Study On Supporting Structure's Mechanical Properties Of Large Sections Of Loess Tunnel

ABSTRACT:Vast loess distribution in China, in the loess region a large number of railway lines, extension and private lines built in recent years. During this period, there were many problems such as large deformation, leakage of water, lining cracking etc. surrounding the construction. Therefore, the rational design of supporting structure is the key to the loess tunnel design, which calls for mechanical properties of supporting structure have full knowledge and understanding. As the complexity of the engineering geology and the uncertainty of construction factors, specific study for the supporting structure force characteristics under the large section of loess is little currently. A lot of design confusion has been severely restricted the loess tunnel construction development. Paper combines a loess railway tunnel in construction, advance a systematic in-depth study on the mechanical properties of pipe roof protection system and supporting structure, the interaction between surrounding rock, initial support and secondary lining, the main results are as follows:1) By numerical simulation, for poor geological section of loess tunnel, advance a whole truth three-dimensional simulation of tunnel simulation under the ordinary support (no advance protection measures) and long pipe-shield pre-support. According to the results, analyzed the mechanical properties and support effect of pipe-shield pre-support;2) By numerical simulation, analysis on the supporting structure of loess tunnel, rock stress state and mechanical behavior changes under the different construction time and different stiffness of initial support. Based on the control of rock deformation, give a reasonable proposal for construction time, stiffness of initial support;3) By numerical simulation, for different stiffness ratio between secondary lining and initial support, analyzed the support structure's own force, the interface stress passed between rock, initial support and secondary lining;4) By field monitoring, have the force law of loess tunnel initial support and secondary lining. Loess has a significant rheological property, structure supporting a large part of the force to withstand additional load generated by rock rheology. In addition, the force of supporting structure is not evenly distributed in space symmetry, which should be considered in the design.