| At the end of the 20th century, severe weather and extreme events was caused by the global warming, such as the dislocation of seasonal prevalencethe, the greater change of the daily temperature, the tremendous fluctuation of rainfall, frequently occurring extreme events and so on. Floods, landslides, fire, drought, tornadoes, hurricanes, typhoon and etc are the most common disasters. 19 provinces of sourthern China are hit by low temperature, rain, snow and freezing weather in 2008. This disaster influence is greater and the heavy history of calamity is infrequent. Guizhou, Yunnan, Sichuan, Chongqing and Guangxi these 5 provinces have a period with high-temperature, less rainfall, which led to severe drought weather for decades since at autumn in 2009. The magnitude 7.1 earthquake occurred in the Tibetan Autonomous Prefecture of Yushu in Qinghai Province on April 14, 2010, which caused many casualties of the victims. These extreme events'occurrence, not only bring the heavy losses to the country and the people, but also a much more test to water conservancy projects.For the earth-rock dam, it can cause great damage to the safety of the people's life and property for the river downstream when the dam is overtopped. Especially for cascade hydropower station in the river basin, the flood safety of control reservoir directly relates to the whole basin safety. It is necessary to carry on accurate analysis of risk. The risk of earth-rockfill dam problems are studied under the contions that extreme floods and low temperature in south of China. It's a part of project"Calculation of risk assessment method and evaluation software development of dam break"of Hydrochina Zhongnan Engineering Corporation.(1)The maximum design flood into reservoir is caculated by using the extended three-parameter Burrâ…«distribution. This method overcomes the shortcoming of the artificial selection experience frequency points, statistical parameters are calculated through iteration, it is much more smipler. Hydrological conditions of flood into reservoir, hydraulic conditions of discharge capacity, boundary conditions between capacity and the level, the initial conditions of flood limited water level, these uncertainty factors are considered. Based on stochastic differential equation, dam overtopping risk is studied. The science basis is provided for economically and reasonably selected the scale of the building and operation modes.(2)The compressive strength, the tensile strength, the elastic modulus and other mechanics parameter indexes of building materials are got from the similar experiments researches. The results are based on the conditions of low temperature and freeze thawing. Finally, the calculation parameters of case are determined.(3)To take Sanbanxi CFRD for an example, the influence of extreme floods, freezing and freeze thawing on mechanical properties of building materials are studied, numerical simulation study about stress and deformation under the conditions of extreme floods, low temperature and freeze thawing by using Flac3D. The dam stability can be obtained during these two working situations. It turned out that the stress and deformation of CFRD meet the safety requirments.
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