Jack Lynch Tunnel
River Lee | |
Route | N40 |
---|---|
Operation | |
Work begun | 1995 |
Opened | May 1999 |
Operator | Egis Road and Tunnel Operation Ireland |
Technical | |
Length | 610 metres (670 yd) (immersed tube tunnel section) 1.8 kilometres (1.1 mi) (total roadway) |
No. of lanes | 2 cells of 2 each |
Operating speed | 80 km/h |
Tunnel clearance | 8.5 metres (28 ft) (external) |
Width | 24.5 metres (80.4 ft) (external) |
The Jack Lynch Tunnel (
It takes the road under the
The tunnel has two cells, each with two traffic lanes and two footpaths, and a central bore for use in an emergency only. Pedestrians and cyclists are expressly forbidden from using the tunnel.
History
The idea of a crossing of the River Lee downstream of the city came from civil engineers employed by Cork
No road development in Ireland prior to that date had required such a large investment,
A sworn
In 1989, the government recommended a further feasibility study to consider the need for a crossing and the technical, economic and operational aspects of the various crossing options. The study confirmed the findings of the original
In 1992, the Minister approved a Bridge Order for a four lane immersed tube tunnel. In the intervening time, the Irish government had also established the National Roads Authority (NRA) to advance the long-term development of the national roads network. Declan O'Driscoll was appointed the Chief Engineer of that authority and together with J.D. Shinkwin, Director of Ewbank Preece OhEocha, and W.A. Fitzgerald, Cork City Engineer, formed an informal Technical Steering Committee for the Tunnel Project.
Financing and contracting
The IR£70 million design and construct contract was awarded by the Cork Corporation on behalf of the
In the early 90s, Ewbank Preece OhEocha (formerly DeLeuw Chadwick OhEocha, and later to become part of Mott MacDonald) supervised a major geotechnical investigation, conducted a hydraulic study of the river, and carried out an environmental impact study. Ewbank Preece OhEocha, in association with Symonds Travers Morgan, produced a conceptual design and tender documents for Cork Corporation on a design and construct format based on geometric and performance specification. Thirteen parties showed interest in the contract. From these, four consortia were selected and Cork Corporation made a final contract decision in December 1994. As is typical on a large-scale project of this type, the chosen contractor was a joint venture of Tarmac Walls JV, formed by Tarmac Construction, now known as Carillion, and P.J. Walls (Civil) Ltd.,[7] part of Ireland's Walls Group. Subcontractors then handled many of the key tasks of construction.
Construction
Construction involved the excavation of a large casting basin where the tunnel elements or pieces were constructed. After construction of elements was complete, the casting basin was filled with water and joined to the adjacent
Construction techniques
The chosen method of construction was the immersed tube technique. In this method, a trench is dredged in the bed of the water channel. Tunnel sections are constructed in the dry, for example in a casting basin, a fabrication yard, on a ship-lift platform or in a factory unit. The ends of the section are then temporarily sealed with bulkheads. Each tunnel section is transported to the tunnel site – usually floating, occasionally on a barge, or assisted by cranes. In the Jack Lynch Tunnel, the 610-metre-long reinforced concrete immersed tube tunnel is made up of five elements, each around 122 metres long, 24.5 metres wide and 8.5 metres high. The northern approach was formed by a 120-metre-long floated open 'boat' section – the first of its kind.[6]
Excavation and dredging
Dredging International was the chosen dredging contractor, and the value of the dredging contract is stated by them at €12.4 million. The scope of works consisted of dredging the main tunnel trench and subsequently backfilling the completed construction with sand and gravel. The contract provided also for restoration of the riverbed profile and the addition of a rock protection layer. Between May 1996 and March 1999, the company excavated 785,000 tonnes of silt and alluvium and 300,000 tonnes of sand and gravel.[8]
The trench was dredged primarily by a series of specialised vessels, in several stages and with different equipment. Much of the main trench for the Lee Tunnel was excavated by the backhoe dredger "Zenne". Two barges were used to transport the dredged material 19 km (12 mi) downriver and from there to a disposal site four miles offshore. The cutter dredger "Vlaanderen XIX" removed the underlying fluvioglacial material. A second cutter dredger, "Vlaanderen XV", was deployed to breach the casting basin perimeter, or "bund". A rock layer was encountered on part of the trench line, which was dealt with by the jack-up platform "Zeebouwer". The "Big Boss" vessel was employed to remove the rock. This backhoe dredger was equipped with a "Backhoover" (in effect, a "mini" precision dredger). This system proved extremely effective in removing very thin layers of recently deposited material immediately prior to immersion of the tunnel elements.[8]
Constructing the immersed tube
Building the tunnel structure required the
Each box section comprised two 9.8-metre-wide dual lane traffic tubes and a 1.35-metre-wide twin walled central tube for services and emergency access. The 1.2-metre-thick base slab was cast first, followed by the 50-centimetre-thick central walls. The outer walls and roof were cast together in a single operation, in six nominal 20-metre lengths, using special travelling formwork. This was struck inside the formed section, moved along to the next length and then jacked up into position, each within a 72-hour cycle. Each 1000-cubic-metre pour required approximately 1500 square metres of formwork. The inside shutters for the outer walls were vertical steel section panels and Alform Beam walers, which were attached to the top slab of the special steel traveller, while the outer shutters were crane handled vertical steel section panels with Alform Beam or steel channel walers.
The open top boat unit, measuring approx 40 metres wide (including two 7.2-metre wings at its widest point), 120 metres long, and up to 10 metres high, was cast in two operations using standard formwork. The boat unit and all the tunnel section elements were cast using grade 40N concrete with a percentage of ggbfs cement replacement, reinforcement being high strength and 16 to 40 mm diameter.
Tunnel operation
The tunnel is currently operated and maintained by Egis Road and Tunnel Operation on behalf of Transport Infrastructure Ireland.[11] Egis took on that role in 2015. Prior to that it had been operated and maintained by Cork City Council.
The road surface was laid in 1998/1999 and the tunnel opened for traffic on 21 May 1999,[12] roughly 20 years after the first formal studies had been prepared. The final cost of the whole scheme including feeder roads and not just the tunnel itself was IR£105 million (approx €133 million).[13] The tunnel has two separate two-lane bores (each lane 3.75 m wide). There is a service walkway about 1 metre across which doubles as an emergency escape. During periods of maintenance, one tube may be closed and the other used for bi-directional traffic. The environment within the tunnel is controlled by a closed circuit TV system (CCTV), traffic control and Supervisory Control and Data Acquisition (SCADA) system. External photometers linked to the SCADA system provide a level of tunnel lighting most compatible with ambient light levels outside. To assist drivers in adjusting their eyes, lighting gradually brightens as they approach an exit.[9]
There are six emergency exits in each traffic bore for pedestrians that lead into the central bore (pedestrian exit), the exit doors are at each end of the central bore.
Jet fans located within niches in the roof of the immersed tube sections provide longitudinal ventilation, and the tunnel is equipped with fire and life safety equipment.[6]
Despite the cost of its construction and operation the tunnel is not tolled. The Feasibility Study for the tunnel envisaged that the crossing could have a toll of 30 pence (in 1981 IR£)[4] (approximately €1.07 in 2020),[14] but the concept of a toll was dropped after political opposition. It was felt that, because of the proximity of the tunnel to the city, the imposition of tolls would tend to encourage some drivers to avoid the tunnel and continue using the city centre streets thus minimising the benefits of the tunnel.
An immersed tube tunnel of similar length has been constructed in Limerick,
See also
References
- ^ "TII Traffic Counter Data Jack Lynch Tunnel". nratrafficdata.ie. TII. Archived from the original on 25 April 2016.
- ^ "Home > Jack Lynch Tunnel". Jacklynchtunnel.ie. Retrieved 18 August 2014.
- ^ Greater Cork Area Land Use/Transportation Study. Skidmore, Owings & Merrill, the MVA Consultancy, and LUTS Team. Cork 1976
- ^ a b c d Bardas Chorcai; Down-Stream Crossing of the River Lee, Feasibility Study. DeLeuw Chadwick O'hEocha, Consulting Engineers, November 1981
- ^ a b Seanad Éireann – Volume 122 – 17 May 1989 Adjournment Matter: Cork City River Crossing. http://historical-debates.oireachtas.ie/S/0122/S.0122.198905170009.html Archived 7 June 2011 at the Wayback Machine
- ^ a b c "Jack Lynch tunnel - Tunnels - Mott MacDonald". mottmac.com. Archived from the original on 29 October 2013.
- )
- ^ a b "Ireland – Cork – River Lee Tunnel". Archived from the original on 8 October 2007. Retrieved 16 June 2007.
- ^ a b "Traffic Management in Cork". CGTA. Archived from the original on 13 March 2008.
- ^ "River Lee Immersed Tunnel". rmdkwikform.net. Archived from the original on 29 September 2007.
- ^ "Toll fears as running of Cork's Jack Lynch Tunnel to be outsourced". irishexaminer.com. Irish Examiner. 11 November 2014.
- ^ "Cork City Council > Our Services: Roads & Transportation Directorate: Jack Lynch Tunnel". corkcity.ie. Archived from the original on 16 February 2007.
- ^ "Jack Lynch Tunnel thrills the 'Real' Taoiseach". Irish Examiner. 22 May 1999. Archived from the original on 27 April 2012.
- ^ "CPI Inflation Calculator". CSO. Retrieved 2 June 2020.
- ^ Limerick Tunnel : What is the Limerick Tunnel?