Characterization of Complete Radial Displacement of Tunnel Using a Horizontal Inclinometer

ABSTRACT Measuring the displacement of a tunnel is prerequisite in evaluating the stability, which also makes it possible to understand the geological condition ahead of the tunnel face. In fact, the displacement of a tunnel occurs before, during and after the excavation. Generally, the measurement is undertaken only behind the face, which allows a certain amount of displacement, the so-called ‘pre-measurement-displacement’. The measured displacement is only a part of the total radial displacement. Therefore, the pre-measurement-displacement should be determined in order to characterize the complete radial displacement of the tunnel. A horizontal inclinometer was used to measure the degree of settlement ahead of the tunnel face at the study site, which was relatively easy to install from the other portal of the tunnel. The results from the measurement of the settlement ahead of the face enabled a complete radial displacement curve to be constructed using a nonlinear regression analysis. It was found that the crown displacement of the tunnel at the study site started to occur at a distance equivalent to three times of the tunnel diameter ahead of the tunnel face. Taking into consideration the complete displacement characteristics, the possible settlement could be about 40% of the total displacement of the tunnel. Based on the complete radial displacement, it was possible to determine the appropriate support characteristics and the time of installation.