Modeling and Verification of Early Age Thermal Stress in Second Lining Concrete of NATM Tunnels

Abstract

The objective of this research is to establish proper modeling of FEM simulation for early thermal stress in second lining concrete of NATM tunnels. The proposed model was verified by field measurements. Stresses at the crown and at the sides close to the invert of the second lining were investigated using the established FEM model. First, a simulation scheme was proposed considering thermal behaviors in detail and was sufficiently verified using tunnel monitoring data obtained from a previous study. It was observed that accurate modeling was indispensable for the variation of air temperature and for thermal properties of waterproofing membrane to obtain dependable temperature simulation results. Second, appropriate modeling for several kinds of joints and important inputs related to early thermal stress such as effective Young’s modulus, autogenous shrinkage development, and setting of hardening time were proposed. Simulation results of structural strain and stress were verified by measurement data in a recently constructed tunnel. Slight difference between simulation results and measurement might be partially due to the material model idealizations and due to the structural imperfections in actual structures. From the stress distributions extracted from the simulation re-sults, it was observed that the crown cracks might be non-penetrating cracks and the cracks close to invert might be penetrating cracks.