Study On Mechanism And Predicting Method Of Landslide Hazard Triggered By Extremely Heavy Rainfall

For meeting the service needs of predicting and warning landslides triggered by extremely heavy rainfall, based on mechanism of landslide induced by torrential rainstorm and its predicting theory, by monitoring and experiment in eight trial grounds, the impacts of rainfall on underground water table, pore water pressure, soil stress and landslides stability are studied. The influence of vegetation coverage on landslide is discussed. With historic data, risk division is researched and the temporal-spatial distribution features of landslide induced by heavy rainfall are analyzed. Combining trail data and statistics method, the precipitation values used to predicting and warning landslides are given. Operational forecasting and warning system of landslide disasters triggered by heavy rainfall on Web-GIS is developed, which has been tested in conventional operation.(1) The temporal-spatial distribution features of landslide induced by heavy rainfall are revealed. Characteristics of Jiangxi provincial landslides can be described mainly as types of shallow layer. The structure of landslide is expressed mostly in form of integral movement. Landslides happened in hilly land are more than other conditions. Amount and volume of landslides in sharp slope are lager than that of terrain slope relatively and gently. Considering effects of height, large numbers of landslides appear in height between 100 to 400 meters above sea level. Most of landslides take place in raining season. A great of landslides are triggered by heavy rainfall, which takes a proportion of 87% in May to July and especially 70% in June. The times of landslide disasters happened in daily rainfall with 100 to 400mm are 70% on totals. Most landslide disasters occur nearly the same time with precipitation period and minority lags. Regions having 5 to 6 heavy rainfall days general in a year attribute to susceptibility areas of landslides.(2) Daily comprehensive rainfall index to forecast landslides are investigated. By analyzing data since 1960s, precipitation-inducing landslides not only relate to currently rainfall but also lie on previous raining procedure. The influence of daily precipitation on landslide can persist one to ten days. Declined coefficient is introduced into comprehensive rainfall model, which is used to calculate effective rainfall. Daily changes and function of evaportranspiration on the index are studied.(3) The dynamic process and mechanism of landsides triggered by extremely heavy rainfall are revealed. The function of precipitation on landslide is a dynamic process. When raining water impregnate into landslide mass, it can increase water content and volume weight of rock soil mass, intenerate soil, enhance rock soil capacity, and also becomes lubricant while penetrating into bedrock surface under weathering rock mass or layer cutting with water, which diminish anti-slide force and cause landslide. Superficial landslide in torrential rainfall are due to short time function of violent precipitation, in the case, landslide mass quickly arrive to saturation situation that lead to ground displacement sharply, as water penetrate promptly and make ascending of soil saturation degree and pore water pressure, reducing slope substance strength and ending with happening landslide, addressing above as superficial landslide mechanism.(4) Critical values of precipitation to forecast landslides are investgated, which provide bases for predicting and warning landslide disasters. Eight observation grounds in susceptibility areas in Jiangxi province are devised to monitoring changes of water table, pore water pressure, stress of gliding zone, and landslide mass movement. Based on observing data and historic records, the purpose is to study models of landslidesstability and search criterions for predicting or warning landslide disasters. By monitoring and experiment, it is proved that landslide hazards can be predicted. Critical rainfall value to induce landslide acquiring from field trial is in consonance with statistics results.(5) Changes of water tab...