Research On Section Extraction And Deformation Analysis Based On Point Cloud Data Of Subway Tunnel

In recent years,with the acceleration of urbanization in our country,the scale of urban construction is getting bigger and bigger.However,under the influence of limited road land resources,urban transportation is under increasing pressure on the ground.As a result,many cities began to build underground rail transit.Subway tunnel is a narrow and narrow underground space,in the construction and operation process,in order to ensure the safety of the subway tunnel structure to be monitored.Conventional monitoring methods such as Electronic Total Station are greatly affected by the environment and inefficient.With the rapid development of 3D laser scanning technology and the improvement of measurement accuracy,it is widely used in precision engineering measurement,which provides a new and efficient technical method for the deformation monitoring of subway tunnels.In this paper,FARO Focus 3D X330 3D laser scanner is used to obtain the tunnel point cloud data of Shenyang Subway Line 2 from Olympic Sports Center Station to Yingpan Street Station.Using CloudCompare point cloud processing software and Matlab data analysis software to filter and remove noise of metro tunnel point cloud,point cloud extraction and deformation analysis,the main research contents and achievements of this paper are as follows:(1)This paper analyzes the research status of the application of subway tunnel monitoring and 3D laser scanning technology in tunnel monitoring,and establishes the technical route to first extract the central axis of the tunnel,then intercept the point cloud data of the tunnel section according to the central axis,and finally analyze the deformation of the tunnel section.(2)Filter point cloud data of tunnel to denoise preprocessing.In this paper,an effective combination filtering method is proposed:Firstly,the statistical filtering method is used to filter the whole tunnel point cloud and remove the outlier noise points.Based on the Gaussian curvature of the point cloud,the improved mean filter and bilateral filter Method for smoothing.It provides more accurate point cloud data for tunnel section extraction and deformation analysis.(3)Study on Curve Fitting Method of Tunnels.According to the four commonly used method of curve fitting,the least square method is improved by experimental comparative analysis and random sampling consistency algorithm.This method is used as a curve fitting method for extracting the central axis of the tunnel and fitting the deformation contour to the contour line of the tunnel.(4)Extraction of point cloud data of tunnel section.First,we extract the central axis of the tunnel.By analyzing the existing extraction methods and combining with the geometrical characteristics of the tunnel,a method that can fit the axis of the tunnel is proposed.According to the plane orthogonal relation between the tangent vector of the central axis and the tunnel section,the point cloud slice of a certain thickness is taken as the point cloud data of the tunnel section.Through the analysis of the tunnel point cloud slice experiment,the optimum section thickness parameters are selected.(5)Deformation analysis of the tunnel section.The extracted tunnel cross-section point cloud data is projected flatly and fitted to an elliptic curve,and the long and short semi-axes of the fitted ellipse and the design radius are calculated.The deformation analysis of subway tunnel single-phase data,multi-period data and tunneling direction are respectively carried out.Through a series of studies in this paper,we can confirm to some extent that it is feasible to apply 3D laser scanning technology in tunnel monitoring,and provide effective reference for the following research work,which is of great practicability.