A monitoring system from Mabey Hire has produced an M25 success story – preventing congestion from unplanned closures by getting real-time data to decision-makers.
As one of the world’s largest orbital motorways and carrying 15% of the UK’s motorway traffic, any maintenance closures of the M25 must be carefully planned to avoid major disruption.
As a result, having real-time, easily accessible and accurate data on the structural condition of all bridges and key infrastructure on the motorway is essential. That’s why Mabey Hire’s structural monitoring technology was recently deployed.
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, placing internal loads on the concrete. As a result, Mabey Hire was contracted by Octavius Infrastructure to supply a range of its structural monitoring equipment.
Working closely with Octavius Infrastructure, Allan Martin, Mabey Hire’s senior monitoring engineer, personally devised and supervised the installation of a bespoke package of sensors. These remained in place for an eight-week period, during which time the client was fed continuous live readings.
Mr Martin explains: ‘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 and allow them to move in relation to one another, whether due to changing loads or temperature variations.
‘At each of the five locations requiring monitoring, we installed two sensors (Linear Variable Differential Transformer – LVDT) that were fitted to custom built brackets anchored to the soffit of the deck at the bearing face and the bearing shelf. This allowed us to monitor the movement of the bearings against temperature, to see whether they had seized or were operating sufficiently. The LVDTs were connected to a wireless logger, which powered the sensor and monitored the readings, wirelessly transmitting them across the structure to a single main gateway. This is then wirelessly uploaded to our Insite portal.’
The sensors were programmed to monitor the longitudinal movement of the bridge deck across each bearing, with the ability to precisely monitor movement in one direction to 0.01mm. All bearings were fixed longitudinally, hence there was no need to monitor transverse movement. Temperature sensors were also installed at all five locations.
Mr Martin adds: ‘Our Insite portal displays the data for easy analysis, with the bridge deck’s movement over the bearing plotted against temperature in real-time. Crucially, it showed that the levels of movement and the bearings’ present performance remained satisfactory. This meant that planned works rather than emergency work could be scheduled – 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, comments: ‘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.’
Structural monitoring solutions are a valuable tool within the highways sector as a means of asset management. Having easily readable and understandable data on the structural performance of an asset can help aid future maintenance programmes, better inform improvement works and even prolong the life of an asset by helping asset owners, highway agencies and contractors develop more of a detailed understanding of the behaviour of our country’s vital infrastructure.
