Abstract:When single-plane sliding block has more than one joint face,double-plane sliding block has more than two joint faces,and the block is above these joint faces,some defections of stability calculation in traditional block theory may occur. So,block-dividing limit equilibrium analysis method is presented. The method divides block along the intersection edge of joint faces and neglects the vertical shear force between dividing-blocks i.e. takes horizontal normal force and shear force into account;as to an assumed sliding direction,by satisfying vertical force equilibrium of every dividing-block and whole force equilibrium in the sliding direction,the factor of stability can be solved. However,the non-equilibrium force in the horizontal direction perpendicular to the assumed sliding direction is always existent, because the block is usually non-symmetrical and the assumed sliding direction is not the practical one. By changing the sliding direction from 0° to 360°,when the non-equilibrium force gets to zero,the solutions satisfy force equilibrium in three othogonal directions;and the actual potential sliding direction can be determined rather than assumed. In this case,the factor of stability is minimum or close to minimum,whose meaning is similar with Pan¢s principle of the maximum and the minimum. The method can solve well the stability analysis of multiple sliding-planes block. By contrasted with traditional block theory,the method is validated;and the continuous change of factor of stability and sliding direction with gradual transition from non-symmetrical double-face sliding to single-face sliding can be interpreted properly. At last,a practical engineering case is studied.