Reinforced Soil Walls and Slope Reinforcement
2019
Gatwick, Sussex
Highways England
Kier Group
CAN Geotechnical Ltd
M23 JN 8 – 10 MORTORWAY IMPROVEMENTS
Completed Structure
Site before construction
Green Terramesh® and soil nails during construction
Green Terramesh® and soil nails during construction
Vegetation established in Green Terramesh®
Problem
The M23 is a crucial part of the UK strategic road network connecting Crawley, Gatwick Airport and Brighton to the M25 motorway, which routes into London and the rest of the UK.
As part of the M23 junction 8 to 10 Smart Motorways scheme, Highways England proposed to upgrade 10 miles of the existing M23 to operate as a smart motorway by converting hard shoulders into permanent running lanes. This creates four lanes of carriageway in both directions between the junctions.
As part of the work, the northbound segregated left turn needed to be widened to allow an extra lane on the carriageway. This widening needed to utilise minimal space to not increase the project envelope.
Solution
Due to the small amount of available land a traditional reinforced earth solution would not fit. For this reason, the designers chose a hybrid reinforced earth and soil nail solution. This utilised Maccaferri’s BBA HAPAS 120-year design life Green Terramesh with hollow bar soil nails through the front face.
The units have an integral steel mesh geogrid ‘tail’ which is installed within the compacted structural backfill to provide soil reinforcement. Green Terramesh units also feature a heavy-duty welded mesh panel behind the front face and bracing struts to support the face at the appropriate angle during construction, removing the need for external shutters or face support. As all these elements are incorporated into the unit at the factory, it reduces work on site and makes the installation much quicker and safer than with other ‘soil bag’ or wrapped face style geogrid structures.
Seeded topsoil is placed immediately behind the face to establish vegetation on the slope.
Once installed, vegetation is established fairly rapidly and once fully established contributes a natural appearance to the engineered solution. This provides habitat to flora and fauna whilst also improving local air quality through the absorption of CO2 from the atmosphere.