Development of Soil Cracks in Granite Benggang Area Under Wetting-drying Cycles

[Objective] Soil cracks can change soil structure, reduce soil stability, and then accelerate the development of hill collapse. It is of great practical significance to study deeply the fracture development law of granite Benggang area under wetting-drying cycles. [Methods] 7 samples of granite slope soil were taken as the research objects, including the upper part of the slope (US), the middle part of the slope (MS), the lower part of the slope (DS), the red soil layer of wall collapse (RL), the transition layer of wall collapse (TL), the sand layer1 of wall collapse (SL1) and the sand layer2 of wall collapse (SL2). The wetting-drying cycles experiments were carried out with these samples. Combined with digital image processing technology, the soil surface cracks are quantitatively analyzed. [Results] (1) Soil Rsc, Na and soil fragmentation degree in granite Benggang area increase with the decrease of water content, the Rsc, Na, Wa and La of 7 sample points show a gradual decrease with the increase of dry and wet alternating times. (2) The connectivity of cracks in the red soil layer in the upper part of the slope, the middle part of the slope and the sand layer of the wall collapse are significantly positively correlated with the sand content. The Rsc at each sampling point is significantly positively correlated with saturated water content, organic matter content, cation exchange capacity, and free iron oxide content. Sampling points with high clay/sand content show a significant positive correlation with clay/sand content. [Conclusion] There are differences in the development of dry shrinkage cracks in different layers of soil of granite Benggang area, but the development rules are basically three stages: preparation stage, rapid development stage and stable development stage. The cracks of red soil layer on the upper part of the slope of granite soil are mainly shrinkage cracks, and the shrinkage cracks of red soil layer in the lower part of the slope are less.