DWM Plant Limited were employed by Harry Fairclough to undertake works on a logistically challenged scheme for Warrington borough council. Sever flooding on a residential estate required urgent attention to prevent a reoccurrence of previous floods from 2008. A scheme was designed to provide attenuation for storm water during period of heavy rainfall.
Due to the design and build nature of the contract several options were considered, ranging from permanent sheet piled structure, RFC storage tank, and segmental shafts, however the scheme to be adopted was a 2.8m diameter Tubosider tank system. During the evaluation process of the tender consideration about the logistical aspects had to be considered predominantly the single access to the site through a 3.0m wide access, this would mean that all deliveries of plant and temporary works equipment, excavated material to be disposed of and suitable backfill material to be imported, all within a residential estate.
Due to the ground conditions consisting of medium dense sands, and a high water table 1.0m below ground level. A robust temporary works solutions would be required: this consisted of 9.0m long L604 sheet piles (250No) and a 406*406 heavy duty bracing system while attention had to be made in choice of piling equipment given to close proximity of residential houses. Thus a RTG RG16 telescopic leader rig c/w variable moment vibratory hammer was used to install the piles without disruption to the local residents.
The works involved installing the sheet piles and hydraulic braces, followed by excavation of the cofferdam and installation of the 2.8m diameter tank system to form a labyrinth of inter connecting pipework all controlled by a specialised pump station.