Study On Mechanical Behaviors And Controlling Technology Of Large Deformation In Soft Rock Tunnel

In this paper,the subject investigated is Ma Yakou tunnel,which is one of highway tunnels between Fengjie and Wushan in Chongqing.The highway is one paters of state's key highway from Lanzhou to Hangzhou.To research distribute situation of displacement situation,stress and plastic zone and the stability of tunnel after various excavation programmes and support programmes through monitoring measure on-site and to make same numerical simulations on different excavation and support programmes to soft rock tunnel.In ordel to choice a reasonable excavation and support programmes for this project.In this paper,the research mainly provide to the followingconclusions:â‘ Using the information of on-site monitoring to analyse characteristics of adjacent rock deformate to the soft rock tunnel of large deformation before and after disaster detailly and failure mode of preliminary bracing.The result of analysis indicates that:The deformation of preliminary bracing is largely,highly and lasted for a long time.Thare are more failure modes for preliminary bracing and large scope of rock destruction.It is even larger scope of rock destruction when preliminary bracing is unreasonable support programmes and not timely.â‘¡Expond the basic principles and characteristics of finite difference method. Using the numerical simulation method by FLAC analyse stress and strain characteristics of the tunnel with different excavation programmes in actual projects. The research reported that:It is difference such as the grade and nature of stress concentrated,the scope of a plastic zone and its density,the location and size of deformation with different excavation programmes,that is,different unloading sequence to parts of tunnel rock.It is very effectively to reduce the number of disturbances and timely closure the preliminary bracing in controlling deformation and development of plastic zones in soft rock tunnel.In a word,it is minimumly to deformation and stress relaxation with double-wall pit excavation programme in five excavation programmes. This excavation programme is more suitable for the engineering environment.It is an ideal excavation programme.â‘¢By using numerical simulationc with FLAC analysis stress and strain characteristics of the tunnel with different support programmes in actual projects.The research reported that:It is more satisfactory results to control of sprayed concrete tunnel arch displacement including arch top settlement and lumbar arch convergence with preliminary bracing is Shotcrete-Grouting and Shotcrete and Bolt-Grouting.It is effectively to control Curved-wall convergence and tunnel invert floor lift by filling tunnel invert timely.It is effectively to control the adjacent rock stress relaxe and plastic zone expend by increasing the length of cables.â‘£By discussing the mechanism of action and effectiveness to different exaction and support programmes in soft rock tunnel.Combine the analysis result of on-site monitoring with numerical simulation on the basis of deformation mechanism to further analyse the field of displacement,stress and the distribution of plastic zone and failure modes of preliminary bracing after excavation and support in large deformation of soft rock tunnel.After that,the result of analyse presents the technology programmes to control the large deformation in soft rock tunnel.