Terrestrial laser scanning-assisted roughness assessment for initial support of railway tunnel

The assessment of initial support roughness is of utmost importance in ensuring waterproofing and structural safety in tunnel projects. However, existing measurement methods and evaluation systems fall short of meeting the requirements of efficiency, accuracy, and coverage for roughness measurement and acceptance procedures. This paper introduces an automated measurement method for the initial support roughness utilizing terrestrial laser scanning. This approach significantly enhances the efficiency, accuracy, and automation level of measuring roughness for initial support. In addition, the paper proposes evaluation indicators, such as average deviation, root mean square deviation, and three-dimensional chord ratio, to assess the overall and local roughness of initial support. By extending the assessment of roughness from two-dimensional to three-dimensional, this study improves the accuracy, comprehensiveness, and richness of roughness evaluation. Experimental validation confirms the accuracy and applicability of the proposed method. Furthermore, this paper thoroughly examines the effect of different step length values within the detection area on the accuracy and discriminability of the evaluation indicators when assessing the overall roughness of the initial support. Chromatograms are used to visually present and locate roughness in different areas, greatly aiding in the assessment and treatment of surface diseases in initial support.