02-Bristlecone VC Geotech Report - Updated June 22 2010

ENVIRONMENTAL • GEOTECHNICAL • GEOLOGY • HYDROGEOLOGY • MATERIALS

MAMMOTH OFFICE: 549 OLD MAMMOTH ROAD, MAMMOTH LAKES, CA 93546 • Phn: (760) 934-3992 Fax: (760) 934-8832

BISHOP OFFICE: 873 NORTH MAIN STREET, SUITE 150, BISHOP, CA 93514 • Phn: (760) 873-6800 Fax: (760) 873-6888

PALM DESERT OFFICE: 44489 TOWN CENTER WAY STE D-478 PALM DESERT CA 92260

www.sierrageotechnicalinc.com

June 22, 2010 Project No. 3.30993.1

United States Forest Service 351 Pacu Lane Bishop, CA 93514

Attention: Nora Gamino

Subject: UPDATED FOUNDATION RECOMMENDATIONS

Schulman Grove Visitor Center White Mountains, California

Reference: FOUNDATION AND SEISMICITY RECOMMENDATIONS

Schulman Grove Visitor Center White Mountains, California

SGSI Report dated March 16, 2010

Dear Ms. Gamino:

Included herein are updated foundation recommendations for the reconstruction of the Schulman Grove Visitors Center. All conclusions and recommendations contained within the above referenced report are considered valid with exception of the recommendations included herein.

We appreciate the opportunity to be of service to you. Should you have any questions regarding this report, please do not hesitate to contact us.

Respectfully, SIERRA GEOTECHNCIAL SERVICES, INC.

Joseph A. Adler Thomas A. Platz Principal Geologist Principal Engineer

CEG 2198 PE C41039

June 22, 2010 Project No. 3.30993.1

Due to winter conditions and USFS time constraints Sierra Geotechnical Services Inc (SGSI) was unable to perform a field investigation in March 2010. Conclusions and recommendations included in the referenced report were based on our knowledge of the site area, as well as laboratory soil test results provided by the USFS from the building area. SGSI therefore recommended that we be allowed to “ground truth” site soil conditions to confirm our geotechnical recommendations and to also provide added foundation design recommendations for the inclusion of a 4 to 5 foot retaining wall.

SGSI has recently visited the site, logged a single backhoe excavated test pit, and collected bulk samples for laboratory testing.

FOUNDATION PREPARATION AND DESIGN

Foundations should be designed in accordance with structural considerations and the following recommendations. These recommendations are presented as minimum design recommendations; and supercede those included in the above referenced report. Upon the completion of structural plans, Sierra Geotechnical Services Inc. should review the foundation loads and embedment in order to confirm the implementation of the recommendations herein.

Preliminary Building Foundation Preparation and Design

An allowable soil bearing pressure of 4,000 pounds per square-foot (psf) and a friction coefficient for concrete/soil of 0.40 may be used for the design of footings founded entirely upon either competent fill or competent alluvial deposits. The allowable bearing value may be increased by one-third for short duration loading which includes the effects of wind or seismic forces.

Conventional Foundation Construction

Footings may be constructed according to California Building Code requirements regarding width. Exterior and interior foundations shall be founded within competent native soils. Exterior foundations shall have a minimum embedment depth of 24-inches below outside adjacent grade. Interior foundations shall have a minimum embedment depth of 18-inches below adjacent grade.

Foundation Setback

We recommend a minimum horizontal setback of H/3 (H = height of the slope) be maintained from the face of slopes to the bottom outside edge of all structural footings and settlement-sensitive structures. Utility trenches that parallel or nearly parallel structure footings should not encroach within a 1:1 plane extending downward and outward from the outside edge of the footing.

Concrete Slab-on-Grade Floors

Slab thickness shall be a minimum of 4-inches. In areas where heavy equipment or loading will stress the slab, the thickness will meet the requirements of the Structural Engineer of record.

Minimum slab reinforcement shall consist of #4 rebar placed at 18-inches on center each way. The slab reinforcement shall be placed, vertically, in the middle of the slab. In areas where heavy equipment or loading will stress the slab, the reinforcement will meet the requirements of the Structural Engineer of record.

Concrete slabs should be underlain by a 1-inch layer of clean sand (SE greater than 30) to aid in concrete curing, which is underlain by a 10-mil (or heavier) moisture barrier, which is, in turn, underlain by a 1-inch layer of clean sand to act as a capillary break. All penetrations and laps in the moisture barrier should be appropriately sealed.

For design of slabs and estimating their deflections, a modulus of subgrade reaction (k) of 100 pci may be used for re-compacted materials.

Lateral Earth Pressures for Walls

Retaining Wall Lateral Earth Pressure in Equivalent Fluid Weight (pcf)

Active Case Passive Case Horizontal 34 330 At-Rest 51

Wall footings should be designed in accordance with structural considerations. If both the passive and frictional resistances are assumed to act together than we recommend that a minimum factor of safety of 2.0 is used for design.

The passive resistance value may be increased by one-third when considering loads of short duration, including wind or seismic loads. The horizontal distance between foundation elements providing passive resistance should be a minimum of three times the depth of the elements to allow full development of these passive pressures.

The total depth of retained earth for design of cantilever walls should be the vertical distance below the ground surface measured at the wall face for stem design or measured at the heel of the footing for overturning and sliding.

Wall backcut excavations less than 5-feet in height can be made near vertical. For backcuts greater than 5-feet in height, but less than 35-feet in height, the backcut should be flattened to a gradient of not steeper than 1:1 (horizontal to vertical) slope inclination. For backcuts in excess of 35-feet in height, specific recommendations should be requested from the geotechnical consultant.

APPENDIX A

EXPLORATORY TEST PIT LOGS

A subsurface field investigation was performed on June 3rd, 2010 that included the excavation of one exploratory test pit with a Backhoe equipped with a 24” bucket within the proposed construction areas. A geologist from our office logged the excavations as they were advanced.

Logs of the exploratory test pits are presented herein. The approximate location of the exploratory test pit is shown on Figure 1.

Bulk samples and of the soils encountered were obtained during the field investigation for laboratory testing. Laboratory test results are included in Appendix B.

SIERRA GEOTECHNICAL SERVICES INC.

P.O. BOX 5024

MAMMOTH LAKES, CA 93546

(760) 934-3992

TEST PIT LOGS

JOB NO. 3.30993.1 BY _J. Adler

PROJECT Schulman Grove DATE: 6/3/2010

TEST

PIT

DEPTH

(FT)

U.S.C.S.

GROUP

SYMBOL

SAMPLE

DEPTH

PERCENT

MOISTURE

DRY

DENSITY

(pcf)

DESCRIPTION

Topsoil/Colluvium Dark brown to brown, moist, loose to medium dense, silty, very fine to fine SAND, abundant roots, moderate rock fragments.

Brown, moist, dense, silty, very fine to fine SAND, few roots, abundant rock fragments. Rock content 35% of deposit.

Weathered Dolomite Highly weathered, with silty sand matrix.

Abundant angular to subangular fragments to 12” Fragments up to 55% of deposit.

0 - 1½

1½ - 4

4 - 5

SM

SM

Total Depth 5-feet. No groundwater observed.

Backfilled 6/3/2010

Notes: S. side of structure; e-w orientation; approximately 15-20’ s. of existing slab. Equip - JD 410 w/ 24” bucket. Rock content will increase to east of excavation.

APPENDIX B

LABORATORY TESTING

Laboratory tests were performed on the representative test samples to provide a basis for development of design parameters. Soil materials were visually classified in the field according to the Unified Soil Classification System (USCS). Selected samples were tested for the following parameters: Classification and grain size distribution, direct shear, expansion, maximum dry density (Proctor), and sand equivalent. Laboratory tests were performed in general accordance with the American Society of Testing and Materials (ASTM) procedures.

The results of our laboratory testing along with summaries of the testing procedures are presented herein. The results of USCS classifications are presented on the test pit logs (Appendix A).

LABORATORY TESTING

Classification or Grain Size Tests: Typical materials were subjected to mechanical grain-size analysis by sieving from U.S. Standard brass screens (ASTM Test Method D422). The data was evaluated in determining the classification of the materials. The grain-size distribution chart is presented in the test data and the Unified Soil Classification (USCS) is presented in the trench logs.

Direct Shear Tests: One direct shear strength test was performed on a representative remolded sample tested to evaluate strength characteristics of foundation soils in accordance with ASTM D3080. The sample was inundated to approximate saturated conditions and tested under various normal loads, using a motor-driven, strain-controlled, and direct-shear testing apparatus at a strain rate of less than 0.001 to 0.5 inches per minute. The test results are presented herein.

Sample Location

Sample Description Friction Angle

(degrees) (relaxed)

Apparent Cohesion (psf)

TP-1 @ 2-3’ Brown, silty, very fine to fine

SAND

31 260

Expansion Index: The expansion potential of selected materials was evaluated by the Expansion Index Test, ASTM 4829. Specimens were molded under a given compactive energy to approximately the optimum moisture content and approximately 50 percent saturation or approximately 90 percent relative compaction. The prepared 1-inch thick by 4-inch diameter specimens were loaded to an equivalent 144 psf surcharge and inundated with tap water until volumetric equilibrium was reached. The results of these tests are presented in the table below:

Sample Location Sample Description Expansion

Index Expansion Potential

TP-1 @ 2-3’ Brown, silty, very fine to fine SAND 3.6 Very Low

Maximum Density Tests: The maximum dry density and optimum moisture content of typical materials were determined in accordance with ASTM Test Method D1557. The results of these tests are presented in the table below:

Sample Location Sample Description Maximum

Dry Density (pcf)

Optimum Moisture

Content (%) TP-1 @ 2-3’ Brown, silty, very fine to fine

SAND

118.0 12.5

SGSI

K:\03 SGS on Triadvault\Joe Adler\OWENS VALLEY AND OTHER- Reports and Drawings\3.30993 USFS Schulman Visitors Center\3.30993.1\Sieve Analysis.doc

SIERRA GEOTECHNICAL SERVICES INC.

P.O. BOX 5024, MAMMOTH LAKES, CALIFORNIA 93546

(760) 934-3992; (760) 934-8832 Fax

SIEVE ANALYSIS OF FINE AND COARSE AGGREGATES

Per CTM 202 / ASTM C136 (underline one)

Project: Schulman Grove Visitors Center Job No.: 3.30993.1 Client: USFS Tested by: PS Sampled by: JAA Delivered by: JAA Sample Date/time: 6/3/2010 Delivered Date/time: 6/3/2010 Sample Location: TP-1 @ 2-3’ Test Date: 6/2010 Description: Colluvium - Silty, very fine to medium SAND (SM)

Dry Sample Total Weight (g): 4729 #4 Minus Dry Wt. (g): 514/349 % Passing by Dry Weight:

Sieve Size

Inches mm Mesh

Wt.

Ret.

Ret.

Pass.

Wt.

Ret.

Ret.

Pass.

Coarse

Fine Specified

2.0 50.0 2” 654 14 86 86

1.5 37.5 11/2” 927 20 80 80

1.0 25.0 1” 1278 27 73 73

0.750 19.0 3/4” 1551 33 67 67

0.500 12.7 1/2” 1915 40 60 60

0.375 9.5 3/8” 2079 44 56 56

0.187 4.75 #4 2445 52 48 48

0.0937 2.36 #8 50 10 90 43

0.0469 1.18 #16 82 16 84 40

#20

0.0234 0.60 #30 101 20 80 38

#40

0.0117 0.30 #50 117 23 77 37

#80

0.0059 0.15 #100 154 30 70 34

0.0029 0.075 #200 276 54 46 22

PAN 349

TOTAL

Underline “WASH” if #200 wash analysis was done.

Remarks: Wash

P.O. BOX 5024, MAMMOTH LAKES, CALIFORNIA 93546

(760) 934-3992; (760) 934-8832 Fax

Expansion Index

Per ASTM D4829

Sampled by: JAA Delivered by: JAA Sample Date/time: 6/3/2010 Delivered date/time: 6/3/2010 Sample Location: S. Side of Proposed Structure Test Date: 6/11/2010 Description: TP-1 @ 2-3’ (SM)

Expansion Index - 3.6 Potential Expansion - Very Low

Expansion Index (EI) Potential Expansion

0-20 Very Low

21-50 Low

51-90 Medium

91-130 High

>130 Very High

Remarks:

PS Logged for Billing

Tested by

DIRECT SHEAR DIAGRAM

y = 0.5891x + 260

0 500 1000 1500 2000 2500 3000 3500

NORMAL STRESS (psf)

SH

E

A R

S T

R E

N G

T H

(p sf

Boring No: TP-1 Sample Depth: 2-3-feet

Friction Angle: 31 degrees Cohesion: 260 psf

Dry Density: 106.2

Date Tested: 6/11/2010

SCHULMAN GROVE VISITORS CENTER

3.30993.1

SAND EQUIVALENT TEST

Per CTM 217

Sampled by: JAA Delivered by: JAA Sample Date/time: 6/3/2010 Delivered date/time: 6/3/2010 Sample Location: S. Side of Proposed Structure Test Date: 6/11/2010 Description: Colluvium

Test Number Sand Value Clay Value % Sand/Clay

1 17 71 24

2 16 75 21

3 17 69 25

Average Sand Equivalent 23

Calcium Chloride Solution Temp = 75º Sedimentation Time = 20 min per point

Remarks:

PS 60 min Logged for Billing

Tested by Total Time