Study On Formation Conditions And Prevention Countermeasures Of Granite Weathering Landslide In Western Yunnan

With the rapid development of society,the degree of people taking for and exploiting the nature is more and more intense and a variety of constructions and human daily activities all have reformed the terrain of nature.Especially in mountainous areas,the stability of mountain slopes are more susceptible to the above situation and be destroyed and then producing a series of landslides and other problems.As one of geological disasters in recent years,landslide threaten human life and property safety seriously,so it attracts more and more attentions of people,and the weathered landslide problem of granite is particularly noteworthy.With a boundary Lancang River,large areas of its western in Yunnan distribute a large granite body with intense weathering.Therefore,this paper takes weathered granite landslides in western of Yunnan as research objects,on the bases of systematic field survey and collection of relevant information to classify weathered granite landslides as position of sliding surface,mechanical properties,the scale and the slope,joints and fissures and so on firstly,and then to count up and analyze the characteristics of the physical and mechanical parameters of the weathering layers.To take advantage of different angles and ways to analyze the characteristics and formation conditions of it and then to analyze the stability of the typical landslide case and to discuss appropriate countermeasures of the landslide.Through statistical analysis,Classification according to the position of sliding surface in the study area can be divided into four types,The position of the sliding surface on the boundary between the eluvial slope soil layer and fully weathered layer,the fully weathered layer and strong weathered layer,the strong weathered layer and medium weathered layer,the fourth type is the sliding surface passes through a plurality of weathering layers.The development of these landslides are associated with the situation of the toe of slope influenced by disturbance.The results showed that in the study area,the toe of slope is interfered to eluvial slope soil layer,landslide probability is 70%,when the toe of slope is interfered to fully weathered or strongly weathered layer,landslide probability is 73.3%or 88.9%respectively.What show that probability of occurrence of landslides is the maximum when the toe of slope is interfered to strongly weathered layer and in this case,if the landslides happen,the development of sliding surface at the interface between strong~medium will be the most,and rainfall in most of the landslide triggering factors.Through the analysis,the eluvial slope soil layer,fully weathered layer and strong weathered layer of granite,the weathering degree is very high,its structure is loose.When during the rainy season,because of the poor permeability of medium weathered granite,a relatively impermeable layer forms at the interface of strong~medium weathered layer,water can not infiltrate fast and freely,then a lot of water collect at the interface,and result in the formation of this interface to be slip surface is easier.The landslide in study area are mostly small,drawing and its overall slope is in the 30~50°range,The development of joints and fissures in the area has a certain influence on the development of the landslide.With weathering degree of granite is gradually weakened from the surface to the depths the shear strength index is gradually increased,moisture content,void ratio and compression factor is gradually decreased.The correlation between moisture content and shear strength index is good,the regression coefficient is more than 0.75,but the correlation between void ratio and shear strength is poor,the regression coefficient is lower than 0.6,it shows that water content has great influence on cohesion and internal friction angle,and the void ratio is smaller than that of the internal friction angle.The geological environment of the study area is very complicated,so there are too many slope topography here,granite has a lot of joints and fissures and is strongly weathered.Therefore,the scale of the weathered layer is relatively large,and its structure is loose,its stability is poor.The mineral composition of the clay minerals in the granite is mainly kaolinite,Kaolinite is easy to be softened by water,which leads to the decrease of the shear strength of soil.Above is the internal factors of landslide development in the study area.The main external factors of the landslide are abundant precipitation in the rainy season in the region,strong groundwater activity,and human disturbance of the slope,the destruction of its original stress balance is common,so it is easy to induce landslide.The results of the stability analysis and evaluation of landslide show that more landslides in the study area is in a stable state in the natural state,and the stability of the slope will rapidly decrease in the continuous heavy rain or earthquake emergency situation,and Landslide hazard will be subsequent.Therefore it need to strengthen prevention and control urgently and to take the corresponding control means according to the different characteristics of the landslide.