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.
Highlights
Among various subway tunnel construction methods, shield-driven tunneling has been widely adopted in soft soils owing to its flexibility, cost-effectiveness, high speed, and small disturbance to the ground surface [1,2,3]
If the segmental rotation is a rigid body rotation, the joint opening angle would be equal to the sum of the rotation angles of the segments on both sides of the joint
H where θ is the joint opening angle; Δopening is the opening value of the joint measured by Δ1, Δ2, and Δ3 under PBM and by Δ4, Δ5, and Δ6 under NBM; Δclosure is the closure value of the joint, measured by Δ4, Δ5, and Δ6 under PBM and by Δ1, Δ2, and Δ3 under NBM; and h is the height of the joint section
Summary
Among various subway tunnel construction methods, shield-driven tunneling has been widely adopted in soft soils owing to its flexibility, cost-effectiveness, high speed, and small disturbance to the ground surface [1,2,3]. There exist many problems with this method such as leakage, concrete cracking and spalling, steel corrosion, and sliding and opening deformation of lining joints, and the occurrence of these conditions worsens with metro operation [7, 8] Almost all of these issues are interrelated and are linked to the tunnel structure deformation [9]. As metro tunnels generally have a shallow depth and are constructed in soft soils, large tunnel deformations may trigger ground settlement and cause damage to the surface structures [13, 14]
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