Multi-factor Restraint Mechanism Of Large-scale High Speed Long-runout Collapse-slide-flow Events In Emeishan Basalt

The distribution of Permian system top series Emeishan basalts layer in southwest china is rhombus shape that the direction of long diagonal line is north-south approximately. The covering overlay area is about 300,000 square kilometers, the basalt outcrop area is 37,538 square kilometers and the mean thickness can reach as thick as 705 meters. In addition to the high and steep slopes and other natural forms, the basalts often become the foundation rock mass of large-scale hydropower project. In recent years, a number of landslides in this lithology have caused disastrous consequences:On November 23,1965, a large high speed rockslide in the Lanni gully of Yunnan province buried five villages and caused 444 deaths; Another large rockslide with volume of 9000,000m3 burst forth in Touzhai of Yunnan province on September 23,1991.This rockslide caused 216 deaths. So conducting a study on the mechanism of the large scale high speed and long-range Emeishan basalts falling-sliding-flowing events has an important theoretical and academic value, and can provide the theoretical basis for the engineering investigation and design, construction and safety operation of the large-scale construction projects. This paper studied the Lanni gully landslide and Touzhai landslide. The main work in this paper is as follows:(1) Identified the tectonic reworking, structural dynamic environment, new tectonic activity, seismicity of the distribution of Permian system top series Emeishan basalts, studied the rock physical and mechanical properties of the basalts and analyzed the mechanical parameters. Studying the genesis of rock mass of Emeishan basalts, which are primordial, tectonic retrofit and supergene reform.(2) Accordance with time and space, the landslide was plotted out three stages:set-out, short-range and long-range. The sliding mass slide rapidly in the set-out stage, flew with a higher velocity in the short-range stage and turned into the debris flow in the long-rang stage.(3) Analyzed the mechanism of the Lanni gully and Touzhai landslide, described the evolution of the landslides, tectonic changes, supergene reform and weathering effect on the rock mass. Studied the mechanism of the high speed and long ran out of the landslides in the dynamics. And summarized it as energy aggregation in rocks and the difference between the release of residual strength, as well as air-cushion effect and ground effect.(4) Weathering,especially the chemical weathering, was an ignored factor to reduce the mechanical of the rock mass. Chemical weathering often took place in the structural planes, micro-fractures and inter-granular defects. Because these parts are the most weak sites of the rock.therefore, although the weathering degree of the landslide masses was at a common level, the impetus for the evolution of landslide is very obvious.