Monitoring and Simulation Analysis of Deep Foundation Pit Excavation of Subway Station in Watery and Weak Stratum

Under watery and weak stratum conditions, deformation regulations and instability conditions of each stage of a deep foundation pit construction for a subway station become more complicated than those in more common areas, thus causing major security problems. This study used and examined open-cut deep foundation pit engineering of a subway station under construction and considered watery and weak stratum characteristics. The finite difference method was used to simulate the support structures of the deep foundation pit excavation process while considering the station main body structure, initial ground stress, construction process, and stratum physical and mechanical parameters. Meanwhile, the actual construction process was monitored and ground settlement, enclosure structure horizontal displacement, supporting axial force, and influence of engineering drainage analyzed. This study found that the monitoring stability value of the enclosure structure was slightly less than the predicted value from numerical calculations. The changing trends of both monitored and simulated values were in accord with theoretical analysis. These results showed that ground settlement grew rapidly in the middle excavation stage. The maximum horizontal displacement of the enclosure wall occurred at the upper part of about 1/3rd depth of the foundation pit. The supporting effect of steel supports was better than that of reinforced concrete support. After the drainage was stable, the final average ground settlement value of monitoring points caused by foundation pit drainage was 7.69 mm. The enclosure structure and inside support structure of the station deep foundation pit could guarantee the stability of surrounding rock during construction. These results provided guidance for the design optimization and construction of similar engineering projects.