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

本文试图利用落重法从冲击载荷试验结果中估计地面的变形和强度参数。分析中采用的应力-应变关系为屈服前的线性弹性，屈服后基于Mohr-Coulomb屈服准则的相关流动规律。利用Newmark β法，可以得到冲击加速度、速度和位移的时程。其次，我们使用Toyoura砂和风化砂进行了大量的失重测试。通过对监测到的加速度进行积分计算得到的估计位移值与高速摄像机观测到的位移值和最终的位移值几乎相同。拉扎传感器观测到的位移。基于数值分析的参数化研究表明，激波速度受材料参数的影响很小，位移对材料参数的反分析很有帮助。由于最终位移同时受变形模量和摩擦角φ的影响，很难分别反算变形模量和摩擦角。由于近地表围压较小，地表上的变形模量变得相当小。考虑到这些特性，变形模量由单独进行的静加载试验估算。采用变形模量对冲击载荷试验结果进行了较好的数值模拟。基于这种方法，可以从冲击载荷试验中反求摩擦角。当土质沉积物具有黏聚力和摩擦角两种强度分量时，通过改变落差高度重复冲击载荷试验，有可能对这两种强度分量分别进行反向分析。

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.