Analysis on the Deformation of typical landslides at Yunyang County in the Three Gorges Reservoir region based on monitoring data

The study aims to analyze the correlation between landslides and rainfall by collecting of landslide monitoring data and annual rainfall data at Yunyang in 2004.Taking Yangliubang landslide and Liekoushan landslide as examples,the study further analyzed the correlation between deep displacement,ground deformation and rainfall.Located in the western part of Three Gorges Reservoir, Yunyang is a county with many geological hazards.As it enters into the rainy season in May,both the frequency and the amount of rainfall will increase.There were 9 heavy storms last year,each of them had resulted in the abnormality of landslides,especially the storms in June and August which caused huge and noticeable ground deformation.The months in which deformation appears most frequently correspond with those of storms.With the growing amount of rain,the number of landslides increases.It is found that when the amount of rainfall is greater than 10mm,there will be cracks in landslides,malposition of platforms and deep displacement;when the amount of rainfall is greater than 50mm,there will be an increase in the abnormal condition of landslides and even occurs mudflow.It is also found that after rainstorm,gently-sloped strata easily produce in small openings extremely great water pressure which results in the abnormality of landslides.Meanwhile,because there is a muddy and softening tendency happening in shale and mudstone when meeting water,slide of strata is produced.After heavy rainstorm,a large amount of surface water permeate the ground,and the sudden increase in the amount of ground water causes the corresponding increase in the amount of water in loose accumulative rock and decrease in the intensity of mudstones.Thus deformation occurs in some areas.However,as the result of the influence of various factors,such as geographical conditions,there is no significant correlation between the scale of landslides and the amount of rain.According to macrogeological survey and previous drilling data,Liekoushan and Yangliupang landslides,under which are layers of clastic sandstone and mudstone,are covered with over 15m thick layers of powdery clay and gravel.After the heavy rainfall,rain water permeates the layer of mudstone and clay through cracks and causes it to become softened.As the result of this,the layer will lose its stability.