Tunnel design and excavation are complex problems that require in-depth studies and a lot of data. Since the second half of the 20th century, scholars have developed new methods in order to better understand the behaviour of the rock mass and provide appropriate construction solutions. These methods, which are used worldwide, all focus on the importance of monitoring during excavation.

This paper describes studies carried out on a new system developed to monitor tunnel deformations during both construction and operation. We developed two different kinds of instrumentation using 3D Modular Underground Monitoring (MEMS)-based sensors, which provide information about convergence of tunnels sections (CIR-Array) and about 3D deformations a few metres inside the rock mass (RAD-Array). This kind of instrumentation is rapid and easy to install, has a high reading frequency (which permits statistical analysis of the data, thus increasing the reliability and efficiency of the system) and features automated storage and presentation of results. Other important aspects are the possibility to extend the monitoring phase beyond construction, and the economy of the system in comparison with other monitoring systems.

We carried out a series of laboratory tests reproducing a real-scale tunnel shape by means of a fibreglass rod, to which known deformations were applied. Each deformed shape was measured using different techniques along with the CIR-Array or RAD-Array systems; in particular, photogrammetry and topography, which are two techniques commonly used to investigate tunnel deformations in current practice. We compared the results in order to ascertain the sensitivity and accuracy of each method and evaluate the two systems. The aim of this paper is to collate and analyse the results obtained in order to highlight the potential application of the systems.

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