Thermo-mechanical coupled analysis for tunnel lining with circular openings

Under heavy load condition, tunnel linings are often designed to be quite thick. This leads to the common temperature control problem of mass concrete, whereby cement hydration heat and uneven heat dissipation during concrete pouring can cause lining cracks. Currently, pouring concrete in different areas or increasing the heat dissipation measures in the concrete curing stage are the main measures to alleviate this problem. In this paper, a new type of longitudinal circular opening structure for tunnel linings is proposed. To meet the requirements of bearing capacity, this tunnel lining type can realize effective heat reduction and heat dissipation. Firstly, a field test is conducted to obtain the structural temperature and internal force to verify the rationality of the design. Then, the thermo-mechanical (TM) finite element method is employed to investigate the temperature variations, crack width, and internal force of the steel bar under different circular opening sizes. Meanwhile, the influence of the circular opening size on the heat dissipation performance and bearing capacity of the lining is presented, as well as a method for constructing an optimal circular lining size. The results show that cooling openings can decrease the peak temperature of concrete while simultaneously increasing the cooling efficiency early in the pouring stage. The lower and upper bounds of the circular opening are limited by thermally induced stress and tunnelling-induced stress, respectively. In this research, the reasonable hole size in a thick lining is proven to be effective and safe in the Longdongbao tunnel.