| Karst is one of the most common geological hazards in the tunnel construction in southwest China.The interrelationship between the construction of the tunnel in karst region and existing caves have a direct impact on the safety and economic benefits of the tunnel project Therefore it is primary and urgent to tackle with the effect of concealed cave on surrounding rocks when designing and constructing a tunnel.In this paper,through studying the section of tunnel containing concealed karst cave and performing the FLAC3D numerical simulation experiments,the writer analyzes and summarizes the influence laws of single and multiple concealed karst cave on tunnel surrounding rock,and choose a typical karst section to monitor and then verify the conclusions.The main contents and achievements of this paper are as follows:First,combined with the engineering condition,Zhai tunnel has revealed cave and tunnel geological prediction,concealed karst caves on tunnel area were summarized,its distribution mainly in the following categories: tunnel and different distance,the same distance from the concealed karst tunnel,the same position,but the shape of different sizes of concealed karst cave,located in the tunnel in different position of the concealed karst cave,many hidden caves exist in the surrounding tunnel.Second,combined with the theory of rock mechanics analysis of influence factors of concealed karst surrounding rock of the tunnel,and according to the actual situation of German village concealed karst tunnel,different distance,different size,different shape and position as the representative of the numerical simulation analysis of factors.Third,using MIDAS,GTS and FLAC3D numerical simulation software,the influence of single concealed karst cave and multiple concealed karst caves on the surrounding rock of tunnel is studied,and the following conclusions are drawn:1、The blind caves with different distances and sizes are single factor variables: with the increase of the cavern area,the X force and deformation of the vault of the tunnel increase correspondingly,and the force and deformation of the Z decrease gradually.With the increase of the distance between the cave and the tunnel,the stress and deformation of the surrounding rock decrease correspondingly.2、With different high span ratio（i.e.different long axis and short axis ratio）of the concealed karst cave into the single factor variable: the tunnel arch shoulder x to the stress concentration zone,arch shoulder x to large deformation,when the height span ratio increased from 0.5 to 1,X to abutment deformation also increases;when the Gao Kua ratio increased from 1 to 1.5,X to the spandrel arch abutment deformation decreases,Z to stress and deformation to Z with the increase of height span ratio becomes large.3、In different positions of the concealed karst cave into the single factor variables: when the cave in the side wall of tunnel,tunnel x,Z deformation to stress and displacement map for asymmetric pattern;when the cave in the tunnel arch shoulder extension line,the tunnel arch shoulder will be Z to the stress and deformation in Z direction concentrated area.4、When there are concealed karst caves at the top of the tunnel vault and the side wall,there will be a large Z deformation in the vault and sidewall,and there is a z stress concentration zone at the same time.5、When the top and bottom plate below the tunnel roof of concealed karst cave exist at the same time,the vault will have a larger deformation in Z direction,and Z to the stress concentration zone;reverse Z to the stress concentration zone exists to the floor,and deformation in Z direction.6、When there are concealed karst caves at one side of the tunnel wall and the bottom of the slab,there will be a large Z deformation at the side wall,and there is a z stress concentration zone at the same time.The deformation of the Z and the z stress of the floor will be reduced.7、When the tunnel vault and the side wall and the bottom side of the top bottom concealed karst caves exist at the same time,the vault and the side wall will produce larger deformation in Z direction,and Z to the stress concentration area;reduce the floor to the deformation and stress to Z.Fourth,through monitoring and measuring the typical karst section #K21+145 of Dezhai tunnel,this paper verifies the correctness and rationality of the influence law of concealed karst cave on surrounding rock. |
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