geotechnical exploration elyson basin b off porter road … · 2020. 9. 25. · astm d420 using...

GEOTECHNICAL EXPLORATION

ELYSON BASIN B Off Porter Road

Harris County, Texas ALPHA Report No. H201519

July 30, 2020

Prepared for:

NASH FM 529, LLC10940 W. Sam Houston Pkwy North, Suite 300

Houston, Texas 77064 Attention: Mr. Dan Whitton

Prepared By:

TABLE OF CONTENTS

ALPHA REPORT NO. H201519

PURPOSE AND SCOPE .................................................................................................... 1PROJECT CHARACTERISTICS ...................................................................................... 1FIELD EXPLORATION .................................................................................................... 1LABORATORY TESTS .................................................................................................... 2GENERAL SUBSURFACE CONDITIONS ...................................................................... 25.1 Local Geology ......................................................................................................... 25.2 Subsurface Stratigraphy .......................................................................................... 25.3 Depth-to-Water ....................................................................................................... 3DETENTION BASIN AND DRAINAGE CHANNEL RECCOMENDATIONS ............ 36.1 Global Stability Analysis ........................................................................................ 36.2 Clay Liner for the Pond ........................................................................................... 56.3 Slope Erosion Protection......................................................................................... 6

6.3.1 Grass Cover ................................................................................................. 66.3.2 Riprap .......................................................................................................... 66.3.3 Concrete Lining ........................................................................................... 6

6.4 Groundwater Seepage and Dewatering ................................................................... 7BURIED PIPE RECOMMENDATIONS ........................................................................... 77.1 Foundation .............................................................................................................. 87.2 Bedding Materials ................................................................................................... 87.3 Backfill .................................................................................................................... 87.4 Excavation Safety ................................................................................................... 97.5 Excavation Bottom Stability ................................................................................... 97.6 Bracing Pressures .................................................................................................... 97.7 Lateral Earth Pressures ........................................................................................... 97.8 Excavation Dewatering ......................................................................................... 107.9 Junction Boxes ...................................................................................................... 117.10 Headwalls and Wingwalls ..................................................................................... 12CONSTRUCTION CONSIDERATIONS ........................................................................ 138.1 Site Preparation and Grading ................................................................................ 138.2 Constructability ..................................................................................................... 148.3 Fill Compaction .................................................................................................... 158.4 Utilities and Deep Fills ......................................................................................... 158.5 Wet Weather Conditions ....................................................................................... 168.6 Groundwater ......................................................................................................... 16LIMITATIONS ................................................................................................................. 16

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APPENDIX A Vicinity Map ................................................................................................................................ A-1 Boring Location Plan ................................................................................................................... A-2 Methods of Field Exploration ...................................................................................................... A-3 Logs of Borings Key to Soil Symbols and Classifications Cross Section of Proposed Drainage Channel Cross Section of Proposed Detention Basin Slope Stability Analysis Result Pressure Distribution for Internally Braced Flexible Walls

APPENDIX B Methods of Laboratory Testing .......................................................................................B-1

ALPHA Report No. H201519

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PURPOSE AND SCOPE

The purpose of this geotechnical exploration is for ALPHA TESTING, INC. (“ALPHA”) to evaluate for NASH FM 529, LLC (“Client”) some of the physical and engineering properties of subsurface materials at selected locations on the subject site with respect to formulation of geotechnical design parameters for the proposed construction. The field exploration was accomplished by securing subsurface samples from widely spaced borings performed across the project site. Engineering analyses were performed from results of the field exploration and results of laboratory tests performed on representative samples.

Also included are general comments pertaining to reasonably anticipated construction problems and recommendations concerning earthwork and quality control testing during construction. This information can be used to evaluate subsurface conditions and to aid in ascertaining whether the construction meets project specifications.

Recommendations provided in this report were developed from information obtained in borings depicting subsurface conditions only at the specific boring locations and at the particular time designated on the Log of Boring sheets. Subsurface conditions at other locations may differ from those observed at the boring locations, and subsurface conditions at the boring locations may vary at different times of the year. The scope of work may not fully define the variability of subsurface materials and conditions that are present on the site.

The nature and extent of variations between borings may not become evident until construction. If significant variations then appear evident, our office should be contacted to re-evaluate our recommendations after performing on-site observations and possibly other tests.

PROJECT CHARACTERISTICS

It is proposed to construct a detention basin and channel off Porter Road about 0.3 miles north of F.M. 529 in Harris County, Texas. We understand the detention basin will have a maximum depth of 17.8 ft with 6 ft of amenity depth. The drainage channel will be about 12 ft deep. It is our understanding that no structures will be constructed within 40 ft of the top of the slope. A vicinity map showing the project’s general location is provided as Figure A-1, in Appendix A of this report. At the time of the field explorations, the project site was covered with grass.

FIELD EXPLORATION

Subsurface conditions were explored by drilling nine (9) borings in general accordance with ASTM D420 using standard rotary drilling equipment to a depth of 30 ft. The approximate location of each test boring is shown on the Boring Location Plan, Figure A-2, in Appendix A of this report. Details of drilling and sampling operations are briefly summarized in Methods of Field Exploration, Figure A-3 in Appendix A of this report.

Subsurface conditions observed during the field exploration are presented on the boring logs, in Appendix A of this report. The boring logs contain our field and laboratory test results, as well as our Field Technician's and Engineer's interpretation of conditions believed to exist between actual samples retrieved. Therefore, these boring logs contain both factual and interpretive information. Lines delineating subsurface strata on the boring logs are intended to group soils having similar engineering properties and characteristics. They should be considered


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approximate as the actual transition between soil types (strata) may be gradual. A Key to Soil Symbols and Classifications used on the boring logs is presented in Appendix A of this report.

LABORATORY TESTS

Selected samples of the subsurface materials were tested in the laboratory to evaluate certain engineering properties as a basis in providing recommendations for foundation design and earthwork construction. A brief description of testing procedures used in the laboratory can be found on Figure B-1 Methods of Laboratory Testing, in Appendix B of this report. Individual test results are presented on the boring log sheets.

GENERAL SUBSURFACE CONDITIONS

5.1 Local Geology

Based on a review of literature and public maps in our library, as well as our experience, the project site lies within the Coastal Prairies Province of the Gulf Coastal Plains Physiographic Region of Texas and is underlain by soils common to the Lissie Formation.

The Lissie Formation is approximately early Pleistocene in age. The Lissie outcrop is continuous except where cut by modern river valleys, or where covered by Holocene windblown deposits in South Texas. At outcrop, the Lissie Formation is composed of fine-grained sand and sandy clay and unconformably overlies and onlaps the Willis Formation. In the subsurface, the Lissie is defined as the interval between the Willis and the Beaumont Formations. The Lissie is dominated by non-marine depositional systems in the onshore part of the Texas Coastal Plain, although shore-zone facies are prominent in some coastal counties. Lissie Formation deposition was strongly influenced by glacial-interglacial cycles on the North American continent. High-frequency, glacio-eustatic, sea-level fluctuations resulted in shorter depositional episodes, thinner genetic sequences, and greater erosional downcutting.

The Lissie Formation ranges in thickness from about 100 feet at outcrop to greater than 700 feet at the coast. The Lissie Formation dips coastward about 5 to 20 feet per mile, and is 500 to 1,000 feet deep at the modern shoreline. Lissie Formation depositional facies patterns are similar to those of the Willis Formation, and include dip-oriented fluvial channel sands separated by interchannel muds, and grading downdip into shore-parallel sands and muds. In Lissie fluvial systems, individual sand bodies are 20 to 100 feet thick, whereas interbedded muds are generally less than 20 feet thick. In general, the Lissie Formation is less sandy than the Willis Formation.

5.2 Subsurface Stratigraphy

In general, soils consisting of sandy silt (ML), silty sand (SM), sandy silty clay and/or clayey sand (SC) were encountered from the ground surface extending to depths of about 2 to 8 ft followed by sandy clay (CL) and/or clay (CH) extending to a depth of about 13 ft. Silty sand (SM) was then encountered below the sandy clay/clay, extending to the boring termination depth (30 ft).

The letters in parenthesis represent the soils' classification according to the Unified Soil Classification System (ASTM D 2488). More detailed stratigraphic information is presented on the Logs of Boring sheets attached to this report.


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5.3 Depth-to-Water

Borings were drilled using dry-auger techniques in an attempt to measure depth-to-water in the open boreholes. Free water was not encountered in the borings during drilling.

The silty sand, clayey sand and sandy silt encountered in the borings are considered relatively permeable and are anticipated to have a rapid response to water movement. However, sandy clay and clay soils encountered in the borings are considered relatively impermeable and are expected to have a relatively slow response to water movement. Therefore, several days of observation would be required to evaluate actual groundwater levels within the depths explored. Also, the groundwater level at the site is anticipated to fluctuate seasonally depending on the amount of rainfall, prevailing weather conditions and subsurface drainage characteristics.

DETENTION BASIN AND DRAINAGE CHANNEL RECCOMENDATIONS

The detention basin will be up to 17.8 ft deep (EL 157.8 to EL 140.0) and constructed with side slopes no steeper than 3 horizontal to 1 vertical (3H:1V) below the static water elevation (EL 146) and no steeper than 4 horizontal to 1 vertical (4H:1V) above the static water elevation. The drainage channel will be up to 12 ft deep with side slopes no steeper than 5 horizontal to 1 vertical (5H:1V). The global stability analyses assume that no structures will be constructed within 40 ft of the top of the slope. Cross sections of the proposed detention basin and drainage channel provided by the client are presented in Appendix A. We understand that this project will not be under the jurisdiction of the Harris County Flood Control District.

Based on the borings and on our experience with test borings in this area, we anticipate granular soils (silty sand, sandy silt and clayey sand) and cohesive soils (clay, sand clay and sandy silty clay) could be exposed along the planned pond side slopes and along the bottom. Granular soils and sandy clay soils with high sand content are highly susceptible to erosion and will not retain water. A clay liner will be required if it is desired to retain water. Recommendations for a clay liner are provided in Section 6.2 of this report.

6.1 Global Stability Analysis

Slope stability analyses for the detention basin (location of Borings SB-1 through SB-7) and drainage channel (Borings SB-8 and SB-9) were performed for this study using the SLIDE™ 7.0 computer program, which is distributed by Rocscience™. The modified Bishop method of analysis was used. SLIDE™ 7.0 program generates numerous trial failure surfaces (within specified geographic limits), computes a factor of safety for each trial surface, and reports the lowest safety factor for stability. The factor of safety against global/slope movement is defined as the ratio of resisting forces (or moments) to driving forces (or moments). A factor of safety of unity indicates the forces within a slope soil mass are at a point of imminent movement (failure), while factors of safety in excess of 1.0 indicate general stability for the condition analyzed.

Slope stability analysis results are discussed below. Slope stability analyses were performed for the cross section of the pond and drainage channel provided by the client. The pond will have a 3H:1V slope below the static water elevation (EL 146) and 4H:1V slope above the static water elevation with a maximum height of 17.8 ft. The drainage channel will have a slope that is no steeper than 5H:1V. The results of the global stability analyses are presented in Appendix A. These figures contain a graphical cross-section and tabular summary of the soil and groundwater


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conditions, and surcharge conditions used in the analyses. The figures also include stability analyses results showing the critical trial failure circle generated with computed associated factors of safety.

Soil conditions of native materials used for the stability analyses of the detention basin and drainage channel were based on results of test borings and laboratory tests. Soil strength parameters used in the stability analyses were evaluated and selected using undrained test data (including hand penetrometer, unconfined compression tests) and were conservatively estimated based on previous work experience with similar soils of the same geologic origin. Three critical soil profiles (Cases 1 through 3) were used for the analysis of the pond and one critical soil profile (Case 4) was used for the analysis of the channel. A summary of the soil properties used for stability analyses are presented in Table A:

TABLE A SOIL PROPERTIES USED FOR GLOBAL STABILITY ANALYSES

DEPTH,FT

SOIL TYPE

Undrained Parameters

(Short Term)

Consolidated Undrained Parameters (Rapid

Drawdown)

Consolidated Drained Parameters

(Long Term) Shear

Strength, c (psf)

Friction Angle, ϕ (degrees)

Shear Strength, c’

(psf)

Friction Angle, ϕ’ (degrees)

Shear Strength, c’’ (psf)

Friction Angle, ϕ’’ (degrees)

Case -1 (Boring SB-1) and Case -4 (SB-8)

0 to 4 Sandy Silt (ML) 0 20 0 20 0 20

4 to 13 Sandy Clay (CL) 1,200 0 180 16 160 18

13 to 30 Silty Sand (SM) 0 32 0 32 0 32

Case -2 (Boring SB-6)

0 to 2 Sandy Silty Clay (CL-

ML) 0 20 0 20 0 20

2 to 6 Clay (CH) 400 0 200 14 180 16

6 to 13 Sandy Clay (CL) 1,200 0 180 16 160 18

13 to 30 Silty Sand (SM) 0 32 0 32 0 32

Case -3 (Boring SB-7)

0 to 4 Sandy Silt (ML) 0 20 0 20 0 20

4 to 8

Silty Sand (SM)/Claye

y Sand (SC)

0 28 0 28 0 28


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8 to 13 Sandy Clay (CL) 1,200 0 180 16 160 18

13 to 30 Silty Sand (SM) 0 32 0 32 0 32

Results of our global stability analyses for the detention pond slope and the various conditions are summarized in Table B. The table presents the minimum computed factor of safety against global stability failure.

TABLE B COMPUTED FACTORS OF SAFETY FOR GLOBAL STABILITY ANALYSES

CONDITION COMPUTED FACTOR OF SAFETY

(FOS) MINIMUM REQUIRED FOS Case-1 Case-2 Case-3 Case-4

Short Term 2.9 2.8 2.2 3.8 1.5

Long Term 2.2 2.2 2.2 2.9 1.5

Rapid Drawdown 1.9 2.1 1.9 2.8 1.3

The computed factors of safety considering global stability in the tables above are generally considered to be adequate for the proposed detention pond and channel slopes. Therefore, the pond and channel slopes are considered to be globally stable. The factors of safety in Table B are based on maintaining a static water level at EL 146 ft as indicated on the client’s Cross Section B-B and shown on the global stability analyses outputs. These factors of safety also assume that no structures will be built within 40 ft of the top of the slope. It is recommended vegetation be maintained along all exposed slopes to reduce erosion. Erosion protection such as rip-rap, concrete and/or reinforced mats may also be required to prevent erosion and minor sloughing of the embankment soils in the long term (See Section 6.3).

Even though the global stability results indicate adequate factors of safety for a global condition, our experience indicates that slopes steeper than about 4H:1V may incur minor sloughing and shallow skin slides due to shrinking and swelling of high plasticity clays or erosion of soils. Shallow skin failures should be continuously monitored and repaired to reduce deterioration of embankment slopes and potential for greater failures. Vegetation or erosion protection should be maintained along the slopes to reduce the potential for shallow slides and erosion.

6.2 Clay Liner for the Pond

Based on the borings, silty sands, sandy silt, clayey sand and/or sandy clay soils with relatively high permeability will likely be encountered in the pond excavation. A clay liner should be provided in areas where it is required to retain water (note that our global stability analyses are based on maintaining a static water level in the pond). We recommend a minimum liner thickness of 2 ft.

Some of the on-site clay soils may be used as clay liner material provided they meet the following requirements. If clay material is encountered at the bottom of the pond, it should be


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verified to have a minimum thickness of 2 ft and should also meet the following requirements. The clay liner should extend from the bottom of the ponds to at least the top of the planned water level. In general, clay liner material should have the following properties:

Hydraulic Conductivity: Less than 1 x 10-7 cm/sec Liquid Limit: Greater than 45 Plasticity Index: 25 – 50 Percent Passing No. 200 Sieve: 70 or greater Pinhole Dispersion Test Method A: ND1 – ND2

After removing the vegetation and prior to placing the clay liner, the site preparation guidelines provided in Section 8.1 of this report should be followed. The clay liner material should be compacted in accordance with the recommendations provided in Section 8.3 of this report.

6.3 Slope Erosion Protection

We understand that the side slopes of the pond are to be no steeper than 3H:1V below the static water elevation and no steeper than 4H:1V above the static water elevation. The drainage channel will have a slope that is no steeper than 5H:1V. Erosion is usually expected with these slopes, especially where sandy soils are encountered. Excessive erosion can lead to a loss of ground and gradual sloughing of the slopes. Consequently, progressive slope failures can occur. Dressing of the slopes with erosion control systems can improve long-term performance. Our recommendations for erosion protection of detention pond and channel slopes are as follows:

6.3.1 Grass Cover

Grass cover can provide a suitable erosion protection system provided the root systems can sustain the peak velocities from the rain water. Periodic observation of side slopes should be planned to identify areas that may require a more positive erosion protection system.

6.3.2 Riprap

Riprap consisting of stone or broken concrete rubble may be used for erosion protection in the detention ponds. Protection of the toe is critical for providing acceptable stability along the embankment.

6.3.3 Concrete Lining

This type of erosion control system is effective when placed on top of subgrade soils compacted to at least 95% of maximum standard density (ASTM D698) at a moisture content between optimum and +3% of optimum. The minimum concrete lining thickness should be 5 inches and be reinforced in each direction with reinforcement equal to about 0.5 percent of the concrete area. Areas on the sloped surfaces where the loose or soft soils encountered should be removed, moisture conditioned and recompacted to at least 95% of maximum density (ASTM D698). Drainage holes should be placed at fixed intervals in the lower portion of the concrete lining not exceeding 15 feet to prevent hydrostatic pressure build-up behind the concrete liner.


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6.4 Groundwater Seepage and Dewatering

Free water was not encountered during this investigation. However, from our experience with similar soils, groundwater seepage could be encountered at shallow depths in excavations for the pond and channel. Granular soils were encountered at various depths in the borings. Based on the borings and our experience with test borings in this area, we anticipate granular soils (silty sand, sandy silt or clayey sand) will be exposed along the planned pond side slopes and along the bottom. Excavation slope and bottom instability will occur if groundwater is encountered in silty sand, sandy silt and clayey sand soils. To accomplish excavation below the water level, it will be necessary to either dewater the site to allow for excavation in the sandy soils, or it will be necessary to excavate below the groundwater level using a dredging technique.

Typically, the Contractor is responsible for designing, installing and maintaining a dewatering system for groundwater control and taking precautions to avoid distress to nearby existing structures, as a result of dewatering. Dewatering systems should be designed, installed and monitored by personnel qualified and experienced with dewatering soils in the Houston Metropolitan area. We recommend the Contractor consider retaining a dewatering expert to assist in identifying, implementing and monitoring the most suitable and cost-effective method to control groundwater. The contractor should have a groundwater control plan in-place prior to beginning excavation at this site. Groundwater control systems should be in accordance with the Harris County Specifications, Item 436 “Well Pointing”. The following is intended to provide guidance to the Contractor for dewatering systems.

In saturated cohesionless soils, groundwater is typically controlled by the installation of vacuum well points. Close well point spacing (typically on the order of 5 to 15 ft) is generally required if the soils are fine-grained. The practical maximum depth for using vacuum well points is considered to be about 15 ft. When groundwater control is required below 15 ft, deep wells with submersible pumps have generally proved successful.

Generally, the groundwater depth should be lowered to a depth of at least 3 ft below the planned excavation bottom to provide a firm working surface. Extended and/or extensive dewatering can result in settlement of existing structures in the vicinity; the Contractor is to take necessary precautions to monitor and minimize the effects on these structures.

BURIED PIPE RECOMMENDATIONS

We understand that storm pipes are planned for this project. The maximum invert depth is expected to be less than 20 ft below existing grades and that open-cut methods are planned to be used for installation. Bedding and backfill recommendations for the proposed storm sewer lines should be in accordance with the Harris County Specifications, Item No. 433 – Cement Stabilized Sand, Bedding and Backfill material.

The following sections provide our recommendations with respect to buried pipe design including the foundation, bedding and backfill. In addition, installation considerations and guidelines are also provided with respect to excavation safety, shoring and bracing, and excavation dewatering.


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7.1 Foundation

Based on the boring information and the embedment depths provided, we anticipate the soils at the bottom of the trench excavations could consist primarily of stiff to hard clays as well as loose to medium dense granular soils. These soils are generally considered suitable for support of buried pipes. The bottoms of trench excavations should expose strong competent soils and should be dry and free of loose, soft, or disturbed soil. If fill soils are encountered at the base of trench excavations, their competency should be verified through probing and density testing. Soft, wet, weak, or deleterious materials should be over-excavated to expose strong competent soils.

At locations where soft or weak soils extend for some depth, over excavation to stronger soils may prove infeasible and/or uneconomical. In the event of these areas are encountered, we recommend that the bottom of the trench excavation be over-excavated by 1 to 2 ft, and replaced with an open-graded aggregate that will allow for drainage of water, as well as provide a stable working platform. A non-woven geotextile fabric should be placed along the bottom of the over excavated area before backfilling.

7.2 Bedding Materials

The bedding materials should be selected to ensure the most uniform contact between the pipe and the foundation as possible. Granular soils such as bank run sand, concrete sand, pea gravel, crushed limestone, or cement treated sand may be used as the bedding material. It is essential that bedding materials are placed (i.e., thickness of layer and compactive effort) in conformance with Harris County Specifications, Item No. 433 – Cement Stabilized Sand, Bedding and Backfill material.

7.3 Backfill

We recommend backfill materials and placement be in accordance with Harris County Specifications, Item No. 433 – Cement Stabilized Sand, Bedding and Backfill material. We recommend that the trench backfill above the pipe bedding should be placed and compacted in accordance with the recommendations in Section 8.3. In addition, backfill for trenches should not be started until the storm sewer line is properly bedded in accordance with the recommendations outlined. We anticipate the trench backfill will generally consist of excavated soils. Materials removed from the trench excavations will generally be suitable as backfill above the bedding, provided they are not saturated and do not contain organic matter, debris, or other deleterious material.

We understand utility embedment depths at this site could be about up to about 20 ft below existing grades. From our experience, trench backfill in excess of about 10 to 12 ft in thickness is prone to post-construction settlements due to compression of the soils from self-weight, even if these fills are properly placed and compacted. This settlement could be about 1 to 2 percent of the thickness of the fill. The potential for this settlement should be considered when designing pavements. To reduce the risk of fill settlement, the portion of the fill below a depth of 10 ft below final grade should be compacted to a minimum of 100 percent of the material’s maximum standard Proctor dry density (ASTM D-698) as recommended in Section 8.4.


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7.4 Excavation Safety

We understand that the utilities will be about 20 ft deep below the existing grade. The contractor or others shall be required to develop an excavation safety plan to protect personnel entering the excavation or excavation vicinity. The collection of specific geotechnical data and the development of such a plan, which could include designs for sloping and benching or various types of temporary shoring, is beyond the scope of the current study. Any such designs and safety plans shall be developed in accordance with current OSHA guidelines and other applicable industry standards.

7.5 Excavation Bottom Stability

The stability of an excavation bottom is dependent on the excavation geometry, soil strength parameters of the bearing soils, and most importantly the location of groundwater. In general, clay (cohesive) materials were encountered at the borings and we would expect excavations to extend primarily in these materials. Excavations within cohesive soils are not susceptible to a reduction in effective stress conditions due to the relatively short period of time excavations are open. That is, the stress conditions within cohesive soils generally do not move from an undrained (short-term) to drained (long-term) condition. As such, the bottom stability of excavations within cohesive soils is controlled by the shear strength of the bearing soils.

It is important to note that the discussion does not consider layered soil profiles. For example, a charged sand layer that lies below a clay layer will cause significant seepage pressures on the bottom of an excavation within the overlying clay layer, especially as the excavation approaches the sand layer. When encountered, these areas must be considered on a case-by-case basis by the Geotechnical Engineer-of-Record.

In granular soils, excavation bottom stability is generally controlled by the presence (or absence) of groundwater. For dry excavations in granular soils, we expect excavation bottoms should be stable. However, excavation bottom instability should be anticipated where groundwater is encountered within granular soils. Groundwater was not encountered during this investigation. If groundwater is encountered during construction, excavation dewatering will be required and is discussed in more detail in Section 7.8.

7.6 Bracing Pressures

In order to properly design the supports for shielding workers within an excavation, the type of shoring planned for use, as well as the geometry (i.e., the vertical spacing of struts) must be known. The Department of the Navy’s method1 for determining the pressure distribution for internally braced flexible walls is presented in Appendix A.

7.7 Lateral Earth Pressures

Equivalent fluid density values for computation of lateral soil pressures acting on retention systems were evaluated for the natural soils that were encountered in our borings. These values, as well as corresponding lateral earth pressure coefficients and estimated unit weights, are presented in Table C.

1“Foundations and Earth Structures,” Department of the Navy, (1982), Naval Facilities Engineering Command, DM-7.2, Alexandria, VA, p 7.2-100.


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TABLE C LATERAL EARTH PRESSURES

Backfill Type

Estimated Total Unit

Weight (pcf)

Active Condition At-Rest Condition Passive Condition Earth

Pressure Coefficient,

ka

Equivalent Fluid

Density (pcf)

Earth Pressure

Coefficient, ko

Equivalent Fluid

Density (pcf)

Earth Pressure

Coefficient, kp

Equivalent Fluid

Density (pcf)

Sandy Silty Clay/Sandy Clay/Clay

125 0.61 76 0.76 95 1.63 203

Clayey Sand/Sandy

Silt 115 0.35 40 0.52 60 2.88 331

Silty Sand 115 0.31 36 0.47 54 3.25 374 Free-

Draining Granular

120 0.28 34 0.44 53 3.54 425

The values tabulated in Table C under “Active Conditions” pertain to flexible retention systems free to tilt inward as a result of lateral earth pressures. For rigid, non-yielding walls the values under “At-Rest Conditions” should be used.

The values presented in Table C do not include the effect of surcharge loads such as construction equipment, vehicular loads, or future storage near the structures. Nor do the values account for possible hydrostatic pressures resulting from groundwater seepage entering and ponding within the cut soils. However, these surcharge loads and groundwater pressures should be considered, if applicable, in designing any structures subjected to lateral earth pressures.

7.8 Excavation Dewatering

Typically, the Contractor is responsible for designing, installing and maintaining a dewatering system for groundwater control and taking precautions to avoid distress to nearby existing structures, as a result of dewatering. Dewatering systems should be designed, installed and monitored by personnel qualified and experienced with dewatering soils in the Houston Metropolitan area. We recommend the Contractor consider retaining a dewatering expert to assist in identifying, implementing and monitoring the most suitable and cost-effective method to control groundwater. The contractor should have a groundwater control plan in-place prior to beginning excavation at this site. Groundwater control systems should be in accordance with the Harris County Specifications, Item 436 “Well Pointing”. The following is intended to provide guidance to the Contractor for dewatering systems.

In cohesive soils where seepage is usually low, groundwater is generally managed by collection in trench bottom sumps for pumped disposal. Care should be taken to have a redundant pumping system that allows for overnight pumping. Water must not be allowed to pond in the trench bottoms. The softening of soils can lead to instability and sloughing of trench side walls. In addition, if cohesive soils contain lenses/layers of water-bearing granular or cohesionless soils, they may have to be dewatered using techniques for cohesionless soils.

In saturated cohesionless soils, groundwater is typically controlled by the installation of vacuum well points. Close well point spacing (typically on the order of 5 to 15 ft) is generally required if


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the soils are fine-grained. The practical maximum depth for using vacuum well points is considered to be about 15 feet. When groundwater control is required below 15 ft, deep wells with submersible pumps have generally proved successful.

Generally, the groundwater depth should be lowered to a depth of at least 3 ft below the planned excavation bottom to provide a firm working surface. Extended and/or extensive dewatering can result in settlement of existing structures in the vicinity; the Contractor is to take necessary precautions to monitor and minimize the effects on these structures.

Although groundwater was not encountered during this investigation, seasonal fluctuations and/or unforeseen environmental conditions may result in water being encountered at other locations and at shallower depths. We therefore suggest the Contractor provide a line item for dewatering in the bid package in case dewatering is required.

7.9 Junction Boxes

We understand junction boxes are planned for the project. These structures are expected to bear about 13 to 20 ft below final grade. The subgrade materials are expected to provide adequate foundation support for junction boxes, provided the soils remain in a relatively undisturbed condition. The junction boxes bearing at depths of about 13 to 20 ft below final grade could be dimensioned using an allowable net bearing pressure of 3,000 psf on native soils. The recommended bearing pressure includes a factor of safety of at least 3 against shear failure of foundation soils.

Resistance to lateral forces at thrust blocks will be developed by friction along the base of the thrust block and passive earth pressure acting on the vertical face of the block. We recommend a coefficient of base friction of 0.3 along the bottom of the thrust block. Passive earth pressures are provided in Table C. A surcharge of at least 250 psf should be considered for vehicular traffic loads imposed on the junction boxes at the surface.

The junction box structures should be designed to resist full hydrostatic uplift. Frictional forces between the concrete walls and the supporting soils should be neglected for the upper 5 ft due to construction disturbance. As such, the only resistance to potential uplift forces in this zone will be the self-weight of the concrete. An allowable friction value of 200 psf may be used below a depth of 5 ft along the walls of the junction boxes, assuming competent surrounding soils and proper contact with these soils. The concrete thickness of the walls or the base may be increased to increase dead load. A factor of safety of 1.1 may be used for hydrostatic uplift for structures considering only the self-weight of the concrete.

In addition, the base slab can be extended laterally beyond the edge of the junction box walls to utilize the buoyant weight of soil above the slab extension to resist uplift. Friction between the soil and the junction box structure must be neglected if this method of increasing uplift resistance is utilized. We recommend using a buoyant unit weight of 90 pcf for the concrete and 60 pcf for the soil to compute uplift resistance.


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7.10 Headwalls and Wingwalls

We understand that headwalls with wings will be installed at the ends of the storm pipes in the channel. Furthermore, we understand the bottom of the structures will be about 12 to 14 ft below the ground surface and will be constructed by open cut excavations. The headwalls and wingwalls should be designed in general accordance with the TxDOT Standard Specifications for Construction and Maintenance of Highways, Streets and Bridges, 2014, Item 466, “Headwalls and Wingwalls.”

We understand that the headwalls and wingwalls will be supported on a strip footing type foundation. We recommend an allowable bearing pressure of 3,000 psf for the walls bearing on undisturbed native soils.

Resistance to sliding will be developed by friction along the base of the footings and passive earth pressure acting on the vertical face of the footing and a key installed in the base of the footings, if required. We recommend a coefficient of base friction of 0.3 be used along the bottom of the footing. The available passive earth resistance on the vertical face of the footing and a key constructed in the base of the footing may be calculated using an allowable passive earth pressure of 100 psf, per ft of depth below a depth of 1 ft from adjacent grade.

The soils at the foundation bearing level are prone to disturbance once exposed. It may be necessary to protect the foundation subgrade with a layer of crushed stone aggregate, cement-stabilized sand, or a lean concrete mudmat. Also, soft and/or otherwise unsuitable materials encountered at the foundation bearing level should be removed to expose suitable firm native soils. The resulting excavation can be backfilled to the design foundation bearing level with crushed stone aggregate base, lean concrete, or cement-stabilized sand.

Cement-stabilized sand materials should be in accordance with the TxDOT Standard Specifications for Construction and Maintenance of Highways, Streets and Bridges, 2014, Item 400, “Excavation and Backfill for Structures”. Cement stabilized sand should be compacted to a dry density of at least 95 percent of standard Proctor maximum dry density (ASTM D 558). The moisture content during placement should be within the range of -3 to +3 percentage points of optimum moisture.

Equivalent fluid density values for computation of lateral soil pressures acting on the walls were evaluated for the natural soils that were encountered in our borings (both native materials and these materials being used as controlled fill). These values, as well as corresponding lateral earth pressure coefficients and estimated unit weights, are presented in Section 7.7.

Free draining granular (clean sand or gravel) used as backfill behind wall should consist of a sand, gravel, or sand-gravel mixture with a maximum nominal particle size of 2 inches and not more than 5 percent passing a No. 200 sieve.

Any fill associated with the walls should be placed and compacted in accordance with the recommendations contained in Section 8.3 of this report.


13

CONSTRUCTION CONSIDERATIONS

Variations in subsurface conditions could be encountered during construction. To permit correlation between test boring data and actual subsurface conditions encountered during construction, it is recommended a registered Professional Engineering firm be retained to observe construction procedures and materials.

Some construction problems, particularly degree or magnitude, cannot be anticipated until the course of construction. The recommendations offered in the following paragraphs are intended not to limit or preclude other conceivable solutions, but rather to provide our observations based on our experience and understanding of the project characteristics and subsurface conditions encountered in the borings.

8.1 Site Preparation and Grading

All areas supporting foundations, paving, clay liners and other areas to receive new fill should be properly prepared.

After completion of the necessary stripping, clearing, and excavating and prior to placing any required fill, the exposed subgrade should be carefully evaluated by probing and testing. Any undesirable material (organic material, wet, soft, or loose soil) still in place should be removed.

The exposed subgrade should be further evaluated by proof-rolling with a heavy pneumatic tired roller, loaded dump truck or similar equipment weighing approximately 20 tons (10 tons for pond clay liner) to check for pockets of soft or loose material hidden beneath a thin crust of possibly better soil.

Proof-rolling procedures should be observed routinely by a Professional Engineer or his designated representative.

Any undesirable material (organic material, wet, soft, or loose soil) exposed should be removed and replaced with well-compacted material (acceptable clay liner material for clay liner area) as outlined in Section 8.3.

Prior to placement of any fill, the exposed subgrade should then be scarified to a minimum depth of 6 inches and recompacted as outlined in Section 8.3.

If fill is to be placed on existing slopes (natural or constructed) steeper than six horizontal to one vertical (6:1), the fill materials should be benched into the existing slopes in such a manner as to provide a minimum bench-key width of five (5) ft. This should provide a good contact between the existing soils and new fill materials, reduce potential sliding planes, and allow relatively horizontal lift placements.

The contractor is responsible for designing any excavation slopes, temporary sheeting or shoring. Design of these structures should include any imposed surface surcharges. Construction site safety is the sole responsibility of the contractor, who shall also be solely responsible for the means, methods and sequencing of construction operations. The contractor should also be aware that slope height, slope inclination or excavation depths (including utility trench excavations)


14

should in no case exceed those specified in local, state and/or federal safety regulations, such as OSHA Health and Safety Standard for Excavations, 29 CFR Part 1926, or successor regulations. Stockpiles should be placed well away from the edge of the excavation and their heights should be controlled so they do not surcharge the sides of the excavation. Surface drainage should be carefully controlled to prevent flow of water over the slopes and/or into the excavations. Construction slopes should be closely observed for signs of mass movement, including tension cracks near the crest or bulging at the toe. If potential stability problems are observed, a geotechnical engineer should be contacted immediately. Shoring, bracing or underpinning required for the project (if any) should be designed by a professional engineer registered in the State of Texas.

Due to the nature of the clayey and sandy soils found near the surface at the borings, traffic of heavy equipment (including heavy compaction equipment) may create pumping and general deterioration of shallow soils. Therefore, some construction difficulties should be anticipated during periods when these soils are saturated.

8.2 Constructability

Based on the borings performed for this study, non-plastic silty sand, sandy silt and low plasticity sandy silty clay were observed near the ground surface at some of the boring locations. These non-plastic and low plasticity soils will cause sloughing of the slopes. As such, construction difficulties should be anticipated, especially during the wet season or immediately after rain events.

Although having a thin layer of non-plastic or low plasticity soils overlying cohesive soils is typical of this geologic region, our experience suggests that the local contractors find these materials troublesome and can often be the source of change orders, construction delays, and budget over runs. The following recommendations are intended to address the site access and workability problems that will occur due to the presence of surficial non-plastic or low plasticity soils and are provided in descending order of preference:

1. The most appropriate method of dealing with surficial non-plastic or low plasticity soils is to remove them and replace them with suitable cohesive fill soils. After successfully passing a proofroll as discussed above in Section 8.1, suitable cohesive fill soils should be placed and compacted as discussed below in Section 8.3.

2. Lime-fly ash or cement modification of the non-plastic or low plasticity soils could be utilized to aid in compaction and to provide a working surface. Recommendations for application rates and placement procedures for lime-fly ash or cement modification can be provided upon request.

3. Based on our experience, the most difficult method of dealing with the surficial non-plastic or low plasticity soils would be to rework the soils using conventional moisture control and compaction methods. However, even properly placed and compacted sandy soils will not have enough shear strength (bearing capacity) to hold up to construction traffic or weathering when exposed at the ground surface. As such, the surficial non-plastic or low plasticity soils would require continual repair and maintenance until the planned basin and/or channel constructed.


15

8.3 Fill Compaction

Clay soils to be used as fill at the site should be compacted to a dry density of 95 to 100 percent of standard Proctor maximum dry density (ASTM D 698) and within the range of 1 percentage point below to 3 percentage points above the material's optimum moisture content. Clayey soil materials used as fill should be processed and the largest particle or clod should be less than 6 inches prior to compaction.

Granular soils to be used as fill at the site outside of the building pad should be compacted to a dry density of at least 95 percent of standard Proctor maximum dry density (ASTM D 698) and within the range of 2 percentage point below to 2 percentage points above the material's optimum moisture content. It may be necessary to mix about 2 to 4 percent cement into the granular soils to improve the compaction characteristics of these materials.

Compaction should be accomplished by placing fill in about 8-inch thick loose lifts and compacting each lift to at least the specified minimum dry density. Field density and moisture content tests should be performed on each lift.

8.4 Utilities and Deep Fills

In cases where utility lines and/or deep fills are more than 10 ft deep, the fill/backfill below 10 ft should be compacted to at least 100 percent of standard Proctor maximum dry density (ASTM D 698) and within –2 to +2 percentage points of the material's optimum moisture content. The portion of the fill/backfill shallower than 10 ft should be compacted as previously outlined. Density tests should be performed on each lift (maximum 12-inch thick) and should be performed as the trench is being backfilled.

Even if fill is properly compacted, fills in excess of about 10 ft are still subject to settlements over time of up to about 1 to 2 percent of the total fill thickness. This should be considered when designing pavement over utility lines and/or other areas with deep fill.

If utility trenches or other excavations extend to or beyond a depth of 5 ft below construction grade, the contractor or others shall be required to develop an excavation safety plan to protect personnel entering the excavation or excavation vicinity. The collection of specific geotechnical data and the development of such a plan, which could include designs for sloping and benching or various types of temporary shoring, is beyond the scope of this study. Any such designs and safety plans shall be developed in accordance with current OSHA guidelines and other applicable industry standards.


16

8.5 Wet Weather Conditions

Due to the nature of the surficial soils, construction operations may encounter difficulties due to wet or soft surface soils becoming a general hindrance to equipment, especially following periods of wet weather. If the subgrade cannot be adequately compacted to the minimum densities as described previously, one of the following measures will be required: 1) removal and replacement with select fill, 2) chemical treatment of the soil to dry and improve the condition of the subgrade, or 3) drying by natural means if the schedule allows. Based on our experience with similar soils in this area, chemical treatment is generally the most efficient and effective method to increase the supporting value of wet and weak subgrade. ALPHA TESTING should be contacted for additional recommendations if chemical treatment is needed due to soft and wet subgrade.

8.6 Groundwater

Groundwater was not encountered in the borings. However, from our experience with similar soils, groundwater seepage could be encountered at shallow depths in excavations for foundations, utility conduits, and other general excavations. The risk of seepage increases with depth of excavation and during or after periods of precipitation. Standard sump pits and pumping may be adequate to control seepage on a local basis for relatively shallow excavations. Supplemental dewatering procedures (such as, but not limited to, submersible pumps in slotted casings or well points) may be required for excavations into granular soils that encounter groundwater.

LIMITATIONS

Professional services provided in this geotechnical exploration were performed, findings obtained, and recommendations prepared in accordance with generally accepted geotechnical engineering principles and practices. The scope of services provided herein does not include an environmental assessment of the site or investigation for the presence or absence of hazardous materials in the soil, surface water or groundwater. ALPHA, upon written request, can be retained to provide these services.

ALPHA is not responsible for conclusions, opinions or recommendations made by others based on this data. Information contained in this report is intended for the exclusive use of the Client (and their designated design representatives), and is related solely to design of the specific structures outlined in Section 2.0. No party other than the Client (and their designated design representatives) shall use or rely upon this report in any manner whatsoever unless such party shall have obtained ALPHA’s written acceptance of such intended use. Any such third party using this report after obtaining ALPHA’s written acceptance shall be bound by the limitations and limitations of liability contained herein, including ALPHA’s liability being limited to the fee paid to it for this report. Recommendations presented in this report should not be used for design of any other structures except those specifically described in this report. In all areas of this report in which ALPHA may provide additional services if requested to do so in writing, it is presumed that such requests have not been made if not evidenced by a written document accepted by ALPHA. Further, subsurface conditions can change with passage of time. Recommendations contained herein are not considered applicable for an extended period of time after the completion date of this report. It is recommended our office be contacted for a review of the contents of this report for construction commencing more than one (1) year after


17

completion of this report. Non-compliance with any of these requirements by the Client or anyone else shall release ALPHA from any liability resulting from the use of, or reliance upon, this report.

Recommendations provided in this report are based on our understanding of information provided by the Client about characteristics of the project. If the Client notes any deviation from the facts about project characteristics, our office should be contacted immediately since this may materially alter the recommendations. Further, ALPHA is not responsible for damages resulting from workmanship of designers or contractors. It is recommended the Owner retain qualified personnel, such as a Geotechnical Engineering firm, to verify construction is performed in accordance with plans and specifications.

VICINITY MAP

CLIENT PROJECT NAMEPROJECT NUMBER PROJECT LOCATION

N

Key Map used with permission.

FIGURE A-1

NASH FM 529, LLC Elyson Basin BH201519 Harris County, Texas

tacosta

Arrow

tacosta

Oval

tacosta

Line

tacosta

Text Box

Project Site

BORING LOCATION PLAN

FIGURE A-2

CLIENT PROJECT NUMBER

PROJECT NAME PROJECT LOCATION

Site plan provided by the Client.


tacosta

Oval

tacosta

Oval

tacosta

Oval

tacosta

Oval

tacosta

Oval

tacosta

Oval

tacosta

Oval

tacosta

Oval

tacosta

Oval


A-3 METHODS OF FIELD EXPLORATION

Using standard rotary drilling equipment, a total of nine (9) test borings were performed for this geotechnical exploration at the approximate locations shown on the Boring Location Plan, Figure A-2. The boring locations were staked by using a handheld GPS device as shown on the site plan provided during this study. The locations of the test borings shown on the Boring Location Plan are considered accurate only to the degree implied by the method used to define them.

Relatively undisturbed samples of the cohesive subsurface materials were obtained by hydraulically pressing 3-inch O.D. thin-wall sampling tubes into the underlying soils at selected depths (ASTM D 1587). These samples were removed from the sampling tubes in the field and examined visually. One representative portion of each sample was sealed in a plastic bag for use in future visual examinations and possible testing in the laboratory.

In addition, representative samples of the subsurface materials were obtained employing split-spoon sampling procedures in general accordance with ASTM Standard D 1586. Disturbed samples were obtained at selected depths in the borings by driving a standard 2-inch outside diameter split-spoon sampler 18 inches into the subsurface material using a 140-pound hammer falling 30 inches. The number of blows required to drive the split-spoon sampler the final 12 inches of penetration (N-value) is recorded in the appropriate column on the boring logs presented in Appendix A of this report.

Logs of all borings are included in the Appendix of this report. The logs show visual descriptions of subsurface strata encountered using the Unified Soil Classification System. Sampling information, pertinent field data, and field observations are also included. Samples not consumed by testing will be retained in our laboratory for at least 14 days and then discarded unless the Client requests otherwise.

Client:Project:Start Date: End Date:Drilling Method:

BORING NO.:

PROJECT NO.:

Location:Surface Elevation:West:North:Hammer Drop (lbs / in):

Dep

th, f

eet

Gra

phic

Log

MATERIAL DESCRIPTION

Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %

GROUND WATER OBSERVATIONS

On Rods (ft):After Drilling (ft):After Hours (ft):

NASH FM 529, LLCElyson Basin B

6/10/2020 6/10/2020CONTINUOUS FLIGHT AUGER

1

H201519

Harris County, TX

140 / 30

NONEDRY

6513 W. Little York Rd.Houston, Texas 77040Phone: 713-360-0460Fax: 713-360-0481www.alphatesting.com

5

10

15

20

25

30

35

Light brown SANDY SILT

4.0

- with root fibers from 0' to 2'

Light gray SANDY CLAY with ferrous nodules

13.0Tan, reddish tan SILTY SAND

30.0BORING TERMINATED AT 30 FEET

0.5 12

13

4.0 1568 45 16 29

4.0 14

3.5 14

14

9

9

8

6

18

14

19

18

Sheet 1 of 1

2.4


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





2

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown, SANDY SILT

2.0Light gray SILTY SAND

6.0Light gray SANDY CLAY with ferrous nodules

13.0Tan, reddish tan SILTY SAND

30.0BORING TERMINATED AT 30 FT

0.5 9

16

20

4.5+ 15 40 15 25

3.0 14

1447

11

10

7

6

8

20

18

20

58

Sheet 1 of 1

2.6


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





3

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SILTY SAND

2.0Light brown, light gray SANDY CLAY with sand seams and layers

13.0

- with ferrous nodules from 8' to 13'

Tan, reddish tan SILTY SAND


1148 NP NP NP

3.0 13

2.5 18

4.0 30

3.5 20

9

11

9

8

18

22

15

18

Sheet 1 of 1

1.8


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





4

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SANDY SILT with clay pockets and root fibers


13.0Tan, reddish, brown SILTY SAND


1.0 11

3.0 18 48 18 30

3.5 20

3.5 14

3.5 15

9

10

9

8

21

14

18

17

Sheet 1 of 1

2.2

2.4(UU)


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





5

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SILTY SAND

4.0Gray, light gray SANDY CLAY

13.0

- with sand seams and layers from 6' to 8'


Tan, reddish, tan SILTY SAND


1140

11

4.0 17

2.0 26 42 15 27

5

11

10

9

8

25

22

18

24

Sheet 1 of 1


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





6

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SANDY SILTY CLAY

2.0Light brown, light gray CLAY with sand

6.0


Light gray, tan SANDY CLAY

13.0

- with ferrous nodules, sand seams and layers from 10' to 13'

Tan, reddish, brown SILTY SAND


2.0 13

1.0 25

1.5 2674 68 20 48

2.5 18

3.0 16

9

11

9

8

18

18

15

25

Sheet 1 of 1

0.8

2.3


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





7

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SANDY SILT with sand and root fibers

4.0Light brown SILTY SAND

6.0Light brown CLAYEY SAND

8.0Light gray SANDY CLAY with sand seams and layers

13.0Reddish, tan SILTY SAND


2.5 13 16 14 2

1.0 18

13

20

2.5 17

820

10

9

8

6

8

22

19

18

21

Sheet 1 of 1


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





8

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SANDY SILT with root fibers


13.0Tan, reddish, tan SILTY SAND


9

11

3.5 16

3.5 1462 52 19 33

2.5 16

10

8

8

8

26

18

20

22

20

Sheet 1 of 1

1.6


BORING NO.:

PROJECT NO.:


Dep

th, f

eet

Gra

phic

Log


Sam

ple

Type

Rec

over

y %

RQ

DTX

Con

e or

Std

.Pe

n. (b

low

s/ft,

in)

Pock

etPe

netro

met

er (t

sf)

Unc

onfin

ed C

omp.

Stre

ngth

(tsf

)%

Pas

sing

No.

200

Sie

veU

nit D

ry W

eigh

t(p

cf)

Wat

er C

onte

nt, %

Liqu

id L

imit

Plas

tic L

imit

Plas

ticity

Inde

x

Swel

l, %





9

H201519

Harris County, TX

140 / 30

NONEDRY


5

10

15

20

25

30

35

Light brown SANDY SILT


18.0Tan, reddish SILTY SAND


9

10

2.5 1566 38 15 23

2.5 13

3.0 14

3.0 13

8

8

8

23

19

18

24

Sheet 1 of 1

2.3

VERY LOOSELOOSEMEDIUMDENSEVERY DENSE

RELATIVE DENSITY OF COHESIONLESS SOILS (blows/ft)

0 TO 45 TO 1011 TO 3031 TO 50OVER 50

SHELBY TUBE (3" OD exceptwhere noted otherwise)

SPLIT SPOON (2" OD except wherenoted otherwise)

AUGER SAMPLE

ROCK CORE (2" ID except wherenoted otherwise)

PARTICLE SIZE IDENTIFICATION (DIAMETER)

(CL), Low Plasticity CLAY

(SP), Poorly Graded SAND

(GW), Well Graded GRAVEL

(GC), CLAYEY GRAVEL

(GM), SILTY GRAVEL

BOULDERSCOBBLESCOARSE GRAVELFINE GRAVELCOURSE SANDMEDIUM SANDFINE SANDSILTCLAY

TRACELITTLESOMEAND

1 TO 1011 TO 2021 TO 3536 TO 50

RELATIVE PROPORTIONS (%)

VERY SOFTSOFTFIRMSTIFFVERY STIFFHARD

LESS THAN 0.250.25 TO 0.500.50 TO 1.001.00 TO 2.002.00 TO 4.00OVER 4.00

COMPRESSIVE STRENGTH OF COHESIVE SOILS (tsf)

RELATIVE DEGREE OF PLASTICITY (PI)SHALE / MARL

(SC), CLAYEY SAND

(SW), Well Graded SAND

(SM), SILTY SAND

(ML), SILT

TEXAS CONE PENETRATION

FILL

LIMESTONE

(MH), Elastic SILT

SANDSTONE

(GP), Poorly Graded GRAVEL

LOWMEDIUMHIGHVERY HIGH

4 TO 1516 TO 2526 TO 35OVER 35

SAMPLING SYMBOLS

(OL), ORGANIC SILT

(OH), ORGANIC CLAY

KEY TO SOIL SYMBOLSAND CLASSIFICATIONS

8.0" OR LARGER3.0" TO 8.0"

0.75" TO 3.0"5.0 mm TO 3.0"

2.0 mm TO 5.0 mm0.4 mm TO 5.0 mm

0.07 mm TO 0.4 mm0.002 mm TO 0.07 mmLESS THAN 0.002 mm

SOIL & ROCK SYMBOLS

(CH), High Plasticity CLAY



NASH FM 529, LLCHarris County, TexasElyson Basin B

H201519

PRESSURE DISTRIBUTION FOR INTERNALLYBRACED FLEXIBLE WALLS



Cross section provided by the Client.


CROSS SECTION OF THE PROPOSED DRAINAGE

CHANNEL



Cross section provided by the Client.


CROSS SECTION OF THE PROPOSED DETENTION

BASIN

Analysis Description Short Term Condition- Case 1Client NASH FM 529, LLCDrawn By RSFile Name ST.slimDate 07/16/2020

ProjectH201519: Elyson Basin B

SLIDEINTERPRET 7.020

Analysis Description Long Term Condition - Case 1Client NASH FM 529, LLCDrawn By RSFile Name LT.slimDate 07/16/2020



Analysis Description Long Term Condition- Case 2Client NASH FM 529, LLCDrawn By RSFile Name LT.slimDate 07/16/2020



Analysis Description Rapid Drawdown Condition -Case 1Client NASH FM 529, LLCDrawn By RSFile Name RDD.slimDate 07/16/2020

ProjectH201519 Elyson Basin B


Analysis Description Rapid Drawdown Condition- Case 2Client NASH FM 529, LLCDrawn By RSFile Name RDD.slimDate 07/16/2020




B-1 METHODS OF LABORATORY TESTING

Selected samples were examined and classified by a qualified member of the Geotechnical Division and the boring logs were edited as necessary. To aid in classifying the subsurface materials and to determine the general engineering characteristics, natural moisture content tests (ASTM D 2216), Atterberg-limit tests (ASTM D 4318), and gradation tests (percent of material passing a No. 200 sieve, ASTM D 1140) were performed on select samples. A calibrated pocket penetrometer was used to approximate the unconfined compressive strength as an indicator of soil consistency for all in-tact cohesive samples. Unconfined compression strength tests (ASTM D 2166) were also performed on representative samples. Results of all laboratory tests described above are provided on the accompanying Log of Boring sheets.

geotechnical exploration elyson basin b off porter road … · 2020. 9. 25. · astm d420 using...

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