Making level ground

09 June 2015

Built during the Cold War era of the 1950s, the NATO aviation fuel storage and pumping station that Princen had to demolish and then carry out site remediation on was used to transfer aviation fuel shipped to the port of Zeebrugge to a network of fuel pipelines that serviced military facilities and civil airports across Europe. Clearing the site represents the first phase of a much larger scheme – the Stevin project – that aims to upgrade the region’s electricity grid. The work is being done for Elia, Belgium’s high-voltage transmission system operator, which operates 5,000 miles (8,000 km) of lines and underground cables throughout the country.

The project aims to upgrade the electricity grid between Zomergem and Zeebrugge to allow for the transmission of electricity from the growing number of offshore windfarms in Belgian waters (and incidentally allow the shut-down of four nuclear power stations in Antwerp). The current full capacity of the available high voltage transmission lines has already been reached, but more offshore wind farms are in the planning stage, hence the requirement for increased capacity

The project consists of three main components. Firstly is the laying of a double 380 kV high-voltage line between Zomergem and Zeebrugge, some of it overhead and some of it underground; secondly, the construction of a new high-voltage substation in Zeebrugge (the site that Princen prepared), which will convert electricity from 380 kV to other voltage levels; and thirdly, the construction of two new stations in Bruges and Damme where electricity transmission will transition from underground to overhead facilities. A new high-voltage substation will also be built in Zomergem.

The Zeebrugge part of the overall project is in itself a major undertaking, with the site being home to 16 transformers when construction is complete, a process that will take some four years. It will be supplied by six high voltage transmission lines from the windfarms offshore and from the substation a 400 kV transmission line will carry electricity inland.

The Stevin Project is crucial in connecting offshore wind farms and renewable energy facilities in West Flanders, and is considered vital to Belgium’s achieving its goal of having 13% of its electricity supply coming from renewable sources by 2020. The project will boost economic development in West Flanders and other projects will also establish power links with the UK and Germany.

Founded in 1998 by Wesley Princen, the company has evolved from construction to more specialised electricity projects. With its small pool of very carefully selected operators, all of whom are certified to work in proximity of live high-voltage power lines, the company has participated in numerous complex and demanding electrical development schemes in the past and is currently involved in the bidding process for other elements of the Stevin project, as well as a number of other electricity infrastructure projects that are due to commence in the next few years.

Princen currently is doing almost all the earthwork and demolition work for electricity infrastructure projects for Alia in the Flanders region of Belgium, including the replacement of oil-filled transmission cables with polyethylene replacements – work that has to be completed throughout Belgium by 2020.

The Zeebrugge project included the demolition of two heavily reinforced storage tanks, each of which once contained 5 million litres (1.1 million gallons) of kerosene. Each was buried under 1 m (3.3 ft) of sand, and had a 60 cm (2 ft) thick reinforced concrete top plate and slightly thinner reinforced concrete side walls.

In addition to the tanks, there were two heavily armoured reinforced concrete bunkers that housed the necessary high pressure pumps that transferred the fuel through the pipelines, and a number of other buildings around the site, including guardhouses and associated residential structures. In addition, all the underground cables and pipes had to be found and dug up, and at the end of the demolition phase, the site had to be totally clean and exactly level.

In a first for the region, Princen recently took delivery of the first Volvo EC480D HR high reach demolition excavator to be deployed in the Benelux countries along with associated Dehaco attachments. It is equipped with a short, straight boom and arm configuration. This was deployed to the site to deal with the physical demolition of the more robust structures.

According to operator and owner Wesley: “With the short boom, I have a pin height of 14 m and because of the machine’s weight of 63 tonnes, additional counterweight and 4 m track width, I can work with a 4.8 tonne crusher with excellent stability,” Wesley added. “I also like the hydraulically variable undercarriage and Volvo’s hydraulic joint, which makes tool changes quick and easy.”

Ground conditions had an impact on Princen’s selection of the other earthmoving equipment on the site. The company opted for tracked dumpers instead of articulated haulers to move materials during earthmoving operations, since in wet conditions the ground surface very quickly could turn into a quagmire because of its clay nature, a fact that was not helped by the fact that the ground surface in many places was very close to, if not at, the groundwater level.

Levelling the sloping site with height differences of up to 3 m (10 ft) involved the recycling of some 12,000 tonnes of concrete and 50,000 m3 of earth.

Given the clay conditions and high water table, the ground surface had to be prepared for the construction of the new substation, which will require covering the entire site with sand 0.7 m deep. The sand used for this was recovered from the site and stored until the work began - in total, 95% of the materials used to level the site was recycled. The project began in mid-December 2015 and the demolition and the clean-up phase were completed on schedule.

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