Analysis On Twin Arch Tunnel

The twin arch tunnel is a new tunnel form which has such advantages as occupying less land, higher utilization ratio of space, conveniently linking with out lines of tunnel, good suitability to topography and so on. But because the section form of a twin arch tunnel is more complex than one of a single arch tunnel and most twin arch tunnels are located near slopes, the effect of construction process on the stability of the surrounding rock and the slopes more significant. This paper takes a practical twin arch tunnel as an object of study and simulates the construction process by using Finite Element Method(FFM). The focus of analysis is on the stability of the surrounding rock and the slope. The study presents some suggestions for the reasonable design and construction of twin arch tunnels.Firstly, the theory and formula for simulating the tunnel excavation by FEM are introduced and some basic concepts in analysis are presented. The steps of simulation by using ANSYS are described in detail and the validity of simulation are demonstrated through two numerical examples. Then, the problems and limitations in present criteria of the surrounding rock stability in underground engineering are analyzed. For evaluation the stability of tunnel. The safety factor of strength Reduction Method in FEM is introduced, and the basic principle, the yielding criteria and the safety factor are discussed in a deep-going way. Based on these, the plane strain FEM model is established and the effect of the geometrical parameters of slope on the stability of surrounding rock is analyzed. Some influence laws of the distance between the twin arch tunnel and the slope on the stability of the surrounding rock are obtained.The mechanical behaviors of the structure the surrounding rock and the slope are analyzed in detail when adopting two different construction schemes of Three Pilot Holes Method construction. The locations and the development pattern of plasticity regions are investigated, and the safety factor of the tunnel and the potential plane of sliding of slope are determined by use of Strength Reduction Method in FEM. Finally, the three dimensional FEM model is established and the space effect and the development pattern of plasticity region in construction process are analyzed. The results from 3-D FEM are compared with ones from 2-D FEM and the space effect of tunnel excavation is discussed in particular.