Weatherlees WWTW

Demolition project background

The demolition contract was at the Southern Water Waste Water Treatment works in Sandwich, Kent.

In the early 1990’s, a warehouse was constructed over four settlement tanks to contain and process the odours arising from the waste water treatment process. The gasses created are highly corrosive, and progressively rusted the steel frame warehouse to the point where it was beginning to fail structurally. DDS were commissioned to dismantle the above ground structure whilst the 4no settlement tanks below were left operating.

 

 

Specification

  • Install site welfare and segregate working area from the rest of the Southern Water Site.
  • Liaise with Morrison’s Utility Services/Southern Water to confirm the disconnection of services to superstructure to be removed.
  • Coordinate erection of scaffolding along front and back elevations (for access).
  • Remove cladding to the roof.
  • With the use of a 2no. 70 tonne crawler cranes, remove corroded purlins whilst immediately installing 450mm deep alloy beams to brace the warehouse and fulfil the structural role of the removed purlins.
  • Install 4no engineered scaffold towers, each propping two runs of rafter beams under the ridge.
  • Install portable temporary foundations for a 135 tonne crawler crane.
  • Using all 3no. crawler cranes in unison, dismantle above ground structure.
  • Remove from site all waste materials arising.
  • Demobilise from site, leaving it in a safe, clean and tidy condition.

Achievements and Successes

  • At over 75m wide, the warehouse was one of the largest single span structures in Europe.
  • The building was found to be a “butler” building; all elements of it, from purlins to cladding sheets, had a role to play in keeping the building stable. This required a carefully thought out dismantling sequence as not to compromise stability at any point throughout the works.
  • The settlement tanks below the superstructure had to be kept live through the works. Furthermore access had to be given to Southern Water on short notice.
  • DDS had to work extensively to prepare an innovative and autonomous demolition solution. This required ongoing collaboration between a number of parties, including our Structural Engineers, Morrison Utility Services, Southern Water, our Scaffolding Contractor, Crane Hire Companies etc.
  • The weights of the lifts combined with the relatively tight confines meant that each rafter beam had to be removed in two lifts. This required a combined total of 3no. Cranes working in unison.
  • The remainder of the site was live and had to remain accessible; traffic diversions had to implemented and maintained to facilitate this.
  • Complications arose in the early stages of the project; however DDS overcame obstacles to make up lost time and still managed to achieve our initial forecast completion date.