Lower Wharf Street, Ashton-Under-Lyne, Greater Manchester – UK

Project Overview

Retaining Wall SAJ/1848 is a substantial sandstone masonry structure, standing 8.8m tall and 14m long that supports the northwest side of the railway between Guide Bridge and Stalybridge stations. The wall exhibited significant bulging in its upper section, located approximately 5m from the railway line, raising safety concerns. A prior structural investigation involved drilling 10 core samples through the wall to determine its thickness and the nature of the backfill materials. The findings revealed made ground and soft clays with evidence of voids behind the wall. To address the issue, Network Rail’s internal design team collaborated with Platipus to develop a mechanical anchored solution with a 120-year design life. To confirm the theoretical specification three test anchors were installed through the wall to evaluate the bearing capacity of the surrounding soils.

Solution

A total of 54 B4 aluminium bronze anchors were specified for the project, arranged in four rows. These anchors were driven 8m beneath the railway at an angle of 15° below horizontal and proof-loaded to 39kN. To meet Network Rail’s requirement for recessed aluminium bronze pattress plates, 127mm core holes were drilled to receive the anchors, followed by an additional 250mm core hole to ensure a clean, recessed finish. Given the limited working space and the height of the wall, the installation was carried out using an excavator alongside operatives working from a mobile elevating work platform. During the installation phase, five of the 54 anchors near the bulging section of the wall failed to achieve the required load due to highly saturated soils and evidence of significant voids. To address this, the anchor heads were upgraded to the larger B6 anchors and driven to a depth of 10m, successfully meeting the design load requirements.