152_BR Western Avenue Bridge is located in Ealing, West London, and has been identified as one of the existing bridges requiring mitigation works due to ground movements caused by the HS2 Northolt Tunnel works. The bridge is owned by Transport for London (Surface Transport) and spans over 2no. London Underground Central Line tracks and 2no. Network Rail tracks.
A ground movement assessment (GMA) carried out by a previous consultant determined that mitigation works were required, and RBG was brought in initially to carry out an enhanced ground movement assessment on this structure to confirm these findings.
RBG was in agreement that these works were required and were appointed to carry out mitigation works, which consist of replacement of the existing bearings on the western abutment.
Key technical challenges
The scope for the mitigation works included an options report summarising a number of different mitigation options, including replacement, modification or “do nothing” approach in relation to the existing bearings. Following discussions with the Contractor and Bearing supplier and designer, the preferred option was agreed and developed to Approval in Principle, Detailed Design and Construction.
The preferred option consists of jacking the western abutment and leaving the bridge deck on temporary jacks which allow for the tunnelling movements, with an emergency backstop restraint system, followed by replacement of the bearings, maintaining the original articulation.
Added Value
RBG carried a detailed structural assessment using non-linear staged 3D finite element analysis, which allowed for an accurate set of forces and movements required for the design of the new bearings. Furthermore, through good engineering judgement and sensitivity checks, RBG minimised the number of bearings to be replaced to 1no., as opposed to all the bearings on that abutment.
Sustainable Methodologies and Outcomes
By replacing only 1no. bearing as opposed to all the bearings on the abutment, and incorporating temporary bearings on the jacks, the proposed solution avoided fabrication, delivery and installation of 5no. pot bearings, which would also require potentially more than one rail night time possession and cause further disruptions to the road above.
Project Metrics
Client:
HS2, Transport for London (TfL)
Contractor:
SCS JV (Skanska, Costain & Strabag)
RBG Role:
Design
Completion:
2024
Project Metrics
Sector:
Rail, Roads & Highways
RBG Service:
Structural, Geotechnical