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    Assnmt 11

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    Assnmt 11

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    dtryu

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    Assnmt11

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    62 views2 pages

    Assnmt 11

    Uploaded by

    RK MEHTA
    dtryu

    Copyright:

    © All Rights Reserved
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    of 2

    INDIAN INSTITUTE OF TECHNOLOGY MADRAS, CHENNAI

    Department of Civil Engineering


    CE 3350 Geotechnical Engineering
    Assignment # 1: Shear Strength of Soils
    Note: Make suitable assumptions wherever necessary.
    1. A layer of sand extends from ground level to a depth of 9 m and overlies a layer of clay, of very
    low permeability, 6 m thick. The water table is 6 m below the surface of the sand. The saturated
    unit weight of the sand is 19 kN/m3 and that of the clay 20 kN/m3 ; the unit weight of the sand
    above the water table is 16 kN/m3. Over a short period of time the water table rises by 3 m, and
    is expected to remain permanently at this new level. Determine the effective vertical stress at
    depths of 8 and 12 m below the ground level (a) immediately after the rise of the water table,
    and (b) several years after the rise of the water table.
    2. Three uniformly distributed loads of 100 kPa each are applied to 10 10 m square areas on the
    soil profile shown in Fig. 1. Undisturbed samples of the clay were taken prior to construction,
    and consolidation tests indicated that the average preconsolidation stress is about 110 kPa, the
    average compression index is 0.50, and the average recompression index is 0.02. Estimate the
    total consolidation settlement for the clay layer only under the center of the middle loaded area.

    Fig. 1
    3. Explain (a) Peak and residual shear strength of clay soils, (b) Peak and ultimate angle of shearing
    resistance of sands, (c) Angle of repose, (d) Critical void ratio of sand, (e) Liquefaction
    phenomenon in sands, and (f) Significance of the pore pressure coefficients.
    4. A triaxial test was conducted on a granular soil under CD condition. The sample failed when the
    effective minor principal stress was 150 kN/m2 and the principal effective stress ratio was 4.2.
    Determine ' and the deviator stress at failure analytically. Draw the Mohr stress circle and the
    Mohr strength envelope. The same specimen was tested under CU condition with the total cell
    pressure held constant at 150 kN/m2. The porewater pressure at failure was 80 kN/m2.
    Determine, both analytically and graphically, the major principal stress (effective) at failure, the
    total deviator stress at failure and u . If the same specimen is tested in the CU test but at a cell
    pressure of 250 kN/m2, what will be the pore pressure at failure? (a) CD test ' = 38; ' 1 = 360
    1.1

    kN/m2; ' d = 480 kN/m2 (b) CU test '1 = 294 kN/m2; ' d = 224 kN/m2 ; u = 25.3and (c) u f =
    180 kN/m2.
    5. Direct shear (shear box) tests were conducted on a moist, fine sand with D 50 = 0.2 mm. The fines
    content (particles less than 0.075 mm) is less than 1%. The results of the tests are:

    (a) Plot the vertical load versus the horizontal load. (b) Do the data align with a straight line
    through the origin? If not, explain why it is not so, assuming that the data are correct. (c)
    Recommend the friction angle to be used for the foundation design of a 10-story-high building.
    Explain your recommendation.
    6. The results of three consolidated-undrained (CU) triaxial tests on identical specimens of a
    particular soil are:

    Determine c' and '. What would be the expected pore pressure at failure for 3 = 100 kPa?
    7. A normally consolidated clay soil has = 20 and ' = 28. If a consolidated-undrained test is
    cond u cted on th is clay with an all arou nd p ressure of 3 = 148.35 kN/m2, what would be the
    magnitude of the major principal stress, 1 , and the pore water pressure, u, at failure?
    8. A 15 m thick normally consolidated (NC) clay layer is shown in Fig. 2. The plasticity index of the
    clay is 18. Estimate the undrained cohesion as would be determined from a vane shear test at a
    depth of 8 m below the ground surface. Use the equation:

    Fig. 2
    1.2

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