Cross-section Measurement And Deformation Analysis Of Tunnel Based On 3D Laser Scanning

With the increasing economic strength and vast territory,the number of tunnel projects is the largest in the world,and the scale is also the largest in the world.With the rapid growth of science,technology and economic strength,the number of tunnels is still increasing rapidly.Tunnel engineering is ubiquitous,involving high-speed rail,highway,urban rail transit and almost all other areas of transport,can be said to have mastered the country’s economic lifeline.Due to the influence of blasting,the settlement and deformation of the tunnel are very large during the construction period.It needs to be monitored to ensure the safe operation of the project.The traditional tunnel measurement method is to set up discrete monitoring points first,and then to monitor these discrete points artificially and periodically for deformation monitoring.This method can only represent the deformation of the whole tunnel by local individual points,and can not describe the details of the tunnel environment.It is inefficient and labor-intensive.As a new technology,three-dimensional laser scanning has the advantages of high efficiency,high precision,comprehensive information and no contact with the measured object.It is very effective to apply the three-dimensional laser scanning to tunnel measurement to realize three-dimensional model reconstruction,section measurement and deformation analysis.In this paper,a tunnel project in Baoji,Shaanxi Province,is used to measure the cross-section of the tunnel and analyze the deformation of the tunnel through the point cloud data obtained by three-dimensional laser scanning.In this paper,the technical principle of three-dimensional laser scanning system is studied.Aiming at the special environment of narrow tunnel,the scanning modeling accuracy is analyzed and experimented,and a set of high-efficiency data acquisition method based on three-dimensional laser scanning is sorted out.In the whole step,a new scanning scheme is proposed to collect field data,followed by data pre-processing,including point cloud stitching,point cloud denoising,point cloud thinning,coordinate system one,and RANSAC algorithm is introduced to fit the central axis.The vertical cylinder method is proposed to obtain the cross-section points,and the cross-section points are fitted by the curve based on smooth spline.Finally,the complete cross-section map is obtained.In deformation analysis,this paper puts forward the reliability analysisstandard of point cloud fitting accuracy,carries out the overall deformation analysis and local deformation analysis of the tunnel,finds the model error of the gravity center method when the point cloud density is not uniform,and proposes the dichotomy method to eliminate the model error.Finally,the deformation prediction is completed by the improved gray prediction model,which improves the prediction accuracy and reliability.