Responses of shield tunnel structure under action of asymmetric thrust
To investigate the effects of asymmetric shield thrust on the mechanical properties of a tunnel structure during small radius curved advancing,a refined finite element model of the shield tunnel in Guifeng Mountain was established.The numerical model employed a damaged plastic constitutive model of concrete considering the nonlinear properties of the segmental lining.The mechanical behavior of the shield tunnel under asymmetric thrust was systematically analyzed using the established numerical model.The results showed that:① the cross-sectional deformation of the segment adjacent to the tail of the shield exhibits ex-trusion deformation towards the heavy load side under asymmetric thrust;②the vertical and transverse bending moments,induced by the asymmetric thrust,on the shield tunnel are much larger than those along the circumferential direction.Additionally,the in-fluence of asymmetric thrust on the circumferential shear force on the tunnel is significant.③ the mechanical state of the shield tunnel along the longitudinal direction is transferred from a whole-section compression state to a compression-bending state thanks to the pressure difference between different thrust jacks.A dramatic concentration of compressive stress occurs at the cir-cumferential joints of segmental rings on the side with larger thrust,particularly at the T-shaped joints.The concrete of the seg-mental lining can easily crack in this area if there are assembly errors in the segments.Additionally,the longitudinal bolts embed-ded in the circumferential joint on the side with smaller thrust will gradually be in tension as the pressure difference among the thrust jacks increases.This keeps some circumferential joints in a state of tension,leading to a potential risk of waterproof failure in the shield tunnel.Therefore,when a shield drives along a curved alignment,the pressure of the different thrust jacks should be adjusted rationally,the assembly quality of the segmental lining should be strictly controlled,and the monitoring of seepage in the joints of the shield tunnel should be enhanced.
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