To produce even more drinking water from surface water, De Watergroep is significantly expanding the De Gavers Water Production Centre (WPC) in Harelbeke. That the WPC remains in operation while the works are ongoing was just one of the challenges in this project.

WPC De Gavers is located on Beneluxlaan in the municipality of Stasegem, adjacent to the E17 motorway and the Kortrijk-Bossuit canal. From this canal, De Watergroep draws the water that undergoes various processes and is then supplied to the public drinking water network. The pumped water is pretreated until it has the quality of bathing water, and then flows gravitationally towards the 60-ha Gavermeer lake in the Provincial Domain De Gavers. After about 4 months in this flow-through basin (with self-cleaning effect), the water is pumped back to the WPC, where it is post-treated and purified through various processes and upgraded to drinking water. This is then pumped to the reservoirs and water towers in the Kortrijk-Harelbeke-Waregem region. Via distribution pipes, the water reaches the customers. At the start in 1995, WPC De Gavers produced 15,000 m3/day. Through expansion and refinement of the installations over the years, the production capacity today amounts to 32,000 m3/day.

Mission

The processing volume will be increased to 50,000 m3/day by expanding/replacing the after-treatment capacity. Specifically, a post-treatment building will be erected and the activated carbon filter building will be expanded (including connecting tunnel) so that water can be pumped through 6 instead of the current 4 activated carbon filters. As the pre- and post-treatment capacity increases, that for rinse water treatment must also be increased. Therefore, a sediment thickener and the foundation slabs for 5 DynaSand filters will be added. Also important is the construction of an underground buffer tank to collect rainwater so that it can be pumped through to the Gavermeer lake.

Weak soil - heavy loads

Typical of this type of project are the large downward forces due to the heavy technical installations and the presence of huge amounts of water. This was in contrast to the weak soil consisting of Ypres clay. Therefore, all new elements on the site are founded on 610-millimetre-diameter piles and to a depth of 10 to 12 metres. Those piles are designed for both compression and tension, as the underground water level is quite high. Because of the multitude of installations that each create heavy loads, and because of the different scenarios - the contents of tanks and pipes can vary from empty to full and everything in between - it was necessary to calculate an unusually high number of load combinations.

Waterproof

The basic design was fairly straightforward due to the use of cast in situ concrete. But evidently, the building owner has very strict waterproofing requirements. This affected our calculation of both concrete and steel strength to avoid deformations and cracking. There are also a huge number of throughputs of cable ducts, pipes and tubes - often up to 80 cm in diameter - through floors and walls. These too all need to be designed and executed waterproof, so our detailing of the plans is huge. Another challenge lay in the fact that with the new buildings, we were building on to 4 existing buildings. Here too, a lot of coordination was needed to properly align the levels of water pipe throughputs to allow gravity to do its job.

Complex

The weak subsoil, the multitude of diverse pipes and installations, and the great concern for waterproofing makes for a complex design in terms of structural engineering. Additional challenges include the fact that the design and implementation phases overlap, and that the day-to-day operation of the WPC must not be compromised. This requires constant fine-tuning of the plans and, at the same time, continuous attention to great detailing.