The Pinglu Canal is the first canal project that connects rivers to the sea in China since 1949. In its channel bed

mudstone substrate accounts for a high proportion

and part of the channel is dry excavation. A possibility exists that the mudstone strata will disintegrate after being exposed and submerged in water; disintegrated sediment particles will be transported and deposited under the action of water flow

increasing the risk of sediment siltation in the channel. Previous studies on mudstone have focused more on its disintegration characteristics after wet-dry cycling

but less on its re-immersion disintegration under different exposure to air-drying conditions. In this study

we conduct an experiment on the characteristics of mudstone disintegration under the conditions of free immersion using a self-designed device that measures the mudstone exposed to air-drying first and then immersed in water. We focus on a systematic study on the disintegration behaviors of mudstone effected by different time periods of air-drying exposure

different immersion starting instants

and different mudstone sample qualities. Results show the disintegrating process can be divided into three stages－slow disintegration

rapid disintegration and slowing-down disintegration. Mudstone with a longer air-drying exposure time period has a more volume expansion and more cracking in the period of water immersion

and thus has a higher proportion of cumulative disintegration. The average particle size of disintegrated particles is roughly 0.1 mm; the longer air-drying exposure

the more uniform the particle size distribution. Finally

based on the results of mudstone disintegrating at different air-drying time

we have derived a relationship of disintegration time T versus initial water content w

laying a basis for further study of mudstone disintegration and channel siltation mechanism.