Study On Reverse Entrance Through Excavation Technology Of Variable Cross Section And Its Application In Shallow-buried Tunnels

With the rapid development of China's economy,the pace of urbanization is gradually accelerated,the improvement of urbanization rate means that a large number of people flock to the cities,so traffic jams becomes an urgent problem to be solved.Subway gradually developed into the backbone of the urban traffic and has became a significant symbol of modern city due to its advantages of low noise,low pollution,large capacity and high speed,the urban rail transit has become the first choice to solve the city traffic congestion.Since the subway generally buried shallower and located in the downtown area,the ground buildings and underground pipe network is densely covered,it's particularly important to ensure that the surface subsidence is kept in a certain range during tunnel construction.The study based on the practical engineering of Changsha subway line 2 Furong square station No.4 entrances and exits.a systematic study and discussion on the “variable section excavation technology” of the tunnel is carried out,it can provide guidance for the construction of subway in the future.The main contexts of this thesis are summarized following:?1?It illustrates the construction principle of shallow-buried excavation method and obtains the best construction method of tunnel through comparing and analyzing the main method of shallow-buried excavation.It describes the supporting mechanism of the shallow buried tunnel and analyzes the reasons of the surface settlement and the law of ground settlement of the shallow tunnel.?2?The monitoring scheme of this project is established and the whole process of the tunnel construction process is monitored,then the data are processed,it's final purpose for our to summarize the changing regularity of surface and hole deformation observation,vault sink,clearance convergence and predict the final settlement of tunnel,which provide a reference for the support time of the two lining.?3?Using FLAC^3D numerical simulation software establish the numerical model,the model mainly considers the influence factors such as the angle of variable cross-section excavation,the excavation step distance,the radial small catheter,the distance between the pipe and arrangement area of pipe shed.Through the analysis of the changing rule of these factors on the vault sink,clearance convergence,the best construction methods and supporting scheme can be acquired,which can provide feasible reference and basis for design and construction.Finally,based on the comparison and analysis of the numerical results and monitoring data,it can concluded than the data are basically consistent,which means that the excavation method and the supporting measures are basically reasonable,which can provide reference for the similar projects in the future.