The existing section of pipeline across the River Humber needed to be replaced because the riverbed profile had changed over time, exposing the pipeline. Some work was carried out a few years ago to keep the pipeline buried on the riverbed, but a long-term solution was needed. The River Humber Gas Pipeline Replacement Project is a £100m design and build contract issued by National Grid to replace the Feeder 9 high pressure gas pipeline under the River Humber. A 5.4 km long, 1050 mm diameter gas pipe bypassed the existing pipeline which was installed in 1984. A slurry TBM mined a 3.65-meter diameter tunnel around 35 meters under the riverbed. The tunnel lining was constructed from 225 mm of thick interlocking segments. Once the tunnel was finished, a new 42-inch diameter gas pipeline was designed to be laid inside it.
The solution entailed creating a cost-effective backfill grout mix designed to satisfy the following client specification:
During tender, Normet produced a cost-effective mix at our labs, which adhered to the clients mix design requirements. Prior to the first ring build Normet engineers were present on site to optimise and audit the grout batching plant operation. This ensured that the grout quality and batching operation was an easy and efficient process for the client.
Normet provided on-site training to engineers enabling them to test the quality of the grout they produced. Defining a set procedure and specification for testing allowed the client to take control and actively measure the quality of the grout they were producing.
The introduction of Normet’s chemicals and technical team ensured zero grout wastage throughout the project. Porr/Skanska/A.Hak was extremely happy with the backfill grout design; Normet project engineering provided the backfill grout specification based on the project parameters and personal experience. Furthermore, Normet analysed the grout on site and offered regular audits to ensure the agreed specification was fulfilled.