Research On Instability Analysis For Surrounding Rock And Supporting Structure Of Highway Tunnel Based On Risk

The stability of the surrounding rock and supporting structure has always been the topical issue for the tunnelling and underground engineering, but the present study is only on the purely technical level, the study based on risk analysis has not yet been undertaken. In order to make the technical, economic and safety balanced and optimized , this paper discusses how to study the stability proplem of the surrounding rock and supporting structure according to risk management theory at the Baiyun tunnel project,some main works and results are as follows:(1) The stability of surrounding rock and supporting structure is quantificationally analyzed by reliability theory. Firstly, from the perspective of deformation of surrounding rock, a stiffness limit state equation is set up to judge the stability of surrounding rock and supporting structure. Secondly, from the perspective of axial force the bolts bear, a strength limit state equation is set up to judge the stability of surrounding rock and supporting structure. Considering the variability of parameters of rock and supporting structure, through the Monte-Carlo finite element analysis, instability probabilities of the surrounding rock and supporting are gotten at every excavation step.(2) Firstly, the limit state function about the stability of primary supporting structural is established, and then the variabilities of stochastic variable parameters are studied;with monitoring datas at Section ZK42 +330 of Baiyun tunnel, risk analysis was carried out by @ RISK which is a risk software, and we discussed in detail how to determine the instability probability of supporting structure through these datas.(3) Considering a number of tunnel collapse cases and features of design and construction, fault tree about stability of the surrounding rock and supporting structure is prepared.Through expert research ,the probabilities of basic events are gotten;the concept of fuzzy sets is introduced and the probabilities of basic events are replaced by the fuzzy probabilities, with triangular fuzzy uncertainty probability as a substitute;The analysis results of the third and forth chapters are deemed to the conditions probabilities of the fault tree, and then the fault tree fuzzy operations are done, so fuzzy failure probabilities of the top event are gotten. All the basic events affecting the occurrence probability of the top event are vertified by a sensitivity analysis, so we can make sure the effective measures to reduce the instability probability of the surrounding rock and supporting structure.(4) According to the"pressure arch theory"and the statistics of geometrical parameters of the excisting collapse accidents, as well as engineering measures taken after the collapses, then the direct economic losses suffered can be canculated, combined with previous studies of instability probabilities, then we can get the risk.