Going under ground

24 April 2008

Restricted site conditions presented challenges for all aspects of the construction.

Restricted site conditions presented challenges for all aspects of the construction.

Each Year 500 Kg Of Domestic Waste Is generated by each resident in the French capital of Paris but work is currently underway to improve the disposal of some this rubbish. The Isséane domestic waste processing plant, which is currently being built to the south west of the city, will be able to handle more than 500000 tonnes of material a year.

The € 526 million Isséane is being built for Syctom, the processing syndicate responsible for domestic waste disposal for 5,5 million people - 9% of France's population. In keeping with the aim of reducing environmental impact, the majority of the new building, which is currently Paris's largest construction site, will be underground.

Waste delivered to the new plant will be sorted for recycling and the remainder will be incinerated in a less environmentally harmful manner than the existing nearby facility that Isséane replaces. The site will have its own cogeneration plant, making it self-sufficient for electricity. Steam produced from the heat generated by waste incineration will also be available to heat buildings in the area. Airborne emissions will be hot air, at 400 °C, instead of smoke, and the ash will be taken away by boat.

The 42 month construction contract is being carried out by a joint venture which is headed up by France-based contractor Razel - a subsidiary of Germany's Bilfinger + Berger - which is known for its expertise in earthmoving. In total there are 55 contractors involved in the scheme but the main work is being carried out by Bilfinger + Berger, Demathieu et Bard, SEFI, Soletanche, SPIE and Urbaine de Travaux.

Bordering the site and boxing it in are roads at each end, a railway line and the river Seine and a nearby heliport also has implications for the tower cranes on site. The river - while important as a means of transporting spoil and materials to and from the site - also presented problems for construction of the foundations, which needed constant de-watering.

The first phase of work included driving over 120 steel piles up to 70 m below ground level. Walls for the plant were also constructed at up to 50 m below ground using 95000 m3 of concrete and 6500 tonnes of reinforcing steel. Between the side wall and the river is 5000 m of 30 mm diameter horizontally drilled steel ties.

Work has now progressed onto the second and final phase. A total of 600000 m3 of earth has been moved from the site and around 10% of it was contaminated. It was expected that the top 3 m of soil from the site, which was once occupied by a car manufacturer, would need to be de-contaminated but it this had to be extended to 8 m.

Removing the spoil from site was done using a fleet of 50 tonne dumpers and transported from the site by boat. The boats were loaded from a temporary quay, built by Razel, via a specially pdesigned chute system to break the fall the spoil during loading. Using the river saved an estimated 40000 truck loads from travelling by road, according to Razel.

At the peak of the earthworks up to 5000 tonnes-equivalent to 600 (15 m3) trucks - of earth was being moved off the site each day. But to fast track work on site, the earthmoving and concrete pouring needed to be carried out simultaneously. The site record was 1300 m3 of concrete poured in one day, the equivalent of 150 mixer trucks.

Logistics

Restricted site conditions presented challenges for all aspects of the construction and the complicated logistics took a long time to work out, according to Patrice de Ré, who is in charge of cranes and other equipment on site for Razel. Space is severely limited on the 400 m x 100 m site with no room for materials storage. This means that everything has to be delivered in the right sequence, just in time and placed at the point of use as soon as possible, making cranes vital to the work.

Cranes on site are a mix of top slewing saddle jib tower cranes, large crawlers and mobile telescopics and are being used for placing structural steel weighing up to 30 tonnes, rebar assemblies, and the plant's furnaces and other equipment. The 98 tonne furnaces were transported to site by boat from where they were built in Croatia. In late January, when CE visited the site, this machinery was being installed using heavy lift crawler cranes. It took two days to install the two furnaces, the catalysers and the conveyors.

All heavy transport on site and crane works during the industrial assembly of the waste incineration plant is being carried out by Sarens France. According to Sarens, the biggest challenge is to make all the lifts in the presence of the tower cranes overhead and the 400 people working on the confined site. In addition, most of the lifting work takes the loads below ground so lifts are controlled using instructions by radio.

In late January there were three tower cranes on site but at peak times on the project there will be up to eight. The largest will be a Liebherr 550 with 60 m jib where it will pick 6,2 tonnes. The remaining cranes are all Potains - three MD 345s (one with 50 m jib and two with 60 m jibs), three MD 265s (with 55, 50 and 45 m jibs) and an MD 238 with 55 m jib. Tallest of the towers, with an underhook height of 61,5 m (to the level of its base, which is 5,5 m below ground), is one of the 60 m jib MD 345 Potains.

Each of the tower cranes is fitted with anti-collision systems, wireless wind alarms, computers for calculation and monitoring and air beacons because of the neighbouring heliport. The anti collision systems have wireless connections, to avoid downtime caused by site damage to cabling. In addition to protecting against collisions between the cranes, the system also manages prohibited zones over the site's neighbours.

Razel and the other joint venture partners are currently on schedule to complete work on Isséane by June 2007.

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