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    Unit-III Bearing Capacity

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    Putin
    This document discusses bearing capacity of soils and different methods to determine ultimate bearing capacity of foundations. It describes modes of shear failure in soil, theories proposed by Terzaghi, Meyerhof, Skempton and Hansen to calculate bearing capacity. It also discusses plate load tests which are field tests done to determine bearing capacity and settlement characteristics of soil. The document provides formulas to calculate bearing capacity of footings on slopes and worked examples to determine ultimate load for different footing configurations based on soil properties.

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    Unit-III Bearing Capacity

    Uploaded by

    Putin
    53 views30 pages
    This document discusses bearing capacity of soils and different methods to determine ultimate bearing capacity of foundations. It describes modes of shear failure in soil, theories proposed by Terzaghi, Meyerhof, Skempton and Hansen to calculate bearing capacity. It also discusses plate load tests which are field tests done to determine bearing capacity and settlement characteristics of soil. The document provides formulas to calculate bearing capacity of footings on slopes and worked examples to determine ultimate load for different footing configurations based on soil properties.

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    This document discusses bearing capacity of soils and different methods to determine ultimate bearing capacity of foundations. It describes modes of shear failure in soil, theories proposed by Terzaghi, Meyerhof, Skempton and Hansen to calculate bearing capacity. It also discusses plate load tests which are field tests done to determine bearing capacity and settlement characteristics of soil. The document provides formulas to calculate bearing capacity of footings on slopes and worked examples to determine ultimate load for different footing configurations based on soil properties.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    53 views30 pages

    Unit-III Bearing Capacity

    Uploaded by

    Putin
    This document discusses bearing capacity of soils and different methods to determine ultimate bearing capacity of foundations. It describes modes of shear failure in soil, theories proposed by Terzaghi, Meyerhof, Skempton and Hansen to calculate bearing capacity. It also discusses plate load tests which are field tests done to determine bearing capacity and settlement characteristics of soil. The document provides formulas to calculate bearing capacity of footings on slopes and worked examples to determine ultimate load for different footing configurations based on soil properties.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 30

    BEARING CAPACITY OF SOILS

    Basic Definitions:
    Modes of shear failure

    Depending on the stiffness of foundation soil and depth of foundation, the following are the
    modes of shear failure experienced by the foundation soil.

    1. General shear failure


    2. Local shear failure
    3. Punching shear failure
    Limitations

    Determination of Ultimate Bearing Capacity:


    Terzaghi’s Analysis
    Meyerhof’s Analysis
    Skempton’s Analysis
    Hansen’s Analysis
    J. Brinch Hansen (1970) proposed what is referred to as general bearing capacity
    equation.
    Bearing Capacity of Footings on Slopes
    1. It is a field test for the determination of bearing capacity and settlement characteristics of
    ground in field at the foundation level.
    2. The test involves preparing a test pit up to the desired foundation level.
    3. A rigid steel plate, round or square in shape, 300 mm to 750 mm in size, 25 mm thick acts as
    model footing.
    4. Dial gauges, at least 3, of required accuracy (0.002 mm) are placed on plate on plate at
    corners to measure the vertical deflection.
    5. Loading is provided either as gravity loading or as reaction loading. For smaller loads
    gravity loading is acceptable where sand bags apply the load.
    6. In reaction loading, a reaction truss or beam is anchored to the ground. A hydraulic jack
    applies the reaction load.
    7. At every applied load, the plate settles gradually. The dial gauge readings are recorded after
    the settlement reduces to least count of gauge (0.002mm) & average settlement of 2 or more
    gauges is recorded.
    8. Load Vs settlement graph is plotted as shown. Load (P) is plotted on the horizontal scale and
    settlement (∆) is plotted on the vertical scale.
    9. Red curve indicates the general shear failure & the blue one indicates the local or punching
    shear failure.
    10. The maximum load at which the shear failure occurs gives the ultimate bearing capacity of
    soil.
    Advantages of Plate Load Test are
    1. It provides the allowable bearing pressure at the location considering both shear failure and
    settlement.
    2. Being a field test, there is no requirement of extracting soil samples.
    3. The loading techniques and other arrangements for field testing are identical to the actual
    conditions in the field.

    Disadvantages of Plate Load Test are


    1. The test results reflect the behaviour of soil below the plate (for a distance of ~2Bp), not that
    of actual footing which is generally very large.
    2. It is essentially a short duration test. Hence, it does not reflect the long term consolidation
    settlement of clayey soil.
    3. Size effect is pronounced in granular soil. Correction for size effect is essential in such soils.

    1.
    What is the ultimate bearing capacity of a square footing resting on the surface of a saturated clay of
    unconfined compressive strength of 100 kN/m2.

    2.
    Determine the ultimate bearing capacity of a square footing of 1.5 m size, at a depth of 1.5 m, in a pure
    clay with an unconfined strength of 150 kN/m2. ɸ = 0° and γ = 17 kN/m3.

    ..
    3.
    A square footing, 1.8 m × 1.8 m, is placed over loose sand of density 16 kN/m3 and at a depth of 0.8m.
    The angle of shearing resistance is 30°. Nc = 30.14, Nq = 18.4, and Nγ = 15.1. Determine the total load
    that can be carried by the footing.

    4.
    The footing of a column is 2.25 m square and is founded at a depth of 1 m on a cohesive soil of unit
    weight 17.5 kN/m3. What is the safe load for this footing if cohesion = 30 kN/m2; angle of internal
    friction is zero and factor of safety is 3. Terzaghi’s factors for φ = 0° are Nc = 5.7, Nq = 1, and Nγ = 0.
    5.
    A circular footing is resting on a stiff saturated clay with ucc (qu) = 250 kN/m2. The depth of
    foundation is 2 m. Determine the diameter of the footing if the column load is 600 kN. Assume a factor
    of safety as 2.5. The bulk unit weight of soil is 20 kN/m3.

    6.
    7.

    8.

    9.
    10.

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