A Photogrammetric System for Tunnel Underbreak and Overbreak Detection

Overbreak and underbreak exerts negative impacts on the peripheral rocks mass around the excavation area, and also affects the construction cost and safety of the underground structures. Although a wide variety of monitoring and computing methods have been developed and applied to detect the tunnel overbreak and underbreak, these methods are constantly doubted for high cost of instruments. In this paper, a photogrammetric system with advantages of accuracy and efficiency is proposed for detection and prevention of tunnel overbreak and underbreak in construction. The proposed system employs an image matching method based on improved Hausdorff distance and image interlace scanning and region growing principles for higher efficient marker recognition, and uses the cubic parametric interpolation spline method to approximate the tunnel section profile. 3-dimensional reconstruction is also integrated in the system for better visualization and volume calculation of underbreak and overbreak. The reliability of the system is verified and successfully implemented in a practical tunnel excavation project, indicating its potential application scenarios in similar projects.