ln the analysis of involving polygonal-shaped surface rock slope stability, the "Equivalent K Method" can be used. It is common to assume that adjacent blocks are separated by a vertical rupture surface, which lies on two inclined discontinuity surfaces. However, this assumption lacks theoretical rigour. Following the principle of rockslide stability, the authors took the dips of rupture planes as design variables and considered the overall safety factor as the objective function. The authors tried to find out the minimum safety factor using the complex method. The results show that the overall safely factor K could be minimum when the rupture surface is vertical for most conditions, especially when the shear strengths of adjacent slip surfaces arc quite close to each other. These results show that the above commonly accepted assumption in practice is reasonable to some extent.
Many hydraulic structures were built on a rock foundation with weak layer and fissure. The stability of the structure was effected by such foundations. Limit equilibrium method is an effective way to solve such stability problems, and is widely used by engineers. It also complies with the code and has been successfully applied to practice. But this method cannot determine the factor of safety correctly for the case of complex geologic structure. For example, in the case of polygonalshaped surface rock slope, the dips of the joint surfaces between the blocks must be assumed for seeking the overall safety factor. However, different assumed dip angles will produce different safety factors. Because the change in dip angles not only alters the external force acting on each block, but also alters the interaction among the blocks. It is of practical interest to seek the minimum safety factor by varying the dip angles. In this paper, the authors study the effect of different dips of joint surfaces on the overall safety factor and present an optimization technique to solve such rock slope stability problems.
In the analysis of multi-slide surface rock slope by means of the "Equivalent K Method", it is generally considered that there exists a rupture surface between two adjacent blocks (Figure I). The complicated system equilibrium can thus be considered at the block level. A large amount of calculating work is involved. The standard method(Gian 1992) is to assume that the block is separated by a vertical rupture surface, which lies on two incline discontinuity surfaces. However, this assumption lacks theoretical rigour. Pan (1980) has presented the principle of rock slide stability: when the rock slope lost its stability, failure will occur along pre-existing slide that has least resistance.
Following the principle of rockslide stability, the authors took the dips of rupture planes as design variables and considered the overall safety factor as the objective function. The minimum safety factor K will be searched by changing the variables. 4. EXAMPLE Figure 3 shows the rock slope of interest. Table 1, Table 2, Table 3.
