High Capacity Bar Anchors for Liverpool FC’s New Main Stand
Liverpool Football Club are in the middle of expanding their main stand on Anfield Road to increase the seat capacity to 54,000, with work continuing all through the football season.
The new main stand features considerably increased depth and height and will be sheltered by a large cantilevered roof. The huge overhang of the roof is supported by backstays that had to be anchored down in the ground by 12 No. high capacity DYWIDAG Bar Anchors.
The ground anchors consist of 75mm Ø DYWIDAG Prestressing Steel Threadbars that were pregrouted at the DSI factory in Southam to ensure compliance with BS8081:2015 for permanent anchors. With an ultimate strength of 4,500kN, the tendons are the highest capacity threadbars manufactured. The boreholes for the 14m long DYWIDAG Bar Anchors were drilled into the sandstone bedrock using a down the hole hammer (DTH) with air mist flush. This new flush mechanism features flushing jets within the stabilizer collar of the hammer that are arranged with different orientations to create a vortex effect. As a result, dust is fully suppressed, and drilling performance is increased by 10-15%.
Prior to the installation of the production anchors, three trial anchors were installed that were equipped with bond isolators consisting of foam collars. The foam collars were placed at the interface between the active and passive wedge zones to ensure the bond developed in the grout body of the passive zone cannot strut against the upper grout body within the active zone, to develop a disproportionally high load, which could be mistaken as the bond performance within the fixed length. Following the successful load testing of all trial anchors, the DYWIDAG Anchors were approved for installation.
Due to the weight of the anchor segments, 40kg/m, each section had to be lifted using a DYWIDAG captive bar lifting shackle, and placed within the borehole. A tremie pipe was attached to the lead section, to ensure that the anchors were grouted from the base up, once fully installed. The installation method involves installing the first section with a coupler fork to hold it in position, then lifting the second section into position, rotating it fully to ensure correct engagement of the coupler, followed by a short lift to take the load and remove the coupler fork. This process is repeated for each additional section.
Following installation to depth, the anchors were grouted via the tremie pipe to the surface. Afterwards, grout levels were checked to ensure that there had been no undue settlement. Then, the top meter of each anchor was washed back with water using a lance, to ensure that there was sufficient void space at the top of the annulus to accommodate the bearing plate/stub tube assembly as well as to avoid any potential for strutting during stressing. Once the grout had set, the washback water was blown out by air.
Each anchor was then stressed by DSI stressing technicians and locked-off in accordance with the specification, enabling the full restraint to be mobilized for the cantilevered roof. This project is the second in which DSI UK has worked with Liverpool FC (the Reds). Previously, DSI UK supplied permanent DYWIDAG Strand Anchors for the refurbishment of the stadium’s famous Kop stand.