When the Environment Agency discovered evidence of significant movement in a timber pile retaining wall on the River Hull, the potential consequences were severe. Most of the city of Kingston upon Hull, where the river joins the Humber estuary, is below high tide level. If the wall failed, several nearby properties and a dual carriageway were at immediate risk, and there was also a danger of pollution from nearby oil reclamation storage tanks. The city centre was only two miles away.
Babtie Consultants was called in to evaluate the situation and recognised that the wall could fail at any time. AV Technology was appointed to install a structural monitoring system to warn of any imminent problems while remedial work was planned and executed.
AVT installed a system comprising electrolevel tilt sensors just above high tide level, temperature sensors, and a level meter to record the state of the tide. Readings were sent automatically every 10 minutes to a datalogger, from where they were transmitted by GSM modem to AVT's offices for analysis on a daily basis.
If pre-set levels of movement were reached, a warning siren and a flashing beacon would be triggered, while SMS text messages would be sent to key people at AVT, Babtie and contractor Mowlem. AVT personnel could then access the latest data remotely.
The project entered a critical phase when remedial work began. Mowlem installed temporary steel walings across the front of the timber wall, then drove 20m steel piles into the river bed in front of it. The gap between the steel piles and existing wall was backfilled with stone.
Although movement of the wall triggered several alarms during the course of work, the monitoring system gave all concerned the confidence to continue in the knowledge that there would be adequate warning of impending problems.
AVT senior project manager Neil Parkinson says: 'The key to successful structural monitoring is being able to analyse and interpret large amounts of information and then make intuitive and predictive risk assessment decisions relating to the condition of the structure. Good communication and the ability to work closely with other interested parties are also vital.'