凝土重力坝沿坝基深层缓倾角软弱结构面的抗滑稳定是工程设计的一个关键技术问题，深层抗滑稳定分析主要采用刚体极限平衡的等安全系数法。在深层抗滑稳定分析中发现，抗力角的合理选取及抗力体底滑面角的确定对计算成果的可靠性至关重要。通过对亭子口重力坝深层抗震抗滑稳定性的分析研究，提出了抗力角的取值原则，即其最大值不能超过坝趾基岩竖直面上主应力方向与水平面的夹角，以及以抗力最小为原则确定抗力体底滑面与水平面的夹角；并依此原则用刚体极限平衡等安全系数法分析论证了该重力坝表孔坝段初步设计方案深层抗震抗滑的稳定性。

 The rigid body limit equilibrium method is widely used in study on the stability against sliding of gravity dam subjected to earthquake along weak strata in rock foundation .In the study process it was found that the determination of the resisting force angle γ provided by the resisting body and the sliding angle β of the resisting body are extremely important to the reliability of analysis results .The principle determining both angles is put forwarded in this paper. The maximum value of the resisting force angle should be smaller than the included angle of the principle stress direction on the vertical plane in foundation at dam toe and horizontal plane under basical loading; the sliding angle of the resisting body should be correspongding to the minimum value of the resisting force in the equilibrium equation .The stability against sliding of the Tingzikou gravity dam along weak strata in rock foundation is studied based on the principles mentioned above.