3D-FEM analysis on stability of shaft with conduit jacked synchronously in two directions

Because of the restriction of construction time, the method of two-direction jacking is employed in shaft No.6 Power Tunnel Project of south Tibet Road in Shanghai, China. A nonlinear elasto-plastic simulation is carried out with three-dimension FEM program. The analysis emphasises on the following aspects: firstly, the stabilities of backup wall and slurry wall while two-direction jacking is running; secondly, the maximum displacement in X direction induced by four or six jack apparatuses; thirdly, the relationship between jacking force and displacement of backup wall; finally, the impaction to direction of resultant of jacking force while backup wall reaches to maximum displacement in X direction. The results indicate that the design scheme of the project is feasible. It can ensure the stability of the slurry wall and backup wall, and does not affect the precision of jacking direction. Moreover, the results provide relevant parameters for optimum design of the project.