Comparison of different excavation sequences of large-span unsymmetrical arcade tunnel

Abstract

The stress and deformation of surrounding rock and lining of arcade tunnel are influenced much by different excavation methods and sequences. Especially, when constructing unsymmetrical arcade tunnel, there is a choice of excavating larger or smaller hole first. With Ma Zhai Ding Tunnel project as background, different excavation sequences of large-span unsymmetrical arcade tunnel are simulated with Finite Element Method (FEM). In this paper, the deformation and mechanical state variation of surrounding rock and lining, as well as the unsymmetrical effect due to the asymmetry of the tunnel are studied. The choice of excavation sequences of unsymmetrical arcade tunnel depends on the shape of the ground surface, especially for tunnels shallowly buried. Three kinds of ground surface conditions are considered in this paper: inclined upward, inclined downward, and horizontal. In each type of ground surface, different excavation sequences are simulated: excavating larger hole first, or, excavating smaller hole first. In order to verify the computational results, they are compared with the corresponding measured data. It is found that when excavating the main holes of arcade tunnel, the first excavating one should release more stress. It can cause less amount of final vertical displacement and tensile stress of surrounding rock at the top of the arch. For symmetrical tunnel in the case that the ground surface inclines, it is better to first excavate the hole having thicker earth covering; for unsymmetrical tunnel in the case that the ground surface is horizontal or inclines upward, it is better to excavate lager hole first. For unsymmetrical tunnel in the case that the ground surface inclines downward, the choice of excavating procedure depends on the inclined angle. If the angle is small, the larger hole should be excavated first; otherwise, the smaller hole should be excavated first. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.