Geomechanics Lab Report

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| 3/29/2011 | | | | CIVL462 – Laboratory ReportGeomechanics 2 | | | | | | Justin Hill 3463527 Group 2 | CIVL462 – Laboratory Report Geomechanics 2 Direct Shear Test Introduction The shear strength is one of the most important engineering properties of a soil as it is required whenever a structure is built. Structures require foundations in the ground and solid foundations are dependent on a soil’s shearing resistance. Moreover, the shear strength is needed for engineering situations such as calculating the pressure exerted by a soil on a retaining wall, sheet piling, determining the stability of slopes or cuts and determining the bearing capacity for foundations. In this Laboratory, a direct shear device will be used to determine the shear strength of a cohesionless soil. In this case, dry river sand was used. The shear strength is directly related to the angle of internal friction. From plotting shear stress versus horizontal displacement for different vertical confining stresses, the maximum shear stress for each can be obtained. After several trials, a plot of maximum shear stress versus vertical (normal) confining stress is produced. A straight line approximation for the Mohr-Coulomb failure envelope can then be drawn. The friction angle is thus calculated from the slope of the failure envelope. As with any experiment, the more tests taken for different normal stresses, the more accurate the Mohr-Coulomb failure envelope will be. Experimental Procedure * Weigh the initial mass of soil and record it. * Measure the height, width and length of the shear box and record it. * Place the sample in the shear box, leveling off the top and then weigh the sample again to compute the mass of soil used. * Assemble the direct shear device, initializing the three gauges to zero. (Horizontal dial reading,

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