GENERAL OVERVIEW OF WORKS

Tanton Bridge widening works required the existing downstream elevation (parapets, spandrels, wingwalls, copings, pilasters) of the bridge to be dismantled and the arch barrel extended by approximately 5.8m. The elevation was then rebuilt on the new line. River re-alignment was also needed.

The works included TM works, temp/scaffold works, arch support, sheet piles, new RC foundations, dismantle/rebuilding downstream walls, remove/install new road resurfacing, new drainage gulley, new kerb line, new verge line, concrete mass infills and footstep construction.

PBS was responsible for the execution of the works detailed in the contract drawings and documents. This included the design of all temporary works, scaffolding, temporary arch supports and permanent sheet piling. PBS implemented a full road closure with the use of our specialist subcontractor Oneway TM. Traffic Management was in accordance with Chapter 8 Highway Specifications.

 ACTIONS COMPLETED

Specific Health and Safety documentation was developed for this scheme including Lift Plans, Spill Response Procedures for working near water and dynamic Method Statements for the rebuilding of the stone bridge.

Early procurement of materials allowed the scheme to be completed on programme during the first national lockdown in 2020.

Rawcliffe Bridge is a three span post tensioned bridge consisting of two balanced cantilever approach spans and a central suspended span, spanning over the Dutch River near Goole.

GENERAL OVERVIEW OF WORKS

The scheme included carrying out construction works to re-open Rawcliffe Bridge to vehicle loadings of 44 tonne and improve the current condition of the bridge structure. A new bridge deck and road construction were included with minor maintenance works. In summary the activities involved in the repair works included: 

Additional works

TENDON IMPREGNATION SCHEME

The council had performed inspections to the various bridge elements over the last 20 years and found the ground anchoring Macalloy bars to be in poor condition and the concrete encapsulated post-tensioned tendons to be suffering significant corrosion.

CHALLENGES ARISING

If these defects were not rectified it could have led to structural failure of the bridge. These defects, and the requirement to rectify without demolishing the bridge, raised some unique engineering problems. The replacement of the Macalloy bars is a complex but relatively well-known civil engineering process using tried and tested techniques. However, the corrosion protection of concrete encapsulated post-tensioned tendons within concrete bridges, without demolishing and re-building of a significant portion of the bridge, had not previously been completed in this country using our proposed techniques.

SOLUTIONS DELIVERED

PBS procured a specialist sub-contractor with expertise in corrosion protection and worked in a collaborative fashion with the council to agree on an innovative method of corrosion protection that would achieve the required structural outcome but without the cost and time involved in reconstructing large sections of the bridge. The innovative technique we utilised was pumping under pressure a proprietary hydrocarbon and silicon-based material that has the ability to impregnate and saturate the full length of the tendons, with only small amounts of demolition being required to find the location of the tendons and for the pumping pits. This film pumped in under pressure formed a protective layer around the tendon. The film was able to travel the full length of each tendon using the voids within the existing grout and the interstitial spaces between the wires in the tendons. This film stops the existing corrosion process and provides improved resistance to future corrosion.

RESULT

This was the first time this methodology and proprietary product had been used in the UK. The works were completed in two phases. Phase one was to demonstrate and evaluate the means and methods for the impregnation process on only one tendon. The information collected during the phase one works helped with the planning, methodology and budgeting for phase two. Phase two involved impregnating all forty tendons. Using the technique developed all tendons within the bridge decks were successfully protected from corrosion and the works were completed in a much faster and more economical manner that existing techniques would have allowed.

Kirkby Malham Bridge is a single arch masonry Grade 2 listed bridge (which spans Kirkby Beck) that required widening for safety reasons. There were no existing footpaths on the bridge but the widening allowed for footpaths to be incorporated. The bridge is at the bottom of an incline, just adjacent to the main crossroads in the centre of the village, and there had been accidents in the past due to the narrowness of the bridge and poor sight lines at the junction. The bridge parapets had also been impacted and damaged by errant vehicles.

GENERAL OVERVIEW

PROGRAMME OF WORKS 

The works were carried out in phases as required by North Yorkshire County Council.

Phase 1

Installation of the scaffolding/temporary support works

Install temporary bridge across the existing bridge

Install sheet piles and excavate to extend abutments

Phase 2

Remove existing road surface

Remove existing curb line/verge line

Remove existing drain outlet

Excavate existing earth works

Phase 3

Dismantle existing bridge section, including abutments

Dismantle existing parapet

Dismantle existing side wall parapets

Phase 4

Excavate working areas

Excavate ground for foundations

Install formwork for foundations

Case concrete foundations

Phase 5

Construct new abutment stone work

Construct new bridge arch stone work

Cast concrete mass infill

Construct new bridge parapet

Construct new stone work parapet and side walls

Cast concrete mass infill sections/install dowels

Remove scaffold/temporary works

Phase 6

Install new curb line

Install new verge line

Install new drain outlet

Install new 2.No ducts

Install new road surface

Install new road markings

Phase 7

Remove traffic management

Remove temporary bridge

Phase 8

Removal of all site waste, including materials and equipment.

GENERAL OVERVIEW OF WORKS

BECK HILL BRIDGE CONSTRUCTION

Beck Hill Bridge was designed by the council designers as an integral bridge. This means that the bridge was not split into the two abutments, with the bridge deck inserted between, sat on bearings that allow movement without articulation joints. The integral bridge was designed as a monolithic structure that can accommodate the forces associated with expansion and contraction of the members.

CHALLENGES ARISING

The design raised significant issues as to how this integral bridge could be constructed as designed. The challenges the integral bridge design raised were that no kicker was allowed to be poured, to prevent a visible construction joint. Kickers are important as they provide an initial first pour to start the concrete structure off in the correct position and a bottom edge for the concrete shutters to be fixed against.

Due to the requirement for a continuous pour each abutment had to be poured in one complete and continuous pour from the narrow pinch point at the top of the abutment where the high quantity of re-bar prevented adequate access for tremie pipes and pokers to vibrate the concrete. The abutment also required a sloping profiled formwork front face, which presented problems in how the concrete could be poured and compacted in one continuous operation, from the top pinch point, to the bottom from face of the sloping face, without potentially having visible honeycombing of the concrete on the patterned face due to lack of vibration.

SOLUTIONS TO THE CHALLENGES

To overcome these construction challenges PBS carried out research into the available shutter support systems and concrete compaction equipment and how this could be adapted to suit our scheme. PBS designed an in-situ concrete shutter foundation system to support the shutters self-weight, as well as that of the concrete, and to allow the setting out of the shutters in the correct location. PBS also designed a grid system of tubes, both horizontal and vertical which would allow the pokers to be dropped from the top of the abutment and inserted from the sides, giving vibration to all required areas of the abutment including the sloping front face. These tubes were designed and installed to not conflict with the specified reinforcement and were installed at the same time as the re-bar.

PBS designed and fabricated rigid extension handles onto the concrete pokers so that they could be guided into the far reaches of the abutment in the tubes and removed safely. During the pour as the depth of the concrete rose up the shutter the plastic tubes were raised/removed at strategic points so that they did not end up being cast in with the abutment. PBS had an independent structural engineer assess the concrete pour on completion and the engineer commented in the report that he was very impressed with PBS’ ingenuity in overcoming these challenges.

The bridge is a three span composite steel and concrete structure carrying two lanes of the A645 over the River Aire.

The embankment approaches to the structure suffered from significant settlement since construction. This was an ongoing road maintenance problem, but had also impacted the adjacent bridge structure. The abutments of which were being pushed towards the bridge deck, such that the deck was subject to a propping force.

This scheme involved preventing any significant future settlement and as far as possible and repaired damage already caused to the structure.

The embankments at the Drax & Goole side were excavated down and rebuilt from a depth of 6m, this included for replacing the existing embankment fill with lightweight LECA material fill.

The scheme involved the removal and reconstruction of curtain walls, allowing abutments to move to equilibrium position and also the replacement and resetting of all abutment bearings.

A monitoring system was installed to the bridge by Mabey Hire, which would raise alerts when movement was detected throughout the structure. The system monitored the strain in the bridge beams, the load in the hydraulic cylinders; at each cylinder or restraint LVDT’s were installed in order to measure any vertical, transverse and longitudinal movements of the bridge beams or abutment.

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