| The loess is widely distributed in our country,and it has a special engineering property compared with other soil tunnels.After the excavation of loess tunnel,there exists weak self-stability,fast deformation speed and long continuous deformation time,but the locking anchor tube and pipe shed supporting techniques can control the excessive deformation of loess tunnel effectively.At present,the application of anchor pipe and pipe shed mainly relies on the experience of field construction and lacks theoretical guidance.Relying on the Ke Ke Wan Tunnel in Henan Province,this paper investigates the working mechanism of the lock-foot anchor pipes and pipe stalls and the stability of surrounding rock by means of analytic calculation and numerical simulation.Our main research activities are as follows:(1)On the basis of consulting a large number of literature,the current classification standards for the depth and shallow buried of general soil tunnel and loess tunnel are summarized,several commonly used surrounding rock pressures are investigated,and a calculation method of surrounding rock pressure suitable for Colawan Tunnel is obtained combining with the actual situation on site.(2)Based on the Pasternak theory of beam on elastic foundation,a mechanical analysis model of pipe shed is established considering the weakening of the constraint of the unstable section in front of the palm surface.The deformation and stress of pipe shed under the first footage of tunnel excavation were obtained,and the influences of different pipe shed diameters,pipe shed spacing,excavation footage and excavation height on the deformation and stress of pipe shed were analyzed.The analysis results show that the larger the diameter of pipe shed,the more gentle the deformation and internal force curve,but the increase of pipe shed diameter does not significantly improve the pre-support effect of pipe shed.The deformation and stress of pipe shed increase with the increase of footage length,excavation height and circumferential spacing,because the increase of footage length and excavation height will increase the range of surrounding rock pressure,and the increase of circumferential spacing will increase the surrounding rock pressure acting on a single pipe shed.(3)Further,the deformation value of pipe shed at the paw surface under the first excavation advance is taken as the initial displacement value of the next cycle excavation,and considering the constraint effect of the initial support on pipe shed,the overall deformation of pipe shed after the completion of excavation is obtained through iterative calculation.In this paper,the final deformation of four kinds of pipe shed diameters under different excavation penetration,excavation height and circumferential spacing is analyzed.The results show that the pipe shed deformation is mainly concentrated in the early stage of tunnel excavation,and the overall deformation is concave.Considering the actual situation of the Coke Bay Tunnel,it is suggested that the excavation footage should be 0.5m,the excavation height of the upper step should be 3m,the diameter of pipe shed should be 108 mm,and the distance between pipe shed should be 0.4m.(4)Based on the theory of structural mechanics and Pasternak’s theory of beam on elastic foundation,a joint load model of anchor pipe with locking foot and steel arch is established in this paper.The results show that the main deformation and internal force of the lock anchor pipe are concentrated at the end of the lock anchor pipe.Increasing the diameter of the lock anchor pipe can better bear the load of surrounding rock,and its deformation and stress curve distribution is more smooth.However,the large diameter of the lock anchor pipe has greater disturbance to the surrounding rock when drilling.Changing the setting Angle of anchor pipe of lock foot will also affect the stress state of anchor pipe of lock foot.Considering that the change of arch foot of steel arch frame is mainly related to the load at the end of anchor pipe of lock foot,the setting Angle should be set to a larger value.Considering the actual situation of the Coke Bay Tunnel,it is recommended that the diameter of the anchor pipe of the lock foot be 42 mm and the setting Angle be 45°.(5)In this paper,the surface settlement,vault settlement and horizontal convergence of loess tunnel controlled by lock-foot anchor pipe and pipe shed are comprehensively analyzed by numerical simulation.The results show that the locking anchor pipe can effectively control the overall deformation of the tunnel,and the tunnel shed can greatly reduce the vertical deformation of the tunnel,especially at the entrance of the tunnel,the ground settlement and vault settlement are significantly reduced.However,the locking anchor pipe has a better effect than the tunnel shed in controlling the horizontal convergence of the tunnel.(6)In this paper,the influence of different diameter of pipe shed,different diameter of anchor pipe of lock foot,different excavation penetration and whether pipe shed grouting on tunnel deformation is studied.The results show that the large diameter pipe shed and anchor pipe can effectively improve the overall deformation of tunnel surrounding rock,and the increase of excavation footage will lead to the significant increase of surface settlement.Grouting reinforcement mainly improves the ability of controlling the settlement of tunnel vault. |
PDF Full Text Request