Near real-time circular tunnel shield segment assembly quality inspection using point cloud data: A case study

This paper introduces a near real-time digital method of circular tunnel shield segment assembly quality inspection using point cloud data (PCD) since the conventional manual inspection is untimely and incomplete for a segment assembly process. A three-dimensional (3D) laser scanner is used to capture the geometry information of newly assembled segment-rings via segment-ring PCD (srPCD). With a focus on dislocation and deformation, customized algorithms for segment-rings are proposed, including srPCD pre-processing, segment seam PCD extraction and dislocation and deformation calculation. The dislocation between adjacent segments within one ring and that between adjacent rings as well as the single ring ovality are inspected forthwith. A particular srPCD calculation software is developed based on the proposed algorithms and is implemented in a case study of a practical shield tunnel project. The inspection results validate the effectiveness of the proposed digital method and its advantages over the traditional way, signifying that the dislocation between adjacent rings is most likely to overrun during the assembly process. The error status and variation tendency of the segment-ring dislocation and deformation can also be observed on the srPCDs from progressive measurements when the segment-rings are supported by the shield shell. These show the benefits of the proposed method for shield tunnel construction quality management.