Innovative Technologies for Monitoring Underground excavations during construction and usage

Tunnel design and excavation are complex problems which requires a lot of studies and data. Starting from the half of the last century, new methods like NATM and ADECO-RS were developed in order to better understand the behaviour of the rock mass and provide proper construction solutions. In particular, all these methods are now used worldwide and focus on the importance of the monitoring during the excavation processes to prevent instability or review the design assumptions. The paper describes the studies carried out on a new technology developed to monitor tunnel deformations during both construction and exercise phases. In particular, two different kinds of instrumentation have been developed using 3D MEMS based sensors. The first one, called CIR-Array, is a chain of nodes (Tunnel Link) equipped with an 3D accelerometer and a thermometer. It provides information about convergence of tunnels sections. The second one, called RAD-Array, is a mixed system that incorporates MEMS nodes (Radial Link) and multi-base extensometer. It provides information about the 3D deformations some meters inside the rock mass. The importance of this kind of instrumentation is related to the rapid and easy installation, to the high frequency of readings (which permits a statistical approach, increasing reliability and efficiency) and to the recording automation. Other important features are the possibility to extend the monitoring after the construction phase during tunnel operations and the relative low cost, if compared with other monitoring systems. The tests were conducted reproducing a theoretical real scale original tunnel shape in our laboratory using a fiber glass rod and then generate known deformation. Sensors have been installed along the section every 0.5 meters. Different deformations have been simulated and, for each one, data of different nature were collected using CIR-Array or RAD-Array, photogrammetry, laser distance meter and topography. Results are compared in order to understand the sensitivity and accuracy of every method and evaluate CIR-Array / RAD – Array solutions. New technologies have also been subjected to reliability test. The aim of this paper is to collect and analyse the preliminary results obtained to highlight the potential application of the technology