Study On The Deformation And Control Of Subway Station Construction Under Through High-pressure Tower

With the acceleration of urbanization, the subway has become an important vehicle for people to travel. As the subway station is mostly located in the city bustling area, the constructions face many risks from underground pipelines, traffic congestion and numerous building structures. Therfore, it is hard to avoid the situation of subway station construction under through high-pressure tower. Although, there are some research on tunnel excavation under through high-pressure tower for the moment, but the research on complicated process PBA method construction under through the tower whose independent foundations are shallowly buried are found rarely. For this purpose,this paper is supported by a construction project of new subway station under through high-pressure tower at Beijing Metro Line 16. In this paper, the research methods of numerical simulation, field measurement and literature researching are used to carry out a series of analysis and research on how to ensure the normal use of high-pressure tower and control it' s deformation. The main research contents and conclusions are as follows:(1) Study on the current situation before construction and ascertain deformation controlling index of high-pressure tower above the subway station. The tower is identified as level 1 risk source, by status quo investigation and analysis of the project overview of the station and the tower. According to literature material, relevant standards of tall structure and numerical simulation analysis, the deformation control indexes of serviceability limit state and ultimate capacity limit state are obtained. To ensure the normal operation of the tower, the differential settlement controlling index of the high-pressure tower foundation is determined as 16mm when subway station construction under through the tower.(2) Study on the deformation law and scheme comparison of excavation when subway station construction under through the tower. Through numerical simulation analysis, this paper performes scheme comparison of excavating pilot tunnel sequences,excavating buckle arch sequences and distance between excavation faces. Based on the analysis above, the optimized construction scheme is plan 2 of pilot tunnel (the lower pilot tunnel first, then the upper; the middle first, then the side) & plan "Middle-side" of buckle arch & plan "20m of the distance between excavation faces". The analysis and calculation of the deformation indicates that the differential settlement of the tower's foundations can't meet the deformation control requirement. Therefore, basing on the optimized construction scheme, the soil above the tunnel should be specifically strengthened in advance before excavation.(3) Study on the strengthening measures to control the differential settlement of the tower's foundations. Basing on the optimized construction scheme, a scheme comparison of three kinds of thickness of the deep-hole grouting soil is performed. Then,the result shows that the plan of thickness of 1.5m is the optimized one and can effectively control the differential settlement. The result of the analysis of parameters of the deep hole grouting soil suggests that the elasticity modulus and internal friction angle can be moderately increased to control the deformation as necessary.(4) Study on deformation monitoring, controlling and data analysis of construction process. Deflection distribution control standard is set out by combining deflection distribution control method and numerical simulation. Then, comparison of the data of field monitoring and this standard can approach the purpose of process control and guarantee the measuring points under deformation control. Comparison of measured values and numerical simulation values indicates that numerical simulation can reflect the law of the actual excavation process.In conclusion, using the optimized construction scheme and the advanced strengthening measures of deep-hole grouting can guarantee that station construction underneath passes the tower successfully and does not affect its normal use. Finally, this paper's research results can play a guiding role in this project and provide a reference for similar projects in the future.