Automated flatness quantization and assessment for tunnel initial support based on terrestrial laser scanning

The quantification and assessment of the surface flatness of the initial tunnel support play a crucial role in the quality acceptance process. Currently, the traditional measurement method predominantly relies on manual inspection, which is time-consuming and susceptible to errors. This study proposes an automated measurement and evaluation method for assessing the flatness of the initial support surface, utilizing terrestrial laser scanning technology. An innovative approach is introduced through the offset elevation datum expressed by a surface function. Furthermore, to address the limitations of the existing standard system's evaluation indicators for initial support surface flatness, five three-dimensional indicators are proposed, focusing on undulation amplitude and uniformity. Field tests are conducted, and the results of the evaluation indicators are presented in the form of color cloud diagrams. The deviation values are calculated by measuring the coordinates of the control points along the tunnel vault axis using a total station, yielding an average error rate of 3.55%. This result verifies the effectiveness and accuracy of the proposed method.