Study on the generation mechanism of landslides in terms of the weathering zones of rocks

为了阐明浅层滑坡的形成机制，本文研究了花岗岩、熔结凝灰岩和沉积岩的风化剖面、形成机制及其与滑坡形成的关系。主要研究结果如下：1）花岗岩的风化作用主要表现为微片状风化和球状风化。卸荷作用形成的微岩席状花岗质岩石在几米深的深度内强烈松动，并有一个轮廓分明的前缘。这个松动的区域增加了它的厚度，最后滑动。球状风化作用是通过微破裂和化学淋滤进行的。地质时代形成的中等风化花岗岩，经人工切割或自然剥蚀暴露后，迅速松动至几米深，雨水优先通过这一松动带入渗。饱和度、孔隙压力的产生和吸力损失引起的粘聚力的降低是影响孔隙水动力特性的主要因素 ...更多信息 这些松散的物质的离子化成为滑坡产生的基本因素。2）凝灰岩从未焊接到强焊接凝灰岩。未焊接的熔结凝灰岩被风化，形成一个轮廓分明的前缘，作为新鲜可渗透凝灰岩和上覆的渗透性较差的风化凝灰岩之间的毛细屏障。雨水入渗增加了风化凝灰岩的重量，降低了凝聚力，因为吸力消失。3）气相结晶熔结凝灰岩在新鲜或水化不透水凝灰岩与上覆强风化透水凝灰岩之间具有明显的风化前缘。前缘的风化凝灰岩在强烈的化学淋滤作用下，沿坡面剥离。风化凝灰岩的饱和、孔隙压力的产生以及吸力丧失导致的黏聚力的降低是滑坡形成的基本因素。4）沉积岩一般具有氧化和溶解前缘，这是岩石与渗入水的连续反应所造成的。这种风化过程和由此产生的力学性质的变化是常见的沉积岩滑坡类型的主要原因，这些沉积岩具有沿着或低于氧化前缘的滑动面。少

To clarify the generation mechanism of shallow landslides, I studied the weathering profiles, their formative mechanisms, and the relationships between the profiles and landslide generation for granitic rocks, ignimbrite, and sedimentary rocks. The major results are as followings :1) As major weathering processes of granitic rocks, micro-sheeting and spheroidal weathering were recognized. Granitic rocks, which are micro-sheeted by unloading, are loosened intensively to a depth of a few meters with a well defined front. This loosened zone increases its thickness and finally slides. Spheroical weathering proceeds by micro-cracking and chemical leaching. Moderately weathered granite, which are made through geological time, is loosened rapidly to a depth of a few meters when it is exposed by artificial cutting or natural denudation ; rainwater infiltrates through this loosened zone preferentially. The saturation, generation of pore pressure, and the decrease of cohesion by the loss of suct … More ion of this loosened material become the basic factors for the generation of landslide.2) Ignimbrite varies from unwelded to strongly welded tuff. Unwelded ignimbrite is weathered to have a well-defined front, which acts as a capillary barrier between the fresh permeable tuff and the overlying less permeable weathered tuff. Infiltrating rainwater increases the weight of the weathered tuff and decreases its cohesion because of suction disappearance. These are the basic factors of the landslide of unwelded ignimbrite.3) Vapor-phase crystallized ignimbrite has a well defined weathering front between the fresh or hydrated impermeable tuff and the overlying strongly weathered, permeable tuff. The weathered tuff on the front is exfoliated parallel to slope surface by the intensive chmical leaching. The saturation, generation of pore pressure, and the decrease of cohesion by the loss of suction of this weathered tuff become the basic factors for the generation of landslide.4) Sedimentary rocks generally have oxidation and dissolution fronts, which are made by the sequential reaction between the rocks and the infiltrating water. This weathering process and the resultant change of mechanical properties are the major causes of the common type of landslide of sedimentary rocks, which have slip surfaces along or below the oxidation front. Less