Hotshots_Geotechnical_Report.pdf

THIS DRAFT DOCUMENT IS FOR INTERNAL REVIEW PURPOSES ONLY AND IS NOT TO BE DISCLOSED TO ANY

THIRD PARTY WITHOUT THE EXPRESS PERMISSION OF CONDOR.

GEOTECHNICAL ENGINEERING STUDY

GROVELAND HOTSHOTS BUILDING

UNITED STATES DEPARTMENT OF AGRICULTURE

FOREST SERVICE

GROVELAND, CALIFORNIA

Prepared for

Mary McGrath Architects

505 17 th

Street, Suite 200

Oakland, CA 94612

510.208.9400

Prepared by

Condor Earth Technologies, Inc.

21663 Brian Lane

Sonora, CA 95370

209.532.0361

July 22, 2015

Condor Project No. 7091

Copyright 2015, Condor Earth Technologies, Inc.

All Rights Reserved

THIRD PARTY WITHOUT THE EXPRESS PERMISSION OF CONDOR

ii

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 PROJECT DESCRIPTION

2.0 SCOPE OF WORK

3.0 FINDINGS

3.1 GEOLOGIC SETTING

3.2 SITE AND SUBSURFACE CONDITIONS

4.0 CONCLUSIONS AND RECOMMENDATIONS

4.1 GENERAL

4.2 SEISMIC HAZARDS

4.3 SOIL CORROSION EVALUATION

4.4 GRADING AND EARTHWORK

4.4.1 General Grading Recommendations

4.4.2 Site Preparation

4.4.3 Excavations

4.4.4 Engineered Fill

4.4.5 Final Cut and Fill Slopes

4.4.6 Utility Trenches

4.4.7 Subdrainage

4.4.8 Surface Drainage

4.5 FOOTINGS

4.6 SLABS-ON-GRADE

4.7 ASPHALT PAVEMENT

4.8 CONCRETE PAVEMENTS

5.0 ADDITIONAL SERVICES

6.0 LIMITATIONS

REFERENCES

LIST OF TABLES

Table 1 Soil Corrosion Test Summary Table 2 Engineered Fill Gradation Criteria

ATTACHMENTS

FIGURES

Figure 1 Vicinity Map

Figure 2 Site Plan

Figure 3 Geologic Map

Figure 4 Typical Fill Slope

APPENDIX A

Boring Exploration Logs

USGS Design Maps Detailed Report

APPENDIX B

Laboratory Test Results

APPENDIX C

ASTM E1643-11

ASTM E1745-11

GEOTECHNICAL ENGINEERING STUDY

GROVELAND HOTSHOTS BUILDING

UNITED STATES DEPARTMENT OF AGRICULTURE

FOREST SERVICE

GROVELAND, CALIFORNIA

1.0 INTRODUCTION

This report presents the results of a geotechnical engineering study performed by Condor Earth

Technologies, Inc. (Condor) for the proposed Hotshots Building being designed by Mary McGrath

Architects for the United States Department of Agriculture Forest Service in Groveland, California. The site address is 24545 California Route-120, Building 2505, Groveland, CA 95321. Approximate coordinates are 37.822938° latitude and -120.098838° longitude. The approximate site location is shown on Figure 1, Vicinity Map.

The purpose of the geotechnical study was to evaluate the surface and subsurface conditions at the site in order to develop geotechnical criteria for design and construction of the project. This report presents geotechnical findings, conclusions, and recommendations for earthwork, foundations, and pavements for use by you and your other design professionals and contractors.

1.1 PROJECT DESCRIPTION

The proposed improvements and grading are shown on Figure 2, Site Plan. The project will consist of constructing a new building and vehicular asphalt pavement. The building will be a one-story wood-framed structure with a concrete slab-on-grade floor situated slightly above the adjacent exterior ground surface to the south and up to 5 feet below the adjacent exterior ground surface to the north. The building plan dimensions will be about 60 by 90 feet. The building will be constructed partially at a relatively level area currently occupied by a building (to be demolished), and partially at an area where the existing ground surface slopes down to the existing building. We anticipate that grading for the building pad will consist of a cut up to about 5 feet high and fills of less than about ½-foot to prepare a level building pad and to facilitate surface drainage. A retaining wall will support the cut.

Should the project differ or be modified from that described above, Condor should be given the opportunity to check whether the recommendations contained in this report are appropriate and consider whether additional exploration or analysis is warranted.

2.0 SCOPE OF WORK

Our work was performed in general accordance with our email dated April 7, 2015. Specifically, the scope of our services consisted of the following:

1. Explored, classified, and sampled subsurface materials by means of drilling two vertical borings to maximum depths of 15 feet using our subcontractor’s truck-mounted drill rig equipped with continuous-flight solid-stem augers (4-inch diameter) and split-spoon samplers driven by hammer. One boring was southwest of the existing building near the entrance and one boring on the pavement southeast of the existing building in the parking area. Our Staff Geologist was at the site to log the materials encountered in the borings and to collect representative samples for visual classification and laboratory testing. The approximate locations of the borings are shown on Figure 2, Appendix A. The soil boring logs are presented in Appendix B.

Geotechnical Engineering Study

Groveland Hotshots Building

United States Department of Agriculture

Forest Service

Groveland, California

2. Selected soil samples were tested in the laboratory to measure their pertinent index and engineering properties. The laboratory test results are presented in Appendix B.

3. Evaluated the findings from the study to develop geotechnical conclusions and recommendations for the project

4. Prepared this written report, which summarizes our findings, conclusions, and geotechnical recommendations. Specifically, the report contains the following:

Anticipated subsurface conditions at the building and pavement subgrades

Mitigating the effects of expansive soil

Subsurface drainage requirements on the upslope side of the building

Geologic hazards, including potential for liquefaction, ground surface rupture from faulting, expansive soil, slope instabilities, and any requirements for additional investigation and mitigation

Geotechnical engineering issues for design and construction of earthwork, footings, and pavement

Seismic design according to the 2013 California Building Code

Earthwork, including site and subgrade preparation, material property requirements for fill, and fill compaction requirements

Footings, including minimum depths, allowable bearing capacity, and resistance to horizontal loads

Retaining walls, including lateral earth pressure and subsurface drainage

Design R-value for asphalt pavement and requirements for thickness of asphalt and aggregate base layers for various traffic indices

The impact of soil corrosivity of buried metal, concrete, and concrete reinforcement

3.0 FINDINGS

3.1 GEOLOGIC SETTING

The site is located within the central Sierra Nevada, a high mountain range extending nearly 400 miles from the Mohave Desert in the south, through eastern California, to the Cascade Range in the north. The

Sierra Nevada ranges from 50 to 80 miles wide and, east of the project site, its crest reaches an altitude of more than 11,000 feet. The basement rock of much of the central Sierra Nevada Range consists of metamorphic rocks of Paleozoic and Mesozoic age that have been intruded by the Mesozoic granitic plutons of the Sierra Nevada Batholith. Granitic rock is widely exposed throughout the higher elevations of the Sierra Nevada. Within Tuolumne County, the older basement rocks are locally overlain by the eroded remnants of younger Tertiary-age continental volcanic rocks and Quaternary-age glacial till and alluvium (Huber and others, 1989).

On-going tectonic uplift and westward tilting of the Sierra Nevada has been occurring since the late

Cenozoic along the Frontal fault system bounding the range on the east. The combined uplift and tilting of the Sierra block has created an asymmetric mountain range having a steep eastern scarp and a gentle western slope that dips beneath the accumulated sediments of California’s Great Central Valley

(Wakabayashi and Sawyer, 2000). In response to on-going uplift and tilting, the west-flowing streams of the Sierra have incised deep canyons. Several episodes of glaciation during the last 2 million years have

United States Department of Agriculture

Forest Service exposed the underlying basement rock and created alpine landscapes throughout the higher elevations, scoured the river canyons, and generated extensive glacial outwash deposits in the Great Central Valley.

The geologic processes of tectonic uplift and erosion continue to act on the Sierra Nevada to the present.

The site location is shown on the attached Geologic Map, Figure 3, which shows that the site is underlain by the Paleozoic Calaveras Formation which is underlain by younger Mesozoic granite. Younger deposits attributed to the Tertiary Auriferous Gravels and the Tertiary Mehrten Formation are present upslope and across the state highway but may be present at the site at the surface in the form of colluvial deposits that have been washed downslope.

3.2 SITE AND SUBSURFACE CONDITIONS

The site has been developed and includes buildings, pavement, and underground or overhead utilities.

Observations of the existing topography and utilities indicate that a swale or gully had existed west of building 2505 prior to development. The possible swale area currently has a storm water drop inlet and piping and presumably was filled with soil and rock when a cut was made into the hillside for the current building pad. Fill material also appears to have been placed south of building 2505 to provide a vehicular travel pathway and parking. The more natural ground surface north of the site slopes down to the south at about an overall gradient of 10 to 1 (horizontal to vertical). However, there are localized areas south of the site where the fill slope gradient steepens to about 5 to 1, where fill material was pushed out. Rocks are abundant in the exposed surface soils typically ranging from 12 to 24-inches in diameter.

Based on the results of our subsurface investigation and laboratory testing the site of the proposed replacement building is underlain by sand and lean clay with cobble and boulders attributed to the

Calaveras Complex, which is overlain by varying depths of colluvium or undocumented fill consisting of silty sand and lean clay with cobbles and boulders. The fill material appeared to extend to a depth of five feet in boring B-1 and to 10 feet in boring B-2, however, the exact depths cannot be determined.

The existing asphalt concrete (AC) pavement is in moderately good condition. The AC thickness measured at the boring locations varies from about 3 inches to greater than 4 1/4 inches and aggregate base material (AB) was not encountered.

Past grading of the building and parking areas appear to have created the varying conditions encountered in the two borings. Therefore, the anticipated conditions beneath the proposed building and parking improvements could vary significantly. While clay soils with varying amounts of rock were encountered in both borings, boring B-1 (closest to the existing building) encountered five feet of silty sand before encountering the clay soils underlying the silty sand. In B-2, the clay soils are present immediately beneath the pavement section. It is possible that the silty sand was imported in order to provide non-clay soils beneath the building. The clay soils are potentially expansive, but are anticipated to be only low expansion potential based on lab test results and field classification. Additional recommendations for mitigating the varying conditions at the site are contained in the following sections of the report.

4.0 CONCLUSIONS AND RECOMMENDATIONS

4.1 GENERAL

Based on the findings from this investigation, it is our opinion that the proposed Hotshot building and associated improvements can be constructed as planned, provided the recommendations presented in this report are incorporated into their design and construction. The primary geotechnical concerns for design

United States Department of Agriculture

Forest Service and construction of the project are the presence of undocumented fill with clay which may be expansive, the presence of boulder-sized floaters which may be difficult to excavate or process as filly, providing adequate stability for the proposed fill slopes, and providing uniform support under the entire structure.

Foundations and concrete slabs placed directly on the varying soils could undergo erratic settlement when loaded. Overexcavation and compaction and/or replacement of these near-surface soils will be required where they remain beneath proposed improvements. The overexcavated soils will be suitable for reuse as compacted fill after removal of oversized rock, debris and deleterious matter in areas of pavement and fill slopes.

4.2 SEISMIC HAZARDS

No saturated loose sand or low-plasticity silts are anticipated beneath the proposed improvements, and no active faults were encountered at the project site. Consequently, liquefaction and ground rupture from faulting are not considered significant hazards.

We recommend the following values for structural design according to the 2013 CBC and USGS. These values are based on: site Class C; Risk Category III; PGA= 0.140; PGAM=0.168; Ss = 0.436; S1 = 0.204;

Fa = 1.200; and Fv = 1.596.

Adjusted Maximum Considered Earthquake Spectral Response Accelerations

SMS 0.523

SM1 0.325

Design Spectral Acceleration

SDS 0.349

SD1 0.217

We recommend the using the following design values:

SDS 0.42

SD1 0.27

4.3 SOIL CORROSION EVALUATION

The corrosion potential of near-surface soil was evaluated by means of resistivity, pH, and chemical analysis of a selected bulk sample taken from B-1 at a depth of 3 feet. The test was performed by Cooper

Testing Labs, Inc., Palo Alto, California. The electrical resistivity of the sample was measured with distilled water added to create the standardized condition of saturation. The samples were chemically analyzed for major anions and cations, and pH. Results of the corrosion test are presented in Appendix B.

Table 1

Soil Corrosion Test Summary

Sample Description

Minimum Resistivity

(ohm-cm) pH

Chloride Content

(ppm)

Sulfate Content

(ppm)

B-1 @ 3 feet 1,837 7.0 10 14

Resistivity tests performed on the soil sample indicated that the soils are moderately corrosive to buried metal objects as indicated by result of 1,837 ohm-centimeters. A commonly accepted correlation between

United States Department of Agriculture

Forest Service soil resistivity and corrosivity towards ferrous metals is provided in the following table developed by the

National Association of Corrosion Engineers (NACE):

Soil Resistivity Corrosivity

Less than 500 ohm-cm Very corrosive

500 to 1,000 ohm-cm Corrosive

1,000 to 2,000 ohm-cm Moderately corrosive

2,000 to 10,000 ohm-cm Mildly corrosive

Over 10,000 ohm-cm Progressively less corrosive

All buried iron, steel, cast iron, ductile iron, galvanized steel and dielectric coated steel or iron should be properly protected against corrosion depending upon the critical nature of the structure. All buried metallic pressure piping such as ductile iron firewater pipelines should be protected against corrosion.

Standard concrete mixes and related materials are suitable based on the analysis conducted. While a comprehensive discussion or evaluation of the site corrosivity or mitigation measures is outside the scope of this study, these corrosion test results suggest the site soil do not require special concrete to mitigate corrosive conditions. As a guide, Caltrans considers a site corrosive if the soil contains more than 500 ppm of chlorides, more than 2,000 ppm of sulfates, has a minimum resistivity of less than 1,000 ohm-centimeters, or has a pH of 5.5 or less (Caltrans, 2000).

4.4 GRADING AND EARTHWORK

4.4.1 General Grading Recommendations

Removal of existing clay soils should be performed in areas supporting new building or concrete flatwork improvements to a depth of 18 inches below the top of finish subgrade, where concrete slab-on-grade improvements are planned. Clay soils were encountered in B-2, but were not encountered in B-1.

Therefore, the lateral extent of clay soils to be removed from the proposed building area is unknown. The removed clays soils should be replaced with existing site silty sand or import with a Plasticity Index (PI) of less than 5. We anticipate that the upper five feet of the materials encountered in B-1 will achieve this criterion, but that most of the clay soils onsite will not meet this criterion.

All building concrete improvements, including interior and exterior slab-on-grade, and any other permanent improvements, should be supported by at least 12 inches of subgrade compacted to at least

90% relative compaction (ASTM D1557). The compaction requirement includes existing soils where grade changes are minimal and existing soils meet the requirements of the above paragraph.

Refer to Section 4.1.1 for specific removal requirement beneath the proposed building.

4.4.2 Site Preparation

Organic topsoil, vegetation, debris, and any other unsuitable material should be stripped and removed within the limits of grading. Soils should be considered organic if they contain more than 2 percent

(by weight) of organic material, or have excessive visible organics as determined by the Geotechnical

Engineer. Where the removal of large trees is required, it will be necessary to remove all major root systems (roots greater than 2 inches in diameter), and then fill the excavations with properly placed fill compacted to at least 90 percent relative compaction based on ASTM Test Method D-1557

United States Department of Agriculture

Forest Service

(ASTM D-1557). The cleared vegetation and debris should be removed from the site. Soils loosened by other stripping activities should be excavated to expose firm undisturbed earth. All loose surface soils remaining beneath the proposed improvements, as determined by the Geotechnical Engineer, should be removed to expose firm, undisturbed native ground. We anticipate that the upper 18 to 24 inches of native soils in areas that have not been previously graded will be loose. Overexcavation of any hard rock exposed at the subgrades for the building may be required, as determined by the Geotechnical Engineer, to provide a more uniformly compressible pad in order to reduce differential settlement potential.

Once the stripped and prepared exposed surface has been approved by the Geotechnical Engineer or qualified representative, the resulting soil surface beneath proposed fill and improvements should be scarified to a depth of 6 inches, water conditioned to near optimum water content and compacted to a minimum of 90 percent relative compaction based on ASTM D-1557. The approved soil surface may then be brought to final grade with placement of engineered fill.

Subgrades loosened from construction activity and exposure should be scarified, moisture conditioned, and compacted prior to covering them. A Geotechnical Engineer should approve subgrades before they are covered.

4.4.3 Excavations

On-site excavations are expected to encounter medium dense to dense silty to clayey sand and sandy clays with isolated cobble- and boulder-sized rock floaters. We anticipate that these soils can generally be excavated with moderate effort using conventional heavy-duty earth moving-equipment, such as a moderate-sized dozer with rippers.

Although the site is likely to be generally dry during the summer and fall, perched groundwater or localized seepage may be encountered during the rainy season. Cuts exposing seepage and/or weak soils should be evaluated as soon as possible by the Geotechnical Engineer and/or Engineering Geologist to determine whether the slope should be flattened. If seepage or saturated soils are encountered during grading, recommendations for subdrainage or special grading should be provided, as needed, by the

Geotechnical Engineer.

The contractor is responsible for maintaining safe working conditions and should monitor all excavations for any evidence of incipient instability until the excavations are backfilled or retained. It is the contractor’s responsibility to follow the current Occupational Safety and Health Administration (OSHA) regulations (California Construction Safety Orders, Title 8).

4.4.4 Engineered Fill

Engineered fill used to support foundations, slabs-on-grade, or driveway and parking areas should meet the requirements given in this section. Engineered fill should be inorganic, have a liquid limit less than

35 and a plastic index less than 15, and meet the following gradation criteria:

Table 2

Engineered Fill Gradation Criteria

Sieve Opening Percent Passing by Weight

4-inch square 100

¾-inch square 70 minimum

U.S. No. 4 60 minimum

United States Department of Agriculture

Forest Service

Additionally, any engineered fill placed within 18 inches of the access road subgrade should preferably have an R-value of at least 20. Laboratory tests indicated that the site soils had an R-value of 27 and a plasticity index of 11.

Based on our site investigation, native soils should meet the above requirements for engineered fill provided the materials are stripped and properly processed. Processing may include crushing the boulder-sized material and/or use a “grizzly” so it will meet gradation requirements for engineered fill. Boulder-sized material can be used as rip-rap and placed on the face of fill slopes.

Soil or rock that does not meet or cannot be processed to meet the requirements in Table 2 should be wasted outside the limits of grading or used in agricultural or landscape areas.

Inorganic import material, having a low potential for expansion and meeting the criteria given in this section, may also be used as engineered fill. A sample of any proposed import material should be provided to the Geotechnical Engineer and tested to confirm its suitability prior to transporting the material on-site.

Engineered fill composed of suitable on-site materials meeting the specifications given in Table 2 or approved import material should be placed in horizontal layers not exceeding 8 inches in loose thickness, water conditioned to at least the optimum value, and compacted to the following minimum values based on ASTM D-1557:

90 percent relative compaction per ASTM D1557 beneath new structures and slabs-on-grade, and within an area extending 5 feet outside structure and slab areas.

95 percent relative compaction per Caltrans 216 for the upper 12 inches of all driveway and parking area subgrades.

Where fill is placed on an existing slope steeper than 5H:1V, a keyway should be constructed below the toe of the fill and the fill should be benched into competent soil/rock, as shown on Figure 4, Typical Fill

Slope. The width of the keyway bottom should be at least one-half of the fill slope height or 10 feet, whichever is smaller. All fill should be embedded into firm natural soil or bedrock as it is brought up in layers to remove all loose or soft material beneath the fill. A subdrain should be installed at the back of the keyway and/or where seepage is observed, if required. Keying and benching of fills should be observed by the Geotechnical Engineer or a qualified representative.

To reduce the possibility of surficial failures (slope failures which occur in material within 2 to 3 feet of the finished face of slope), the fill material should be uniformly compacted to the finished face of the fill slope, so that the strength of material will be as high and the permeability as low near the surface as it is in the well compacted core of the fill. Or, the slope could be over-built and then cut back to an adequately compacted finish slope. Proper temporary and permanent erosion protection should be provided on all fill and cut slopes.

All finished surfaces should be graded to drain away from foundations. Subgrade surfaces should be finished true to line and grade and present a smooth, firm, unyielding surface, and should be maintained moist and free of shrinkage cracks until covered by permanent construction. The Geotechnical Engineer shall approve all subgrades before they are covered.

United States Department of Agriculture

Forest Service

4.4.5 Final Cut and Fill Slopes

Permanent cut slopes should be inclined as steep as 2H:1V (2 horizontal to 1 vertical) unless a specific design is provided for the location and ground conditions. The top of all permanent cut slopes should be rounded to meet existing grade. If seepage or saturated soils are encountered during grading, recommendations for subdrainage or special grading should be provided, as needed, by the Geotechnical

Engineer.

Permanent fill slopes constructed of engineered fill should be made no steeper than 2H:1V. If more steeply inclined fill slopes are desired, these fills should be reinforced with geogrids. Vertical spacing of geogrids is usually 12 to 18 inches, and lengths of geogrids are typically about two-thirds to one times the height of the fill slope. For 1.5H:1V fill slopes less than 10 feet in height, a two-foot thick layer of rip-rap can be placed on the slope face in lieu of reinforcing the fill slope with geogrids. A filter fabric such as Mirafi 1120N or equal should be placed beneath the rip-rap to reduce soil erosion.

4.4.6 Utility Trenches

Trench excavations for utilities should be bedded and backfilled in accordance with the requirements of the service provider (utility company) or local jurisdiction. Bedding sand should be placed from 4 inches below the conduit or pipe to at least 1 foot above the conduit or pipe. Bedding sand typically has a Sand

Equivalent value of at least 30. The intent of this requirement is to provide a bedding sand material that flows into the pipe haunches more easily during backfilling operation, so that voids at the pipe haunches are reduced and improved pipe sidewall support is provided by the backfill. Condor should observe and approve the bedding sand and specialized backfilling procedures during construction.

Sand bedding should not be jetted into place, but should be mechanically compacted to a minimum of 90 percent relative compaction (ASTM D-1557). Within the driveway and parking areas, the upper 12 inches of backfill in utility trenches (including culvert and sprinkler lines) should be compacted to 95 percent relative compaction (ASTM D-1557) as recommended for engineered fill, to reduce settlement and to provide a stable road subgrade. If possible, the trench backfill should be compacted following rough grading but prior to final grading and compaction. Trench backfill need only be compacted to 85 percent relative compaction (ASTM D-1557) in unimproved areas or in areas more than 5 feet beyond the edges of structures, pavements, concrete slabs-on-grade, or other flatwork.

Trench plugs designed to interrupt and redirect the flow of concentrated surface runoff and subsurface water percolating through trench bedding and backfill should be considered for utilities with gradients exceeding about 5H:1V. The trench plugs should extend the full depth of the trench and fit tightly against the trench sidewalls and bottom. The trench plugs may be constructed of cast-in-place lean concrete, sacked concrete, and sacks filled with fine-grained soil, polyurethane foam, bentonite, or other impermeable material. Sacks filled with coarse-grained soils should not be used.

4.4.7 Subdrainage

Groundwater drainage systems installed for the fill slope keyways or cut areas are expected to intercept seasonal shallow groundwater. If wet or seeping conditions, or evidence of seasonal seepage is encountered elsewhere during site grading, additional subdrains are recommended. The design of the subdrains depends on the topography, specific seepage conditions and flow rate, and the characteristics of adjacent improvements. We recommend that the Geotechnical Engineer evaluate the need for

United States Department of Agriculture

Forest Service subdrainage based on our review of the project plans and, if needed, prepare a subdrain design. The contractor should be prepared to install subdrains if the need arises.

4.4.8 Surface Drainage

Surface drainage should be planned to prevent ponding and enable water to drain away from the tops and bottoms of slopes, slabs-on-grade, and toward suitable collection or discharge facilities. Surface drainage should be designed to capture upslope runoff and direct it away from the cut and fill slopes. In unpaved areas, a positive surface drainage gradient of at least 4 percent is recommended within 10 feet of all structures. Outside this area a surface gradient of at least 2 percent is recommended to allow for rapid removal of surface water. Driveways should be designed with minimum gradients of about 2 percent in their principal direction of drainage, unless drainage reaches are short or specifically designed for flatter gradients. Roof drainage systems should be planned to direct rainwater away from foundations.

Concentrated water should not be discharged onto bare ground or slopes, but should be carried in pipes or lined channels to suitable disposal points. Because soils generally have a moderate potential for erosion, we recommend that approved temporary and permanent erosion control measures be implemented to limit erosion. Soils on graded slopes should be fertilized, mulched, and planted as soon as possible after grading with erosion-resistant vegetation. These plants should be watered lightly, at appropriate intervals, until growth is established.

Good surface drainage should be provided to divert water away from the proposed cut and fill slopes.

Concentrated surface flows can erode and gully slopes, and may lead to instability. All concentrated flows should be collected in a lined-channel and discharged at a suitable location well away from adjacent slopes. Potential for fill settlement and runoff with a relatively high velocity from flows up-gradient, should be considered for design. We estimate that post-construction fill settlement could be about 1/4 inch for every 5 feet of fill thickness.

4.5 FOOTINGS

Footings should be embedded at least 18 inches below the lowest adjacent soil subgrade and found in existing site soils or engineered fill. We define soil subgrade as the prepared soil beneath floor slabs, aggregate layers, and landscape soil. Isolated and continuous footings should be at least 18 inches and 12 inches wide, respectively. Footings should have the minimum widths and thicknesses specified by the

2013 CBC.

Footings bearing may be designed using an allowable bearing capacity of 2,500 pounds per square foot

(psf) for dead plus normal duration live loads. This allowable bearing capacity value may be increased by one-third for total load conditions, including wind and seismic.

For resistance to lateral loads, base friction resistance may be calculated using a friction coefficient of

0.35. Passive resistance may be calculated using an equivalent fluid unit weight of 300 pounds per cubic foot (pcf) for sustained loads. Both passive pressure and base friction may be combined in calculating total lateral resistance. Passive resistance contributed by the top 12 inches of soil should be neglected unless a concrete slab-on-grade or pavement covers the ground. Gaps between the footing or keyway and the adjacent ground should be completely backfilled using engineered fill, concrete or lean cement slurry with a 28-day unconfined compressive strength of at least 100 psi.

United States Department of Agriculture

Forest Service

Any loose soil encountered beneath footings, as determined by the Geotechnical Engineer, should be replaced with concrete or lean cement slurry with a 28-day unconfined compressive strength of at least

100 psi. The Geotechnical Engineer should approve footing excavations before reinforcing steel and concrete is placed to verify competent soils are present.

4.6 SLABS-ON-GRADE

Refer to Sections 4.4.1 for specific soils requirements beneath concrete slabs-on-grade.

During foundation and utility trench excavation operations, the soil subgrade within concrete slabs-on-grade areas may become disturbed. When, in the opinion of the Geotechnical Engineer, this has occurred, the subgrade should be uniformly moisture conditioned and rerolled to provide a firm, smooth, non-yielding surface compacted to at least 90 percent relative compaction (ASTM D-1557).

Slab-on-grade floors and exterior slabs should be underlain by at least 4 inches of clean, free-draining gravel or crushed rock (slab drain rock graded between ¼-inch and 1½-inch) to act as a capillary moisture break. Where moisture vapor through the floor slab would be objectionable, the capillary break material should be covered with a vapor retarder. The vapor retarder should be at least 15 mil in thickness, and meet the material requirements in ASTM Standard Specification E-1745 (such as Stego or equal). Vapor retarders should be installed according to ASTM E-1643 and the manufacture’s specifications, and include overlapping seams by 6 inches, taping seams, and sealing penetrations in the vapor retarder.

The American Concrete Institute (ACI) Committee document “Guide for Concrete Slabs that Receive

Moisture-Sensitive Flooring Materials” (ACI 303.2R.6) provides guidelines for reducing moisture migration through slabs-on-grade. This document advises that concrete slabs be cast directly on the moisture retarder (ACI 303.2R.6, Section 9.3) and provides guidelines for selecting vapor permeance, tensile strength and puncture resistance. When casting the slab directly on the vapor retarder, a reduced joint spacing, low shrinkage mix design, or other appropriate measures should be used to control slab curl.

The ACI guide also notes that a maximum water-cement ratio of 0.5 will yield satisfactory performance for many projects. Water-reducing admixtures may be useful in achieving workability at low water-cement ratios. Control joints should be provided at appropriate intervals to control the location of shrinkage cracks. After proper curing, the slab should be allowed to dry then tested to check that the moisture transmission rate is appropriate for the intended floor covering.

Where dampness of the slab is not objectionable, the vapor retarder and capillary break material may be omitted and the slab may be constructed directly on the prepared subgrade or on a layer of compacted

Caltrans Class 2 Aggregate Base rock (AB).

To minimize shrinkage cracking, concrete slabs should be reinforced with No. 3 rebar spaced 18 inches on center each way. Control joints should also be provided at appropriate intervals to control the location of shrinkage cracks.

United States Department of Agriculture

Forest Service

4.7 ASPHALT PAVEMENT

Our recommendations for flexible asphalt pavement sections are based on the Caltrans Flexible

Pavement Design Method as presented in Chapter 600 of the Caltrans Highway Manual, Sixth Edition, and include the use of safety factors in the calculations of the required gravel equivalent (GE) of the AC layer. We used a design R-value of 20 based on our laboratory test results and conditions encountered in our borings.

We suggest that an R-value test be performed once rough grade has been achieved to confirm that the pavement subgrade meets or exceeds the design R-value. Similarly, any proposed import or excavation spoils should be tested to confirm they have an R-value of at least 20. We anticipate that some of the proposed road subgrades in the cut area will consist of clay with an R-value as low as 5. We recommend that where encountered, and as determined by the Geotechnical Engineer, that such clays be overexcavated to a depth of at least 12 inches below the design subgrade and replaced with compacted, engineered fill that has an R-value of at least 20.

The following table presents the resulting recommended pavement design sections for various traffic indices (TIs).

Design Thickness (inch)

R-Value = 20

Traffic Index (TI) AC AB

4 4.0 4.5

6 5.0 8.0

8 6.0 12 AC = Asphalt Concrete

AB = Class 2 Aggregate Base

All trench backfills for culverts, utilities, and pipes underlying the proposed driveway and parking areas should be properly placed and compacted to at least 90 percent relative compaction (ASTM D-1557) to provide a stable subgrade. The upper 12 inches of all driveway and parking area subgrades should be compacted to at least 95 percent relative compaction (CAL 216). AB material should comply with the minimum requirements for Class 2 AB specified in Caltrans Standard Specifications, Section 26 and should be compacted to at least 95 percent relative compaction (CAL 216). Paved areas should be sloped and adequately drained to prevent surface water or subsurface seepage from saturating the pavement subgrade soil.

Areas where the existing asphalt concrete (AC) pavement has a high concentration of alligator cracks may be within small depressions, and that runoff and water from snowmelt collected in these areas, weakened the subgrade soil, and contributed to the distress. Other areas with alligator cracking may have been caused by shear stresses from turning tires of slow moving or not moving large trucks. Where the existing asphalt has significant alligator cracks and an overlay is anticipated, we recommend covering the existing pavement with sheet products such as Petrotac, Miratak, or equal that is intended for situation where the cracks are up to 3/8 inches in width, and functions to reduce the potential for the cracks to propagate through the overlay.

United States Department of Agriculture

Forest Service

4.8 CONCRETE PAVEMENTS

A modulus of subgrade reaction, kv (30-inch circular plate) of 150 psi, may be used for design of vehicular concrete pavement. We recommend that exterior concrete pavements consist of at least

2 inches of AB beneath at least 6 inches of concrete.

The concrete used should have a 28-day compressive strength of at least 3,000 psi, and should have entrained air to resist damage from freezing.

Expansion/contraction joints should be constructed at a maximum spacing of 15 feet. Where the outer edge of a concrete pavement meets asphalt pavement, the concrete slab should be thickened by

50 percent at a taper not to exceed a slope of 1 in 10.

5.0 ADDITIONAL SERVICES

Condor recommends that we review project plans and specifications to check that the intent of our recommendations have correctly been incorporated into the design. The review of plans and specifications prior to issuance for bidding and construction often aids in reducing or preventing confusion or oversight during construction. If Condor does not review the geotechnical elements of the plans and specifications, another qualified Geotechnical Engineer should thoroughly review this report and concur with its conclusions and recommendations or provide alterative recommendations.

The geotechnical recommendations and design criteria given in this report are sensitive to the location, design details, and any special requirements of the project. Subsurface conditions at the site are variable and it is not possible to anticipate all conditions that may be encountered during construction. The assumed subsurface conditions used to develop our recommendations are based on limited exploration and may require adjustment based on actual ground conditions revealed during construction.

Consequently, we recommend that Condor provide geotechnical observation and testing services during grading and construction of foundations and pavements to check that the ground conditions are as assumed, that the intent of our recommendations were followed during construction, and that the geotechnical aspects of the work are performed in accordance with the approved plans and specifications.

The Geotechnical Engineer of Record or qualified representative should visit the site periodically during construction to test, observe, and advise during site preparation, grading and earthwork, paving, and construction of foundations, subdrains, slabs-on-grade, and retaining walls. These observations should be supplemented with periodic density and compaction testing of subgrade and engineered fills to evaluate conformance with the recommendations contained in this report.

6.0 LIMITATIONS

The geotechnical conclusions and recommendations presented in this report are intended for planning and design of the proposed building, access road and related improvements. The geotechnical conclusions and recommendations given in this report should not be used for a different site or project or if changes are made that materially alter the proposed project.

The analyses and recommendations presented in this report are based upon the data obtained from the exploratory soil borings, and general field reconnaissance observations made during the site investigation. Subsurface exploration of any site is necessarily confined to selected locations, and subsurface conditions may, and usually do, vary between and around these locations. The logs of the exploratory borings do not provide a warranty as to the conditions that may exist beneath the entire site.

United States Department of Agriculture

Forest Service

The extent and nature of subsurface soil, bedrock, and groundwater variation may not become evident until construction begins. It is possible that variations in soil or groundwater conditions may occur beyond the soil boring locations and may dictate further study, consultation, or design revision. Any person associated with this project who observes conditions or features of the site or its surrounding areas that are different from those described in the report should immediately notify Condor.

This report was prepared in accordance with the generally accepted standards of geotechnical engineering practice which exist in Northern California at the time the report was written. No other warranty, express or implied, is made. It is the owner’s responsibility to see that all parties to the project, including the designers, contractors, and subcontractors are made aware of this report in its entirety.

Note that changes in the standards of practice in the field of geotechnical engineering, changes in site conditions such as new excavations or fills, new agency regulations, or modifications to the proposed project are grounds for this report to be professionally reviewed. In light of this, there is a practical limit to the usefulness of this report without critical professional review. It is suggested that two years be considered a reasonable time for the usefulness of this report.

Respectfully submitted, CONDOR EARTH TECHNOLOGIES, INC.

Bill A. Cook III. Ronald L. Skaggs

Certified Engineering Geologist (CA #2534) Geotechnical Engineer (CA #2295)

Senior Geologist Vice President

X:\Project\7000_prj\7091 McGrath Architects\Reports\DR 20150722 GES.doc

United States Department of Agriculture

Forest Service

REFERENCES

American Concrete Institute, 2006, Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring

Materials, ACI 302.2R-06, 66 pp.

California Building Standards Commission, 2013, 20013 California Building Code, California Code of

Regulations, Title 24, Part 2, Volume 2 of 2.

Cao, T., Bryant, W.A., Rowshandle, B., Branum, D., and Wills, C.J., 2003, The Revised 2002 California

Probabilistic Seismic Hazard Maps, June 2003, available on-line at:

http://www.consrv.ca.gov/cgs/rghm/psha/index.htm.

Huber, N.K. and others, 1989, Geologic map of Yosemite National Park and Vicinity, California, U.S.

Geologic Survey Miscellaneous Investigation Series Map I-1874, 1 Sheet.

U.S. Geological Survey, Earthquake Hazards Program – Seismic Design Values for Buildings Website:

http://earthquake.usgs.gov/research/hazmaps/design/index.php.

Wakabayashi, J., and Sawyer, T.L., 2000, Neotonics of the Sierra Nevada – Basin and Range Transition, California, with Field Trip Stop Descriptions for the Northeastern Sierra Nevada, in Field Guide to the Geology and Tectonics of the Northern Sierra Nevada, National Association of Geoscience

Teachers, Far-Western Section, Fall Conference – 2000, California Division of Mines and Geology

Special Publication 122, pp. 173 -212.

http://www.consrv.ca.gov/cgs/rghm/psha/index.htm http://earthquake.usgs.gov/research/hazmaps/design/index.php

DRAFT

APPENDIX A

Boring Exploration Logs

APPENDIX B

ASTM E1643-11

ASTM E1745-11

Designation: E1643 − 11

Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs1

This standard is issued under the fixed designation E1643; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

1. Scope

1.1 This practice covers procedures for selecting, designing, installing, and inspecting flexible, prefabricated sheet mem-branes in contact with earth or granular fill used as vapor retarders under concrete slabs.

1.2 Conditions subject to frost and either heave or hydro-

static pressure, or both, are beyond the scope of this practice.

Vapor retarders are not intended to provide a waterproofing function.

1.3 The values stated in inch-pound units are to be regarded

as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.4 This standard does not purport to address all of the

safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.

2. Referenced Documents

2.1 ASTM Standards:2

E1745 Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs

E1993 Specification for Bituminous Water Vapor Retarders Used in Contact with Soil or Granular Fill Under Concrete Slabs

F710 Practice for Preparing Concrete Floors to Receive Resilient Flooring

2.2 Other Standard:3

ACI 302.2R–06 Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials

3. Significance and Use

3.1 Vapor retarders provide a method of limiting water

vapor transmission and capillary transport of water upward through concrete slabs on grade, which can adversely affect floor finishes and interior humidity levels.

3.2 Adverse impacts include adhesion loss, warping, peeling, and unacceptable appearance of resilient flooring;

deterioration of adhesives, ripping or separation of seams, and air bubbles or efflorescence beneath seamed, continuous floor-ing; damage to flat electrical cable systems, buckling of carpet and carpet tiles, offensive odors, growth of fungi, and unde-sired increases to interior humidity levels.

4. Manufacturer’s Recommendations

4.1 Where inconsistencies occur between this practice and

the manufacturer’s instructions, conform to the manufacturer’s instructions for installation of vapor retarder.

5. Material, Design, and Construction

5.1 See ACI 302.2R–06 for material, design, and construc-

tion recommendations.

5.2 See Specifications E1745 and E1993 for vapor retarder

specifications.

5.3 Vapor Retarder Material Selection—The following cri-

teria should be considered when selecting a vapor retarder material.

5.3.1 Local building code and regulatory requirements.

5.3.1.1 Comply with local building code and regulatory

requirements as a minimum consideration.

5.3.2 The water-vapor permeance of the vapor retarder

material.

5.3.2.1 The water vapor permeance of the vapor retarder

material shall be at such a rate so that adverse impacts to floor finishes and coatings do not occur

1 This practice is under the jurisdiction of ASTM Committee E06 on Perfor-mance of Buildings and is the direct responsibility of Subcommittee E06.21 on Serviceability.

Current edition approved Oct. 1, 2011. Published October 2011. Originally approved in 1994. Last previous edition approved in 2010 as E1643 – 10. DOI:

10.1520/E1643-11.

2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.

3 Available from American Concrete Institute (ACI), P.O. Box 9094, Farmington Hills, MI 48333-9094, http://www.concrete.org.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

Copyright by ASTM Int'l (all rights reserved); Tue Apr 21 13:01:53 EDT 2015 Downloaded/printed by Lillian Babcock (Condor Earth Technologies, Inc.) pursuant to License Agreement. No further reproductions authorized.

http://dx.doi.org/10.1520/E1745 http://dx.doi.org/10.1520/E1745 http://dx.doi.org/10.1520/E1993 http://dx.doi.org/10.1520/E1993 http://dx.doi.org/10.1520/E1993 http://dx.doi.org/10.1520/F0710 http://dx.doi.org/10.1520/F0710 http://www.astm.org/COMMIT/COMMITTEE/E06.htm http://www.astm.org/COMMIT/SUBCOMMIT/E0621.htm

5.3.2.2 Refer to X1.6 for discussion on water vapor trans-

mission rate of vapor retarder.

5.3.2.3 The perm rating determined under these criteria

shall supersede that in references 5.2 should this value be less than required under references in 5.2.

5.3.3 The types and amounts of deleterious compounds in

the soil on the building site.

5.3.3.1 Review building site soil analyses for deleterious

materials and compounds and select a vapor retarder material that will withstand exposure to such deleterious materials or compounds.

5.3.4 The tensile strength and puncture resistance of the

vapor retarder material.

5.3.4.1 Select a vapor retarder material capable of with-

standing potential construction site damage.

5.3.5 The type of base material on which the vapor retarder

is to be installed.

5.3.5.1 Select vapor retarder material capable of withstand-

ing tear or puncture damage due to the type, gradation, and texture of the base material to be installed below the material.

Prepare base material to minimize risk of puncture, for example, by rolling or compacting.

5.3.6 The expected exposure of the vapor retarder to ultra-

violet rays.

5.3.6.1 Assess expected exposure of the vapor retarder

material to ultra violet rays and select a material capable of withstanding such exposure and maintain its capability to perform its intended function.

6. Placement

6.1 Level and compact base material.

6.2 Install vapor retarder material…