The Surrounding Rock Stability And Support Measures Analysis Of Underground Cavern With Large Cross Section

With the fast development of the economic and technology of China,and as the construction technology of underground engineering improves,the use of underground space is increasingly.In the area with poor geotechnical conditions,more and more tunnels with large cross section and long axis are being built.The differences of surrounding rock deformation due to different excavation methods,the chose of support measures and the chose of the support time are the two main problems of designer and constructor.This paper analysises the feature of surrounding rock deformation due to different excavation methods,different support measures and different support time.The primary work and achievements are as follows:(1)Summarize the common analysis and calculation model of underground cavern at present, evaluate the applicability of each model.Introduce the theory of underground surrounding rockmass stability analysis,plasticity,and the coupling theory of the support and the surrounding rock.(2)Select a shallow underground tunnel with large cross section for the study section,through the establishment of full-face excavation method excavation model,analysis the rock deformation and distribution of plastic zone around the tunnel in circumstances of different footage and different distance between the lining and the working face of the tunnel.Numerical analysis shows that:in shallow tunnel with large cross section excavated by full-face method, the plastic zone of forth type surrounding rock and fifth type surrounding rock are very different.The plastic zone of forth type surrounding rock are mainly in surrounding side wall corner,and in surrounding wall as a whole in fifth type surrounding rock.The the depth of plastic zone in fifth type surrounding rock is also greater than the forth type surrounding rock.In the forth type surrounding rock and fifth type surrounding rock,the vertical deformation was significantly influenced by the excavation footage.(3)A shallow buried large cross-section tunnel which was located in forth type surrounding rock and excavated by two sidewall drift method was chosed as the research object a 3D elastic-plastic excavation supporting model was established.The analysis indicated that: the thickness of the lining has great influence on the distribution of plastic zone of surrounding rock,however little influence on the surrounding rock stress distribution.The support time of the lining has great influence on the distribution of plastic zone and extreme value of surrounding rock.(4)Take the the diversion tunnel with large cross-section of a hydropower station import gradient in southern part of China for example.Analysis the excavation and support process of the import part of the tunnel with 3D numerial simulation methods.Evaluate the excavation and support scheme.The conclusion of the analysis can provide reference for similar projects.