Calculation Method of Tunnel Over-Under Excavation Based on Point Cloud Data

[Objective] During tunnel construction using the drilling and blasting method, over-excavation and under-excavation issues are always unavoidable. To accurately identify over-under excavation positions and calculate the over-under excavation, an excavation calculation model based on tunnel longitudinal section lines is proposed for this issue. [Method] Point cloud data collected by the 3D laser scanner are pre-processed and the tunnel central axis is extracted. The 3D Delaunay algorithm is applied for curved surface reconstruction of point cloud data, and the transverse and longitudinal section lines are extracted on the curved surface. Over-under excavation areas are calculated by comparing actual cross-section profile lines with theoretical profile lines. Combined with cubic spline curve fitting results of longitudinal section lines, the over-under excavation areas per unit radius are obtained, thereby conducting analysis of the functional relationship between over-under excavation areas and tunnel mileage. [Result & Conclusion] Combining transverse section over-under excavation area with cubic spline curve fitting results of longitudinal section lines, and the method for calculating over-under excavation volumes by integrating along longitudinal section lines, the volume element changes along the tunnel mileage direction in terms of volume element shape are taken into account. The minimum unit of over-under excavation volumes is simplified into a curved prismoid, enabling over-under excavation volume calculation through integration. When applied to the actual tunnel over-under excavation analysis, under identical volume element division condition, the proposed calculation model demonstrates higher calculation accuracy than other calculation methods, while intuitively displaying tunnel over-under excavation situation through chromatograms and contour maps.