Study On Damage Characteristics And Seismic Countermeasures Of Shield Tunnel Under Fault Movement

With the development of underground structure engineering,shield tunnel structure is inevitably required to cross the fault.Therefore,it is particularly important to study the deformation reaction and mechanics regularity of shield tunnel structure under fault movement.The overall soil-tunnel model is usually adopted for tunnel response analysis under fault movement at present,but the analysis time is relatively long.Now,a quasi-static elastic-plastic analysis method is proposed to improve the computational efficiency and accuracy.Establishing 3D shell-spring finite element model based on secondary development of ABAQUS in Python.Simulating the shield segment by using the reinforced concrete damaged plasticity constitutive model,simulating the stagger jointed bolt with the six degrees nonlinear spring element,simulating the soil-structure interaction with the soil spring and setting up boundary spring to eliminate the boundary effect.Applying the fault displacement on the far end of the soil-spring gradually and analyzing the response and damage rule of tunnel in normal fault,reverse fault and strike-slip fault respectively.Accordingly putting forward a series of seismic countermeasures and its effects are studied.The results are as follows:(1)Under the action of normal fault,the lining tensioned along the axial direction,the lining wall foot is the most prone to tension and compression damage.The axial tensile deformation of the segment is much larger than that of the annular one.Shear deformation occurred in both annular and axial direction.The tensile failure of axial bolts plays a controlling role under normal fault.(2)Under the action of reverse fault,the lining compressed along the axial direction,the lining arch waist is the most prone to tension and compression damage.The axial tensile and shear deformation of the segment are greater than that of annular one.The shear failure of axial bolts plays a controlling role under reverse fault.(3)Under the action of strike-slip fault,the lining bends along the axial direction,the lining arch crown is most prone to tensile and compressive damage.The axial tensile deformation of the segment is much larger than that of the annular one.Shear deformation occurred in both annular and axial direction.The shear failure of axial bolts plays a controlling role under strike-slip fault.(4)Improving the strength grade of bolts have a certain effect on improving the allowable fault displacement of the structure and have the greatest effect on normal fault.It is not obvious to improve the bearing capacity of structure when the concrete strength grade,reinforcement ratio and bolt strength grade are increased.By replacing the soil near the fault with soft soil and improving the strength of bolts,the allowable fault displacement increased by 2-3 times under different fault types.Therefore,this measure has a very obvious effect on the resistance of shield tunnel to fault movement,which can be used as a reference for the seismic countermeasures of shield tunnel under fault movement.