Fdeng Civil Engineering Technology Constructing the Conwy Tunnel

Aims and Objectives Aims – To investigate the construction process for the Conwy Tunnel. Objectives – to understand the Geological conditions and the visual impact a new crossing would have on the town of Conwy. To discuss the social problems created by the increased traffic travelling through North Wales. The innovative solution to the problem and the alternative tunnelling techniques available at the time.

The Historical A5 across North Wales The first major road in North Wales the A5 was constructed by Thomas Telford, and this included two suspension bridges, one crossing the Menai Straits and the other the Conwy Estuary. The A5 which starts at the Marble Arch in London and finishes at the Admiralty Arch in Holyhead, was constructed in the early 1800’s as a result of complaints from Irish MP’s who were campaigning for better communication links between Dublin and London. The communications network of that time were stage & mail coaches, which prior to the construction of this road, were only capable of reaching Shrewsbury.

The A55 Expressway As society developed, and with the introduction of the Motor Car, the number of people wishing to travel across North Wales increased dramatically, to a point where the A5 could not cope with the level of traffic involved. Tourism suddenly became a very important industry to North Wales as every year many people came to North Wales on Holiday. Unfortunately the traffic problems this increase in traffic created, would also put off a lot of potential holidaymakers. This industry relied heavily on Civil Engineering to put a structure in place to allow people to travel easily and safely throughout North Wales, this lead to the creation of the A55 expressway.

The A55 Expressway The Modern Expressway has created a fast dual carriageway linking the port of Holyhead to Chester, reducing travel times and traffic congestion in towns across North Wales. This route is also part of the European route E22 stretching 5320km across Britain, through the Netherlands, Germany, Sweden, Latvia and into Russia. However there was one town along the route of the A55 that for over 50 years had suffered from Traffic congestion, and caused a huge bottleneck.

The A55 Expressway One of the worst spots for Traffic congestion in North Wales was the town of Conwy. Anybody having to travel through North Wales had to drive through this Historical Town. As the amount of traffic increased and the size of Heavy Goods Vehicles increased, the problem got worse, and was described as the worst bottleneck in Wales. This problem took Engineers 50 years to find a solution to the problem

The Conwy Tunnel Trying to fine a solution to crossing the River Conwy, threw up a number of problems. One of these being the Geology of the area. However to protect the Historical town of Conway, and offer some relief to the local people from the traffic a solution had to be found, so what are the options ?

The Conwy Tunnel The two main options available for engineers were either. 1. Build a bridge (There are already three bridges across the River) and the only real bridge solution would be a suspension bridge. The visual impact of this across the estuary would be unacceptable. 2.Dig a Tunnel.(Traditional method for this would be a tunnel boring machine) however this would require the tunnel to be constructed in hard rock, situated at a greater depth than the immersed tube. Increased cost and the diverse geology of the area would make this type of operation difficult.

The Conwy Tunnel The solution was to build the first immersed tube tunnel in this country. Six 118m tunnel sections, weighing 30,000tonnes each were built in a purpose built dry dock, in an area that is now the Conwy Marina. In the Photograph we can see six tubes have been constructed, and are being given a bituminous waterproof coating. Each of these sections were then floated out into the river and sunk into a dredged out channel cut into the river bed.

The Conwy Tunnel This photograph shows us the route taken by the tunnel. On either side of the river bank the tunnel approaches are being constructed, which will eventually bring the A55 under the River Conwy You can see the tubes ready to be floated out into the river, and water starting to flood the dry dock area, in preparation to float out each individual section.

The Conwy Tunnel Once all the immersed tubes had been constructed they were floated out into the river. Each of these tubes weighed in at 30,000 tonnes, and were guided into position by a pontoons. The sinking of the tubes took place during periods of low tide to ensure they were each gradually sunk into the correct position

The Conwy Tunnel A trench had been cut into the bed of the river. The pontoons then had the job of carrying each section over the top of the trench, and then sinking each tube into position. Ballast water tanks in each section were used, to sink or float each tube.

The Conwy Tunnel As well as building the tunnel, there was also around 6km of dual carriageway to be constructed. Bridges, underpasses and the main North Wales Railway line to contend with, made this a huge Civil Engineering project.

The Conwy Tunnel

The Conwy Tunnel

The Conwy Tunnel Conclusion. The Conwy Tunnel built between 1986 and 1991 at a cost of £102 million pounds was the solution to the worst bottle neck in Wales, and curing the traffic congestion for the town of Conwy. The solution has benefitted North Wales and finally connected Holyhead to Chester via the A55 expressway, offering a much improved road system. And what of the future? A road tunnel under the Irish Sea to Dublin?