Mechanism and preventive measures of slurry leakage at shield tail brushes under abnormal shutdown condition—A case study

Based on an underwater shield tunnel project,this study introduces the phenomenon of abnormal shutdown and the measures designed to mitigate problems in construction.On the strength of the analysis of the slurry leakage causes during re-tunneling,the mech-anism of slurry leakage induced by jack retraction was studied,and treatment measures of leakage at shield tail brushes were elaborated upon.The results show that the sudden change of stratum leads to an abnormal shutdown,and a sharp increase in the slurry pressure at the shield cut location leads to the slurry penetrating the gap between the outer wall of the shield shell and the soil,increasing the risk of instantaneous breakdown at shield tail brushes.The radial displacement of the outer wall of the segments caused by retractions of three jacks and a single jack along the circumferential direction distinctly shows three regions and four regions,respectively.The radial shrink-age of the outer wall of the segments at the jack retraction position decreases the tightness between the shield tail brushes and the outer wall of the segments.The expansion of the outer wall of the segments at the surrounding position,especially at the lower position,increases the slurry level to the radial shrinkage position of the segments,which increases the risk of slurry leakage.Furthermore,when the shield machine faces an abnormal shutdown,re-tunneling,and assembly of segments,the jack can be gradually retracted from top to bottom.The slurry leakage degree can be observed when retracting,and the corresponding measures can be taken for timely plugging.According to the leakage degree,it can be determined whether to replace the shield tail brushes to reduce the risk of large-scale leakage accidents.