Utilization of unconfined compression strength --- Correction of stress reliese and disturbance in unconfined compression tests ---

对从日本各地收集的“未扰动试样”的有效应力状态进行了调查，目的是估计试样在经过取样、修整和准备进行无侧限压缩试验后的残余有效应力。从理论上推导了沿滑移圈动员的不排水强度。将沿滑圈的平均不排水强度与修正后的无侧限抗压强度进行比较，表明了无侧限抗压强度在软土基础稳定性分析中的适用性和局限性。对24例软粘土的实际破坏历史进行反分析，结果与无侧限抗压强度研究结果吻合较好。研究结论如下：1。试样扰动和应力释放对安全系数的影响在0.1以内。加载速率对现场安全系数的影响约为0.2。这表明施工方法和施工顺序的选择对软基稳定性的影响大于对试样扰动程度的影响。导出了在分析软粘土稳定性时，与试验得到的无侧限抗压强度相乘的修正系数作为塑性指数的函数。

Effective stress state of "undisturbed samples" collected from all over japan was investigated aiming at estimating the residual effective stress in the samples after experiencing sampling, trimming and being ready to be subjected to unconfined compression tests. The undrained strength mobilized along the slip circles was theoreticall derived. The average undrained strength along the slip circle being compared with the corrected unconfined compression strength indicated the appropriateness and the limitation of the usage of unconfined compression strength in the stability analysis of soft clay foundations. The backanalysis of 24 case histories of actual failure of soft clay showed a reasonable agreement with the results obtained from the investigation on unconfined compression strength. the conclusions are as follows:1. The effect of sample disturbance and stress release corresponds to within 0.1 in terms of the factor of safety.2. The effect of loading rate in the field corresponds to about 0.2 in terms of the factor of safety. This indicates that the selection of construction method and construction sequence is more influencial to the stability of soft foundations rather than the degree of sample disturbance is.3. The correction factor to be multiplied with the experimentally obtained unconfined compression strength in analysing the stability of soft clays is derived as a function of the plasticity index.