Construction of Mooring Platform for Cawood Barge.
The remit for this contract was to install a steel mooring platform for the Environment Agencies Cawood Barge which is used for rock placing on the River Welland and out into the Wash. The contract required working in tidal conditions and involved removal of birdcage scaffold from around existing pre driven case piles, the installation of a new temporary working platform, the removal of accumulated silt, cutting down of case piles, fitting of new steel pile caps and the installation of steelwork/bracings.
The existing case piles had been driven two years previously by the Environment Agency so the first job was to survey the verticality of the piles and to plot positions to allow the pile caps to be made individually to correct any discrepancies in the piling. A 35t long reach machine was then mobilised to site to remove the accumulated silt between the piles to get down to the working platform level. This section of works was conducted in partnership with the scaffold company who removed the old birdcage and installed the new platform.
Once the working platform was in place operatives then marked out the levels of the piles and cut them down to allow the fitting of the new pile caps. The pile caps were fitted, levelled and welded into position prior to placing the main bearer beams. The temporary working platform was then removed to allow installation of the lower cross bracings. This work had to be undertaken at lowest tides situated around the Autumn equinox as that was the only tidal window to allow installation of the lowest bracings. When these bracings had been installed top cross bracings were then fixed in place and timber planks installed on cross beams. Four 305mm x 305mm H beam piles 14m long were then driven at the back of the mooring platform for the barge to lay up against and four 360mm diameter 14m long case piles were driven as mooring posts for the barge.
The contract was carried out in tidal conditions with very small working windows and was completed to programme and undertaken under full construction design & management regulations with Land & Water Services as Principal Contractor.
It was anticipated that there was 4,400t of silt to be removed, half of which was expected to be hazardous Land and Water Services could see flaws in the historic silt test results and therefore undertook additional sampling and detailed testing which enabled the silt to be reclassified as 100% non-hazardous. Furthermore rather than dredge down to the previously over dredged hard bed level, Land & Water designed a solution which reduced the volume of silt to be removed, and therefore the cost of the works, but provided the Environment Agency with a firm and level bed for future access and maintenance.
