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

本文基于考虑应变硬化和应变软化的弹粘塑性模型，采用有限元分析方法，研究了隧道闭口区的长期失稳问题。研究的目的是探讨隧道围岩随时间变化而产生长期失稳的机理。特别关注了由于应变软化和土体的时变特性而引起的地应力的重新分布。在此基础上，提出了一种新的隧道长期失稳评价方法和隧道加固效果评价方法。研究发现，由于土的时变性，作用在隧道衬砌上的土压力是不断变化的。研究还发现，洞穴的存在可能会极大地改变弯矩的分布，并可能导致混凝土开裂。采用既有洞室注浆、锚杆加固、钢拱加固等补救措施，有效地降低了衬砌的截面受力。将计算结果与长期积累的现场测量结果进行了比较和校核。数值分析结果表明，该方法能够较好地模拟隧道长期失稳的机理，并对加固效果进行合理的评价，为现场应用该方法提供了可能。

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