Evolution characteristics of freeze–thaw-induced sandstone damage under water immersion conditions in Changdu, Tibet, China

Freeze–thaw (F–T) weathering of rocks can degrade macroscopic properties through changes in the pore structure, which may have effects on the triggering mechanism of geological hazards in cold regions. In this study, sandstone specimens of 50 mm diameter and 205 mm height were subjected to immersion and F–t-tests, computed tomography (CT) scanning, and uniaxial compression tests. The CT slice areal porosity was used to divide the bottom portion of specimens into a non-immersed part, water migration transition region, and submerged part. The pore-throat networks of these parts were established, and the distribution characteristics of the pores were investigated. The results showed that sandstone weathering can lead to the deterioration of uniaxial compressive strength, accompanied by a change in pore structure. Specifically, distribution of the specimens' areal porosity changed dramatically along the axial direction under the F–T cycles, however, the heterogeneity coefficient of the submerged part changed slightly. The equivalent radius of dominant pores in the non-immersed part was primarily concentrated within 100 μm, while the counterparts of the transition region and submerged part trend towards 200–400 μm under F–T cycles, with a proportion of these pores showing a 3.2- to 6.4-fold increase. The uniaxial compressive strength of the bottom portion of the specimen infiltrated by water gradually decreased as the F–T cycles progressed. The absolute permeability simulation demonstrated that the permeability of the specimens gradually increased as the number of F–T cycles increased. In this particular case, it was assumed that the region far away from the submerged part with lower water content first froze and blocked the pathway of water migration, profitably affecting the F–T deterioration. The conclusions summarised herein will benefit descriptions of the effect of freeze–thaw action under immersion conditions to guide the prevention of geological engineering disasters in cold regions.