NATIONAL GRID LNG BUND WALL, ISLE OF GRAIN, UK

The liquid gas storage tank with a 50,000 m3 capacity was commissioned in 1981. It is surrounded by a 19.5 m high x 63.4 m diameter x 520 mm/470 mm thick reinforced-concrete bund wall to provide secondary containment in the event of a rupture of the steel tank. Externally wrapping the bund wall to provide restrainment are 14 no preloaded multi-wire bands in horizontal rebates and sealed for corrosion protection with a gunite coating. 

In December 2012 CCL was called upon to provide a design and operational solution to replace the existing restrainment system to the outside of the bund wall. Based n lowering the capacity of storage during the works, the bespoke solution involved the design of special anchors capable of restraining bursting forces of 223 tonnes per anchor. CCL’s solution included the safe detensioning of the existing wire from around the bund wall using a post-tensioned assisted strap restrainment system.

Upon completion of the restrainment system, the load in the wire-wrapped tendons was released using a purposely-designed man basket access and disc cutter. Once all of the loaded bands had been detensioned a complete scaffold was erected around the whole circumference to enable the safe removal of the wire system. Surface preparation of the rebates and surrounding areas was then undertaken using concrete planers. Concrete repairs and coating protection of the recesses could now be completed.

Unbonded strands with a UTS of 279 kN in a special HDPE greased sleeve providing enhanced durability were installed individually, with 20 no in each recess and 3 additional bands in the lower section. Anchors were installed on each band of strands located around the outside of the bund, then stressed to allow the concentrated forces to be resisted for the full height of the bund wall.

Upon completion of 5,575 tonne of restrainment stress, the tank was aesthetically weatherproof coated by CCL. The operations director from CCL was based on-site for the duration of the project.