The Study Of Construction Methods For Big-Span Metro Tunnels In Soft Ground

Based on the big-span metro tunnels, the thesis primarily studies the mechanical characteristic, the stability and the construction methods about the big-span tunnels.Besides of the study developments about the big-span tunnels home and aboard, the paper analyze the basic mechanical characteristic of big-span tunnels and the influence factor, which includes shape of cross section, high-span ratio and invert. At the same time, the stability of big-span tunnel with influence factor such as section size, high-span ratio and depth is studied. Then, the paper summarizes the basic method of tunneling, and primarily studies the proper method for big-span tunnels, which includes basic method and assistant method, and carries out the evaluation of construction methods. Finally, the paper discusses the application of it in the Guang Zhou Metro project.By way of the theory analysis, the paper considers that the high-span ratio is a basic mechanical parameters that influence the stability and endurance of tunnels structure and surrounding rock. In the same time, the paper reveals that the invert play a important role in keeping the stability and endurance of tunnels structure and surrounding rock. In addition, the re-distribution of stress is not equable when tunnel is excavated, so the sustaining measure for surrounding rock near the wall foot should be reinforced and select thus cross-section former, of which, the arch lining is thickening from top to sides. There are several available tunneling methods for big-span tunnel. The method that applies to the project must be selected taking account of the geological condition and the ability of construction. In the Guang Zhou Metro project, the double drift method is proved that it is competent when excavating tunnels in the disadvantageous condition of the soft ground, shallow depth and big span.