Dam leakage potential related to karstification in limestone bedrock: Effects of temperature and stress-induced anisotropy

Abstract

Increased leakage at dam sites due to the dissolution widening of fractures in the sub-surface soluble rocks, i.e., karstification, poses a great threat to the longevity of dam structures. The elevated hydraulic gradient induced by impounded water may significantly accelerate karstification, dramatically increasing leakage by several orders of magnitude. Many previous numerical studies on karstification and leakage at dam sites have overlooked the effects of stress-dependent aperture heterogeneity and anisotropy as well as vertical temperature variations. In this study, we quantified the effects of stress and temperature on leakage dynamics using a coupled thermo-hydro-chemical model incorporating stress-dependent initial aperture fields. Results indicate that stress-induced aperture fields play a primary role in dissolution behaviors compared to the temperature effect. Initial aperture anisotropy controls the preferential penetration directions of dissolution fronts, and anisotropic stress conditions may accelerate breakthrough by up to 40% compared to an isotropic stress condition. The consideration of temperature effect leads to a delayed breakthrough by 10%–16% due to mineral precipitation (chemical control) and elevated fluid viscosity (hydraulic control). The temperature effects are also dependent on the different dissolution pathways controlled by aperture anisotropy and become more pronounced under a low initial rate where breakthrough times may be further delayed by up to 30%. This study offers valuable implications for designing engineering strategies in limestone bedrock dam construction to mitigate leakage hazards and extend structural longevity.