Rational permeability coefficient of a permeable lining for composite tunnel lining structures

Various factors influence the tunneling are simplified considering the axial symmetry of the composite lining structure.The analytical expressions for the seepage field,stress,and displacement in the surrounding rock and those for the grouting circle,permeable lining,and ordinary lining are obtained according to the principle of effective stress.The seepage discharge,plastic zone,stress,and displacement around a tunnel affected by the different permeability coefficient ratios between the permeable lining and surrounding rock are studied.The reasonable value of permeability coefficient for the permeable lining are discussed.The results show that the grouting circle controls the tunnel seepage discharge well and has a reasonable permeability coefficient and an optimal radius.The grouting circle controls the plastic zone development in the surrounding rock,i.e.,the thicker the grouting circle,the smaller the plastic zone in the surrounding rock.The tunnel seepage discharge and the effective stress in the grouting circle and lining increase gradually with the increasing of permeability coefficient ratio and tend to be stable after the ratio reaches 0.1.Comprehensive analysis on the factors such as the stability of tunnel seepage discharge,the plastic zone of the surrounding rock and the stress around the tunnel indicates that it is relatively reasonable for the permeability coefficient ratio to be greater than or equal to 0.1.