Abstract:

In order to study the reinforcement effect of grouting on the exposed fault zone of opencut foundation pit, taking the the foundation pit project of Nanjing Metro Shangyuanmen Station as an example, the coupling interaction between seepage field and surrounding rock stress field in excavation process is considered. The corresponding finite element analysis model is established to simulate the coupling system consisting of soft broken layer, grouting reinforcement zone, foundation pit retaining wall and surrounding rock. The characteristics of seepage field, displacement field and stress field of surrounding rock before and after grouting are studied. Finally, the horizontal displacement at the retaining wall of the foundation pit, the surface settlement outside the foundation pit, the distribution of the plastic zone of surrounding rock, the deformation of surrounding rock in the foundation pit and the variation rule of the water inflow in the foundation pit are obtained. The results show that: (1)Both lateral displacement and ground subsidence of the foundation pit are effectively controlled by grouting reinforcement of fault zone at the bottom of foundation pit. Compared with that before grouting, the maximum horizontal displacement and the accumulated settlement of ground surface are reduced by more than 50%, which can meet the engineering requirements; (2)The range of plastic zone in the bottom of foundation pit is obviously reduced, and the diffusion of plastic zone outside the foundation pit is restrained effectively; (3)Grouting in the fault zone of the bottom of foundation pit has changed the distribution of seepage field and effectively reduced the water inflow of foundation pit. The water gushing amount of the foundation pit is gradually reduced from the original 94 m3/h to 4 m3/h, and the water reduction rate is 96%; (4)The coring rate of site drilling is 75%-80% after the grouting. The excavation reveals a large number of veins formed by splitting, which proves that the grouting can effectively control the weak fault fracture zone exposed by the open excavation foundation pit.

Key words: metro station foundation pit, fault zone, grouting reinforcement effect, excavation of foundation pit, numerical simulation, underground diaphram wall