S1445-05-24_Fresno_C130_Barracks_GI-Geohaz_FINAL_12.21.pdf

PREPARED FOR:

CAL FIRE, TECHNICAL SERVICES UNIT

1300 U STREET, SUITE 100

SACRAMENTO, CALIFORNIA 95818

PREPARED BY:

GEOCON CONSULTANTS, INC.

3160 GOLD VALLEY DRIVE, SUITE 800

RANCHO CORDOVA, CALIFORNIA 95742

GEOCON PROJECT NO. S1445-05-24 DECEMBER 2021

Fresno C130 Barracks 2311 N. Clovis Avenue

Fresno, California

GEOLOGIC HAZARDS EVALUATION

AND GEOTECHNICAL INVESTIGATION

GEOLOGIC HAZARDS EVALUATION

AND GEOTECHNICAL INVESTIGATION

Fresno C130 Barracks 2311 N. Clovis Avenue

Fresno, California

Project No. S1445-05-24 December 23, 2021

VIA ELECTRONIC MAIL

Daniel O’Brien Manager of Environmental Services Department of General Services Project Management and Development Branch Real Estate Services Division 707 3rd Street, 4th Floor West Sacramento, California 95605

Subject: GEOLOGIC HAZARDS EVALUATION AND GEOTECHNICAL INVESTIGATION

CAL FIRE AIR ATTACK BASE (AAB) C130 BARRACKS

2311 N CLOVIS AVENUE

FRESNO, CALIFORNIA

Mr. O’Brien:

In accordance with Agreement No. 5901-C, Task Order No. 23 dated June 10, 2021, we performed a geologic hazards evaluation and geotechnical investigation for the proposed C130 barracks located at the Fresno Air Attack Base (AAB) in Fresno, California.

The purpose of our study was to (1) perform a Geologic Hazards Evaluation meeting the current California Geological Survey guidelines and (2) evaluate the subsurface conditions at the site and provide geotechnical recommendations for design and construction of the proposed improvements. In our opinion, no adverse geological or geotechnical conditions were encountered that would preclude re-development at the site provided recommendations of this report are incorporated into the design and construction of the project.

The accompanying report presents our findings and conclusions from our study. Please contact us if you have any questions concerning the contents of this report.

Respectfully Submitted, GEOCON CONSULTANTS, INC.

Brenda P. Fernandez, EIT John C. Pfeiffer, PG, CEG Senior Staff Engineer Senior Geologist

Jeremy J. Zorne, PE, GE Senior Geotechnical Engineer

TABLE OF CONTENTS

GEOLOGIC HAZARDS EVALUATION AND GEOTECHNICAL INVESTIGATION PAGE

1.0 INTRODUCTION AND PURPOSE

1.1 Scope of Services

2.0 SITE AND PROJECT DESCRIPTION

2.1 Site Location and Description

2.2 Current Topography

2.3 Project Description

3.0 SOIL AND GEOLOGIC CONDITIONS

3.1 Site and Regional Geology

3.2 Existing Pavement

3.3 Alluvial Fan Deposits (Alluvium)

4.0 GROUNDWATER

5.0 GEOLOGIC HAZARDS

5.1 Mapped Geologic Hazard Zones

5.2 Surface Fault Rupture

5.3 Seismicity

5.4 Liquefaction

5.5 Lateral Spreading

5.6 Unsaturated Seismic Settlement

5.7 Seismic Site Classification / Seismic Design Parameters

5.8 Landslides and Slope Stability

5.9 Tsunamis and Seiches

5.10 Flooding and Dam Failure Inundation

5.11 Expansive Soil

5.12 Soil Corrosion Screening

5.13 Volcanic Activity

5.14 Naturally Occurring Asbestos

5.15 Oil Fields & Methane Zones

5.16 Radon

6.0 CONCLUSIONS AND RECOMMENDATIONS

6.1 General

6.2 Soil and Excavation Characteristics

6.3 Materials for Fill

6.4 Grading

6.5 Foundations

6.6 Interior Slabs-on-Grade

6.7 Slab-on-Grade Moisture Protection Considerations

6.8 Retaining Walls and Lateral Loads

6.9 Concrete Flatwork

6.10 Pavement – Hot Mix Asphalt

6.11 Pavement – Rigid Concrete

6.12 Site Drainage and Moisture Protection

7.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS

8.0 LIST OF REFERENCES

TABLE OF CONTENTS

(Continued)

FIGURES

Figure 1 – Vicinity Map Figure 2 – Site Plan Figure 3 – Proposed Development Plan Figure 4 – Regional Geologic Map Figure 5 – Cross-Section A-A’ Figure 6 – Regional Fault Map Figure 7 – Regional Seismicity Map

APPENDIX A

FIELD EXPLORATION PROGRAM

Figure A1 – Key to Logs Figures A2 through A6 – Logs of Exploratory Borings (B1 through B4)

APPENDIX B

LABORATORY TESTING PROGRAM

Table B1 – Expansion Index Test Results Table B2 – R-Value Test results Figure B1 – Summary of Laboratory Results Figure B2 – Atterberg Limits Figure B3 – Grain Size Distribution Figure B4 – Moisture-Density Relationship Figure B5 – Triaxial Shear Strength – CU Test

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GEOLOGIC HAZARDS EVALUATION AND GEOTECHNICAL INVESTIGATION

1.0 INTRODUCTION AND PURPOSE

This report presents the results of our geologic hazards evaluation and geotechnical investigation for the proposed new barracks at the Fresno Air Attack Base (AAB) located at 2311 North Clovis Avenue in Fresno, California. The approximate site location is depicted on the Vicinity Map, Figure 1.

Per the Division of the State Architect (DSA) requirements (DSA IR A-4.13), a Geologic Hazards Evaluation subject to review by the California Geological Survey (CGS) is required for the project.

The purpose of our study was to (1) perform a Geologic Hazards Evaluation meeting the current CGS guidelines and (2) evaluate the subsurface conditions at the site and provide geotechnical recommendations for design and construction of the proposed improvements.

1.1 Scope of Services

To prepare this report, we performed the following scope of services:

• Performed a limited geologic literature review to aid in evaluating the geologic and seismic conditions present at the site. A list of referenced material is included in Section 9.0 of this report.

• Reviewed available conceptual plans to select exploratory boring locations.

• Performed a site reconnaissance to review project limits, determine exploration equipment access, and mark out the proposed exploration locations.

• Notified subscribing utility companies via Underground Service Alert (USA) a minimum of two working days (as required by law) prior to performing excavations at the site.

• Paid required fees and obtained a soil boring permit from the City of Fresno Public Works Department.

• Performed four (4) exploratory borings (B1 through B4) with a truck-mounted drill rig equipped with 8-inch diameter hollow-stem augers to depths ranging from approximately 5 to 51½ feet.

• Obtained representative samples from the exploratory borings.

• Logged the borings in general accordance with the Unified Soil Classification System (USCS).

• Upon completion, backfilled the exploratory borings with neat cement grout or soil cuttings in accordance with the City of Fresno permit requirements.

• Performed laboratory tests to evaluate pertinent geotechnical parameters.

• Prepared this report summarizing our findings, conclusions, and recommendations regarding the geotechnical aspects of site improvements as presently proposed.

Approximate locations of the exploratory borings are shown on the Site Plan, Figure 2 and Proposed Development Plan, Figure 3. Details of our field exploration program including exploratory boring logs are presented in Appendix A. Details of our laboratory testing program and test results are summarized in Appendix B.

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2.0 SITE AND PROJECT DESCRIPTION

2.1 Site Location and Description

The site consists of an approximate 2-acre parking lot for the Fresno AAB located at 2311 North Clovis Avenue in Fresno, California. The Fresno AAB is bounded by the Fresno Yosemite International Airport to the west, East Aircorp Way to the north, North Clovis Avenue to the east, and East McKinley Avenue to the south. Approximate site coordinates are 36.7710 degrees north and -

119.7008 degrees west. The Fresno AAB consists of an office building, three additional buildings, seven mobile trailers, four fire retardant tanks, container units, a shed, a tower, concrete flatwork, a parking lot, and landscaping. The current site configuration is shown on the Site Plan, Figure 2.

2.2 Current Topography

The site is relatively flat and level. Based on topographic information provided by CAL FIRE, site elevations range from approximately 334 to 336 feet above mean sea level (MSL). Topography in the immediate surrounding area based on USGS mapping is shown on the Vicinity Map – Figure 1. As shown on Figure 1, the site and vicinity does not include any significant slopes or topographic features.

Site-specific topography is shown on the Proposed Development Plan, Figure 3.

2.3 Project Description

The project consists of constructing a new approximate 4,800-square-foot barracks building within the existing Fresno AAB parking lot. Associated improvements will likely include underground utility infrastructure, paved drives/parking areas, and landscaping. Anticipated structural loading values are not yet available; however, we assume relatively light to moderate structural loading for the proposed new building. The new single-story building will likely be of modular and/or conventional wood-frame and/or masonry construction and will be supported on a conventional shallow foundation with an interior concrete slab-on-grade. The building will be constructed at-grade, without a basement or other below-grade structures. New pavement areas will likely consist of flexible hot mix asphalt (HMA) and/or rigid Portland cement concrete (PCC). Given the relatively flat and level topography of the site, we anticipate minor grading with cuts and fills on the order of 3 to 5 feet or less. Some underground utilities may require deeper excavations. Approximate locations and features of the proposed improvements are shown on the Proposed Development Plan, Figure 3.

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3.0 SOIL AND GEOLOGIC CONDITIONS

We identified soil and geologic conditions by reviewing referenced geologic literature (Section 8.0), observing exploratory borings, and performing geologic reconnaissance of the site and surrounding area. The soil descriptions provided in this report include the USCS symbol where applicable.

3.1 Site and Regional Geology

Based on our review of published geologic maps of the area, the site is located near the eastern edge of the Great Valley geomorphic province of California. The Great Valley (Sacramento and San Joaquin Valleys) of California is a long structural depression or down-warped trough, with the axis of the trough lying close to the eastern front of the Coast Ranges geomorphic province. In general, the northern portion of the San Joaquin Valley is underlain by Quaternary continental deposits (alluvial deposits) and late Tertiary age marine and continental sedimentary rocks, which rest on a basement complex consisting of granitic rocks of the Sierra Nevada.

Published geologic mapping depicts the site vicinity underlain by Quaternary-age fan deposits, which are alluvial deposits generally consisting of interbedded mixtures of sand and silt (CGS, 1965). The subsurface conditions encountered during our field investigation at the site were generally consistent with the mapped geology of the area. A portion of the geologic map covering the site vicinity is presented as Figure 4. A generalized geologic cross-section of the site is presented as Figures 5.

3.2 Existing Pavement

We encountered approximately 4 inches and 4½ inches of HMA pavement in Borings B4 and B3, respectively. We did not observe an aggregate base (AB) layer below the HMA.

3.3 Alluvial Fan Deposits (Alluvium)

Below the pavement in Borings B3 and B4 and at the ground surface in Borings B1 and B2, we encountered alluvial fan deposits (alluvium) to the maximum depth explored of approximately 51½ feet. The alluvium generally consists of layers of very stiff to hard silt (ML) and loose to very dense silty sand (SM) and poorly graded sand (SP). Relative density and consistency generally increases with depth, with the looser and softer materials closer to the ground surface.

Soil conditions described in the previous paragraphs are generalized. The exploratory boring logs included in Appendix A detail soil type, color, moisture, consistency, and USCS classification of the soils encountered at specific locations and elevations.

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4.0 GROUNDWATER

We did not encounter groundwater in our exploratory borings (B1 through B4) performed on September 16, 2021 to a maximum depth of 51½ feet.

We reviewed available depth-to-groundwater data on the California Department of Water Resources (DWR) Sustainable Groundwater Management Act (SGMA) Data Viewer (https://sgma.water.ca.gov/webgis/?appid=SGMADataViewer#gwlevels). The SGMA Data Viewer website indicates that depth to groundwater at the site ranges from approximately 90 to 100 feet (Spring 2020).

It should be noted that fluctuations in the level of groundwater may occur due to variations in precipitation, temperature, and other factors. Depth to groundwater can also vary significantly due to localized pumping, irrigation practices, and seasonal fluctuations. Therefore, it is possible that groundwater may be higher or lower than the levels observed during our investigation.

5.0 GEOLOGIC HAZARDS

5.1 Mapped Geologic Hazard Zones

The site is not located in any currently established official geologic hazard zones (e.g. liquefaction, active faulting, landslides) established by CGS or the local agency specific plan.

5.2 Surface Fault Rupture

Based on our research, analyses, and observations, the site is not located on any known “active” earthquake fault trace. In addition, the site is not contained within an Alquist-Priolo Earthquake Fault Zone. Therefore, we consider the potential for ground rupture due to onsite active faulting to be low. In order to determine the distance to known active faults within 50 miles of the site, we used the 2013 Caltrans Fault Database KML overlay file for Google Earth. Principal references used within the 2013 Caltrans Fault Database are the 2010 Fault Activity Map of California (Jennings and Bryant, 2010) and Working Group on California Earthquake Predictions (WGCEP), Uniform California Earthquake Rupture Forecast Version 3. Results are summarized in Table 5.2. Figure 6, Regional Fault Map, depicts the location of the site relative to mapped faults in the region.

TABLE 5.2

REGIONAL FAULT SUMMARY

Fault Name Approximate Distance from Site (miles)

Maximum Earthquake Magnitude, Mw

Great Valley 12 45.6 6.3 Great Valley 11 45.8 6.5 Great Valley 13 46.6 7.0

San Andreas Fault 70.4 7.9 Owens Valley 81.9 7.2

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5.3 Seismicity

As with all of California, the site has experienced historic earthquakes from various regional faults.

The seismicity of the region surrounding the site was formulated based on research of an electronic database of earthquake data. Based on our review of available reports published by CGS and the United States Geological Survey (USGS), the site has not experienced reported ground failure due to past earthquakes. The epicenters of recorded earthquakes with magnitudes equal to or greater than 5.0 within 100 miles of the site are depicted on the Regional Seismicity Map, Figure 7.

5.4 Liquefaction

Liquefaction is a phenomenon in which saturated cohesionless soils are subject to a temporary loss of shear strength due to pore pressure buildup under the cyclic shear stresses associated with earthquakes.

Primary factors that trigger liquefaction are: strong ground shaking (seismic source), relatively clean, loose granular soils (primarily poorly graded sands and silty sands), and saturated soil conditions (shallow groundwater). Due to the increasing overburden pressure with depth, liquefaction of granular soils is generally limited to the upper 50 feet of a soil profile.

Based on the subsurface conditions encountered at the site, including groundwater depths on the order of 90 to 100 feet and very dense granular and hard cohesive soils, liquefaction potential at the site is expected to be low during seismic events. Mitigation and specific design measures with respect to liquefaction are not necessary for the project.

5.5 Lateral Spreading

Because the site topography is generally flat and level and there is no adjacent free-face or sloping geometry, lateral spreading is not anticipated.

5.6 Unsaturated Seismic Settlement

Strong seismic shaking can induce settlement of unsaturated, loose sandy soil. Based on the results of our subsurface investigation, the site is underlain by medium dense to very dense silty sand and hard cohesive soil. Therefore, unsaturated seismic settlement is not a significant hazard for the site.

5.7 Seismic Site Classification / Seismic Design Parameters

Seismic design of the structure should be performed in accordance with the provisions of the 2019 California Building Code (CBC) which is based on the ASCE/Structural Engineering Institute (SEI) publication: ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI, 2017). We used the Structural Engineers Association of California (SEAOC) and Office of Statewide Health Planning and Development (OSHPD) web application Seismic Design Maps (https://seismicmaps.org/) to evaluate site-specific seismic design parameters in accordance with ASCE 7-16.

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For seismic design purposes, sites are classified as Site Class “A” through “F” as follows:

• Site Class A – Hard Rock;

• Site Class B – Rock;

• Site Class C – Very Dense Soil and Soft Rock;

• Site Class D – Stiff Soil;

• Site Class E – Soft Clay Soil; and

• Site Class F – Soils Requiring Site Response Analysis.

We evaluated seismic Site Class in accordance with Chapter 20 of ASCE 7-16. As discussed in Sections 5.4, 5.5, and 5.6, site soils are not susceptible to liquefaction, lateral spreading, or significant seismic settlement; therefore, Site Class “F” does not apply. Based on the subsurface conditions at the site, the three required criteria for Site Class “E” (Section 20.3.2 of ASCE 7-16) do not apply. Based on the average penetration resistance measured in our borings, the site may be classified as Site Class “D” (“Stiff Soil”) per Table 20.3-1 of ASCE 7-16.

For the purposes of evaluating code-based seismic parameters for design, we assumed a seismic Risk Category I, II, or III (per the CBC) for the project. Results are summarized in Table 5.7A.

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TABLE 5.7A

ASCE 7-16 SEISMIC DESIGN PARAMETERS

SITE CLASS “D” – STIFF SOIL

Parameter Value ASCE 7-16 Reference

MCER Ground Motion Spectral Response Acceleration – Class B (short), SS 0.553g Figure 22-1

MCER Ground Motion Spectral Response Acceleration – Class B (1 sec), S1

0.219g Figure 22-2

Site Coefficient, FA 1.357 Table 11.4-1 Site Coefficient, FV 2.162* Table 11.4-2

Site Class Modified MCER Spectral Response Acceleration (short), SMS 0.751g Eq. 11.4-1

Site Class Modified MCER Spectral Response Acceleration (1 sec), SM1

0.473g* Eq. 11.4-2

5% Damped Design Spectral Response Acceleration (short), SDS 0.501g Eq. 11.4-3

5% Damped Design Spectral Response Acceleration (1 sec), SD1

0.316g* Eq. 11.4-4

Long Period Transition Period, TL 12 Seconds Figs. 22-14 through 22-17 TS = SD1 / SDS 0.6 Seconds Chapter 11

* Per Section 11.4.8 of ASCE/SEI 7-16, a ground motion hazard analysis (GMHA) shall be performed for projects on Site Class “D” sites with long-period spectral acceleration (S1) greater than or equal to 0.2g, which is true for this site. However, Section 11.4.8 also provides exceptions which indicate that the ground motion hazard analysis may be waived provided the exceptions are followed. Using the code-based values presented in the table above, in lieu of performing a ground motion hazard analysis, requires that the exceptions outlined in ASCE 7-16 Section 11.4.8 be followed.

Specifically for this site/project, Exception No. 2 would apply which states that a GMHA is not required for: Structures on Site Class D sites with S1 greater than or equal to 0.2, provided the value of the seismic response coefficient Cs is determined by Eq. (12.8-2) for values of T ≤ 1.5Ts and taken as equal to 1.5 times the value computed in accordance with either Eq.

(12.8-3) for TL ≥ T > 1.5Ts or Eq. (12.8-4) for T > TL.

Table 5.7B presents additional seismic design parameters for projects with Seismic Design Categories of D through F in accordance with ASCE 7-16 for the mapped maximum considered geometric mean (MCEG).

TABLE 5.7B

ASCE 7-16 SITE ACCELERATION DESIGN PARAMETERS

Parameter Value ASCE 7-10 Reference

Mapped MCEG Peak Ground Acceleration, PGA 0.239g Figure 22-7 Site Coefficient, FPGA 1.361 Table 11.8-1

Site Class Modified MCEG Peak Ground Acceleration, PGAM 0.326g Section 11.8.3 (Eq. 11.8-1)

Conformance to the criteria presented in Tables 5.7A and 5.7B for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a maximum level earthquake occurs. The primary goal of seismic design is to protect life and not to avoid structural damage, since such design may be economically prohibitive.

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5.8 Landslides and Slope Stability

The regional topography is rolling, the site topography is relatively flat, and there are no significant slopes on or adjacent to the site. Therefore, landslides and slope instability are not hazards for the site.

5.9 Tsunamis and Seiches

The site is located approximately 115 miles from the Pacific Ocean and is not located near any large body of water. Therefore, tsunamis (seismic sea waves) or seiches (wave oscillations in an enclosed or semi-enclosed body of water) are not hazards for the site.

5.10 Flooding and Dam Failure Inundation

Based on the Flood Insurance Rate Maps (FIRM) prepared by the Federal Emergency Management Agency (FEMA) (Map No. 06019C1590H), the site is located approximately 2,200 feet north from “Zone AE” which is “Special flood hazard areas subject to inundation by the 1% annual chance flood. Base flood elevations determined.” (FEMA, 2009). The project civil engineer should determine site grades accordingly.

Our review of regional topographic maps and aerial photography indicates that the site is located approximately 15 miles south of Friant Dam (Millerton Lake) and approximately 21 miles west-southwest of Pine Flat Dam (Pine Flat Lake). Based on the California Governor’s Office of Emergency Services Dam Inundation Maps (May 2014), the site does not appear to be located within the inundation zones of any lake. Therefore, dam failure inundation is not considered to be a hazard for the site.

5.11 Expansive Soil

Laboratory Plasticity Index (PI) and Expansion Index (EI) tests on near surface soil samples indicate low plasticity and corresponding low expansion potential (Appendix B). Mitigation or specific design measures with respect to expansive soil are not necessary for this site.

5.12 Soil Corrosion Screening

We performed pH, resistivity, chloride, and sulfate tests on one sample to generally evaluate the corrosion potential of the soil with respect to proposed subsurface structures. These tests were performed in accordance with California Test Method (CTM) Nos. 643, 422, and 417. The results are presented in Table 5.11A and should be considered for design of underground structures.

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TABLE 5.12A

SOIL CORROSION PARAMETER TEST RESULTS

(CALIFORNIA TEST METHODS 643, 417, AND 422)

Sample No. Sample Depth (ft.) pH

Minimum Resistivity (ohm-cm)

Chloride (ppm)

Sulfate (ppm)

B1-Bulk 0 – 5 7.1 2,950 3.5 15.7

Soil with a low pH (higher acidity) is considered corrosive as it can react with lime in cement to leach out soluble reaction products and result in a more porous and weaker concrete. Per Caltrans Corrosion Guidelines (Caltrans 2018), soil with a pH of 5.5 or lower may be corrosive to concrete or steel in contact with the ground.

Soil resistivity is the measure of the soil’s ability to transmit electric current. Corrosion of buried ferrous metal is proportional to the resistivity of the soil. A lower resistivity indicates a higher propensity for transmitting electric currents that can cause corrosion of buried ferrous metal items. In general, the higher the resistivity, the lower the rate for corrosion. Per Caltrans Corrosion Guidelines (Caltrans 2018), resistivity serves as an indicator parameter for the possible presence of soluble salts and it is not included as a parameter to define a corrosive area for structures. A minimum resistivity value for soil less than 1,100 ohm-cm may indicate the presence of high quantities of soluble salts and a higher propensity for corrosion.

Based on the laboratory minimum resistivity test results and Caltrans criteria, soil at the locations tested does not have a higher propensity for corrosion.

Table 5.11B presents a summary of concrete requirements set forth by the California Building Code (CBC) Section 1904 and American Concrete Institute (ACI) 318 for possible chloride exposure. Chlorides can break down the protective oxide layer on steel surfaces resulting in corrosion. Sources of chloride include, but are not limited to, deicing chemicals, salt, brackish water, seawater, or spray from these sources.

TABLE 5.12B

REQUIREMENTS FOR CONCRETE EXPOSED TO

CHLORIDE-CONTAINING SOLUTIONS

(AFTER ACI 318 TABLES 19.3.1.1 and 19.3.2.1)

Chloride Severity

Exposure Class Condition

Maximum Water to Cement Ratio by Weight

Minimum Compressive Strength (psi)

Not Applicable C0 Concrete dry or protected from moisture N/A 2,500

Moderate C1 Concrete exposed to moisture but not to external sources of chlorides N/A 2,500

Severe C2 Concrete exposed to moisture and an external source of chlorides 0.40 5,000

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The appropriate Chloride Severity/Exposure Class should be determined by the project designer based on the specific conditions at the location of the proposed structure. Further guidance is provided in ACI 318.

Table 5.11C presents a summary of concrete requirements set forth by CBC Section 1904 and ACI 318 for sulfate exposure. Similar to chlorides, sulfates can break down the protective oxide layer on steel leading to corrosion. Sulfates can also react with lime in cement to soften and crack concrete.

TABLE 5.12C

REQUIREMENTS FOR CONCRETE EXPOSED TO

SULFATE-CONTAINING SOLUTIONS

(AFTER ACI 318 TABLES 19.3.1.1 and 19.3.2.1)

Sulfate Severity

Exposure Class

Water-Soluble Sulfate (SO4) Content Cement

Type

(ASTM

C 150)

Maximum Water to Cement Ratio by Weight1

Minimum Compressive

Strength (psi)

Percent By Mass

Parts Per Million (ppm)

Not Applicable S0 SO4 < 0.10 SO4 < 1,000 No Type

Restriction N/A 2,500

Moderate S1 0.10 < SO4 < 0.20

1,000 < SO4 <

2,000 II 0.50 4,000

Severe S2 0.20 < SO4 < 2.00

2,000 < SO4 <

20,000 V 0.45 4,500

Very Severe S3 SO4 > 2.00 SO4 > 20,000 V+Pozzolan or Slag 0.45 4,500

Notes:

1. Maximum water to cement ratio limits are different for lightweight concrete, see ACI 318 for details.

Based on the laboratory test results, the Sulfate Severity is classified as “Not Applicable” and the Exposure Class is S0. The concrete mix design(s) should be developed accordingly. The presence of water-soluble sulfates is not a visually discernible characteristic; therefore, other soil samples from the site could yield different concentrations. Additionally, over time landscaping activities (i.e., addition of fertilizers and other soil nutrients) may affect the concentration.

Geocon does not practice in the field of corrosion engineering and the above information is provided as screening criteria only. If corrosion sensitive improvements are planned, we recommend that further evaluations by a corrosion engineer be performed to incorporate the necessary precautions to avoid premature corrosion on buried metal pipes and metal or concrete structures in direct contact with the soils.

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5.13 Volcanic Activity

The nearest active volcanic area to the site is the Long Valley Caldera, located approximately 78 miles northeast of the site (USGS, 2021). Due to the large distance between the site and the Long Valley Caldera, the potential for impacts to the site due to regional volcanic activity is low.

5.14 Naturally Occurring Asbestos

The site is not located within an area mapped as an ultramafic rock unit (CGS, 1965). Naturally occurring asbestos (NOA) minerals (chrysotile, tremolite, actinolite) are more likely to be encountered in areas with ultramafic or sheared metavolcanic rocks due to metamorphic processes. Based on the site geology, which consists of Quaternary-aged alluvial fan deposits, the likelihood of NOA being present at the site is considered to be low.

5.15 Oil Fields & Methane Zones

Based on a review of the California Division of Oil, Gas and Geothermal Resources (DOGGR) online mapping system, the site is not located within the boundaries of an oil or gas field. No oil or gas wells are mapped in the immediate vicinity of the site (DOGGR, 2021). However, due to the voluntary nature of record reporting by the oil and gas well drilling companies, wells may be improperly located or not shown on the location map. Other wells could be encountered during construction. Any wells encountered would need to be properly abandoned in accordance with the current requirements of DOGGR.

5.16 Radon

The United States Environmental Protection Agency’s (USEPA) Map of Radon Zones (USEPA, 2021) depicts the radon potential in each U.S. County. Areas in Zone 1 have the highest radon potential, and those in Zone 3 have the lowest. Fresno County is depicted on the map in Zone 2 (i.e., moderate potential). Zone 2 areas are predicted to have average indoor radon screening levels ranging from 2 to 4 picocuries per liter (pCi/L). Therefore, there is a moderate potential for radon at the site. Based on the radon exposure mapping and the site geology, enclosed areas in contact with the ground should be tested for radon exposures. Areas with high radon levels may require mitigation measures.

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6.0 CONCLUSIONS AND RECOMMENDATIONS

The following discussion summarizes our findings and presents our conclusions based on the results of our geotechnical investigation including literature review, site observations, subsurface exploration, laboratory testing results, and engineering analysis.

6.1 General

6.1.1 No soil or geologic conditions were encountered during our investigation that would preclude construction of improvements at the site as planned, provided the recommendations contained in this report are incorporated into the design and construction of the project.

6.1.2 The primary geotechnical constraint identified in our investigation is the presence of existing variably loose, near-surface alluvial soil, existing HMA pavement, and existing underground utilities within the proposed barracks building area. Complete removal of existing pavement and utilities will be required as part of site development. Resulting disturbed soil will require removal and re-compaction. In addition, remedial grading in the form of over-excavation and re-compaction will be required to suitably densify near-surface alluvial soil within the proposed building area.

6.1.3 Conclusions and recommendations provided in this report are based on our review of referenced literature, analysis of data obtained from our exploratory borings, laboratory testing program, and our understanding of the proposed development at this time.

6.1.4 We should review the project plans as they develop further, provide engineering consultation as needed during final design, and perform geotechnical observation and testing services during construction.

6.2 Soil and Excavation Characteristics

6.2.1 Grading and excavations at the site may be accomplished with standard to moderate effort using heavy-duty grading/excavation equipment. Based on the presence of granular, near-surface soils, we anticipate temporary excavations, such as footings and utility trenches, may experience sloughing/caving. Foundation excavations may require forming. It is the contractor’s responsibility to provide sufficient and safe excavation support as well as protecting nearby utilities, structures, and other improvements which may be damaged by earth movements.

6.2.2 Temporary excavation slopes must meet Cal-OSHA requirements as appropriate. Excavation sloping, benching, the use of trench shields, and the placement of trench spoils should conform to the latest applicable Cal-OSHA standards. The contractor should have a Cal-

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OSHA-approved “competent person” onsite during excavation to evaluate trench conditions and to make appropriate recommendations where necessary. It is the contractor’s responsibility to provide sufficient and safe excavation support as well as protecting nearby utilities, structures, and other improvements which may be damaged by earth movements.

6.2.3 The excavation support recommendations provided by Cal-OSHA are generally geared towards protecting human life and not necessarily towards preventing damage to nearby structures or surface improvements. The contractor should be responsible for using the proper active shoring systems or sloping to prevent damage to any structure or improvements near underground excavations.

6.2.4 If grading occurs during or after the wet season (typically winter and spring), or in periods of precipitation, in-place and excavated soils will likely be wet. Earthwork contractors should be aware of moisture sensitivity of the near-surface silty/granular soils and potential compaction/workability difficulties.

6.2.5 Earthwork operations in these conditions will likely be difficult with low productivity. Often, a period of at least one month of warm and dry weather is necessary to allow the site to dry sufficiently so that heavy grading equipment can operate effectively. In addition, soil below existing pavements is often wet, regardless of the time of year. Conversely, during dry summer and fall months, dry clay soils may require additional grading effort (discing, mixing, or other means) to attain proper moisture conditioning.

6.3 Materials for Fill

6.3.1 Excavated soils generated from cut operations at the site are suitable for use as fill in structural areas provided they do not contain deleterious matter, organic material, cementations or rock larger than 6 inches in maximum dimension.

6.3.2 Import material should be primarily granular with a “low” expansion potential (Expansion Index less than 50), a Plasticity Index less than 15, be free of organic material and construction debris, not contain rock larger than 6 inches in greatest dimension, and contain sufficient fines to act as a binder to reduce caving potential when excavated.

6.3.3 Environmental characteristics and corrosion potential of import soil materials should also be considered. Proposed import materials should be sampled, tested, and approved by Geocon prior to its transportation to the site.

6.4 Grading

6.4.1 Earthwork operations should be observed and fills tested for recommended compaction and moisture content by a representative of Geocon.

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6.4.2 References to relative compaction and optimum moisture content in this report are based on the latest American Society for Testing and Materials (ASTM) D1557 Test Procedure.

Structural building pad areas should be considered as areas extending a minimum of 5 feet horizontally beyond the outside dimensions of buildings, including footings and overhangs carrying structural loads.

6.4.3 Prior to commencing grading, a pre-construction conference with representatives of the client, grading contractor, and Geocon should be held at the site. Site preparation, soil handling and/or the grading plans should be discussed at the pre-construction conference.

6.4.4 Site preparation should begin with complete removal of existing pavement and underground utilities (as required). Existing trees and similar large vegetation and associated roots larger than 1 inch in diameter should be completely removed. Smaller roots may be left in-place as conditions warrant as evaluated by our representative. Topsoil and surface vegetation consisting of grasses and other similar vegetation (if present) should be removed by stripping to a sufficient depth to remove organic-rich materials. Material generated during stripping is not suitable for use within 5 feet of structures or within pavement areas but may be placed in landscaped or non-structural areas or exported from the site.

6.4.5 Excavations or depressions resulting from site clearing operations, or other existing excavations or depressions, should be restored with engineered fill in accordance with the recommendations of this report.

6.4.6 After site preparation, the proposed building pad should be over-excavated to a depth of at least 2 feet below bottom of new footings or 2 feet below the existing ground surface, whichever is deeper. Over-excavation outside of the building pad area (such as in pavement and concrete flatwork areas) is not specifically required unless disturbed and/or wet/unstable soil conditions are encountered.

6.4.7 The exposed soil at the bottom of the over-excavation should be scarified 12 inches, uniformly moisture-conditioned at or above optimum moisture content and compacted to at least 90% relative compaction. Scarification and re-compaction operations should be performed in the presence of a Geocon representative to evaluate performance of the subgrade under compaction equipment loading and to identify any loose or unstable soil conditions that could require additional excavation.

6.4.8 Engineered fill consisting of onsite native sources and/or import fill material should be compacted in horizontal lifts not exceeding 8 inches (loose thickness) and brought to final design elevations. Each lift should be moisture-conditioned at or above optimum

Geocon Project No. S1445-05-24 - 15 - December 23, 2021 moisture content and compacted to at least 90% relative compaction. The top 12 inches of building pads, whether completely at-grade, by excavation, or filling should be uniformly moisture-conditioned at or above optimum moisture content and compacted to at least 90% relative compaction.

6.4.9 The top 6 inches of final vehicular pavement and concrete flatwork subgrade, whether completed at-grade, by excavation, or by filling, should be uniformly moisture-conditioned at or above optimum moisture content, compacted to at least 95% relative compaction and be stable. The 95% relative compaction requirement applies to the top 6 inches of pavement area subgrade; however, underlying materials must be sufficiently compacted and stable. We recommend proof-rolling the subgrade with a loaded water truck (or similar equipment with high contact pressure) to verify the stability of the subgrade prior to placing AB. We note that deeper scarification, removals, moisture-conditioning, and compaction efforts may be required in order to achieve overall stability and compaction.

6.4.10 Underground utility trenches within structural areas should be backfilled with properly compacted material. Pipe bedding, shading, and trench backfill should conform to the requirements of the appropriate utility authority. Material excavated from trenches should be adequate for use as general backfill above shading provided it does not contain deleterious matter, vegetation, or cementations larger than 6 inches in maximum dimension. Trench backfill should be placed in loose lifts not exceeding 8 inches, moisture-conditioned at or above optimum and compacted to at least 90% relative compaction. Compaction should be performed by mechanical means only; jetting of trench backfill is not recommended.

6.5 Foundations

6.5.1 Provided the building pad is graded in accordance with the recommendations of this report, the proposed building may be supported on conventional shallow foundations bearing on engineered fill.

6.5.2 To reduce potential for moisture variations beneath the buildings, foundations should consist of continuous perimeter footings with isolated interior spread footings or continuous footings. Perimeter footings should be continuous around the entire perimeter of the structure without breaks or discontinuities. Continuous footings should be at least 12 inches wide and spread footings should be at least 18 inches square. All footings should be embedded at least 12 inches below lowest adjacent pad grade.

6.5.3 Underground utilities running parallel to footings should not be constructed in the zone of influence of footings. The zone of influence may be taken to be the area within 18 inches laterally of the footing, beneath the footings, and within a 1:1 plane extending out and down from the bottom of the footing.

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6.5.4 Foundations proportioned as recommended above and bearing on at least 2 feet of engineered fill may be designed using an allowable soil bearing capacity of 2,500 pounds per square foot (psf) for combined dead plus live loads. This value may be increased by one-third to evaluate all loads, including wind or seismic forces.

6.5.5 Foundations designed in accordance with the recommendations above should experience total settlements of less than 1 inch and differential settlements of approximately ½ inch over a distance of approximately 30 feet. The majority of the settlement will be immediate and will occur as the loads are applied during construction.

6.5.6 Allowable passive pressure used to resist lateral movement of footings may be assumed to be equal to a fluid weighing 300 pounds per cubic foot (pcf). The allowable coefficient of friction to resist sliding of footings is 0.3 for concrete against soil. Combined passive resistance and friction may be utilized for footing design provided that the frictional resistance is reduced by 50%.

6.5.7 Continuous footings should be reinforced with at least two No. 4 reinforcement bars, one each placed near the top and bottom of the footing to allow footings to span isolated soil irregularities. The reinforcement recommended above is for soil characteristics only and is not intended to replace reinforcement required for structural considerations. The project structural engineer should evaluate the need for additional reinforcement.

6.5.8 A Geocon representative should observe all foundation excavations prior to placing reinforcing steel or concrete to verify that the exposed soil conditions are consistent with those anticipated. If unanticipated soil conditions are encountered, foundation modifications may be required.

6.6 Interior Slabs-on-Grade

6.6.1 Slab thickness and reinforcement should be determined by the structural engineer based on anticipated loading. However, at a minimum, slabs should be at least 4 inches thick and reinforced with No. 3 reinforcing bars placed 24 inches on center, each way. Structural requirements may require additional reinforcement or thicker concrete slabs.

6.6.2 If the near-surface soils of building pad become dry prior to constructing the slab-on-grade, the building pad should be re-moistened by soaking or sprinkling such that the upper 12 inches of soil is at or above optimum moisture content at least 48 hours before concrete placement. Our representative should verify moisture conditions prior to slab-on-grade construction.

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6.7 Slab-on-Grade Moisture Protection Considerations

6.7.1 Migration of moisture through concrete slabs or moisture otherwise released from slabs is not a geotechnical issue. However, for the convenience of the owner and design team, we are providing the following general suggestions for consideration by the owner, architect, structural engineer, and contractor. The suggested procedures may reduce the potential for moisture-related floor covering failures on concrete slabs-on-grade, but moisture problems may still occur even if the procedures are followed. If more detailed recommendations are desired, we recommend consulting a specialist in this field.

6.7.2 In areas where floor coverings are planned, a minimum 10-mil-thick vapor barrier meeting ASTM E1745-97 Class C requirements may be placed directly below the slab, without a sand cushion provided the slab-on-grade concrete water-cement ratio is 0.45 or less. To reduce the potential for punctures, a higher quality vapor barrier (15 mil, Class A or B) may be used. The vapor barrier, if used, should extend to the edges of the slab and should be sealed at all seams and penetrations.

6.7.3 At least 4 inches of ½- or ¾-inch crushed rock, with no more than 5 percent passing the No. 200 sieve, may be placed below the vapor barrier to serve as a capillary break.

6.7.4 The concrete water/cement ratio should be as low as possible. The water/cement ratio should not exceed 0.45 for concrete placed directly on the vapor barrier. Midrange plasticizers could be used to facilitate concrete placement and workability.

6.7.5 Proper finishing, curing, and moisture vapor emission testing should be performed in accordance with the latest guidelines provided by the American Concrete Institute, Portland Cement Association, and ASTM.

6.8 Retaining Walls and Lateral Loads

6.8.1 Design of retaining walls and buried structures may be based on the lateral earth pressures (equivalent fluid pressure) summarized in Table 6.8.1.

TABLE 6.8.1

RECOMMENDED LATERAL EARTH PRESSURES

Condition Equivalent Fluid Density

Active 40 pcf At-Rest 60 pcf Seismic1 Not Applicable

1. Based on research by Lew, et al. 2010, the seismic increment of earth pressure may be neglected if the maximum peak ground acceleration (PGA) at the site is 0.4 g or less. The Site Class Modified MCEG Peak Ground Acceleration (PGAM) for this site is 0.33g; therefore, the seismic increment of earth pressure may be neglected.

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6.8.2 Unrestrained walls be designed using the active case. Unrestrained walls are those that are allowed to rotate more than 0.001H (where H is the height of the wall). Walls restrained from movement (such as basement walls) should be designed using the at-rest case. The soil pressures above assume that the backfill material within an area bounded by the wall and a 1:1 plane extending upward from the base of the wall will be composed of the existing onsite soils.

6.8.3 Retaining wall foundations with a minimum depth of 12 inches may be designed using the allowable bearing capacity provided in Section 6.5.4 of this report. To resist lateral movement of retaining wall foundations, an allowable passive earth pressure equivalent to a fluid density of 300 pcf for footings or shear keys poured neat against properly compacted engineered fill soils or undisturbed natural soils. This allowable passive pressure is based on the assumption that a horizontal surface extends at least 5 feet or three times the depth of the footing or shear key, whichever is greater, beyond the face of the retaining wall foundation. If this surface is not protected by floor slabs or pavement, the upper 12 inches of material should not be included in the design for lateral resistance. An allowable friction coefficient of 0.3 may be used for resistance to sliding between soil and concrete. Combined passive resistance and friction may be utilized for design provided that the frictional resistance is reduced by 50%.

6.8.4 Retaining walls greater than 2 feet tall (retained height) should be provided with a drainage system adequate to prevent the buildup of hydrostatic forces and should be waterproofed as required by the project architect. Positive drainage for retaining walls should consist of a vertical layer of permeable material positioned between the retaining wall and the soil backfill. The permeable material may be composed of a composite drainage geosynthetic or a natural permeable material such as crushed gravel at least 12 inches thick and capped with at least 12 inches of native soil. A geosynthetic filter fabric should be placed between the gravel and the soil backfill. Provisions for removal of collected water should be provided for either system by installing a perforated drainage pipe along the bottom of the permeable material, which leads to suitable drainage facilities.

6.8.5 The recommendations presented above are generally applicable to the design of rigid concrete or masonry retaining walls with a level backfill and having a maximum retained height of 10 feet. In the event that walls higher than 10 feet or other types of walls are planned, Geocon should be consulted for additional recommendations

6.9 Concrete Flatwork

6.9.1 Concrete flatwork not subjected to vehicular traffic may be directly underlain by subgrade soil that is uniformly moisture-conditioned above optimum moisture content and compacted to 90% relative compaction. If desired, a 4-inch thick layer of AB compacted to 95% relative compaction may be placed below concrete flatwork as a levelling course.

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6.9.2 Concrete jointing and reinforcement (if used) should be detailed in accordance with ACI or PCA guidelines.

6.9.3 Exterior concrete flatwork should be structurally independent of building foundations except at doorways where dowels should be used to reduce vertical offset that could affect door operation.

6.10 Pavement – Hot Mix Asphalt

6.10.1 We performed Resistance-Value (R-Value) testing on a representative bulk soil sample from proposed at-grade pavement areas. Our testing resulted in an R-Value of 73 (Appendix B).

To account for subgrade soil variability, we recommend using an R-Value of 40 for design.

Table 6.10.1 provides alternative pavement sections based on the design methods of Caltrans’ Highway Design Manual using a design subgrade R-value of 40.

TABLE 6.10.1

FLEXIBLE PAVEMENT SECTIONS

Parking Areas Traffic Index = 5.0

Driveways, Light Truck Traffic, Fire Truck Areas

Traffic Index = 6.0

HMA, inches 3.0 3.5 AB, inches 4.0 5.5

Total Section, inches 7.0 9.0

6.10.2 The recommended alternative pavement sections are based on the following assumptions:

1. Subgrade soil has an R-Value of 40.

2. Class 2 AB has a minimum R-Value of 78 and meets the requirements of Section 26 of Caltrans’ latest Standard Specifications.

3. Class 2 AB is compacted to 95% or higher relative compaction…