The challenge
The Merstham Viaduct is on one of the motorway’s busiest interchanges, forming a vital part of the south-east strategic road network between the M25 and M23. When routine inspections of the viaduct’s bearing pads took place in early 2022, questions were raised regarding the degree of movement the bearings were permitting and whether in fact they might have fused solid. As a result, we were contracted by Octavius Infrastructure to supply a range of structural monitoring equipment.
Our solution
Working closely with Octavius Infrastructure, Allan Martin, our Senior Monitoring Engineer, devised a bespoke package of sensors which he personally supervised the installation of. The sensors duly remained in place for an eight-week period, during which time the client was fed continuous live readings.
Allan Martin explained: “The M25-M23 viaduct dates from the mid-1980s and has a series of bearing plates at different levels. These separate the main deck from the abutments and piers, allowing them to move in relation to one another. The five sets of separate monitoring systems were fitted to special steel plates anchored to the bearing shelf and the deck soffit, This allowed us to monitor the movement of the bearings against temperature, to see whether they had seized or were operating sufficiently; with all the data being transmitted wirelessly to a central gateway on site featuring an internal modem. This then wirelessly uploaded to our Insite portal.
“Insite supplies extremely precise measurements of the bridge deck’s thermal movement in real time and crucially showed that while the bearing plates will shortly require replacement, their present performance remains satisfactory. This meant that planned works rather than emergency work could be scheduled – both saving money and helping to reduce disruption for road users. As a specialist in temporary works and monitoring, Mabey Hire is also in a strong position to be able to provide both the necessary jacking and monitoring of the bridge structure during future repairs.”
Octavius Infrastructure’s senior engineer on the project, Said Enany, commented: “We are a preferred framework contractor for Connect Plus, which takes care of the whole M25 network. In this instance, we are the principal contractor responsible for the work being carried out to the Merstham Viaduct.
“While we have worked with Mabey Hire in the past, this is the first time we have made use of the company’s monitoring equipment. We were very happy with the service we received from the technical department and the data supplied by the sensors via Insite confirmed that we did not need to take urgent action regarding replacement of the bearings.”
