LECA® LIGHTWEIGHT FILL SPECIFIED FOR M6 JUNCTION 10 IMPROVEMENTS

Over 8000m3 of LECA® LWA was specified for the latest Highways England project on the M6 Junction 10 improvements in Walsall, designed and construction by Main Contractor John Sisk & Sons Ltd.

The new highway project involved the development of two new semi-integral bridges alongside an embankment with a 20 degree skew. There were technical problems discovered and limited space due to existing live carriageways, which required a robust lightweight reinforced earth backfill for the abutments to reduce the total settlements at the formation level and to reduce piled foundations extents and to minimise differential settlement.

From further investigation from the designers, LECA® LWA was selected as a suitable solution for many engineering and logistical reasons. It was during the design phase, the main questions sought from the Clients Representative included the earthwork material classification for LECA® LWA and whether the specification of LECA LWA would require a departure from the MCDHW Specification for Highway Works – Series 600 Specification. Through discussions with the technical representative Robert Branford at LECA® UK, it was concluded that there would be a departure required and that the LECA® LWA could be classified as Fill to Structures Class 6T, lightweight expanded clay aggregate (10-20mm).

Through multiple recent case studies in the UK, where LECA® LWA was successfully installed on similar highway projects involving the development of integral bridge abutments, a departure was successfully submitted by Main Contractor’s Designer Capita Pell Frischmann to specify LECA® LWA for the M6 Junction 10 development. The key case studies highlighted included the A41 Stone Bridge, River Thane, Aylesbury; the A120 Stansted to Braintree developmet; the A4146 Fenny Stratford Southern Bypass over the River Ouzle, Buckinghamshire; the A27 Southerham to Beddingham Improvement and the A2/ A282 Dartford Improvement.

FACTS

Amount of material: 8000m3 of LECA® LWA (10-20mm)

Interesting Fact: There were technical problems discovered and limited space due to existing live carriageways, which required a robust lightweight reinforced earth backfill for the abutments to reduce the total settlements at the formation level and to reduce piled foundations extents and to minimise differential settlement.

Delivery Method: Walking Floor

Designer: Capita Pell Frischmann

Main Contractor: John Sisk & Sons Ltd

Feedback from Main Contractors

Charles Jackson, Engineer at John Sisk & Son Limited who were awarded the role of contractors for this project said “LECA® LWA was utilised on our site due to the need of minimising loadings onto the existing ground. The nature of the material made the installation process unchartered for me as an engineer.”

Charles Jackson, Engineer at John Sisk & Son Limited continues “This process was made much easier by Robert Branford (Geotechnical Sales Manager) and his team with explanations, case studies, photographs and videos from previous projects which gave us an insight into how that material can be transported, installed and compacted.”

For the development, the Geogrid system from Tensar was applied in combination with LECA® LWA (See image). Through the previous combination of LECA® LWA with Tensar to lock the fill in place, this provided the developers the confidence to continue with the development.

Charles Jackson, Engineer at John Sisk & Son Limited provides comment on the logistical requirements of the project, “Delivery of the material was seamless, conversations between myself, LECA and Hargreaves meant we were able to make amendments to the delivery numbers as and when required with short notice periods.”

“For installation, we were working within a confined area on the edge of a live carriageway. We also had to transport the material up and over a newly installed 6m abutment which made the task a highly sensitive one. Due to these constraints we opted to use WM Plant Hire who specialise in long reach excavators. We used a CAT 321D which had a zero-tail swing, the operator used a clam shell bucket to lift the material from ground level and into the works area ready for compaction.”