The centerpiece of the project is this dramatic Biodiversity Nest, to be built around the central observation tower. The design is based on the elaborate nests created by weaverbirds. © Kilian O’Sullivan
The Eden Project has commissioned a walkway at the canopy level of its Tropical Biome with a platform that will be modeled on the elaborate nests of weaverbirds.
May 14, 2013—At first glance, Cornwall, in the United Kingdom, is an exceedingly unusual location for a rain forest, much less a walkway above a rain forest. Although sunny and mild by U.K. standards, the nearly 1,400 sq mi peninsula, which is bordered by the Celtic Sea and the English Channel, has an average temperature in the summer of just 56°F.
However, in 2000 the Eden Project, a visitor attraction that focuses environmental initiatives, converted a reclaimed kaolinite quarry in the former mining region into an expansive ecological educational area complete with a series of large steel and thermoplastic geodesic domes that form two biomes. The smaller biome encompasses 1.3 acres and simulates a Mediterranean climate. The larger, the Tropical Biome, covers 3.9 acres and soars to a height of approximately 100 m in the center.
It is within the Tropical Biome, where the trees have grown expansively over the past 13 years, that work is nearly complete on the first phase of a walkway through the tree canopies that will be called the Rainforest Canopy Walk. The project was designed by Blue Forest, of Tunbridge Wells, United Kingdom, and Jerry Tate Architects, of London, with structural engineering by Sinclair Knight Merz, also of London. It is being constructed by Ease, of Cornwall.
The project includes two 16 m long bridges that connect to a central viewing platform. The entire structure is approximately 7 m above the biome’s floor. The kaolinite beneath the soil provided an extremely stable base for drilled anchors.
The greatest challenge was the environment inside the biome, which is maintained at 86°F and 60 percent humidity. That severe environment, combined with strict sustainability goals and a modest budget, put a sharp focus on material choices.
The structures comprise galvanized structural steel with timber decking. The unforgiving environment meant that the team had to precisely design all of the steel members, including all of the connector locations, so that the galvanization would not be damaged and could continue to protect the connection points.
The walkway will offer dramatic views of the tree canopy, 7 m
above the ground in the Tropical Biome. © Blue Forest and Jerry
“There is no drilling into the galvanized steel,” says Laurence Pinn, an architect with Jerry Tate Architects, who is working on the project. “Because of that climate, even the galvanized steel that has been there since the project started has shown twice as much degradation as it would in a normal, external environment.”
Redwood was chosen for the wood decking, Pinn says. The decking won’t have the same life span as will the steel members, but any woods that might have matched the steel in longevity were ruled out because of the imperative to use renewable materials. “Inevitably within that environment, without using a tropical hardwood it’s very difficult to get something which would have that kind of life span,” Pinn says. “When you’re building something which allows people to understand why we need to save the rain forests, it’s quite difficult to then build [it] out of tropical hardwood.”
The centerpiece of the project is the dramatic Biodiversity Nest, a central observation tower that will have a 30 m square floor plate and eventually be surrounded by twisting wooden ribs that will rise an additional 7 m from the platform.
“We were briefed to create a form based on the nest of a weaverbird,” says Pinn. “We felt a ribbed structure would be fitting and relatively simpler [to construct] than a woven one.”
Material choices were a challenge for the warm, humid biome.
The walkways comprise galvanized structural steel and timber
decking. © Blue Forest and Jerry Tate Architects
The cladding of the nest has proved to be a design challenge, Pinn says. In addition to bearing the constant heat and humidity of the site, the design must be easily constructable in an enclosed environment while the biome remains open to the public. Smaller wooden members shaped with a computerized numerical control (CNC) machine will be connected together to create the unique, organic shape.
“The idea was that all of these long strings would be made out of pieces of two-foot timber which would then be tacked together, like a bike chain,” Pinn says, and then wrapped around the structure.
The ribbed structure isn’t meant to protect visitors from the elements, Pinn says. “It doesn’t actually have to do any waterproofing work,” he explains. “It just gives it a covering in terms of protecting from the light. You end up with something that we think looks quite interesting and should be possible to construct within the constrained environment.”
The Biodiversity Nest and a third bridge—a rope bridge that will connect to the nest via two protruding masts—are not part of the first phase of the project. The Eden Project is currently working to develop funding sources for the next phase.