Study On The Influence Of The Structure Of The Key Wall On Gravity Dam Safety Performance Against Deep Sliding

Gravity dam is a common hydraulic structure, mainly relying on its own gravity to maintain stability. But normally the dam foundation exists joints,cracks, faults or weak intercalations with complex structure, and these structural planes form unknown sliding path easily under water pressure. Once it happens deep sliding, which will threaten the downstream people’s lives and property and cause incalculable losses, besides, sometimes the judgment about geological structure defects of the foundation in the survey is not accurate,which may be a larger hidden trouble. Therefore, analyzing and evaluating the problem of deep stability against sliding of gravity dam objectively and accurately and putting forward reasonable reinforcement measures now is a common and important task when designing gravity dam which is on complex foundation.At present the designs of gravity dam often set key wall to improve dam stability against deep sliding by cutting off the weak intercalations, but how to evaluate correctly the effect of key wall? In the previous designs we often regarded it as a structural measure and safety stock. There are still no unifiedunderstanding and regularity research literature about how much the effect of the key wall is.So the finite element strength reducing method and the maximum shear strength permitting relative displacement instability criterion are used based on ANSYS software to analyze quantitatively how the width, slope and position of key wall affect dam safety factor against deep sliding.In this paper, the concrete research contents are as follows:(1) Research status of analytical method of deep stability against sliding of gravity dam and improving stability against sliding of the building by setting key wall is explained in detail. The finite element strength reducing method is adopted and introduced mainly on the basis of referring to lots of relevant literature and research needs.(2) The common instability criterions of finite element strength reducing method are summarized and their shortnesses are analyzed, the most important one of which is that the result is influenced easily by artificial fuzzy judgment,and it is hard to get accurate and objective solution, finally it will end up with a rough range.(3) In view of this, this article puts forward the maximum shear strength permitting relative displacement instability criterion in order to reflect quantitatively the effect of the key wall parameters to the gravity dam safety factor against deep sliding. The relative displacement of upper and downpoints of the weak intercalation is restricted to permissible range, which is subject to that the feature point of the weak intercalation occurs shear failure.(4) The APDL(ANSYS Parameter Design Language) is used to change the key wall parameters quickly and easily, and the load is applied by the load step to analyze the relationships between gravity dam safety factor against deep sliding and the key wall parameters.For the example in this paper, the main results are as follows:(1) The safety factor increases with the width of the key wall increasing in the whole, the width of key wall is linearly related to the safety factor approximatively within a certain range, and the relationship between the ratio of the key wall width and the dam height and the safety factor is established,which is a dimensionless quantity, making the conclusion more universal.(2) The safety factor increases with the slope of the key wall increasing in the whole, the slope of key wall is linearly related to the safety factor approximatively within a certain range, but the effect of slope of the key wall to the safety factor is smaller than width of the key wall.(3) Under the same conditions, the key wall that is set in the dam toe can have better anti-sliding effect than in the dam heel.