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

为明确浅层滑坡的发生机制，研究了花岗岩、火成岩和沉积岩的风化剖面及其形成机制，以及与滑坡发生的关系。主要研究结果如下：1)花岗岩的主要风化过程为微片状风化和球状风化。由于卸荷作用而形成微片状的花岗质岩石，在几米深处被密集地松动，前缘轮廓清晰。这个松动带的厚度增加，最后滑动。球化风化主要通过微裂解和化学浸出进行。中等风化的花岗岩是在地质时期形成的，当人工切割或自然剥蚀使其暴露在外时，会迅速松动到几米深；雨水优先通过这个松散的区域渗入。这种松散物质的饱和、孔隙压力的产生以及因吸力损失而导致的粘聚力的降低成为滑坡发生的基本因素。2)火成岩从未焊接到强焊接的凝灰岩不等。未焊接的褐煤经风化后有一个明确的锋面，在新鲜的可渗透凝灰岩和上覆的渗透性较差的风化凝灰岩之间起着毛细屏障的作用。雨水的渗入增加了风化凝灰岩的重量，并因吸力消失而降低了凝灰岩的粘聚力。这些都是造成未焊无烟煤滑坡的基本因素。(3)气相结晶烟灰岩在新鲜或水合不透水凝灰岩与上覆的强风化透水凝灰岩之间有明确的风化锋。前缘风化凝灰岩在剧烈的化学淋滤作用下与坡面平行剥落。这种风化凝灰岩的饱和、孔隙压力的产生以及吸力的丧失导致粘聚力的降低成为滑坡发生的基本因素。4)沉积岩一般具有氧化和溶蚀前缘，这是岩石与入渗水的连续反应形成的。这种风化过程和由此产生的力学性质变化是沉积岩常见滑坡类型的主要原因，这些滑坡的滑面沿氧化锋或在氧化锋以下。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