Residual Strength of Soils and Its Application in Landslide Stability Analysis

土体剪切变形的残余状态是土体在剪切过程中体积变化为零的状态，是剪切平面上的土体颗粒全部向剪切方向重新定向的状态。滑坡体表层土的强度受滑坡体长期滑动后的残余状态的支配，因此土的残余状态在滑坡体稳定性问题中起着重要的作用。因此，研究滑坡土在残余状态下的强度特性并将其应用于稳定性分析具有重要意义。本研究包括两个主要的实验室研究：1)滑坡土的强度特性和2)粘土矿物对土壤强度的影响。将调查结果应用于滑坡稳定性分析。从四国不同的滑坡地点获得了代表不同地质条件的土壤样品进行实验室试验。采用直接剪切和简单剪切两种剪切原理对其强度特性进行了研究，并采用x射线衍射分析对其矿物特性进行了研究。调查结果总结如下：首先，发现直剪式环剪仪测得的强度与单剪式环剪仪测得的强度在许多方面存在差异。这是因为直接剪切型装置具有预先规定的剪切面，这可能导致细颗粒含量高的土壤的残余强度较低，粗颗粒含量高的土壤的残余强度较高。相比之下，简单的剪切型仪器得到的结果相对准确，因为土样在整个深度最弱的平面上被剪切。二是四国滑坡土抗剪强度很低，主要原因是滑坡体表层土中含有大量膨胀粘土矿物。x射线衍射试验表明，变质岩型滑坡土中膨胀绿泥石含量较高，对降低土体强度有重要作用。(3)稳定性分析结果表明，滑坡体表层土体，特别是在发生大型滑坡的情况下，已达到残留状态，这一点通过对部分活动滑坡的反分析得到了证实。最后，认为将实验室确定的强度参数应用于滑坡稳定性分析在许多方面比进行反分析更为可行。少

Residual state of a soil in shear deformation is a state when change in soil volume during the shear is zero, and it is attained when all the soil particles on the shear planes get reoriented toward the shear direction. Residual state of soil plays a significant role in landslide stability problems because strength of slip surface soil is governed by the residual conditions after having slid for a long duration. It is therefore important to investigate the strength behaviors of landslide soils at their residual states and to employ them in the stability analysis. This research includes two major lab investigations: 1) strength properties of landslide soils and 2) influence of clay minerals on soil strength. The investigation results were then employed in carrying out stability analysis of the landslides. Several soil samples were obtained from various landslide sites in Shikoku representing various geological conditions for the lab tests. The strength properties were investigated by ri … More ng shear apparatuses based on direct as well as simple shear principles, and the mineral properties were investigated by x-ray diffraction analysis. The investigation results are summarized as follows.First, the strength measured by direct shear type ring shear apparatus was found to differ in many aspects from that by the simple shear type. It is because the direct shear type apparatus possesses a pre-specified plane of shear, which may result in a lower residual strength of a soil with higher content of finer particles and a higher strength of a soil with higher percentage of coarser particles. In contrast, a simple shear type apparatus gives comparatively accurate results because the soil sample gets sheared though the weakest plane in the entire depth of specimen. Second, the shear strength of landslide soils in Shikoku was investigated to be very low, which is mainly due to a significant amount of expansive clay minerals in the slip surface soil. The x-ray diffraction tests revealed that the amount of expansive chlorite in landslide soils originated from metamorphic rocks in particular is high, which plays a significant role in lowering the soil strength. Third, the stability analyses results showed that the slip surface soils, especially in case of large-scale landslides have reached the residual state, which was confirmed by back analysis of some active landslides. Finally, it was considered that application of lab-determined strength parameters in stability analysis for the landslides is more feasible in many aspects than carrying out back analysis. Less