STUDY ON MECHANICAL BEHAVIOURS OF DESIGNING AND CONSTRUCTION FOR CENTER PILLAR OF DOUBLE-ARCHED TUNNEL
连拱隧道中隔墙设计与施工力学行为研究

During the construction of double-arched tunnel, the role of center pillar is of great importance. As a key load-bearing component in double-arched tunnel support, it will influence the stability and construction cost as well as long-term safety of double-arched tunnel. Therefore, the assumption of loads acting on center pillar is of an important consideration in structure design. Through the analysis of the loads acting on center pillar during double-arched tunnel construction procedure, the mechanical model for calculation of practical loads acting on center pillar is set up. By using FLAC, twenty-one kinds of cases for double-arched tunnel in surrounding rock masses with Classes II - IV are studied. The covering depths from 0.5D to 2.0D as well as the three construction methods consisting of three-drift and center-drift coupled with bench cut and full-face methods are considered. Based on analysis of the loaded characteristics of center pillar and magnitude changes of actual loads, the two estimation formulae of loads acting on the center pillar in place of the assumption of the total overburden load for design of center pillar structure are proposed. Furthermore, the optimum construction methods corresponding to the different classes of rock masses are recommended. The achieved results are successfully applied to the modification design of double-arched tunnels of Jinhua--Lishui--Wenzhou Expressway in East China. The results demonstrate that the assumption of proposed loads acting on center pillar is reasonable, and the optimum construction methods can save construction cost and shorten construction period of double-arched tunnel.