Study on landslide mechanism and mechanical property of clay due to large deformation

为研究滑坡的力学行为，进行了恒定偏应力作用下粘土的孔压加载试验。通过对土样的观测，得出了孔压变形的两个阈值。一种是屈服点，由孔隙率和平均有效应力空间与膨胀线的差异定义。另一个是土样变形较大，偏应力不能保持恒定的破裂点。经过一系列试验，屈服点位于临界状态线上。在破坏点，土样已经变得不均匀，并逐渐变形。土体因超固结而发生剪切膨胀，随水分运移而变形。它使土壤随着时间的推移而长时间变形。这被认为是滑坡缓慢失稳的原因之一。用Hashiguchi模型进行数值模拟，较好地反映了孔压加载试验的土体性状。它预测，最初过度固结的土壤将通过重复的孔压加载达到正常固结状态。在孔压作用下，在孔隙率和平均有效应力空间内得到了破坏点线。对这条故障点曲线进行了经验检验，但原因对故障点曲线的影响仍留待将来的研究对象研究。对重复孔压荷载作用下土体的稳定状态进行了数值研究。研究发现，这取决于平均有效应力的恢复。当回复率较大时，土体承受较大的孔压荷载。从应变水平的角度出发，对土体进行了环剪试验，研究了残馀状态下的抗剪角度。剪切抗剪角度变小，变形较大，激发了缓坡滑坡的发生。

Pore water pressure loading test on clay under constant deviator stress has been conducted to investigate the behavior of landslide. From the observation on soil specimen, two thresholds in pore water pressure for deformation were obtained. One was a yield point defined from the discrepancy from the swelling line in the void ratio and mean effective stress space. The other was a failure point where the soil specimen deforms largely and the deviator stress could not keep constant. A series of tests resulted in the yield points locating on the critical state line. At the failure point the soil specimen already got heterogeneous and deformed progressively. The soil dilated with shear due to overconsolidation and deformed with water migration. It caused the soil deformed with time for a long time. It was thought a reason for the slow failure of landslide. Numerical simulation with the Hashiguchi model well presented the soil behavior of pore water pressure loading test. It predicted the soil, which was initially overconsolidated, would get to the normally consolidated state by the repeats of pore water pressure loading. The failure point line was obtained in the void ratio and mean effective stress space for pore water pressure loading. This failure point line was empirically examined, but the effect of causes on the failure point line was still left to future stubjects. The steady state of soil after the repeats of pore water pressure loading was investigated numerically. It was found to depend on the recovery in mean effective stress. When the recovery was large, the soil would stand for larger pore water pressure loading. From the viewpoint of strain level, the ring shear test was conducted on the soil to investigate the angle for shear resistance at the residual state. The angle for shear resistance got lower with large deformation and it inspired the landslide for gentle slope.