Abstract: To investigate crack evolution characteristics and strength degradation patterns of expansive soil channel slopes subjected to dry-wet cycles, we conducted cyclic dry-wet tests on expansive soil with varied compactness from a channel in northern Xinjiang. Surface crack parameters were extracted using image processing technology, while shear strength was determined via direct shear testing. The relationship between cohesion and crack rate was analyzed. Our findings indicate that, under cyclic drying and wetting, cohesion decay accelerates with higher compaction, while internal friction angle generally decreases. The increase in crack rate slows as compaction rises. The relative crack area initially increases, followed by a decrease. Finally, we established a relationship between cohesion and surface crack rate through fitting. This enables the calculation of expansive soil’s cohesive force based on its surface crack rate. The research findings provide crucial insights into understanding the instability and failure of expansive soil channel slopes under severe dry-wet fluctuations.

Key words: water delivery channel, expansive soil, wetting-drying cycles, fracture evolution, shear strength