A COMPARISON STUDY ON EXCAVATION SEQUENCE OF UNSYMMETRICAL LOADING TUNNEL IN WEAK SURROUNDING ROCK

The present paper studies the deformation control of the soft surrounding rock tunnel caused by different excavation sequences of core-keeping ring cut method. The study is combined with engineering example of Dongtou Mountain tunnel. Firstly, with the tunnel model and various input parameters, the method of MIDAS numerical simulation is employed to analyze and compare the deformation of surrounding rock and maximum principal stress in different stages when the tunnel is under different excavation sequences. Finally the paper analyzes the combination of numerical simulation results and actual monitoring results. The results of the evaluation demonstrate that in the construction of Dongtou Mountain tunnel, the stability and deformation of surrounding rock are better guaranteed when the deeper side of the tunnel is first excavated rather than the shallower side. The reduction degrees of rock positions from large to small are shallow buried in the arch, shallow buried in the arch foot, deep buried in the waist, deep buried in the arch foot and vault in the descending order, respectively. The maximum principal stress decreases obviously in shallow buried side in the arch. Therefore, the better working condition is chosen and the effect of different excavation sequences on the deformation of surrounding rock of the tunnel is shown. The results provide references to the information-oriented construction of tunnel, and the guidance for design and construction of Dongtou Mountain and other tunnels in similar geological condition.