Analysis Of Mechanical Effect Of Subway Station Constructed By PBA Method

With the development of economic construction,subway construction has entered the golden stage of development,and many construction methods emerge as the times require.However,due to the continuous reduction of the utilization rate of surface space and the increasingly complex urban environment,the traditional construction methods are no longer suitable for urban subway construction,PBA method in shallow excavation method is a flexible and adaptable construction method based on the combination of excavation method and frame structure construction method.A lot of engineering practice has proved that PBA method is an effective measure to reduce the impact of subway construction on existing road traffic under complex conditions,and has achieved remarkable economic benefits.At present,the theory of PBA is far less abundant than engineering practice,which is extremely unfavorable to the popularization of PBA.Based on the construction project of Dongba Mid-street Station on Beijing subway Line 3,this essay uses MIDAS-GTSNX finite element software to carry out numerical simulation analysis for the main station construction of using PBA construction method,and strive to grasp its mechanism of action for future projects.The main work content and research results are as follows:(1)According to the geological conditions of the main project of Dongba Mid-street Station,use the MIDAS-GTSNX finite element software and fully combine the main project’s own characteristics to carry out three-dimensional geological modeling,and briefly describe the principle of the Modified Mohr-Coulomb model.(2)Based on the analysis of the variation law of surface settlement and settlement trough in different construction stages,it is concluded that the surface settlement caused by pilot tunnel excavation stage is the largest,followed by arch buckle stage;During the excavation stage of pilot tunnel,the settlement trough appears in the form of "single-double-single",and finally stabilizes at the beginning of the structure center line in the form of single groove.(3)Analyze the mechanical changes of stratum stress,the internal force of primary support and main arch of pilot tunnel,the stress of cast-in-place pile and crown beam,and the internal force of central column during construction.The results show that the stress situation of the side pile is complex,which not only bears the vertical load of the stratum,but also is affected by the lateral earth pressure of the soil outside the side pile;Through the simulation,it is found that the center column is the most stressed vertical support component.(4)Comparing the variation law of surface settlement and settlement trough under different excavation sequence of pilot tunnel,the peck curve is used to verify the variation law of settlement trough,and the optimal construction scheme is "first down then up,first edge then middle,upper and lower staggered,excavation across tunnels";The peak value of the settlement trough moves from both sides of the structure to the center line of the structure,and finally stabilizes at the center line of the structure.The settlement curve is normally distributed in the center line of the structure,the formation loss rate is between 0.65% and 0.75%...