软硬互层围岩隧道二次衬砌开裂特征及原因分析

Analysis of Cracking Characteristics and Causes of Tunnel Secondary Lining in Interbedded Soft and Hard Rocks

软硬互层围岩隧道施工期间二次衬砌开裂屡见不鲜。以在建的G544线永丰隧道为依托,通过现场测试、力学试验和理论分析对隧道二次衬砌裂缝特征及开裂原因展开分析。研究结果表明:先行洞(右洞)二次衬砌裂缝数量较后行洞(左洞)多且呈非对称分布,主要聚集在右边墙及部分拱腰处,以环向裂缝为主;二次衬砌开裂主要是由于高地应力环境下隧道开挖使倾斜软硬岩层之间产生不协调变形,从而使支护结构承受较大围岩压力,导致具有设计缺陷的二次衬砌发生开裂;围岩强度的各向异性和地下水的分布不均,致使二次衬砌裂缝分布不均;左、右洞的开挖顺序不同使左、右洞的开裂程度不同。

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.