基于车载扫描点云的地铁盾构隧道椭圆度分析

Ellipticity Analysis of Subway Shield Tunnel Based on Vehicle Scanning Point Cloud

椭圆度是衡量地铁盾构隧道管片变形的重要指标之一,由于地铁隧道中存在道床管线,导致隧道点云中会存在大量到内壁距离不等的非隧道内壁点,会对椭圆度分析产生影响。对于道床一般利用直通滤波来处理,但轨道超高时处理效果不佳;对于其他附属物通过设置距离阈值方法来处理,但阈值难以预先准确确定。为解决以上问题,依据盾构隧道点云分布特点,提出一种道床点距离阈值剔除、附属物点分级定权剔除算法。结果表明,算法给出的椭圆度MAE为0.085‰,优于直接最小二乘法和RANSAC算法。基于某地铁隧道56个单环隧道的激光点云,对算法性能进行测试,各环椭圆度MAE均值为0.174‰、各环椭圆度标准差均值为0.216‰,较RANSAC算法分别提升19.1%、19.7%,证明该方法能够有效消除地铁隧道点云中非隧道内壁点的影响,椭圆度计算结果具有较好的稳健性。

Ellipticity is an important indicator for measuring the deformation of subway shield tunnel segments.The key to ellipticity analysis is the points on the inner wall of the tunnel.Because there are rail beds and pipelines in the subway tunnel,there are many non-inner wall points in the tunnel point cloud with varying distances from the inner wall,which will affect the analysis of ellipticity.Currently,the commonly used method is to use a straight-through filter to process rail beds,but the effect is not good when there is a large clearance between the rails and the bed.For other attachments,the distance threshold method is used,but there is a difficulty in accurately determining the threshold in advance.This paper proposed a distance threshold elimination method for rail bed points and a grading weighting elimination algorithm for attachment points,based on the distribution characteristics of the shield tunnel point cloud.The method ensured that the points used in ellipticity calculation were all inner wall points,improving the accuracy of subway shield tunnel ellipticity analysis.Simulation data shows that the MAE of ellipticity obtained by the algorithm proposed in this paper is 0.085‰,which is better than the direct least squares method and RANSAC algorithm.Based on laser point clouds of 56 single-ring subway tunnels,the performance of the algorithm is tested,with the average MAE of ellipticity for each ring being 0.174‰and the average standard deviation of ellipticity for each ring being 0.216‰,which is respectively 19.1%and 19.7%higher than the RANSAC algorithm.This demonstrates that the proposed method can effectively eliminate the influence of non-inner wall points in subway tunnel point clouds,and the ellipticity calculation results are robust.