Research On Risk Control And Safe Excavation Of The Shield Tunnel Undercrossing Yellow River

Permeable sand and gravel stratum has the characteristics of large porosity,strong permeability,small cohesion,sensitive formation and high water content,therefore tunneling with shield in such strata may cause a lot of construction technology problems.This paper relies on Lanzhou metro line 1,and studies the shield initiation of sand and gravel stratum,the treatment measures of shield face collapse,the technology of shield cutter detachment,and the technology of cutter-changing.This study can provide reference for the construction of similar project,main results of the study are as follows:(1)According to construction experience and data investigation,this paper studies the control of shield tunneling in strong permeable sand and gravel stratum from the aspects of stratum reinforcement of shield initiation,determination of initial excavation parameters and key process of shield initiation.In addition,this paper uses FLAC3 D to simulate the tunneling parameters in sandy gravel stratum,studies the optimization of tunneling parameters and the control of ground settlement.(2)According to construction experience and data investigation,this paper summarizes the cutter-changing technology of SPB under the condition of permeable sand and undercrossing the Yellow River.(3)With reference to the landslide collapse accident encountered during the construction,the treatment measures for collapse of the face and the prevention methods during follow-up construction are discussed when applying slurry shield construction in water-permeable sand and gravel stratum.(4)This paper summarizes and analyzes the stuck condition of cutter encountered during the construction of Lanzhou Metro Line 1 and that during other constructions of the metro.The treatment measures have been studied and has formed a set of cutter detachment technology for large particle size water-rich sand-gravel stratum.(5)According to the actual construction situation on site,this paper summarizes and analyses other construction faults and treatment measures,such as stagnant discharge of cobble accumulator,failure of gravel crusher and failure of safety door opening and closing,fast wear of cutter head and cutter,etc.