Research On Overhead Risks Of Earth-rock Cofferdams Under Cascade Hydropower Development Conditions

With the rapid development of Chinese hydropower industry in recent years,the development of hydropower in the eastern and central regions has basically been completed.With the implementation of the Western Development Strategy,the southwestern region has entered a phase of comprehensive development.However,part of the dams which are under construction or proposed construction exist overburden phenomenon.Under this geological condition,the preferred diversion structures are earth-rock cofferdams and diversion tunnels,and the cofferdams are temporary buildings.It is important to do the analysis of the safety for temporary buildings cofferdams.If the cofferdams are overcrowded and cause damages,the loss is incalculable.The safety for earth-rock cofferdams can’t be ignored by engineers and technicians.It is of great significance to strengthen the emphasis and research on the safety of earth and stone cofferdams.This paper mainly studies the risk calculation of overlying earth-rock cofferdams,that is,the probability that the water level of the cofferdam exceeds the top of the cofferdam.It is related to how to estimate the overcrowding risk of the cofferdam objectively.There are many factors that are difficult to predict and control which are as follows:(1)The randomness of flood storage,such as the uncertainty of flood peak flow and flood volume,and the uncertainty of the duration of flooding process.(2)The diversion capacity of the diversion building,the uncertainty of the discharge capacity of the diversion system and the hydraulic parameters of the discharge building.Coupling the uncertainties of flood process and discharge flow capacity in the diversion system to study the risk of overcrowding in the retaining of earth-rock cofferdams,using the Monte Carlo method in structural reliability,and rationally handling uncertainties the probability distribution function,using C# language to write the corresponding program,finally the risk rate can be calculated.The research on the overlying risk of earth-rock cofferdams provides a scientific decision-making basis for the safety evaluation of earth-rock cofferdams and has theoretical and practical value.Aiming at the risk of overcrowding of earth-rock cofferdams in a cascade construction environment,and taking full account of the main risk factors under the cascade construction environment,analyzing and calculating the risk of the initial diversion system of the project,and substituting the hydrological and hydraulic data into the analysis model,the risk rate will be calculated.Examples have showed that the risk analysis model and the calculation process are meaningful.