Cracking characteristics and mechanism of entrance section in asymmetrically-load tunnel with bedded rock mass: A case study of a highway tunnel in southwest China

Abstract

Serious cracks of secondary lining appear at the entrance section of a highway tunnel in southwest China after excavation. The entrance section of the tunnel has geological characteristics of bedded rock mass with inclined structural plane, asymmetrically loaded terrain, shallow buried depth, and soft surrounding rock. This paper aims to explore the cracking mechanism of lining at the entrance section and propose reinforcement measures to prevent the structural damage accordingly. Site investigation was conducted to demonstrate the cracking characteristics (process, distribution, width, and depth) of tunnel lining. Cracks mainly appeared on the interior lining of left arch-haunch and right side-wall, as well as on the exterior lining of right arch-haunch. The deformation of secondary lining in cracking section was monitored and analyzed to explore the deformation characteristics after the appearance of cracking and installation of temporary supporting. Then, a three-dimensional finite difference numerical model based on the actual terrain was built to analyze the spatial mechanical characteristics of the entrance section. A deformation analysis model including four zones of the surrounding rock was used to analyze the cracking mechanism of asymmetrically-loaded tunnel with inclined weak structural plane. Finally, ground reinforcement measures and reversed loading to control deformation of bedded rock mass and tunnel structures are proposed. Investigating the cracking case of the tunnel has significance to the excavation of entrance section in relevant engineering.