Study On Instabiligy Mechanism And Safety Control Countermeasures Of Disaster Tunnel With Shattered Rock

With the rapid growth of Chinese economic power and the gradual deepening of the Western Development, tunnels traversing high seismic intensity areas, meizoseismal regions and other complicated zones begin to appear enormously. In these aforementioned areas a strong earthquake will cause damage to original mountains, rendering primarily complex mountainous environment even more dangerous. Therefore, technical difficulty encountered in tunnel construction will increase and frequent aftershock will generate risk to tunnels’safety in the western earthquake stricken regions. As a consequence, the prime problem for pertinent scholars is how to effectively prevent and reduce tunnel disasters happening whilst constructing. So researches on key technical problems for western mountainous tunnels with comparatively complex geologic condition after a strong earthquake, especially for soft rock tunnels influenced severely by an earthquake have great theoretical value and realistic meaning.According to the above analysis, this thesis relies on Guanggan Express Way’s tunnel groups witch traverse the activated fault in the 5.12 Wenchuan earthquake---the Longmen Mountain Active Fault Zone. The research object is many loose but not moved and cracked but not collapsed soft rock tunnels after undergoing strong seismic force. The thesis is based on a wide range of gathered documents, in-situ investigations, in-situ experiments, numerical simulation and other synthetical research methods and has deeply analysed the typical characteristic of soft rock mass. Based on the analysis, the unstable failure mode, catastrophic characteristic and unstability mechanism under aftershock, formation mechanism of soft rock tunnels while constructing in cracked rock mass by earthquake is studied. By in-situ practice, the treatment scheme for unstable failure in these tunnels is further discussed and the achieved research progresses are listed below:(1)The soft rock data collection and research analysis offered by the soft rock tunnel in the meizoseismal area revealthe low density of the soft rock, the low elastic wave velocity, the strong permeability, the significant overhead phenomenon and other basic characteristics, as well as the basic characteristics of the original earth stress getting a certain degree of release.(2)The researches of the phenomena about the instability of the shattered rock and soft rock tunnel, combined with on-site monitoring data analysis reveal the main characteristics of the tunnel surrounding rock-support instability under the conditions and theslough-based form, which is the main form of collapses, and ascertain the main places that the shattered soft rock tunnel instability occurred.(3)The statistical researches and field tests,combined with the numerical simulation and theoretical analysis analyzthe factors and the reasons about the instabilityof the shattered soft rock tunnel, and revealthat the softening effect coming from thelow rock strength, the weak self-stability and groundwateris the important reasonfor instability; the improper construction method, support measures, and construction technology which are leaded by anunclear understanding of the characteristics of the rock during processare also the main reasons for the tunnel surrounding rock-support instability.(4)Through the analysis of the typical case that the wall rock-initial supporting structure buckling failure of the shattered soft rock tunnel at the meizoseismal area during the construction of a tunnel under the effect of aftershocks, using the numerical analysis method to analyze the rule of dynamic response of the wall rock-supporting structure under different structural stiffness and different incident direction of the seismic waves, then a conclusion that initial supporting structures of different stiffness have the same rule of internal forces dynamic response. For the tunnels which only have the initial supporting structure, tensile failure of the hance and springing are more likely to happen. It reveals the rules that different size of hollow defects and different positions impact the internal forces of supporting structure under the effect of aftershocks. Earthquake does not make the hollow sphere influence on the lining significantly expanded. But it will make the stress concentration near the hole, reduce the carrying capacity of the supporting structure, and tensile shear or compression shear cracking or buckling failure are more likely to happen. It ascertains the buckling mechanism the shattered soft rock tunnel buckling mechanism during the construction of a tunnel under the effect of aftershocks.(5)Through the factors and the analysis about the shattered soft rock tunnel instability under the static and dynamic actions, the reinforcement principles which bases on advance reinforced, backfill cavity collapse, groundwater discharge and strengthen support, implement the remediation and reinforcement on test section based on the above principles and through combining with site-specific examples of instability. And proved the reliability of the effect, controlled the stability of the rock, and ensured the safety of the construction and the progress of the construction through on-site monitoring.