ITB 24-42TM Addendum 3 Attachment 7 WM19-126G Coliseum Lake Weir Repairs Part II.pdf

701 Alexander Lee Parkway · Williamsburg, VA 23185 Phone: (757)-564-6452 www.getsolutionsinc.com

REPORT OF

SUBSURFACE

EXPLORATION

AND

GEOTECHNICAL

ENGINEERING

SERVICES

Coliseum Lake Weir Repairs - Part II

Hampton, Virginia

G E T Project No: WM19-126G

July 23, 2019

PREPARED FOR:

Kimley-Horn and Associates, Inc.

4525 Main Street, Suite 1000 Virginia Beach, VA 23462

July 23, 2019

TO: Kimley-Horn and Associates, Inc.

4525 Main Street, Suite 1000 Virginia Beach, VA 23462

Attn: Mr. Stephen Thun, P.E., LEED AP

RE: Report of Subsurface Exploration and Geotechnical Engineering Services

Coliseum Lake Weir Repairs - Part II Hampton, Virginia G E T Project No: WM19-126G

Dear Mr. Thun:

In compliance with your instructions, we have completed our Subsurface Exploration and Geotechnical Engineering Services for the above referenced project. The results of this study, together with our recommendations, are presented in this report.

Often, because of design and construction details that occur on a project, questions arise concerning subsurface conditions. G E T Solutions, Inc. would be pleased to continue its role as Geotechnical Engineer during the project implementation.

Thank you for the opportunity to work with you on this project. We trust that the information contained herein meets your immediate need, and should you have any questions or if we could be of further assistance, please do not hesitate to contact us.

Respectfully Submitted, G E T Solutions, Inc.

Philip A. Wunderly, P.E.

Senior Project Engineer Virginia Lic. No. 047135

Bruce R. Spiro, P.E.

Principal Engineer Virginia Lic. No. 015791

Copies: (1) Client

701 Alexander Lee Parkway Williamsburg, VA 23185 Phone: 757-564-6452 Fax: 757-564-6453 info@getsolutionsinc.com

TABLE OF CONTENTS

1.0 PROJECT INFORMATION

1.1 Project Authorization

1.2 Project Site Location and Description

1.3 Project Construction Description

1.4 Purpose and Scope of Services

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

2.2 Laboratory Testing

2.2.1 Soil Classification and Index Testing

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology

3.2 Previously Reclaimed Land

3.3 Subsurface Soil Conditions

3.4 Groundwater Information

4.0 EVALUATION AND RECOMMENDATIONS

4.1 Hydraulic Conductivity

4.2 Rate of Seepage

4.3 Soil Design Parameters for Sheet Piles (Cofferdams)

4.4 Embankment Discussion-Slope Stability and Settlement

4.5 Clearing

4.6 Subgrade Preparation

4.7 Embankment Fill and Placement

4.8 Anticipated Excavation Characteristics

4.9 Excavation Stability

4.10 Dewatering

5.0 REPORT LIMITATIONS

APPENDIX I BORING LOCATION PLAN

APPENDIX II CLASSIFICATION SYSTEM FOR SOIL EXPLORATION

APPENDIX III SUMMARY OF LABORATORY CLASSIFICATION RESULTS

APPENDIX IV BORING LOGS

APPENDIX V GENERALIZED SOIL PROFILE

APPENDIX VI SLUG TESTING RESULTS

APPENDIX VII FLOW NET ANALYSIS

APPENDIX VIII SLOPE STABILITY ANALYSES

Coliseum Lake Weir Repairs - Part II Hampton, Virginia G E T Project No: WM19-126G

Report of Subsurface Exploration and Geotechnical Engineering Services July 23, 2019 Coliseum Lake Weir Repairs - Part II Hampton, Virginia G E T Project No: WM19-126G

1.0 PROJECT INFORMATION

1.1 Project Authorization

G E T Solutions, Inc. has completed our Subsurface Exploration and Geotechnical Engineering Services for the proposed Coliseum Lake Weir Repair Project in Hampton, Virginia. The geotechnical engineering services were conducted in general accordance with G E T Proposal No. PWM17-366G (Revision 7) dated September 14, 2018. Authorization to proceed with our services was obtained in the form of an individual project order (Number 51).

1.2 Project Site Location and Description

The project site is located along the southeast corner of Coliseum Lake between the Hampton Coliseum and Interstate 64 in Hampton, Virginia. The site consists of an existing earthen embankment dam separating Coliseum Lake (upstream) from Newmarket Creek (downstream).

The water level of Coliseum Lake is controlled by a concrete weir (spillway elevation 0.69 feet, NAVD88). Newmarket Creek is tidally influenced and drains to the southern branch of the Back River. The approximate location of the project site is shown on the map in Figure 1 below which was adopted from the Newport News North and Hampton, VA 2016 USGS topographic quadrangle maps.

Figure 1. Project Site Vicinity Map, not to scale (USGS, 2016)

N

Project Site

NEWMARKET

CREEK

COLISEUM

LAKE

Hampton, Virginia G E T Project No: WM19-126G

Based on a CAD survey file provided by the client, the crest of the embankment dam is at an elevation of approximately 5 feet, NAVD88, with an approximate crest width of 15 feet. The side slopes of the embankment dam are armored with riprap from the crest to some unknown distance below the current water levels on both sides of the dam. The survey indicates the horizontal to vertical ratio of the side slopes along the embankment dam are at 2H:1V (horizontal to vertical). At the time of our site reconnaissance the crest of the dam was covered with tall grass and heavy brush; no significant woody vegetation was present. Conditions observed at the time of our site reconnaissance are included in the following figures (Figures 2 through 5).

Figure 2. Concrete Spillway, downstream (Newmarket Creek is to the left)

Figure 3. Concrete Spillway, upstream (Coliseum Lake is to the right, I-64 is in the background)

Hampton, Virginia G E T Project No: WM19-126G

Figure 4. Downstream slope of dam (Newmarket Creek is to the left)

Figure 5. Upstream slope of dam (Coliseum Lake is to the right)

1.3 Project Construction Description

The proposed project will consist of replacing the existing concrete weir and possibly raising the embankment by several feet.

Hampton, Virginia G E T Project No: WM19-126G

If any of the noted information is incorrect or has changed, G E T Solutions, Inc. shall be informed so that we may amend the recommendations presented in this report, if appropriate.

1.4 Purpose and Scope of Services

The purpose of this study was to obtain information on the general subsurface conditions at the proposed project site. The subsurface conditions encountered were then evaluated with respect to the available project characteristics. In this regard, engineering assessments for the following items were formulated:

1. General assessment of the soils revealed by the borings performed at the proposed project site.

2. General location and description of potentially deleterious material encountered in the borings that may interfere with construction progress or structure performance, including existing fills or surficial/subsurface organics.

3. Slope stability and settlement analysis and construction recommendations for raising the embankment.

4. Determine pertinent hydraulic conductivity and information regarding the groundwater conditions within the project site limits based on the data collected from a temporary groundwater monitoring well and field Hydraulic Conductivity testing (slug testing).

5. Seepage Analysis

6. Evaluation of earthwork requirements, to include subgrade stripping and preparation, dewatering, embankment fill placement procedures and excavation.

The scope of services did not include an environmental assessment for determining the presence or absence of wetlands or hazardous or toxic material in the soil, bedrock, surface water, groundwater or air, on or below or around this site.

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

In order to explore the general subsurface soil types and to aid in developing associated design parameters and recommendations, the following exploration program was performed:

§ Two (2) 70-foot deep Standard Penetration Test (SPT) borings (designated as B-1 and B-2) were drilled along the crest of the dam approximately 130-feet and 70-feet north of the center of the existing weir, respectively.

§ Three (3) 20 to 30-foot SPT borings (designated as MW-1 through MW-3) were drilled along the crest and left abutment (referenced to facing the downstream direction of Newmarket Creek) of the dam.

Hampton, Virginia G E T Project No: WM19-126G

§ A temporary groundwater monitoring well was installed adjacent to each boring location at MW-1 through MW-3 to depths of approximately 12 (MW-1 and MW-2) to 24 feet (MW-3) below the existing site grade for the purpose of field assessment of saturated hydraulic conductivity (Slug Testing). The temporary groundwater monitoring wells were drilled using a 5.25 inner diameter (I.D.) hollow stem auger.

The monitoring wells were constructed of 2-inch diameter, Schedule 40 PVC materials. A section of 0.010-inch slotted screen was placed in the borehole with casing threaded to the top. An appropriately graded sand/gravel pack was placed around the screen and extended one to two feet above the top of the screen. A one to two foot bentonite seal was then placed above the sand/gravel pack and hydrated with potable water. The remainder of the borehole annular space was pumped full of a neat cement grout. The well was then fitted with a PVC slip cap and lockable box cover.

It is noted that a fourth boring was proposed to be completed on the portion of the embankment south of the existing weir. However this area was inaccessible as our drill rig was unable to cross the existing weir. Accordingly, we recommend a follow-up exploration to confirm the findings of this report once the area is accessible.

The SPT borings were performed with the use of hollow stem auger and rotary wash “mud” drilling procedures in general accordance with ASTM D 1586. The tests were performed continuously from the existing ground surface to depths of 10 to 12 feet and at 5 foot intervals starting at a depth of 13 feet. The soil samples were obtained with a standard 1.4-inch I.D., 2-inch outer diameter, 30-inch long split-spoon sampler. The sampler was driven with blows of a 140 lb. automatic hammer falling 30 inches. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded and is shown on the boring logs. The sum of the second and third penetration increments is termed the SPT N-value (uncorrected for automatic hammer and overburden pressure). A representative portion of each disturbed split-spoon sample was collected with each SPT, placed in a glass jar, sealed, labeled, and returned to our laboratory for review.

The boring locations were established by G E T Solutions, Inc. and staked/marked in the field by measuring distances from identifiable landmarks. Upon completion of the soil borings, the holes were backfilled with the grout. Approximate soil boring locations are shown on the attached “Boring Location Plan” (Appendix I) which was developed aerial imagery obtained from Google Earth.

2.2 Field and Laboratory Testing

Soil testing provided by G E T Solutions, Inc. was performed in accordance with American Society for Testing and Materials (ASTM) standards. All soils and materials tests were performed in our AASHTO re:source (formally AMRL) and US Army Corps of Engineers certified Williamsburg laboratory.

Hampton, Virginia G E T Project No: WM19-126G

2.2.1 Soil Classification and Index Testing

Representative portions of all soil samples collected during drilling operations were sealed in glass jars, labeled and transferred to our laboratory in accordance with ASTM D 4220 for classification and analysis. Soil descriptions on the boring logs are provided using visual-manual methods in general accordance with ASTM D 2488 using the Unified Soil Classification System (USCS). Soil samples that were selected for index testing were classified in general accordance with ASTM D 2487. It should be noted that some variation can be expected between samples classified using the visual-manual procedure (ASTM D 2488) and the USCS (ASTM D 2487). A summary of the soil classification system is provided in Appendix II.

Representative split-spoon soil samples were selected and subjected to natural moisture, #200 sieve wash, and Atterberg Limits testing in order to corroborate the visual classification. These test results are presented in Appendix III and on the soil test boring logs provided in Appendix IV. A generalized subsurface soil profile is provided in Appendix V.

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology

The project site lies within the major physiographic province called the Atlantic Coastal Plain.

Numerous transgressions and regressions of the Atlantic Ocean have deposited marine, lagoonal, and fluvial (stream lain) sediments. The regional geology is very complex, and generally consists of interbedded layers of varying mixtures of sands, silts and clays. Based on our review of existing geologic and soil boring data, the geologic stratigraphy encountered in our subsurface exploration generally consisted of marine deposited sands and clays.

3.2 Previously Reclaimed Land

Based on a review of historical aerial imagery obtained from the City of Hampton GIS web-viewer, the project site appears to be land reclaimed during the late 1960s and early 1970s from an area that was heavily excavated during the early 1960s.

3.3 Subsurface Soil Conditions

A summary of the subsurface soil conditions encountered at the SPT boring locations is presented in the following table (Table II).

Hampton, Virginia G E T Project No: WM19-126G

Table II - Subsurface Soil Conditions

Average Depth

(Feet)(1) Stratum Description

Ranges of

SPT(2)

N-Values to

0.2 - 0.5 TOPSOIL Ø 2 to 6 inches of Topsoil -

0.2 - 0.5 to

3.5 - 29.5 FILL Ø SAND (SM and SC) with varying amounts of Gravel, Silt, Clay and fibrous organic material 2 - 20

3.5 - 29.5 to

20 - 31.5 I

Ø SAND (SP-SM and SM) with varying amounts of Gravel, Silt, Clay and fibrous organic material

Ø CLAY (CL and CH) with varying amounts of Sand

Borings MW-1 through MW-3 were terminated in this Stratum

Sand 2 - 12

Clay 2 - 6

26.5 - 31.5 to

II

Ø Silty SAND (SM) with varying amounts of marine shell fragments

Ø Lean CLAY (CL) with Sand and varying amounts of marine shell fragments

“Yorktown Formation”

Borings B-1 and B-2 were terminated in this Stratum

Sand 6 - 12

Clay

Notes: (1) Depth below existing grades

(2) SPT=Standard Penetration Test, N-Values in Blows-per-foot (uncorrected)

The subsurface descriptions are of a generalized nature provided to highlight the major soil strata encountered. The records of the subsurface exploration are included in Appendix IV (Boring Log sheets) and in Appendix V (Generalized Soil Profile) which should be reviewed for specific information as to the individual borings. The stratifications shown on the records of the subsurface exploration represent the conditions only at the actual boring locations. Variations may occur and should be expected between boring locations. The stratifications represent the approximate boundary between subsurface materials and the transition may be gradual.

It is noted that the “Topsoil” designation references the presence of surficial organic laden soil, and does not represent any particular quality specification. It is recommended that this material be tested for approval prior to use as topsoil.

3.4 Groundwater Information

The groundwater level was recorded at the boring locations during drilling and as observed through the relative wetness of the recovered soil samples during the drilling operations. The initial groundwater table was generally determined to occur at depths of 4.9 to 8 feet below existing site grades.

Hampton, Virginia G E T Project No: WM19-126G

During drilling operations, fluid (water-clay slurry) is introduced into the bore holes generally impairing the ability to accurately determine groundwater levels. In addition, as subsurface soils begin to dry, moisture moves upwards through the soil profile by means of capillary action.

Based on the subsurface soil composition (soils containing more than 30% of fines by weight), the initial groundwater level reading (based on the relative wetness of the soils) could be in part attributed to the capillary action of the soils. As such, the reported initial groundwater level may not be indicative of the static groundwater level. The boreholes were backfilled upon completion for safety considerations.

Groundwater levels were measured at the temporary groundwater monitoring wells located adjacent to borings MW-1 through MW-3. The groundwater information associated with these wells is presented in Table III.

Table III – Temporary Well Readings

Boring Location Groundwater Reading, 6/26/2019 (ft)(1)

Groundwater Estimated Elevation, 6/26/2019

(ft, NAVD88)(2)

MW-1 7.1 -1.1

MW-2 4.9 0.1

MW-3 5.0 0.0

Notes: (1) Depth below existing grades

(2) Per survey CAD file provided by the client

In the project’s area, seasonal groundwater fluctuations of ±3 feet are common; however, greater fluctuations have been documented. We recommend that the contractor determine the actual groundwater levels at the time of the construction to determine groundwater impact on the construction procedures, if necessary.

4.0 EVALUATION AND RECOMMENDATIONS

Our recommendations are based on the previously discussed project information, our interpretation of the soil test borings and laboratory data, and our observations during our site reconnaissance. If the proposed construction should vary from what was described, we request the opportunity to review our recommendations and make any necessary changes.

4.1 Hydraulic Conductivity

A slug test was performed at each of the temporary groundwater monitoring wells for the purpose of estimating the hydraulic conductivity of subsurface soils located beneath the groundwater elevation. A slug test is a controlled field experiment in which the water level in a groundwater monitoring well is caused to change suddenly (rise in this case) and the subsequent water level response (displacement) is measured through time in the control well.

Hampton, Virginia G E T Project No: WM19-126G

The slug tests were performed by G E T Solutions, Inc. on June 12, 2019. A data logger was lowered into the monitoring well and the groundwater level was measured. The data logger was then lowered to a depth of approximately 2 feet below the groundwater level to perform the test.

Water was poured into the well with the data logger recording the groundwater level displacement every one second. The groundwater level was recorded until it reached the initial groundwater level. This process was performed twice for test validation. The software program AQTESOLV® Version 4.50 was used to analyze the recorded data for the purpose of estimating the hydraulic conductivity of the subsurface soils. The slug test analyses are presented in Appendix VI.

Based on the results of the slug test, the average horizontal hydraulic conductivity of the soil below the groundwater level was measured to be 1.54 x 10-4 ft/sec.

4.2 Rate of Seepage

Flow nets were used to calculate the rate of seepage (groundwater flow) through the subsurface soils on-site. The concept of a flow net is based on Laplace’s equation of continuity, which describes the steady state flow condition for a given point in the soil mass. The seepage analysis was conducting using the Slide 6.0 software groundwater module. The Slide 6.0 groundwater module is a finite element program used to model groundwater flow in porous media. The flow net groundwater analysis is provided in Appendix VII.

The following assumptions were made during our analysis:

Ø 1.5-foot head difference between Coliseum Lake (water surface elevation of 0.69 feet, NAVD 88) and Newmarket Creek (water surface elevation of -0.81 feet, NAVD 88).

Ø Separation between the ponds is approximately equal to 60 linear feet.

Ø Lateral seepage influence at the embankment location is approximately equal to 175 linear feet.

Ø The subsurface soils are homogeneous across the embankment.

It is noted that the embankment, as revealed by our borings and previous exploration of the site, generally consists of non-uniform soils and materials that are difficult to characterize with regard to uniform hydraulic properties. As such, consideration should be given to the applicability of the results of the seepage analysis provided in this reporting as the assumption of a homogenous subsurface is a highly generalized representation of actual soil conditions.

The rate of seepage through the subsurface permeable layers per 1-foot of unit width of was calculated to be approximately 40 gallons/day. For the entire width of lateral influence stated above (175 feet) the total amount of seepage was calculated to be approximately 7,000 gallons/day (covering an area from the downstream water elevation to a distance of approximately 100 feet downstream of the dam).

Hampton, Virginia G E T Project No: WM19-126G

4.3 Soil Design Parameters for Sheet Piles (Cofferdams)

It is expected that cofferdams will be constructed around the upstream and downstream sides of the existing concrete weir in order to facilitate demolition and construction operations. The cofferdam is expected to consist of sheet pile walls to be designed by others; once the new weir is constructed the sheet piles would be removed.

With regard to the design of the sheet piles to resist lateral earth and hydrostatic pressures, the estimated soil parameters presented in the following table (Table III) can be used.

Table III - Below Grade Estimated Soil Parameters

Soil Type SAND

(SP-SM, SM, SC)

Stratum FILL, I, II

Estimated Moist Unit Weight (pcf) 115

Estimated Saturated Unit Weight (pcf) 120

Estimated Submerged Unit Weight (pcf) 58

Friction Angle, f (degrees) 30

Cohesion, c (psf) 0

Active Soil Pressure Coefficient, Ka

0.33

At-Rest Soil Pressure Coefficient, K0

0.5

Passive Soil Pressure Coefficient, Kp

3.0

Coefficient of Friction 0.38

4.4 Embankment Discussion - Slope Stability and Settlement

The global stability of the slopes of an embankment raised in height by 2 feet were evaluated by using the stability analysis software Slide 6.0 by Rocscience, Inc. Slide 6.0 is a 2-D limit-equilibrium slope stability program for determining the factor of safety of circular and non-circular failure surfaces in rock or soil slopes. Circular failure surfaces were evaluated using the Bishop and Morgenstern-Price methods of analysis. The soil parameters used were estimated from the SPT data, the laboratory test program and from our experience with similar materials.

The computer generated results of the stability analyses are included in Appendix VIII.

The results of the stability analyses indicate that with an increased height of 2 feet, embankment slopes of 3H:1V (Horizontal to Vertical) have an acceptable safety factor per the U.S. Army Corps of Engineers Slope Stability Engineering Manual, EM-110-1906 (FS of 1.5 or greater).

Hampton, Virginia G E T Project No: WM19-126G

Our analysis is focused on the global stability of the geometry of the proposed sloped embankment along the area of study. Our evaluation is limited to typical soil and water conditions, not on drawdown conditions resulting from a storm event.

A minimum amount of fill would be required to raise the existing elevation of the embankment by 2 feet. The magnitude and duration of the settlement associated with this amount of fill is not expected to be significant. As the soils encountered at the boring locations were predominately granular in nature, it is expected that the total settlement (elastic and plastic) induced by the fill materials will be up to 1 inch and will occur during construction. However, it is noted that the settlement magnitude of the existing soils of the FILL Stratum is difficult to predict due to the non-homogenous content and uncertainty regarding means of placement. Accordingly, the expected total settlement may vary across the full length of the embankment. Substantial completion of embankment settlement is expected to occur within 1 to 2 months of establishing rough final grade elevations.

4.5 Clearing

In the case of raising the embankment, the proposed construction area should be cleared by means of removing topsoil material, trees, brush, and other unsuitable materials. It is estimated that a cut of up to 6 inches in depth will be required to remove topsoil material. This cut is expected to extend deeper in isolated areas to remove deeper deposits of organic soils, or unsuitable soils, which become evident during the clearing. Removing larger brush will also consist of stump and large root removal. The stump and large root removal will likely leave holes that may extend several feet in depth. Surface water may accumulate in these holes and lead to subgrade deterioration if not properly addressed. These holes should be backfilled as recommended in Section 4.7. It is recommended that the clearing operations extend laterally at least 3 feet beyond the perimeter of the proposed construction areas, if possible.

To reduce the potential for subgrade improvements (undercutting due to saturated soils in conjunction with heavy construction traffic), it is recommended that the clearing operations be performed during the drier months of the year (historically April through November as indicated by the NCDC Climate Atlas of the United States). This should minimize these potential problems, although they may not be eliminated. If clearing is attempted during the winter months, stabilization of wet soils should be anticipated (undercutting and backfilling with structural fill). However, during the drier months of the year, wet soils could be dried by discing or implementing other drying procedures (stockpiling or spreading in thin lifts) to achieve moisture contents necessary to achieve adequate degrees of compaction. The project’s budget should include an allowance for subgrade improvements as described above.

The undercut and backfill should be performed under the observation of a representative of G E T Solutions, Inc. who will evaluate the composition of the recovered soils.

Recommendations concerning the subgrade improvements (as necessary) will be provided in the field following the testing procedures.

Hampton, Virginia G E T Project No: WM19-126G

4.6 Subgrade Preparation

Once the existing weir has been demolished (and the embankment has been cleared in the case of raising the embankment height), the exposed subgrade soils should be evaluated by the Geotechnical Engineer for stability. Any unstable areas observed during field observations should be undercut and/or stabilized at the direction of the Geotechnical Engineer. Some undercutting of soft materials and replacement with an approved backfill may be required to achieve firm weir slab support. Additional concrete placement may be required as well to fill in any voids that may be revealed during demolition. Once approved by the Geotechnical Engineer, the subgrade should be lined with a geotextile fabric followed by construction of the new concrete weir.

The extent of the subgrade improvements will be evaluated in the field during construction based on the outcome of the field testing procedures (field assessments of subgrade stability).

In this regard, and in order to reduce the potential for subgrade improvements, care should be exercised during the grading and construction operations at the site. The project’s budget should include an allowance for subgrade improvements (undercut and backfill with structural fill or additional aggregate base material).

4.7 Embankment Fill and Placement

Following the approval of the subgrade soils by the Geotechnical Engineer, the placement of the fill required to establish the raised embankment height may begin. Any material to be used for fill on the dam embankment or associated with the weir replacement should be evaluated and tested by G E T Solutions, Inc. prior to placement to determine if they are suitable for the intended use. Suitable dam embankment fill material should consist of clay containing 40% or more by weight of fines (SC, CL, CL-ML, and CH), and be free of rubble, gravel, organics, debris and other unsuitable material.

All embankment fill should be compacted to a dry density of at least 95% of the Standard Proctor maximum dry density, in accordance with ASTM D 698. The moisture content of the dam embankment fill should be within 2 percentage points of the optimum moisture content at the time of placement. In general, the compaction should be accomplished by placing the fill in maximum 8-inch loose lifts and mechanically compacting each lift to at least the specified minimum dry density.

Newly constructed slopes along the embankment should be “benched” into the existing cleared embankment sides in accordance with VDOT Road and Bridge Specification Section 303.04(h) in order to minimize the potential for a slippage failure along that interface. Surface water control measures should be instituted to protect the new fill from erosion. A protective cover of grass or other vegetation should be established on permanent slopes as soon as possible during construction.

We recommend that fill placement be monitored on a full-time basis by a qualified Geotechnical Engineering firm to verify that the specified materials are used and the required degree of compaction is achieved.

Hampton, Virginia G E T Project No: WM19-126G

4.8 Anticipated Excavation Characteristics

Based on the results of this exploration, varying soil conditions and compositions are expected to be encountered throughout the project limits. Open-cut excavations will extend through natural soils that are considered to be relatively “clean” (i.e. soil that is relatively free of deleterious debris that may hinder excavation or installation). Debris typically considered unsuitable consist of wood, glass, organics, plastics, coal, brick or any other material larger than 2 inches in diameter. Soils containing appreciable amounts of deleterious debris should be discarded; however, an effort should be made during excavation to segregate potentially suitable in-situ soils for reuse. Information pertaining to backfill criteria was provided previously in Section 4.7.

4.9 Excavation Stability

The shallow subsurface within the project limits is comprised of clayey and granular soils;

however, the Contractor should anticipate these soils to have relatively little cohesion and have a high potential for caving. Additionally, water seepage at varying elevations should be expected within the side walls of the open cut areas, increasing the potential for caving. Based on these mentioned characteristics, it is recommended that all subsurface soils be considered Type C in accordance with Occupational Safety and Health Administration (OSHA) criteria.

Temporary Slopes

In Federal Register, Volume 54, No. 209 (October, 1989), the United States Department of Labor, Occupational Safety and Health Administration (OSHA) amended its “Construction Standards for Excavations, 29 CFR, part 1926, Subpart P”. This document was issued to better ensure the safety of workmen entering trenches or excavations. It is mandated by this federal regulation that all excavations, whether they be utility trenches, basement excavations, or footing excavations, be constructed in accordance with the new (OSHA) guidelines. It is our understanding that these regulations are being strictly enforced and if they are not closely followed, the owner and the Contractor could be liable for substantial penalties.

Temporary slopes may not be a feasible option. The Contractor is solely responsible for designing and constructing stable, temporary excavations and should shore, slope, or bench the sides of the excavations as required to maintain stability of both the excavation sides and bottom. The Contractor’s responsible person, as defined in 29 CFR Part 1926, should evaluate the soil exposed in the excavations as part of the Contractor’s safety procedures. In no case should slope height, slope inclination, or excavation depth, including utility trench excavation depth, exceed those specified in local, state, and federal safety regulations.

Where temporary slopes are not feasible, shoring by means of sheeting and/or trench shields may be appropriate. Where the stability of adjoining structures, pavements, or other improvements is endangered by excavation operations, support systems such as shoring, bracing, or underpinning may be required to provide structural stability. Shoring, bracing, or underpinning required for this project (if required) should be designed by a Professional Engineer.

Hampton, Virginia G E T Project No: WM19-126G

Shoring

Shoring design and installation should be the responsibility of the Contractor. Shoring systems required for this project should be designed by a Professional Engineer. Shoring systems should be designed to provide positive restraint of trench walls in an effort to protect against lateral deformation that may result in ground cracks, settlement, and/or other ground movements that may affect adjacent underground utilities and pavements as well as surface improvements. The Contractor should be made aware of this potential condition in order that preventative measures can be implemented or repair measures provided for.

Depending on the shoring system used, the removal process may create voids along the walls of the excavations. If these voids are left in place and are significant, backfill and/or the retained soil may shift laterally resulting in settlement of overlying structures/pavements. As such, care should be taken to remove the shoring systems and backfill the trenches in a manner as to not create these voids.

In all cases, the Contractor should select an excavation and/or shoring scheme that will protect adjacent and overlying improvements, including below grade utilities.

We are providing this information solely as a service to our client. G E T Solutions, Inc. is not assuming responsibility for construction site safety or the Contractor’s activities; such responsibility is not being implied and should not be inferred.

4.10 Dewatering

It is expected that dewatering will be required for excavations that extend near or below the existing groundwater table (approximate depth of 4.9 to 13 feet). Dewatering above the groundwater level could probably be accomplished by pumping from sumps. Dewatering at depths below the groundwater level will require well pointing and possibly shoring. Since temporary dewatering will impact construction and be dependent on construction methods and scheduling, we recommend the Contractor be solely responsible for the design, installation, maintenance, and performance of all temporary dewatering systems. Where shoring is employed, the dewatering system should be compatible with the type of shoring to be used. We recommend the Contractor verify groundwater conditions and evaluate dewatering requirements prior to construction.

Lowering the groundwater table during dewatering activities will result in an increase in effective stresses and may induce settlements of the soils underlying adjacent structures/pavements.

Additionally, hydraulic compaction of predominately granular soils (e.g. SP-SM and SM soils) should be anticipated as a result of lowering the groundwater table. We recommend that the dewatering be performed such that the groundwater level is lowered no more than approximately 5 feet below the proposed excavation depth. It may be advantageous to install settlement monuments in areas where dewatering by means of well pointing is required.

It would be advantageous to construct all fills early in the construction. If this is not accomplished, disturbance of the existing site drainage could result in collection of surface water in some areas, thus rendering these areas wet and very loose. Temporary drainage ditches should be employed by the contractor to accentuate drainage during construction. If water collects in foundation excavations, it will be necessary to remove the water from the excavation, remove the saturated soils, and re-test the adequacy of the bearing surface soils to support the design bearing pressure prior to concrete placement.

Hampton, Virginia G E T Project No: WM19-126G

Establishing a system of drainage ditches to carry surface and shallow groundwater away from the constructions areas should reduce grading costs. No permanent subsurface drainage systems are needed for this project.

5.0 REPORT LIMITATIONS

The recommendations submitted in this report are based on the available soil information obtained by G E T Solutions, Inc. and the information supplied by the client and their consultants for the proposed project. If there are any revisions to the plans for this project or if deviations from the subsurface conditions noted in this report are encountered during construction, G E T Solutions, Inc. should be notified immediately to determine if changes in our recommendations are required. If G E T Solutions, Inc. is not retained to perform these functions, G E T Solutions, Inc. can not be responsible for the impact of those conditions on the geotechnical recommendations for the project.

The Geotechnical Engineer warrants that the findings, recommendations, specifications or professional advice contained herein have been made in accordance with generally accepted professional geotechnical engineering practices in the local area. No other warranties are implied or expressed.

As the plans and specifications are completed, the Geotechnical Engineer should be provided the opportunity to review the final design plans and specifications to assure our engineering recommendations have been properly incorporated into the design documents in order that the earthwork recommendations may be properly interpreted and implemented. At that time, it may be necessary to submit supplementary recommendations. This report has been prepared for the exclusive use of Kimley-Horn and Associates, Inc. and their consultants for the specific application to the proposed Weir Repair project at Coliseum Lake in Hampton, Virginia.

APPENDICES

I. BORING LOCATION PLAN

II. CLASSIFICATION SYSTEM FOR SOIL EXPLORATION

III. SUMMARY OF LABORATORY CLASSIFICATION RESULTS

IV. BORING LOGS

V. GENERALIZED SOIL PROFILE

VI. SLUG TESTING RESULTS

VII. FLOW NET ANALYSIS

VIII. SLOPE STABILITY ANALYSES

APPENDIX I

BORING LOCATION PLAN

Boring Location Plan Project: Coliseum Lake Weir Repairs - Part II

Hampton, VA Scale: NTS Project No: WM19-126G Date: 7/11/2019 Client: Kimley-Horn and Associates, Inc. Plot By: PW

SPT Boring Location

MW-3

B-1

B-2

MW-1

MW-2

COLISEUM LAKE

NEWMARKET CREEK

APPENDIX II

CLASSIFICATION SYSTEM FOR SOIL EXPLORATION

Very Loose 4 blows/ft. or less Very Soft 2 blows/ft. or less Loose 5 to 10 blows/ft. Soft 3 to 4 blows/ft.

Medium Dense 11 to 30 blows/ft. Medium Stiff 5 to 8 blows/ft.

Dense 31 to 50 blows/ft. Stiff 9 to 15 blows/ft.

Very Dense 51 blows/ft. or more Very Stiff 16 to 30 blows/ft.

Hard 31 blows/ft. or more

Boulders 8 inch diameter or more Cobbles 3 to 8 inch diameter Gravel Coarse 1 to 3 inch diameter

Medium 1/2 to 1 inch diameter Fine 1/4 to

1/2 inch diameter Sand Coarse 2.00 mm to 1/4 inch

(diameter of pencil lead) Medium 0.42 to 2.00 mm

(diameter of broom straw) Fine 0.074 to 0.42 mm

(diameter of human hair) Silt 0.002 to 0.074 mm

(cannot see particles)

GW - Well-graded Gravel CL - Lean Clay GP - Poorly graded Gravel CL-ML - Silty Clay GW-GM - Well-graded Gravel w/Silt ML - Silt GW-GC - Well-graded Gravel w/Clay OL - Organic Clay/Silt GP-GM - Poorly graded Gravel w/Silt Less than 5 percent GW, GP, SW,SP GP-GC - Poorly graded Gravel w/Clay CH - Fat Clay More than 12 percent GM, GC, SM, SC GM - Silty Gravel MH - Elastic Silt 5 to 12 percent GC - Clayey Gravel OH - Organic Clay/Silt GC-GM - Silty, Clayey Gravel SW - Well-graded Sand SP - Poorly graded Sand PT - Peat SW-SM - Well-graded Sand w/Silt SW-SC - Well-graded Sand w/Clay SP-SM - Poorly graded Sand w/Silt SP-SC - Poorly graded Sand w/Clay SM - Silty Sand SC - Clayey Sand SC-SM - Silty, Clayey Sand

Consistency

Form 18.03.01 Revision 2/11/2019

Coarse Grained Soils Fine-Grained Soils

Highly Organic Soils

50% or more passes the No. 200 sieve

Liquid Limit 50% or greater

Trace

Plasticity Chart

701 Alexander Lee Parkway Williamsburg, Virginia 23185

0-5 5-10

COHESIVE SOILS

(CLAY, SILT and Combinations)

Relative Proportions Descriptive Term

CLASSIFICATION SYSTEM FOR SOIL EXPLORATION

Standard Penetration Test (SPT), N-value

Virginia Beach 5465 Greenwich Road

Virginia Beach, VA 23462

(757) 518-1703 (757) 564-6452

Elizabeth City 504 East Elizabeth St. Suite 2

Elizabeth City, NC 27909

(252) 335-9765

Williamsburg

Strata Changes In the column “Description” on the boring log, the horizontal lines represent approximate strata changes.

Groundwater Readings

Percent

15-25 30-45

Few Little

Groundwater conditions will vary with environmental variations and seasonal conditions, such as the frequency and magnitude of rainfall patterns, as well as tidal influences and man-made influences, such as existing swales, drainage ponds, underdrains and areas of covered soil (paved parking lots, side walks, etc.).

Depending on percentage of fines (fraction smaller than No. 200 sieve size), coarse-grained soils are classified as follows:

Borderline cases requiring dual symbols

Some Mostly 50-100

Standard Penetration Tests (SPT) were performed in the field in general accordance with ASTM D 1586. The soil samples were obtained with a standard 1.4” I.D., 2” O.D., 30” long split-spoon sampler. The sampler was driven with blows of a 140 lb. hammer falling 30 inches. The number of blows required to drive the sampler each 6-inch increment (4 increments for each soil sample) of penetration was recorded and is shown on the boring logs. The sum of the second and third penetration increments is termed the SPT N-value.

CLASSIFICATION SYMBOLS (ASTM D 2487 and D 2488)

More than 50% retained on No. 200 sieve

Relative Density

NON COHESIVE SOILS

(SILT, SAND, GRAVEL and Combinations)

Particle Size Identification

(910) 478-9915

Jacksonville 415-A Western Boulevard Jacksonville, NC 28546

APPENDIX III

SUMMARY OF LABORATORY CLASSIFICATION RESULTS

B-1 5.0 0.075 33 11.0

B-2 7.0 0.075 16 9.0

B-2 9.0 17.0

B-2 11.0 0.075 38 16.0

B-2 14.0 16.0

B-2 34.0 46 21 25 0.075 95 CL 38.0

B-2 59.0 41 21 20 0.075 58 CL 31.0

MW-3 11.0 0.075 24 15.0

SUMMARY OF LABORATORY RESULTS

Plastic Limit

Plasticity Index

Maximum Size (mm)

%<#200 Sieve

Liquid Limit

Satur-ation

Void Ratio

Class-ification

Water Content

Dry Density

(pcf) DepthBorehole

PROJECT NUMBER WM19-126G

CLIENT Kimley-Horn and Associates, Inc.

PROJECT LOCATION Hampton, Virginia

PROJECT NAME Coliseum Lake Weir Repairs - Part II

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G E T Solutions Inc 701 Alexander Lee Pkwy Williamsburg, Virginia 23185

(757) 564-6452

APPENDIX IV

BORING LOGS

2-in Topsoil

Orange-brown, moist, Silty fine to coarse SAND (SM) with trace fine Gravel, medium dense, "FILL"

Dark brown and black, moist, Silty fine to coarse SAND (SM), contains asphalt fragments, medium dense, "FILL"

Brown and gray, moist, Clayey fine to medium SAND (SC) with trace fine Gravel, loose, "FILL"

Dark brown, moist, Silty fine to medium SAND (SM) with trace fibrous organic material, medium dense, "FILL"

Dark brown and brown, wet, Clayey fine to coarse SAND (SC) with trace fine Gravel, medium dense, "FILL"

Dark brown and brown, wet, Silty fine to medium SAND (SM) with trace fine Gravel and trace Clay, very loose, "FILL"

Dark gray and dark brown, wet, Silty fine to medium SAND (SM) with trace fine Gravel, very loose to loose, "FILL"

Tan and brown, wet, Silty fine to coarse SAND (SM) with trace coarse Gravel, loose, "FILL"

Dark gray, wet, Silty fine SAND (SM), very loose

Dark gray, wet, Silty fine SAND (SM), contains marine shell fragments, loose to medium dense, "Yorktown Formation"

10-10-6-6 (16)

3-4-11-5 (15)

3-3-4-5 (7)

7-6-5-4 (11)

7-7-4-4 (11)

2-2-2-2 (4)

1-1-1-1 (2)

0-1-1-2 (2)

3-4-3-5 (7)

3-2-2-2 (4)

2-3-4-4 (7)

0.2

2.0

4.0

6.0

8.0

10.0

12.5

24.8

26.5

31.5

INITIAL (ft) : 8 CAVE-IN (ft) :

Notes:

BORING LOCATION: See Attached Boring Location Plan

HOURS (ft) :

STRATA DESCRIPTION

#2

S am pl e

R ec ov er y (in

B lo w C ou nt s (N

-V al ue s)

RECORD OF SUBSURFACE EXPLORATION

BORING ID

B-1

AFTER

10 20 30 40 50 60 70

Virginia Beach 5465 Greenwich Road

Virginia Beach, VA 23642 757-518-1703

SURFACE ELEVATION (NAVD88) (ft): 5

-5

-10

-15

-20

-25

-30

GROUNDWATER*:

PROJECT LOCATION: Hampton, Virginia

CLIENT: Kimley-Horn and Associates, Inc.

PROJECT NAME: Coliseum Lake Weir Repairs - Part II

DATE COMPLETED: 5/9/2019

D ep th ft)

Water Content -

Sample Type(s):

Liquid Limit

E le va tio n (f t)

S am pl e

T yp e

S am pl e

ID

S tr at a

Le ge nd

The initial groundwater readings are not intended to indicate the static groundwater level.

T hi s in fo rm at io n pe rt ai ns o nl y to t hi s bo rin g an d s ho ul d no t be in te rp re te d a s be in g in di ci tiv e of t he s ite

DRILLER: G E T Solutions, Inc.

Williamsburg 701 Alexander Lee Parkway

Williamsburg, VA 23185 757-564-6452

DATE STARTED: 5/9/2019

LOGGED BY: T. Vaughn

PROJECT NUMBER: WM19-126G

Elizabeth City 106 Capital Trace Unit E Elizabeth City, NC 27909

252-335-9765

Jacksonville 415-A Western Blvd

Jacksonville, NC 28546 910-478-9915

TEST RESULTS

Penetration -

SPT - Standard Penetration Test

DRILLING METHOD(S): Rotary wash "mud" / Hollow Stem Auger

Plastic Limit x x

Dark gray, wet, Silty fine SAND (SM), contains marine shell fragments, loose to medium dense, "Yorktown Formation"

(layer continued from previous page)

Boring terminated at 70 feet below existing grade.

2-3-4-6 (7)

3-4-4-5 (8)

4-4-5-7 (9)

3-3-4-6 (7)

3-4-5-5 (9)

3-3-4-6 (7)

4-5-7-7 (12)

70.0

INITIAL (ft) : 8 CAVE-IN (ft) :

Notes:

BORING LOCATION: See Attached Boring Location Plan

HOURS (ft) :

STRATA DESCRIPTION

#2

S am pl e

R ec ov er y (in

B lo w C ou nt s (N

-V al ue s)

RECORD OF SUBSURFACE EXPLORATION

BORING ID

B-1

AFTER

10 20 30 40 50 60 70

Virginia Beach 5465 Greenwich Road

Virginia Beach, VA 23642 757-518-1703

SURFACE ELEVATION (NAVD88) (ft): 5

-35

-40

-45

-50

-55

-60

-65

GROUNDWATER*:

PROJECT LOCATION: Hampton, Virginia

CLIENT: Kimley-Horn and Associates, Inc.

PROJECT NAME: Coliseum Lake Weir Repairs - Part II

DATE COMPLETED: 5/9/2019

D ep th ft)

Water Content -

Sample Type(s):

Liquid Limit

E le va tio n (f t)

S am pl e

T yp e

S am pl e

ID

S tr at a

Le ge nd

The initial groundwater readings are not intended to indicate the static groundwater level.

T hi s in fo rm at io n pe rt ai ns o nl y to t hi s bo rin g an d s ho ul d no t be in te rp re te d a s be in g in di ci tiv e of t he s ite

DRILLER: G E T Solutions, Inc.

Williamsburg 701 Alexander Lee Parkway

Williamsburg, VA 23185 757-564-6452

DATE STARTED: 5/9/2019

LOGGED BY: T. Vaughn

PROJECT NUMBER: WM19-126G

Elizabeth City 106 Capital Trace Unit E Elizabeth City, NC 27909

252-335-9765

Jacksonville 415-A Western Blvd

Jacksonville, NC 28546 910-478-9915

TEST RESULTS

Penetration -

SPT - Standard Penetration Test

DRILLING METHOD(S): Rotary wash "mud" / Hollow Stem Auger

6-in Topsoil

Brown, moist, Silty fine to medium SAND (SM) with trace fine Gravel, medium dense, "FILL"

Orange-brown, moist, Silty fine to coarse SAND (SM) with trace fine Gravel, medium dense, "FILL"

Dark brown and black, moist, Silty fine to coarse SAND (SM) with trace fine to coarse Gravel, medium dense, "FILL"

Wet below 8 feet

Gray and brown, wet, Silty fine to coarse SAND (SM) with trace fine Gravel, medium dense, "FILL"

Brown and dark brown, wet, Clayey fine to coarse SAND (SC) with trace fine Gravel, very loose, "FILL"

Dark gray, wet, Silty fine to coarse SAND (SM) with trace fine Gravel, very loose

No Sample Recovery

Dark gray, wet, lean CLAY (CL), medium stiff

8-7-7-7 (14)

7-8-7-6 (15)

5-6-8-19 (14)

5-8-12-8 (20)

13-15-5-3 (20)

1-1-1-1 (2)

1-1-1-1 (2)

1-1-1-1 (2)

1-1-1-1 (2)

0-0-0-0 (0)

1-1-4-1 (5)

0.5

2.0

5.0

9.5 10.0

21.5

26.5

31.5

INITIAL (ft) : 8 CAVE-IN (ft) :

Notes:

BORING LOCATION: See Attached Boring Location Plan

HOURS (ft) :

STRATA DESCRIPTION

#2

S am pl e

R ec ov er y (in

B lo w C ou nt s (N

-V al ue s)

RECORD OF SUBSURFACE EXPLORATION

BORING ID

B-2

AFTER

10 20 30 40 50 60 70

Virginia Beach 5465 Greenwich Road

Virginia Beach, VA 23642 757-518-1703

SURFACE ELEVATION (NAVD88) (ft): 5

-5

-10

-15

-20

-25

-30

GROUNDWATER*:

PROJECT LOCATION: Hampton, Virginia

CLIENT: Kimley-Horn and Associates, Inc.

PROJECT NAME: Coliseum Lake Weir Repairs - Part II

DATE COMPLETED: 5/9/2019

D ep th ft)

Water Content -

Sample Type(s):

Liquid Limit

E le va tio n (f t)

S am pl e

T yp e

S am pl e

ID

S tr at a

Le ge nd

The initial groundwater readings are not intended to indicate the static groundwater level.

T hi s in fo rm at io n pe rt ai ns o nl y to t hi s bo rin g an d s ho ul d no t be in te rp re te d a s be in g in di ci tiv e of t he s ite

DRILLER: G E T Solutions, Inc.

Williamsburg 701 Alexander Lee Parkway

Williamsburg, VA 23185 757-564-6452

DATE STARTED: 5/9/2019

LOGGED BY: T. Vaughn

PROJECT NUMBER: WM19-126G

Elizabeth City 106 Capital Trace Unit E Elizabeth City, NC 27909

252-335-9765

Jacksonville 415-A Western Blvd

Jacksonville, NC 28546 910-478-9915

TEST RESULTS

Penetration -

SPT - Standard Penetration Test

DRILLING METHOD(S): Rotary wash "mud" / Hollow Stem Auger

Plastic Limit x x

Dark gray, wet, Silty fine to medium SAND (SM) with trace Clay, contains marine shell fragments, loose, "Yorktown Formation"

Dark gray, wet, Silty fine to medium SAND (SM), contains marine shell fragments, loose, "Yorktown Formation"

Dark gray, wet, Sandy lean CLAY (CL), contains marine shell fragments, stiff, "Yorktown Formation"

Dark gray, wet, Silty fine SAND (SM) with trace Clay, contains marine shell fragments, loose, "Yorktown Formation"

Boring terminated at 70 feet below existing grade.

2-2-4-4 (6)

2-3-3-5 (6)

3-3-3-7 (6)

6-5-4-6 (9)

3-4-5-4 (9)

3-3-5-5 (8)

3-4-6-8 (10)

36.5

41.5

56.5

61.5

70.0

INITIAL (ft) : 8 CAVE-IN (ft) :

Notes:

BORING LOCATION: See Attached Boring Location Plan

HOURS (ft) :

STRATA DESCRIPTION

#2

S am pl e

R ec ov er y (in

B lo w C ou nt s (N

-V al ue s)

RECORD OF SUBSURFACE EXPLORATION

BORING ID

B-2

AFTER

10 20 30 40 50 60 70

Virginia Beach 5465 Greenwich Road

Virginia Beach, VA 23642 757-518-1703

SURFACE ELEVATION (NAVD88) (ft): 5

-35

-40

-45

-50

-55

-60

-65

GROUNDWATER*:

PROJECT LOCATION: Hampton, Virginia

CLIENT: Kimley-Horn and Associates, Inc.

PROJECT NAME: Coliseum Lake Weir Repairs - Part II

DATE COMPLETED: 5/9/2019

D ep th ft)

Water Content -

Sample Type(s):

Liquid Limit

E le va tio n (f t)

S am pl e

T yp e

S am pl e

ID

S tr at a

Le ge nd

The initial…