Research On Tunnel Settlement Monitoring Of "Ji-Yun" Section Of Nanjing Metro Line 2 Based On Optical Fiber Sensing Technology

The settlement of the tunnel has an important influence on the safe operation of the subway,and the accurate monitoring of the settlement of the subway tunnel has a positive effect on the safe operation of the subway and the development of the city.Based on reading a large number of documents,this article adopts methods such as on-site investigation,indoor simulation test,on-site monitoring and analysis,etc,use optical fiber testing technology to monitor the settlement of the Nanjing subway tunnel,select the appropriate monitoring optical cable and lay the high slope ratio,and formulate a set of engineering monitoring plans suitable for the subway tunnel settlement monitoring,the accuracy of the subway tunnel settlement monitoring plan is analyzed,the calculation formula of the tunnel settlement is deduced,and the feasibility of the formula is verified.The main findings are as follows:(1)By analyzing the mechanism of tunnel settlement,it is determined that the inducements of tunnel settlement mainly include the influence of train self weight,train vibration,groundwater,construction of surrounding buildings and stratum settlement.Among them,the "Ji Yun" section of Nanjing Metro Line 2 is mainly affected by stratum settlement.(2)According to the different monitoring technology methods involved in the subway tunnel settlement monitoring scheme designed in this paper,2mm polyurethane tightly wrapped strain sensing optical cable is selected as the distributed strain monitoring optical cable,and the weak grating optical cable is innovatively selected as the promotion optical cable.The tunnel settlement calculation formula that can convert the strain value into settlement is derived.(3)The laboratory simulation test shows that when the suspended weight reaches 0.8kg,the optical cable will produce about 5500??,When the suspended weight reaches lkg,the distributed optical cable will produce about 8500??,In the vertical direction,the optical cable will decrease or increase by 20?30?? regardless of falling or rising by 0.1mm,When the vertical direction drops or rises by 1mm,the optical cable will decrease or increase by 250?300??,The vertical settlement is 1.75,3.5 and 5mm,and the corresponding strain data of weak grating optical cable are 420,840 and 1200??respectively.(4)This paper analyzes the monitoring contents of subway tunnel settlement,arranges horizontal optical cables,corrects the influence of segment joint tension on oblique optical cables,and sets the threshold of distributed horizontal optical cables to ±150??,The strain caused by the change of tension of tunnel segment joint is 25?50??,less impact;(5)According to the analysis of engineering monitoring data,the data of the tunnel changes significantly within 340?470m.During the period from July 19 to August 19,the strain of distributed optical cable increases by about 200??,The settlement calculated by the corresponding weak grating monitoring data increases by about 1.5mm.The data comparison shows that the distributed optical cable strain data is consistent with the displacement settlement data calculated by the weak grating optical cable.Figure[70]table[9]reference[72]...