Analysis Of Ultimate Bearing Capacity Of Surrounding Rock Under Gripper During The Main Girder TBM Tunneling In Soft Rock Ground

With the rapid development of transportation,water conservancy and other infrastructure construction in China,TBM construction is the best choice for deep and long tunnel under complex geological conditions.During open TBM tunneling through soft layer,because of a shortage of surrounding rock bearing capacity,there will be some issues like the gripper can not support,and surrounding rock instability.To solve this problem,based on the construction of Liaoning northwest water supply project(section two)four contract section,the ultimate bearing capacity of surrounding rock under gripper during the main girder TBM tunneling in soft rock ground is analyzed by numerical simulation,theoretical analysis and engineering verification.The main research contents and results are as follows:(1)Based on the review of large amount of relevant literature,the research achievements of TBM gripper and tunnel surrounding rock interaction of both domestic and overseas are analyzed and summarized.On the whole,the research of TBM tunneling gripper supporting force is currently deficient.The estimation of gripper supporting force is mainly based on the engineering experience or the empirical formula.(2)With the numerical modelling analysis software GDEM which combine both finite element and discrete element,a simulation model is established.Reference existing empirical formula and field test data,calculation of load is identified.Deformation law of surrounding rock under gripper of the main girder TBM is analyzed.The failure mode of surrounding soft rock is identified as general shear failure.Damage area is like a spindle which both ends is small,middle section is large.The spindle end closed to the direction is short,and the spindle end away from the direction is long.(3)According to the failure mode calculated by GDEM,geometric form of fracture face of surrounding rock under gripper is firstly identified,and the stress distribution on the fracture face is analyzed.Then,With the plastic limit equilibrium theory of the rock and soil,the formula of ultimate bearing capacity of surrounding rock under gripper during the main girder TBM tunneling in soft rock ground is derived.(4)Based on the formula,six factors(cohesion and internal friction angle of surrounding soft rock,dip angle of bearing capacity,tunnel radius,width and half central angle of gripper)which can influence the ultimate bearing capacity of the surrounding rock are analyzed.The results show that the shear strength and the contact area of the surrounding rock and gripper are the main influencing factors of the ultimate bearing capacity.(5)Comparing the calculation results of the formula of ultimate bearing capacity of surrounding rock under TBM gripper with the empirical formula and field test data,the security factor(reserves)of bearing capacity is typically between 1.4～2.0.It is comparable to the existing standard.The results show that the developed formula is reasonable.The results of this study have important guiding meaning for the design of TBM gripper and the choice of bearing capacity during TBM tunneling in soft rock ground.