During the tunneling process,segments of large-diameter shield tunnels often experience uplift,dislocation,and linear deviation.To address these issues,attitude simulations and field tests are conducted on multiple large-diameter shield engineering projects and construction processes.When the shield main machine operates with a lower head or an attitude misaligned with the tunnel,significant upward buoyancy or horizontal misalignment forces occur at the segments after they exit the shield tail.This force can cause regular dislocation,tunnel alignment deviation,segment cracking,segment breakage,or even leakage.The results reveal that the primary causes of regular segment dislocation and tunnel alignment deviation are the barycenter shift of the shield main machine,the floating of the shield tail and rear segments,and excessive attitude adjustments.Analytical results show that shield attitude and tunnel alignment control are primarily influenced by formation properties,buoyancy,shield equipment,segment structure,and construction control.The phenomenon of segment dislocation can be avoided,and segment attitude and alignment can be effectively controlled by rationally optimizing the weight,barycenter,and grouting system of the shield main machine,strengthening the design of the end structure of the segment ring joint and shear,enhancing shield attitude fitting,controlling tunneling parameters,and innovating grouting technology.
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