Study On Mechanism And Design Method Of Pipe Roof In Shallow Excavation Tunnel

With the rapid development of urban rail transit, construction of tunnels is moreand more common in the city. With tunneling, it needs to effectively limit the sink ofsurface and vault, to maintain the stability of the excavation face. So doingpre-support consolidation before excavation is necessary t. Pipe roof pre-supporttechnology, as an important auxiliary method of tunnel excavation, because it has longpre-refince distance, short construction period, high reliability, while it was more andmore applied to the tunnel construction. At present, however, the design andconstruction of pipe roof are largely based on the experience analogy of engineers, butit can not meet the needs of underground project development. So study on themechanism of pipe roof pre-support in technique field of substructure work will be theexisted research and practical project.This paper was based on the research of domestic and foreign on pipe roofpre-support. From the following aspects: the design and construction of the pipe roof,the mechanical mechanism of pipe roof pre-support, and the numerical simulation ofthe actual project, I do the following work:(1) A variety of advanced support technologies were summarized and analyzed.Basing on the characteristic of pipe roof advanced support, the scope, designparameters and constructing methods of pipe roof were detailedly summarized.Further, methods to solve the engineering problem during the constructing were putforward.(2) The lode scope and calculation formula of pipe roof in the shallow tunnel wasdrawed, which was based on the surrounding rock pressure theories of shallow tunnel;Based on Winkler elastic foundation beam theory and established the mechanicamodel of pipe roof pre-support, the differential equations of correspondingdeformations, turn angles, bending moments and shear were deduced. In practiceengineering, this model can use to calculate the equations of correspondingdeformations and be proved the rationality of model.(3) Taking a shallow tunnel project for example, numerical simulation wascarried out by using program FLAC3D. The compare between the on-support results and pipe-roof support results proved that the function of pipe roof in controlling thesettlement of surface and vault was obvious. The compare between the numericalsimulation results and the monitoring results proves that the numerical simulationmodel is reasonable.