Abstract: Swelling mudstone is one type of special soft rock with a feature of collapsing under drying and wetting cycles. Water immersion tests were conducted in laboratory to examine disintegration behavior of Yanji swelling mudstone under drying and wetting cycles. On the basis of grain size distributions, relative base entropy is proposed to measure the disintegration behavior, and is compared with disintegration ratio. The results show that the groups of different grain sizes change greatly at the initial 3 cycles, and then tend to be stable. With the increase of the number of wetting and drying cycles, the coarse particle content gradually decreases, the fine particle content increases. The particle size changes from the homogeneous to the heterogeneous state, then back to the homogeneous state. There is a significant negative linear relationship between relative base entropy and disintegration ratio. The relative base entropy decreases with the increase of disintegration ratio, implying reasonable and feasible measurement of the grain size distributions using proposed relative base entropy method. The relative base entropy decreases gradually with the increase of the number of drying and wetting cycles, and finally tends to be stable, which agrees well with the changes in the grain size distribution and its derived indexes. Hence, the feasibility and applicability of the proposed approach are verified again, and the relative base entropy can be a new useful index for the quantitative analysis of the disintegration of swelling mudstone. After the excavation of cutting slopes, waterproofing and moisturizing measures should be taken in time to prevent the disintegration and argillitization of swelling mudstone.

Key words: swelling mudstone, drying and wetting cycles, disintegration, grading entropy, disintegration ratio