Abstract: The reinforcement of soil in the passive area of soft soil foundation pit plays an important role in controlling excavation deformation and protecting the surrounding environment. There are few systematic studies, from the point of view of three-dimensional space at present, on the influence of pit bottom reinforcement mode on foundation pit deformation. By means of finite element analysis software ABAQUS and measured engineering data, the deformation of a deep foundation pit of a soft soil subway station in Shanghai was investigated in this paper. The investigations were carried out respectively with respect to conditions of reinforcement of entire basal soil, or reinforcement along pit perimeter, or reinforcement by evenly distributed blocks, and reinforcement by grout struts. Our investigations show clearly thatif the reinforcement by grout struts with the same reinforcement ratio (the ratio of longitudinal length of the reinforcement along the foundation pit to longitudinal length of the foundation pit) is arranged in the foundation pit of same length, the restraining effect of the reinforcement in the center of excavation section on the deformation of the foundation pit is higher than that of the reinforcement on the side of the excavation section.Increasing the reinforcement ratio of the reinforcement by grout struts can effectively reduce deformation of the foundation pit.Among the four different strengthening methods, the reinforcement of entire basal soil has the greatest restraining effect on the deformation of the foundation pit. For a long and narrow soft soil deep foundation pit, the restraining effect of reinforcement by evenly distributed blocks and reinforcement along pit perimeter on excavation deformation are not apparent, and there is little difference with each other.

Key words: deep excavation, soil reinforcement pattern, excavation deformation