INFLUENCE OF TECTONIC STRESS FIELD ON FORMATION AND EVOLUTION OF SUB-HORIZONTAL TRANSLATIONAL LANDSLIDES IN SICHUAN BASIN

The existence of tensional structural planes in sub-horizontal rock slope is very important for the formation and evolution of the sub-horizontal translational landslides. After the occurrence of sub-horizontal translational landslides, the water-filled tensile structural planes can be widened to form a tension trough. We find that the distribution directions of the tension troughs of medium size, medium thickness or above sub-horizontal translational landslidesare almost perpendicular to the tectonic belt at the basin edge. On the bases of others' research results and the analysis of river system of Sichuan Basin inversion of neotectonic stress field, we find that the tension trough strike directionsare close to the principle stress direction of neotectonic stress field. We believe that the formation and development of these sub-horizontal translational landslides are closely related to the stress field of neotectonics. The influences of tectonic stress field on the formation and evolution of sub-horizontal translational landslides are mainly manifested in the transformation of rock mass structure, the control of permeability of structural plane and the influence of hydrological condition of slope. The change of principal stress direction makes the structural plane with compressive(shear) property close to parallel transform into tensile property, resulting in tensile crack extension and expansion of scale. The structural planes are connected with each other along the strike and crosses the layer along the dip. The permeability of the structural plane with the three dimensional stress state is improved remarkably. The permeability, scale, connectivity and opening of the structural plane are simultaneously expanded. The characteristics of vertical and horizontal migration are one of the main factors for the occurrence of sub-horizontal translational landslides and provide the formation and evolution conditions for the occurrence of landslide. Due to the existence of cross-layer tensile structural planes, groundwater is able to migrate vertically to the depth of the slope and have physical and chemical interactions with the deep soft layers, thus providing conditions for the formation of larger scale and thickness of sub-horizontal translational landslides.