Study On The Adaptability Of Double Shield Tbm Tunneling And Its Construction Safety Evalution Under Unfovorable Geological Conditions

Traditional tunnel contruction methods are based on manual excavation,blasting,etc.to break the rock mass,and then transport the slag out of the tunnel,support and lining are carried out according to different surrounding rock conditions.However,in the face of deep tunnels,the traditional mine blasting method will encounter difficulities such as low construction rate,high labor intensity and low security.Correspondingly,the emergence of the tunnel boring machine(TBM)made it possible for the mechanized construction in tunnel.TBM are being applied into more and more tunnel projects,but at the same time,there are more and more problems.As the depth of the tunnel increases,the geological conditions are more and more diversified,and the unfavorable geological conditions will have a great impact on the TBM excavation process,which affects the efficienfy of TBM tunneling,slows down the process of tunnel project and increases the cost.In serious cases,the TBM machine will be stuck in the rock mass and the cutter head or shield machine will be damaged.In this paper,double shield TBM(DS-TBM)is taking as an example and combining with the BBDMP project of water diversion in Bari Babe,Nepal.The tunneling modes of double shield TBM under different geological conditions are analysed,the mechanics response of double shield TBM during tunneling process are deeply studied,numerical model of double shield TBM tunneling process is classified,and the judgement standard of TBM shield jamming in different tunneling modes is proved.The main research outputs and results are as follows:(1)Combining with the previous TBM projects,tunneling modes of double shield TBM under different geological conditions are compared and analysed,the spatial position relationships of TBM components such as front shield,rear shield,gripper shield,pea gravel,segment lining and surrounding rock are studied.(2)The mechanical response of TBM excavation in mudstone and sandstone is analyzed.A fully dynamic construction numerical model of double shield TBM under two different tunneling modes is established based on the consideration of the uneven gap between shield machine and surrounding rock,TBM propulsion parameters(torque and thrust),gripper shield,pea gravel,segment lining,and support provided by gripper shield,etc.The displacement of surrounding rock,the distribution of plastic zone and the internal force of segment lining are discussed in detail.(3)The geometric and mechanical parameters of the joint material model are studied,and the two-dimensional joint slope model is established to verify the validity of this joint model.Based on the developed joints in the Barry fault zone of the BBDMP diversion tunnel in Nepal,a mechanical numerical model of double shield TBM crossing the fault fracture zone is established,and the effects of joint groups on the TBM tunneling with double shields are analyzed.(4)Distribution of LDP curve of surrounding rock in tunnel excavation is analysed,and the interaction mechanism between stratum and TBM is studied based on LDP curve.The necessary conditions and sufficient conditions for judging the shield machine jamming in the double shield TBM excavation process are proposed.The possibility of a shield machine jamming during the tunneling process of the BBDMP diversion tunnel in Nepal is discussed.