The Control Technology In Shallow Unsymmetrical Loading Tunnel Of Soft Surrounding Rock

During tunnel construction, the unsymmetrical loading phenomenon of shallow tunnel caused by the surface slope makes the asymmetry of stress and deformation of supporting structure in the process of tunnel excavation, which can cause serious phenomenon such as collapse, roof caving which affecting the stability of surrounding rock.On the background of chenjiawan tunnel which belongs to the loushao railway reconstruction project, this paper analysis the stability of weak surrounding rock of shallow unsymmetrical loading tunnel with the strength reduction method and the catastrophe theory.According to the measured data of chenjiawan tunnel, using the BMP system to inverse the physical parameters of surrounding rock, and refer to the existing railway tunnel design specification, giving the final physical parameters of surrounding rock.On the base of the physical parameters of surrounding rock that already have,using numerical simulation of the finite element strength reduction method to analysis the plastic zone tendency of surrounding rock with the change of the strength reduction factor, combining with the catastrophe theory, finding the potential failure surface of surrounding rock, and given the typical location of the critical reduction factor and the displacement value. The analysis results show that the potential failure surface of shallow unsymmetrical tunnel in weak rock are different form the assumed potential failure surface that present code of railway and highway that given, the damage type of surrounding rock is not just slips from top to bottom, development of plastic zone through to the surface on the shallow side of arch also affects the force of the supporting structure.Under the condition of different lateral slope and different properties of rock mass to numerically simulate shallow unsymmetrical tunnel, using the research methods, analysis the influence of different lateral slope and different properties ofrock mass to the stability of surrounding rock, comparing the critical reduction factor of typical surrounding rock location. The results show that with the increase of slope,the potential failure surface of surrounding rock appeared early, the stability of surrounding rock is decrease; With the level of surrounding rock increased, the potential failure surface appeared late or even don’t appear, the stability of surrounding rock increase.Using the finite element software to optimize the parameters of step length and step height in the three-step construction methods, by comparing the influence of different step height and step length in the tunnel structure deformation, internal force of supporting structure and the effect of plastic zone of surrounding rock, determining reasonable step height and step length.Finally, given improved measures of the corresponding construction from the aspects of advancing support, surface subsidence control, etc., so that it can gives reference to the similar engineering.