In the early phases of Manchester's Metrolink light rail scheme, the surrounds to the rail lines featured the pavement types found in the locality, such as cobbles and flagstones. However, in the phaze that was to pass through Salford Quays, an area of smart regeneration, the objective was to enhance the development with greenspace, therefore a grassed solution was sought to sit between and alongside the tramlines.
Grass Concrete, as the preferred solution supplier, had a number of challenges to meet.
- The growing medium for the grassed paving needed to be contained, so as not to contaminate the track and adversely influence the earthing
- The paving edge was required to consistently follow the rails with a fixed gap between the two
- The prospect of vandalism was a concern and it was thought that pre-cast blocks could be removed and set on the line potentially causing derailment
- With the rails sitting on an underlying solid concrete slab, there would need to be a drainage system introduced to migrate water as it passed through the grassed paving, wicking it away to the collector drains at the edges of the track
- When completed the paving must be capable of handling maintenance vehicles working on the lines and overhead cables. These vehicles might be of road railer or normal road going construction
Grass Concrete's Grasscrete system was selected for the project as it tackled all of these challenges, with some of the related construction and drainage issues requiring more creative bespoke solutions:
- With an underlying solid concrete slab to support the rails there was no means of achieving the natural direct percolation of surface water normally associated with Grasscrete. To overcome this Grasscrete GC3 was installed over a drainage layer of sand and gravel, in turn laid over the concrete slab featuring a crossfall to the outer edges.
- At each rail channel a perforated kerb was introduced that would enable moisture to pass across the gap without encouraging the build up of debris, a potential issue for the earthing of the electrified system.
- Key to the installation was the introduction of a temporary formwork system that sat over the rail and held captive the kerbs and filter media during casting.
- With access to the track itself being generally limited, most of the installation was carried out using a road-railer 360° excavator working along the track.
- Following completion of the installation, the surface of the Grasscrete was groove cut at key locations to introduce wiring loops for signalisation.
The ribbon of grass paving that weaves its way through Manchester's redeveloped business and cultural quarter is visually impressive.
Completed over 10 years ago, the installation remains just as striking as when it was first completed. Grasscrete fulfilled the brief of providing a green solution whilst enabling essential maintenance. It also addressed concerns around the alternative consideration of pre-cast units, where it was felt that blocks could be lifted by vandals with potential to derail the tram cars.