Deterioration of flawed sandstone after freeze-thaw treatment considering frost heave pressure
Qi Zhang, Yi Liu, Feng Dai
Abstract
Freeze-thaw (F-T) cycle is receiving increasing attention as a primary threat to the long-term stability of rock engineering in high-elevation regions. In this study, artificial F-T cycle tests are first conducted on pre-flawed sandstone specimens with real-time frost heave pressure (FHP) monitoring, followed by subsequent cyclic loading tests with different maximum stresses. Given the water-ice-sandstone interaction, the evolution process of FHP in flaws can be divided into six phases, i.e. initial, silence, eruption, reduction, second-arising, and dissipation phases. Its magnitude exhibits an exponential decrease with increasing F-T cycle number. The influences of F-T cycles and the maximum stress on the fatigue mechanical characteristics of flawed sandstone are revealed. Subjected to higher F-T cycles and maximum stress, larger irreversible strain and less dissipated energy are accumulated inside flawed sandstone specimens, leading to faster damage and lower fatigue life. The three-stage evolution characters of irreversible strain and dissipated energy are both weakened by repeated F-T treatment, i.e. the prolonged initial and accelerated stages and shortened stable stage. In addition, the repeated F-T cycles diminish the impact of prefabricated flaws on cracking behavior of flawed sandstone specimens, and the fatigue failure pattern changes from shear-dominated failure with a transfixion shear band to tensile-dominated failure with massive tensile cracks as the F-T cycle number increases. Employing the scanning electron microscopy (SEM), the underlying damage mechanisms of flawed rocks under the coupling effect of F-T treatment and cyclic loading are discussed. Finally, an F-T-fatigue damage model is proposed based on FHP evolution and irreversible strain, which possesses distinct physical significance and reasonably quantifies the F-T deterioration and fatigue damage accumulation of flawed rocks.