Site: Railway Overbridge and Cutting

Details: Railway Overbridge Replacement

Services:  Geotechnical Consulting

ASL provided geotechnical consultancy services associated with the replacement of railway overbridge as part of design team including Structural Engineer and contractor.

The site comprises a railway overbridge carrying a road over four railway tracks located within a 10m deep cutting and the scheme involved the replacement of the existing bridge, including provision of a temporary bridge to carry pedestrians during the works and temporary works associated with the enabling and construction works.

The principal challenges affecting the bridge replacement were providing access to the bridge site for the demolition plant to limited available space for the placement of the temporary bridge.

ASL carried out slope stability assessments to enable a temporary haul road to be cut along the existing cutting.  The haul road needed to be steep enough to avoid excessive excavation works and also needed to be constructed at a suitable gradient to allow the construction plant to safely access the construction site at the bridge.

ASL also undertook foundation and stability assessments at the locations of the foundation supports, which needed to be positioned on the existing cutting slopes due to the maximum span for the temporary bridge, to ensure that the temporary bridge was adequately supported whilst not adversely affecting the stability of the cutting.

A large crane was required to lift the temporary bridge into place and this need to be located on suitable ground due to the high outrigger loads associated with lifting the temporary bridge. . Due to the limited space available the outrigger were located adjacent to existing retaining walls and in gardens and therefore careful assessment was required to ensure that failure did not occur below outriggers that may have resulted in the crane toppling during lifting and prevent damage to existing walls and houses.

The geotechnical assessments enabled the project to be completed without any stability issues affecting the temporary works and with the minimal excavation and enabling works.