Effect of wetting-drying-freezing-thawing cycles on the swelling behaviour of the Yanji mudstone

One of the most important characteristics of mudstones is their susceptibility to swelling upon absorption of water, which is influenced by climatic processes. This study investigated the swelling pressure and strain of the Yanji mudstone subjected to wetting-drying (W-D), freezing-thawing (F-T) and wetting-drying-freezing-thawing (W-D-F-T) cycles. The swelling curves were analysed using a simulation of the logistic function, and the coefficient of initial swelling (C-is), coefficient of primary swelling (C-ps), coefficient of secondary swelling (C-ss), and ultimate swell were derived from the mathematical simulation. The results show that the cyclic treatments can significantly influence the swelling kinetics and ultimate swell. As the number of treatment cycles increases, C-is increases and then decreases due to the competition between the increasing permeability and the decreasing swelling potential induced by the propagation of cracks and large voids, while C-ps and C-ss decrease because of the compaction and contraction of the aggregates after cyclic treatments. The ultimate swelling pressure and ultimate swelling strain decrease with increasing treatment cycles and the relationships among these parameters were also established, allowing the ultimate swelling pressure and strain of the Yanji mudstone under the full range of seasonal variation to be predicted.