M1 Junction 12 Widening - Bedfordshire

Leca® LWA lightens the load for M1 widening

Widening the 15 mile section of M1 motorway between Junctions 10, south of Luton, and Junction 13 at Milton Keynes demanded the light weight, free draining properties of Leca® LWA. Two 150 metre long embankments either side of the existing motorway were expanded to carry improved approaches for a new bridge structure at Junction 12. The substrate was found to be of poor quality clay that would not support traditional fill without extensive and expensive excavation. Leca® LWA was identified as the ideal solution to achieve the levels required and provide the stability and drainage necessary to carry the new approach road construction, eliminating the requirement of costly excavation and removal of material from site. Working on behalf of the Highways Agency; main contractor Costain Carillion JV and consulting engineers URS Scott Wilson were tasked with facilitating the increase in traffic capacity for this extremely busy section of the M1 by introducing the Hard Shoulder Running Scheme which involved improving the existing hard shoulder to motorway standard to support an additional traffic lane; for this to be successful improvements had to be made at both Junctions 11 & 12.  James Worth site agent for CCJV explained that the poor ground had suffered from settlement problems in the past but was now deemed stable. "However widening operations would create additional loadings in this area which could cause further settlement. It was therefore necessary to use Leca® LWA to provide the fill capacity without the increase in weight. To limit delivery vehicle traffic, the Leca® LWA was brought to site in high capacity ‘walking floor’ trailers and stockpiled ready for use." 14,000m³ of Leca® LWA was delivered to site in "walking-floor" bulk trailers, specially adapted for this project to comply with the requirements of Chapter 8 guidelines for working within the main highway. The Leca® LWA was moved from the stockpile by 25 tonne dumpers to its final location, then spread and compacted by tracked excavators. To prevent migration of the clay substrate into the Leca® LWA fill, a geotextile membrane was spread over the sub-formation prior to the Leca® LWA being installed with a further geotextile layer placed to separate the Leca® LWA from the sub-base capping. A totally natural product, Leca® LWA is formed by heating and firing natural glacial clay in a rotary kiln at temperatures up to 1150°C. 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 applications Leca® LWA reduces the weight on weak substrates and against retaining structures can reduce the weight loading by 75% over traditional fill. Leca® LWA eliminates expensive settlement delays, is easily handled and quickly installed. The Leca® LWA attributes of light weight, ease of handling and installation contributed to a successful project for this part of the M1 motorway improvement.