Analysis And Application Research Of Seepage Stability Of Earth Rock-Fill Dam Under The Condition Of Reservoir Water Level Rising And Falling

Seepage problem seriously affects the reliability of earth rock dam, which not only lead to soil erosion, soil strength index declined, soil seepage failure, even cause the dam landslide,collapse and other disasters. The seepage problem was complex and affected by many factors,for different types of earth rock dam, distribution rules of seepage field and the influence mechanism of dam slope stability were not the same under the different conditions. So how to correctly explore and study the seepage stability problem of earth rock dam is not only a major difficulty of water conservancy project, but also the key to ensure its stable operation.Analysis the sensitivity of seepage parameters about a homogeneous earth dam based on basic theory of seepage, finite element method, limit equilibrium method in this paper. Take the Zhong-ba dam as an example, analyzing steady seepage under different water level conditions, analyzing unsteady seepage under the conditions of reservoir water level rising and drawdown. Then calculate the safety factors of dam slope under different conditions. The main research contents and conclusions are:(1) Analyze the sensitivity of reservoir water level, permeability coefficients, material anisotropy ratios and decline rates of the reservoir water level. The results showed that the decline rate of reservoir water level was the most sensitive factor.(2) Obtaining the results of steady seepage and safety factors of dam slope for the Zhong-ba dam under conditions of the normal water level, the design flood level and the check flood level. The results showed that the biggest discharge per unit were 0.376 m3/d·m,0.400m3/d·m,0.407 m3/d·m and the safety factors of upstream dam slope were 1.527,1.546,1.554, and the safety factors of downstream dam slope were 1.398,1.388, 1.382 under that three conditions. All the results were met the requirements of the specification.(3) Calculation and analysis of the influence of distribution rules of unsteady seepage field and stability of dam slope under the condition of falling speed of the reservoir water level for the Zhong-ba dam. The results showed that: the saturation line of the dam decreased with the decrease of the reservoir water level. The decreasing rate of the saturation line was slower than the falling speed of the upper reservoir water level. The greater the falling speed of reservoir water level, the more significant the lag phenomenon. At the beginning of water level drawdown, partial flow could not even spare time to flow downstream dam, which appearing the reverse flowing phenomenon. The change rule of safety factors for the upstream dam slope had three processes with time, decreasing firstly and then increasing and tending to be stable at last. And the faster the falling speed of the water level, the less the stability of the upstream dam slope.(4)Calculation and analysis the influence of distribution rules of unsteady seepage field and stability of dam slope under different storage conditions for the Zhong-ba dam. The results showed that: the saturation line of the dam increased with the increase of the reservoir water level. The increasing rate of the saturation line was slower than the rising speed of the upper reservoir water level; and the greater the speed of water storage, the more significant lag phenomenon. The change rule of the safety factors for upstream dam slope had three processes with the rising of reservoir water level, increasing firstly and then decreasing and tending to be stable at last. And the faster the rising speed of the water level, the bigger the change of the safety factor at first and the earlier the safety factor is the biggest.The cutoff wall and curtain grouting were used to prevent seepage for the Zhong-ba dam.Which not only can increase the head loss of the core wall, but also cut off the seepage path of the dam foundation effectively, and thus having a significant effect on seepage control. And the faster the falling and the rising rate of the water level, the less the stability of the dam slope. In the actual project, we should choose the reasonable speed to ensure the safe operation of the dam.