Anchors a Way to Stabilise Bridge
Updated: Feb 10, 2021
Anchor Systems (International) were called in to help with a large project as part of the South Alton Masterplan road layout improvements in Hampshire. These included the replacement of Butts Bridge which carried the Mid-Hants Railway, known as the Watercress Line, over the A339. The original brick arched railway bridge was to be replaced with a new steel bridge to allow the road to be widened, removing a notorious traffic bottleneck. The replacement bridge was designed by Jubb and incorporated steep embankments on the approaches to the abutments.
Factor of safety
To ensure that the factor of safety of the slopes was within acceptable limits over the long term, geotechnical engineers specified a system of mechanical ground anchors combined with a suitable geotextile covering. Mechanical ground anchors, such as Anchor Systems’ Vulcan range, are routinely used to stabilise slopes, either in made ground like railway and bridge embankments or in natural ground in cuttings or in foundation excavations.
Vulcan AS-10 anchors were driven through an integral steel mesh
Contractor Knights Brown approached Anchor Systems for advice to determine the correct anchor to meet the load requirements specified while meeting the 120year design life. Anchor Systems believes it is the only manufacturer that can provide complete stainless steel anchors and claims to have the largest range of anchors in the world. After extensive testing, it was determined that the Vulcan AS-30 fitted with 4m of 12mm stainless steel tendon installed to a depth of 4m would be suitable. The specified Greenax revegetation and erosion control mesh was placed on the slope and the Vulcan AS-10 stainless steel anchors driven through the integral steel mesh.
Site restrictions meant that part of the installation works, carried out by Hartmann Construction for Anchor Systems, had to be achieved using a hand-held hydraulic breaker operated from an access platform. The simple installation process meant high production rates were achieved by a two-person team. The anchors were then proof loaded to the specified 10kN and locked off at 6kN using a battery powered pump and hollow hydraulic cylinder.
After testing had proved that the design was within the agreed safety limits, the project was completed successfully.