(Excerpt from piece originally published in World Construction)
An international garden festival exhibition grounds recently built on a 46-ha site was a flat wasteland of industrial landfill, disused oil tank depot, and a silted-up shipyard.
In 1982, when Liverpool, England won approval to hold an international festival, Europeans scoffed. The Germans and Dutch each spent at least five years and $90-million on their festivals held the preceding two years. Liverpool planned to open in less than half the time and with a budget of only $17-million. That the festival opened on time and within 2% of the budget is largely due to skillful site reclamation and to a triad of on-site management firms that provided control of scheduling and construction, design integrity, and costs on a daily basis.
Site reclamation was the first priority. Merseyside Development Corp., a local governmental agency, provided a $13.5-million grant to remove the storage tanks and shipyard structures. This work was planned before the festival was proposed. Once Liverpool won approval for the show, additional work began. At its peak, 35 subcontractors were involved in the reclamation.
One of the first tasks was the removal of silt from the shipyard. Westminster Dredging, a U.K. subsidiary of the Dutch Bos-Kalis Corp., used two C.Z. Eeem cutter-suction dredges to pump silt from the site. The dredges removed an average 10,000 tons of silt a day for eight weeks; 600,000 tones of silt was pumped into an adjacent dock for storage and eventual disposal at sea.
Meanwhile, a C.Z. Seine cutter-suction dredge was moored over Devil’s Ban, a massive sandbar in the Mersey. That dredge pumped 20,000 tons of sand to the shipyard site to replace the silt.
The material was pumped via a submerged pipeline and passed over a mesh that allowed surface water and find grit to return to the river.
Work stopped for several days when weekly sonar scans shows alterations to the ebb tide of the river that might affect the scouring of the Garston Channel, one of the two major shipping channels in the river.
Four weeks after the dredging was completed, the sand bank was back to its original shape. A total of 1.5 million tons of sand was pumped into the site, forming the foundation for a 3,000-car parking lot and creating a stockpile that was used for foundation work in other areas.
Approximately 26 ha of the festival site was covered by an industrial landfill. Reclaiming that site resented several problems.
Settlement a Problem
Settlement was a major concern. The landfill contained 6.4 million tons of rubbish an average 10 meters deep. As last as November 1981 it was still active.
Any construction plans had to consider that the site was gradually sinking as the garbage settled. According to Mike Fletcher, project manager for Norwest Holst Projects Ltd., some areas were settling by as much as 6 mm per week, although that appeared to be leveling off as construction was completed.
Several methods were used to speed compaction.
“The right-of-way of the 425-mm narrow gauge railway that runs through the festival grounds was used as a haul road for several months,” says Tony Potter, Graphics Designer and the man in charge of the reclamation work.
Surcharging was used along a spine road which will remain after the festival ends. Heavy equipment and regular traffic settled the rubble piled along that road.
“We used a sledgehammer approach at the site of the Festival Hall,” admits Potter. The 8000-m2 structure will act as the main exhibition hall during the festival and be converted into a sports and leisure center afterward.
Designed by Arup Associates of London, the $3.45 million structure is a domed pavilion 60-m wide by 195-m long, spanned by a single steel vault and with no interior pillars.
The steel framework was completed eight weeks into the 56-week building schedule by Tubeworkers of Birmingham. The exterior is covered with frosted polycarbonate panels and aluminum for maximum reflectivity and insulation. The dome and paneling were done by Baco and Dutch Glasshouses, an Anglo-Dutch partnership, respectively.
To insure a firm foundation for the hall, approximately 15 to 20 m of garbage (700,000 tons) were dug from the site and replaced with sand from the stockpile collected during dredging. This allowed the building to be constructed directly on a slab without driving support piles. The excavate d rubbish was hauled to other landfills.
Building a windbreak was a second priority. The Mersey is a broad tidal river subject to strong northeast and southeast gales.
As landforming progressed, builders discovered winds could be very high at some points. At the top of a man-made, 40-m-high hill which overlooks the festival grounds, winds were clocked as high as 130 km/hour.
Using scale models of the festival site in a wind tunnel, planners devised a solution: a series of 10-m high hills running parallel to the river. The scalloped landform results in a 60% wind drop from the top of the overlook to its base.
Methane gas posed yet another problem. The biggest concern was that plants would not survive in gas-filled soil. After the site was landformed, it was capped with .75-m of clay which in turn was topped with 100mm of topsoil. The clay was taken from the tank farm.
The primary concern was to make the surface impermeable so the gas will not leech into the topsoil. The clay will crack as settlement continues, but not appreciably. Meanwhile, the methane is removed by a series of 30 wells, each with a sphere of influence of approximately 50 m. A pumping station built just outside the festival property extracts the gas, which will be used to heat the festival hall. Estimates are that the landfill will produce up to 2.5 million therms a year for 20 years, but no commercial buyer has yet been found for the gas.
(End of excerpt)