Thermo-hydro-mechanical behaviour of geothermal energy tunnel in different ground conditions

Abstract

Energy tunnel is attracting increasing attention because it provides an innovative and efficient approach to harvest geothermal energy. Most of the previous studies focused on its thermal performance and little attention was paid to the thermo-hydro-mechanical behaviour during the operation of energy tunnel, such as lining deformation and ground movement. To address this problem, a numerical model that can simulate the coupled thermo-hydro-mechanical behaviour was developed in this study and verified by a field test. Then, comprehensive parametric studies were conducted to investigate the effects of key soil properties and states (i.e. permeability, thermal conductivity, coefficient of thermal expansion (CTE), elastic modulus, Poisson’s ratio and tunnel burial depth) on the mechanical responses of energy tunnel and surrounding soils under cooling. It is found that: (1) CTE and elastic modulus among the above parameters are the most influential parameters for ground settlement and normal stress from soil to lining, respectively; (2) The thermally induced change in normal stress highly depends on the burial depth, with a percentage change of 24% for a shallow tunnel and 5% for a deep tunnel. Based on the guidelines of tunnel management, the thermally induced ground settlement is a more critical aspect than the lining deformation.