Evolution law and mechanism of time-delayed spalling in a deep TBM tunnel: A case study

• Published in: Engineering geology 2023-11, Vol.325, p.107309, Article 107309
• Main Authors: Fan, Chen, Feng, Xia-Ting, Fu, Lianjie, Zhao, Jun, Yang, Chengxiang, Yao, Zhibin, Wang, Jun, Wei, Fei
• Format: Article
• Language: English
• Subjects: case studies; Deep TBM tunnel; engineering; engineers; fields; geology; laboratory experimentation; monitoring; Spatial-temporal lag characteristics; surfaces; Time-delayed spalling; Time-dependent splitting fracture
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2023.107309

Time-delayed spalling is proposed to describe the time-dependent splitting failure near the tunnel periphery, which occurs in several days or several months after excavation. This kind of failure has been frequently encountered in a deep TBM tunnel, endangering workers' security and delaying the construction schedule. In this paper, two typical time-delayed spalling cases were systematically introduced, including geological and supporting conditions. Based on field observation, microseismic monitoring and laboratory creep tests, the characteristics and mechanism of time-delayed spalling were investigated. Results showed that time-delayed spalling is a stress-induced time-dependent failure in the vicinity of tunnel surface and appears as flake or plate-like splitting fracture subparallel to the free surface. Although the failure region where time-delayed spalling happened is intact, discontinuities are scattered in the peripheral region. Time-delayed spalling is sensitive to boundary conditions and timely support is an essential method for preventing time-dependent spalling. This research is helpful to the tunnel excavation under similar geological conditions and provides foundations for the prevention of time-delayed spalling. •This paper makes an all-around introduction to the evolution process and mechanism of time-delayed spalling.•The spatial-temporal characteristics of fracture activities of time-delayed spalling were investigated.•The fundamental drivers of time-delayed spalling and the effective prevention method were analysed.