Long-term deterioration of lining in tunnels

• Stresses in the shotcrete increased with excavation of top heading, bench and invert.
• Load transferred from shotcrete to inner lining with deterioration of shotcrete.
• More rapid load transfer occurred with degradation of cohesion than Young′s modulus.
• Higher bending moment values were observed on the side walls of inner lining.

The long-time degradation of sprayed concrete lining in tunnels was studied using three-dimensional finite element method. During the tunnel excavation the rock deformation and forces in the primary shotcrete lining were observed. The gradual degradation of reinforced shotcrete support over a period of time, its perpetual deterioration under the influence of different physical, chemical, mechanical and biological agents and ground pressure was simulated by reduction of the Young′s modulus, cohesion and friction angle to study the impact of this reduction on the stress distribution and overall stability of the tunnel support system consisting of rock mass, shotcrete and the inner lining. Substantiating shotcrete shell deterioration, the progressive increase of stresses in the inner lining and stress dissipation into the surrounding ground was observed. This provided the possibility to illustrate the main attribute of a particular deterioration process on the basis of the obtained stress distributions of the support elements.