Development of In-situ Test for Estimating Deformation and Strength Parameters from Shock Loading

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This study tries to estimate the deformation and strength parameters of ground from the results of shock loading test using drop of weight. The stress-strain relationship employed in the analysis, is the linear elasticity before yielding, and the associated flow rule based on Mohr-Coulomb yield criterion after yielding. By using Newmark β method, we can get the time history of shock acceleration, velocity and displacement. Secondly we performed a lot of weight drop tests using Toyoura sand and weathered sand. The estimated displacement which is calculated by integrating the monitored acceleration, gives almost the same value as the one observed by high speed video camera and the final.displacement observed by lazar sensor. The parametric study based on numerical analysis shows that the shock velocity is little affected by the material parameters, and that the displacement is useful for back analysis of material parameters. Since the final displacement is affected both by deformation modulus and friction angle φ, it is difficult to back calculate the deformation modulus and friction angle separately. Since the confining pressure is small near ground surface, the deformation modulus becomes considerably small on the ground surface. Considering these properties, the deformation modulus is estimated by the static loading test separately performed. By using the deformation modulus, the results of shock loading test is fairly well simulated by the numerical analysis. Based on this method, it is possible to back calculate the friction angle from the shock loading test. When the soil deposit has two strength components of cohesion and friction angle, there is the possibility that we can back analyze these two strength components separately by repeating the shock loading test with changing the drop height.