Analysis of Cracking Characteristics and Causes of Tunnel Secondary Lining in Interbedded Soft and Hard Rocks
Cracking in the secondary lining are frequently observed during construction of tunnels in interbedded soft and hard rocks.Based on the Yongfeng Tunnel on G544 line under construction,this study analyzes the charac-teristics and causes of secondary lining cracks through on-site testing,mechanical tests,and theoretical analysis.The research results indicate that the secondary lining of the previously excavated tunnel(right tunnel tube)has more cracks than the subsequently excavated tunnel(left tunnel tube),with an asymmetrical distribution mainly con-centrated in the right sidewall and part of the arch waist,predominantly presenting as circumferential cracks.The main reason for secondary lining cracks is the uncoordinated deformation between tilted soft and hard rock layers caused by tunnel excavation under high geostress conditions,resulting in the support structure bearing significant surrounding rock pressure and causing cracks in the secondary lining with design defects.The anisotropy of sur-rounding rock strength and the uneven distribution of groundwater lead to an uneven distribution of secondary lining cracks.The different excavation sequences of the left and right tunnel tubes result in varying degrees of cracking in each tunnel tube.
Tunnel engineeringInterbedded soft and hard surrounding rocksSecondary lining cracksCrack charac-teristicsCause of cracking
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