Desiccation and cracking behaviour of clay layer from slurry state 1 under wetting-drying cycles 2 3

1 Laboratory tests were conducted to investigate the effect of wetting-drying (W-D) 2 cycles on the initiation and evolution of cracks in clay layer. Four identical slurry 3 specimens were prepared and subjected to five subsequent W-D cycles. The water 4 evaporation, surface cracks evolution and structure evolution during the W-D cycles 5 were monitored. The effect of W-D cycles on the geometric characteristics of crack 6 patterns was analyzed by image processing. The results show that the desiccation and 7 cracking behaviour was significantly affected by the applied W-D cycles: the 8 measured cracking water content θ c , surface crack ratio R sc and final thickness h f of 9 the specimen increased significantly in the first three W-D cycles and then tended to 10 reach equilibrium; the formed crack patterns after the second W-D cycle were more 11 irregular than that after the first W-D cycle; the increase of surface cracks was 12 accompanied by the decrease of pore volume shrinkage during drying. In addition, it 13 was found that the applied W-D cycles resulted in significant rearrangement of 14 specimen structure: the initially homogeneous and non-aggregated structure was 15 converted to a clear aggregated-structure with obvious inter-aggregate pores after the 16 second W-D cycle; the specimen volume generally increased with increasing cycles 17 due to the aggregation and increased porosity. The image analysis results show that 18 the geometric characteristics of crack pattern were significantly influenced by the 19 W-D cycles, but this influence was reduced after the third cycle. This is consistent 20 with the observations over the experiment, and indicates that the image processing can 21 be used for quantitatively analyzing the W-D cycle dependence of clay desiccation 22 cracking behaviour.