Numerical Analysis On Tunnel Excavation And Support In Soft Rock

At present, finite element method(FEM) is becoming a major tool for the analysis of tunnels. Many research results can be found in the literatures, however, the interfacial properties of rock mass and shotcrete lining have merely been assumed in most numerical studies. Note that the time-dependent interfacial properties are still unknown. At present, empirical methods are generally applied to carry out the support design of rock tunnels, it is simple and cursory and unscientific. The influence of excavating step and excavating length is less considered. Few works pay attention to the time effect.. So it is necessary to study and discuss to tunnel excavation and lining ulteriorly.At first, a elasto-plastic finite element analysis model was applied to simulate the conventional procedure of tunnel excavation and lining with the finite element. By studying the effects of the parameter of lining, attentions are paid to the problems, such as different coefficients of friction, lining thickness, buried depth, lateral pressure coefficient and rock character. The effects of these factors on the axial force, bending moment and displacement of lining are considered. The mechanics of its performance are studied by researching the deformation of excavation, the force of lining and the distribution of axial force. Secondly, the installation time of lining are analyzed. Thirdly, the interaction between the surrounding rock mass and support and a significant time-dependent variation is studied. Fourthly, a elasto-plastic finite element analysis model was applied to simulate the conventional procedure of tunnel excavation and lining. The numerical modelling considered various factors including excavating sequences, excavating step ,excavating length. Finally, a practical project is studied by the finite element analysis method and the calculated results are compared with the measured results. The main research work and results are remarked as follows:(l)The frictional coefficient of interfacial properties has little effect on thedisplacement,but significant effects on the bending moment, axial force of lining. The rational basis is offered for constructing and designing and finite element analysis subsequently.(2)The time effect on the support of the tunnel lining was carefully analysed. So the tunnel should be supported appropriate and timely. Lengthening the time of the support of the tunnel lining has a little effect on the axial force of the circular tunnel, and have a large influence on the lining of U-shaped.(3) The time-dependent behaviours of interfacial properties can be approximated by exponential or hyperbolic functions of time. The results can be used for theory research and engineering design.(4) The numerical modelling considered various factors including opening size, excavating sequences and excavating step and excavating length The numerical modelling showed that it is favorable to the control out of the displacement and the plastic distribution to adopt the appropriate length and the short step of excavation and the axial pull force of the lining. The rational basis is offered for constructing and designing(5) The results for a practical project showed the validity of the model and the numerical method.