01-Direct-Shear

01-Direct-Shear - Florida International University Department of Civil and Environmental Engineering CEG 4011 L Geotechnical Engineering I

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Florida International University Department of Civil and Environmental Engineering CEG 4011 L Geotechnical Engineering I Laboratory Dr. Luis A. Prieto-Portar PhD, PE, SE. Lab Report #01 The Direct Shear Test (ASTM D-3080) Performed on xx March 2010 Team Members: Member Attendance Writing Assignment Completed
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0 1- The Direct Shear Test of a Soil 1) Introduction: The direct shear test is one of the oldest methods for testing the strength of soils. This test can be performed under different conditions. The soil sample is normally saturated before the test, but the sample can also be tested at the in-situ moisture content. The rate of strain can be varied to create to a test of undrained or drained conditions. This depends on whether the strain is applied slowly for water in the sample to prevent pore-water pressure buildup. Several specimens are tested, at varying confining stresses, to determine the shear strength parameters, the soil cohesion, and the angle of internal friction. Soil Shear strength describes the maximum strength of a soil where significant plastic deformation occurs due to an applied shear stress. The shear strength of a soil mostly depends on the rate at which the shearing occurs. The shear strength is one of the most important engineering properties of a soil because it is required whenever a structure is dependent on the soil’s shearing resistance. The shear strength is applied in engineering situations such as the design of foundations, retaining walls, and pavements in civil engineering applications. In the U.S., the standard defining how the test should be performed is ASTM D 3080. The test is performed on three or four soil specimens. A specimen is placed in a shear box having a cross-sectional area ( A ); a confining stress is applied vertically to the specimen. Testing proceeds by displacing the lower half of the split box and measuring the horizontal shear force ( T ) transmitted through the soil to the upper portion of the box. Testing continues by displacing the lower box horizontally until the sample fails (when the shear force increases to a maximum value and then decreases or remains constant). The load applied and the strain induced is recorded at frequent intervals to determine a stress-strain curve for the applied confining stress.
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The Direct Shear Testing Apparatus The specimens are tested at different confining stresses to determine the shear strength parameters: The shear stress (τ) on the shear plane may be calculated using: The shear strength S of a granular soil may be expressed by the Mohr-Coulomb equation: S = c + σ’ tan Ф Where σ’ = effective normal stress and Ф = angle of friction of soil.
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This note was uploaded on 09/07/2011 for the course CEG 4012 taught by Professor Staff during the Spring '10 term at FIU.

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01-Direct-Shear - Florida International University Department of Civil and Environmental Engineering CEG 4011 L Geotechnical Engineering I

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