Establishment of evaluating method for remedial works against long-term instability of tunnels due to deterioration of surrounding ground

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In this research, based on elasto-viscoplastic model with strain hardening and strain softening, finite element analyses were conducted to investigate the long-tem instability of tunnel in shuttered zone. The purpose of the research is to investigate the mechanism of the long-tem instability of the tunnel due to the time dependent behavior of surrounding ground. Particular attention has been paid to the redistribution of the stress within the ground due to the strain softening and the time dependent behaviors of soils. From the analysis, a new approach for assessing the long-term instability of tunnel and the effectiveness of the remedial work carried out for the tunnel was proposed. It is found that due to the time dependent behavior of the ground, the earth pressure acting on the tunnel lining changes constantly. It is also found that the existence of a cave may greatly change the distribution of the moment and may lead to the cracking of concrete. The remedial work, that is, the injection of mortar into existed cave, rock bolts and steel arching are found to be very effective in reducing the section force of lining. The calculated results are compared and checked with the results obtained from field measurements accumulated in a long period. It is found from the numerical analysis conducted in this research is capable of simulating the mechanism of long-term instability of tunnel and evaluating the effectiveness of the remedial works to a reasonable accuracy, by which it is possible to apply the method to field projects