Changes in vertical strain and breakage of gravel mudstone due to wetting and drying cycles coupled with temperature changes in the oedometer test.

This study investigates gravel mudstone's compression and particle breakage characteristics subjected to wetting and drying (W/D) cycles, known as slaking. A modified oedometer apparatus was developed to simulate the W/D cycle coupled with a heating and cooling cycle under different vertical stress conditions. In addition, a needle penetration test was carried out to investigate the penetration resistance of a specimen along the W/D cycles. Oedometer test results indicated that vertical strain from the W/D cycles stabilized once the void ratio approached that of the reconstituted fine-grained state of the material. Additionally, the void reduction induced by each cycle showed a linear relationship with the excess void ratio above the reconstituted state under the given vertical stress condition. Throughout the W/D cycles, the increase in relative particle breakage was limited under higher stress conditions, where the void ratio played a key role in controlling breakage. Penetration resistance increases with increasing particle size and density. The particle size decreases, but the density increases along the W/D cycles. This trade-off increases penetration resistance during the initial W/D cycles due to densification, but limits further improvement in later cycles as particle breakage becomes more dominant.