Equal safety factor (K) method is recommended for double-slide mode in the code for design of concrete gravity dams(SL319-2005)

but there is no unified standard for the determination of the resistance angle between two blocks and it is very sensitive to the calculating result. In this paper

the resistance angle is discussed in detail. In order to get reasonable resistance angle of two blocks

Sarma method

finite element method and the slice-free method of limit equilibrium method are used for the anti-sliding stability of double-slide mode; then a suggestion for determining the resistance angle is given. Finally the stability against deep slide of concrete gravity dam is analyzed and the critical slip surface of double-slide mode is searched.