Concrete is widely used for lining structure in underground facility and unfortunately it is often attacked by coupling effects of external sulfate and triaxial compressive stress transferred from surrounding soil or rock formations. In this text, a model is developed to depict the coupling effects of mechanical loading and external sulfate attack on concrete lining. The total strain is composed of elastic strain and plastic strain characterised by modified Drucker–Prager criterion, and the deterioration of mechanical properties is related to both mechanical damage and chemical damage. The former considers microcracks generation through micromechanical operations, and the latter is defined by the molar concentration of total sulfates in concrete. A simple diffusion equation is deduced from the sulfate ions diffusion-reaction process to depict the distribution of the total sulfates in both solution and solid phase. A relationship between chemical damage and sulfates concentration is established based on experimental results. The proposed model is then implemented into COMSOL multiphysics to analyse the long-term stability of concrete lining subjected to external sulfate attack in a tunnel. The numerical results show that the simulation results match the experimental data.
In geo-engineering applications, the effective thermal properties (ETPs) of cracked rock are strongly dependent on the configuration of the cracks and the thermal properties of the saturating fluid, which differs from that of the rock matrix. In this study, methods for predicting the ETPs of cracked rock are investigated. The effects of various factors such as the crack distribution, the type of saturating fluid and the applied stress on the ETPs are analysed. Formulas for the effective thermal conductivity (ETC) and the effective thermal expansion (ETE) are developed in a discrete form based on the homogenisation method, where the interactions of the cracks in different directions are neglected. To analyse the effects of the crack distribution and the type of saturating fluid on the ETC and the ETE, an example of saturated rock with one family of cracks is considered. The results reveal that the crack distribution has a significant anisotropic effect on both the ETC and the ETE. The difference in the bulk moduli of the rock matrix and the fluid in the cracks also has an important effect on the ETE. The behaviour of the ETC and the ETE of granite at various levels of stress is analysed with triaxial compression tests. The growth of microcracks induced by the applied stresses causes significant anisotropy in both the ETC and the ETE. This study provides insight into the factors that affect the ETC and the ETE and methods to estimate the ETC and the ETE of cracked rock in geo-engineering applications.
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