The design and build contract – a joint PFI project between NCC and SITA UK – was won by BAM Nuttall in June 2008. Royal Haskoning’s role was to bring our considerable expertise in the construction of waste management facilities to provide detailed design, technical and architectural assistance.
The IWMF consists of two integrated structures: the Materials Recycling Facility (MRF), which is designed to separate and sort 50,000 tonnes per year of domestic recyclable waste, such as newspapers, cardboard, plastic bottles and cans, and the Waste Transfer Station (WTS), which will process 70,000 tonnes of non-recyclable waste per year before transfer to the Tees Valley where it will be used to generate electricity.
Our design also included office and amenity buildings, a series of bulk storage bays, parking areas, access roads, weighbridges and surface and foul water disposal.
The site itself posed a number of technical challenges. The land survey identified an existing pond in the north west corner of the site and there was an 8m height difference across the site. To achieve a suitable base level for the facility, BAM Nuttall had to undertake a cut and fill operation of some 40,000m3 of in-situ material.
Ground investigations also identified a layer of clay fill, which had never been surcharged. In order to minimise settlement problems beneath the MRF, the un-compacted clay fill material was removed as part of the preparation works. A substantial amount of fill material was needed beneath the WTS to achieve the required base level.
The tight construction programme did not allow sufficient time for this fill material to be pre-loaded in order to negate settlement problems. The design solution was to place the WTS on a mat of stone columns with large push walls founded on concrete piles.
The layout of the MRF and the WTS dictated the shape and overall design of the facility. The WTS had to accommodate a vast storage area for holding residual house hold waste prior to its transportation in bulk to Tees Valley and the MRF unit needed to house large quantities of hi-tech waste processing equipment for paper, plastic and metal sorting.
A single large concrete push-wall was built between the two buildings which also doubled up as the support system for the roof structure of the WTS. This simplified solution removed the need for two separate concrete push walls either side of a ground supported frame. This form of construction was also adopted for the bulk storage bays so the top hat steel roof frame sat directly on top of the push walls instead of needing two separate structures.
In order to reduce problems with heave and settlement of the office and amenity building floor slabs a system of suspended concrete beams was adopted. This system of floor construction enabled the floor to be secured in just one and a half days as opposed to the normal two weeks required for ground slabs.
Finally, we looked at a number of environmental solutions for the disposal of foul and surface water such as building a small treatment plant with a retention pond or adopting a sustainable drainage system. The final decision was to pump foul water through a specially constructed 750m by 8m high rising main to an existing foul water manhole. Micro boring technology allowed us to minimise disruption to the site by keeping the surrounding road infrastructure running.
The facility is due to be operational by the 2nd quarter of 2009.
Click here for the 'Taking the pressure off landfill' PDF download.