Short term or long term, monitoring is all about detecting changes in position. Projects may last for a few minutes (monitoring the test loading on some item), through periods of some months, up to projects which have been running for several decades.

In all cases, it is critical to set up the monitor system correctly. You only get one chance to get time related data; mess it up and the data is gone forever.

The timescales chosen are also important. Monitoring needs to be carried out over a sufficient period to span beyond any background movements which might occur. In complex cases, there may be a whole series of different factors causing movement, with frequencies ranging from under an hour to over a year. All these can combine to make interpretation of the data very difficult, unless the monitor intervals have been chosen with great care. Sometimes it is even necessary to carry out monitoring of the monitoring, to establish how short term patterns affect the full results.

A new bridge over the Newcastle to Carlisle railway line at the Metrocentre created a difficult monitoring challenge, as some months of piling into very weak ground, together with thrust boring for services, was expected to cause significant movement to the tracks. Reference targets had to be resistant to weather, vibration and to any disturbance caused during track packing operations. With several hundred targets they also needed to be identifiable. The targets were formed up on backing plates which were mounted using a flexible acrylic adhesive. As the illustration shows, they have survived in place for more than seven years.

More details on monitoring are available from the download section.

Long life rail targets road bridge monitor