Automatic multi total station monitoring of a tunnel

Abstract

A tunnel has been under construction for the Lisbon Metro network on the muddy bed of river Tagus. An incident during the jet-grouting for the muddy soil treatment led to flooding of a specific sector of the tunnel and to the need for repair works. Consequently, a decision has been made to monitor with a short time resolution the movements of that sector before, during and after reparation works. This includes the period in which the tunnel will be in use for its regular operation, with commuters using the subway. Given these general conditions with severe inter-visibility limitations, as well as the cost restraints, an automatic monitoring system has been designed and put in place, resorting to four LEICA TC2003 motorised total stations and to the available commercial software, LEICA GeoMoS. The computational procedure of the mentioned software implies a network configuration, in which every total station set up needs a cluster of control points associated with that particular setup in order to perform a space resection. However, it is often difficult to find stable points inside a tunnel under monitoring let alone during repair works. Therefore, to overcome this difficulty, adjustment software - EpochSuite – has been integrated into the monitoring system. Since it runs after the collection of data, the adjustment software makes it possible to perform a more robust and accurate computation of displacement vectors of signalised object points, which represent the tunnel under study. EpochSuite uses a database management approach that is particularly useful in handling many monitoring epochs and uses automatic outlier detection tools. This paper reports on the network configuration, the instrumental setup and the software framework in which the automatic monitoring system actually operates.