Effect Of Mechanics And Optimum Process In Excavating Multi-arch Tunnel

Multi-arch tunnel is widely used in practice because of its advantages of small area of project, the flowing line and good connection between the tunnel and bridge. However, owing to its large span, small ratio of its altitude and span, complicated procedure of construction and repeated disturbance to surrouding rock, its characteristics are very complex during the different excavating stages. Therefore, it is significant to know and understand the mechanical characteristics of excavating and supporting as well as to optimize the process of construction for the design and construction of the multi-arch tunnel.Relying on Chenjiaqiao tunnel project, the construction process of tunnel under different surronding rock conditions and various construction methods has been analyzed with 3D FEM analysis of MIDAS/GTS program, combined with the study of the characteristics and the current construction methods of multi-arch tunnel in dometic and abroad.The mechanic behavior problems under complex construction process has been studied. The construction process has also been optimized by the analysis of the monitoring measured data. The main contents of the research in this paper as follows:1. The 3D elastoplastic model of multi-arch tunnel has been set up, which contains gradeâ…¢,â…£andâ…¤surrouding rock, in gradeâ…¢surrouding rock with such two methods as middle-pilot-and-half-section and middle-pilot-and-full-section, in gradeâ…£andâ…¤surrouding rock with such a method as three-pilot. The stress of the surrouding rock and supporting structure in typical excavation stage under these three excavation methods has been simulated and analyzed.2. The monitoring data in Chenjiaqiao tunnel has been analyzed and it has been compared with the simulated data.The results show that the numerical simulation is reliable.3. The reasonable distance between preliminary support and excavation face in gradeâ…¢surrouding rock has been analyzed. The space effect during the tunnel construction and the transaction between the left hole and the right hole have also been analyzed. In the end, the reasonable distance of working face in one hole and between the left hole and right hole has been listed.