Study On Surrounding Rocks Stability Of The Unsymmetrically Loading Tunnel In Geological Bedding Strata Based On The Catastrophe Theory

In nature,layered rock mass is widely distributed.Its anisotropic mechanical properties complicate the stress on tunnels' surrounding rock,which makes surrounding rock's instability and destruction easier to happen in the process of construction under these geological conditions.Instability process of the surrounding rock is a process of non-liner mutation.In order to truly reflect such non-liner mutation during the destruction of surrounding rock,and to master the instability of surrounding rock,it's necessary to combine existing approaches with non-liner theory to process research on stability of surrounding rock.In view of this,this thesis will base on a high-speed railway tunnel construction project in southwest,which cuts through a geological section with unfavorable bedding strata,make a research on the surrounding rock's stability at the very beginning of digging with numerical simulation results and catastrophe theory.And finally,this thesis will make a comparison between the monitoring data and the catastrophe analysis results.Key research results are as follows:(1)With finite element numerical simulation software,this thesis simulates construction process of the target section under 30-degree,45-degree,and 60-degree dip angle of rock stratums,and analyzes surrounding rocks' stress,deformation characteristics and laws on crucial sections when the height of upper step excavation changes from 7m to 9m.The study finds that in the early stage of excavation,amplitude of variation on surrounding rocks' stress and deformation curves under the three dip angles of rock stratum is small.And sharpest change happens 0.8D(D represents tunnel diameter)behind target section.As the excavation is far away from target section,stress and deformation are tending to be stable.In the final stage of excavation,stress and deformation of surrounding rocks on the left and right show asymmetric distribution.Deformation values of the section's vault,left spandrel,and left hance increase as rock stratums' dip angle increases,while right spandrel and right hance decrease.Data values of control points on both sides of target section all increase,except the point on right hance,which firstly increase then decrease.And,the total stress of right hance get its maximum under 45-degree dip angle of rock stratum—2.74 Mpa,which differs by 0.62 Mpa from left hance.(2)Introducing catastrophe theory,this thesis constructs cusp catastrophe model of displacement mode around the tunnel of the target section,adopting such methods as fitting,transformation,and dichotomy to search for the loss of stability.Conclusions can be drawn: under 30-degree,45-degree,and 60-degree dip angle of rock stratums,the loss of stability separately happens 0.8D,0.4D,and 0.4D before target sections.At the same time,stress of surrounding rock,high-affected scope,corresponding vault sedimentation and convergence change around have been confirmed.(3)Combining with actual field conditions,this thesis constructs strict monitoring double-control measurement.By analyzing actual field monitoring data of the target section under 30-degree dip angle of rock stratum,this thesis searches out that surrounding rock velocity is transfinite at the monitoring early stage,trend of instability appears,which verifies the reliability of high-affected scope established according to catastrophe analysis.Vault sedimentation within the high-affected scope and convergence change around all less than the change of catastrophe analysis results,which shows that strengthened support measures adopted after monitoring measurement early-warning control the deformation of surrounding rock,preventing the catastrophe instability of surrounding rock occur.