Analysis Of Stress-Strain And Stability For Longitudinal RCC Cofferdam Foundation In Liuku Hydropower Station

The stability of cofferdam's foundation is the critical factor influencing construction process. The foundation of longitudinal RCC cofferdam in Liuku hydropower station is sandstone alluvium and the bed rock is cracked. The elastic modulas of cofferdam's bed rock is very small (E0=0.04～0.048Gpa),so the stability of RCC longitudinal cofferdam foundation in Liuku hydropower station is the critical technique problem. The seepage,stress-strain and stability are studied using 2D and 3D non-linear finite element method; then particle swarm optimization method is applied to the stability research of cofferdam's slope. The main research contents and achievements are as follows: 1.The seepage field of three typical 2D sections and 3D unit of cofferdam's foundation is studied using finite element method. The result shows that the general pattern of water head and seepage distribution derived from 2D and 3D seepage analysis is similar. The regularity is that the water head falls down rapidly through two anti-seepage walls, but subsides slowly in sandstone alluvium and bed rock. The engineering effect of two anti-seepage walls is notable. 2.Firstly the stress-strain state of three typical 2D sections is studied using 2D non-linear finite element method. Then the shear,axial force and bending moment of anti-seepage walls and cushion are calculated on this basis and the reinforcement scheme of them is verified and improved. The result indicates that the displacement of cofferdam body is large due to low elastic modulas of the bed rock in cofferdam's foundation; maximum and minimum principal compression stress of cofferdam body and its foundation is increasing as the elavation falls; the stress concentration exists in the joint of cofferdam body and anti-seepage walls; the reinforcement of cushion should be increased. 3.Strength reserve safety factor method is adopted to study the failure mechanism and failure process paths of three typical 2D sections and 3D unit under several working conditions. Finally the strength reserve safety factor of cofferdam's foundation is obtained. In flood season, the safety factor Kc of cofferdam's foundation is 1.80. 4. The application of particle swarm optimization method that is a new swarm intelligence searching method in searching for critical slip surface of slope engineering is studied and applied to the stability analysis of the cofferdam's slope. It demonstrates the practicability of particle swarm optimization method in slope engineering.