Geotechnical Engineering Report 19229.pdf

ECS Mid-Atlantic, LLC Geotechnical Engineering Report

Salem Water Treatment Plant - Well House 4 & 5

1300 Tidewater Street Salem, Virginia

ECS Project No. 12:19229

April 2, 2021

April 2, 2021

Mr. Larado Robinson City of Salem 1300 Tidewater Street Salem, VA 24153

ECS Project No. 12:19229

Reference: Geotechnical Engineering Report Salem Water Treatment Plant-Well Houses 4 & 5 Salem, Virginia

Dear Mr. Robinson:

ECS Mid-Atlantic, LLC (ECS) has completed the subsurface exploration, laboratory testing, and geotechnical engineering analyses for the above-referenced project. Our services were performed in general accordance with our agreed to scope of work. This report presents our understanding of the geotechnical aspects of the project along with the results of the field exploration and laboratory testing conducted, and our design and construction recommendations.

It has been our pleasure to be of service to the City of Salem during the design phase of this project. We would appreciate the opportunity to remain involved during the continuation of the design phase, and we would like to provide our services during construction phase operations as well to verify subsurface conditions assumed for this report. Should you have any questions concerning the information contained in this report, or if we can be of further assistance to you, please contact us.

Respectfully submitted, ECS Mid-Atlantic, LLC

Hunter B. Ingram III, EIT Brandon M. Quinn, PE Project Engineer Office Manager hingram@ecslimited.com bquinn@ecslimited.com

Brian S. Wyatt, PE Principal Engineer bwyatt@ecslimited.com

Salem Water Treatment Well Houses 4 & 5 April 2, 2021 ECS Project No. 12:19229 Page i

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Project Location/Current Site Use/Past Site Use

2.2 Proposed Construction

3.0 FIELD EXPLORATION AND LABORATORY TESTING

3.1 Site Geology

3.2 Subsurface Characterization

3.2.1 Well House 5

3.2.2 Well House 4

3.3 Groundwater Observations

3.4 Laboratory Testing

4.0 DESIGN RECOMMENDATIONS

4.1 Karst Risk Commentary

4.2 Foundations

4.2.1 General

4.2.2 Well House 5

4.2.3 Well House 4

4.2.4 Micropiles

4.3 Below Grade WallS

4.4 Seismic Design Considerations

5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 Subgrade Preparation

5.1.1 Stripping and Grubbing

5.1.2 Proofrolling

5.1.3 Site Temporary Dewatering

5.2 Earthwork Operations

5.2.1 Existing Man-Placed Fill

5.2.2 Structural Fill

5.3 Foundation and Slab Observations

5.4 Utility Installations

6.0 CLOSING

APPENDICES

Appendix A – Drawings & Reports

Site Location Diagram

Boring Location Diagram

Subsurface Cross-Section(s)

Salem Water Treatment Well Houses 4 & 5 April 2, 2021 ECS Project No. 12:19229 Page ii

Appendix B – Field Operations

Reference Notes for Boring Logs

Subsurface Exploration Procedure: Standard Penetration Testing (SPT)

Boring Logs B-1 through B-2

Appendix C – Laboratory Testing

Laboratory Test Results Summary

Plasticity Chart

Salem Water Treatment Plant-Well Houses 4 & 5 April 2, 2021 ECS Project No. 12:19229 Page 1

EXECUTIVE SUMMARY

This Executive Summary is intended as a very brief overview of the primary geotechnical conditions that are expected to affect design and construction. Information gleaned from the Executive Summary should not be utilized in lieu of reading the entire geotechnical report.

Our exploration showed deep, variable fill soils at the proposed location of Well House 5. Based upon the results of our exploration, we have provided two foundation options, mass undercut and replacement to construct a mat foundation or pre-bored micropiles that penetrate the fill and bear in bedrock. For Well House 4 we recommend a mat foundation bearing on a 12-inch-thick bed of compacted VDOT #57 stone.

The foundation excavation should be carefully evaluated by ECS for unsuitable bedding material present in the river jack.

Based upon the results of our borings and prior experience at the site, we have categorized this site with a site class “D”.

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1.0 INTRODUCTION

The purpose of this study was to provide geotechnical information for the design foundations for the proposed well houses at the City of Salem Water Treatment Plant property. The project will include the construction of two approximately 150 square foot, 20-foot-tall, elevated well houses, one on the north side of the Roanoke River and the other on the south. The recommendations developed for this report are based on project information supplied by Arcadis and the City of Salem.

Our services were provided in accordance with our Proposal No. 14520-PR dated February 17, 2021, as authorized by the City of Salem on February 24, 2021. The scope of work was performed in accordance with the current On-Call services contract between ECS and the City of Salem.

This report contains the procedures and results of our subsurface exploration and laboratory testing programs, review of existing site conditions, engineering analyses, and recommendations for the design and construction of the project.

The report includes the following items:

Observations from our site reconnaissance including current site conditions, surface drainage features, and surface topographic conditions.

A review of the published geologic conditions and their relevance to your planned development.

A subsurface characterization and a description of the field exploration and laboratory tests performed. Groundwater concerns relative to the planned construction, if any, will be summarized.

Final logs of the soil borings and records of the field exploration prepared in accordance with the standard practice for geotechnical engineering. A boring location plan will be included, and the results of the laboratory tests will be plotted on the final boring logs or included on a separate test report sheet.

Recommended allowable soil bearing pressure(s) for conventional shallow foundations (spread footings) and estimates of predicted foundation settlement. We also provide recommendations for suitable intermediate foundations/ground improvement options or deep foundations for the instance estimated settlements of shallow foundations are not tolerable.

Recommendations for lateral earth pressures likely to develop on below-grade walls.

Recommendations for site retaining walls including lateral earth pressures, sliding resistance coefficients, and allowable bearing pressures.

Evaluation of the on-site soil characteristics encountered in the soil borings. Specifically, we will discuss the suitability of the on-site materials for reuse as engineered fill to support grade slabs and pavements. We will also include compaction requirements and suitable material guidelines.

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Recommendations for seismic site classification in accordance with the International Building Code (IBC 2015).

2.0 PROJECT INFORMATION

2.1 PROJECT LOCATION/CURRENT SITE USE/PAST SITE USE

The sites are located near the current Salem Water Treatment Facility at 1300 Tidewater Street in the City of Salem, Virginia. The location of Well House 5 is approximately three-tenths of a mile east of the existing facility on the north side of the Roanoke River. The location of Well House 4 is approximately two-tenths of a mile east of the intersection of Mill Lane and West Riverside Drive on the south side of the Roanoke River.

At the time of our visit, the ground surface over both sites was grass covered. The ground surface at the location of Well House 5 was noticeably covered by trash, construction materials, metal, and other rubble.

The Well House 5 site is overall bounded to the north by Tidewater Street; to the south by the Roanoke River; to the east by a wooded area/vacant lot; and to the west by the existing Water Treatment Plant.

The Well House 4 site is overall bounded to the north by West Riverside Drive; to the south by the existing SERVPRO warehouse; to the east by a wooded area/vacant lot; and to the west by a gravel drive leading to 1351 West Riverside Drive. Figure 2.1.1 shows the locations of the two Well House Sites (see full site location diagram in Appendix A)

Figure 2.1.1. Site Locations

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Underground utilities consisting of sewer and electric were marked parallel and perpendicular to the Roanoke River at the Well House 5 site, while underground water lines were marked parallel to West Riverside Drive in the vicinity of the Well House 4 site.

Historical aerial images show that the location of Well House 5 was previously a warehouse structure on the northern portion of the site closest to Tidewater Street and what a appears to be a smaller, residential structure on the south eastern portion of the site that both pre-date the construction of the existing water treatment plant between 1996 and 2003. Over the years, it appears there were several trailer/vehicles and other items stored on the site. Between 2018 and 2019 both structures were demolished and many of the trees were cleared from the site.

Historical aerial images show that the location of Well House 4 was wooded as recently as 2016 and that the warehouse on the property also pre-dates the construction of the existing water treatment facility.

Published topographical maps show that site grades in the vicinity of the proposed well houses range from approximately El. 1024 feet to El. 1027 feet and El. 1018 feet to El. 1020 feet for Well Houses 5 & 4, respectively.

2.2 PROPOSED CONSTRUCTION

The following information explains our understanding of the planned development including proposed buildings and related infrastructure.

SUBJECT DESIGN INFORMATION / ASSUMPTIONS

Building Footprint (s) Approximately 150 square feet each

# of Stories 2 stories above grade; approximately 5 feet below grade

Usage Well pump house

Framing Pre-cast masonry walls (assumed)

Vertical Load Maximum vertical load of approximately 275 kips

Horizontal loads Maximum horizontal shear load of approximately 15 kips

Lowest Finish Floor Elevation

Approximately 5 feet below current grade

*Assumed load are based on similar structures built in the area. If final design loads exceed our assumed loads, this report needs to be revised to update our foundation recommendations, bearing capacity, and settlement calculations.

3.0 FIELD EXPLORATION AND LABORATORY TESTING

Our exploration procedures are explained in greater detail in Appendix B including the insert titled Subsurface Exploration Procedures. Our scope of work included drilling two borings. Our borings were located with a handheld GPS unit while referencing Google Earth aerial imaging (showing desired boring locations provided by your office) and estimating angles from existing site features. Their approximate locations are shown on the Boring Location Diagram in Appendix A.

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3.1 SITE GEOLOGY

The project site is located within the Salem Quadrangle of the Ridge and Valley Province in Southwestern Virginia. Specifically, the site area is located within the Roanoke Valley, which is a northeast-southwest trending lowlands extending for some 20 miles around the City of Roanoke and whose floor is characterized by easily eroded limestones and shales.

Specifically, the site is located on the Salem Thrust Sheet, which is bordered to the north by the Salem Fault and to the south by the Max Meadows Fault. These are low angle overthrust faults that brought the Elbrook Formation of Cambrian Age into contact with younger Ordovician rock. The entire Salem Thrust Sheet exposes the Elbrook Formation, with the Max Meadows Fault as the defining boundary with its sister Rome formation. The rock of the Elbrook Formation weathers to residual soils consisting of orangish brown Silts, Clays, and Saprolites of variable thickness. The Elbrook Formation is known for its potential sinkhole development, subsidence, and solution cavities.

The project areas are located along the Roanoke River which flows eastward through a flood plain containing a thick veneer of alluvial material overlying the Elbrook and Rome Formations. Young alluvium is present in the current stream channel and flood plain. The transition from these young alluvial materials to hard rock is often times abrupt, with little or no residual soil or saprolite present. The project site is located within this recent flood plain.

The carbonate rock formations located in this area typically consist of limestone and dolomite. Carbonate materials solution in water over long periods of time, resulting in loss of rock material. The solution process typically occurs along planes of more soluble material and causes the formation of interconnected seams and cavities within carbonate formations. The rate of solutioning is also affected by rates of groundwater flow and groundwater chemistry; however, typical solutioning rates are on the order of one inch in 1,000 years. These seams and cavities are frequently filled with soft material which has not dissolved or materials that have infiltrated into the seam or cavity from above. The continued exposure to solution activities can result in the formation of caverns, such as Dixie Caverns near Salem, Virginia.

Sinkholes can also result from the collapse of material bridging over the top of caverns formed during the solution process.

Differential solution activity results in a highly-variable rock surface with soil-filled slots commonly encountered between pinnacles of more solution-resistant rock. Since solution activity is caused by groundwater flow, solution channels are commonly interconnected with narrow zones of solution activity extending from large solution features.

In carbonate materials, such as the subject site, the boundary between soil and rock is not sharply defined.

HWR (a transitional zone from residual soil to bedrock), is normally found overlying the parent bedrock.

HWR is defined, for engineering purposes, as residual material exhibiting a relict rock structure with Standard Penetration resistance greater than 100 blows per foot (bpf). Because weathering is facilitated by fractures, joints, and the presence of less resistant rock types, the profile of the HWR and hard rock surface is typically irregular and erratic, even over relatively short horizontal distances. Also, it is not unusual to find natural lenses and boulders of hard rock “floating” in zones of HWR within the soil mantle, well above the general bedrock level.

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3.2 SUBSURFACE CHARACTERIZATION

The subsurface conditions encountered were generally consistent with published geological mapping. The following sections provide generalized characterizations of the soil strata. Please refer to the boring logs in Appendix B.

Our subsurface characterization has been supplemented with the use of the subsurface data obtained from the Well Yield and Water Quality Report for Production Wells 4 and 5 prepared for the City of Salem by Golder and Associates, dated August 7, 2020, which showed bedrock elevations for Well House 5 and Well House 4 of approximately 18 feet and 16 feet, respectively.

3.2.1 Well House 5

Approximate Depth (ft)

Stratum Description Ranges of SPT(2) N-values (bpf)

0-1.0 (Surface cover) n/a Topsoil

N/A

1.0-18.0 I FILL, Firm to Stiff LEAN CLAY and SILT, moist; underlain by debris fill consisting of boulders and concrete fragments; underlain by a grout layer assumed to be resting on bedrock

8-10

~18.0 (1) II Bedrock, mapped as Limestone N/A

Notes:

(1) Approximate bedrock depth is based upon test well drilling report and prior exploration in the area

(2) Standard Penetration Testing

3.2.2 Well House 4

Approximate Depth (ft)

Stratum Description Ranges of SPT(1) N-values (bpf)

0-2.5 (Surface cover) n/a Topsoil

N/A

2.5-7.5 I Alluvium, Very Loose, SILTY SAND, moist 3-4

7.5-14.5 II Alluvium, Limestone boulders and River Jack N/A

~16.0(1) III Bedrock, mapped as Limestone N/A

Notes:

(1) Approximate bedrock depth is based upon test well drilling report and prior exploration in the area

(2) Standard Penetration Testing

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A graphical presentation of the subsurface conditions is shown on the Subsurface Cross Section Diagram(s) included in Appendix A.

3.3 GROUNDWATER OBSERVATIONS

Water was introduced to the borehole during coring operations, and therefor accurate measurements of groundwater depth could not be made. Before coring commenced, groundwater seepage into our borings was not observed during our exploration at the depths explored. However,, given the proximity of the test well locations to the Roanoke River, groundwater levels may fluctuate rapidly depending upon the season and should be considered during construction scheduling.

3.4 LABORATORY TESTING

The laboratory testing consisted of selected tests performed on samples obtained during our field exploration operations. Classification and index property tests were performed on representative soil samples. The laboratory testing program included natural moisture content tests (ASTM D2216), percent passing the No. 200 sieve tests (ASTM D1140), and Atterberg Limits tests (ASTM D4318). The results of all laboratory testing conducted are included in the Appendix of this report.

Each sample was visually classified based on texture and plasticity in accordance with ASTM D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedures) which includes USCS classification symbols, and ASTM D2487 Standard Practice for Classification for Engineering Purposes (Unified Soil Classification System (USCS). After classification, the samples were grouped in the major zones noted on the boring logs in Appendix B. The group symbols for each soil type are indicated in parentheses along with the soil descriptions. The stratification lines between strata on the logs are approximate; in situ, the transitions may be gradual.

4.0 DESIGN RECOMMENDATIONS

4.1 KARST RISK COMMENTARY

The site is mapped to be underlain by geologic parent rock which is known to be carbonate in nature.

However, based on our exploration the subsurface did not exhibit karst overburden soil characteristics.

Additionally, during our site reconnaissance karst surface features were not observed on the property or immediate vicinity. Therefore, we define the risk of future sinkhole development on this site as low.

4.2 FOUNDATIONS

4.2.1 General

Our subsurface investigation showed that the soil conditions differ significantly at the locations of Well House 5 and Well House 4. In general, the soil conditions at Well House 5 are poor, and we have therefore provided two options for support of the proposed structure in the following subsections. In general, the soil conditions at Well House 4 indicate a shallow spread foundation solution as summarized in the following subsections.

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4.2.2 Well House 5

The soil conditions encountered at the proposed location of Well House 5 consisted of an approximately 10-foot-thick layer of stiff FILL soils which consisted of SILT (ML) with boulders and other construction debris. Below the finer material and boulders, an approximately 5 to 8-foot-thick grout layer was encountered during drilling operations, presumably to as part of the test well construction. The soils encountered at the location of Well House 5 are not adequate to support the proposed structure on traditional shallow spread footings bearing in the uncontrolled fill. Therefore, we have provided the following two options for support of Well House 5:

Option 1: Mass Undercut and Replacement

To provide uniform bearing conditions for shallow foundations an undercut of all fill material, including the grout layer, down to bedrock or a suitable bearing stratum which is approximately 18 below current grades based on the information provided would be required. The undercut should be performed within the footprint of the building and with in the zone of influence of the footing(s) defined by a plane projected at a 1H:1V ratio from each footing edge. The undercut should be backfilled with compacted select material such as VDOT #21A/21B to the desired bottom of footing elevation as discussed in the following sections of this report. It is possible that this deep excavation will extend below groundwater. An ECS representative should observe the footing excavations to confirm an adequate bearing stratum. If subgrades are prepared in this way, the proposed Well House 5 may be supported by a mat foundation designed in accordance with the shallow spread footing recommendations below for Well House 4.

Option 2: Micropiles

To avoid excessive undercut volumes that would be required for Option 1, micropiles may be used to support the proposed structure. An experienced specialty contractor should be utilized and bore through the existing boulders, deleterious materials, and grout layer and into the bedrock. Micropiles would be installed in the pre-bored holes that would transfer the load through the debris fill to an adequate bearing stratum of hard rock.

4.2.3 Well House 4

The soil conditions encountered at the proposed location of Well House 4 consisted of an approximately 5-foot-thick layer of very loose alluvial SILTY SAND underlain by larger alluvial boulders “river jack”. Based upon the approximate foundation bearing elevation on the plans provided, it appears that the alluvium will be mostly removed as part of the foundation excavation. However, the alluvial soils should be undercut to the river jack layer or bedrock. The undercut should be replaced with compacted select backfill such as VDOT #21A/21B if the desired bearing elevation is within this stratum. The proposed Well House 4 can be constructed on mat foundation bearing on a 12-inch-thick layer of VDOT #57 Stone to help facilitate load transfer to the large alluvial material and protect the mat foundation of over stress due to point loading on a non-uniform bearing stratum. An ECS representative should be on site to observe the footing excavations and confirm that all unsuitable material has been removed.

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Provided subgrades are prepared as recommended in this report, the proposed structure can be supported by mat foundations as outlined above. We recommend the foundation design use the following parameters:

Design Parameter Mat Foundation

Net Allowable Bearing Pressure(1) 3,000 psf

Acceptable Bearing Soil Material Compacted VDOT #21A/B or similar select material up to 12 inches below bottom of mat; VDOT #57 Stone as a final drainage/stress distribution layer

Minimum Footing Embedment Depth (below slab or finished grade) (2)

24 inches

Minimum Exterior Frost Depth (below final exterior grade)

24 inches

Estimated Total Settlement (3) Less than 1- inch

Estimated Differential Settlement (4) Less than ¾ inches between columns

SOIL PARAMETER ESTIMATED VALUE

Coefficient of Passive Earth Pressure (Kp) 3.0

Soil Moist Unit Weight (γ) 120 pcf

Cohesion (C) 0 psf

Interface Friction Angle [Concrete on Soil] (φf) 30°

Sliding Friction Coefficient [Concrete on Soil] (μ) 0.55

Passive equivalent fluid pressure 360H (psf)

4.2.4 Micropiles

It is our opinion that Well House 5 may be supported on a micropile foundation system extended in to rock. Micropiles are presented as a viable, potentially less expensive option to deep undercut and replacement or conventional deep foundations. The geotechnical capacity of the micropiles is based on the grout to ground (in this case, rock) resistance, or side friction, of the pile around the perimeter of the micropile bond zone. The contribution of end bearing to the capacity is typically neglected due to the small surface area of the end of the micropile. For structural design purposes, a total allowable axial

ECS Project No. 12:19229 Page 10 compression capacity of 100 kips is recommended per pile (F.S. = 2.5) for the proposed foundation support. Given that capacities are independent of end bearing, uplift capacities will also be 100 kips per pile.

Although means and methods will be determined by the micropile installer, we anticipate the micropiles will be installed per Type A requirements (gravity grout only). Pressure grouting (Type B micropiles) would not increase capacities because the bond zone will be within rock. We recommend that additional capacity attributable to skin friction within the overburden soils be neglected due to the potential for karst voids, very soft soil conditions, and unpredictable thickness of the overburden. We recommend that each pile cap for isolated columns have a minimum of three piles for eccentricity loading purposes.

Based on our understanding, the proposed structure FFE will be approximately 5 feet below existing grades. The pile lengths required to extend through the fill, boulders, and grout layer into bedrock are estimated to be on the order of 35 feet below existing grades, based on the available boring and test well data. The lengths are based on estimated minimum bond lengths into hard rock of 15 feet. This is based on poor quality (RQD) rock; however, if better quality rock is indicated through either additional geotechnical exploration or through pile load testing, then the minimum bond lengths may be reduced.

The depths of the micropiles should be field verified through load testing and visual observations during installation by ECS. Spacing of the micropiles should be at least three diameters apart.

Based on our preliminary design calculations, we recommend that the minimum diameter of the casing for the micropiles be 7.5 inches, allowing for a grout zone (uncased) diameter of 8.5 inches. We recommend that the unbonded pile length above the rock surface remain permanently cased to avoid grout loss during construction and prevent buckling of the element. The reinforcing steel should be installed the full length of the pile. The cement grout used for the micropiles should have a minimum 28-day compressive strength of 5,000 pounds per square inch (psi). Lower grout strengths are not sufficient for the load test requirements; however, higher strengths may be required following the structural design.

Based on past conversations with a micropile installer/designer, we anticipate that allowable lateral capacities of up to about 4 kips per pile will be readily available without the addition of an inner casing to the pile section. If higher lateral loads are required, battered piles may be utilized. Typical battering angles for this case are 20 to 45 degrees from the vertical plane.

It is noted that the complete design of the micropile elements should be completed as by an experienced design professional. We recommend that the contractor be provided with a performance specification for bidding, design, and construction purposes. This should consist of a target allowable vertical capacity of 100 kips per pile and a minimum lateral load capacity to be specified by the structural engineer. For purposes of this report, we have estimated that nominal (ultimate) grout-to-rock bond strength of 30 psi for the poor quality rock is reasonable; however, these values may be subject to change by the installer’s design team. Ultimately, we recommend that the micropile installer be responsible for the final geotechnical and structural design of the micropile elements, subject to review by the primary design team and ECS. Such design should account for possible buckling within any possible upper, very soft residual soils.

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4.3 BELOW GRADE WALLS

We recommend that below grade walls be designed to withstand at-rest lateral earth pressures and surcharge loads from adjacent building foundations, and/or streets. These recommendations apply to a “drained” condition which is where there is drainage material behind below grade walls that prevents hydrostatic water pressures on the back of the below grade wall.

To accomplish a drained condition, drainage materials such as a free draining gravel, geocomposite drainage panels, weep holes, and an underslab drainage system should be used.

We recommend that walls that are restrained from movement at the top be designed for a linearly increasing lateral earth pressure. The following figure depicts our recommended at-rest lateral earth pressure condition for a “drained below-grade wall” with restrained wall top:

Figure 4.3.1

Surcharge loads imposed within a 45-degree slope from the base of the restrained wall should be considered in the below grade wall design. These surcharge loads should be based on an at-rest pressure coefficient, k0, of 0.5. Care should be used to avoid the operation of heavy equipment to compact the wall backfill since it may overload and damage the wall; in addition, such loads are not typically considered in the design of below grade walls.

4.4 SEISMIC DESIGN CONSIDERATIONS

Seismic Site Classification: The International Building Code (IBC) 2015 requires site classification for seismic design based on the upper 100 feet of a soil profile. At least two methods are utilized in classifying

Surcharge Load (psf)

H

Lateral Earth Pressure = 60 H psf (For below grade walls restrained from movement at top and bottom, drained conditions only)

Horizontal Pressure from Surcharge = 0.5 x Vertical Surcharge

This diagram is not suitable for the design of Support of Excavation or temporary shoring systems.

ECS Project No. 12:19229 Page 12 sites, namely the shear wave velocity (vs) method and the Standard Penetration Resistance (N-value) method. The second method (N-Value) was used to classify this site.

SEISMIC SITE CLASSIFICATION

Site Class

Soil Profile Name Shear Wave Velocity, Vs, (ft./s) N value (bpf)

A Hard Rock Vs > 5,000 fps N/A

B Rock 2,500 < Vs ≤ 5,000 fps N/A

C Very dense soil and soft rock 1,200 < Vs ≤ 2,500 fps >50

D Stiff Soil Profile 600 ≤ Vs ≤ 1,200 fps 15 to 50

E Soft Soil Profile Vs < 600 fps <15

Based upon our interpretation of the subsurface conditions, the appropriate Seismic Site Classification is “D” as shown in the preceding table.

Ground Motion Parameters: In addition to the seismic site classification, ECS has determined the design spectral response acceleration parameters following the IBC methodology. The Mapped Responses were estimated from the USGS website https://www.usgs.gov/natural-hazards/earthquake-hazards/design-ground-motions. The design responses for the short (0.2 sec, SDS) and 1-second period (SD1) are noted in bold at the far right end of the following table.

GROUND MOTION PARAMETERS [IBC 2015 Method]

Period (sec)

Mapped Spectral Response

Accelerations (g)

Values of Site Coefficient for Site Class

Maximum Spectral Response Acceleration

Adjusted for Site Class (g)

Design Spectral Response

Acceleration (g)

Reference Figures 1613.3.1

(1) & (2) Tables 1613.3.3

(1) & (2) Eqs. 16-37 &

16-38 Eqs. 16-39 &

16-40

0.2 SS 0.205 Fa 0.8 SMS=FaSs 0.164

SDS=2/3

SMS

0.109

1.0 S1 0.078 Fv 0.8 SM1=FvS1 0.062

SD1=2/3

SM1

0.042

The Site Class definition should not be confused with the Seismic Design Category designation which the Structural Engineer typically assesses. If a higher site classification is beneficial to the project, we can provide additional testing methods that may yield more favorable results.

5.0 SITE CONSTRUCTION RECOMMENDATIONS

5.1 SUBGRADE PREPARATION

5.1.1 Stripping and Grubbing

The subgrade preparation should consist of stripping all vegetation, rootmat, topsoil, existing fill, and any soft or unsuitable materials from the 5-foot expanded building and 2-foot expanded pavement limits, and

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5 feet beyond the toe of Structural Fills. Borings performed in “undisturbed” areas of the site contained an observed 6 or 7 inches of topsoil. Deeper topsoil or organic laden soils may be present in wet, low-lying, and poorly drained areas. In wooded areas, the root balls may extend as deep as about 2 feet and will require additional localized stripping depth to completely remove the organics. ECS should be retained to verify that topsoil and unsuitable surficial materials have been removed prior to the placement of structural fill or construction of structures.

5.1.2 Proofrolling

Prior to fill placement or other construction on subgrades, the subgrades should be evaluated by an ECS field technician. The exposed subgrade should be thoroughly proofrolled with construction equipment having a minimum axle load of 10 tons [e.g. fully loaded tandem-axle dump truck]. Proofrolling should be traversed in two perpendicular directions with overlapping passes of the vehicle under the observation of an ECS technician. This procedure is intended to assist in identifying any localized yielding materials.

Where proofrolling identifies areas that are unstable or “pumping” subgrade those areas should be repaired prior to the placement of any subsequent Structural Fill or other construction materials. Methods of stabilization include undercutting, moisture conditioning, or chemical stabilization. The situation should be discussed with ECS to determine the appropriate procedure. Test pits may be excavated to explore the shallow subsurface materials to help in determining the cause of the observed unstable materials, and to assist in the evaluation of appropriate remedial actions to stabilize the subgrade.

5.1.3 Site Temporary Dewatering

Limited Excavation Dewatering: Based upon our subsurface exploration at this site, as well as significant experience on sites in nearby areas of similar geologic setting, we believe construction dewatering at this site will be mainly limited to removing accumulated rainwater and some minor seepage from the support of excavation (SOE). It appears that the permanent static groundwater for this site is well below the planned deepest excavation. However, if Option 1 above is chosen as the construction alternative, more extensive construction dewatering may be required.

Deep wells should not be required for the temporary dewatering system. However, the dewatering operations can be handled by the use of conventional submersible pumps directly in the excavation, temporary trenches, or French drains.

5.2 EARTHWORK OPERATIONS

5.2.1 Existing Man-Placed Fill

Fill Content: SILT underlain by boulders, construction debris and concrete/grout layer

Fill Removal in Building Areas: If Foundation Option 1 is chosen, all existing fill should be removed from below the planned pavement and building areas.

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5.2.2 Structural Fill

Prior to placement of Structural Fill, representative bulk samples (about 50 pounds) of on-site and/or off-site borrow should be submitted to ECS for laboratory testing, which will typically include Atterberg limits, natural moisture content, grain-size distribution, and moisture-density relationships (i.e., Proctors) for compaction. Import materials should be tested prior to being hauled to the site to determine if they meet project specifications. Alternatively, Proctor data from other accredited laboratories can be submitted if the test results are within the last 90 days.

Satisfactory Structural Fill Materials: Materials satisfactory for use as Structural Fill should consist of inorganic soils with the following engineering properties and compaction requirements.

STRUCTURAL FILL INDEX PROPERTIES

Subject Property

Building and Pavement Areas (Borrow Soils) LL < 50, PI<25

Building and Pavement Areas (On-site Soils) LL < 60, PI < 30

Max. Particle Size 4 inches

Max. organic content 5% by dry weight

STRUCTURAL FILL COMPACTION REQUIREMENTS

Subject Requirement

Compaction Standard Standard Proctor, ASTM D698

Required Compaction 95% of Max. Dry Density

Moisture Content +/-3 % points of the soil’s optimum value

Loose Thickness 8 inches prior to compaction

On-Site Borrow Suitability: Significant natural deposits of soils that meet the definition for satisfactory structural fill are not present on the site.

Fill Placement: Fill materials should not be placed on frozen soils, on frost-heaved soils, and/or on excessively wet soils. Borrow fill materials should not contain frozen materials at the time of placement, and all frozen or frost-heaved soils should be removed prior to placement of Structural Fill or other fill soils and aggregates. Excessively wet soils or aggregates should be scarified, aerated, and moisture conditioned.

5.3 FOUNDATION AND SLAB OBSERVATIONS

Protection of Foundation Excavations: Exposure to the environment may weaken the soils at the footing bearing level if the foundation excavations remain open for too long a time. Therefore, foundation concrete should be placed the same day that excavations are made. If the bearing soils are softened by surface water intrusion or exposure, the softened soils must be removed from the foundation excavation bottom immediately prior to placement of concrete. If the excavation must remain open overnight, or if

ECS Project No. 12:19229 Page 15 rainfall becomes imminent while the bearing soils are exposed, a 1 to 3-inch thick “mud mat” of “lean” concrete should be placed on the bearing soils before the placement of reinforcing steel.

Footing Subgrade Observations: Most of the soils at the foundation bearing elevation are anticipated to be suitable for support of the proposed structure. It is important to have ECS observe the foundation subgrade prior to placing foundation concrete, to confirm the bearing soils are what was anticipated.

Slab Subgrade Verification: Prior to placement of a drainage layer, the subgrade should be prepared in accordance with the recommendations found in Section 5.1.2 Proofrolling.

5.4 UTILITY INSTALLATIONS

Utility Subgrades: The soils encountered in our exploration are expected to be generally suitable for support of utility pipes. The pipe subgrades should be observed and probed for stability by ECS. Any loose or unsuitable materials encountered should be removed and replaced with suitable compacted Structural Fill, or pipe stone bedding material.

Utility Backfilling: The granular bedding material should be at least 4 inches thick, but not less than that specified by the civil engineer’s project drawings and specifications. We recommend that the bedding materials be placed up to the springline of the pipe. Fill placed for support of the utilities, as well as backfill over the utilities, should satisfy the requirements for Structural Fill and Fill Placement.

Excavation Safety: All excavations and slopes should be constructed and maintained in accordance with OSHA excavation safety standards. The contractor is solely responsible for designing, constructing, and maintaining stable temporary excavations and slopes. 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. ECS is providing this information solely as a service to our client. ECS is not assuming responsibility for construction site safety or the contractor’s activities; such responsibility is not being implied and should not be inferred.

6.0 CLOSING

ECS has prepared this report to guide the geotechnical-related design and construction aspects of the project. We performed these services in accordance with the standard of care expected of professionals in the industry performing similar services on projects of like size and complexity at this time in the region.

No other representation, expressed or implied, and no warranty or guarantee is included or intended in this report.

The description of the proposed project is based on information provided to ECS by our client. If any of this information is inaccurate or changes, either because of our interpretation of the documents provided or site or design changes that may occur later, ECS should be contacted so we can review our recommendations and provide additional or alternate recommendations that reflect the proposed construction.

ECS Project No. 12:19229 Page 16

We recommend that ECS review the project plans and specifications so we can confirm that those plans/specifications are in accordance with the recommendations of this geotechnical report.

Field observations, and quality assurance testing during earthwork and foundation installation are an extension of, and integral to, the geotechnical design. We recommend that ECS be retained to apply our expertise throughout the geotechnical phases of construction, and to provide consultation and recommendation should issues arise.

ECS is not responsible for the conclusions, opinions, or recommendations of others based on the data in this report.

APPENDIX A – Diagrams & Reports

Site Location Diagram Boring Location Diagram Subsurface Cross-Sections

3/31/2021

Service Layer Credits: Esri, HERE, Garmin, (c) OpenStreetMap contributors

²

ENGINEER

SCALE

12:19229

PROJECT NO.

SHEET

DATE

BMQ

CITY OF SALEM

SALEM WTP WELL HOUSES 4 & 5

1300 TIDEWATER STREET, SALEM, VIRGINIA

SITE LOCATION DIAGRAM

0 2,0001,000

Feet

AS NOTED

B-2

B-1

3/24/2021

Service Layer Credits: Esri, HERE, Garmin, (c) OpenStreetMap contributors

²

ENGINEER

SCALE

12:19229

PROJECT NO.

SHEET

DATE

HBI

CITY OF SALEM

SALEM WTP WELL HOUSES 4 & 5

1300 TIDEWATER STREET, SALEM, VIRGINIA

BORING LOCATION DIAGRAM

0 400200

Feet

AS NOTED

1020 1020

1019 1019

1018 1018

1017 1017

1016 1016

1015 1015

1014 1014

1013 1013

1012 1012

1011 1011

1010 1010

1009 1009

1008 1008

1007 1007

1006 1006

1005 1005

0.

.1

.9

.9

1004.00

Legend Key Topsoil

SILTY

SAND

Boulders & Cobbles

Notes:

1- EOB: END OF BORING AR: AUGER REFUSAL SR: SAMPLER REFUSAL.

2- THE NUMBER BELOW THE STRIPS IS THE DISTANCE ALONG THE BASELINE.

3- SEE INDIVIDUAL BORING LOG AND GEOTECHNICAL INFORMATION.

4- STANDARD PENETRATION TEST RESISTANCE (LEFT OF BORING) IN BLOWS PER

FOOT (ASTM D1586).

Plastic Limit Water Content Liquid Limit X─────────⚫─────────△

[FINES CONTENT%]

BOTTOM OF CASING

LOSS OF CIRCULATION

WL (First Encountered)

WL (Completion)

WL (Seasonal High Water)

WL (Stabilized)

Fill

Possible Fill

Probable Fill

Rock

GENERALIZED SUBSURFACE SOIL PROFILE Section line 2

Salem WTP Well Houses 4 & 5 City of Salem

1300 Tidewater Street, Salem, Virginia 24153 Project No: 12:19229 Date: 04/02/2021

MC = 17.3

MC = 15.1

MC = 20.3

*B -2

EOB

@14.5'

Topsoil

SM

Boulder s &

Cobbles

HIngram Line

HIngram Typewriter Approximate proposed bottom of footing

1027 1027

1026 1026

1025 1025

1024 1024

1023 1023

1022 1022

1021 1021

1020 1020

1019 1019

1018 1018

1017 1017

1016 1016

1015 1015

1014 1014

1013 1013

1012 1012

1011 1011

1010 1010

1009 1009

1008 1008

1007 1007

1006 1006

1005 1005

.4

2.

6.

1004.00

Legend Key Topsoil

Lean

CLAY

Debris Fill

Concrete

Notes:

1- EOB: END OF BORING AR: AUGER REFUSAL SR: SAMPLER REFUSAL.

2- THE NUMBER BELOW THE STRIPS IS THE DISTANCE ALONG THE BASELINE.

3- SEE INDIVIDUAL BORING LOG AND GEOTECHNICAL INFORMATION.

4- STANDARD PENETRATION TEST RESISTANCE (LEFT OF BORING) IN BLOWS PER

FOOT (ASTM D1586).

Plastic Limit Water Content Liquid Limit X─────────⚫─────────△

[FINES CONTENT%]

BOTTOM OF CASING

LOSS OF CIRCULATION

WL (First Encountered)

WL (Completion)

WL (Seasonal High Water)

WL (Stabilized)

Fill

Possible Fill

Probable Fill

Rock

GENERALIZED SUBSURFACE SOIL PROFILE Section line 1

Salem WTP Well Houses 4 & 5 City of Salem

1300 Tidewater Street, Salem, Virginia 24153 Project No: 12:19229 Date: 04/02/2021

*B -1

A

AR

@5.5'

EOB

@5.5'

PL = 17 MC = 17.1 LL = 26

[78.2%]

MC = 16.8

*B -1

AR

@5.5'

EOB

@5.5'

Topsoil

CL

*B -1

C

AR

@5.0'

EOB

@15.0'

Debris Fill

Concret e

HIngram Line

HIngram

Approximate proposed bottom of footing

APPENDIX B – Field Operations

Reference Notes for Boring Logs Subsurface Exploration Procedure: Standard Penetration Testing (SPT) Boring Logs B-1 through B-2

REFERENCE NOTES FOR BORING LOGS

MATERIAL1,2

1Classifications and symbols per ASTM D 2488-17 (Visual-Manual Procedure) unless noted otherwise.

2To be consistent with general practice, “POORLY GRADED” has been removed from GP, GP-GM, GP-GC, SP, SP-SM, SP-SC soil types on the boring logs.

3Non-ASTM designations are included in soil descriptions and symbols along with ASTM symbol [Ex: (SM-FILL)].

4Typically estimated via pocket penetrometer or Torvane shear test and expressed in tons per square foot (tsf).

5Standard Penetration Test (SPT) refers to the number of hammer blows (blow count) of a 140 lb. hammer falling 30 inches on a 2 inch OD split spoon sampler required to drive the sampler 12 inches (ASTM D 1586). “N-value” is another term for “blow count” and is expressed in blows per foot (bpf). SPT correlations per 7.4.2 Method B and need to be corrected if using an auto hammer.

6The water levels are those levels actually measured in the borehole at the times indicated by the symbol. The measurements are relatively reliable when augering, without adding fluids, in granular soils. In clay and cohesive silts, the determination of water levels may require several days for the water level to stabilize. In such cases, additional methods of measurement are generally employed.

7Minor deviation from ASTM D 2488-17 Note 14.

8Percentages are estimated to the nearest 5% per ASTM D 2488-17.

Reference Notes for Boring Logs (1-29-2021).doc © 2021 ECS Corporate Services, LLC. All Rights Reserved

COHESIVE SILTS & CLAYS

UNCONFINED

COMPRESSIVE

STRENGTH, QP4

<0.25

0.25 - <0.50

0.50 - <1.00

1.00 - <2.00

2.00 - <4.00

4.00 - 8.00

>8.00

SPT5

(BPF)

CONSISTENCY7

(COHESIVE)

GRAVELS, SANDS & NON-COHESIVE SILTS

SPT5

DENSITY

<5 5 - 10

11 - 30 31 - 50

>50

Very Loose Loose

Medium Dense Dense

Very Dense

WATER LEVELS6

RELATIVE

AMOUNT7

Trace

With

Adjective (ex: “Silty”)

COARSE

GRAINED

(%)8

<5

FINE

GRAINED

(%)8

<5

DRILLING SAMPLING SYMBOLS & ABBREVIATIONS

PARTICLE SIZE IDENTIFICATION

DESIGNATION PARTICLE SIZES

Hollow Stem Auger Power Auger (no sample) Bulk Sample of Cuttings Wash Sample Shelby Tube Sampler Split Spoon Sampler

Rock Quality Designation % Rock Sample Recovery % Rock Core, NX, BX, AX Rock Bit Drilling Pressuremeter TestSS

ST

WS

BS

PA

HSA

RQD

PM

RD

RC

REC

Boulders Cobbles

Gravel:

Sand:

Silt & Clay (“Fines”) Fine Medium

Coarse Fine Coarse

0.074 mm to 0.425 mm (No. 200 to No. 40 sieve) <0.074 mm (smaller than a No. 200 sieve)

0.425 mm to 2.00 mm (No. 40 to No. 10 sieve)

2.00 mm to 4.75 mm (No. 10 to No. 4 sieve)

4.75 mm to 19 mm (No. 4 sieve to ¾ inch) ¾ inch to 3 inches (19 mm to 75 mm) 3 inches to 12 inches (75 mm to 300 mm) 12 inches (300 mm) or larger

>50 31 - 50 16 - 30

9 - 15 5 - 8 3 - 4 <3

Very Hard Hard

Very Stiff

Stiff Firm Soft

Very Soft

ASPHALT

CONCRETE

GRAVEL

TOPSOIL

VOID

BRICK

AGGREGATE BASE COURSE

GW

GP

GM

GC

SW

SP

SM

SC

ML

MH

CL

CH

OL

OH

PT

WELL-GRADED GRAVEL

gravel-sand mixtures, little or no fines

POORLY-GRADED GRAVEL

gravel-sand mixtures, little or no fines

SILTY GRAVEL

gravel-sand-silt mixtures

CLAYEY GRAVEL

gravel-sand-clay mixtures

WELL-GRADED SAND

gravelly sand, little or no fines

POORLY-GRADED SAND

gravelly sand, little or no fines

SILTY SAND

sand-silt mixtures

CLAYEY SAND

sand-clay mixtures

SILT

non-plastic to medium plasticity

ELASTIC SILT

high plasticity

LEAN CLAY

low to medium plasticity

FAT CLAY

high plasticity

ORGANIC SILT or CLAY non-plastic to low plasticity

ORGANIC SILT or CLAY high plasticity

PEAT

highly organic soils

WL (First Encountered)

WL (Completion)

WL (Seasonal High Water)

WL (Stabilized)

FILL POSSIBLE FILL PROBABLE FILL ROCK

FILL AND ROCK

25 - 45

10 - 20

30 - 45

10 - 25

SUBSURFACE EXPLORATION PROCEDURE:

STANDARD PENETRATION TESTING (SPT)

ASTM D 1586

Split-Barrel Sampling

Standard Penetra on Tes ng, or SPT, is the most frequently used subsurface explora on test performed worldwide. This test provides samples for iden fica on purposes, as well as a measure of penetra on resistance, or N-value. The N-Value, or blow counts, when corrected and correlated, can approximate engineering proper es of soils used for geotechnical design and engineering purposes.

• Involves driving a hollow tube (split-spoon) into the ground by dropping a 140-lb hammer a height of 30-inches at desired depth

• Recording the number of hammer blows re-quired to drive split-spoon a distance of 12 inches (in 3 or 4 Increments of 6 inches each)

• Auger is advanced* and an addi onal SPT is performed

• One SPT test is typically performed for every two to five feet

• Obtain two-inch diameter soil sample

*Drilling Methods May Vary— The predominant drilling methods used for SPT are open hole fluid rotary drilling and hollow-stem auger drilling.

SPT Procedure:

DE

PT

H (F

T)

SA

M

PL

E

N U

M

BE

R

S-1

S-2

SA

M

PL

E

TY

PE

SS

SS

SA

M

PL

E

DI

ST

IN

RE

CO

VE

RY

(I N

DESCRIPTION OF MATERIAL

Topsoil Thickness[12.00"] (CL) FILL, LEAN CLAY WITH SAND, brown, moist, rm

Refusal encountered at 5.5 feet.

END OF DRILLING AT 5.5 FT

W

AT

ER

L

EV

EL

S

EL

EV

AT

IO

N (F

T)

BL

O

W S/

6"

3-3-5 (8)

3-5-5 (10)

Plas c Limit Water Content Liquid Limit X─────────⚫─────────△

17.1

16.8

[78.2%]

CLIENT:

City of Salem

PROJECT NAME:

Salem WTP Well Houses 4 & 5

PROJECT NO.: BORING NO.:

12:19229 B-1

DRILLER/CONTRACTOR:

Blue Ridge Drilling, Inc.

SHEET:

SITE LOCATION:

1300 Tidewater Street, Salem, Virginia 24153

LOSS OF CIRCULATION

NORTHING:

3631690.9

EASTING:

11024859.2

STATION: SURFACE ELEVATION:

1026.0

BOTTOM OF CASING

THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN-SITU THE TRANSITION MAY BE GRADUAL

WL (First Encountered)

WL (Comple on)

WL (Seasonal High Water)

WL (Stabilized)

Dry BORING STARTED:

BORING

COMPLETED:

EQUIPMENT:

ATV

Mar 17 2021

Mar 17 2021

LOGGED BY:

HI

CAVE IN DEPTH:

HAMMER TYPE:

DRILLING METHOD:

4.50

Auto

3.25" HSA

GEOTECHNICAL BOREHOLE LOG

STANDARD PENETRATION BLOWS/FT

ROCK QUALITY DESIGNATION & RECOVERY

RQD

REC

CALIBRATED PENETROMETER TON/SF

[FINES CONTENT] %

HIngram Typewriter Remarks: Auger refusal likely occurred on boulders within the fill

H (F

T)

SA

M

PL

E

N U

M

BE

R

SA

M

PL

E

TY

PE

SA

M

PL

E

DI

ST

IN

RE

CO

VE

RY

(I N

DESCRIPTION OF MATERIAL

Boring O set 5 feet 44 degrees northeast of B-1: Auger Probing to next sample depth

Refusal encountered at 5.5 feet.

END OF DRILLING AT 5.5 FT

W

AT

ER

L

EV

EL

S

EL

EV

AT

IO

N (F

T)

BL

O

W S/

6"

Plas c Limit Water Content Liquid Limit X─────────⚫─────────△

CLIENT:

City of Salem

PROJECT NAME:

Salem WTP Well Houses 4 & 5

PROJECT NO.: BORING NO.:

12:19229 B-1A

DRILLER/CONTRACTOR:

Blue Ridge Drilling, Inc.

SHEET:

SITE LOCATION:

1300 Tidewater Street, Salem, Virginia 24153

LOSS OF CIRCULATION

NORTHING:

3631694.6

EASTING:

11024858.1

STATION: SURFACE ELEVATION:

1026.0

BOTTOM OF CASING

THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN-SITU THE TRANSITION MAY BE GRADUAL

WL (First Encountered)

WL (Comple on)

WL (Seasonal High Water)

WL (Stabilized)

BORING STARTED:

BORING

COMPLETED:

EQUIPMENT:

ATV