Objective  The aim was to explore the crack development law of the bund and its effect on the soil shearing strength in the process of moisture dissipating, and in order to provide a scientific basis for revealing the instability mechanism of the bund.

  Method  A typical bund in purple soil sloping farmland was chosen as a case to explore the relationship between crack development and soil shearing strength through simulation experiments to observe the moisture dissipating and crack development process of the bund soil and test the soil’s shearing strength.

  Result  The development of cracks on the bund had obvious stage characteristics, and the area ratio, area perimeter ratio, shape index and fractal dimension of cracks generally showed that they increased rapidly at first, then expanded slowly and tended to be stable. The stages of crack development had different effects on the soil shearing strength and its parameters. The shearing strength, cohesion and internal friction angle of the samples with crack development and no crack development had no significant changes in rapid development phase (31% ≥ w> 22%), while the crack development had a greater impact on the soil shearing strength and cohesion in the slow expansion and basically stable phase (22% ≥ w> 10%). Under the experimental conditions, the soil shearing strength of the samples with crack development was smaller than that of the samples without crack development as a whole, and the soil shearing strength gradually increased with the moisture dissipating. The difference between the shearing strength of the samples with cracks and no crack depended mainly on the soil cohesion. The soil cohesion tended to be a minimum (10.97 kPa) when the mass fraction of moisture content was at about 20% within testing range. The cohesion of the samples with crack development changed slightly with moisture dissipating, while the internal friction angle increased linearly with moisture dissipating. The shearing strength of the cracked soil was mainly affected by the internal friction angle.

  Conclusion  The development of soil cracks in purple soil farmlands has obvious stage characteristics. It has a significant effect on the shearing strength of soil, and it is more obvious when the moisture content is low. The influence of crack development on soil cohesion is greater than that of internal friction angle.