3. Geotechnical Report - 5_26_2020.pdf

Copyright © 2020 by ENGEO Incorporated. This document may not be reproduced in whole or in part by any means whatsoever, nor may it be quoted or excerpted without the express written consent of ENGEO Incorporated.

USFS SEQUOIA NF NEW SUPERVISOR’S OFFICE

PORTERVILLE, CALIFORNIA

GEOTECHNICAL EXPLORATION

SUBMITTED TO

Mr. Dan Dameron

MFDB Architects, Inc.

111 Scripps Drive

Sacramento, CA 95825

PREPARED BY

ENGEO Incorporated

May 26, 2020

PROJECT NO.

17115.000.000

GEOTECHNICAL

ENVIRONMENTAL

WATER RESOURCES

CONSTRUCTION SERVICES

29025 Avenue Penn, Valencia, CA 91355 (925) 866-9000 Fax (888) 279-2698 www.engeo.com

Project No.

17115.000.000

Mr. Dan Dameron MFDB Architects, Inc.

111 Scripps Drive Sacramento, CA 95825

Subject: USFS Sequoia NF New Supervisor’s Office 480 North Henrahan St.

Porterville, California

GEOTECHNICAL EXPLORATION

Dear Mr. Dameron:

ENGEO prepared this geotechnical report for MFDB Architects, Inc. for the planned USFS Sequoia NF office expansion in Porterville, California, as outlined in our agreement dated October 1, 2019. We characterized the subsurface conditions at the site to provide the enclosed geotechnical recommendations for design.

We look forward to reviewing the project plans and specifications and providing geotechnical observation and testing services during construction.

If you have any questions or comments regarding this report, please call and we will be glad to discuss them with you.

Sincerely, ENGEO Incorporated

Tyler Morelli, GIT Jonathan Boland, GE tm/jcb/jf

MFDB Architects, Inc. USFS Sequoia NF New Supervisor’s Office

17115.000.000 Geotechnical Exploration

i of ii May 26, 2020

TABLE OF CONTENTS

LETTER OF TRANSMITTAL

1.0 INTRODUCTION

1.1 PURPOSE AND SCOPE

1.2 PROJECT LOCATION

1.3 PROJECT DESCRIPTION

2.0 FINDINGS

2.1 MAP AND AERIAL PHOTO REVIEW

2.2 GEOLOGY AND SEISMICITY

2.2.1 Geology

2.2.2 Seismicity

2.3 FIELD EXPLORATION

2.4 SURFACE CONDITIONS

2.5 SUBSURFACE CONDITIONS

2.6 GROUNDWATER CONDITIONS

2.7 LABORATORY TESTING

3.0 CONCLUSIONS

3.1 EXPANSIVE SOIL

3.2 EXISTING FILL

3.3 SEISMIC HAZARDS

3.3.1 Ground Rupture

3.3.2 Ground Shaking

3.3.3 Liquefaction

3.4 SOIL CORROSION POTENTIAL

3.5 2018 IBC SEISMIC DESIGN PARAMETERS

3.6 STATIC AND PERCHED GROUNDWATER

4.0 CONSTRUCTION MONITORING

5.0 EARTHWORK RECOMMENDATIONS

5.1 EXISTING FILL REMOVAL

5.2 EXPANSIVE SOIL MITIGATION

5.3 GENERAL SITE CLEARING

5.4 SOIL MOISTURE CONDITIONS

5.5 ACCEPTABLE FILL

5.6 FILL COMPACTION

5.6.1 Grading in Structural Areas

5.6.2 Landscape Fill

5.7 UNDERGROUND UTILITY TRENCH BACKFILL

5.7.1 Trench Backfill - Structural Areas

5.8 SITE DRAINAGE

5.9 LANDSCAPING CONSIDERATION

TABLE OF CONTENTS (Continued) ii of ii May 26, 2020

6.0 FOUNDATION RECOMMENDATIONS

6.1 CONVENTIONAL FOOTINGS WITH SLAB-ON-GRADE

6.1.1 Footing Dimensions and Allowable Bearing Capacity

6.1.2 Waterstop

6.1.3 Reinforcement

6.1.4 Foundation Lateral Resistance

6.1.5 Settlement

7.0 CONCRETE SLABS-ON-GRADE

7.1 INTERIOR CONCRETE FLOOR SLABS

7.1.1 Minimum Design Section

7.1.2 Slab Moisture Vapor Reduction

7.2 EXTERIOR FLATWORK

8.0 RETAINING WALLS

8.1 LATERAL SOIL PRESSURES

8.2 RETAINING WALL DRAINAGE

8.3 WALL BACKFILL

8.4 FOUNDATIONS

9.0 PAVEMENT DESIGN

9.1 FLEXIBLE PAVEMENTS

9.2 RIGID PAVEMENTS

9.3 PAVEMENT SUBGRADE AND AGGREGATE BASE COMPACTION

9.4 CUT-OFF CURBS

10.0 GROUND HEAT EXCHANGE

11.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS

SELECTED REFERENCES

FIGURES

APPENDIX A – Exploration Logs

APPENDIX B – Laboratory Test Data

APPENDIX C – CERCO Analytical Site Corrosivity Evaluation

Page | 1 May 26, 2020

1.0 INTRODUCTION

1.1 PURPOSE AND SCOPE

ENGEO prepared this geotechnical report for design of USFS Sequoia NF Office expansion in Porterville, California. We prepared this report as outlined in our agreement dated October 1, 2019, and associated amendments. MFDB Architects, Inc. authorized ENGEO to conduct the following scope of services.

• Service plan development

• Review of select geotechnical documents, geologic maps, historical aerial photographs, and geologic hazard maps

• Subsurface field exploration

• Soil laboratory testing

• Engineering analyses and conclusions

• Report preparation

For our use, we received the following.

1. KASL Consulting Engineers; SQNF Supervisors Office Conceptual Design; December 12, 2019;

one page.

2. Porterville SO Preliminary Geotechnical Site Evaluation; undated; two pages.

3. Sequoia N.F. Supervisor’s Office Design Prospectus, May 23, 2019, 42 pages.

This report was prepared for the exclusive use of our client and their consultants for design of this project. In the event that any changes are made in the character, design or layout of the improvements, we must be contacted to review the conclusions and recommendations contained in this report to evaluate whether modifications are recommended. This document may not be reproduced in whole or in part by any means whatsoever, nor may it be quoted or excerpted without our express written consent.

1.2 PROJECT LOCATION

The approximately 2-acre property is located at the northeast corner of North Henrahan Street and East Morton Avenue in Porterville, California. The property is identified as a portion of Assessor’s Parcel Number (APN) 253-050-030. Figure 1 shows the site boundaries, and Figure 2 shows the proposed building footprint, pavement areas, as well as our exploratory locations. The existing USFS facility borders the site to the north, residential properties border the site to the east, and North Henrahan Street and East Morton Avenue border the site to the west and south, respectively.

A former rail alignment is located to the west of North Henrahan Street.

1.3 PROJECT DESCRIPTION

Based on our discussions with the project team and our review of the information provided, we understand that the following site improvements are proposed.

Page | 2 May 26, 2020

1. An approximately 11,000-square-foot, single-story, wood-framed office building with planned footing foundation and a concrete slab-on-grade floor.

2. Paved entry lanes, parking, and drive aisles.

3. Underground utilities and other infrastructure improvements.

4. Site retaining walls less than 4 feet in height with level backfill.

5. Exterior concrete walkways and flatwork.

Structural loads, grading, and final improvement details are yet to be determined; however, we assume that structural loads will be representative of the proposed wood-framed construction and that cuts and fills of less than 5 feet in thickness may be required to establish a drainable site.

2.0 FINDINGS

2.1 MAP AND AERIAL PHOTO REVIEW

We reviewed select historical aerial photographs dated back to 1934 and select available published geologic maps for relevant information regarding geotechnical and geological aspects of the site. The property appears to have remained relatively unchanged since the aerial photograph taken in 1969. The aerial photograph from 1934 indicates four structures on site, located in the southern and western portions adjacent to the roadways.

2.2 GEOLOGY AND SEISMICITY

2.2.1 Geology

The site is located on the southwestern side of the Sierra Nevada range, in the San Joaquin Valley, within the southern portion of the Great Valley geomorphic province of California. The Great Valley is an alluvial plain about 50 miles wide and 400 miles long in the central part of California where sediments have been continuously deposited for about the last 160 million years.

According to published geologic maps by Matthews and Burnett (1965), Quaternary fan deposits (Qf) and Pleistocene non-marine sedimentary deposits (Qc) underlie the site, with Mesozoic granodiorite (gr) to the east and ultrabasic intrusive rocks (ub) to the north, south and east, and Pre-Cretaceous metavolcanic rocks to the northeast (Figure 3).

2.2.2 Seismicity

The site is not located within an Earthquake Fault Special Study Zone and only a few earthquakes of low magnitude have occurred in this region. Refer to Figure 4 for a Regional Faulting and Seismicity map that shows known USGS faults and former earthquake epicenters and magnitudes.

The following table summarizes the distances to mapped, active regional faults and estimated maximum magnitude within approximately 70 miles of the site. We used the USGS Spatial Query tool that is based on the USGS 2008 National Seismic Hazard Maps used to develop the 2018 International Building code seismic parameters.

Page | 3 May 26, 2020

TABLE 2.2.2-1: Active Faults Capable of Producing Significant Ground shaking at the Site

FAULT NAME DISTANCE FROM SITE

(MILES)

MAXIMUM MOMENT

MAGNITUDE*

Great Valley 14, Kettleman Hills 51 7.1 So. Sierra Nevada 56 7.5 White Wolf 56½ 7.1 Independence 58 7.1 Great Valley 13, Coalinga 62 7.0 Owens Valley 63 7.3 Little Lake 64 6.8 San Andreas 70½ 7.9

*Average of Ellsworth & Hanks

2.3 FIELD EXPLORATION

Our field exploration included drilling four borings at various locations on the site. We performed our field exploration on March 30, 2020. An ENGEO representative observed the drilling and logged the subsurface conditions at each location. We retained a truck-mounted CME drill rig and crew to advance the borings using 8-inch-diameter hollow-stem auger methods. Due to the depth of the borings, permits through Tulare County were not required and the borings were backfilled with soil cuttings.

The approximate locations of our borings are shown on Figure 2. The location and elevations of our explorations are approximate and were estimated using recreational grade handheld GPS; they should be considered accurate only to the degree implied by the method used. A summary of the exploration surface elevations and total exploration depths are provided in Table 2.3-1.

TABLE 2.3-1: Exploration Summary

EXPLORATION

LOCATION

APPROXIMATE

SURFACE ELEVATION

(FEET, NAVD88)

TOTAL DEPTH

(FEET)

1-B-01 457 36½ 1-B-02 460 36 1-B-03 464 6½ 1-B-04 457 6½

We obtained soil samples at various intervals using standard penetration test (SPT) samplers with a 2-inch outside diameter (O.D. split-spoon sampler) and California Modified samplers with 2½-inch inside diameter (I.D.). Blow counts were obtained by dropping a 140-pound hammer through a 30-inch free fall. The sampler was driven 18 inches and the number of blows was

PHOTO 2.3-1: Drill Rig On Site

Page | 4 May 26, 2020 recorded for each 6 inches of penetration. We have not converted the blow counts presented on the borelogs using correction factors.

We used the field logs to develop the report logs in Appendix A. The logs depict subsurface conditions at the exploration locations for the date of exploration; however, subsurface conditions may vary with time. The soil type, color, consistency, and visual classification provided in the logs are in general accordance with the Unified Soil Classification System.

2.4 SURFACE CONDITIONS

During our field exploration, we observed that the subject property is essentially a vacant lot that appears to be used as overflow parking and equipment storage for the USFS Sequoia National Forest – Porterville Work Center. The perimeter of the site is fenced and overhead power lines are located along both adjacent streets. The majority of the site surface was covered with short grassy vegetation and the central portion of the site was covered with highly weathered/crushed asphalt. We also observed several small storage sheds in the northeastern portion of the site.

The ground surface is relatively flat and gently slopes from the northeast to the southwest. Surface elevations (WGS84) at the site range from approximately 465 feet in the northeast to 456 feet in the southwest based on Google Earth data.

2.5 SUBSURFACE CONDITIONS

Our explorations typically encountered stiff to hard clay and silt with varying amounts of sand and gravel within the maximum explored depth of 36½ feet. A layer of medium dense to dense silty sand, approximately 3 to 4½ feet thick, was encountered in Borings 1-B-01 and 1-B-02 at depths of 10½ and 18 feet below ground surface, respectively. Additionally, in Borings 1-B-01 and 1-B-02, we encountered undocumented fill extending approximately 2 to 3½ feet below the ground surface. Plasticity Index (PI) tests on representative soil samples resulted in PIs of 4, 37, and 41, indicating low- to high-expansion potential. Additionally, an expansion index (EI) test was run on a lean clay sample yielding a value of 35, indicating low expansion potential.

Consult the Site Plan and exploration logs for specific subsurface conditions at each boring location. We did not encounter noticeably weak or compressible soil in our exploratory borings.

We provide additional information about specific subsurface conditions in the exploration logs included in Appendix A. The logs contain the soil type, color, consistency, and visual classification in general accordance with the Unified Soil Classification System. The logs graphically depict the subsurface conditions encountered at the time of the exploration.

2.6 GROUNDWATER CONDITIONS

We did not observe static or perched groundwater in the subsurface explorations. Based on our review of publicly available groundwater data from the California Department of Water Resources, Groundwater Information Center GIS portal, groundwater in the vicinity ranged from approximately 40 to 105 feet below ground surface between 2011 and 2018. Fluctuations in the level of groundwater may occur due to variations in rainfall, irrigation practice, and other factors not evident at the time measurements were made.

2.7 LABORATORY TESTING

We performed laboratory tests on select soil samples to evaluate some of their engineering properties. For this project, we performed laboratory testing as shown in the table below.

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TABLE 2.7-1: Laboratory Testing

SOIL CHARACTERISTIC TESTING METHOD LOCATION OF

RESULTS

Natural Unit Weight ASTM D7263 Appendix A Natural Moisture Content ASTM D2216 Appendix A Plasticity Index ASTM D4318 Appendix B Expansion Index ASTM D4829 Appendix B Sieve and Hydrometer ASTM D422 Appendix B Grain Size Distribution ASTM D1140 Appendix B Unconfined Compression ASTM D2166 Appendix B Limited Corrosion Testing Various Appendix C

Moisture contents and dry densities are recorded on the boring logs in Appendix A; other laboratory data are included in Appendices B and C.

3.0 CONCLUSIONS

From a geotechnical engineering viewpoint, in our opinion, the proposed project may be designed as planned, provided the geotechnical recommendations in this report are properly incorporated into the design plans and specifications. The primary geotechnical concerns that could affect the proposed improvements are expansive soil and undocumented fill. We summarize our conclusions below.

3.1 EXPANSIVE SOIL

We observed potentially expansive clay near the surface of the site in our borings. Our laboratory testing indicates that the soil may exhibit low- to high-shrink/swell potential with variations in moisture content.

To reduce the potential for damage to the planned building, we recommend that the upper 2 feet of the building pad, and extending at least 10 feet laterally beyond, be underlain by low-expansive import fill. Due to the relatively flat nature of the site, selective grading to mitigate expansive soil may not be a practical alternative. We recommend that other structural elements, such as pavements and flatwork be designed for highly expansive soil conditions.

We also provide specific grading recommendations for compaction of clay soil at the site. The purpose of these recommendations is to reduce the swell potential of the clay by compacting the soil at a high moisture content and controlling the amount of compaction. Expansive soil mitigation recommendations are presented in Section 5.2 of this report.

3.2 EXISTING FILL

Our borings indicate that the soil beneath the proposed building pad may be underlain by approximately 2 to 3½ feet of undocumented fill. Additionally, undocumented fill may be encountered in other areas on site, such as the locations of the former structures indicated on the 1934 aerial photograph.

Non-engineered fill can undergo excessive settlement, especially under new fill or building loads.

Without proper documentation of existing fill placed on the site, we recommend complete removal

Page | 6 May 26, 2020 and removal or recompaction of the existing fill as engineered fill. We present fill removal recommendations in Section 5.1. Refer to Figure 2 for the approximate lateral extent of undocumented fill on site.

3.3 SEISMIC HAZARDS

Potential seismic hazards resulting from a nearby moderate to major earthquake can generally be classified as primary and secondary. The primary effect is ground rupture, also called surface faulting. The common secondary seismic hazards include ground shaking and ground lurching.

The following sections present a discussion of these hazards as they apply to the site. Based on topographic and lithologic data, the risk of regional subsidence or uplift, soil liquefaction, lateral spreading, landslides, tsunamis, flooding or seiches is considered low to negligible at the site.

3.3.1 Ground Rupture

Since there are no known active faults crossing the property and the site is not located within an Earthquake Fault Special Study Zone, it is our opinion that ground rupture is unlikely at the subject property.

3.3.2 Ground Shaking

To mitigate the shaking effects, structures should be designed using sound engineering judgment and the 2018 International Building Code (IBC) requirements, as a minimum. Seismic design provisions of current building codes generally prescribe minimum lateral forces, applied statically to the structure, combined with the gravity forces of dead-and-live loads. The code-prescribed lateral forces are generally considered to be substantially smaller than the comparable forces that would be associated with a major earthquake. Therefore, structures should be able to: (1) resist minor earthquakes without damage, (2) resist moderate earthquakes without structural damage but with some nonstructural damage, and (3) resist major earthquakes without collapse but with some structural as well as nonstructural damage. Conformance to the current building code recommendations does not constitute any kind of guarantee that significant structural damage would not occur in the event of a maximum magnitude earthquake; however, it is reasonable to expect that a well-designed and well-constructed structure will not collapse or cause loss of life in a major earthquake (SEAOC, 1996).

3.3.3 Liquefaction

Soil liquefaction results from loss of strength during cyclic loading, such as imposed by earthquakes. Soil most susceptible to liquefaction are clean, loose, saturated, uniformly graded, fine-grained sand. Our explorations did not encounter significant amounts of sandy material. The sand encountered in our borings was a medium-dense to dense consistency and contained a significant amount of fine-grained material. In addition, groundwater was not encountered to the terminal depth of our borings. For these reasons and based upon engineering judgment, it is our opinion that the potential for liquefaction at the site is low during seismic shaking.

3.4 SOIL CORROSION POTENTIAL

We obtained one representative soil sample and submitted to a qualified analytical lab for determination of pH, resistivity, sulfate, and chloride. The results are summarized in the table below.

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TABLE 3.4-1: Corrosivity Test Results

SAMPLE

LOCATION DEPTH PH RESISTIVITY

(OHMS-CM)

CHLORIDE

(MG/KG)

SULFATE

(MG/KG)

1-B-01 10.5’ 8.45 2,100 N.D. 24

* ASTM D4327. N.D. – Non detect.

The CBC references the American Concrete Institute Manual, ACI 318-14, Section 19.3.1 for structural concrete durability requirements. According to ACI Table 19.3.1.1, this sample is categorized as S0 sulfate exposure class. Other corrosion considerations can be found in the Cerco Analytical summary letter included in Appendix C. Following site grading and import of select fill, we will obtain an additional near-surface soil sample for analytical testing to confirm these corrosion conclusions. If desired to investigate this further, we recommend a corrosion consultant be retained to evaluate if specific corrosion recommendations are advised for the project.

3.5 2018 IBC SEISMIC DESIGN PARAMETERS

Based on the subsurface conditions encountered, we characterized the site as Site Class D. We provide the 2018 IBC seismic design parameters in Table 3.5-1, which include design spectral response acceleration parameters based on the mapped Risk-Targeted Maximum Considered Earthquake (MCER) spectral response acceleration parameters.

TABLE 3.5-1: 2018 IBC Seismic Design Parameters: Latitude: 37.073592 Longitude: -119.011552

PARAMETER VALUE

Site Class D Mapped MCER Spectral Response Acceleration at Short Periods, SS (g) 0.576

Mapped MCER Spectral Response Acceleration at 1-second Period, S1 (g) 0.223

Site Coefficient, FA 1.339 Site Coefficient, FV Null* MCER Spectral Response Acceleration at Short Periods, SMS (g) 0.771

MCER Spectral Response Acceleration at 1-second Period, SM1 (g) Null*

Design Spectral Response Acceleration at Short Periods, SDS (g) 0.514

Design Spectral Response Acceleration at 1-second Period, SD1 (g) Null*

Mapped MCE Geometric Mean (MCEG) Peak Ground Acceleration, PGA (g) 0.249 Site Coefficient, FPGA 1.351 MCEG Peak Ground Acceleration adjusted for Site Class effects, PGAM (g) 0.337

*Requires site-specific ground motion hazard analysis per ASCE 7-16 Section 11.4.8

Considering the structure size, we estimate the fundamental periods of the proposed building to be less than 1.5Ts Therefore, the structural engineer may consider exception(s) of Section 11.4.8 of ASCE 7-16 as follows:

“A ground motion hazard analysis is not required for structures… where, 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) of ASCE 7-16 for values of 𝑇 ≤ 1.5𝑇𝑆

Page | 8 May 26, 2020 and taken as equal to 1.5 times the value computed in accordance with Eq. (12.8-3) of ASCE 7-16 for 1.5𝑇𝑠 < 𝑇 ≤ 𝑇𝐿.”

We recommend that we collaborate with the structural engineer of record to further evaluate the effects of taking the exceptions on the structural design and identify the need for performing a site-specific seismic hazard analysis. We can provide a scope for site-specific seismic hazard analysis and ground motion study under separate cover, if needed.

3.6 STATIC AND PERCHED GROUNDWATER

It does not appear that the static groundwater level beneath the site is likely to affect the proposed development. However, perched water can:

1. Impede grading activities.

2. Cause moisture damage to sensitive floor coverings.

3. Transmit moisture vapor through slabs causing excessive mold/mildew build-up, fogging of windows, and damage to computers and other sensitive equipment.

4. Cause premature pavement failure if hydrostatic pressures build up beneath the section.

We provide recommendations to reduce the effects of perched water in Sections 5.4, 7.1.2, and 9.4.

4.0 CONSTRUCTION MONITORING

Our experience and that of our profession clearly indicate that the risk of costly design, construction, and maintenance problems can be significantly lowered by retaining the design geotechnical engineering firm to:

1. Review the final grading and foundation plans and specifications prior to construction to evaluate whether our recommendations have been implemented, and to provide additional or modified recommendations, as needed. This also allows us to check if any changes have occurred in the nature, design, or location of the proposed improvements and provides the opportunity to prepare a written response with updated recommendations.

2. Perform construction monitoring to check the validity of the assumptions we made to prepare this report. Earthwork operations should be performed under the observation of our representative to check that the site is properly prepared, the selected fill materials are satisfactory, and that placement and compaction of the fill has been performed in accordance with our recommendations and the project specifications. Sufficient notification to us prior to earthwork is important.

If we are not retained to perform the services described above, then we are not responsible for any party’s interpretation of our report (and subsequent addenda, letters, and verbal discussions).

5.0 EARTHWORK RECOMMENDATIONS

As used in this report, relative compaction refers to the in-place dry unit weight of soil expressed as a percentage of the maximum dry unit weight of the same soil, as determined by the ASTM D1557 laboratory compaction test procedure, latest edition. Compacted soil is not

Page | 9 May 26, 2020 acceptable if it is unstable; it should exhibit only minimal flexing or pumping, as observed by an ENGEO representative. The term “moisture condition” refers to adjusting the moisture content of the soil by either drying if too wet or adding water if too dry.

We define “structural areas” as any area sensitive to settlement of compacted soil. These areas include, but are not limited to building pads, sidewalks, pavement areas, and retaining walls.

We define “low expansion potential” soil as soil with an Expansion Index (EI) less than 50.

5.1 EXISTING FILL REMOVAL

Remove existing fill from structural areas to competent native soil, as evaluated by ENGEO.

Figure 2 displays the approximate lateral extent of existing fill at the site. The lateral extent and depth of fill are expected to vary and the owner may want to plan a contingency budget for unexpected conditions. Consult the exploration logs in Appendix A for fill depths at specific locations.

5.2 EXPANSIVE SOIL MITIGATION

To reduce the risk of structural damage associated with the variably expansive soil conditions, we recommend constructing the upper 2 feet of the building pad and 10 feet laterally beyond with low-expansion potential import fill.

5.3 GENERAL SITE CLEARING

Areas to be developed should be cleared of surface and subsurface deleterious materials, including existing building foundations, slabs, buried utility and irrigation lines, pavements, debris, and designated trees, shrubs, and associated roots. Following clearing, the site should be stripped to remove organic materials to a depth of at least 2 to 3 inches below the surface.

Remove strippings from the site or, if considered suitable by the landscape architect and owner, use them in landscape fill.

The exposed surface in areas below the planned finished site grades should then be processed, cleaned and backfilled with suitable material compacted to the recommendations presented in Section 5.6. ENGEO should be retained to observe and test site preparation and backfilling.

It may also be feasible to mulch organics in place, depending on the amount and type of vegetation present at the time of grading as well as the proposed mulching method. If desired, ENGEO can evaluate site vegetation at the time of grading to assess the feasibility of mulching organics in place.

5.4 SOIL MOISTURE CONDITIONS

The contractor should anticipate encountering excessively over-optimum (wet) soil moisture conditions during winter or spring grading, and under-optimum (dry) soil moisture conditions during summer and fall grading. Wet or dry soil can make proper compaction difficult or impossible.

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These soil conditions can be mitigated by:

1. Frequent spreading and mixing to aerate wet soil or to mix in water for dry soil,

2. Mixing with drier materials if wet and wetter materials if dry,

3. Mixing with a lime, lime-flyash, or cement product if wet, or

4. Stabilizing with aggregate or geotextile stabilization fabric, or both if wet.

Options 3 and 4 should be evaluated by ENGEO prior to implementation.

5.5 ACCEPTABLE FILL

On-site soil and rock material is suitable as fill material provided it is processed to remove concentrations of organic material, debris, and particles greater than 3 inches in maximum dimension. The undocumented fill material is acceptable for re-use as engineered fill on site provided it is placed at least 10 feet beyond the building envelope.

Imported fill materials for the building pad area should meet the above requirements and have a Plasticity Index (PI) less than 10, and an Expansion Index (EI) value less than 50. Allow ENGEO to sample and test proposed imported fill materials at least 10 days prior to delivery to the site for PI, EI, gradation, sulfate, and compaction testing. If environmental test results for import are not available, additional sampling and testing may be recommended.

5.6 FILL COMPACTION

5.6.1 Grading in Structural Areas

For low-expansion potential soil, the contractor should perform subgrade compaction prior to fill placement, following cutting operations, and in areas left at grade as follows.

1. Scarify to a depth of at least 8 inches.

2. Moisture condition soil to at least 2 percentage points above the optimum moisture content.

3. Compact the subgrade to at least 90 percent relative compaction. Compact the upper 6 inches of finish pavement subgrade to at least 95 percent relative compaction prior to aggregate base placement.

After the subgrade soil has been compacted, the contractor should place and compact acceptable low-expansion potential fill as follows.

1. Spread fill in loose lifts that do not exceed 8 inches.

2. Moisture condition lifts to at least 2 percentage points above the optimum moisture content.

3. Compact fill to a minimum of 90 percent relative compaction; Compact the upper 6 inches of fill in pavement areas to 95 percent relative compaction prior to aggregate base placement.

For expansive subgrade soil, the contractor should perform subgrade compaction prior to fill placement, following cutting operations, and in areas left at grade as follows.

1. Scarify to a depth of at least 8 inches.

2. Moisture condition soil to at least 4 percentage points over the optimum moisture content.

Page | 11 May 26, 2020

3. Compact the soil to between 87 and 92 percent relative compaction. Compact the upper 6 inches of finish pavement subgrade to at least 90 percent relative compaction prior to aggregate base placement.

After the subgrade has been compacted, the contractor should place and compact acceptable expansive fill as follows.

1. Spread fill in loose lifts that do not exceed 8 inches.

2. Moisture condition lifts to at least 4 percentage points over the optimum moisture content.

3. Compact fill to between 87 and 92 percent relative compaction; compact the upper 6 inches of fill in pavement areas to at least 90 percent relative compaction prior to aggregate base placement.

Pavement aggregate base should be compacted to at least 95 percent relative compaction at a moisture condition at or slightly above the optimum.

5.6.2 Landscape Fill

For landscape only (no pavers, benches, or hardscape) areas, process, place and compact fill in accordance with Sections 5.6.1, except compact to at least 85 percent relative compaction

(ASTM D1557).

5.7 UNDERGROUND UTILITY TRENCH BACKFILL

The contractor is responsible for conducting trenching and shoring in accordance with CALOSHA requirements. Project consultants involved in utility design should specify pipe bedding materials.

5.7.1 Trench Backfill - Structural Areas

The contractor should place and compact low-expansion potential trench backfill as follows.

1. Trench backfill should have a maximum particle size of 3 inches.

2. Moisture condition trench backfill to at least 1 percentage point above the optimum moisture content. Moisture condition backfill outside the trench.

3. Place fill in loose lifts not exceeding 12 inches.

4. Compact fill to a minimum of 90 percent relative compaction.

The contractor should place and compact expansive trench backfill as follows.

1. Trench backfill should have a maximum particle size of 3 inches.

2. Moisture condition trench backfill to at least 4 percentage points above the optimum moisture content. Moisture condition backfill outside the trench.

3. Place fill in loose lifts not exceeding 12 inches.

4. Compact fill to between 87 and 92 percent relative compaction (90 percent minimum relative compaction at depths of 5 feet or more below finish grades).

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Jetting of backfill is not an acceptable means of compaction. We may allow thicker loose lift thicknesses based on acceptable density test results, where increased effort is applied to rocky fill, or for the first lift of fill over pipe bedding.

5.8 SITE DRAINAGE

The project civil engineer is responsible for designing surface drainage improvements. With regard to geotechnical engineering issues, we recommend that finish grades be sloped away from buildings and pavements to the maximum extent practical to reduce the potentially damaging effects of expansive soil. The latest International Building Code Section 1804.4 specifies minimum slopes of 5 percent away from foundations. Where lot lines or surface improvements restrict meeting this slope requirement, we recommend that specific drainage requirements be developed. As a minimum, we recommend the following.

1. Discharge roof downspouts into closed conduits and direct away from foundations to appropriate drainage devices.

2. Do not allow water to pond near foundations, pavements, or exterior flatwork.

5.9 LANDSCAPING CONSIDERATION

As the near-surface soil is moderately to highly expansive, we recommend greatly restricting the amount of surface water infiltration near structures, pavements, flatwork, and slabs on grade. This may be accomplished by.

Selecting landscaping that requires little or no watering, especially within 3 feet of structures, slabs-on-grade, or pavements.

Using low precipitation sprinkler heads.

Regulating the amount of water distributed to lawn or planter areas by installing timers on the sprinkler system.

Providing surface grades to drain rainfall or landscape watering to appropriate collection systems and away from structures, slabs-on-grade, or pavements.

Preventing water from draining toward or ponding near building foundations, slabs-on-grade, or pavements.

Avoiding open planting areas within 3 feet of the building perimeter.

We recommend that these items be incorporated into the landscaping plans.

6.0 FOUNDATION RECOMMENDATIONS

We developed foundation recommendations using data obtained from our field exploration, laboratory test results, and engineering analysis. The foundation recommendations presented below are based on the upper 2 feet of the building pad area being constructed with low-expansive potential soil, as detailed in Section 5.2.

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6.1 CONVENTIONAL FOOTINGS WITH SLAB-ON-GRADE

The proposed building can be supported on continuous footings bearing in competent native soil or compacted fill.

6.1.1 Footing Dimensions and Allowable Bearing Capacity

TABLE 6.1.1-1: Minimum Footing Dimensions

FOOTING TYPE *MINIMUM DEPTH

(INCHES)

MINIMUM WIDTH

(INCHES)

Continuous 24 12

Isolated 24 18

* below lowest adjacent pad grade

Isolated footings should be connected by reinforced tie beams to form a rigid grid and minimize differential movement between foundation supports. Minimum footing depths shown above are taken from lowest adjacent pad grade. Design foundations recommended above for a maximum allowable bearing pressure of 2,500 pounds per square foot (psf) for dead-plus-live loads.

Increase this bearing capacity by one-third for the short-term effects of wind or seismic loading.

The maximum allowable bearing pressure is a net value; the weight of the footing may be neglected for design purposes. Footings located adjacent to utility trenches should have their bearing surfaces below an imaginary 1:1 (horizontal:vertical) plane projected upward from the bottom edge of the trench to the footing.

6.1.2 Waterstop

If a two-pour system is used for footings and slab, the cold joint between the exterior footing and slab-on-grade should be located at least 4 inches above adjacent finish exterior grade. If this is not done, then we recommend the addition of a waterstop between the two pours to reduce moisture penetration through the cold joint and migration under the slab.

6.1.3 Reinforcement

The structural engineer should design footing and tie-beam reinforcement to support the intended structural loads without excessive settlement. Reinforce continuous footings with top and bottom steel to provide structural continuity and to permit spanning of local irregularities. At a minimum, design continuous footings to structurally span a clear distance of 5 feet.

6.1.4 Foundation Lateral Resistance

Lateral loads may be resisted by friction along the base and by passive pressure along the sides of foundations. The passive pressure is based on an equivalent fluid pressure in pounds per cubic foot (pcf). We recommend the following allowable values for design:

• Passive Lateral Pressure: 300 pcf

• Coefficient of Friction: 0.35

The above allowable values include a factor of safety of 1.5. Increase the above values by one-third for the short-term effects of wind or seismic loading.

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Passive lateral pressure should not be used for footings on or above slopes.

6.1.5 Settlement

Provided our report recommendations are followed and given the proposed construction (Section 1.3), we estimate total and differential foundation settlements to be less than approximately 1 and ¾ inches, respectively, over a distance of 50 feet.

7.0 CONCRETE SLABS-ON-GRADE

7.1 INTERIOR CONCRETE FLOOR SLABS

7.1.1 Minimum Design Section

Provided the site is graded with low expansion potential soil (PI less than 10 and EI less than 50) in the upper 2 feet of the building pad (Section 5.2), we recommend the following minimum design for interior concrete floor slab(s) and capillary break section.

1. Provide a minimum concrete thickness of 6 inches. Place minimum steel reinforcing of No. 4 rebar on 16-inch centers each way within the middle third of the slab to help control the width of shrinkage cracking that inherently occurs as concrete cures.

2. Place 6 inches of mechanically compacted clean crushed rock (100 percent passing the

¾-inch sieve and less than 5 percent passing the No. 4 Sieve) over processed subgrade.

Note, this is not considered part of the 2 feet of low-expansive fill below pad grade.

The structural engineer should provide final design thickness and additional reinforcement, as necessary, for the intended structural loads.

7.1.2 Slab Moisture Vapor Reduction

When buildings are constructed with concrete slabs-on-grade, water vapor from beneath the slab will migrate through the slab and into the building. This water vapor can be reduced but not stopped. Vapor transmission can negatively affect floor coverings and lead to increased moisture within a building. When water vapor migrating through the slab would be undesirable, we recommend the following to reduce, but not stop, water vapor transmission upward through the slab-on-grade.

1. Construct a moisture retarder system directly beneath the slab-on-grade (on top of the crushed rock capillary break) that consists of a vapor retarder membrane sealed at all seams and pipe penetrations and connected to all footings. Vapor retarders shall conform to Class A vapor retarder in accordance with ASTM E 1745, latest edition, “Standard Specification for Plastic Water Vapor Retarders used in Contact with Soil or Granular Fill under Concrete Slabs”.

2. Use a concrete water-cement ratio for slabs-on-grade of no more than 0.50.

3. Provide inspection and testing during concrete placement to check that the proper concrete and water cement ratio are used.

4. Moist cure slabs for a minimum of 3 days or use other equivalent curing specified by the structural engineer.

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The structural engineer should be consulted as to the use of a layer of clean sand or pea gravel (less than 5 percent passing the U.S. Standard No. 200 Sieve) placed on top of the vapor retarder membrane to assist in concrete curing.

7.2 EXTERIOR FLATWORK

Exterior flatwork includes items such as concrete sidewalks, steps, and outdoor courtyards exposed to foot traffic only. Provide a minimum section of 4 inches of concrete over 4 inches of aggregate base. Compact the aggregate base to at least 90 percent relative compaction (ASTM D1557). Thicken flatwork edges to at least 10 inches to help control moisture variations in the subgrade and place wire mesh or rebar within the middle third of the slab to help control the width and offset of cracks. Construct control and construction joints in accordance with current Portland Cement Association Guidelines.

8.0 RETAINING WALLS

8.1 LATERAL SOIL PRESSURES

Design proposed retaining walls to resist lateral earth pressures from adjoining natural materials and/or backfill and from any surcharge loads. Provided that adequate drainage is included as recommended below, design walls restrained from movement at the top to resist an equivalent fluid pressure of 60 pounds per cubic foot (pcf). In addition, design restrained walls to resist an additional uniform pressure equivalent to one-half of any surcharge loads applied at the surface.

Design unrestrained retaining walls with adequate drainage to resist an equivalent fluid pressure of 40 pcf plus one-third of any surcharge loads.

The above lateral earth pressures assume level backfill conditions and sufficient drainage behind the walls to prevent any build-up of hydrostatic pressures from surface water infiltration and/or a rise in the groundwater level. If adequate drainage is not provided, we recommend that an additional equivalent fluid pressure of 40 pcf be added to the values recommended above for both restrained and unrestrained walls. Damp-proofing of the walls should be included in areas where wall moisture would be problematic.

Construct a drainage system, as recommended below, to reduce hydrostatic forces behind the retaining wall.

8.2 RETAINING WALL DRAINAGE

Construct either graded rock drains or geosynthetic drainage composites behind the retaining walls to reduce hydrostatic lateral forces. For rock drain construction, we recommend two types of rock drain alternatives:

1. A minimum 12-inch-thick layer of Class 2 Permeable Filter Material (Caltrans Specification

68-2.02F) placed directly behind the wall, or

2. A minimum 12-inch-thick layer of washed, crushed rock with 100 percent passing the ¾-inch sieve and less than 5 percent passing the No. 4 sieve. Envelop rock in a minimum 6-ounce, nonwoven geotextile filter fabric.

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For both types of rock drains:

1. Place the rock drain directly behind the walls of the structure.

2. Extend rock drains from the wall base to within 12 inches of the top of the wall backfill.

3. Place a minimum of 4-inch-diameter perforated pipe (glued joints and end caps) at the base of the wall, inside the rock drain and fabric, with perforations placed down.

4. Place pipe at a gradient at least 1 percent to direct water away from the wall by gravity to a drainage facility, or place on top of the footing with ample gradient between the end of the subdrain and the discharge location.

ENGEO should review and approve geosynthetic composite drainage systems prior to use.

8.3 WALL BACKFILL

Backfill behind retaining walls should be placed and compacted in accordance with Section 5.

Use light compaction equipment within 5 feet of the wall face. If heavy compaction equipment is used, the walls should be temporarily braced to avoid excessive wall movement.

8.4 FOUNDATIONS

Retaining walls may be supported on continuous footings designed in accordance with recommendations presented in Section 6.1.

9.0 PAVEMENT DESIGN

9.1 FLEXIBLE PAVEMENTS

Based on the predominance of highly plastic surficial clay soil on site, it is our opinion that a Resistance Value (R-value) of 5 is applicable for design. KASL provided Traffic Index (TI) values of 4.5, 5, and 6 for parking areas and drive aisles, respectively. We developed the following recommended pavement sections using Topic 633 of the Caltrans Highway Design Manual (including the asphalt factor of safety), presented in Table 9.1-1 below.

TABLE 9.1-1: Recommended Asphalt Concrete Pavement Sections

TRAFFIC INDEX ASPHALT CONCRETE

(INCHES)

CLASS 2 AB

(INCHES)

4.5 3 8 5 3 10 6 4 12

Note: AB is aggregate base Class 2 material with minimum R = 78.

Once actual subgrade soil is exposed during rough grading, additional R-value sampling and testing could be performed to optimize the pavement sections presented above. The civil engineer should determine the appropriate traffic indexes based on the estimated traffic loads and frequencies.

9.2 RIGID PAVEMENTS

Use concrete pavement sections to resist heavy loads and turning forces in areas such as fire lanes or trash enclosures. Final design of rigid pavement sections, and accompanying

Page | 17 May 26, 2020 reinforcement, should be performed based on estimated traffic loads and frequencies. We recommend the following minimum design sections for rigid pavements:

• Use a minimum section of 6 inches of Portland Cement concrete over 6 inches of Caltrans

Class 2 Aggregate Base.

• Concrete pavement should have a minimum 28-day compressive strength of 3,500 psi.

• Provide minimum control joint spacing in accordance with Portland Cement Association guidelines.

9.3 PAVEMENT SUBGRADE AND AGGREGATE BASE COMPACTION

Compact finish subgrade and aggregate base in accordance with Section 5.6. Aggregate Base (AB) should meet the requirements for ¾-inch maximum Class 2 AB in accordance with Section 26-1.02B of the latest Caltrans Standard Specifications.

9.4 CUT-OFF CURBS

Saturated pavement subgrade or aggregate base can cause premature failure or increased maintenance of asphalt concrete pavements. This condition often occurs where landscape areas directly abut and drain toward pavements. If desired to install pavement cutoff barriers, they should be considered where pavement areas lie downslope of any landscape areas that are to be sprinklered or irrigated, and should extend to a depth of at least 4 inches below the base rock layer. Cutoff barriers may consist of deepened concrete curbs or deep-root moisture barriers.

If reduced pavement life and greater than normal pavement maintenance are acceptable to the owner, then the cutoff barrier may be eliminated.

10.0 GROUND HEAT EXCHANGE

Based on our findings and review of the proposed development, we consider the site to be highly suitable for using a ground heat-exchange (GHX) system to achieve energy savings and to potentially eliminate the need for outdoor air conditioner units, if desired.

For the thermal properties of the soil and groundwater conditions at the site, a closed-loop GHX system would likely be well suited and could be implemented on the proposed building.

As project planning progresses into architectural design, we can meet with you, your architect, and your MEP designer to further assess and develop GHX energy saving opportunities and efficiencies.

11.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS

This report presents geotechnical recommendations for design of the improvements discussed in Section 1.3 for the USFS Sequoia NF Porterville office project. If changes occur in the nature or design of the project, we should be allowed to review this report and provide additional recommendations, if any. It is the responsibility of the owner to transmit the information and recommendations of this report to the appropriate organizations or people involved in design of the project, including but not limited to developers, owners, buyers, architects, engineers, and

Page | 18 May 26, 2020 designers. The conclusions and recommendations contained in this report are solely professional opinions and are valid for a period of no more than 2 years from the date of report issuance.

We strived to perform our professional services in accordance with generally accepted principles and practices currently employed in the area; there is no warranty, either express implied. There are risks of earth movement and property damages inherent in building on or with earth materials.

We are unable to eliminate all risks; therefore, we are unable to guarantee or warrant the results of our services.

This report is based upon field and other conditions discovered at the time of report preparation.

We developed this report with limited subsurface exploration data. We assumed that our subsurface exploration data are representative of the actual subsurface conditions across the site. Considering possible underground variability of soil and groundwater, additional costs may be required to complete the project. We recommend that the owner establish a contingency fund to cover such costs. If unexpected conditions are encountered, ENGEO must be notified immediately to review these conditions and provide additional and/or modified recommendations, as necessary.

Our services did not include excavation sloping or shoring, soil volume change factors, flood potential, or a geohazard exploration. In addition, our geotechnical exploration did not include work to determine the existence of possible hazardous materials. If any hazardous materials are encountered during construction, the proper regulatory officials must be notified immediately.

This document must not be subject to unauthorized reuse, that is, reusing without written authorization of ENGEO. Such authorization is essential because it requires ENGEO to evaluate the document’s applicability given new circumstances, not the least of which is passage of time.

Actual field or other conditions will necessitate clarifications, adjustments, modifications or other changes to ENGEO’s documents. Therefore, ENGEO must be engaged to prepare the necessary clarifications, adjustments, modifications or other changes before construction activities commence or further activity proceeds. If ENGEO’s scope of services does not include on-site construction observation, or if other persons or entities are retained to provide such services, ENGEO cannot be held responsible for any or all claims arising from or resulting from the performance of such services by other persons or entities, and from any or all claims arising from or resulting from clarifications, adjustments, modifications, discrepancies or other changes necessary to reflect…