Study On The Tunnel Convergence Analysis Based On 3D Laser Scanning

In recent years,the construction scale of tunnel is rapidly increasing with the investment in infrastructure in China.During the excavation of a tunnel,the in situ stresses are redistributed around the excavated area.The redistribution of the stress field results in a tendency for closure of the void created by the excavation.This closure or deformation is generally referred to as convergence when it occurs in a tunneling environment.The magnitude of deformation is related to the rockmass conditions,the magnitude,orientation and ratio of the in situ stresses,the excavation method and rate,and the type and location of installed support.Monitoring tunnel convergence is an integral part of modern design,construction and maintenance.The use of terrestrial laser scanning(TLS)technique in engineering surveys is gaining an increasing interest due to the advantages of non-contact,rapidity,high accuracy and largescale.Millions of accurate 3D points(mm level accuracy)can be delivered by this t echnique with a high point density in a short time(up to 1 million points per second),which makes it a potential technique for obtaining the tunnel profile.A method of tunnel convergence analysis based on 3D laser scanning is proposed in this paper.Frist,the best scan plan for tunnel is designed,in which the points data of the tunnel profile is obtained.Then the cross section data is fitting to the best fit ellipse.With the best fit ellipse,the tunnel convergence is analysed in EFA and LPA.A sensitivity test with synthetic LiDAR profile data was conducted.The results of the sensitivity analysis show that the combined EFA and LPA analysis can accurately measure levels of change within the level of raw accuracy of the LiDAR point cloud.According to the proposed method in this paper,a tunnel is scanned with the scan distance of 8.14 m,using a Leica Scan StationC10 3D laser scanner.Then the convergence analysis of EFA and LPA is conducted with the tunnel profile data.The results indicate that it is a effective method to measure the convergence and expansion areas of the tunnel profile.