Development of assessment method of flow phenomena based on undrained shear and grain crushing characteristics measurement

近年来滑坡灾害中造成人员伤亡最多的流动现象，是由于滑面呈液态状态，抗剪能力严重降低造成的。Sassa等研究表明，这些现象是由土体颗粒在剪切区破碎和体积收缩引发的“滑面液化”引起的。利用Sassa开发的地震诱发滑坡的岩土滑坡模拟器，以坡角、地质、岩土性质、滑面深度、饱和度等参数为基础，对“滑面液化潜力”的评价新方法进行了研究，以建立地震诱发滑坡的流动现象扩展和程度评价方法。在2002会计年度，取得了以下成果：(1)改进了用于研究土壤样品中谷物破碎特性的便携式“碎粒仪”。地震诱发滑坡岩土工程模拟器样箱内土样形成的透镜状多剪切带的详细微观结构。(2)利用地震诱发滑坡的岩土滑坡模拟器，应用三维地震加速度记录对1995年小古根-南部地震诱发的二川滑坡场地的土样进行分析，得到了潜在滑动面附近土层的剪切行为特征。在一系列试验中得到如下结果：(a)在主震后产生超孔隙压力，但位移很小的材料发生了无滑动表面液化；(2)在主震后刚发生位移的土层中，由于颗粒破碎和超孔压的产生会引起滑面液化，因此超孔压的产生会引发快速-长跳动。(3)建立了1995年孝古肯-南部地震引发的宝川高尔夫球场滑坡土壤循环加载过程中超孔压产生的新方法。基于排水剪切试验中颗粒破碎后的体积变化和一维压缩系数。该方法表明，排水（不排水）恒应力试验数据可以评估全饱和不排水条件下的超孔隙压力生成。这也意味着(1)中描述的装置即使在原位也能进行滑动表面液化势的测量

Flow phenomena which brought about most of the casualties in landslide disaster of these years, are caused by liquid-like state of sliding surface and serious reduction of shear resistance. Sassa et al. showed these phenomena are caused by "sliding surface liquefaction" triggered by soil grain crushing in the shear zone and volumetric shrink. This study is focused on the examination of new evaluation method of "sliding surface liquefaction potential" in order to establish methodology of assessment of extension and degree of flow phenomena, with use of geotechnical landslide simulator for earthquake-induced landslides which Sassa developed, based on the parameters of slope angle, geology, geotechnical property, depth of sliding surface, saturation degree, etc.In the fiscal year 2002 following achievements were obtained(1) Portable "Grain Crushing Apparatus" which is designed for investigate grain crushing characteristics of soil samples, was improved. Detail microstructure of lens-like … More shear zones of soil samples formed in the, sampel box of the Geotechnical Landslide Simulator for Earthquake-triggered Landslides. Rather interesting fact that the grain crushing much proceeded in the upper and lower boundaries of the shear zone(2) Shear behaviour characteristics of the soil layer in the vicinity of the potential sliding surface with use of the Geotechnical Landslide Simulator for Earthquake-triggered Landslides by applying three dimensional earthquake acceleration record on the soil samples taken from the Nikawa Landslide site which was triggered by the 1995 Hyogoken-Nambu Earthquake. In the test series, following results were obtained (a) no-sliding surface liquefaction took place in the material that which showed very little displacement although generated excess pore pressure just after the main shock ; (b) rapid-long runout can be triggered in the soil layers that which showed displacement just after mainshock due to excess pore pressure generation, because grain crushing and excess pore pressure generation causes sliding surface liquefaction(3) A new method was developed to assess excess pore pressure generation during cyclic loading in the soils taken from 1995 Takarazuka-Golf Course Landslide which was triggered by the Hyogoken-Nambu Earthquake, based on volume change due to grain crushing in the drained shear test and one-dimensional coefficient of compressibility. This method shows that drained (not undrained) constant stress test data can assess the excess pore pressure generation in the fully-saturated and undrained condition. Also it implies that the apparatus described in (1) enables sliding surface liquefaction potential measurement even in situ Less