Optimizing profile line interval for enhanced accuracy in rock joint morphology and shear strength assessments

Abstract

2D profile lines play a critical role in cost-effectively evaluating rock joint properties and shear strength. However, the interval (ΔIL) between these lines significantly impacts roughness and shear strength assessments. A detailed study of 45 joint samples using four statistical measures across 500 different ΔIL values identified a clear line interval effect with two stages: stable and fluctuation-discrete. Further statistical analysis showed a linear relationship between the error bounds of four parameters, shear strength evaluation, and their corresponding maximum ΔIL values, where the gradient k of this linear relationship was influenced by the basic friction angle and normal stress. Accounting for these factors, lower-limit linear models were employed to determine the optimal ΔIL values that met error tolerances (1%–10%) for all metrics and shear strength. The study also explored the consistent size effect on joints regardless of ΔIL changes, revealing three types of size effects based on morphological heterogeneity. Notably, larger joints required generally higher ΔIL to maintain the predefined error limits, suggesting an increased interval for large joint analyses. Consequently, this research provides a basis for determining the optimal ΔIL, improving accuracy in 2D profile line assessments of joint characteristics.

Keywords

• Rock joint
• Roughness
• Shear strength
• Size effect
• Profile line interval effect