为解决现有超欠挖快速检测方法不能有效适应变截面隧道的问题，提出一种基于图像三维重建技术的变截面大断面隧道超欠挖检测方法。该方法以变截面隧道轴线作为流线、以设计开挖断面作为迹线，通过截面放大系数k表征隧道变截面的特征，构建适用于变截面隧道的曲面计算方程，形成变截面隧道设计开挖轮廓计算算法。依托花江峡谷大桥六枝岸隧道式锚碇工程，布置控制点并采集现场照片，基于图像三维重建技术对隧道锚实际开挖变截面轮廓进行点云重建与三维曲面重建，采用网格射线法对比实际开挖和设计变截面轮廓，计算超欠挖；
以现场实际喷射混凝土量与全站仪测量结果作为参考指标，对变截面超欠挖检测方法的准确性进行验证。研究结果表明： 该方法能够实现对变截面隧道各开挖循环超欠挖的快速、准确检测，检测结果平均相对偏差率仅1.50%，偏差率低于传统检测方法(2.83%)。该方法提升了隧道超欠挖检测方法的适用范围，现场应用效果良好，可为变截面隧道开挖质量控制提供可靠依据。
The existing over- and under-excavation detection methods cannot effectively adapt to variable
tunnel sections. To address this issue, an over- and
under-excavation detection method based on three-dimensional image reconstruction technology is proposed for variable
large cross-sectional tunnels. The tunnel axis serves
as the streamline, and the designed excavation cross-section
acts as the reference line. The variable-section
characteristics of the tunnel are represented by a section enlargement factor k, which is
used to construct a surface calculation equation suitable for such tunnels and
to form a calculation algorithm for the designed excavation contour. The
proposed method was applied to the Liuzhi-side tunnel
anchorage project of the Huajiang Canyon bridge. The control points are
established, and field photographs are collected. The actual excavation
contours of the variable-section tunnel anchorage are
reconstructed as point clouds and three-dimensional
(3D) surfaces using 3D image reconstruction technology. The grid-ray method is then employed to compare the actual excavation with
the designed variable section profiles, enabling the calculation of the over- and under-excavation. The accuracy of the
proposed method is validated by comparing its results with actual sprayed
concrete volumes and total station measurements. The results demonstrate that
the proposed method enables rapid and accurate detection of over- and under-excavation for each excavation
cycle in the variable-section tunnels. The average
relative deviation rate of the detection results is only 1.50%, which is
significantly lower than that of traditional methods (2.83%). The proposed
method expands the applicability of over- and under-excavation detection techniques, demonstrates excellent performance
in field applications, and provides a reliable basis for quality control during
the excavation of variable-section tunnels.
