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News Release from: AV Technology | Subject: Consultancy
Edited by the Manufacturingtalk Editorial
Team on 06 September 2004
Successful Outcome On The River Hull
A combination of modern measurement and communication technology, together with traditional civil engineering techniques, has ensured success in a River Hull flood wall repair.
A combination of modern measurement and communication technology, together with traditional civil engineering techniques, has ensured that a section of old wooden retaining wall along the banks of the River Hull has been safely and successfully repaired, without any danger of flooding or pollution Working closely with main contractor Mowlem and Babtie Consultants, structural monitoring experts AV Technology, have carried out a comprehensive six month monitoring programme to assess the condition of a 50 metre stretch of retaining wall adjacent to Ann Watson Street, less than two miles from the city centre
This article was originally published on Manufacturingtalk on 28 Feb 2007 at 8.00am (UK)
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The tidal River Hull has been an important industrial waterway since mediaeval times and flows for 20 miles from the Driffield Navigation before emptying into the Humber estuary at Kingston on Hull.
In the past few decades, parts of the river infrastructure have fallen into disrepair and the Environment Agency has been keeping a close check on conditions.
Most of the city of Hull lies below high tide level and any breach of defences could have devastating consequences.
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During routine inspections of the banks, it was noticed the timber pile wall at Ann Watson Street showed evidence of significant movement, resulting in the cracking of the reinforced concrete defence wall.
This not only placed several properties and a nearby dual carriageway at risk, but also threatened the danger of serious pollution from oil reclamation storage tanks at adjacent land owned by Rix Petroleum.
Babtie Consultants were called in to evaluate the situation and recognised that the wall could collapse at any time.
Stockport based AV Technology were appointed to install a structural monitoring system to assess the ongoing situation.
This was designed to warn of any imminent problems in the interim period while the work was planned and during the repair phase.
As with many parts of the river bank, ascertaining ownership is extremely difficult and the Environment Agency took it on themselves to fund the work with contributions from the two main interested parties, Hull Borough Council and Rix Petroleum.
AV Technology have considerable expertise in such 'watch and warn' projects.
To measure the movement of the wall, ceramic electro-level tilt sensors were fitted to 16 vertical beams just above high tide level.
For protection and waterproofing, the sensors were mounted inside tough IP67 rated GRP enclosures and fully potted with epoxy resin.
For additional protection, metal cages were fitted around the enclosures.
Temperature sensors were also included in the enclosures.
During the course of a day, the river level can vary by up to five metres and therefore a level meter was also installed so that the system could also record tidal data.
The sensors were then connected back to a multi-channel data logger housed in an adjacent warehouse.
The system has onboard storage capacity for up to 1 million readings and included several automatic alarms which were triggered by pre-calculated levels of movement.
If movement reached 'Warning' level, a siren and flashing amber beacon were activated, while if 'Alarm' level were reached, the siren would be accompanied by a red flashing beacon.
Alarm conditions also initiated SMS text messages to key personnel at AVT, Mowlem and Babtie.
The system operated continuously and readings were taken from all the sensors every 10 minutes.
Data were transmitted back to AVT's offices via a GSM modem where they were downloaded for analysis on a daily basis.
The modem also allowed AVT to interrogate the system in the event of receiving an alarm text message.
Text messages included the value of the maximum tilt together with specific beam identification.
Collecting data is only a small part of the work AVT carry out.
As AVT's Special Projects Division Manager, Neil Parkinson explains: "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 a particular structure.
All round good communication and the ability to work closely with other interested parties are also vital ingredients.
In projects such as the Ann Watson Street one, the working environment is far from perfect and a far cry from conditions found in the laboratory.
We are used to working in difficult, and often remote, areas with limited facilities, and have developed a high level of ingenuity to ensure that our equipment can operate without problems." The most crucial time in the project was when work started, where any disturbance could rapidly change the status of the wall.
It was clear that the wooden beams would have to remain in place and the work was carried out in stages.
Firstly Mowlem installed temporary steel supports or 'walings' across the front of the wooden beams and then 20 metre steel piles were driven into the riverbed just in front of the wall.
The gap between these and the existing wall was then backfilled with stone to the high tide level.
Once this had been completed, the instrumentation could be removed and it was considered safe to remove the top sections of timber before the final backfilling to footpath level was carried out.
As Keith Slaney from The Environment Agency concludes: "This was a tricky situation and any premature failure of the wall would have been disastrous.
We worked closely with the parties involved and a blend of skill and good communication assured a positive outcome.
The monitoring system gave us the confidence to carry the work out that we would have adequate warning of impending problems.
During the monitoring period, the movement of the wall triggered several alarm situations and necessary precautionary measures were taken to ensure the safety of personnel.
A quantity of big-bags filled with rock were available on the adjacent bank in case of emergency but were fortunately not needed." All work on the retaining wall has now been completed and in addition the previously overgrown and pot-holed footpath has been replaced with a greatly improved new concrete promenade. Request a free brochure from AV Technology ...
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