Study On Stability Analysis Of Three-Dimensional Slopes And Gravity Dams

Three dimensional features exist universally in landslides and instabilities of dam foundations. The research presented in this thesis focuses on the issues in the stability analysis of three dimensional slopes and gravity dams. The emphases are as follows:1. Once a soil slope is led to the limit equilibrium state through the finite element-strength reduction technique, usually, the critical slip surface goes through the points at which the equivalent plastic strain takes the maximum in vertical direction. First, some vertical lines are arranged along a horizontal area. Then, along each of the vertical lines the point with the maximum equivalent plastic strain is found out. Last, the separate points are smoothed by means of the thin-plate smoothing spline for three dimensional slopes and the least squares for two dimensional slopes. Thus the position of the critical slip surface is determined.2. Using the continuum-based finite element approach in conjunction with the strength reduction technique, one can easily find out the factor of safety of a slope with rather high precision, but will encounter some obstacles in the accurate location of the corresponding three-dimensional critical slip surface. On the basis of the Mohr-Coulomb failure criterion and the stress field in the limit equilibrium state of the slope, it is deduced that the three dimensional critical slip surface is the solution of the Cauchy problem of a quasi-linear partial differential equation of first order. Using the method of characteristics for the problem, the three dimensional critical slip surface that may take any shape can be determined without the specification of its geometry.3. Up to now, for three dimensional slip surfaces there is no analytical solution available being as a benchmark to check the method for locating the three dimensional critical slip surfaces. An experiment study on the three dimensional slope is conducted to verify the'Cauchy problem of three dimensional critical slip surfaces of slopes'. It is indicated that the failure surfaces from the experiment and the computation are in well agreement except some objective factors. The flaws in the convex slope will become bigger and bigger with a uniform load increasing on the slope crest. That belongs to the spalling destroy. At the limit state of slopes, some slip masses separated by fissures and the slip surface comes into being.4. In the design code of gravity dams, only equilibrium of forces is considered in the equal factor of safety method for evaluating stability of gravity dams against deep slide in foundation, ignoring kinematical admissibility. To meet kinematical admissibility, based on Sarma's assumption, it is suggested that the interface between the upstream and downstream blocks be specified as a fracture plane and have the same factor of safety as the upstream and downstream sliding surfaces. Few changes are made in the existing algorithm, but the factor of safety, and both the magnitude and direction of resisting force can be obtained simultaneously, which are important in the design of gravity dams.5. In the design of a gravity dam, any dam monolith must be checked if the stability against sliding along a potential failure surface in the foundation meets the requirement specified by the design code. Till to now, such check is usually carried out using 2-dimensional limit equilibrium methods.2-dimensional analyses are sometimes too conservative to meet the requirement. For this purpose, in the settings of the limit equilibrium methods a rigorous 3-dimensional procedure is developed, which can accommodate failure surfaces of any shape and satisfy all equilibrium conditions. Meanwhile, the procedure considers the reinforcement of concrete plugs which are laid between the sliding body and the rock foundation.6. To check the engineering practicability of the methods suggested in this thesis, some project cases are employed. The results indicate that these methods are of value in project cases.