Study On Real-time Automatic Monitoring System For Stripping Disease Between Monolithic Concrete Bed And Shield Segments

At present,thousands of monolithic track bed stripping diseases have been found in many operating lines of Chengdu Metro,which have the characteristics of universality and postponement.Different from the diseases that occurred in the muddy soft soil stratum in the past,Chengdu Metro is built in the sand pebble and mudstone stratum with good stability and high strength.Numerical analysis method is used to establish the shield tunnel model of Chengdu Metro under the load of train load.Referring to the calculation results,a scheme is made for the monitoring of wheel load,crack displacement and segment settlement in some sections of Chengdu Metro Line 9,forming a complete monitoring system.(1)Based on the parameters of the 8-car formation A-type metro train used in Chengdu Metro Line 9,the single wheel exciting force is calculated based on the discrete elastic support beam model as 90 k N.The result is substituted to calculate the shield tunnel with different grouting filling rate,and the rule of the segment settlement difference changing with the grouting filling rate is obtained.The maximum segment settlement is obtained as3.007 mm.(2)Through the study of the existing wheel load monitoring methods,the scheme of wheel load monitoring is completed by using the full bridge strain gauge.Considering the actual situation in the tunnel,the number of strain gauges,the installation and the layout position of strain gauge are determined.Based on the calculation of the max bending moment under different spans,the calibration experiment of the rails used in the main line of line 9 is designed.In addition,two experiments with fastening spacing of 0.6m and 0.65 m are designed as the error estimation interval during the site monitoring.(3)According to the characteristics of existing cracks,a two-dimensional joint meter for crack monitoring in this project is designed.It can measure the changes of horizontal and vertical crack displacement in the cross section of the line at the same time.It is convenient to install and can work underwater for a long time,also convenient to analyze the principle in many aspects.(4)The image monitoring method using CCD industrial camera and laser transmitter is designed to monitor the instantaneous settlement of segment under dynamic loads.According to the minimal distance between train bogies,the frame rate of CCD camera used is determined to be at least 30.(5)In order to ensure the accuracy of the monitoring data,the signal transmission mode of 4-20 m A electric current is selected,and a complete dynamic monitoring system during the trial operation of shield tunnel is formed.The scheme is determined for the launch of monitoring work,and provided reference for the monitoring work of similar projects.