A horizontal convergence monitoring method based on wireless tilt sensors for shield tunnels with straight joints.

Convergence monitoring is of great importance to evaluate the tunnel health condition. This paper introduces a real-time convergence monitoring system of shield tunnel with straight joints based on wireless tilt sensors. Wireless tilt sensors have the advantages of real-time monitoring, flexibility and ease of installation, no interruption to tunnel operation and no demand of inter-visibility. A model of calculating horizontal convergence from tunnel inclination for different diameter tunnels is proposed. Optimal sensor measurement positions are adopted to improve the accuracy of the proposed model. For a shield tunnel with six segments, one wireless sensor is installed at the optimal position of 123° with a maximum relative error of 6%. For a large diameter shield tunnel with ten segments, two wireless tilt sensors installed at the optimal positions of 107° and 143° are obtained. The absolute errors of tunnel horizontal convergence for the two sensors scheme are less than 0.33 mm, which shows the high precision of this scheme. The proposed model is verified for tunnels with asymmetric deformation induced by surcharge load. The proposed model has a maximum relative error of 4.5% in layered ground. A field monitoring case of Shanghai metro tunnel proves the applicability of the proposed method. [ABSTRACT FROM AUTHOR]