Tracking Systems for Monitoring the Movements of the Existing Bridge Deck

The contractor has utilised a combination of two tracking systems for monitoring the movements of the existing bridge deck during works to replace and widen an existing rail bridge with minimal disruption to the rail networks.

The project required the replacement of a railway overbridge structure. As part of this, the clear span was to be increased from 17.50m to 22.60m. The existing South abutment was to be wrapped in reinforced concrete to create the new South abutment. Then the North abutment was to be newly constructed 5.00m North of its existing location.

Prior to the main blockade works for the existing bridge demolition and replacement, a large proportion of the new North abutment was to be constructed while maintaining an operation railway classed as the pre-blockage enabling works.

This included:

• Retaining existing railway embankment, track and associated assets
• Bored pile installation to support new pile caps
• New pile cap construction

The main problem they had to overcome, was the temporary works required to retain the existing railway with allowable track displacement in line with the Network Rail requirements, they overcame this problem by implementing the following methods:

• 2No sheet pile walls parallel to track tied together using cross ties and walers for additional support
• The element above had to be designed to cater for the LIVE train surcharge load of 50kN/m²
• 2No sheet pile walls perpendicular to track secured using mechanical anchors
• The element above had to be designed to cater for the loads imposed from the existing railway embankment
• All of the above had to consider the deflections of the sheet pile walls, cross tie loads, waler loads and mechanical anchor loads