Analysis of the monitored behaviour of a hydraulic tunnel using structural and statistical models

Abstract

The Castelo do Bode hydraulic tunnel is part of the Lisbon water supply system. During its con-struction a monitoring system was implemented, aiming at monitoring the behaviour of the con-crete tunnel lining and of the surrounding rock mass, and including visual inspections. This work presents the monitoring system and introduces the relevant aspects of the analysis of the tunnel lining behaviour, based on the observed structural response to the imposed actions, namely the hydrostatic internal and external pressures, thermal variations, contact pressures and time effects. Two types of models are used: i) a structural model, based on axisymmetric analyt-ical solutions of concentric permeable rings allows setting a reference situation from which it is possible, by comparison, to assess the tunnel’s structural response; ii) a quantitative interpreta-tion model, based on semi-empirical assumptions and error minimization statistical techniques, allows the quantification of the effect of each action on the observed structural response. It is shown that the tunnel’s behaviour observed during its service life can be effectively re-produced using these two approaches. Some considerations are made about the deterioration of the tunnel and the follow-up of its structural response.