Abstract: Effective shear zone of structural plane directly affects its shear performance. Based on the previous analysis of roughness and contact state of structural plane, the quantitative analysis method of effective shear zone of matching structural plane is studied by combining the topographic features scanning and illumination technology. The results show that: (1) Under the light source irradiation, the bright part of the structural surface reflects the effective shear zone during the shearing process. Statistical analysis of 3D bright area percentage (BAP^3D) at different incidence angles shows that with the increase of incident angle, BAP^3D is approximately S-shape. (2) The ratio of effective shear area to total area of structural plane is defined as structural plane effective shear coefficient JEC. By combining with the Patton model, the optimal incident angle of light source was theoretically determined as φ_B=90°–(φ_b+i ) (φ_b represents basic friction angle of structural plane, and i represents average undulating angle of structural plane). At this point the bright area is consistent with the actual effective shear area, the corresponding BAP^3D is effective shear coefficient JEC of the structural plane. (3) Considering the effective shear coefficient, the Barton model is modified and a modified shear mechanical model of structural plane is established. Validation analysis shows that the model can accurately estimate the shear strength of matching structural plane．

Key words: structural plane, illumination technology, optimal incident angle, effective shear zone, effective shear coefficient