Abstract: To investigate the influence of the initial structure of uncemented coarse-grained soil on shear zone, visual direct shear tests were conducted on coarse-grained soils with different initial structures.The variation characteristics of shear zone under different normal stresses were obtained, and the relationship between the initial structure of coarse-grained soil and the thickness of shear zone was determined.Image recognition methods were employed to extract quantitative indicators of the initial structure, such as particle roundness, flatness, orientation angle, porosity, and coordination number.The gray correlation method was then used to analyze the contribution of each quantitative indicator to the shear zone thickness.The results show that the initial structure of uncemented coarse-grained soil directly affects the formation and development of shear zones.Among the factors, particle contact relationships dominate the influence on shear zone thickness, followed by particle shape and arrangement.As normal stress increases, the influence of particle shape on shear zones becomes more pronounced.The irregular geometric characteristics of particles are amplified under stress, further affecting the morphology and evolution of shear zone.These findings provide valuable insights for research on the initial structure of coarse-grained soil.