In light of geo-hazard control in the reservoir area of Three Gorges Project in China

the calculation of critical height of rock-soil elastoplastic area before anti-slide pile on declining sliding surface is carried out with limit equilibrium theory of space wedge block. Firstly

the usual methods of calculating rock-socketed length of anti-slide pile are described

such as engineering geological method and strength controlling method. Secondly

two theories

elastic and elastoplastic theories used to calculating rock-socketed length are compared. Thirdly

the critical height of elastoplastic area of mass before piles is put forword when the slipping surface is declining; meanwhile

the relationships among critical height and angle of sliding surface

resist force of rock and strength parameters of rock are discussed. Finally

taking a project in Wanzhou city of Three Gorges Resevior area for example

the critical elastoplastic height of rock-soil before anti-slide is given; and rules have been found that the critical height h shows a exponential distribution along sliding surface angleθ and cohesion c of rock

and linearly distribution along the resist forceσand friction angleφof rock .According to these rules

we can give proper correction to anti-slide pile’s rock-socketed length and critical height of elastoplastic area of rock-soil before anti-slide pile.