A Method to Monitor the Circular Deformation of Metro Shield Tunnels in Soft Soils

Abstract

With regard to the metro shield tunnels in soft soils, large circular deformation, such as large longitudinal joint opening and horizontal diameter convergence, is a main cause of water leakage and is detrimental in tunnel operation. Implementing the circular deformation monitoring system contributes to the safe operation and longterm maintenance of tunnels. Although there are many ways to obtain deformation information, measuring inclination of segments is one of the most effective ways, and it is convenient to derive the deformation from the inclination data. A real-time monitoring system using wireless sensor network for circular deformation monitoring has been developed and deployed in an section tunnel of Shanghai metro line 13. The monitoring section is between West Nanjing Road and Natural Museum Station and characterized by densely surrounding buildings and nearby large foundation pit excavation. Under the above project background, the field monitoring data are analyzed and presented to evaluate the circular deformation. Based on compatibility of deformation, the simplified formulas are proposed to derive the horizontal diameter convergence using the inclination variation of four lining segments. Data acquired through total station is compared with the proposed method to verify the accuracy of the monitoring system. The results indicate that the monitoring system is reliable, reasonable and can be further applied, and the difference between proposed method and manual data is in an allowable variation range