| China has a vast territory and complex geological conditions.With the implementation of strategic planning such as western development and "One Belt and One Road",tunnel engineering in China is gradually extending to the region with high ground stress in the west.Due to the extremely high ground stress,the soft rock is squeezed seriously and deformed greatly,so the tunnel construction in this area often faces the problem of great deformation,which seriously endangers the safety of supporting structure.This problem has become the bottleneck restricting the normal construction of tunnels.The deformation and failure of surrounding rock is closely related to its stress state,so the premise to solve this problem is to fully understand the unloading mechanical characteristics of soft rock with high in-situ stress caused by excavation,and on this basis,to further clarify the mechanical influence of supporting members on surrounding rock.At the same time,although there are many kinds of soft rocks,their mechanical properties are similar to a certain extent.Therefore,this paper comprehensive use of literature investigation,theoretical analysis,numerical simulation and other research methods,taking a typical soft rock—mudstone tunnel as an example,based on its mechanical properties under high in-situ stress unloading path,the mechanical mechanism of active support—prestressed bolt and high-performance shotcrete was studied,the main conclusions are as follows:1.With literature research,theoretical analysis,taking typical soft rock—mudstone in tunnel for example,the soft rock in triaxial stress characteristics under loading and unloading paths are analyzed,the correction relation between rock strength parameters under high in-situ stress unloading condition and normal condition and the variation of deformation parameters with confining pressure is given,the law of parameter degradation after unloading failure of soft rock is clarified and the mechanical mechanism of active support is revealed based on it.2.By means of literature investigation,theoretical analysis and numerical simulation,the distribution law of compressive stress produced by prestressed bolt in surrounding rock is clarified,the formula for calculating the range of continuous compressive stress produced by the systematic prestressed bolt is obtained,based on the degradation law of mechanical parameters after unloading failure of typical soft rock,the reinforcement mechanism of prestressed bolt to surrounding rock is proved,the supporting effect of prestressed bolt considering the variation of mechanical parameters of surrounding rock is revealed.3.Through literature research and numerical simulation,the effect of shotcrete support and the influence of various parameters on it are revealed,based on the degradation law of mechanical parameters after typical soft rock unloading failure,the supporting mechanics mechanism of shotcrete is proved,the supporting effect of high-performance shotcrete considering the variation of mechanical parameters of surrounding rock is determined.The above research results can provide a certain reference for the design of soft rock tunnel support structure with high in-situ stress. |
