Updated Geotech Report 40.1938r 06.22.2020.pdf

ECS Mid-Atlantic, LLC

Subsurface Exploration and Geotechnical Engineering Services

Erie VAMC – Primary Care Renovation/Addition

City of Erie, Erie County, Pennsylvania

ECS Project Number 40:1938

May 26, 2020 Revised June 22, 2020

May 26, 2020

Revised June 22, 2020

Mr. Paul Wes Bridges CB Design Group 950 North Washington Street, Suite 100 Alexandria, Virginia 22314

ECS Project No. 40:1938

Reference: Subsurface Exploration and Geotechnical Engineering Services Erie VAMC – Primary Care Renovation/Addition City of Erie, Erie County, Pennsylvania

Dear Mr. Bridges:

As authorized by the acceptance of ECS Mid-Atlantic, LLC (ECS) Proposal No. 40:1709-GP, dated January

04, 2019, we have completed the subsurface exploration and geotechnical engineering analysis for the above-referenced project in Erie County, Pennsylvania.

The enclosed report discusses the subsurface exploration procedures, presents the results of our subsurface exploration, laboratory testing programs, and presents our geotechnical considerations for the proposed addition. Additional information with regard to construction considerations, as well as other factors which may influence construction at the site, are discussed in detail in the accompanying report. We have reviewed The International Building Code (IBC) 2018 seismic classification requirements for the site. This report has been revised to reflect these changes.

We have enjoyed being of service to CB Design Group on this project. If you have any questions with regard to the information and recommendations presented in the accompanying report, or if we may be of further assistance to you, please do not hesitate to contact us.

Respectfully submitted, ECS Mid-Atlantic, LLC

Michael P. Krepsik, P.E. Jeffrey A. Shelton, P.E., LEED® AP

Geotechnical Department Manager Branch Manager/Principal Engineer mkrepsik@ecslimited.com jshelton@ecslimited.com mailto:mkrepsik@ecslimited.com mailto:jshelton@ecslimited.com

Erie VAMC – Primary Care Renovation/Addition Revised June 22, 2020 ECS Project No. 40:1938 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

2.4.1 Site Civil Features

2.4.2 Structural Information/Loads

3.0 FIELD EXPLORATION

3.1 Field Exploration Program

3.1.1 Test Borings

3.2 Regional/Site Geology

3.3 Mine Subsidence Mapping

3.4 Soil and Rock Characterization

3.5 Groundwater Observations

4.0 LABORATORY TESTING

5.0 DESIGN RECOMMENDATIONS

5.1 Building Design

5.1.1 Building Foundations

5.1.2 Ground Supported Slabs

5.1.3 Temporary Excavation Support

5.1.4 Below-Grade Walls

5.1.5 Seismic Design Considerations

5.2 Site Design Consideration

5.2.1 Temporary and Permanent Slopes

5.2.2 Pavement Sections

6.0 SITE CONSTRUCTION RECOMMENDATIONS

6.1 Subgrade Preparation

6.1.1 Demolition

6.1.2 Stripping and Grubbing

6.1.3 Proofrolling

6.1.4 Site Temporary Dewatering

6.1.5 Subgrade Stabilization

6.2 Earthwork Operations

6.2.1 Existing Man-Placed Fill

6.2.2 Structural Fill Materials

6.2.3 Compaction

6.3 Foundation and slab observations

6.4 Utility Installations

6.5 General Construction Considerations

7.0 CLOSING

ECS Project No. 40:1938 Page ii

APPENDICES

Appendix A – Drawings & Reports

Site Location Diagram (Sheet 1 of 4)

USGS Topographic Map (Sheet 2 of 4)

Regional Geologic Map (Sheet 3 of 4)

Boring Location Diagram (Sheet 4 of 4)

Generalized Subsurface Soil Profile A-A’

Design of Future Foundation Adjacent to Existing Foundation Diagram

Lateral Earth Pressure – Below-Grade Wall Detail

Appendix B – Field Operations

Reference Notes for Boring Logs

Boring Logs B-1 through B-5

Appendix C – Laboratory Testing

Laboratory Test Results Summary (1 page)

Atterberg Limits Testing Results (1 page)

Grain Size Analysis Results (1 page)

ECS Project No. 40:1938 Page 1

EXECUTIVE SUMMARY

The following summarizes the main findings of the exploration, particularly those that may have cost impacts on the planned development. Further, our principal foundation recommendations are summarized. Information gleaned from the executive summary should not be utilized in lieu of reading the entire geotechnical report.

The geotechnical exploration performed for the planned building addition included five (5) soil test borings utilizing soil drilling techniques to achieve depths of up to 25 feet below the existing ground surface (bgs).

Existing fill materials were encountered in each of the borings performed. The fill materials consisted of GRAVEL WITH SAND (GP), LEAN CLAY (CL), and CLAYEY SAND WITH GRAVEL (SC), with varying amounts of Sand, Gravel, and brick fragments. The existing fill materials exhibited SPT N-values of 7 blows per foot (bpf) to 15 bpf, corresponding to a firm to stiff consistency for cohesive soils and a loose to medium dense relative density for the granular materials. Beneath the existing fill materials, natural soils generally consisted of SAND WITH CLAY AND GRAVEL (USCS Classification SP-SC), LEAN CLAY (CL), SILT (ML), and CLAYEY GRAVEL (GC), with variable amounts of Silt, Sand, Gravel, and Rock Fragments.

The natural soils exhibited SPT N-values ranging from 3 bpf to 46 bpf, corresponding to a soft to hard consistency for the cohesive soils and very loose to very dense relative density for the granular materials soils. Blow counts generally increased with depth. Weathered rock and/or auger refusal was not encountered in the borings within the depths explored.

We anticipate that the proposed building foundations will bear in competent natural soils or compacted structural fill. Based on the results of our borings, it is our opinion the proposed building may be supported by traditional shallow foundations consisting of a spread and/or continuous foundation system. Foundations may be designed for an allowable soil bearing pressure of 3,000 psf when founded on suitable natural soils, or new structural fill after undercutting existing fill to natural soils. Foundations should not be placed on uncontrolled existing fill materials. If existing fill is encountered beneath building foundations, foundations should be undercut to natural soils. Properly placed structural fill composed of suitable native site soils or approved off-site borrow materials after undercutting the existing fill should also be capable of supporting bearing pressures of this capacity.

Natural soils suitable to support these bearing pressures are those natural soils indicated on the attached boring logs having a minimum SPT N-value of 10 bpf for a 3,000 psf bearing capacity.

Recommendations for foundations are presented in Section 5.1 Building Design. Generalized

Subsurface Soil Profile A-A’ in Appendix A has been prepared to depict the subsurface profiles encountered in the test borings, the anticipated shallow foundation bearing elevations, and the approximate limits of the below-grade basement level.

We recommend the structural engineer anticipate settlement of the structures. Based on anticipated column loads and allowable bearing pressures, for foundations constructed to bear on competent, existing site soils, or new fill, total settlement tolerances should be on the order of 1 inch, with differential settlement on the order of ½ inch or less.

ECS Project No. 40:1938 Page 2

Where adjacent foundations are founded at different elevations, the subgrade elevation of the upper foundations should be below a line extending from the bottom of the lower foundation up at a slope of 1H:1V. This is particularly applicable depending on the proximity and relationship between the new foundations and the existing foundations of the adjacent structure. An Adjacent Foundation Diagram is included in Appendix A of this report.

The existing fill materials may remain in-place under the proposed floor slab provided they are stable during proofrolling operations discussed in Section 6.1.3 Proofrolling. Similarly, portions of the existing fill may also remain under proposed pavements. Localized undercutting of unsuitable existing fill soils should be expected. If existing fill is left in-place below the floor slab and pavement areas, some risk of future settlement would exist. This risk can be eliminated by the complete removal of the undocumented fill or construction of a structural floor slab. Otherwise, the risk can be reduced by

“stiffening” slabs with additional reinforcing steel, and/or removing and replacing portions of the existing fill beneath the building. The use of geosynthetics may also be appropriate to improve unstable subgrades. Additional details are provided in the following sections.

Below-grade walls will be required to construct the basement level on the northern end of the proposed addition at depths up to approximately 13 feet below existing site grades. Design of below-grade site walls to facilitate construction of the lower levels is outside the scope of services for this report; however, general recommendations for the design of below-grade walls are presented below.

Below-grade walls should be designed to withstand lateral earth pressures and surcharge loads. For below-grade walls that are restrained from rotating at the top and are properly drained, the walls may be designed for an equivalent fluid pressure of 60 pounds per square foot (psf) per foot of wall height.

For any below-grade walls that will also act as retaining walls and are free to rotate, an equivalent fluid pressure of 50 psf per vertical foot of wall is recommended. These lateral earth pressure recommendations reflect the moderate strength/clayey soils present on site, assumes that soils of

“very low” expansion potential (LL less than or equal to 40 and PI less than or equal to 20) are used for the wall backfill, and that drainage of the backfill is provided as discussed below. An equivalent fluid pressure of 45 psf/ft may be used if imported granular soils, such as SM or more granular, are used as wall backfill. The wall design should also account for any surcharge loads within a 45° slope from the base of the wall. Our general recommendations regarding the application of lateral earth pressure is included in the “Lateral Earth Pressure – Below-Grade Walls” detail in Appendix A of this report.

The project site was evaluated with respect to Site Seismic Design Class. Based on our interpretation of the IBC 2015 Building Code, Section 1613 and Table 1613, the project site should be considered a

“Site Class D” for seismic design considerations. The Site Class definition should not be confused with the Seismic Design Category designation, which the Structural Engineer typically assesses.

ECS Project No. 40:1938 Page 3

1.0 INTRODUCTION

1.1 GENERAL

This report presents the results of our subsurface exploration, and geotechnical engineering analysis for the project site located in the City of Erie, Erie County, Pennsylvania. The approximate location of the site is indicated on the Site Location Diagram (Sheet 1 of 4) included in Appendix A of this report.

1.2 SCOPE OF SERVICES

Based on the proposed development plan, including the 20% Schematic Design Submission package, (prepared by CB Design Group, dated February 6, 2020), a total five (5) borings were performed at the subject site. Test borings were referenced as B-1 through B-5. Each of the borings were performed within the proposed addition footprint. The borings were scheduled to extend to an approximate depth of 25 feet bgs and were able to extend to their scheduled depths.

The number and general location of the borings were chosen by the ECS and were located in the field by a representative of ECS using our Global Positioning System (GPS) equipment. Topographic information was not supplied on the drawings provided. Therefore, we have not included elevations on the boring logs included in Appendix B of this report. Based on observations from our site visit and considering the developed nature of the site as a surface parking lot, we estimate the elevation difference between test boring locations is on the order of ± 2 feet.

The approximate boring locations are depicted on the Boring Location Diagram (Sheet 4 of 4) included in Appendix A of this report. The Boring Location Diagram was developed from the drawing within the submission package titled Phasing Plans (Sheet No. GI102), prepared by CB Design Group, dated

December 20, 2019.

A detailed breakdown of the services provided is included in the list below.

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

b. A review of the published geologic conditions and their relevance to your planned development, including historic mining. A site-specific mining study is not included.

c. A subsurface characterization and a description of the field exploration and laboratory tests performed. Ground water concerns relative to the planned construction, if any, are summarized.

d. 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 is included, and the results of the laboratory tests are plotted on the final boring logs or included on a separate test report sheet.

ECS Project No. 40:1938 Page 4

e. Measurement of the topsoil, pavement, and/or existing fill thicknesses at each boring location and notation of this information on the logs and in the text of the report.

f. Recommended allowable soil bearing pressure(s) for conventional shallow foundations

(spread footings) and estimates of predicted foundation settlement. If required, we provided recommendations for suitable intermediate foundations/ground improvement options or deep foundations in the event estimated settlements of shallow foundations are not tolerable.

g. Recommendations for slab-on-grade construction, including subgrade modulus, and recommendations for subgrade improvements and underslab subdrainage recommendations, if necessary.

h. Recommended design criteria for lateral earth pressure coefficients (active, passive, and at-rest) for below-grade walls. Design of bellow-grade walls, including global stability analysis, was not requested and is not included in our current scope.

i. Evaluation of the on-site soil characteristics encountered in the soil borings. Specifically, we have discussed the suitability of the on-site materials for reuse as structural fill to support on-grade slabs and pavements. We have also included compaction requirements and suitable material guidelines.

j. Evaluation of depth to rock, if encountered, and recommendation for rock excavation and removal, including blasting, as reuse of rock materials as structural fill.

k. Recommendations for seismic site classification in accordance with the International Building

Code (IBC 2015). This analysis will be based on the Standard Penetration Test (SPT) method described in Section (1613.5.2) of IBC.

l. Estimate the California Bearing Ratio (CBR) values for the site soils and provide recommendations for use in preliminary design of asphalt or concrete pavements. If necessary, we have provided recommendations for subgrade stabilization.

m. Recommendations for additional testing and/or consultation that might be required to complete the geotechnical assessment and related engineering for this project.

1.3 AUTHORIZATION

Our services were provided in accordance with the Standard Form of Agreement, dated January 18, 2019, as authorized by Mr. Paul Wesley Bridges, P.E. on March 17, 2020.

ECS Project No. 40:1938 Page 5

2.0 PROJECT INFORMATION

2.1 PROJECT LOCATION

The project site is located at 135 E. 38th Street in the City of Erie, Erie County, Pennsylvania. The site is developed as the Erie VA Medical Center campus, with associated asphalt parking lots. Specifically, the project site for the current study is located within the northeastern asphalt parking lot of the medical center. The site is generally bound by residential properties to the west, East 38th Street to the north, Old French Road to the east, and the US Naval Reserve Training Center to the south. The following figure depicts the approximate location of the project site. A Site Location Diagram (Sheet 1 of 4) is also included in Appendix A of this report.

Figure 2.1.1 Project Site

2.2 PAST SITE HISTORY/USES

A Phase 1 ESA was not available at the time of this report preparation. A brief review of historic aerial photography suggests that site has been developed as a medical center, dating back to at least 1969.

Several additions appear to have been constructed in the following years, with two additions constructed sometime between 1987 and 1993 and one addition constructed between 2009 and 2010.

The northeastern parking lot was constructed between 2009 and 2013. By 2015 the project site appears to have been developed into its current configuration.

ECS Project No. 40:1938 Page 6

2.3 CURRENT SITE CONDITIONS

Based on our review of the supplied aerial photograph and field observations, the site is developed as the Erie VA Medical Center campus, with associated asphalt parking lots. Specifically, the project site for the current study is located within the northeastern asphalt parking lot of the medical center. The site is generally bound by residential properties to the west, East 38th Street to the north, Old French

Road to the east, and the US Naval Reserve Training Center to the south. Based on our review of aerial photography, the site generally appears to be flat and level.

Existing topographic contours were not provided at the time of exploration on the drawings provided by CB Design Group. According to the USGS Erie South, PA Quadrangle dated 2016, elevations across the project site appear to be generally flat and level, at an elevation of EL. 840 MSL. A copy of the

USGS Topographic Map (Sheet 2 of 4) is included in Appendix A of this report.

2.4 PROPOSED CONSTRUCTION

Based on the information provided, we understand that the proposed construction consists of the construction of an addition to the existing medical center along the northeastern side of the site. The first floor addition is anticipated to be 11,689.57 SF with a 5,612.60 SF basement level. Based on the plans provided, it appears the basement will be located within the northern portion of the new addition. The second floor roof framing plan (Drawing SF102) indicates considerations for a future second level.

2.4.1 Site Civil Features

Stormwater management (SWM) areas and site retaining walls were not depicted on site plans, nor requested; therefore evaluation of these features is not included in our scope of services. Our scope is limited to geotechnical exploration and recommendations related to the proposed addition.

2.4.2 Structural Information/Loads

Detailed project information, such as structural loading conditions was not available at the time of this report preparation. Based on the proposed construction for the new addition, we anticipate the addition will consist of steel framing with exterior concrete walls transmitting moderate column and wall loads and floor loads not exceeding 150 psf.

The description of the proposed project is based on the information provided by you and members of the project team. If any of this information is inaccurate, either due to our misunderstanding or design changes that may occur at a later date, we recommend that ECS be contacted in order to provide alternative recommendations that may be warranted.

ECS Project No. 40:1938 Page 7

3.0 FIELD EXPLORATION

3.1 FIELD EXPLORATION PROGRAM

The field exploration was planned with the objective of characterizing 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.

3.1.1 Test Borings

Prior to drilling operations, Pennsylvania One Call was contacted to locate and clear/mark underground utilities at the site. Due to a concern over private utilities adjacent to the existing structure, ECS contracted a 3rd party private utility service to locate and mark utilities within a 10-foot radius of staked boring locations. Boring locations were adjusted in the field, if necessary, based on these markings.

The soil borings were performed with a D-50 track-mounted auger drill rig which utilized continuous flight, hollow stem augers to advance the boreholes. Drilling fluid was not used during the drilling at each boring location. The boreholes were backfilled with the spoils generated during drilling, and patched with cold-patch asphalt, where appropriate, following completion of drilling operations. Some post-drilling settlement should be expected and may require future maintenance to repair any settlement and prevent a tripping hazard. This maintenance is not included in our scope of services or fees.

In the soil borings, representative soil samples were obtained by means of the split-barrel sampling procedure in general accordance with ASTM Standard D 1586. In this procedure, a 2-inch O.D., split-barrel sampler is driven into the soil a distance of 18 or 24 inches by a 140-pound hammer falling 30 inches. The number of blows required to drive the sampler through a 12-inch interval is termed the

Standard Penetration Test (SPT) value and is indicated for each sample on the boring logs. This value can be used as a qualitative indication of the in-place relative density of cohesionless soils and, in a somewhat less reliable way, the consistency of cohesive soils.

A field log of the soils encountered in the borings was maintained by the on-site ECS representative.

After recovery, each sample was removed from the sampler and visually classified. Representative portions of each sample were then sealed in jars and brought to our laboratory for further visual examination.

3.2 REGIONAL/SITE GEOLOGY

Based on the PA Department of Conservation and Natural Resources Geologic Map (PA DCNR), dated

2016 the project site is mapped as being underlain by the Girard Shale (Dg) Formation of the Upper

Devonian System. The Girard Shale Formation consists primarily of light to medium gray, very fine-grained shale with some siltstone. According to the Engineering Characteristics of the Rocks of

Pennsylvania (PA Geologic Survey report EG-1, dated 1982), the bedrock topography is masked by glacial material. This formation is part of the Eastern Lake Section of the Central Lowlands

ECS Project No. 40:1938 Page 8

Physiographic Province. A copy of the Regional Geologic Map (Sheet 3 of 4) is included in Appendix A of this report.

3.3 MINE SUBSIDENCE MAPPING

In addition to the geologic mapping of the site, we also reviewed the information contained on the

Pennsylvania Department of Environmental Protection (PA DEP) Mine Subsidence Insurance Maps.

Based on the information reviewed, the project site does not appear to be located within the limits of mapped underground or surface mining. A site-specific mining study has not be included as part of our scope of services.

3.4 SOIL AND ROCK CHARACTERIZATION

The soils identified in the attached boring logs are generally consistent with our understanding of the site history as well as the regional geology information and publically available sources. The groundcover at the site consisted of approximately 5 to 6 inches of asphalt and approximately 2 inches of aggregate base course beneath the asphalt.

Existing fill materials were encountered in each of the borings performed. The fill materials consisted of GRAVEL WITH SAND (GP), LEAN CLAY (CL), and CLAYEY SAND WITH GRAVEL (SC), with varying amounts of Sand, Gravel, and brick fragments. The existing fill materials exhibited SPT N-values of 7 blows per foot (bpf) to 15 bpf, corresponding to a firm to stiff consistency for cohesive soils and a loose to medium dense relative density for the granular materials.

Beneath the existing fill materials, natural soils generally consisted of SAND WITH CLAY AND GRAVEL

(USCS Classification SP-SC), LEAN CLAY (CL), SILT (CL), and CLAYEY GRAVEL (GC), with variable amounts of Silt, Sand, Gravel, and Rock Fragments. The natural soils exhibited SPT N-values ranging from 3 bpf to 46 bpf, corresponding to a soft to hard consistency for the cohesive soils and very loose to very dense relative density for the granular materials. Blow counts generally increased with depth.

Weathered rock and/or auger refusal was not encountered in the borings within the depths explored.

3.5 GROUNDWATER OBSERVATIONS

Observations for groundwater were made during sampling and upon completion of drilling operations in each of the boring locations. In auger drilling operations, water is not introduced into the boreholes during soil drilling, and the groundwater position can often be determined by observing water flowing into or out of the borings. Groundwater was encountered in Borings B-1 and B-5 at an approximate depth of 23 feet bgs. The remaining borings were dry during and after drilling operations.

Perched water conditions are common at the interface between granular and cohesive soils, where surface water becomes trapped on top of the less permeable clays. Perched water within granular seams within the fill soils or at the fill/natural soil interface is also common. It is possible that water seepage and accumulation may be observed in deeper excavations allowed to remain open for an extended duration.

ECS Project No. 40:1938 Page 9

The highest groundwater observations are normally encountered in late winter and early spring;

therefore, groundwater observations in our most recent borings are expected to be somewhat representative of the seasonal maximum water table. Variations in the location of the long-term water table may occur as a result of changes in precipitation, evaporation, surface water runoff, and other factors not immediately apparent at the time of this exploration. Recommendations with regard to site dewatering are included in the 6.1.4 Site Temporary Dewatering section of this report.

ECS Project No. 40:1938 Page 10

4.0 LABORATORY TESTING

Representative soil samples were selected and tested in our laboratory to check field classifications and to determine pertinent engineering properties. The laboratory testing program included visual classifications, moisture content tests, Atterberg Limits, and grain size analysis. All data obtained from the laboratory tests are included on the respective boring logs or on separate sheets in the Appendix of this report.

Each soil sample was classified on the basis of texture and plasticity in accordance with the Unified Soil

Classification System (USCS). The group symbols for each soil type are indicated in parentheses following the soil descriptions on the boring logs. A brief explanation of the Unified System is included with this report. The various soil types were grouped into the major zones noted on the boring logs.

The stratification lines designating the interfaces between earth materials on the boring logs and profiles are approximate; in situ transitions may be gradual, rather than distinct.

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 disposition.

ECS Project No. 40:1938 Page 11

5.0 DESIGN RECOMMENDATIONS

The following sections provide recommendations for foundation design, soil supported slabs, pavements, and seismic design parameters. The primary factor that will affect the proposed development is the presence of surficial existing fill beneath the site. Additional recommendations and design details are provided herein.

The recommendations outlined in this report are based on the five (5) borings performed at the site, the laboratory testing and analysis, and the information provided to us by you and other design team members. Additional recommendations and design details are provided herein.

5.1 BUILDING DESIGN

5.1.1 Building Foundations

A finished floor elevation was not provided for the proposed addition. However, we understand that the northern portion of the addition will contain a below-grade basement level, while the southern portion of the addition will bear at or near existing site grades. Generalized Subsurface Soil Profile A-

A’ in Appendix A has been prepared to depict the subsurface profiles encountered in the test borings, the anticipated shallow foundation bearing elevations, and the approximate limits of the below-grade basement level.

Existing fill was encountered in each of the borings performed to depths of approximately 4 to 6 feet bgs. We anticipate that the existing fill encountered in Borings B-3, B-4, and B-5 will be removed to facilitate the below- grade basement level. Since approximately 6 feet of existing fill was encountered in Test Borings B-1 and B-2, we recommend that existing fill encountered below foundations be undercut to natural soils and the resulting over-excavation be backfilled with lean concrete or compacted structural fill to the planned foundation bearing elevation(s).

We anticipate that the proposed building foundations will bear in competent natural soils or new structural fill. Based on the results of our borings, it is our opinion the proposed building may be supported by traditional shallow foundations consisting of a spread and/or continuous foundation system. Foundations may be designed for an allowable soil bearing pressure of 3,000 psf when founded on suitable natural soils, or new structural fill after undercutting the existing fill to natural soils. Foundations should not be constructed on uncontrolled existing fill materials. If existing fill is encountered beneath building foundations, existing fill should be undercut to natural soils and the resulting over-excavation be backfilled with lean concrete or compacted structural fill to the planned foundation bearing elevation(s). Properly placed structural fill composed of suitable native site soils or approved off-site borrow materials after undercutting the existing fill should also be capable of supporting bearing pressures of this capacity. Natural soils suitable to support these bearing pressures are those natural soils indicated on the attached boring logs having a minimum SPT N-value of 10 bpf for a 3,000 psf bearing capacity.

Localized undercuts below the foundations may be required to achieve the recommended bearing

ECS Project No. 40:1938 Page 12 pressure due to the potential for variations in the existing fill depth, natural soil strength, and depending on construction sequencing and weather. Where undercutting is performed, the excavation should be backfilled with properly compacted fill or lean concrete to the original design bearing elevation. If compacted fill is used to backfill overexcavated areas, the overexcavation should be extended a horizontal distance of 1 foot for each foot of undercut. Open-graded gravel (i.e. AASHTO

#57 stone) should not be used to backfill foundation undercuts as this could result in a reservoir condition, allowing the accumulation of water and potential softening of the bearing soils. All foundation installation should be observed on a full time basis by the geotechnical engineer or qualified testing agency to determine actual undercut depths, if required.

The allowable soil bearing pressure refers to that pressure which may be transmitted to the foundation bearing soil in excess of the final minimum surrounding overburden pressure. During construction, the bearing capacity at the final foundation excavation should be tested in the field by the geotechnical engineer or a qualified testing agency to document that the in-situ conditions at the bottom of each foundation excavation is adequate for the design loads.

We recommend the structural engineer anticipate settlement of the structures. Based on anticipated column loads and allowable bearing pressures, for foundations placed to bear on new structural fill or natural soils, total settlement tolerances should be on the order of 1 inch, with differential settlement on the order of ½ inch or less.

We recommend that continuous foundations have a minimum width of 18 inches and that isolated column foundations have a minimum lateral dimension of 24 inches. The minimum dimensions recommended above help reduce the possibility of foundation bearing failure and excessive settlement due to local shear or "punching" action. In addition, foundations should be placed at a depth to provide adequate frost cover protection. Therefore, we recommend foundations in unheated areas and perimeter foundations subject to climatic variations are located at a minimum depth of 42 inches below finished grade or in accordance with local building code requirements. Interior foundations can be located on acceptable bearing materials at nominal depths compatible with architectural and structural considerations.

Depending on the excavation methods used to reach the bearing elevation, it is possible that the bearing surface may be disturbed during excavation. The recommended bearing pressure provided above is based on the foundations bearing directly on undisturbed materials. Should the bearing subgrade be disturbed during excavation, the foundations will need to be further undercut to undisturbed materials or the disturbed materials removed and replaced as described in Section 6.2

Earthwork Operations.

Where adjacent foundations are founded at different elevations, the subgrade elevation of the upper foundations should be below a line extending from the bottom of the lower foundation up at a slope of 1H:1V. This is particularly applicable depending on the proximity and relationship between the new foundations and the existing foundations of the adjacent structure. An Adjacent Foundation Diagram is included in Appendix A of this report.

ECS Project No. 40:1938 Page 13

If excavation below an adjacent foundation of the existing structure is required, the project structural engineer should be contacted to observe the existing conditions and provide additional recommendations. Precautions should be taken not to undermine the existing foundations of the adjacent buildings.

5.1.2 Ground Supported Slabs

Existing fill to approximate depths of 4 to 6 feet bgs was encountered in each of the test borings performed at the site. The existing fill materials may remain in-place under the proposed floor slab provided they are stable during proofrolling operations discussed in Section 6.1.3 Proofrolling.

Localized undercutting of unsuitable existing fill soils should be expected. If existing fill is left in-place below the floor slab areas, some risk of future settlement would exist. This risk can be eliminated by the complete removal of the undocumented fill or construction of a structural floor slab. Otherwise, the risk can be reduced by “stiffening” slabs with additional reinforcing steel, and/or removing and replacing portions of the existing fill beneath the building. The use of geosynthetics may also be appropriate to improve unstable subgrades. Additional details are provided in the following sections.

For the preparation of the ground-supported slabs, bearing on existing fill materials or new structural fill, the general recommendations provided in the section entitled 6.1 Subgrade Preparation should be followed. Subgrade materials should then be thoroughly compacted to the criteria in the 6.2 Earthwork

Operations section of this report.

We recommend that the slabs-on-grade be underlain by a minimum of 6 inches of granular material having a maximum aggregate size of 1.5 inches and no more than 2% fines. This granular layer will facilitate the fine grading of the subgrade and help prevent the rise of water through the floor slab.

Prior to placing the granular fill, the floor slab subgrade soils should be properly compacted and be free of standing water, mud, or frozen soil. Before the placement of concrete, a vapor barrier should be placed on top of the granular material to provide additional moisture protection.

The following figure depicts our floor slab recommendations.

Figure 5.1.2.1

1. Drainage Layer Thickness: 6 inches

2. Drainage Layer Material: GRAVEL (GW)

3. Subgrade compacted to 100% maximum dry density per ASTM D698

Concrete Slab Vapor Barrier

Granular Capillary Break/Drainage Layer

Compacted Subgrade

ECS Project No. 40:1938 Page 14

Subgrade Modulus: The composition of the floor slab subgrade is expected to consist of site Silty soils.

A modulus of subgrade reaction, “k”, of 100 pci can be used for design of the slab on grade based on the primarily SILTY soils encountered in the borings near the surface, subject to a passing proofroll observation. The modulus of subgrade reaction value is based on a 1 ft by 1 ft plate load test basis.

Slab Isolation: Ground-supported slabs should be isolated from the foundations and foundation-supported elements of the structure so that differential movement between the foundations and slab will not induce excessive shear and bending stresses in the floor 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.

In order to reduce the crack width of any shrinkage cracks that may develop near the surface of the slab, we recommend mesh reinforcement or reinforcing steel, as determined by the structural engineer, be included in the design of the floor slab.

Even though ground-supported slabs may be constructed during the warm months of the year, exposure of the interior slabs to freezing temperatures can result in frost heave if constructed during colder months. Consequently, to reduce the potential for frost heave beneath any previously installed slabs, it is recommended that any foundation excavations and/or unpoured sections within the slab area be pumped out to reduce water flow into the subbase and/or subgrade materials. In addition, all slab joints should be sealed to reduce surface water infiltration into the subbase materials.

5.1.3 Temporary Excavation Support

A temporary excavation system is expected to be required for the construction of the below-grade basement area. A free-draining system consisting of soldier piles and wood lagging is recommended.

The system could be braced externally using tiebacks, where possible. However considering that the proposed development is to be performed at a developed site, tiebacks may not be feasible; therefore, rakers or other forms of site internal bracing may be required. Spacing of the soldier piles and braces should be determined by a structural analysis. However, we recommend that the maximum center line to center line spacing of the soldier piles not exceed 8 feet. In addition, wooden lagging should have a minimum thickness of 3 inches. As stated previously, in areas where tiebacks are not feasible, an internal bracing system of rakers would be required. Rakers should be braced against toe blocks or other reaction points that have been designed to carry the load.

The temporary earth retention system should be installed deep enough to allow for “stepping down” of site utilities and underslab subdrainage system to a minimum of 3 feet below the proposed utility/underdrainage elevations. In the event that a step down is required, construction difficulties can be avoided with regard to undermining the installed soldier piles when the necessary below-grade feature is being placed.

If tiebacks are used, we recommend a performance test be performed on 10% of randomly selected tiebacks. The performance test evaluates the tieback load carrying capacity, deflections during loading, ECS Project No. 40:1938 Page 15 and movements with respect to time. We also recommend 100% of tiebacks be proof tested. Both the proof and performance testing shall be conducted in accordance with PTI standards.

The contractor should avoid stockpiling excavated materials immediately adjacent to the excavation walls. We recommend that stockpile materials be kept back from the excavation a minimum distance equal to one-half the excavation depth to avoid surcharging the excavation walls. If this is impractical due to space constraints, the excavation walls should be retained with bracing design for the anticipated surcharge loading.

Where the Support of Excavation (SOE) system is immediately adjacent to existing structures or critical utilities, at-rest pressures should be selected by the SOE design-build contractor when establishing the design Lateral Earth Pressures.

5.1.4 Below-Grade Walls

Below-grade walls will be required to construct the basement level on the northern end of the proposed addition at depths up to approximately 13 feet below existing site grades. Design of below-grade site walls to facilitate construction of the lower levels is outside the scope of services for this report; however, general recommendations for the design of below-grade walls are presented below.

We anticipate that the proposed below-grade walls will be constructed as a cast-in-place concrete cantilever retaining wall that will support the northern side of the new building. The following design recommendations are provided to guide the design engineer responsible for the final wall design.

Detailed design drawings and specifications for the new retaining walls can be provided as an additional service once the final wall type has been selected, if requested.

Below-grade walls should be designed to withstand lateral earth pressures and surcharge loads. For below-grade walls that are restrained from rotating at the top and are properly drained, the walls may be designed for an equivalent fluid pressure of 60 pounds per square foot (psf) per foot of wall height.

For any below-grade walls that will also act as retaining walls and are free to rotate, an equivalent fluid pressure of 50 psf per vertical foot of wall is recommended. These lateral earth pressure recommendations reflect the moderate strength/clayey soils present on site, assumes that soils of

“very low” expansion potential (LL less than or equal to 40 and PI less than or equal to 20) are used for the wall backfill, and that drainage of the backfill is provided as discussed below. An equivalent fluid pressure of 45 psf/ft may be used if imported granular soils, such as SM or more granular, are used as wall backfill. The wall design should also account for any surcharge loads within a 45° slope from the base of the wall. A base sliding coefficient of 0.3 may be used for analyses for wall foundations bearing upon on soil. Our general recommendations regarding the application of lateral earth pressure is included in the “Lateral Earth Pressure – Below-Grade Walls” detail in Appendix A of this report.

The following table summarizes the soil parameters recommended for below-grade retaining wall design:

ECS Project No. 40:1938 Page 16

Table 5.1.4.1 – Recommended Soil Parameter for Retaining Walls

Soil Type - Unified Soil Classification

Unit Weight

(pcf)

Internal Angle of Friction

Cohesion (tsf)

Equivalent Fluid

Pressure (Active) (psf/ft)

Equivalent Fluid

Pressure (At-Rest) (psf/ft)

Site Soils – CL/ML 120 26 ----- 50 60

Select Import – e.g PennDOT 2A

130 36 ----- 40 45

The retaining wall should be designed so that the resultant of the overturning forces remains in the central one-third of the footing. The foundations for the proposed retaining wall should be designed for a net allowable soil bearing pressure on the order of 3,000 psf, provided that the foundations are founded upon suitable natural soils. Furthermore, sliding resistance of retaining walls can be achieved either through the use of a shear key or through the frictional forces developed at the base of the retaining wall. A shear key, if installed, can be designed for a passive pressure of 300 psf per foot of depth.

At least a one-foot annular space between the outside of the walls and excavation should be backfilled with an inorganic, free draining granular material, free of debris. Outside this zone, the below-grade walls may be backfilled with inorganic materials, free of debris, and that meet the requirements outlined in Section 6.2.2 Structural Fill Materials of this report. The fill placed adjacent to the below-grade walls should not be overcompacted. Heavy earthwork equipment should maintain a minimum horizontal distance away from the below-grade walls of 1 foot per foot of vertical wall height. Lighter compaction equipment should be used close to the below-grade walls. The thickness of the lifts should be no more than 6 inches where light-weight compaction equipment is used; however, lifts may need to be thinner depending on the type of equipment used. The ground surface adjacent to the below-grade walls should be kept properly graded to prevent ponding of water adjacent to below-grade walls.

To reduce excessive pressures against the below-grade walls, and to reduce the settlement of the wall backfill below the overlying slab, it is recommended that the wall backfill be compacted to a minimum of 95% of the maximum dry density determined in accordance with ASTM D-698. Where the fill will be supporting pavement, slabs or other structures, the upper 1 foot of fill should be compacted to

100% of the maximum dry density referenced above. The fill placed adjacent to the below-grade walls should not be overcompacted. Heavy earthwork equipment should maintain a minimum horizontal distance away from the below-grade walls of 1 foot per foot of vertical wall height. Lighter compaction equipment should be used close to the below-grade walls.

Suitable man-made drainage materials may be use in lieu of the granular backfill, adjacent to the below-grade walls. Examples of suitable materials include Enka Mat, Mirafi, or Geotec drains. These materials should be covered with a filter fabric having an Apparent Open Size (AOS) consistent with the size of the soil to be retained. The lateral earth pressures indicated above are applicable for either granular backfill or the manufactured drainage medium. The material should be placed in accordance

ECS Project No. 40:1938 Page 17 with the manufacturer’s recommendations and connected to either the perimeter drain system which in turn should be properly drained from sumps or by gravity.

We recommend that any below-grade spaces of the proposed structure be provided with a perimeter drainage system. This system may consist of 4-inch perforated, closed-joint drain tiles located around the perimeter of the lowest level, outside the walls, slightly below the lowest floor level. These drain lines should be surrounded by a minimum of 6 inches of free draining granular filter material having a gradation compatible with the size of the openings utilized in the drain lines and surrounding soils to be retained. The geotextile used should be reviewed and approved by the geotechnical engineer. The granular drainage material should be wrapped with geotextile fabric. As previously mentioned, we recommend that the lowest level floor slab be underlain by a minimum of 6-inches of free draining granular material. The underslab drainage layer and the drain lines should either be hydraulically connected and outlet to daylight to remove any water that may accumulate or directed to an interior sump pit and pumped for removal.

5.1.5 Seismic Design Considerations

The subsurface exploration completed at this site included the drilling of borings to depths on the order of +/- 25 below the existing site grades. The International Building Code (IBC) 2018 requires site classification for seismic design based on the upper 100 feet of a soil profile. Where site-specific data is not available to a depth of 100 feet, appropriate soil properties are permitted to be estimated by the registered design professional preparing the soils report based on known geologic conditions.

Utilizing the data obtained from Standard Penetration Resistance (ASTM D 1586-84) tests conducted in the borings and our previous experience at neighboring sites, a mean SPT “N”-value within 100 feet of the ground surface was determined. Three methods are utilized in classifying sites, namely the shear wave velocity, vs, method; the unconfined compressive strength, su, method; and the Standard

Penetration Resistance, N-value method. The latter method was used in classifying this site.

Table 5.1.5.1: 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 on our interpretation of the IBC 2018 Building Code Section 1613.3.2, and Chapter 20 of ASCE 7, the project site should be considered a “Site Class D” for seismic design considerations. The Site Class definition should not be confused with the Seismic Design Category designation, which the Structural

Engineer typically assesses. ECS can provide additional analysis and testing, if desired, to further evaluate the site class or provide site-specific response spectra if it is determined by the structural

ECS Project No. 40:1938 Page 18 engineer that an improvement in the site class or design spectral coefficients for the project site will result in significant economic savings in the final design.

5.2 SITE DESIGN CONSIDERATION

5.2.1 Temporary and Permanent Slopes

Our scope of services did not include specific analysis of proposed temporary slopes. However, in general, temporary excavation slopes cut in the native soils should be no steeper than 1H:1V or as indicated by OSHA protocol. Temporary fill slopes constructed of site native silty or clayey soils should be limited to a maximum gradient of approximately 2H:1V. The temporary slopes should also be thoroughly vegetated to help reduce erosion of the surficial soils. During foundation excavation, we recommend that the existing on-site soils be examined and sloped back at gradients in accordance with

OSHA 29 CFR 1926

Permanent slopes constructed of native…