Shear Strength of Soil

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Shear Strength of Soil © 2004 Brooks/Cole Publishing / Thomson Learning™ Direct shear test in sand: (a) schematic diagram of test equipment; (b) plot of test results to obtain the friction angle φ’ 1 © Learning™ / Thomson Publishing 2004 Brooks/Cole Variation of friction angle φ’ with void ratio for Chattachoochee River sand (after Vesic, 1963) Soil Sampling σ’1 σ’3 σ’3 = K σ’1 σ’1 2 Triaxial Test Equipment Sequences of stress application in © Learning™ / Thomson Publishing 2004 Brooks/Cole triaxial test 3 © 2004 Brooks/Cole Publishing / Thomson Learning™ Plot of deviator stress vs. axial strain-drained triaxial test Triaxial Testing Application of cell pressure (sigma 3): UNCONSOLIDATED (U) – No drainage allowed e constant (fixed) if Sr =1 - CONSOLIDATED (C) – Drainage allowed when applying cell pressure e decreases due to sample consolidation. 4 Triaxial Testing Application of deviatoric stress (σ1): Deviator stress = σ1 – σ3 Undrained (U) No drainage allowed e constant (fixed) if Sr =1 - Drained (D) Drainage allowed when applying cell deviator stress e decreases due to consolidation. Stress applied so slow no excess pwp Triaxial Tests UU – Unconsolidated Undrained UD – Unconsolidated Drained CU - Consolidated Undrained CD - Consolidated Drained 5 Undrained Soil Strength Parameters (Su, φ = 0) Note: Always test soil at void ratio on the field Skempton’s Porewater Coefficients Δμ B = Δσ 3 Developed “B” for a measure of degree of Water saturation 6 © 2004 Brooks/Cole Publishing / Thomson Learning™ Peak- and residual-strength envelopes for clay 7 Skempton’s Porewater Coefficients Developed “A” parameter for indication of sample OCR Δμ A = i (σ1 −σ3)i where : Δμi = (μi − μo ) μo = initail pore pressure μi = pore pressure at point of interest (σ1 −σ3)i = deviatoric stress at point of interest What about negative values of Af Soil Strength M-C Failure Envelope Test 1 Failure Circle Sample will fail at intersection τfailure (2) with envelope τ’ τfailure (1) Test 2 Failure Circle c’ σ1(2) σ3(1) σ1(1) σ1(3) σ1(Failure) σ3(2) σ1(1) σ1(2) σ1(3) σ1(Failure) σ’n NOTE: all stresses are effective Each test is performed at a set void ratio 8 Drained Soil Strength Parameters (c’, φ’) Soil Strength Envelope 9 Soil Strength sinφ’= tanα’ Stress Path of Sample (σ1 - σ3)/2 = t 3 Radius of Circle α’ 2 t 1 t = d' + S tan α' S d = c' cos φ' d tan ψ = sin φ' s s = (σ1' + σ3')/2 Centre of Circle Unconfined compression test in progress (courtesy of Soiltest, Inc., Lake Bluff, IL) 10 Unconfined compression test: © Learning™ / Thomson Publishing 2004 Brooks/Cole (a) soil specimen; (b) Mohr’s circle for the test; (c) variation of qu with the degree of saturation © 2004 Brooks/Cole Publishing / Thomson Learning™ Variation of friction angle φ’ with plasticity index for several clays (after Bjerrum and Simons, 1960) 11.

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Direct Shear Tests Used in Soil-Geomembrane Interface Friction Studies
DIRECT SHEAR TESTS USED IN SOIL-GEOMEMBRANE INTERFACE FRICTION STUDIES August 1994 U.S. DEPARTMENT OF THE INTERIOR Bureau of Reclamation Denver Off ice Research and Laboratory Services Division Materials Engineering Branch 7-2090 (4-81) Bureau of Reclamat~on ..........................................................................................TECHNICAL REPORT STANDARD TITLE PAGE I I. REPORT NO. ................................................................................................. ................................................................................................. I 4. TITLE AND SUBTITLE 1 5. REPORT DATE August 1994 Direct Shear Tests Used in 6. PERFORMING ORGANIZATION CODE Soil-Geomembrane Interface Friction Studies 7. AUTHOR(S) 8. PERFORMING ORGANIZATION Richard A. Young REPORT NO. R-94-09 9. PERFORMING ORGANIZATION NAME AND ADDRESS lo. WORK UNIT NO. Bureau of Reclamation Denver Office Denver CO 80225 12. SPONSORING AGENCY NAME AND ADDRESS Same 1 14. SPONSORING AGENCY CODE DIBR 15. SUPPLEMENTARY NOTES Microfiche and hard copy available at the Denver Office, Denver, Colorado 16. ABSTRACT The Bureau of Reclamation Canal Lining Systems Program funded a series of direct shear tests on interfaces between a typical cover soil and different geomembrane liner materials. The purposes of the testing program were to determine the shear strength parameters at the soil-geomembrane interface and to examine the precision of the direct shear test. This report presents the results of the testing program. 17. KEY WORDS AND DOCUMENT ANALYSIS a. DESCRIPTORS-- water conservation1 geosyntheticsl canal lining/ b. IDENTIFIERS- c. COSA TI Field/Group CO WRR: SRIM: 18. DISTRIBUTION STATEMENT 19. SECURITY CLASS 21. NO. OF PAGES (THIS REPORT) 59 Available from the National Technical Information Service, Operations Division UNCLASSIFIED 20. SECURITY CLASS 22. PRICE 5285 Port Royal Road, Springfield, Virginia 22161 (THIS PAGn UNCLASSIFIED DIRECT SHEAR TESTS USED IN SOIL-GEOMEMBRANE INTERFACE FRICTION STUDIES by Richard A.
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