| Engineering rock masses are cut by many kinds of structural planes which causes the obvious characteristic of heterogeneity. It is indicated by engineering practice that after excavation in the rock massed cut by structural planes, big displacement, local failure and even the failure of whole tunnel structures are often encountered. To study the failure mechanism of tunnel under the influence of structural planes is deemed to be very important to the mining and under ground engineering practice.Due to the heterogeneity, anisotropy and discontinuity of rock masses, the analytical method is insufficient to solve the complex stability problems of tunnel. Nowadays, the common way to analyze the influence of structural planes on tunnel stability is to use the field monitoring method combined with model tests, or to use the statistical method. Although these methods are very useful to get information of tunnel stability, they can only give out the final results instead of the failure process evolvement. Although model test is the main means of study on the engineering structure failure, the high cost, long periods and difficulties of parameters adjusting in the limited models have consumedly restricted its usage in the stability analysis of tunnel. Another big problem is the difficulties on simulating those disasters triggered by geological and engineering reasons in laboratory. Although many domestic and oversea scholars have done a lot of works on the stability of rock masses, the understanding of failure mechanism of rock mass, especially the progress failure of rock mass under the influence of structural planes is still far from being complete.In this paper, a numerical code called RFPA is used to study the failure and displacement mechanism of tunnel under the influence of structural planes, which is based on the understanding of heterogeneity of rock masses. The constitutive model of this code is based on the damage theory and statistical theory, which'can reflect the progress failure of rock mass vividly. Compared with the traditional loading method used in the study of tunnel stability, a new method called Strength Reduction Method (SRM) is used, by which the degradation and deformation process of rock masses caused by excavation can be closely connected with the geological formation and the tectonic stress. Numerical models that can simulate the deformation, damage and progress failure are established by considering the progress degradation of rock mass. The main contents are as follows:The SRM, which can simulate the gradually degradation phenomena of rock masses during and after excavation, is used in the stability analysis of rock tunnel. The deformation, damage and failure mechanism of tunnel under the unloading condition are analyzed and the reliability of SRM in the stability analysis is evaluated.The deformation and failure characteristics of layered roof of tunnel are analyzed and the influence of thickness of layered formation and lateral pressure coefficient on the failure mechanism is also studied. Meanwhile the failure mode and deformation characteristic of tunnel in dip layered rock mass are analyzed and the applicable condition of the geographical method given by Goodman in 1976 is discussed. The failure mechanism of the vertically stratified rock masses is also studied and the limitations of beam-board theory used nowadays are pointed out.The influence of the fault distribution and fault dip on the stability of tunnel is studied. The influence of fault thickness and tectonic stress on the failure mechanism of tunnel is discussed and an elementary method of judging the failure zone is given out.The failure mechanism of tunnel in rock masses cut by two sets of joints is analyzed. The influence of the attitude of bed of joints, the connectivity of joints and the lateral pressure coefficient on the stability and safety factor are also discussed.By using Lenovo Shenteng 1800 parallel computer, the mechanism of zonal disintegration around deep buried single and twin tunnels in layered formations are analyzed. The occurrence condition of zonal disintegration and the factors that affect it are studied.
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