Long-term stress monitoring and in-service durability evaluation of a large-span tunnel in squeezing rock

Abstract

The long-term safety and in-service durability of tunnels in squeezing rock are the focus of tunnel management and maintenance. Previous studies mainly focused on the disaster-causing mechanism, prediction method, and control technology of large deformation during the construction of squeezing rock tunnels. So far, only few studies have concentrated on the long-term safety of in-service highway/railway tunnels in squeezing rock tunnels, resulting in unclear long-term mechanical response of tunnel structure and lack of data support for safety evaluation and durability prediction. Therefore, we conducted long-term, real-time, and continuous monitoring on the structural stress of the Lianchengshan Tunnel, which suffered severe large deformation during the construction, and performed a regression analysis on the structural stress by constructing four typical stress-time mathematical models. Subsequently, we evaluated the long-term safety and in-service durability of the tunnel structure based on a stress prediction. The results of our study show that the structural stress of the tunnel is not stabilized during the operation period but fluctuates periodically with an annual cycle. Moreover, the structural stress peak presents an increasing trend with the service life. The rheology of the surrounding rock composed of chlorite schists in Lianchengshan Tunnel is dominated by steady creep and decay creep. Despite a risk of local cracking or damage of concrete before the design service life due to excessive stress at individual positions of the secondary lining, such as the inverted arch, the safety factors of the secondary lining in the early stage (within 30 years) are higher than the threshold of 2.0. This indicates that the early safety of the tunnel structure can achieve the service requirements. The results of our study provide a reference for the long-term safety evaluation and in-service durability prediction of squeezing rock tunnels with high geo-stress.