| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 94 === A large direct shear test device with double shear planes was first developed in Feng-Chia University in 2005. It was proved that there is a tendency for the obtained results to be better than those obtained from using traditional direct shear test device with single shear plane. However, it was found in the developing process that the normal forces, acting on both the upper and the lower shear planes by applying downward vertical force only from the top side of the specimen, actually cannot transmit totally from the upper shear plane to the lower one. To allow the normal forces acting on both the upper and lower shear planes to be equal, a new system for applying forces was redesigned. Then, the new test device accompany with a traditional large direct shear test device were utilized to perform direct shear tests for four different types of sands such that special functions and features for the newly developed device can be studied.
Results from this thesis reveal that (1) the new device with a system that can apply forces simultaneously from both top and bottom sides of a specimen to its upper and lower shear planes has the tendency to provide reasonable test results; (2) as compared with the single-shear-plane direct shear test device, the double-shear-plane one can provide better test results; (3) it was indicated by the test results from different types of sands that when shear velocities are in the range of slow, the resulting shear strength is increased with the increase in shear velocity, however, when shear velocities are increased from the range of slow to that of fast, the resulting shear strength is decreased with the increase in shear velocity; (4) a smaller increment of the coefficient of lateral earth pressure is obtained for the middle shear box as compared with those obtained from the upper and lower ones; such results directly indicate the complexity of stress distributions in the direct shear test specimen.
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