地震后效应平推式滑坡形成演化特征

平推式滑坡在四川盆地红层地区广泛分布,常发育在岩层倾角小于10°的近水平岩层斜坡区,大量案例调查中发现,部分平推式滑坡的演化过程表现出显著的地震后效应.通过对2个典型案例的分析总结认为,除了5种必备的平推式滑坡形成条件外,地震后效应下平推式滑坡发育特征还具备一些特殊性:多发育在低山地貌区高陡斜坡地震放大效应较为强烈的部位;岩性组合多为中厚层~厚层砂岩夹薄层泥岩;坡体内部均发育一组规模较大且走向与坡面近于平行的陡倾结构面;强震后形成与坡面近于平行的张拉裂缝仍具有储水条件.同时,此类平推式滑坡震前都存在轻微的变形迹象,其演化过程受到地震强烈干预,地震在坡体内部产生垂直竖向张拉裂缝,并对层间薄层软岩产生强烈剪切作用,极大地加快其泥化进程,在震后几年内促成斜坡具备暴雨作用下的启动条件.

Formation and Evolution Process Analysis of Earthquake after Effect Sub-Horizontal Translational Landslides

Sub-horizontal translational landslides are widely distributed in red beds in Sichuan basin,and develop in the slope area close to the horizontal stratum where the dip angles of layers are less than 10°.During landslide cases investigation,remarkable earthquake after effect had been found in evolution process in many cases.By analysis and summary of some sub-horizontal translational landslides of this kind,it has been found that,except some necessary conditions,such kind of landslides show more special develop characteristics:they always happen in high and steep slope in low mountain landform,where seismic amplification effect is strong;the lithologic assemblages are mostly middle-thick^thick sandstone with interbed thin layer mudstone;one group large scale steep structural planes with strike almost parallel to slope surface exist in slope;tension cracks formed in earthquake still can store water.Such kind of sub-horizontal translational landslides show slight deformation before the earthquake.The evolution process is intervened by earthquake intensely.Earthquake causes vertical tensile cracks in the slopes and also produces shearing action on the inter-layer thin soft rock.This will accelerate argillization and become the culprit for the landslides in heavy rains in the several years immediately after the earthquake.