The Research On The Base Tunnel Convergence Laser Displacement Rangefinder In Tunnel Convergence Monitoring

In tunnel construction,crown displacement and clearance convergence are the easiest obtained monitoring data,which can most directly reflect the stability of the tunnel after excavation.It’s a must to be tested in tunnel monitoring.Therefore,monitoring on the tunnel deformation appears to be especially important.According to Code for Monitoring Measurement of Urban Rail Transit Engineering,in clearance convergence monitoring,the accuracy of laser displacement sensor shall be no less than 2 mm.However,in the deformation monitoring method of Technical Specification for Monitoring Measurement of Railway Tunnel,laser displacement sensor is not adopted.The asset accuracy for crown settlement and convergence monitoring around the tunnel is from 0.5 to 1.0 mm.It’s hard for ordinary laser displacement sensors to reach this accuracy.In this study,methods such as standardization and calibration are used to improve the accuracy of the laser displacement rangefinder,to make it reach the required accuracy in Technical Specification for Monitoring Measurement of Railway Tunnel.Then it can make further exploration after gaining principles in online monitoring of railway tunnel.In laser ranging,uncontrollable tunnel space environmental factors,such as temperature,humidity,illumination,wind speed,dust concentration,light transmittance,machine’s vibrational frequency etc.,may exert an influence on ranging accuracy.Compared with the study on the influence of environmental factors on measurement accuracy in regular dimensional measurement,the study on that in laser ranging is with more distinguished features: high measurement requirement,uncontrollable environment,unstable environmental parameters and complex influence factors etc.It can be seen that related study in laser ranging is of a great practical significance.The convergence gauge and dial indicator at 0.01 mm accuracy are used together with the laser displacement rangefinder to monitor the convergence deformation of the tunnel at the same time,and discover the specific rules of the influence of main environmental difference factors on its accuracy.In the end,the real time online difference correction will be reached,to realize high precision laser ranging and meet required accuracy.