One of the first major Network Rail Projects to utilise the benefits of Leca® Lightweight Expanded Clay Aggregate under track was in 2007 on the West Coast Mainline between Milton Keynes and Bletchley, where in excess of 2000m³ was used to lighten the load on the rail embankment expansion.
Over recent years Network Rail’s multi million pound modernisation programme for the West Coast Mainline required substantial embankment improvements. On the Milton Keynes to Bletchley section, plans called for the existing four track lines through Milton Keynes station to be expanded to six in order to provide additional fast reversible and fast down lines. The existing embankment was widened to carry these two new lines but two major pipelines, a 2.4m surface water pipe and a 900mm foul water sewer crossed the area, both of which could not afford additional loads being exerted above them. Leca® Lightweight Expanded Clay Aggregate provided the project with an effective embankment fill without the weight burden of traditional fill materials.
The scheme called for the widening of 800 metres of embankment and cutting to accommodate the new lines pathway with a 30m section to be retained with a new wall some 5 metres in height. The contract was carried out by Buckingham Group Contracting Limited and the design provided by Amey PLC Group. The existing earth embankment slope was cleared of all topsoil and vegetation and the clay cut into “benches” to carry the fill material in a stable pattern enabling a true key between the differing strata.
The ground upon which the retaining wall foundation was laid was initially reduced to a sound substrate and built back up to level with Leca® Lightweight Expanded Clay Aggregate ready to receive the new 4.65m wide reinforced concrete retaining wall slab.
The retaining wall was then cast to an average height of 5 metres, 425mm wide at the base and tapering to 275mm wide at the top. Traditional rear wall drainage consisting of 150mm diameter perforated plastic pipe was located at the heal of the wall and ran along the entire length of the base ready to receive percolating water from the new embankment and avoid increased pressure from surface water run-off.
The new rail embankment was then filled with Leca® Lightweight Expanded Clay Aggregate to 1 metre below the top of the retaining wall and capped with 350mm of 6F5 stone aggregate and recycled rail ballast before laying the tracks.
A totally natural product, Leca® Lightweight Expanded Clay Aggregate 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® Lightweight Expanded Clay Aggregate 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 applications Leca® Lightweight Expanded Clay Aggregate reduces the weight on weak substrates and against retaining structures can reduce the weight loading by 75% over traditional fill. Leca® Lightweight Expanded Clay Aggregate eliminates expensive settlement delays, is easily handled and quickly installed.