An extremely challenging project for CMP which involved working in the Loughor Estuary. Here the tide provided a 6 meter rise and fall, with water flowing at peak rates of 8 knots.
Two jack-up barges were supplied and operated by CMP who used these to carry out the piling works. With deck loading capacities of 450 and 250 tonnes the two barges provided the perfect solution to work close to the live railway whilst drilling rigs and cranes were situated on board to construct the deep piled foundations.
The 1.2 meter diameter piles were formed by firstly installing sacrificial steel casings which were vibrated into the soft ground. A special piling gate was constructed off the edge of the barge to allow the casing to be held tight in position. This helped achieve the 50mm tolerance required by the specification. The piles were then drilled up to 30 meters into the sea-bed which consisted of alluvium, sandstone and siltstone. Heavy duty pre-fabricated reinforcement cages where then installed before concrete was placed into each pile by tremmie method. Concrete was delivered pre-mixed and pumped along the existing viaduct up to 250m from the pump to the pile location.
To add to the challenging conditions lifting operations were restricted to meet the railway working regulations, which meant that lifting in the direction of the railway would only be permitted during gaps between train movements. CMP introduced specialist lifting plans to ensure works could continue efficiently with zero-risk to the railway infrastructure.
The project programme required working continuously for 24 hrs a day 7 days a week. Over 45 men were employed by CMP to cover the continuous working and rotate shifts over the 10 week programme.
18 piles were completed ahead of programme and the team then moved onto assisting Carillion with installing the new bridge cross-heads over the new piles.
Loughor Viaduct Railway Replacement
Swansea, South Wales
April 07, 2016