Numerical approach for design of tunnel concrete lining considering effect of fiber reinforcements

Abstract

Concrete lining is usually installed onto shotcrete and steel support in the road tunnels constructed by NATM for the purpose of improvement of the safety factor for unknown phenomena, interior finishing, prevention of water leakage and so on. In a road tunnel with two lanes in Japan, unreinforced concrete lining with a thickness of 30 cm are generally installed regardless of ground condition. These specifications such as thickness, material have not been determined by the calculation, but on the basis of the previous experience. However, recently the occurrence of many cracks on tunnel lining has been found in some road tunnels, and falling of concrete flakes off tunnel lining has become a serious social issue. The prevention of occurrence of cracks on tunnel lining is urgently necessary. One of the solutions to these problems lies in designing tunnel lining theoretically considering the load-carrying capacity of concrete lining and load acting on lining. In the first part of this paper, model experiments using full-scale tunnel concrete lining specimens as shown in Fig. 1 were carried out to clarify the mechanism of collapse of tunnel lining under various kinds of load conditions and the effect of fiber reinforcements. In the second, in order to establish the numerical analysis method that is able to estimate the load-carrying capacity of the tunnel lining and the effect of fiber reinforcements, numerical analysis using FEM considering the development of cracks were carried out and the results were compared with experimental results. Finally, the load-carrying capacity of concrete lining under assumed load conditions and the condition where fiber reinforcements is effective were investigated by FEM analysis through case studies using an actual tunnel figures. The main conclusions obtained from the study are as follows: (1) The structural load-carrying capacity is governed by the sectional failure due to the compressive failure at two more sections and the steel fiber-reinforced concrete (SFRC) has little effect of improving the structural load-carrying capacity under the load condition that the axial force is dominant comparing with that of bending moment. The structural load-carrying capacity is governed by the development of cracks to a certain extent and the SFRC has the effect of improving the structural load-carrying capacity under the loading condition that the bending moment is dominant. (2) FEM analysis considering the occurrence and development of cracks is effective in estimating the load-carrying capacity of tunnel concrete lining and the effect of steel fiber reinforcements. (3) The high-strength concrete rather than the SFRC has the effect of improving the load-carrying capacity of the concrete lining in the case where the tunnel lining is constrained by the soil mass and distributed load act on the whole concrete lining. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.