Analysis Of Floating Impacts Of Groundwater On A Existing Underground Structure

With the development of urbanization, urban land resources become scarcer, and the traffic is in more crowded stage. Into the twenty-first century, many of our cities, especially medium and large cities, begin constructing more subways, underpasses, underground shopping malls and other underground structures for using underground space efficrently. Because of the layout variety and the large depth of underground structure, the anti-floating of underground structures becomes more important. The presente specifications for the anti-floating design of underground structures and the anti-floating measures in construction are not strict and clear in China, only some qualitative description and requirements on water buoyancy were listed. However, due to various reasons, underground structures anti-floating failure incidents frequently occur in practical engineering, how to properly carry out anti-floating design and ensure the rational use of anti-floating measures in construction become the focus of the anti-floating of engineeringIn this paper, an anti-floating incident of a underground commercial plaza was taken as a case which occured anti-floating failure incidents, and finite element models were established for calculation and analysis with Midas GTS. Four conditions were discussed: the water table was 1 meter under the base plate, and 4 meters, 6.7 meters, 8.2 meters up the base plate. By analyzing the displacement and bending characteristics of the raft plate in the four conditions, two stages are establish based on that the change of the displacement and bending moment of raft plate under different groundwater levels: the first stage, the soil which supports the structure bears compressive stress,and the change of the displacement and bending moment of raft plate is little; the second stage, the soil which supports the structure bears tensile stress, and the underground structure have been floated, the displacement and bending moment of the raft plate of the underground structure are influenced remarkably with groundwater level rising. Meanwhile, based on the comparison of the different conditions, the features of the displacement and the bending moment of the underground structure are found.Finally, the change of the displacement and bending moment of the raft plate have been analyzed and evaluated with increasing weight when the underground structures anti-floating failure occurs in the 8.2m groundwater level. The results can be an appropriate reference for the anti-floating design, rapidly handling anti-floating failure incident and reinforcement of some anti-floating underground structures similar to the underground structure.