Client: National Highways
Principal Contractor: Freyssinet
Works Commenced: 2023
Works Completed: 2024
Patrixbourne Bridge is a three-span supported overbridge constructed in 1974. The structure is located to the south of Canterbury and carries the A2 over Patrixbourne Road and the Nail Bourne waterway. The superstructure is formed of two decks to the East and to the West, each consisting of 12 precast prestressed reinforced concrete beams.
The structure is supported by rubber strip bearings at the North abutment and over the piers, while the South abutment features twenty-four sliding laminated rubber bearings. Previous inspections identified that the bearings at the South abutment were in poor condition, with corrosion on several components.
As part of National Highways’ Scheme Delivery Framework (SDF), Freyssinet was awarded main bearing replacement works after an extensive Early Contractor Involvement (ECI) period. Scope of works was split as below:
- Early Contractor Involvement:
a. Development of concept and coordination with PWD
b. Provision of Approval in Principle for Temporary Works submission
c. Detailed design to issue for construction of temporary works for jacking
d. Provision of design for scaffold access
e. Intrusive site surveys to locate tendons within existing pre-stressed beam soffits.
f. Mock-ups for anchors install in limited space.
g. Design, manufacture and delivery of 24 bearings, supplied by Freyssinet Products Company (FPC) (22no. free and 2no. guided). - Main works contract:
a. Bearing replacement works
Freyssinet collaborated with National Highways to determine the design and programme for the replacement of the 24 existing bearings. As well as replacing the bearings, a permanent stainless-steel soffit plate was attached to the soffit of the precast prestressed beams in the vicinity of the guided bearings in order to tie them together laterally.
To facilitate the works, Freyssinet UK’s Technical Solutions team designed temporary works arrangements, including the jack stacks and steel restraint system to enable the installation of permanent works. The sequence of works included:
- Undertake enabling works and install access scaffolds and working platforms as required.
- Implement traffic management.
- Install steel corbel and undertake local break-out to enable installation of jacking assemblies/jack stacks.
- Undertake bridge jacking and support and restrain abutment on/by temporary works.
- Remove existing bearings.
- Construct bearing plinths, install replacement bearings.
- De-jack deck and load replacement bearings.
- Dismantle lateral restraint and temporary RC block, re-instate footway waterproofing and surfacing.
- Remove jacking assemblies/jacking stacks and remove mortar beds. Remove steel corbel and reinstate.
- Dismantle access scaffolds and working platforms, clear site.
- Remove all traffic restrictions above and below deck.
Technical challenges and solutions
Blind masonry plate produced by FPC
To ensure timely delivery of bearings to site, masonry plates for longitudinally guided bearings (connecting the soffit of existing prestressed concrete beams to replacement bearings) were delivered without holes as anchor positions could only be confirmed once on site. Templates were used to project hole position from the soffit of existing beams onto masonry plates.
Steel corbel
Due to geometric constraints, a temporary steel corbel was to be anchored into the abutment wall to provide support to the jacking point in the vicinity of the longitudinally guided bearings. The steel corbel is set at a lower position to allow local break-out of the bearing plinth and shelf.
Lateral restraint and temporary concrete block
When supported on jacks, a temporary lateral restraint was provided through a steel plate bolted to the deck. The lateral restraint consisted of a plate bearing against a temporary reinforced concrete block, transferring lateral forces to the abutment back wall.
The lateral restraint provided restraint to individual decks when supporting jacking positions (after jacking of the deck). Transverse forces were transferred from the deck through post drilled connections into the lateral restraint plate. Vertical plates, connected to the lateral restraint plate, transferred transverse forces to the temporary RC block. The temporary RC block was then anchored into the abutment wall, which allowed the transverse forces to be transferred to the abutment. This solution was designed and checked using the strut and tie method, and anchor testing was specified in accordance with National Highways guidance.
A collaborative working relationship between all parties was developed during ECI stage, which contributed to the successful delivery of the scheme. A mock beam workshop held before work started on site was also benefical developing the programme and RAMS, and as a result the project was finished on time and on budget, to a high standard of quality and safety.
The SDF SE Structures Delivery Team for the A2 Patrixbourne project was shortlisted in the Bridge Project Team of the Year category at the NCE Bridges Awards. The shortlisted team, comprising of Jacobs, National Highways, Freyssinet, and VolkerLaser showed ‘exemplary teamwork’ on the Patrixbourne Road (A2) and Quarry Hill Road (A21) bridge bearing replacement schemes. The judges praised the partnership, commenting: “Through mutual trust, all parties innovated beyond standard designs, ensuring the success of both construction and future maintenance in these critical schemes. The team’s bespoke solutions minimised the impact on the environment and road users while ensuring value for the client, ultimately the taxpayers, showcasing the true success of this award-worthy collaboration.”