No abstract

For in-service metro shield tunnels in soft soils, large circular deformations are a major concern because they usually lead to various problems, such as water leakage, joint openings, and concrete cracks. However, the monitoring of circular deformation depends mainly on manual surveying, and the automatic monitoring methods developed in recent years generally have low economic applicability and are not widely implemented. In this study, an automatic and cost-effective system was presented to monitor circular deformation in shield tunnels by using only inclinometers. Experiments were conducted to prove the assumption that each segment can be regarded as a rigid body and to investigate the position of the joint rotation center. Then, a method for monitoring circular deformation based on the rigid body and plane section assumptions was proposed. The joint opening angle, maximum joint opening width, horizontal diameter convergence, and bolt strain were calculated from rotation angles of segments which can be monitored directly by inclinometer. A case study was conducted for a section of a metro shield tunnel with an ongoing pit excavation nearby. The rotation of segments was measured using MEMS inclinometers, and the data were transmitted using ZigBee and general packet radio service (GPRS) wireless communication technology. Results show that the proposed system could be implemented to improve transportation safety in relevant situations and similar conditions.

No abstract

Shield tunnels in soft soils are inevitably subject to large differential settlement during construction and long-term operation, which can lead to various diseases and then impair structural safety and durability. Due to the inefficiency of traditional inspection methods, timely and accurate monitoring methods are necessary to ensure the safe operation and long-term maintenance of tunnels. In this study, a computer vision-based monitoring method for differential settlement of shield tunnels was developed and implemented. The monitoring area is located in an interval tunnel of a subway line in Shanghai during the freezing construction of its side channel. The influence of camera position’s micro-change was considered. The field equipment mainly consists of high-resolution industrial CMOS (complementary metal oxide semiconductor) digital camera sets, LED (light emitting diode) lights and power modules. The differential settlement relative to datum points are obtained and vertical displacement of one ring acquired by total station is compared with the proposed method to verify the feasibility of the monitoring system. The results indicate that the monitoring system is reliable and can be further applied.