Analysis On Dam Slope Stability During Rapid Drawdown Of Reservoir Water Level

There is no clear understanding of quantitative change of stability for dam slope underrapid drawdown of water level and the standard of rapid drawdown is not clear, so someresearch is carried out in this paper.Some cases of unstable failure of earth-rock dam under drawdown of water level areenumerated and the failure mechanism of which is summarized. Research methods andresearch progress in slope stability under rapid drawdown of water level are also introducedbriefly.Assume rapid drawdown of water levelInstantaneously happens, in the dam seepage freesurface remained unchanged, numerical simulation analysis is adopted to analyze the stabilityof dam slope, quantitatively analyze various factors affecting the stability of dam slope. Theresults of the study show that, the relationship between dam slope safety factor and threefactors included the internal friction angle of the dam materials, the range of rapid drawdown,the dam slope gradient is basicly linear, dam material cohesion and the dam slope safetycoefficient basic into parabola relationship. According to the characteristic the various factorsinfluence the safety factor,calculate, analyze and fitting to get the relationship between thedam material cohesion, angle of internal friction, the range of rapid drawdown, the dam slopegradient.The influence of permeability coefficient、drawdown speed and range of water level onseepage field in the dam is researched by the method of numerical simulation. Drawdown ofwater level may cause backward seepage which is harmful to keep stable of the upstream dam.permeability coefficient、drawdown speed and range of water level influence on the positonand seepage gradient of escape point、the postion of highest point of saturation line and therate of water head before and after drawdown of water level.According to the results of dam seepage field in the period of water drawdown bynumerical simulationthe, the definition of the existing rapid drawdown is discussed.Existing graphical method is complicate and not intuitive, which is suitable to low heightslope. A new graphical method is proposed, in which coordinate parameters are improved.The new graphical method is applicable to most of medium and low earth-rock dam. Thecharacteristics of fitting curve by the graphical method show a hyperbolic relationshipbetween the dam material cohesion and angle of internal friction with the same safetycoefficient. Acoording to the functional relationship of factors like dam material cohesion、 angle of internal friction、 drawdown range of water level、 dam slope rate etc. with stabilitycoefficient of dam slope, a simplified calculation method for stability of dam slope underrapid drawdown of water level is proposed.