Combined effects of solution environment and freeze-thaw cycling on the crack propagation characteristics in sandstone during loading

The failure of ancient rock ruins is affected by freeze-thaw cycles is an important phenomenon in cold region. The degree of freeze-thaw damage be significantly influenced and show an obvious difference during the complex solution environments. However, few studies have been conducted to investigate the combined effects of complex solution environments and freeze-thaw (F-T) cycles to the crack propagation mechanism of loading freeze-thawed sandstones. To study the coupling effects of complex solution environments and freeze-thaw on argillaceous sandstone in ancient ruins, the physical and mechanical properties were investigated through weighing tests, ultrasonic tests, and uniaxial compression tests. The complete failure process of each sample was concurrently monitored using a combination of AE and MS techniques. The crack propagation mechanism at different scales was systematacially investigated through a comparative analysis of microseismic (MS) and acoustic emission (AE) signal characteristics. Additionally, the orthogonal test was designed to effectively analyse the sensitivity of the primary influencing factors to freeze-thawed damage. The findings indicate that:(1) NaCl concentration influences the frost heave force and salt crystallization pressure. While pH levels impact the integrity of the rock structure, leading to significant changes in volume expansion and frost heave force. These aspects are regarded as the main causes of sandstone softening. (2) Compared to the NaCl concentration, varying pH have a more pronounced effect on the freeze-thawed damage. (3) The micro-cracks propagation during loading process is classified into three stages: initial compaction, incubation, and rapid propagation. The macro-cracks propagation is divided into two stages: uniform propagation and rapid propagation. With the increase of NaCl concentration and acidity of solution, the relative duration of incubation in micro-cracks propagation decreased, while the relative duration of uniform propagation in macro-cracks increased. When NaCl concentration and acidity surpass a specific threshold, both the micro-cracks and macro-cracks rapidly propagate from the beginning of the loading process.