مهندسی عمران شریف (Feb 2018)
INVESTIGATION OF THE EFFECT OF ANISOTROPY ON THE PORE WATER PRESSURE GENERATION OF LOOSE ANISOTROPIC CONSOLIDATED BABOLSAR SAND
Abstract
Direction of loading and magnitude of the intermediate principal stress have significant effect on the soil responses. In many of in-situ loadings, the direction of major principal stress does not coincide with the deposition direction of the soil. In addition, the magnitude of the intermediate principal stress should be exerted in the three-dimensional loading condition. A reliable assessment of the soil behavior and a good estimation of the soil parameters need to do tests in similar condition with in-situ. Therefore, the testing apparatus should be able to control the loading direction in various stress paths. Typical equipment used in the geotechnical laboratory does not have the ability to control the magnitude and direction of principal stresses. The cyclic hollow cylinder apparatus can control the magnitude and direction of the principal stresses and impose minimum non-uniformity on the specimens. The hollow cylinder apparatus used in this study is fully automated and can simultaneously control the five loading axe (i.e., the vertical load, torque, inner cell pressure, outer cell pressure and back pressure). The main specifications of the specimens are as follows: 100mm outside diameter, 60mm inner diameter, and 200mm height. Babolsar sand obtained from the South coast of the Caspian Sea was selected as test materials. The consolidation control options allow the various anisotropic consolidation statuses. Moreover, the load could be exerted as cyclic or monotonic. In this paper, the effects of major principal stress direction, induced shear stress during consolidation, and cyclic stress ratio on the pore water pressure were investigated. Therefore, the undrained cyclic hollow cylinder tests were performed on the loose anisotropic consolidated specimens. Results showed that, the major principal stress direction during consolidation has no significant effect on the excess pore water pressure generation. However, increases of cyclic stress ratio and shear stresses during consolidation would increase the residual excess pore water pressure. The empirical model proposed by Booker et al. and a dissipated energy-based model were used to predict residual excess pore water pressure of loose anisotropic consolidated Babolsar sand. The regressions analysis was led to modification of the model of Booker at al. and simplification of the dissipated energy-based model.
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