Mechanism Of Cutterhead Jamming In Fault Zone Tunnelling By TBM And Its Applications

Tunnel boring machine(TBM)has been widely used in the constructions of long deep tunnel in China due to its safety,highly efficient and green construction.In TBM construction,it is inevitable to pass through water-rich weak geological bodies such as the fault fracture zone.Because the excavation support method is not flexible enough,the instability and collapse of the tunnel face occur frequently.Due to the extrusion of collapsed surrounding rock,TBM cutterhead is easily jam,which may result in serious losses.This paper focuses on the key scientific problems of ’the interaction mechanism between surrounding rock and TBM cutterhead and the mechanism of cutterhead jamming’.The methods of theoretical analysis,model test,numerical simulation and field test are comprehensively used to analyze the influence mechanism of various factors on the mechanism of cutterhead jamming.The interaction of machine-rock is revealed.The disaster identification method of cutter head jamming is established.Furthermore,the comprehensive prevention and control countermeasures of the jamming has been put forward.Then the application verification was carried out in the project.The main work and innovation results of this study are as follows:(1)The TBM tunneling model test system was developed.Based on the principle of ’machine-soil’ system similarity,a TBM scale model and a fault fracture zone tunneling model test system are developed by using DSUC double shield TBM as prototype machine.The system breaks through the experimental technical problems of integration of tunneling,slag discharge,monitoring and automatic control in the process of TBM miniaturization.The whole process similar simulation of TBM passing through the fault fracture zone could be realized.Taking the TBM cutterhead jamming in the fault fracture zone of the Xujiamaidao-Maidao Tunnel of Qingdao Metro Line 2 as the simulation case,the jamming event was successfully restored.The reliability and accuracy of the test system were verified.It reveals the evolution law of multivariate information such as cutterhead torque,thrust,slag discharge rate,cutterhead earth pressure,shield friction and surrounding rock stress and displacement field in the process of cutterhead jamming.(2)The influence mechanism of multi-factors on TBM cutterhead jamming were revealed.Based on the TBM simulation system,the influence mechanism of several factors on the TBM load and the stress and displacement field of the surrounding rock is studied.The factors include the width of the fault fracture zone,the buried depth of the tunnel,the friction angle of the soil in fault fracture zone,the TBM advancing speed and the cutterhead rotate speed.The identification method of fault fracture zone in TBM tunnels and the disaster evolution law of typical cutterhead jamming are analyzed and summarized.(3)The influence law of the interaction between TBM and surrounding rock was analyzed.With the finite element software ABAQUS,the dynamic simulation of the whole process of TBM tunneling through the fault fracture zone is realized.At the same time,the soil arching effect in front of the excavation,the stress and displacement field of the stratum and the evolution of TBM load with the excavation process are analyzed.(4)The theoretical criterion of TBM cutterhead jamming is established.Based on the results of model test and numerical simulation,the relative slip mode of strata ahead of the excavation face of TBM in the fault fracture zone is analyzed and summarized.Considering the soil arching effect,the ’composite arch-truncated cones’ mechanical model of the loose collapse area ahead of the cutter head is proposed,and the calculation method of the ultimate support force of the excavation face is established.On this basis,the formation mechanism of cutterhead torque is analyzed,and the calculation method of cutterhead torque under the limit state of excavation face and the theoretical criterion of cutterhead jamming machine are proposed.The superiority and accuracy of the limit support force calculation method proposed in this paper are verified by comparing with the existing methods and trapdoor experiments.(5)The comprehensive prevention and control countermeasures of cutterhead jamming were put forward.The risk identification method of cutterhead jamming for TBM over crushing zone construction and the jamming removal method are proposed.Based on the TBM jamming removal case in Yinsong Project in Jilin,the research results are successfully applied.