The Elan Valley Aqueduct is a crucial source of water supply for Birmingham and its adjacent areas. The aqueduct is approximately 120 km long, discharges 300 million litres of water every day into the reservoir at the Frankley Water Treatment Works and supplies water to about 1.2 million people. There was a need to refurbish and modernise the aqueduct in order to preserve it for the future. For this purpose, a new conduit with a tunnel 1.8 km in length and 3 metres in diameter was proposed to be constructed. For the construction of the bypass conduit, a horizontal working platform 160 metres in length with a maximum height of 14 metres was required to support the construction load – the 1,000 tonne crane used to assemble the tunnel boring machine (TBM) and the 150 tonne TBM.
For this, Geosynthetics Limited proposed the construction of a reinforced soil wall (RSW) with StrataGrid™ and site-won material to surround the location of the cofferdam for the TBM launch shaft. The length of the RSW was 160 metres, with a maximum height of 14 metres and a slope angle of 85 degrees. A reinforced working platform was constructed on top of the reinforced soil wall with selected granular material of 970 mm thickness and a biaxial geogrid to distribute the load. For the face, a B1131 steel mesh was used and each layer was protected with a Landlok erosion control mat. This technique helped in considerable cost savings as compared to the conventional method, and was environment friendly and enhanced the construction speed.