一类含裂隙岩质边坡的滑动弱化逐步破坏机理

MECHANISM OF PROGRESSIVE FAILURE OFA KIND OF FAULTED ROCK SLOPE DUE TO SLIP-WEAKENING

含裂隙的岩土材料在剪切作用下,随着剪应变的增加,裂纹端部一定区域内的强度会表现出滑动弱化的现象。岩土材料这种性质的变化不同于粘性土结构性破坏,也不同于剪胀。在一定的载荷作用下,坡体内裂隙端部的滑动弱化使坡体内的应力重新分配,从而使得应力集中加剧,裂隙尖端进一步扩展,造成岩体结构性的破坏,乃至整个滑面的贯通直至发生滑坡。因此,滑动弱化是一类含裂隙岩质边坡滑坡的机理。

Slip-weakening is one of the characteristics of faulted rock material under a certain loading condition. Non-uniform rock structure may exist in the vicinity of the slip surface in a rock slope. Some portions of the slip surface may be mutually penetrated but the others may not. For the latter case, the cracks or the fault surfaces will undergo shear deformation before a successive surface forms under certain loadings. As the slipped portion advances, slip-weakening occurs over a distance behind the crack tip. In the weakening zone, the shear strength will decrease from its peak value to residual friction level. The stress will redistribute along the crack surface. Therefore the changed local stress concentration will cause the crack to extend and the ratio of penetration of the slip surface will increase. From the large-scale view of the whole slip surface, the shear strength will decrease due to the damage of the interior rock structure, and the faulted rock behaves as a softening material. Such a kind of mechanism happens in many practical landslides subjected to strong earthquakes. It should be noted that this mechanism is different from that of the breakage of structural clay, in which the geological material is regarded as a medium containing structural lumps and structural bands. The strain-softening property exhibited in the structural clay is the result of structure damage (i.e. the disintegration of the soil structure). The softening behavior of faulted rock should be regarded as a comprehensive result of the whole complicated process including slip-weakening, stress redistribution, crack tip extension and the penetration of slip surfaces. This process is accompanied by progressive failure and abrupt structural damage. The size of slip-weakening zone is related to the undergoing strain. Therefore, once a landslide is initiated (local or integrated), the effect of slip-weakening will exist in a certain length behind the crack tips until the formation of the whole slip surface even without dynamic loading.