Thermo-temporal behavior of a high geothermal tunnel throughout the construction process

Understanding temperature field evolution during construction is essential for thermal control in high-geothermal tunnels. In this study, field monitoring was conducted to obtain the distributions of rock temperature ( T R ), ambient temperature ( T e ), and wind speed ( v w ), while laboratory tests were performed to characterize the temperature-dependent thermal properties of surrounding rock, initial shotcrete, and secondary lining concrete. Based on tunnel ventilation conditions, a transient heat transfer model incorporating the thermo-temporal effect (TTE) of material thermal properties was developed and validated through numerical simulations. The results show: (1) The surrounding rock, initial shotcrete, and secondary lining concrete all exhibit clear temperature-dependent thermal behavior. Their specific heat capacity increases with temperature, while the thermal diffusivity decreases across all materials. In contrast, thermal conductivity shows material-dependent trends, remaining nearly constant in the surrounding rock but increasing significantly in both concrete types. (2) The influences of T R , T e , and W v on peak tunnel temperature, peak heat dissipation, and the temperature difference between the lining center and edge were quantified, revealing distinct response patterns across construction stages. (3) Compared with constant-property models, the proposed TTE model reduces the prediction error of secondary lining temperature by 17.6%. Additionally, a multivariate prediction model was developed, enabling accurate estimation of temperature extremes and heat dissipation demands during construction.