Research on the Formation Mechanism of Shear Zone in the Neogene Mudstone Landslide

The shear zone is the main control factor for the translational and rotational landslides.Different geometric forms of landslides were selected to analyze the process of structural change and the mechanical mechanisms of the bedding-parallel shear zone in Neogen period mudstones. The results show that there are weak layers, with high clay content, in translational landslides and rotational-translational landslides, such as those with bedding-parallel shear zone, while rotational landslides are composed of homogeneous material. The bedding-parallel shear zone can be divided into two parts: the main shear zone and the secondary shear zone. The main shear zone has an S-C fabric, the C plane has a strong scratch, and the S plane develops in high plastic mudstones. The clay contents of the main shear zone in a bedding-parallel sliding zone are greater than 50%, while the absolute content of minerals mixed with illite and montmorillonite exceeds to 20%. Creep and rapid slip are the main forms of structural deformation of the shear zone. Creep deformation mainly develops in the sliding zone with high amounts of clay particles; the microstructural adjustment of the slip zone shows no crack expansion and the clay minerals are a viscous flow. Progressive creep induced by water pressure and gravity will cause the acceleration of the creep and rapid sliding. Rapid sliding deformation, which is due to repeated shear, occurs along the fixed shear fracture-surface.