P=4.5

P=4.5

P=4.5

P=4.5

P=4.5

P=3.5

P=4.25

N=27

N=25

N=89

N=46

N=55

N=50

3.19

Natural Moisture Content and

Atterberg Limits

Plastic Limit

Moisture Content

Liquid Limit

ATTERBERG

LIMITS(%)

E S

T

IM

A T

E D

A N

G

LE

O F

IN

T

E R

N A

L F

R

IC

T

IO

N

O T

H E

R T

E S

T S

R

E M

A R

K S

SPT

LI

Q

U

ID

L

IM

IT

LL

1.0 2.0 3.0 4.0

20 40 60 80

10/3/20166120 S. Dairy Ashford Drive Houston, Texas 77072 Phone (281)-933-7388 Fax (281)-933-7293

Water Level

S A

M P

LE

S USC

W A

T E

R L

E V

E L

20 40 60 80

Easting: 3014015.144

133.6 Feet

N P T Cu

SS

Cu (tsf)

U520 Detention Basin Improvements Harris County, Texas

F

IE

LD

S T

R E

N G

T H

D A

T A

U U

S H

E A

R

S T

R E

N G

T H ts f)

C O

N F

IN

IN

G P

R E

S S

U R

E ps i)

M O

IS

T

U R

E C

O N

T E

N T

LOG OF BORING B-1 (PZ-1)

FLIGHT AUGER

Measured: Perched:

DATE

SURFACE ELEVATION

SS (tsf)

Torvane (psf)

Sample Key:

Water Observations: Groundwater was not encountered during drilling operations; caved-in at 20.5 feet. Groundwater was encountered at 42.5 feet in piezometer after 24 hours.

LOCATION

PROJECT NO.:

1.0 2.0 3.0 4.0

PROJECT:

P

LA

S T

IC

L

IM

IT

PL

HG1610135

BLOW COUNT

MATERIAL DESCRIPTION P

A

S S

IN

G

S

IE

V

E

Northing: 13881201.245

D R

Y D

E N

S

IT

Y pc f)

Notes:

PI200 400 600 800

Key to Abbreviations:

D E

P T

H ft.

Shelby Tube Disturbed

F A

IL

U

R E

S T

R A

IN

P

LA

S T

IC

IT

Y

IN

D E

X

LOG_HCFCD P/3 HG-16-10135 HCFCD.GPJ HCFCD.GDT 2/20/17

BORING TYPE:

Est.:

Plate A-1

- SPT Data (Blows/Ft)

- Pocket Penetrometer (tsf)

- Torvane (psf)

- Undrained Cohesion (tsf)

- Shear Strength (P/3, tsf)

CH

CL

SM

SC

Crumb (2'-4'):

Non-Dispersive

D10 (23'-25')=

0.025 mm

FAT CLAY WITH SAND (CH), stiff, high plasticity, reddish brown, w/ sand seams at 0'-2' and 4'-6', moist

LEAN CLAY (CL), stiff to hard, low plasticity, brown…