P01-657-101 100PCT Report GEOTECHNICAL.pdf

Department of Veterans Affairs Jefferson Barracks

St. Louis, MO

Project Number 657-101

(VEG 21.02)

Construct Urgent Care Clinic Building Addition

100% Not For Construction Submittal

Geotechnical Report

December 1, 2022

750 W. HAMPDEN AVE. #300

ENGLEWOOD, CO 80110

Ph (720) 550-6307

SCI ENGINEERING, INC.

130 Point West Boulevard

St. Charles, Missouri 63301 636-949-8200 www.sciengineering.com

JEFFERSON BARRACKS VA URGENT CARE CLINIC ADDITION

ST. LOUIS COUNTY, MISSOURI

August 2021

VETERANS ADMINISTRATION

Owner

VALHALLA ENGINEERING GROUP, LLC

Architect / Structural Engineer

SCI No. 2021-0419.10

DocuSign Envelope ID: D0B2A9D6-9781-4C20-81C5-05C4C30F35B2

8/31/2021

EARTH • SCIENCE • SOLUTIONS

GEOTECHNICAL

ENVIRONMENTAL

NATURAL RESOURCES

CULTURAL RESOURCES

CONSTRUCTION SERVICES

130 Point West Boulevard, St. Charles, Missouri 63301 ■ 636-949-8200

August 31, 2021

Alan Bronson Valhalla Engineering Group, LLC 750 W Hampden Avenue, Suite 300 Englewood, Colorado 80110

RE: Geotechnical Report

Jefferson Barracks VA Urgent Care Clinic Addition St. Louis County, Missouri SCI No. 2021-0419.10

Dear Alan Bronson:

Attached is SCI Engineering, Inc.’s Geotechnical Report, dated August 2020. It should be read in its entirety, and our recommendations applied to the design and construction of the project. Select excerpts from the report are highlighted below:

• Based on our review of the Missouri Department of Natural Resource (MoDNR) GeoSTRAT site, no sinkholes are present on site. However, 12 sinkholes are located within a half mile of the site to the north, east and west of the site. Due to the underlying bedrock conditions, there is a risk of karst development at the site. No karst features were observed at the surface during our walkover.

However, during the second phase of drilling, a possible clay filled void was observed from 32 to 40 feet, which could be evidence of a karst feature. Further discussion and recommendations are provided Section 4.1.

• The existing fill was placed during construction of existing site features; however, documentation regarding the placement and compaction of the fill material is not available, and the results of our field testing suggest that portions of the existing fill may not have been placed and compacted in a controlled manner. Therefore, the engineering properties and performance of the existing fill cannot be predicted with certainty and risk of settlement of the fill underneath the building exists.

However, the use of structural floor slab and deep foundations bearing on bedrock will minimize the risk associated with the existing fill.

• Due to the risk of karst development, existing fill and the foundation system of the existing building, the new clinic addition should be supported on deep foundations, such as drilled piers. Specific recommendations regarding the drilled shafts are provided in the report. We understand a structural slab will also be used in conjunction with the drilled shafts.

• Expansive clay soils are susceptible to excessive volume change with variations in moisture content, which can lead to movement of concrete slabs and foundations of lightly-loaded structures, slabs, retaining walls, or pavements. Where the bearing soils consist of expansive clay soils, we recommend that they be removed to minimum depths of 3 feet beneath the bottom of the floor slab.

We anticipate that spot areas of expansive clay will require remediation below the slab near B-4.

The actual need for, and extents of, remediation should be delineated by SCI personnel in the field during construction.

Alan Bronson 2 August 31, 2021 Valhalla Engineering Group, LLC SCI No. 2021-0419.10

• Based on the data collected, the soils in this area will have a moderate to very high corrosive potential to ductile iron pipe. Based on the results of the sulfate testing and ACI Section 318-19, the site will have a concrete exposure classification of S1, F0, C1, and W1. We assumed an F0 modified since the upper 5 feet of the soil and drilled shaft interaction are ignored. The greatest risk of freeze thaw would also occur in this zone.

• Based on the results of the field exploration and the site-specific seismic evaluation, Site Class C should be used for foundation design, with the following seismic design parameters: Fa = 1.20, Fv = 1.63, SDS = 0.46 and SD1 = 0.22. Based on an Occupancy Category of IV, the Seismic Design Category (SDC) for the structure is D.

We appreciate the opportunity to be of service and look forward to working with you during the construction phase of the project. If you have any questions or comments, please do not hesitate to contact me at 618-206-3008 or jmiller@sciengineering.com.

Respectfully, Julie A. Miller, P.E.

Senior Engineer

Shawnna L. Erter, P.E., D.GE Vice President

JAM/SLE/hmm/tlw

Enclosure

Geotechnical Report

\\SCISTCFPS01\Projects\2021\2021-0419 Jefferson Bks VA Med Ctr - Urgent Care Bldg Addition\GS\Report\2021-0419.10 GS Report.docx mailto:jmiller@sciengineering.com

August 2021 SCI No. 2021-0419.10

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 SITE AND PROJECT DESCRIPTION

3.0 SUBSURFACE CONDITIONS

3.1 Surficial Materials and Existing Fill

3.2 Soil Profile

3.3 Bedrock Geology

3.4 Groundwater

3.5 Corrosivity Potential

3.6 Shear Wave Velocity Survey

4.0 DESIGN RECOMMENDATIONS

4.1 Karst Topography

4.2 Expansive Clay Remediation

4.3 Existing Fill Materials

4.4 Deep Foundation Recommendations

4.4.1 Uplift Capacity

4.4.1.1 Uplift Capacity for Group Action

4.4.2 Lateral Resistance of Piers

4.4.3 Pre-Drilling (for Deep Foundations)

4.5 Seismic Considerations

4.5.1 Design Earthquake

4.5.2 International Building Code Site Classification

4.5.3 Site Specific Seismic Evaluation (SSSE)

4.5.4 Liquefaction Potential Analysis

4.6 Floor Slabs

4.7 Below-Grade Walls

4.8 Site Grading

4.9 Underground Utilities

4.10 Pavement

5.0 SITE DEVELOPMENT AND CONSTRUCTION CONSIDERATIONS

5.1 Site Preparation

5.2 Fill Materials and Compaction

5.3 Deep Foundation Quality Control/Quality Assurance

5.4 Floor Slab Subgrades

5.5 Excavation Bracing Requirements

5.6 Erosion Control and Land Disturbance Monitoring Program

6.0 CONSTRUCTION MONITORING PROGRAM

7.0 LIMITATIONS

August 2021 ii SCI No. 2021-0419.10

TABLES

Table 3.1 - Existing Fill Summary Table 3.2 - Auger Refusal Summary Table 4.1 - Drilled Pier Rock Quality Criteria Table 4.2 - Uplift Capacity Parameters for Drilled Piers Table 4.3 - Recommended Lateral Earth Pressures Table 5.1 - Typical Compaction Requirements for Fill

FIGURES

Figure 1 - Vicinity and Topographic Map Figure 2 - Aerial Photograph Figure 3 - Site Plan Figure 4 - Sinkhole Location and Aerial Photograph

APPENDICES

Appendix A - Boring Log Legend and Nomenclature, Boring Logs, Rock Core Photographs Appendix B - Shear Wave Velocity Profiles

JEFFERSON BARRACKS VA URGENT CARE CLINIC ADDITION

ST. LOUIS COUNTY, MISSOURI

1.0 INTRODUCTION

At the request of Alan Bronson of Valhalla Engineering Group LLC (Valhalla) SCI Engineering, Inc. (SCI) performed a geotechnical study for the proposed development. The purpose of our exploration was to characterize and evaluate the subsurface conditions, provide recommendations for foundations, and address other geotechnical aspects. Our services are provided in general accordance with our proposal, dated

April 13, 2021, with the contracted authorized by both parties on May 5, 2021.

2.0 SITE AND PROJECT DESCRIPTION

SCI understands that an Urgent Care Clinic addition is planned for the Jefferson Barracks Veterans Affairs

Medical Center (VAMC), located at 1 Jefferson Barracks Drive in St. Louis, Missouri. The location of the site is shown on the Vicinity and Topographic Map, Figure 1.

The addition is planned north of the existing 5-story hospital building in a relatively flat area consisting of asphalt pavements, greenspace, and sidewalks. The existing site conditions are shown on the

Aerial Photograph, Figure 2.

Based on the site plan and information you provided, the building addition will be a single-story, slab-on-grade structure, with a footprint of approximately 11,000 square feet. A canopy will extend out west from the proposed addition. Associated parking will be located to the north. The proposed improvements are shown on the Site Plan, Figure 3.

Grading plans were not provided at the time of this proposal; however, we anticipate the finished floor elevation (FFE) of the addition will match the first floor FFE of the adjoining hospital, requiring cuts and fills on the order of 3 feet or less.

Structural loads were not available at the time of this proposal; however, we anticipate that the building addition will be lightly loaded, with column loads of less than 100 kips and wall loads of less than 4 kips per lineal foot.

We have not reviewed, nor are we aware of, any previous studies on this specific site, by SCI or others, that would affect the preparation of this report.

SCI Engineering, Inc. Jefferson Barracks VA Urgent Care Clinic

August 2021 Page 2 of 21

3.0 SUBSURFACE CONDITIONS

Eleven borings (P-1 and P-2, B-1 through B-5, and PH-1 through PH-4) were drilled at the approximate locations shown on the Site Plan. Borings P-1, P-2, and B-1 through B-5 were drilled in May 2021 while the PH-1 through P-4 were drilled in August 2021. The boring locations were staked in the field by SCI personnel using a Trimble handheld global positioning system. Ground surface elevations at the boring locations were provided by Valhalla in and email dated July 22, 2021 for the first phase of borings.

The elevations for the second phase of borings were estimated from the topographic information shown on the Site Plan. Detailed information regarding the nature and thickness of the soils and rock encountered and the results of the field sampling and laboratory testing are shown on the Boring Logs contained in

Appendix A.

3.1 Surficial Materials and Existing Fill

Existing pavements were encountered at the ground surface in Borings B-3, B-4, and B-5 and consisted of approximately 4 inches of asphaltic concrete over 14 to 20 inches of crushed rock. Additionally, existing fill was encountered in B-1 through B-5 and P-1, P-2, and P-4 extending to depths ranging from

2 to 11 feet as summarized in Table 3.1. The fill primarily consisted of lean clay with varying amounts of fat clay, crushed rock, brick, and asphalt. Standard Penetration Tests (SPTs) within the crushed rock fill resulted in an N-value of 23 blows per foot (bpf). N values in the cohesive fill ranged from 4 to 18 bpf.

Moisture contents in the fill ranged from 13 to 30 percent. The fill is most likely associated with the previous developments on the VA property.

Table 3.1 – Existing Fill Summary

Boring Ground Surface Elevation (feet)

Approximate Existing Fill Depth (feet)

Approximate Bottom of Fill Elevation

(feet)

B-1 510.9 6 504.9

B-2 510.8 11 499.8

B-3 508.4 6 502.4

B-4 508.6 7.5 501.1

B-5 507.9 5.5 502.4

P-1 509.4 6.5 502.9

P-2 506.0 3.0 503.0

PH-1 509.5 2.5* 507.0

PH-2 508.5 2* 506.5

PH-4 510.8 2.5* 508.3

* Drillers observations.

August 2021 Page 3 of 21

3.2 Soil Profile

The native soils predominantly consisted of interbedded layers of lean clay (CL in accordance with the

Unified Soil Classification System and ASTM D 2488-06) and fat clay (CH). The native soils extended to depths of boring termination at 10, 15, and 20 feet in P-1, P-2, B-1, B-2, B-4, and B-5. As an exception, auger refusal on limestone bedrock was encountered at depths of approximately 20 to x feet in B-3, and

PH-1 through PH-4. SPTs within the native soils resulted in N-values ranging from 6 to 12 bpf, characterizing the soils as medium stiff in consistency. Moisture contents in the native clay ranged from

21 to 36 percent.

3.3 Bedrock Geology

Documented geology, including the Bedrock Geologic Map of the St. Louis Quadrangle, Missouri and

Illinois, indicates that bedrock at the site consists of the St. Louis Limestone, which is typically dark gray, thin- to- medium-bedded to massive limestone. Thin beds of bluish-gray shale are found throughout the formation. This highly variable unit consists of dolomite, cherty limestone fossiliferous limestone, and evaporites.

Auger refusal was encountered in five borings ranging in depth from 18.5 to 23 feet, at approximate elevations (El.) of 491.3 to 486.5 feet, as summarized in Table 3.2. Auger refusal was not encountered in the remaining borings. Auger refusal is a designation applied to any material that cannot be further penetrated by the power auger without extraordinary effort and is indicative of a very hard or very dense material, usually boulders or bedrock.

Table 3.2 – Auger Refusal Summary

Boring Approximate Ground

Surface Elevation (feet)

Auger Refusal Depth (feet)

Approximate Auger Refusal Elevation

(feet)

B-3 508.4 20.0 488.4

PH-1 509.5 23 486.5

PH-2 508.5 18.5 490.0

PH-3 509.0 20.0 489.0

PH-4 510.8 19.5 491.3

The borings were advanced beyond auger refusal using rock coring in PH-1 and PH-3. In PH-1, the bedrock consisted of slightly weathered limestone extending to a depth of 31 feet. At 31 feet, the limestone was more weathered with clayey shale seams to a depth of 32 feet. From 32 feet to a depth of 37 feet the driller’s augers dropped indicating soft clay or a void. From 37 to 40 feet, fat clay soils were recovered in the core.

August 2021 Page 4 of 21

Slightly weathered limestone was then encountered at a depth of 40 feet until boring termination at 43 feet.

Two feet into the initial run, the driller’s noted no water return. Rock Quality Designations (RQDs) of

22 to 57 percent were recorded in the recovered rock core indicating poor to fair quality rock. Photographs of the rock cores are included in Appendix A.

3.4 Groundwater

Groundwater was not observed during drilling. The groundwater level depends on seasonal and climatic variations, and may be present at different depths in the future. In addition, without extended periods of observation, accurate groundwater level measurements may not be possible, particularly in low permeability soils. Groundwater may be temporarily encountered after a heavy rain event atop the bedrock.

Groundwater may temporarily influence deep foundation construction after heavy rain events.

3.5 Corrosivity Potential

Composite samples from the upper 6 to 8 feet were collected from borings B-1 and B-3 and subjected to laboratory testing designed to evaluate the potential for corrosivity. Such testing included resistivity and pH. The results of the testing indicate that the soils exhibit pH values in the range of 6.44 to 7.98.

Resistivity testing resulted in a range of 980 to 6,200 ohm-cm. Based on the data collected, the soils in this area will have a moderate to very high corrosive potential to ductile iron pipe.

Sulfate tests were conducted and soil sample from a depth of 6 feet in B-1 and B-3 yielding results of 489, and 214 mg/Kg, respectively. According to American Concrete Institute publications ACI-222R and

ACI-318, as well as the Portland Cement Association (PCA) publication Design and Control of Concrete

Mixtures, the measured values indicate a moderate to high risk of corrosion. The corrosion potential for concrete is based on the potential of affecting the reinforcing steel where concrete is in direct contact with soil. Per PCA guidance Type II concrete is recommended where the sulfate values are above 150. As such, Type II concrete should be utilized. As a minimum, ACI-recommended reinforcement cover shall be considered for all concrete structures that will be in direct contact with soil. The addition of fly ash or slag to the concrete mix can also be used to provide increased resistance to corrosion.

Based on the results of the sulfate testing and ACI Section 318-19, the site will have a concrete exposure classification of S1, F0, C1, and W1. We assumed an F0 modified since the upper 5 feet of the soil and drilled shaft interaction are ignored. The greatest risk of freeze thaw would also occur in this zone.

August 2021 Page 5 of 21

3.6 Shear Wave Velocity Survey

Multi-Channel Analysis of Surface Waves (MASW) testing was performed at the site to measure the shear wave velocity with respect to depth and to further evaluate the seismic design criteria for the site. The shear wave velocities were determined in general accordance with accepted geophysical testing procedures.

Two MASW traverses were completed at the approximate locations shown on the Site Plan, Figure 3.

The interpreted profiles of shear wave velocity with respect to depth are enclosed in Appendix B. Analysis of these profiles indicates that the weighted average shear wave velocity in the upper 100 feet of the subsurface profile range from approximately 1,424 feet per second (ft/s) to 1,604 ft/s.

4.0 DESIGN RECOMMENDATIONS

4.1 Karst Topography

Based on our review of the Missouri Department of Natural Resources (MODNR) GeoSTRAT website, the site is underlain by the St. Louis Limestone. This bedrock formation is typically dark gray, thin to medium-bedded to massive limestone containing thin beds of bluish-gray shale. This highly variable unit consists of dolomite, cherty limestone, fossiliferous limestone, and evaporates. Karst geology is also prevalent in this formation. Karst is a topography formed from the dissolution of soluble rocks such as limestone. It is characterized by underground drainage systems with sinkholes and caves.

Based on our review of the Missouri Department of Natural Resource (MoDNR) GeoSTRAT site, no sinkholes are shown on site. However, twelve sinkholes are located within a half mile of the site to the north, east and west of the site. The locations of the nearby sinkholes are shown on an aerial photograph in Figure 4. While no karst features were observed at the surface during our initial site walkover, during the second phase of drilling, a possible clay filled void was observed from 32 to 40 feet. This could be evidence of a karst feature.

Based on the underlying bedrock conditions, there is a risk of karst development at the site. It is difficult to predict whether or not a karst feature will cause settlement of the soils below the structure. However, we understand that drilled shaft foundations bearing on limestone bedrock and a structural slab will be used to minimize impact to the structure were a karst feature to develop on site. Additional exploration using geophysics and additional borings can be used to further delineate any features; however, a similar floor slab and foundation type would be recommended. At a minimum, we would recommend extending the drilled shafts near PH-1 beyond the clay/void area to bear on intact limestone below. Pre-coring could be used below the other foundations to confirm the presence of voids or clay seams as detailed in Section 4.4.

August 2021 Page 6 of 21

4.2 Expansive Clay Remediation

Expansive clay soils are susceptible to excessive volume change with variations in moisture content, which can lead to movement of concrete slabs and foundations of lightly-loaded structures, slabs, retaining walls, or pavements. Where the bearing soils consist of expansive clay soils, we recommend that they be removed to minimum depths of 3 feet beneath the bottom of the floor slab. We anticipate that spot areas of expansive clay will require remediation below the slab near B-4. The actual need for, and extents of, remediation should be delineated by SCI personnel in the field during construction.

The overexcavation should extend at least 2 feet beyond the outside edge of the building footprint to facilitate uniform compaction of the replacement materials and may require additional widening at the building corners to allow equipment access for proper compaction. The overexcavation should be backfilled with properly compacted low plastic soil or one-inch minus crushed limestone.

The methods of treatment described above are based on generally accepted standards in the local engineering community; however, swell pressures and volume change potential greater than can be mitigated by these methods may exist. Consequently, the owner should recognize that there is an inherent, but reduced risk that foundation and floor slab damage may occur, even after remedial treatment of the subgrade soil.

4.3 Existing Fill Materials

The existing fill was placed during construction of existing site features; however, documentation regarding the placement and compaction of the fill material is not available, and the results of our field testing suggest that portions of the existing fill may not have been placed and compacted in a controlled manner. Therefore, the engineering properties and performance of the existing fill cannot be predicted with certainty and risk of settlement of the fill underneath the building exists. However, the use of structural floor slab and deep foundations bearing on bedrock will minimize the risk associated with the existing fill.

4.4 Deep Foundation Recommendations

Due to the potential for karst development, the presence of existing fill, and to match the foundations of the existing structure, the proposed urgent care clinic will be founded on drilled shaft foundations bearing on bedrock.

August 2021 Page 7 of 21

Drilled piers, designed for end-bearing or skin friction in the underlying limestone bedrock are appropriate for support of the structures. For piers designed and constructed in accordance with our recommendations, total settlement should be less than 1-inch, and differential settlement between adjacent footings should be less than ¾-inch.

An allowable end-bearing pressure of 40 kips per square foot (ksf) may be used for piers bearing on competent limestone. This allowable end bearing value will need to be confirmed after the completion of the additional borings. Competent limestone bedrock is defined in Table 4.1 and should be evaluated by pre-drilling of the pier location or probe holes during construction.

Table 4.1 – Drilled Pier Rock Quality Criteria

Depth Below Pier (feet)

Maximum Individual Seam Thickness

(inch)

Maximum Summation of Seam Thickness Within Interval

(inch)

0 – 1/2D* 0.25 0.4

1/2D – D 0.35 0.6

D – 2D 1.25 2.0

* D is the pier diameter.

We anticipate encountering limestone at depths ranging from 20 to 30 feet below the ground surface, with an anticipated rock socket of at least 3 feet. Again, additional borings will confirm this depth and the depth of rock socket. Even with the additional borings, the required rock socket length is dependent on the quality of bedrock encountered, the design loads and structural requirements, and should be determined during pre-drilling (as discussed in Section 4.6.4) or probe hole drilling during construction.

Overages in the quantity of rock coring can result in significant additional costs. To reduce the amount of rock coring, and the need for pre-drilling or probe hole drilling during construction, the foundations may be sized for a reduced net allowable end-bearing pressure of 20 ksf at the auger refusal depth of the drill rig.

The foundation near PH-1 should be extended beyond the void to competent limestone beyond a depth of

37 feet.

Net allowable skin friction values of 0.3 ksf, 1 ksf, and 5 ksf may be used for the native clay soils, weathered limestone, and competent limestone, respectively. Skin friction should be ignored within the existing fill and/or the upper 5 feet of pier, whichever is greater.

August 2021 Page 8 of 21

All piers should be properly reinforced as recommended by the structural engineer. We anticipate that temporary casing and pumping of groundwater of the drilled pier shafts will be required. Concrete placement by tremie method may be necessary if a dry shaft cannot be maintained.

4.4.1 Uplift Capacity

The uplift capacity of the deep foundations should be computed as the sum of the weight of the foundation element and the skin friction between the foundation element and the adjacent soil. The allowable skin friction values (FS=2) shown in Table 4.2 may be used for calculating the uplift capacity of the deep foundation elements, provided a minimum pile spacing of three times the maximum element dimension, is maintained. Uplift capacity should be ignored within the upper 5 feet of the pier/pile, existing fill, and weathered limestone.

Table 4.2 – Uplift Capacity Parameters for Drilled Piers

Material Allowable Skin Friction, ksf, (SFall)

Lean and Fat Clay 0.3

Weathered Limestone 1.0

Limestone 5 ksf - kips per square foot

4.4.1.1 Uplift Capacity for Group Action

The deep foundation groups will act as a block if they are spaced closer than three times the maximum element dimension. In this instance, the uplift capacity should be calculated as follows:

• Σ2(Lg +Bg) x SFall x ∆L + W, where:

o Lg = group length, feet (exterior edge to exterior edge of the foundation elements);

o Bg = group width, feet (exterior edge to exterior edge of the foundation elements);

o SFall = allowable skin friction obtained from Table 4.2;

o ∆L = length of foundation element in each material; and o W = weight of the foundation element, kips.

4.4.2 Lateral Resistance of Piers

After completion of the supplemental borings, SCI will model one iteration of the canopy foundation using L-Pile. Results will be included in the final report.

August 2021 Page 9 of 21

4.4.3 Pre-Drilling (for Deep Foundations)

Consideration could be given to pre-drilling the proposed column locations to verify the deep foundation element bearing elevations that will be required based on structural loads and the quality of the bedrock.

This work includes mobilizing a drilling rig, similar to the rig used to drill the soil borings at this site, prior to the bid phase, to drill to auger refusal and perform rock coring at each proposed column location.

The benefits of pre-drilling include the following:

• A potential increase in the recommended net allowable end-bearing capacity, which could reduce pier/pile diameters;

• Minimizing unforeseen conditions, which may be encountered during construction, such as obstacles or unsuitable bedrock; thereby, allowing contractors to bid a better-defined scope of work; and

• A reduction or elimination in the time and costs associated with probe hole drilling and manned down-hole inspection during construction (for drilled piers).

At your request, SCI can provide a proposal for this service, which is outside of our current scope.

The foundation plans, showing the pier locations, diameters, required rock sockets, and anticipated structural loads for each column would be necessary to develop this proposal.

4.5 Seismic Considerations

Ground shaking at the foundation of structures and liquefaction of the soil under the foundation are the principle seismic hazards to be considered in design of earthquake-resistant structures. Liquefaction occurs when a rapid buildup in water pressure, caused by the ground motion, pushes sand particles apart, resulting in a loss of strength and later densification as the water pressure dissipates. This loss of strength can cause bearing capacity failure, while the densification can cause excessive settlement. Potential earthquake damage can be mitigated by structural and/or geotechnical measures or procedures common to earthquake resistant design.

4.5.1 Design Earthquake

According to International Building Code (2015 edition) (IBC 2015), structures such as those proposed for this project are required to be designed to a design earthquake with a 2 percent Probability of Exceedance over a 50-year exposure period (i.e. a 2,475-year design earthquake). The design earthquake has a

Moment Magnitude (Mw) of 4.9 and a Peak Ground Acceleration of 0.237g, as determined from data provided by the IBC 2015 and the United States Geological Survey National Seismic Hazard Mapping

Project.

August 2021 Page 10 of 21

4.5.2 International Building Code Site Classification

Refraction Micro-tremor data was acquired along Traverses T-1 and T-2 to measure the shear wave velocity in the subsurface soils, with respect to depth, at the locations shown on the Aerial Photograph.

The interpreted profiles of shear wave velocity with respect to depth are contained in Appendix C.

Our analysis indicates that the weighted average shear wave velocity in the upper 100 feet of the subsurface profile at the subject site is approximately 1,424 to 1,604 feet per second (ft/sec), indicating a Site Class C.

4.5.3 Site Specific Seismic Evaluation (SSSE)

In addition to the simplified design method, SCI performed a Site Specific Seismic Evaluation (SSSE) for the project to determine the appropriate response curve and Seismic Design Category for use in designing the project.

The SSSE was performed utilizing synthetic earthquake input provided by the USGS website and a commercially available program ProShake[1] in order to develop a Site Specific Response Curve.

The Design Response Spectrum is a composite curve developed following the procedures presented in

Section 1613 of the IBC 2015 code and Chapter 21 of ASCE 7-10. Based on the analysis, the seismic design parameters for the site are as follows: Fa = 1.20, Fv = 1.63, SDS = 0.46, and SD1 = 0.22, which results in a Seismic Design Category (SDC) of D for sites with an Occupancy Category of IV.

4.5.4 Liquefaction Potential Analysis

The liquefaction potential analysis for the site was conducted using data from the field exploration and laboratory test results and the techniques outlined in the National Center for Earthquake Engineering

(NCEER) Technical Report NCEER-97-0022. Based on our analyses, the soils at the project site have sufficient strength values to resist liquefaction and/or plasticity index that make the threat of liquefaction minimal during the design earthquake. While the amount of the seismically induced settlement is dependent on the magnitude and distance from the seismic event, we estimate that the settlements from the design earthquake will be negligible and relatively uniform in nature, so liquefaction mitigation techniques are not required.

4.6 Floor Slabs

The following recommendations assume a floor load of approximately 150 psf. If sections of the floor slabs will support loads greater than this, underlying subgrade soils below these sections may need to be removed and replaced with compacted/engineered fill. SCI recommends that if the proposed building will include

[1] ProShake, Ground Response Analysis Program, Version 1.12, EduPro Civil Systems, Inc., Sammamish, WA.

August 2021 Page 11 of 21 heavily-loaded floor slab sections, SCI should be provided the opportunity to review the final design plans and specifications to determine if the underlying subsurface soils can adequately support the loads.

Proofrolling, as discussed in Section 5.1, should be accomplished to identify soft or unstable soils that should be removed from the floor slab area prior to fill placement and/or floor slab construction.

We recommend that the floor slabs be designed using a modulus of subgrade reaction, k value, of

100 pounds per cubic inch (pci) based on values typically obtained from 1-foot by 1-foot plate load tests.

This value assumes the slabs will bear on remediated existing fill or newly-placed, low plastic structural fill. Depending on how the slab loads are applied, the value will have to be geometrically modified.

The value should be adjusted for larger areas using the following expression for cohesive and cohesionless soil:

Modulus of Subgrade Reaction, ks = ( 𝑘𝑘

𝐵𝐵

) for cohesive soil; and ks = 𝑘𝑘 �

𝐵𝐵+1

2𝐵𝐵

�2 for cohesionless soil.

where: ks = coefficient of vertical subgrade reaction for loaded area;

k = coefficient of vertical subgrade reaction for 1x1 square foot area; and B = width of area loaded, in feet.

The floor slabs should be supported on a minimum 4-inch-thick layer of crushed stone. This will help to distribute concentrated loads and equalize moisture conditions beneath the slab.

It is generally preferable to maintain structural separation between the floor slabs and the foundation walls and column pads using isolation joints. We also suggest that joints be placed in the floor slabs with spacing

(in feet) equal to approximately three times the thickness of the slab (in inches) in both directions.

Such joints permit slight movements of the independent elements and help reduce random cracking that might otherwise be caused by restraint of shrinkage, slight rotations, heave, or settlement. Where occupied space or moisture sensitive floor coverings are planned, we recommend a 6-mil-thick polyethylene sheeting be placed immediately beneath the floor slab and above the crushed rock or gravel to reduce the transfer of capillary moisture to the slabs. However, without careful attention to curing of the floor slabs, the polyethylene sheeting can cause excessive shrinkage cracking and "curling."

August 2021 Page 12 of 21

The precautions listed below should be followed for construction of slab-on-grade pads. These details will not reduce the amount of movement, but are intended to reduce potential damage, should some settlement of the supporting subgrade take place. Some increase in moisture content is inevitable as a result of development and associated landscaping. However, extreme moisture content increases can be largely controlled by proper and responsible site drainage, building maintenance and irrigation practices.

• Cracking of slab-on-grade concrete is normal and should be expected. Cracking can occur not only as a result of heaving of the supporting soil, but also as a result of concrete curing stresses.

The occurrence of concrete shrinkage cracking, and problems associated with concrete curing may be reduced and/or controlled by limiting the slump of the concrete, proper concrete placement, finishing, curing, and by the placement of crack control joints at frequent intervals, particularly where re-entrant slab corners occur.

• Areas supporting slabs should be properly moisture conditioned and compacted. Backfill in all interior and exterior water and sewer line trenches should be carefully compacted to reduce the shear stress in the concrete extending over these areas.

Exterior slabs should be isolated from the proposed structure. These slabs should be reinforced to function as independent units. Movement of these slabs should not be transmitted to the building foundations or superstructure.

4.7 Below-Grade Walls

Below-grade walls at this site include retaining walls and potentially tall wall foundations designed to accommodate surface grade changes around the building and paved areas of the site. The maximum toe pressure for below-grade walls should not exceed 1,500 psf. If higher bearing pressures are needed, they should be brought to our attention and discussed on a case-by-case basis. Below-grade walls may be designed with an ultimate coefficient of friction between the base of the concrete footing and the soil subgrade of 0.3.

Below-grade walls should also be designed to withstand lateral earth pressures caused by the weight of the backfill, including slopes behind the walls, and any surcharge, such as adjacent floor loads. We recommend the equivalent fluid unit weights tabulated below for lateral earth pressures, in pounds per cubic foot, be used in the design of below-grade walls. Fat clay soils should not be used to backfill below-grade walls.

The indicated values assume that positive drainage is provided to prevent buildup of hydrostatic pressure.

Values for granular material should only be used if the granular backfill extends upwards and outwards the full height of the wall at a slope of 45 degrees or flatter from its base. In this case, exterior granular backfill should be capped with approximately 2 feet of cohesive soil to reduce the potential for surface water

August 2021 Page 13 of 21 infiltration into the granular backfill. With clean granular backfill, filter fabric, such as Mirafi 140N, should be placed along the interface between the soil and granular backfill to reduce the potential for infiltration of the soil into the granular material.

Table 4.3 - Recommended Lateral Earth Pressures

Backfill Type Equivalent Fluid Unit Weights

At-Rest Earth Pressures (pcf)

Active Earth Pressures (pcf)

Cohesive Soil 70 50

Granular Material (1-inch minus) 60 40

Free-Draining, Granular Material (1-inch clean) 50 30

At-rest earth pressures should be used for restrained or fixed-head walls that are restricted from rotation, such as loading dock or basement walls connected to floor joists or beams, or a wing wall attached to a basement wall. Active earth pressures should be used for free-head walls where the base remains fixed and deflection at the top of the wall of approximately 1-inch for each 10 feet of wall height is allowed, such as a retaining wall.

The above values are applicable when the surface of the backfill behind the wall is horizontal.

Upward sloped or loaded backfill will result in increased values. In addition to lateral earth pressures, below-grade walls should be designed to resist any surcharge loads, including shallow building foundations and traffic. These surface loads can be modeled as uniform lateral loads, equivalent to one-half of the surface load, acting at the halfway point on the wall.

A passive soil resistance modeled by an equivalent fluid unit weight of 250 pcf may be used for natural soil against the face of the exterior base of the wall. The upper 2 feet of soil backfilled against the exterior face of the walls and uncontrolled backfill soils should be ignored when calculating the lateral resistance.

Lower passive pressure should be used if the ground surface slopes downward away from the face of the wall.We recommend that all below-grade walls be provided with a drainage system. A minimum 4-inch diameter, perforated drainpipe should be used, and placed at foundation level. Granular drainage material, consisting of 1-inch clean crushed rock, classified as GP by ASTM D 2487, with less than 5 percent of the rock passing the No. 200 sieve, should be placed at a minimum of 6 inches in all directions around the drainage pipe. Synthetic filter fabric, such as Mirafi 140N or equivalent, should encapsulate the drainpipe and granular drainage material. The pipe should be sloped to drain by gravity or to a sump with a pump for below-grade walls where positive drainage by gravity cannot be achieved. Any interior sumps must be isolated “watertight” from the interior subgrade to prevent the movement of moisture from the sump into the underlying soils.

August 2021 Page 14 of 21

4.8 Site Grading

Positive site drainage should be provided to reduce surface water infiltration around the perimeter of the structures and beneath the floor slabs. All grades should be sloped away from the structures. Roof and surface drainage should be collected and discharged such that water is not permitted to infiltrate the backfill of the structures.

Large trees and shrubs should be planted away from exterior footings as they may cause drying and shrinkage of the foundation soils and, with the passage of time, potentially detrimental settlement of the floor slabs and foundations. A minimum distance of 20 feet or the mature tree’s dripline, whichever is greater, is suggested.

We recommend that all final slopes have a maximum inclination of 3 horizontal to 1 vertical (3H:1V), and that a crest of at least 10 feet in width or a distance equivalent to the total height of the slope, whichever is less, be provided around the structures before the surface slopes down and away.

4.9 Underground Utilities

Underground utilities can provide a pathway for water to migrate below the floor slabs. Drain and utility pipes beneath floors should have tight joints to prevent leakage. If utility excavations are backfilled with free-draining granular materials, then cutoffs should be provided at the exterior walls to reduce the potential for water to migrate beneath the buildings. Impermeable cutoffs may consist of a 3-foot-long “plug” of cohesive soil or bentonite soil mix, or a 1-foot-long plug of lean concrete. Soil may be used for the balance of the backfill.

Groundwater is not anticipated to be encountered during the installation of deep utilities. In most situations, small amounts of groundwater seepage into the excavations can be handled by means of gravity ditching and a sump pump. If greater flows are experienced, SCI should be retained to review our recommendations, and provide additional recommendations regarding dewatering.

With the exception of individual service lines to the buildings that intersect foundations perpendicularly, below-grade utilities should not be located within the stress influence zone of the building foundations.

Accordingly, below-grade utilities should be located outside a zone extending 45 degrees downward and outward from the edge of the footings.

August 2021 Page 15 of 21

4.10 Pavement

Selection of the pavement section is dependent on the design life, traffic loads, subgrade strength, drainage characteristics, and the desired level of maintenance. Neither California Bearing Ratio testing nor formal pavement design was a part of our scope for this project. However, for planning purposes, the following recommendations typically result in pavements that perform satisfactorily on similar subgrades under automobile and pickup truck loads. They are intended to roughly provide a pavement requiring routine maintenance for a 5-year period, minor repair and maintenance during the 5- to 10-year life of the pavement, and possibly major repairs and restoration after a 10-year service life.

A flexible pavement section may be used for the parking lot. Parking areas for automobiles and light trucks should consist of a minimum 6-inch-thick crushed stone base with a minimum 3-inch-thick asphaltic concrete wearing surface. In heavy duty drive lanes, the crushed stone base should be thickened to at least

8 inches with an asphaltic concrete wearing surface of 4 inches. Care should be taken to provide drains or drainable transition at locations where pavement sections of varying thickness abut, so as not to trap water within the crushed stone base, which could saturate and soften the subgrade.

Alternately, a rigid concrete pavement section may be used, with less anticipated long-term maintenance.

Parking areas for automobiles and light trucks should consist of a minimum 6-inch-thick, non-reinforced concrete pavement with a crushed stone base of 4 inches. For more heavily trafficked areas, we recommend that the section consist of an 8-inch-thick, non-reinforced concrete pavement, over 4 inches of compacted base rock. This concrete pavement section should also be used to support concentrated wheel loads for trash dumpster pads, approaches, and other areas where trucks will maneuver. To provide resistance against salt and freeze-thaw cycles, we recommend the concrete have a minimum 28-day compressive strength of

4,000 pounds per square inch (psi) and air entrainment of 5 to 7 percent by volume. We also recommend that the maximum joint spacing be approximately 15 feet.

The subgrade should be proofrolled and any soft unsuitable areas should be removed and replaced as discussed in Section 5.1.

5.0 SITE DEVELOPMENT AND CONSTRUCTION CONSIDERATIONS

5.1 Site Preparation

While not encountered during drilling the site has previously been developed, as such, below-grade components of former structures may be encountered between our boring locations. Any existing foundation walls and footings, floor slabs, pavements, cisterns and septic fields, and utilities, as well as

August 2021 Page 16 of 21 their associated backfill, should be removed from below and at least 10 feet beyond the proposed structure footprints. As an exception, deep utilities may be grouted in-place rather than being removed.

However, the existing backfill associated with deep utilities should be removed and replaced or recompacted. Outside this area, existing foundation walls and footings deeper than 3 feet below the proposed subgrade may be left in place. Excavations resulting from the removal of existing structures should be backfilled with properly compacted fill.

The site should be proofrolled by systematically passing over the subgrade to achieve complete coverage with proper compaction or loaded construction equipment, and observing the subgrade for pockets of excessively soft, wet, or disturbed soil, or otherwise unacceptable materials. In particular, any soft areas within the existing fill to remain in place, should be identified during this process. Silty soils are susceptible to excessive pumping or rutting with disturbance such as that caused by construction traffic.

Disturbed areas of silty soils should be undercut and replaced with properly compacted structural fill.

Additional soft areas or otherwise unacceptable materials, if encountered, should be removed and replaced with structural fill or otherwise stabilized as approved by SCI prior to placing additional fill. If removal of soft or unacceptable soils is impractical due to their excessive depth, they should be stabilized or

“bridged over” in a manner approved by SCI. “Bridging” of the soft soils can often be accomplished by working 2- to 4-inch clean crushed rock into the softer soils and then placing a geofabric, such as

Mirafi HP270 or equivalent, prior to placing additional fill.

5.2 Fill Materials and Compaction

Prior to fill placement and compaction, the upper 8 inches of the exposed subgrade should be scarified, moisture conditioned and recompacted. Structural fill should be placed in maximum 8-inch-thick loose lifts and mechanically compacted in accordance with Table 5.1, below. We recommend that any fill placed in building areas have a liquid limit less than 45 and a plasticity index less than 25. If higher plasticity soils are placed within 3 feet of the floor slab subgrades, or 2 feet of the bottom of the footings, then remediation will be required. Acceptable non-organic fill soils include materials designated CL, ML, CL-ML, SP, SW, GP, and GW by ASTM D 2487-11.

August 2021 Page 17 of 21

Table 5.1 - Typical Compaction Requirements for Fill

Material Tested Proctor Type Minimum Percentage Dry Density

Structural Fill (Cohesive) Modified (ASTM D 1557) 90

Standard (ASTM D 698) 95

Structural Fill (Granular) Modified 95

Standard 98

Landscaped Areas (non-load bearing) Modified 88

Standard 92

Utility Trench Backfill Modified 90

Standard 95

Prior to compaction, the soil may require moisture adjustment. During warm weather, moisture reduction can generally be accomplished by disking or otherwise aerating the soil. When air drying is not feasible, a moisture reducing chemical additive, such as hydrated lime, could be incorporated into the soil.

During dry weather, some addition of moisture may be required to facilitate compaction. This should also be done in a controlled manner using a tank truck with a spray bar. The moistened soil should be thoroughly blended with a disk or pulverizer to produce a uniform moisture content. If construction is performed during the winter season, fill materials should be carefully observed to see that no frozen soil is placed as fill or remains in the base materials upon which fill is placed.

Backfill for foundation walls may consist of lean clay, one-inch minus crushed limestone, or controlled low strength material. We advise performing field density tests on at least every other lift to monitor compaction. As an alternate, we suggest using one-inch clean crushed limestone to provide improved drainage and to reduce lateral pressures on the walls. Due to a slight risk of migration of soil fines into the clean rock, a synthetic filter fabric, such as Mirafi 140N or equivalent, should be placed between the soil face of the excavation and the crushed limestone. If clean rock is used, it may be placed in 2-foot-thick lifts and tamped or tracked to achieve adequate densification. Exterior clean rock backfill should be capped with cohesive soil to reduce the potential for surface water infiltration.

Backfill placed next to walls should be compacted with hand operated equipment and not large self-propelled or machine operated equipment, which could result in potential overcompaction and higher lateral pressures. Compaction should be reduced within approximately one-foot of the walls, and the walls should be observed periodically for signs of movement. If movement is detected, it may be necessary to provide bracing and/or change backfill procedures.

August 2021 Page 18 of 21

In addition to the minimum density requirements listed above, the soil must be stable, i.e., not “pumping” or rutting excessively under construction traffic, prior to placing additional fill or constructing foundations, floor slabs, or pavements. Field density tests should be performed on each lift of fill to document that proper compaction is achieved.

5.3 Deep Foundation Quality Control/Quality Assurance

SCI should work with the owner and structural engineer to develop a quality control plan. However, a suggested scope is detailed below.

Pre-drilling is recommended to evaluate the quality of the bedrock and verify that the estimated uplift capacities are present. SCI should be present to document installation of each pier. Down-hole observation, via camera methods should be performed to evaluate the cleanliness and quality of the bearing strata.

A sonic caliper may be used to assess diameter, verticality and aid in volume calculation. SCI should also perform Non-Destructive Testing consisting of Cross Hole Sonic Logging in accordance with

ASTM D6760 for 5 to 10 percent of the production elements.

5.4 Floor Slab Subgrades

Floor slab subgrades may be subjected to construction traffic and exposure to weather for an extended period. In addition, subgrade covered with base rock may be very slow to dry if precipitation occurs after placing the base rock. Therefore, the subgrade should be sloped to provide drainage and placement of the base rock be done as close to the time of pouring the floor slabs as is practical.

Special measures may be required to facilitate construction during wet or cold weather, or where excessive areas of soft soils are identified.