Attachment 16 - GeoTech Report.pdf

ECS Midwest, LLC Geotechnical Engineering Report

Proposed Building Addition

Tomah VA Medical Center Tomah, Wisconsin

ECS Project Number 59:2048

April 3, 2020

April 3, 2020

Mr. Wes Bridges CB Design Group 950 North Washington Street Alexandria, VA 22314 Email: wbridges@cbdg‐ae.com

ECS Project No. 59:2048

Reference: Geotechnical Engineering Report Proposed Building Addition Tomah VA Medical Center Tomah, Wisconsin

Mr. Bridges:

ECS Midwest, LLC (ECS) has completed the subsurface exploration, laboratory testing, and geotechnical engineering analyses for the above‐referenced project. We performed our services in general accordance with our Proposal No. 59:2113‐GP, dated January 27, 2020. This report presents our understanding of the geotechnical aspects of the project, 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 you on this project. We would appreciate the opportunity to continue our services during the remainder of design and provide our services during construction to verify the assumptions of subsurface conditions made for this report. Please contact us should you have any questions concerning the information contained in this report, or if we can be of further assistance to you.

Respectfully submitted, ECS Midwest, LLC

Isaac MacMillan, E.I.T. Matthew A. Meyer, P.E.

Geotechnical Project Manager Geotechnical Department Manager imacmillan@ecslimited.com mmeyer@ecslimited.com

Proposed Building Addition April 3, 2020 ECS Project No. 59:2048 Page i

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1.0 INTRODUCTION

1.1 General

1.2 Scope of Services

1.3 Authorization

2.0 PROJECT INFORMATION

2.1 Project Location

2.2 Past Site History/Uses

2.3 Current Site Conditions

2.4 Proposed Construction

3.0 FIELD EXPLORATION

3.1 Field Exploration Program

3.2 Regional / Site Geology

3.3 Soil Survey Mapping

3.4 Subsurface Characterization

3.5 Groundwater Observations

4.0 LABORATORY SERVICES

5.0 DESIGN RECOMMENDATIONS

5.1 Building Design

5.1.1 Spread Footing Foundations

5.1.2 Floor Slabs

5.1.3 Site Retaining Walls

5.1.4 Seismic Design Considerations

6.0 SITE CONSTRUCTION RECOMMENDATIONS

6.1 Subgrade Preparation

6.1.1 Existing Utilities

6.1.2 Stripping and Initial Site Preparation

6.1.3 Special Subgrade Preparations – Foundations and Floor Slabs

6.1.4 Proofrolling

6.1.5 Site Temporary Dewatering

6.1.6 Subgrade Stabilization

6.2 Earthwork Operations

6.2.1 Engineered Fill Materials

6.2.2 Compaction

6.3 Foundation and Slab Observations

6.4 General Construction Considerations

7.0 CLOSING

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APPENDICES

Appendix A – Drawings & Reports

Site Location Diagram

Boring Location Diagram

Appendix B – Field Operations

Reference Notes for Boring Logs

Test Boring Logs B1‐20 through B4‐20

Appendix C – Supplemental Report Documents

Important Information about This Geotechnical‐Engineering Report

ECS Project No. 59:2048 Page 1

EXECUTIVE SUMMARY

This Executive Summary is solely provided to give a brief overview of the project findings. The summary is abbreviated. Information gleaned from the Executive Summary should not be utilized in lieu of reading the entire geotechnical report.

The geotechnical exploration performed for the proposed building addition included four (4) standard penetration test borings advanced to a depth of 25 feet below the existing grade.

The generalized soil profile indicated by the borings consisted of a topsoil layer overlying alluvial soils which extended to the boring termination depths. However, some of the borings encountered existing fill and possible soils which extended to depths ranging from 2 to 6 feet below the existing grade.

The encountered existing and posisble fill soils consisted of silty sand (SM), and the native alluvial soils consisted of silty sand (SM), sand with silt (SP‐SM), and sand (SP).

In our opinion, the proposed building addition could be suitably supported on a conventional shallow foundation system. However, the existing fill, possible fill, very loose soils, and organic soils encountered in the borings present concerns for the support of foundations and floor slabs. Please refer to the Special Subgrade Preparation – Foundations and Floor Slabs section of this report for additional details regarding the recommended over‐excavation of existing fill, very loose, and organic soils at this site.

In our opinion, the proposed addition could be suitably supported by a shallow foundation system designed for a net allowable bearing pressure of 2,000 pounds per square foot (psf). However, the allowable bearing pressure could be increased to 3,000 psf if the foundations will extend into the denser soils encountered below a depth of 6 feet below the existing grade. Please refer to the Foundation Design section of this report for additional design guidelines.

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1.0 INTRODUCTION

1.1 GENERAL

ECS prepared this report for the purpose of providing the results of our subsurface exploration and laboratory testing, site characterization, engineering analysis, and geotechnical recommendations for the design and construction of foundations, floor slabs, and site retaining walls for the proposed building addition. The report also includes our recommendations concerning geotechnical subgrade preparation, fill placement, dewatering and construction considerations.

1.2 SCOPE OF SERVICES

ECS performed four (4) standard penetration test borings within the vicinity of the proposed addition. We also implemented a laboratory‐testing program to characterize the physical and engineering properties of the subsurface soils.

This report discusses our exploration and testing procedures, presents our findings and evaluations, and includes the following.

A brief description of our field and laboratory test procedures and results.

A description of the observed surface topographical features and site conditions.

A description of area and site geologic conditions.

A description of the interpreted subsurface soil stratigraphy with pertinent available physical properties.

Records of subsurface exploration (test boring logs).

An allowable soil bearing pressure for conventional shallow foundations (spread footings) and estimates of predicted foundation settlement.

General recommendations for slab‐on‐grade design including subgrade modulus, subgrade improvements and underslab drainage.

Recommendations for site retaining wall design.

Recommended seismic site class.

Recommendations for site preparation and construction of engineered fills, including an evaluation of on‐site soils for use as compacted engineered fills, and delineation of potentially unsuitable soils.

Evaluation and recommendations relative to groundwater control.

1.3 AUTHORIZATION

ECS provided services in accordance with our Proposal No. 59:2113‐GP, dated January 27, 2020, as authorized by Mr. Wes Bridges with CB Design Group on January 27, 2020, and includes the Terms and Conditions of Service outlined in the Proposal.

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2.0 PROJECT INFORMATION

2.1 PROJECT LOCATION

The project site is located at the existing VA Medical Center in Tomah, Wisconsin. Specifically, the proposed building addition will be located near the southeast corner of existing Building 404. The site location is shown in Figure 2.1.1 and on the Site Location Diagram in Appendix A of this report.

Figure 2.1.1 Site Location (approximately outlined in red)

2.2 PAST SITE HISTORY/USES

ECS reviewed aerial photographs of the subject site dated 1999, 2003, 2005, 2006, 2008, 2010, 2013, and 2017 available on Google Earth and ESRI Map Service. The aerial photographs indicated Building 404 remained relatively unchanged throughout this time period. Further, the photographs indicated Building 405 was constructed to the east of the project site between 2013 and 2017.

2.3 CURRENT SITE CONDITIONS

At the time of our exploration, the site of the proposed addition consisted of a landscape area. The existing ground surface was relatively flat. ECS determined the surface elevations at the boring locations to be EL. 951.3 feet at Boring B1‐20 through B3‐20 and 951.4 feet at Boring B4‐20.

2.4 PROPOSED CONSTRUCTION

Based on information provided by C&S Engineers, Inc. on March 23, 2020, ECS understands the proposed project will consist of a new 4,560 square foot addition to Building 404. The proposed addition will be a three story steel moment frame structure with cold formed steel cladding and brick veneer. Further, we understand the finished floor elevation of the addition will match the existing building at EL. 953.44 feet, with a crawlspace elevation 6 feet below the floor and accessible attic space above. The maximum unfactored foundation loadings will not exceed 500 kips for

ECS Project No. 59:2048 Page 4 interior columns, 300 kips for exterior columns and columns adjacent to existing foundations, and

3.5 kips per lineal foot for continuous wall foundations.

If ECS’ understanding of the project is not correct or the design changes, especially if the structural loads or elevations are different, please contact ECS so that we may review these changes and revise our recommendations, as appropriate.

Where the borings encounter subsurface conditions that might be detrimental to the support of the proposed construction, ECS has assumed the owner will have an acceptable risk level if the detrimental material remains in place. With this in mind, this report assumes the owner would only be willing to accept a low risk for foundation and utility settlement in excess of 1 inch and floor slab settlement in excess of ½ inch. In addition, we assume the owner would be willing to accept a moderate risk for reduced pavement performance. If these assumptions concerning the owner's acceptable risk level are incorrect, we should be immediately contacted so we can review our recommendations in light of the changed acceptable risk level.

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3.0 FIELD EXPLORATION

3.1 FIELD EXPLORATION PROGRAM

ECS planned the field exploration with the objective to characterize the project site in general geotechnical and geological terms, and to evaluate subsequent field and laboratory data to assist in the determination of geotechnical recommendations.

On February 28, 2020, ECS drilled four (4) standard penetration test borings within the limits of the proposed addition. The drill crew advanced each boring to a depth of 25 feet below the existing grade using a truck‐mounted Diedrich D50 rotary drill rig equipped with continuous flight hollow stem augers (HSA). Prior to drilling, ECS contacted the State of Wisconsin Utility One‐Call Center, Digger’s Hotline, as well as a private utility locating service to clear and mark underground utilities in the vicinity of the project site.

ECS personnel identified the test boring locations in the field using a measuring tape relative to existing site features prior to mobilization of our drilling equipment. The approximate as‐drilled test boring locations are shown on the Boring Location Diagram in Appendix A of this report. ECS personnel determined the surface elevation at the boring locations using conventional leveling techniques, and referenced each of the boring surface elevations to the finished first floor of existing Building 404. According to the preliminary grading and erosion control plan dated February 12, 2020 provided by Quetica, L.L.C., we understand this temporary benchmark to have an elevation of EL. 953.44 feet. We assumed this elevation to be referenced to the North American Vertical Datum (NAVD 88). The surface elevation at each boring location can be found on the boring logs included in Appendix B of this report. Ground surface elevations determined without professional survey are approximate.

The drill crew conducted standard penetration tests (SPTs) in the boreholes at regular intervals in general accordance with ASTM D1586. The obtained standard penetration resistances provide a general indication of soil relative density and consistency. The drill crew chief visually and manually classified the samples in the field using ASTM D2488 as a guide. Field personnel then collected small representative soil samples and returned them to the laboratory for further observation and verification of the field classification

Some borehole backfill settlement or expansion can and will occur over time. Monitoring the boreholes after the initial drilling activities is not within our scope. Settlement or expansion of the borehole backfill can create a trip hazard and should be carefully monitored by the client.

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3.2 REGIONAL / SITE GEOLOGY

Based on the University of Wisconsin Extension Geological and Natural History Survey and U.S.

Geological Survey1,2 the site of the proposed construction lies within Phanerozoic bedrock of the Cambrian System consisting of sedimentary rocks of Paleozoic Age. The bedrock formation generally consists of sandstone with some dolomite and shale, and includes the Trempealeau, Tunnel City, and Elk Mound Groups.

The soil overburden is generally 50 to 100 feet thick and the soils generally consist of nearly level to moderately steep, excessively drained to moderately well drained loamy and sandy soils on stream terraces and uplands. The depth to bedrock profile is illustrated in Figure 3.2.1 below and the approximate site location is marked with a red circle.

(Source: Depth to Bedrock in Wisconsin, University of Wisconsin Extension Geological and Natural History Survey)

Figure 3.2.1

3.3 SOIL SURVEY MAPPING

According to the Soil Survey from the USDA ‐ Natural Resources Conservation Service (websoilsurvey.nrcs.usda.gov), which provides soil information to a shallow depth (generally less than 5 feet), the soils in the site area are mapped as Bilmod sandy loam (466A). These soils are associated with lake terraces on glacial lakes with loamy alluvium over stratified sandy and loamy alluvium. These soils are moderately well drained, classified as being in Hydrologic Soil Group A, and have a moderate potential for frost action.

1 Trotta, L.C. and Cotter, R.D. Depth to Bedrock in Wisconsin. University of Wisconsin Extension Geological and Natural History Survey, U.S. Geological Survey, USGS, 1973.

2 Mudrey, M.G., Brown B.A., and Greenburg, J.K. Bedrock Geologic Map of Wisconsin. University of Wisconsin Extension Geological and Natural History Survey, 1982.

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Soil mapping of the site vicinity is presented in Figure 3.3.1 of this report.

(Source: USDA ‐ Natural Resources Conservation Service)

Figure 3.3.1 Soil Survey Information

3.4 SUBSURFACE CHARACTERIZATION

The encountered subsurface conditions in the borings appeared to match published geological mapping. Table 3.4.1 of this report provides a generalized characterization of the soil strata encountered at the boring locations during our subsurface exploration. For subsurface information at a specific test boring location, refer to the boring logs in Appendix B of this report.

Table 3.4.1 Generalized Subsurface Stratigraphy

Approximate Depth Range

(feet) Strata Description

SPT(1)

N‐value Range (bpf)

Surface ‐‐‐ Approximately 6 to 18 inches of topsoil N/A

2 – 6 I Fill/possible fill: silty sand (SM), encountered in Boring B1‐20, B2‐20 and B4‐20

4 – 9

End of Borings

II

Alluvium: silty sand (SM), sand with silt (SP‐ SM), sand (SP)

4 – 25

Notes: (1) Standard Penetration Test.

Where the drill crew used discontinuous material sampling intervals at the test borings, ECS inferred conditions between sample intervals. The soil stratification shown on the boring logs represents the interpreted soil conditions at the actual boring locations. Variations in the stratification can occur between sample intervals and boring locations. The subsurface conditions at other times and locations on the site may differ from those found at the boring locations. If different site conditions are encountered during construction, ECS should be contacted to review our recommendations relative to the new information.

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The soil classifications noted on the boring logs may not be representative of the entire soil matrix because of the limitations of the split‐spoon sampler, which has a 1⅜‐inch inside diameter.

Materials larger than the 1⅜‐inch inside diameter of the split‐spoon sampler cannot be collected and observed directly. Where possible, the drill crew noted on the boring logs the estimated depth of larger diameter materials, such as cobbles, based on things such as changes in the observed drilling resistance and auger cuttings.

3.5 GROUNDWATER OBSERVATIONS

The drillers observed the boreholes for the presence of groundwater during drilling. We observed groundwater during sampling at a depth of 8 feet below the existing grade in Boring B1‐20, at 6 feet in Boring B2‐20 and B3‐20, and at 7 feet in Boring B4‐20. However, the crew used mud rotary drilling methods to advance the borings below a depth of 15 feet. Therefore, the drillers did not observe a groundwater level at the completion of drilling operations because the drilling mud obscures it.

Because the borings encountered groundwater in relatively free‐draining sandy soil, in our opinion, the observed groundwater levels would be a reasonable indication of the static groundwater condition at the time of drilling. However, variations in the long term water table elevation may occur as a result of seasonal variations in precipitation, evaporation, surface water runoff, lateral drainage conditions, construction activities and other factors. The time of year and the weather history during the advancement of the borings should be considered when estimating groundwater levels at other points in time.

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4.0 LABORATORY SERVICES

The laboratory services performed by ECS for this project included select tests on samples retained from our field exploration operations. The following paragraphs briefly describe the results of the completed laboratory services program.

A geotechnical engineer visually classified each collected soil sample from the test borings on the basis of texture and plasticity using the Unified Soil Classification System (USCS) and ASTM: D2488, Standard Practice for Description and Identification of Soils (Visual‐Manual Procedures) as a general guideline. After classification, the geotechnical engineer grouped the various soil types into the major zones noted on the test boring logs in Appendix B of this report. The group symbols for each soil type are indicated in parentheses before the soil descriptions on the test boring logs. The stratification lines designating the interfaces between earth materials on the test boring logs are approximate; in‐situ, the transitions may be gradual.

The laboratory testing program included tests for moisture content and organic content on a select soil sample recovered from the borings in accordance with relevant ASTM procedures. The laboratory test results can be found in the following table.

Table 4.0.1 Laboratory Test Results

Boring Number

Sample Number

Test Depth (ft)

Moisture Content

Organic Content

B1‐20 S‐3A 4 – 6 15 2.3

The soil samples will be retained in our laboratory for a period of 60 days, after which, they will be discarded unless other instructions are received as to their disposal.

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5.0 DESIGN RECOMMENDATIONS

5.1 BUILDING DESIGN

The following sections provide recommendations for foundation design, soil supported slabs, and site retaining walls.

5.1.1 Spread Footing Foundations

Based on the soils encountered in the borings, in our opinion, the proposed building addition can be suitably supported by conventional shallow spread footing foundations (individual column footings and continuous wall footings) provided the contractor prepares subgrades and engineered fills as discussed herein and the maximum foundation and floor slab loads will not exceed the values outlined in the Proposed Construction section of this report. ECS recommends utilizing the parameters listed in Table 5.1.1 of this report for the foundation design. The structural engineer should design the footings and determine the actual footing size and steel reinforcing requirements.

Table 5.1.1 Foundation Design Design Parameter Column Footing Wall Footing

Net Allowable Bearing Pressure1,2 2,000 psf 2,000 psf

Acceptable Bearing Soil Material

Loose to medium dense native sands (Stratum II) or Engineered Fill

Loose to medium dense native sands (Stratum II) or Engineered Fill

Competent Soils Designated Suitable for the Allowable Bearing Pressure

N ≥ 5 bpf sand N ≥ 5 bpf sand

Minimum Width 30 inches 18 inches

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

48 inches (heated structure)

66 inches (non‐heated structure)

Estimated Total Settlement 1 inch 1 inch

Estimated Differential Settlement3 ½ inch between columns ½ inch over 50 feet

The native soils below the anticipated foundation bearing elevation at the boring locations are expected to be suitable for support of the proposed structure. However, if the foundation excavations encounter native sand soils having an N‐value of less than 5 bpf within one‐half footing width of foundations, existing fill soils below the footing bearing elevation, or soils containing greater than 5 percent organics, these soils should be removed and replaced with compacted engineered fill. Any undercut for foundations should be backfilled as recommended in the Foundation and Slab Observations section of this report.

1. Net allowable bearing pressure is the applied pressure in excess of the surrounding overburden soils above the base of the foundation.

2. Specialty testing, such as pressuremeter tests, may justify the use of a higher net allowable bearing pressure than noted above.

3. Note the differential settlement between the addition and existing construction may approach the estimated total settlement.

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As an alternative to the bearing pressure recommended above, in our opinion, the allowable bearing pressure could be safely increased to 3,000 psf if the foundations are extended into the medium dense sandy soils with SPT N‐values of 7 bpf or higher encountered at a depth of 6 feet below the existing grade.

We recommend the excavation/backfill of foundations be observed and tested full‐time by ECS to check that the soil bearing pressure is consistent with the boring log information obtained during the geotechnical exploration. If the maximum column and wall loads will exceed the estimated values outlined in this report, then notify ECS so we may revise our recommendations as needed.

The foundation bearing grade should be observed and tested, and any undercut for foundations backfilled as recommended in the Foundation and Slab Observations section of this report. As an alternative to soil replacement, strip footing pads could be stepped or thickened, and isolated column pads could be uniformly thickened to extend through unsuitable bearing materials. ECS recommends a structural engineer design stepped or thickened footings.

Adjacent Existing Foundations: Care must be taken to protect the existing structure. Excavations must be done so as to not undermine the existing construction, or otherwise adversely affect the structural integrity of the existing building. Further, differential settlement may occur between the new addition and the existing building. Therefore, we recommend consideration be given to incorporating a complete through joint between the new addition and the existing building. The joint should be capable of tolerating up to 1 inch of potential differential settlement.

Excavations should not extend below adjacent existing foundations unless the contractor provides underpinning or other forms of support. We do not know if additional load will be placed on the existing footings from the new addition. ECS must be contacted if existing foundations will be subjected to additional loads. We recommend test pits be performed in the presence of an ECS representative to determine if existing foundations bear upon fill or native soil and to what degree loads on the existing building foundations may increase. Additional load added to the existing footings will result in some additional settlement. The actual settlement will depend on the added load, the existing load, size of the existing footings, and strength and settlement characteristics of the support soil.

We recommend the foundations for the addition bear at the same elevation as the existing nearby foundations. When the actual existing and proposed building foundation systems and depths can be confirmed, contact ECS to evaluate whether our recommendations need to be altered to accommodate the existing foundation system accordingly. If the new and existing footings will bear at different elevations, a structural engineer should evaluate the stresses to be imposed on the lower foundation system and confirm the structural integrity of the existing building and new addition will be maintained. Parallel foundations should be at least 1.5 footing widths apart (whichever is larger, either existing or new) to help reduce the additional stress imposed on the existing foundations, unless a geotechnical engineer determines the over‐lapping stress imposed by the existing and new foundations are within acceptable limits for the bearing soil. Where parallel foundations are wider than 4 feet apart, their different elevations should not place them within a 45‐degree envelope extending upward and downward from the outside edges of the foundations.

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5.1.2 Floor Slabs

Some of the borings encountered existing fill and possible fill soils which extended to a depth of between 2 and 6 feet below the existing grade. We recommend the over‐excavation of existing fill from within 2 feet of floor slabs. The sections in this report entitled Subgrade Preparation and Earthwork Operations provide recommendations to be followed for the design and construction of the slab‐on‐grade for the building. In our opinion, the native soils and engineered fill placed from a suitable native soil subgrade, and compacted as recommended in this report, could support a concrete slab‐on‐grade. Based on the anticipated subgrade soils and floor loading, the graphic in Figure 5.1.1 of this report depicts our general soil‐supported slab recommendations.

Figure 5.1.1

1. Concrete Slab: Minimum 5 inches thick

2. Drainage Layer: Minimum 6 inches thick

3. Drainage Layer Material: GRAVEL (GP, GP‐GM, GW, or GW‐GM) having a maximum aggregate size of 1 inch and no more than 10 percent passing the No. 200 sieve.

4. Compacted Subgrade: Compacted to at least 95 percent maximum dry density per ASTM D1557.

A thicker slab may be needed depending on the actual floor loads. The structural engineer should determine the actual slab thickness and steel reinforcing requirements. Adequate construction joints, contraction joints and isolation joints should be provided in the slab to reduce the impacts of cracking and shrinkage. Please refer to ACI 302.1R04 Guide for Concrete Floor and Slab Construction for additional information regarding concrete slab joint design.

We recommend slabs‐on‐grade be underlain by a granular drainage layer placed on a properly prepared subgrade as recommended in the Site Construction Recommendations section. The granular material will serve as a capillary break, which if properly designed and installed, can sometimes eliminate the need for a moisture retarder and can assist in more uniform curing of concrete. Where a vapor retarder is considered to provide additional moisture protection, special attention should be given to the surface curing of the slabs to reduce uneven drying of the slabs and associated cracking and/or slab curling. The use of a blotter or cushion layer above the vapor retarder can also be considered for project specific reasons. Please refer to ACI 302.1R04 Guide for Concrete Floor and Slab Construction and ASTM E 1643 Standard Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs for additional guidance on these issues.

Subgrade Modulus: Provided the subgrade is prepared, and the contractor places any engineered fill and the granular drainage layer as recommended in this report, the slab may be designed assuming a modulus of subgrade reaction, kv1 of 200 psi/in (pounds per square inch per inch).

Concrete Slab (1) Vapor Retarder (in accordance with ACI 302)

Granular Capillary Break/Drainage Layer (2), (3)

Compacted Subgrade (4)

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Slab Isolation: Ground‐supported slabs should be isolated from the foundations and foundation‐ supported elements of the structure to reduce shear and bending stresses in the floor caused by differential movement between the foundations and slab. Where the structural configuration prevents the use of a free‐floating slab, the slab should be designed with suitable reinforcement and load transfer devices to preclude overstressing of the slab.

Frost Susceptible Areas: Exterior aprons and sidewalks, and at‐grade floor slabs in unheated or poorly heated structures, such as at doorways and entrance/exit vestibules, may be susceptible to frost heave movement during freezing weather. Additional insulation, installation of subgrade drainage, and/or replacement to the frost depth with non‐frost‐susceptible backfill should be considered for these areas. Pavement and ground surface grades are recommended to be sloped away from the building and flatwork, to reduce water infiltration and potential frost heave problems.

5.1.3 Site Retaining Walls

Site retaining walls are often constructed from the “bottom‐up” and therefore the type of soil used to backfill the wall is chosen or specified by contract. The lateral earth pressures developed behind site retaining walls is a function of the backfill soil type within an approximate 45‐degree angle from the base of the wall upward, often referred to as the Critical Zone.

Lateral Earth Pressures: Retaining walls should be designed to withstand the lateral earth pressures exerted by the backfill. We anticipate that retaining walls associated with the building structures will be rigid walls restrained from rotation by the floor slab. For rigid walls, the "At Rest" (ko) soil condition should be used in the wall design and evaluation. For walls that are free to deflect at their tops, the "Active" (ka) soil condition should be used in the wall design and evaluation. Any surcharge loads imposed within a 45 degree slope of the base of the wall should be considered in the below‐ grade wall design. Using the Rankine method to calculate these pressures, the parameters in Table

5.1.2 are recommended to be used for retaining wall designs. Please contact us for additional consultation if a different method will be used for determining the lateral earth pressures. These parameters are based on the assumption free‐draining granular aggregate meeting the recommendations herein for retaining wall backfill will be placed throughout the “Critical Zone.”

Table 5.1.2 Lateral Earth Pressures

Soil Type Friction Angle, Moist Unit Weight

Active Earth Pressure, Ka

Passive Earth Pressure, Kp

At‐Rest Earth Pressure, Ko

Retaining Wall Backfill

30° 120 pcf 0.33 3.0 0.50

Existing Fill: Silty Sand (SM)

32° 125 pcf 0.31 3.3 0.47

Native Silty Sand

(SM)

34° 125 pcf 0.28 3.5 0.44

Native Sand with Silt (SP‐SM), Sand

(SP)

34° 120 pcf 0.28 3.5 0.44

1 Assumes a flat 0° backslope at the top of retaining walls. Please contact ECS for revised values if the retained soil will have a backslope.

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To resist shear forces, ECS recommends a maximum friction factor of 0.35 for foundations in contact with our recommended aggregate engineered fill or the native sandy soils encountered by the test borings.

Retaining Wall Backfill: Soils used as backfill within the Critical Zone behind retaining walls should have USCS classifications of (GW, GP, SW, SP, GW‐GM, GP‐GM, SW‐SM, SP‐SM, GM or SM) with a maximum of 15 percent fines (i.e., percentage passing No. 200 Sieve size), and minimum angle of internal friction of 30 degrees when compacted to a minimum of 95 percent of its maximum dry density per ASTM D1557. Any soil within the Critical Zone not meeting these criteria should be removed, as determined by ECS at the time of construction.

Foundation Drains: Retaining walls should be provided with a foundation drainage system to relieve hydrostatic pressures which may develop in the wall backfill. This system should consist of a 4‐inch perforated, closed joint drain line located along the backside of the walls above the top of the footing. The drain line should be surrounded by a minimum of 6 inches of AASHTO Size No. 57 Stone wrapped with an appropriate non‐woven filter fabric, such as Mirafi 140‐N or equivalent. The drain pipe systems should connect to the storm sewer system for removal, or common sump crocks equipped with sump pumps that discharge water to the ground surface, away from the below‐ ground walls. We recommend submersible sump pumps and sealed sump crock lids to lessen the in‐flow of subsurface gases, such as radon. The project architect should determine the sump pump locations based upon architectural and structural details of the building. The sump pumps should be equipped with generator or battery back‐up systems to reduce water problems in the event of a power failure.

Wall Drains: All site retaining walls should be drained so that hydrostatic pressures do not build up behind the walls. Wall drains may consist of a 12‐inch wide zone of free draining gravel, such as AASHTO No. 57 Stone, placed directly behind the wall and separated from the soils beyond with a non‐woven filter fabric. Alternatively, the wall drain can consist of a suitable geocomposite drainage board material. The wall drain should be hydraulically connected to the foundation drain.

5.1.4 Seismic Design Considerations

Seismic Site Classification: The International Building Code (IBC) requires the Site Class for seismic design be based on the upper 100 feet of the soil profile. The three parameters used to classify sites are the shear wave velocity (vs); the undrained shear strength (su); and the Standard Penetration Resistance (N‐value). The seismic Site Class definitions for the weighted average of shear wave velocity, shear strength or SPT N‐value in the upper 100 feet of the soil profile are shown Table 5.1.3.

Table 5.1.3 Seismic Site Class Site Class

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

Su value (psf)

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

B Rock 2,500 < Vs ≤ 5,000 fps N/A N/A

C Very dense soil and soft rock 1,200 < Vs ≤ 2,500 fps >50 ≥2,000

D Stiff Soil Profile 600 ≤ Vs ≤ 1,200 fps 15 to 50 1,000 to 2,000

E Soft Soil Profile Vs < 600 fps <15 ≤1,000

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Our scope of services included advancement of the borings to a maximum depth of 25 feet. Based on this data and our experience with the soils in the general site vicinity and engineering judgment, in our opinion the site soils can be characterized as Site Class D. Site Class D is described as stiff soil for the top 100 feet of the site soil profile. The Site Class should not be confused with the Seismic Design Category, which the Structural Engineer typically determines. If a more favorable Site Class is beneficial to the project, ECS would be pleased to discuss additional testing capabilities in this regard.

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6.0 SITE CONSTRUCTION RECOMMENDATIONS

6.1 SUBGRADE PREPARATION

6.1.1 Existing Utilities

ECS recommends either abandoning or relocating existing utilities outside the proposed addition areas. Utilities not reused should be capped‐off and removed or properly abandoned in‐place in accordance with local codes and ordinances. The excavations for utilities to be removed in the influence zone of new construction are recommended to be backfilled with engineered fill. Grading operations must be done carefully so that existing utilities are not damaged or disturbed. Utility invert elevations, depths and sizes should be checked relative to the planned foundation elevations to determine what specific concerns are present.

6.1.2 Stripping and Initial Site Preparation

The subgrade preparation should include stripping organic soils (topsoil) and any other soft/very loose or otherwise unsuitable materials from the 10‐foot expanded building limits and 5 feet beyond the toe of engineered fills, where feasible. ECS should be called on to observe and document that topsoil and other unsuitable surficial materials have been removed prior to the placement of engineered fill or construction of structures. Please note, topsoil removal should not be based on soil coloration alone. After removal of the root mat, it may be possible to leave exposed darker soils in place provided the soil contains no more than 5 percent organic matter as determined by ASTM D2974, has the recommended strength characteristics and is stable under proofroll. A landscape architect should approve any topsoil or other materials proposed for use in future landscape areas.

6.1.3 Special Subgrade Preparations – Foundations and Floor Slabs

Based primarily on information obtained from the soil borings, in ECS's opinion, the proposed structures could be supported on a spread footing foundation system. However, the existing fill, possible fill, and very loose soils encountered in the borings present concerns for the support of foundations and floor slabs.

Existing Fill and Possible Fill

The presence of existing fill and possible fill soils the borings provides a concern for the support of shallow foundations and floor slabs. This material extended to a depth of between 2 feet and 6 feet below the existing grade in the borings. For the possible fill, in the absence of deleterious material (such as organics, bricks or concrete), difficulty can occur in distinguishing the difference between native soil and clean fill from a small sample. Although we anticipate the foundations may extend below this material in some areas, the owner should be aware of the risk for total and/or differential settlement in excess of 1 inch associated with constructing foundations and floor slabs on undocumented fill. Undocumented fill has a risk for higher settlement because of potential variations in the density of this material. The risk also increases where the undocumented fill contains more than 5% organics. An organic content test performed on a sample of the possible fill encountered in Boring B1‐20 indicated the soil had an organic content of 2.3 percent.

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Based primarily on the standard penetration N‐values and organic content test results, in our opinion the risk of total and/or differential foundation and floor slab settlement in excess of 1 inch and ½ inch, respectively, associated with the existing fill at this site would be moderate to high.

Since we assume the owner would not be willing to accept these risks, ECS recommends removing all encountered existing fill from below the foundations and from within 2 feet of floor slabs, and replacement of it with compacted engineered fill in accordance with the Earthwork Operations section of this report.

Very Loose Soils

The very loose (N < 5 bpf) soils encountered in the borings provide another concern for the support of foundations. Boring B1‐20, B2‐20, and B3‐20 encountered very loose soils within the upper 2 to 6 feet of the soil profile. Based on the anticipated foundation loadings and bearing elevation we anticipate special subgrade preparation will be required to remove these very loose soils from below the foundations. The owner should be aware that very loose soil is highly compressible, would be subject to general shear failure at very light loadings, and has a very high susceptibility to disturbance by construction activity. Because of these factors, foundations bearing within one footing width of the very loose soil layer would have a high risk that settlement could exceed 1 inch.

Because we anticipate the owner would not be willing to accept this risk for total settlement in excess of 1 inch, we recommend over‐excavating all very loose soils encountered within one footing width of foundations and then refilling the over‐excavation with compacted engineered fill in accordance with the Earthwork Operations section of this report.

Summary

Because we assume the owner would only be willing to accept a low risk for excessive foundation settlement, we recommend the following:

1. Over‐excavate all encountered existing fill from below the foundations. This includes shallow interior footings placed directly below floor slabs.

2. Remove as much as 2 feet of the existing fill from below the floor slabs and replace with compacted engineered fill.

3. If field observations indicate the possible fill is native, not undocumented fill, then it could be left in place below the foundations and floor slabs providing it has suitable strength.

4. Remove all very loose soils from within one footing width of foundations and replace with compacted engineered fill.

ECS wishes to note, footing excavations subcut below the footing elevation should be oversized one foot horizontally in each direction for every two feet of engineered fill placed below the foundation.

In addition, we strongly recommend ECS document the material exposed in the excavations does not exhibit obvious characteristics that would adversely affect the performance of the foundation system.

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6.1.4 Proofrolling

After the removal of unsuitable surface materials, cutting to the proposed subgrade, and prior to the placement of engineered fill or other construction materials, the exposed subgrade should be observed by ECS. The contractor should thoroughly proofroll the exposed subgrade with previously approved construction equipment having a minimum axle load of 10 tons (e.g. large smooth drum roller). The contractor should traverse the areas subject to proofrolling by the equipment in two perpendicular (orthogonal) directions with overlapping passes of the vehicle under the observation of ECS. This procedure is intended to assist in identifying any localized yielding materials. Unstable or pumping subgrade areas identified during the proofroll should be marked for repair prior to the placement of any subsequent engineered fill or other construction materials. Unstable subgrade repair methods, such as undercutting or moisture conditioning or chemical stabilization, should be discussed with ECS to determine the appropriate procedure(s) with regard to the existing conditions causing the instability. A test pit(s) may be excavated to explore the shallow subsurface materials in the area of the instability to aid in determining the cause of the observed unstable materials and to assist in the evaluation of the appropriate remedial action to stabilize the subgrade.

Some slab areas may be inaccessible to appropriate proofroll equipment. These areas should be evaluated with hand‐operated testing equipment to check the subgrade support characteristics.

Near surface subgrade soils having a high moisture content and/or those having N‐values less than 10 bpf may not pass a proofroll, and may need to be undercut or repaired. Some undercutting or repair of unstable subgrade soils should be anticipated during slab subgrade preparation. If construction will occur during wet times of the year (such as during the spring or fall months) or immediately following extended periods of rain, then seasonal reduction of the near surface soil strength will occur. This may cause additional unstable or pumping subgrade areas for constructability concerns. The actual quantity of the subgrade undercut or stabilization should be determined with the assistance of ECS at the time of construction.

6.1.5 Site Temporary Dewatering

Based on the groundwater levels observed in the test borings, we anticipate the long term static groundwater level at this site is below the anticipated excavation depths. Where excavations extend less than 2 feet below the groundwater level, initial attempts to control water may be accomplished by pumping from sump pits in the excavation bottom, which are backfilled with AASHTO Size No. 57 Stone or open‐graded bedding material. If water control cannot be maintained with sump pumps, or where excavations extend more than 2 feet below the groundwater level, dewatering likely will require installation of a well‐point system or some other dewatering system to aid in maintaining the groundwater level below the excavation bottom. A qualified dewatering contractor should be consulted if groundwater cannot be satisfactorily controlled through the use of sump pumps.

Lowering the static groundwater level can adversely affect nearby structures, utilities and other construction. We recommend any dewatering scheme be reviewed by ECS and a contractor who specializes in this type of work prior to its implementation.

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6.1.6 Subgrade Stabilization

Subgrade Benching: Fill should not be placed on ground with a slope steeper than 5H:1V. The ground should be benched so as to allow for fill placement on a horizontal surface.

Subgrade Compaction: Upon completion of subgrade documentation, the exposed subgrade within the 10‐foot expanded building limits should be moisture conditioned to within +/‐ 3 percent of the soil’s optimum moisture content to a depth of 10 inches, and be compacted with suitable equipment (minimum 10‐ton vibratory roller for granular soils). The subgrade within the expanded building limits should be compacted to a dry density of at least 95 percent of the Modified Proctor maximum dry density (ASTM D1557). Beyond these areas, compaction should be to at least 90 percent. ECS should be called on to document the achievement of proper subgrade compaction.

Subgrade Compaction Control: The expanded limits of the proposed construction areas should be well defined, including the limits for structures, pavements, fills, and slopes, etc. We recommend performing field density testing of subgrade soils at the frequencies listed in Table 6.1.1 of this report.

Table 6.1.1 Frequency of Subgrade Compaction Testing

Location Frequency of Tests

Expanded Building Limits 1 test per 2,500 sq. ft.

Other Non‐Critical Areas 1 test per 10,000 sq. ft.

Subgrade Stabilization: Is some areas, particularly low‐lying, wet areas of the site, undercutting of excessively soft/very loose materials may be considered inefficient. In such areas the use of a reinforcing geotextile or geogrid might be employed, under the advisement of ECS. Suitable stabilization materials may include medium duty woven geotextile fabrics or geogrids. The suitability and employment of reinforcing or stabilization products should be determined in the field by ECS personnel, in accordance with project specifications.

6.2 EARTHWORK OPERATIONS

6.2.1 Engineered Fill Materials

Product Submittals: Prior to placement of engineered fill, representative bulk samples (about 50 pounds) of on‐site and off‐site borrow should be submitted to ECS for laboratory testing, which will include natural moisture content, grain‐size distribution, and moisture‐density relationships for compaction. Import materials should be tested prior to being hauled to the site to determine if they meet project specifications.

Satisfactory Engineered Fill Materials: Engineered fills should consist of approved materials, free of organic matter and debris, contain no particle sizes greater than 3 inches in the largest dimension, and have a Liquid Limit and Plasticity Index less than 40 and 15, respectively. Open‐ graded materials, such as coarser sands and gravels (SP and GP), which contain void space in their mass should not be used in engineered fills unless properly encapsulated within a filter geotextile.

If the fill is to provide non‐frost susceptible characteristics, it must be classified as a clean GW, GP, SW or SP per Unified Soil Classification System (ASTM D‐2487).

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Unsatisfactory Materials: Unsatisfactory engineered fill materials, which do not satisfy the requirements for suitable materials, include topsoil and organic materials (PT, OH, OL), silt (ML), elastic Silt (MH), silty clay (CL‐ML) and high plasticity clay (CH). Topsoil is not recommended to be used as engineered fill, but may be suitable for use within future landscape areas. A landscape architect should approve any topsoil materials proposed for use in future landscape areas.

Pea gravel is not recommended to be used as engineered fill. Pea gravel has round/smooth characteristics, no fines and does not interlock when compacted, which makes it more susceptible to future movement and instability resulting in excessive and variable settlement.

On‐Site Borrow Suitability: The on‐site soil may be feasible to use as engineered fill, but should be further evaluated by ECS prior to its use. On‐site soil used as engineered fill must not contain an adverse amount of organic matter, and must be free of frozen matter, deleterious materials, over‐ sized material (maximum 3‐inch particle diameter), or chemicals that may result in the material being classified as “contaminated.” Depending on the conditions at the time of construction, the use of on‐site soil for foundation support may not be practical, and use of an imported high quality granular material may be needed for foundation support. The soils must be compacted within a narrow range of the materials optimum moisture content. The suitability of engineered fill materials should be checked by ECS prior to placement.

6.2.2 Compaction

Engineered Fill Compaction: Engineered fill within the expanded building limits should be placed in maximum 8‐inch thick loose lifts, moisture conditioned as necessary to within +/‐ 3 percent of the soil’s optimum moisture content, and be compacted with suitable equipment to a dry density of at least 95 percent of…