Application Of 3D Laser Scanning In Monitoring Convergence Deformation Of Operating Subway Tunnel

With the rapid development of the city,the ground transportation can no longer meet the needs of the city,the emergence of metro rail transit effectively alleviate the pressure of urban traffic.Therefore the development and utilization of underground space has become a top priority in urban construction.With the continuous improvement of shield tunnel technology,automated information construction has become the trend of underground engineering development forward,and monitoring the real-time deformation of the project will also be an integral part of it.Whether using the direct contact method or using the total station method,there are respective shortcomings,such as poor detection effect and large workload.In recent years,the deformation monitoring of urban rail transit tunnels has been greatly improved by the adoption of 3D laser scanning technology.Comparing 3D laser scanning technology with traditional contact monitoring and total station monitoring,its features and advantages include: efficient monitoring,low labor requirements,easy installation,low lighting requirements,no need to arrange monitoring points,large area for data collection and obtaining tunnel tiling maps,etc.Under the premise of improving monitoring efficiency,how to ensure the accuracy of monitoring data will again be the challenge.This paper adopts the construction characteristics of 3D laser scanning technology,fixing the 3D laser scanner on the steel frame platform in the middle of the track trolley,so that the 3D laser scanner can scan a 360 degree panoramic view and collect the point cloud information of the tunnel cross-section structure,and the track trolley is equipped with an odometer that moves the measurement distance to record the forward mileage,so that the 3D space of the tunnel can be restored,which largely improves the field measurement The efficiency of the field measurement is greatly improved.The main contents and results of the study are as follows:(1)According to the principle of moving laser scanning,the errors caused by the operator,the instrument itself and the working environment are analyzed,and the corresponding solutions are given.(2)According to the characteristics of data recorded by odometers,two odometers are installed in the mobile laser scanning system,and the mileage of straight line segment,circular curve segment and transition curve segment is corrected.(3)The algorithm verification of two ellipse fitting methods,quadratic curve and characteristic root,shows that the characteristic root method can achieve better fitting effect in the actual fitting process,and the ellipse fitting will affect the convergence accuracy to some extent because it cannot be accurately fitted.(4)Using 3D laser scanner to scan the whole line of Shanghai metro line 11,by doing comparison with the total station measurement data,the measurement accuracy of 3D laser scanner is verified to meet the metro monitoring requirements.Combined with the actual project,the tunnel ring deformation,diameter convergence,disease,corner and wrong platform are analyzed for the Zhenru-Fengqiao Road interval.