Research On Measurement And Analysis Of Subway Tunnel Deformation Based On Laser Scanning

With the rapid development of urban rail transit in China,there are more and more subway lines.In order to ensure the safe and stable operation of the subway,regular deformation monitoring of the subway tunnel is becoming more and more important.Nowadays,laser scanning technology is a new detection technique with high accuracy,high rate and strong initiative in the deformation monitoring of subway tunnel.This method can make up for the shortcomings of the traditional detection method.Therefore,this paper uses the mobile laser scanning technology to scan the tunnel contour.For the obtained data of tunnel laser scanning,how to process the data effectively and apply it to the actual project is the key point of tunnel deformation monitoring.Therefore,this paper mainly studies the processing method and deformation analysis method of the tunnel laser scanning data.This paper first introduces how to use the mobile laser scanning technology to scan the subway tunnel,and puts forward the use of two-dimensional laser scanner to obtain the tunnel section data,and uses the method of radio frequency identification and velocity measurement to obtain the location information of the tunnel section.Then,the tunnel laser scanning data is preprocessed,and the tunnel section data is converted to the tunnel coordinate system in order to compare the two point cloud data when the deformation analysis is convenient.In the process of preprocessing,based on the study of the original point cloud data separation method,the method of extracting the anomaly points by calculating the curvature angle in the support area of the point cloud data is proposed.A set of tunnel section data is selected randomly to verify the effectiveness of the method,and the separation of non-tunnel data can be realized.Secondly,segment Gauss smoothing filter is applied to tunnel surface data.For the pre-processed tunnel laser scanning data,first,a three point B spline curve fitting method based on the main point is proposed for fitting the tunnel section curve.The main points are selected to participate in fitting by calculating the curvature of discrete points,and the local optimization algorithm is proposed to improve the accuracy of curve fitting.Secondly,we study the reverse process of control points in tunnel 3D contour data,the 3D tunnel surface is reconstructed by double three B spline surface fitting method.For the study of deformation method,the whole deformation analysis method is first proposed by combining ellipse fitting.Then combined with the fitting results of the three B spline curves and surfaces,the local deformation analysis of two dimensional sections and 3D surface based on minimum distance projection are proposed.Through experimental data validation,the whole deformation analysis method can effectively determine the convergence of the tunnel section.The local deformation analysis method can determine the concrete convergence or expansion area and the size of the deformation.The analysis error of the local deformation based on MDP is about 2.187 mm,and the error of the 3D surface deformation based on MDP is about 1.84 mm,reaching the expected target.