Project Sheet: Baguely Bridge
- Manchester Metro link
- Volker Steel Foundations
- Site assessment
- Produce design calculations, drawings and specifications for the works
- Supervision of the works.
Description of Project
A new railway line adjacent to Baguley Bridge was proposed as part of the Manchester Metro link Project. The tram line was to run parallel to Southmoor Road, which required partial removal of the embankment supporting the road. The embankment slope therefore had to be supported by temporary works while the bridge parapets were being built.
Volker Steel Foundations were appointed to design a soil nailed retained excavation adjacent to Southmoor Road. The replacement bridge would be 4m to the east of the existing road bridge and was designed to carry the tram over the railway line.
To construct the new bridge, the base of the new abutments needed to be excavated, cutting into the existing Southmoor Road embankment. The angle of the cutting was approximately 70º and required retention. The underlying ground was not suitable for the use of sheet piles; therefore, it was decided that temporary soil nails should be inserted beneath the road.
Sonic Drilling were appointed as the contractor for the works and they appointed GroundSolve Ltd to carry out the design.
It was proposed that there should be five rows of soil nails placed at 1.75m vertical intervals, secured with square plates. The slope would then be covered with a mesh, held down at the crest by hooked anchors.
Any voids within the slope had to be backfilled with sand filled bags so that the 70º angle could be achieved before the mesh was fitted.
The upper section of the slope couldn’t be retained using nails due to the presence of active services. It was therefore required to use gabions which were backfilled with a mix of soil and concrete.
As it was only a temporary structure, the design life of the soil nails was only 6 months. However, they may also be used in the future for economical purposes.
However, during the works the ground conditions were found to be different than those revealed by the boreholes. This necessitated redesign of the works and grouting of sections of the embankment in advance of the installation of the soil nails.