Effects of remoulding and wetting-drying-freezing-thawing cycles on the pore structures of Yanji mudstones

The pore structure governs the physical and mechanical behaviours of geomaterials, thereby affecting the stability of the infrastructures built on these materials. This study investigated the effects of remoulding and wetting-drying-freezing-thawing (W–D–F–T) cycles on the pore structures of two Yanji mudstones using scanning electronic microscopy (SEM), mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) techniques. The results show that the pores of both the yellow-brown and magenta mudstones become rounder and more disordered after remoulding. Remoulding leads to an increase in the inter-aggregate pore volume and a decrease in the intra-aggregate pore volume because of the exposure of intra-aggregate pores after crushing and the compaction of aggregates during the compression process. The W-D-F-T cycles make the pores of the remoulded yellow-brown mudstone more disordered and flatter and induce an increase in the inter-aggregate pore volume due to the formation of cracks and large pores. Meanwhile, the intra-aggregate pore volume decreases owing to the contraction of aggregates during the drying process. According to the increased inter-aggregate pore volume and decreased intra-aggregate pore volume, an increase in the hydraulic conductivity and a decrease in the shear strength can be expected after remoulding and W-D-F-T cycles, which decrease the stability of mudstone slopes.