OB167 Bridge Renewal: Limerick-Tuam Line
 

OB167 Limerick TuamName:  OB167 Bridge Renewal: Limerick-Tuam Line
Location:  Athenry, Co Galway
Client:  Iarnrod Eireann, Track & Signals HQ,
Project Value:  €300,000
Completion Date:  September 2009

Project Description:

The works consisted of the widening of an existing overbridge on the Limerick to Tuam Line near Athenry on the R384. The approach road was widened using ribbed retaining walls of varying heights from 5550 mm to 2067 mm. Each of these wall units were 3000 mm wide and were installed to a schedule of road closures. The existing bridge abutment was also widened using precast concrete sections and then the existing bridge was demolished and the widened bridge was installed. All the ridge and approach wall precast units were supplied free issue by Iarnród Éireann. The works involved substantial site set up and clearance adjacent to the existing bridge. The widened approach walls were built on lands owned by CIE, however, access through private property was required on two of the approach walls. The proposed widened section of bridge was clad in stone reclaimed from the existing bridge and the approach walls were clad in stone to match the original bridge stone.

The works included the provision of a 1300 mm wide footpath on the Athenry side of the bridge and associated service ducting.

The public lighting on the bridge was repositioned and a gas duct was incorporated into the deck. The bridge was waterproofed and resurfaced with HRA top course and an anti-skid surfacing was applied.

The site compound was established within the site boundary at the location convenient to the site and main entrance. A secure compound with adequate storage, offices and car parking were provided in accordance with the contract document. The site compound was secured for the duration of the works.

Site Clearance

The project will commence with the removal of scrub at the location shown below to enable access to the site and to place storage containers.

General Works Prior to Demolition

Once possession of the site was acquired and road closures were in place, mobilisation to the site began and traffic management measures were  put in place as per the drawings. The site was then surveyed for any existing services that may have interfered with the works. Temporary fencing was erected to secure the site where appropriate and minor site clearance works took place such as the removal of hedging from the embankments.

Masonry Tie-in Detail

Coffey Construction then mobilised a gang to commence drilling of the abutment to receive the reinforcement links to stitch the existing to the new works. Once the bars are in place, the formwork will be erected and the area poured. It is more advantageous to carry out this element of works prior to the demolition of the bridge.

Demolition (Friday - 11pm)

All plant that was then required to be on site and parked in the compound. Once the road closure was in place and the Irish Rail Lookout man has given the full TIII possession, the machinery then travelled out from the compound and set up into position ready for the demolition work. During this time, a prefabricated railway line protection system was transported from storage in the compound and placed on top of the rails under the bridge deck and 10m either side of the bridge abutments. From experience, Coffey Construction had no requirement to extend this track protection any more than 10m each side to protect the rails from falling debris.

The demolition of the bridge was carried out using 2 no. 20ton excavators on each side of the bridge. Working together, they assisted each other to minimise the amount of debris falling on the track. The existing road surfacing and backfill were then broken out and the masonry removed down to the springing point of the bridge. The material from the bridge and rubble backfill were then loaded onto 6ton dumpers working in tandem where they tipped the material into the compound for sorting at a later stage. Once all material had sufficiently been removed to the required level for the pre-cast banking seat, a crew was then ready to level this surface by hand and ‘point’ between the voids with non-shrink grout as required. The area was fully fenced off and made safe from the public and the night work for that time had come to an end.

Excavation

Following the demolition of the bridge, the excavators then excavated the foundation for the ‘L’ units and placed the blinding on the areas as the curing process was set in for the placing of the precast units the following night.

Night Time Works

During the Friday, tower lights were set up in various locations around the site. These locations had been investigated previously to maximise light out puts and avoid shadowed areas for example.

Installation of Banking Seats

A crane was mobilised to site early in the morning and set up in the location as pre-agreed by our client under Irish Rail’s lookout supervision. Once set up, delivery lorries started arriving to site with the pre-cast units and were then off loaded in the compound where the crane was set up.

The crane hire company then provided approved lifting gear/chains. Any fallen debris was then removed under the possession.

Works then continued during the day, removing the approach walls and storing them into the compound where they was also a team sorting out the cut limestone with a mini-digger. The daytime works teamhad arranged to have all tower lighting back in place and a fill of fuel ready for the night’s possession team.

Installation of Bridge Deck & Retaining Structures

A banksman then instructed the crane operator as to which units to lift as they were correctly labelled prior to the night works. A 20ton excavator with a Wimmer drill attachment created the 10 no. 70mm holes through the pre-formed holes in the banking seat unit and then drilled down through the existing abutment to a depth of 1.5m below the springing level. Once each hole is complete, a team then followed by installing the dowel bars and grouting up each one into position.

The bridge bearings were then installed. Prior to this, the deck units were installed from one side to the other in that order.

At this stage, the stitching was then poured to tie the bridge deck and complete works on the deck structurally. It was envisaged that there was a tight seal between the pre-cast units however, as experience has taught us silicone will be placed longitudinally down the joints as to create a close to waterproof seal. This will avoid unnecessary dripping of the concrete ‘fat’ onto the line during the vibration stage. The daytime works team had arranged to have all tower lighting back in place and full of fuel ready for the night’s possession team.

Once the installation team had both sides of the North approach units in place, they commenced on the South side installing same. A separate team was ready to backfill the units whereby an excavator was in the compound with a sufficient stock pile of granular material where it loaded 6ton dumpers and transported it to the required area. A mini-digger levelled the material and there was a Bomag 120 roller in place compacting as required. The backfill material was placed in 225mm layers.

On the following day, there was sufficient material to drive through with cars where the bridge was  opened to the public and the full road closure was  lifted and partial closure stilled remained in place under a one-lane traffic lights system. Following closely behind them the masonry team installing the recycled stone facing to the parapets and abutments.

Fencing & Crash Barrier Installation

A subcontractor then carried out the fencing on site and Coffey Construction installed the crash barrier.

Line Marking / Anti-Skid Surfacing

A specialist contractor whom Coffey Construction uses on all Irish Rail projects, both car parks and platforms, carried out this element of works. Other incidental works and reinstatement of the compound area were then followed on the completion of the job before demobilisation off site.

Coffey Group, Athenry, Co. Galway, Ireland Tel: +353 91 844356 Fax: +353 91 844519 Email: info@coffeygroup.com