Stability analysis of a fire‐loaded shallow tunnel by means of a thermo‐hydro‐chemo‐mechanical model and discontinuity layout optimization

• Published in: International journal for numerical and analytical methods in geomechanics 2019-11, Vol.43 (16), p.2551-2564
• Main Authors: Sun, Zizheng, Zhang, Yiming, Yuan, Yong, Mang, Herbert A.
• Format: Article
• Language: English
• Subjects: Collapse; Computer simulation; Criteria; Degradation; Discontinuity; discontinuity layout optimization (DLO); Fire load; Fires; fire‐loaded tunnel; Heating; High temperature; Layouts; Limit analysis; Mathematical models; Optimization; Pore pressure; Pore water pressure; Spalling; Stability; Stability analysis; Structural stability; thermo‐hydro‐chemo‐mechanical (THCM) model; Time dependence; tunnel stability; Tunnels
• ISSN: 0363-9061; 1096-9853
• DOI: 10.1002/nag.2991

Summary When subjected to fire loading, shallow tunnels may experience loss of stability. This may result in large deformations and ultimately in local collapse of such structures. High temperature has a great negative influence on tunnels, not only because of thermal‐induced mechanical degradation of the heated lining but also because of thermal spalling in consequence of the build‐up of pore pressure. Thermal spalling causes quick loss of lining sections. Mechanical degradation sole can be simulated by thermo‐mechanical models, while consideration of mechanical degradation and spalling requires thermo‐hydro‐chemo‐mechanical (THCM) models and a spalling criterion. After simulation of both processes, the stability of a tunnel structure can be assessed by means of limit analysis. In this work, at first, a fully coupled THCM model is developed. Then, by using a “stress vs strength” criterion and a boundary shifting strategy, the coupled mechanical degradation and thermal spalling processes are captured, providing time‐dependent and space‐dependent information of the heated lining. Finally, a novel numerical approach, termed discontinuity layout optimization (DLO), is applied to quantify the stability of the tunnel structure with the help of a factor of safety. The proposed numerical procedure is used to conduct numerical studies with, as well as without, consideration of spalling. The results show that spalling has a great impact on the stability of the tunnel. It reduces the thickness of the lining section and accelerates the heating process of the inner concrete.