When a rail bridge requires replacement, construction time is of vital importance. When the ground foundation material is found to be weak a lightweight solution is required. The low weight, high stability and speedy installation attributes of Leca® LWA solved both problems in the replacement of an old, wrought iron bridge structure in Scotland for Network Rail.
The Stirrat Street Bridge at Paisley was removed and a new, low maintenance permanent-way structure was built to carry the track. As road traffic no longer passed below the bridge, it was determined that the void should be filled to enhance the embankment stability. However, the ground condition survey flagged up that the foundation material in the area was not up to modern load bearing standards and that using traditional heavy fill would overload the existing ground base. Leca® LWA was selected to provide the void fill without overloading the support substrate.
The design work was completed by Mouchel Rail Design Services of Manchester. Duncan Robertson, for main contractor Barhale Construction Plc. was full of praise for Leca® LWA. “A cast concrete raft was laid to spread the load over the poor existing substrate between the brickwork piers of the original structure. A geotextile membrane was laid across this raft, up and over the walls to interlock with the existing embankment material. Then the Leca® LWA was bulked into place and tracked for compaction. Leca® LWA is easy to handle, clean and light. Having formed the embankment joins we removed the bridge and capped the Leca® LWA with 6N and track ballast to carry the lines. For most of this project the ambient temperature was -10°C but thankfully another attribute of Leca® LWA is that it does not freeze so we were able to continue working. The track ballast had to be protected from freezing and was difficult to place on some days.”
A totally natural product, Leca® LWA is formed by heating and firing natural glacial clay in a rotary kiln at temperatures up to 1150ᴼC. This process transforms the clay into lightweight ceramic granules with a hard shell and porous core. With a bulk density of just 0.3 tonnes per cubic metre, Leca® LWA has excellent insulation properties, is free draining, fire resistant, frost resistant and chemically inert with no hazardous properties. Used as a lightweight aggregate fill in many civil engineering and construction applications Leca® LWA reduces the weight on weak substrates and against retaining structures by up to 75% over traditional fill and eliminates expensive settlement delays, is easily handled and quickly installed.
Leca® LWA proved itself to be a valuable material for this Paisley rail bridge replacement project. It provided a strong, stable, lightweight fill solution for the rail network and was installed quickly despite the extremely low temperatures.