The A1, the UK’s longest numbered road, is being upgraded on a 6.5 km section between Birtley and Coal House to reduce congestion. The project adds lanes and replaces the 40-year-old Allerdene Railway Bridge with a wider crossing over the East Coast Main Line.
The A1, spanning over 400 miles between London and Edinburgh, is the UK’s longest numbered and a vital transport corridor. As part of a strategy to upgrade the heavily congested A1 Newcastle Gateshead Western Bypass, a 6.5km stretch between Birtley and Coal House is being improved. Alongside extra lanes to increase capacity, the scheme includes replacement of the 40-year-old Allerdene Railway Bridge, a long-standing source of disruption due to maintenance. The new, wider structure is being built just south of the existing crossing and will carry the A1 over the East Coast Main Line.
For the new bridge embankments, engineers faced soft, fine-grained, compressible glaciolacustrine deposits expected to undergo excessive settlement under load. To ensure stability of the reinforced earth structures and limit differential settlement, the design required a ground improvement solution capable of distributing loads effectively and providing a rigid base beneath the embankments.
To overcome these challenges, the project specified Rigid Inclusion Piles (RIPs) combined with a geogrid reinforced Load Transfer Platform (LTP). RIPs were installed in a regular grid pattern, while the LTP acted as a bridging layer to transfer loads evenly between the piles. At Coal House, the LTP was constructed using alternating layers of fill material separated by high-strength geogrid reinforcement. Naue supplied approximately 80,000m² of reinforcement material.
Naue Secugrid® HS was selected to meet the geotechnical and structural requirements. Manufactured from high-tenacity polyester filaments with an extruded polyethylene coating, it provides tensile strength, robustness and resistance. Its welded junctions promote optimum force distribution, making it suitable for weak or variable ground conditions and applications requiring reliable long-term performance. With longitudinal strengths exceeding 400 kN/m and transverse tensile strength of ≥ 100 kN/m, the material ensures minimal creep and extreme robustness in heavily loaded earthworks.
The Secugrid® HS geogrid solution also supported wider pile spacing. These benefits lowered construction costs, shortened installation time and enhanced operational reliability. Supplied on 50m rolls at 4.75m width, the reinforcement can be quickly rolled out on site, simplifying handling and installation.
By integrating Rigid Inclusion Piles with a Load Transfer Platform reinforced using Naue Secugrid® HS geogrids, the project team achieved a stable foundation for the A1 bridge embankments despite weak subsoil conditions. The system ensured controlled settlement, improved bearing capacity and long-term structural performance. In addition, efficient installation and reduced piling requirements offered significant economic and time-saving advantages, contributing to the overall success of the A1 improvement works.
Secugrid® HS transferred loads evenly between the piles, improving bearing capacity and controlling differential settlement.
The high-strength reinforcement enabled wider pile spacing, reducing piling requirements, construction time and costs.
Wide rolls, simple handling and minimal creep supported efficient installation and reliable performance under heavy loads.
No. 01199
