Thermo-Hydro-Mechanical Simulation of a Tbm Tunnel in Clay Shale

Abstract

Tunnels in argillaceous weak rock formations such as Opalinus (OPA) shale, exhibit highly complex behavior due to coupled thermal, hydraulic, and mechanical (THM) processes. This study focuses on the New Belchen Tunnel (STB), excavated using a Tunnel Boring Machine (TBM) in faulted OPA shale. Previous field measurements and computational investigations demonstrated a strong relationship between temperature and radial pressure buildup around the tunnel. To address this, we numerically analysis the intermediate and long-term performance of the tunnel by modeling coupled interactions between temperature, pore pressure, and mechanical stress. A two-dimensional plane-strain coupled THM model is developed that captures stress and pore pressure profiles, considering tunnel excavation, stress redistribution, construction-induced heat release, and seasonal temperature fluctuations. The results highlight the importance of thermal expansion differences between the tunnel support and OPA shale, as well as temperature’s critical influence on hydromechanical behavior, for accurate stress and deformation estimation over time. The model shows how exothermic reactions during concreting and seasonal temperature variations contribute to stress redistribution and pore pressure evolution in the soft rock mass. The coupled model effectively captures key THM interactions, illustrating how temperature-induced pore pressure reduces effective stress, potentially triggering fractures and swelling-driven deformation within the excavation-damaged zone (EDZ).

Keywords: Thermo-hydro-mechanical modeling, Deep tunnels, Opalinus clay shale, Ground-Tunnel interaction, Mechanized tunneling