Marks Barfield’s Rhizotron and Xstrata Tree Top Walkway 28.05.08

Marks Barfield’s Rhizotron and Xstrata Tree Top Walkway
Marks Barfield’s Rhizotron and Xstrata Tree Top Walkway

words Penelope Shaw

Marks Barfield Architects have designed a 18-metre-high walkway through the canopies of sweet chestnut, lime and deciduous oak trees in Kew Royal Botanical Gardens in London. The 400-tonne steel structure was designed to blend in without harming its sensitive environment.

The walkway aims to give an insight into the ecology of trees from the roots to the canopy. Visitors enter the “Rhizotron” first, a large crack in the ground leading to a semi-submerged concrete structure with a viewing area showing underground root structures. From the Rhizotron, a lift and stairs lead to the “Xstrata Tree Top Walkway”.

“The structure is obviously in a very beautiful place,” says Julia Barfield of Marks Barfield architects. “We wanted to be sympathetic to the setting, but not in any way mimic nature, just do something unashamedly manmade that would be visually quite minimal.” To achieve this they started with the most essential element, the handrail, and generated the walkway and trusses from this starting point.

Marks Barfield’s Rhizotron and Xstrata Tree Top Walkway

The truss diagonal supports are spaced out based on the Fibonacci sequence, creating denser areas of support where needed. “We decided to be a little playful with the trusses,” says Barfield. “Using the Fibonacci code gives them a random look but in fact it is just like in nature, following hidden laws and numerical sequences.”

The 200-metre walkway comprises of 12 modular trusses connected by 10 three-metre round “node” platforms, with a much larger platform at the mid-way point; each module was prefabricated and then assembled on site. Other than the laminated sweet chestnut timber used for the handrail, the entire structure is made out of weathering steel. “It requires very low maintenance and is very long lasting,” says Barfield. “The protective layer of rust that forms is mottled and very beautiful, it gives a very manmade material quite a natural feel.”

Marks Barfield’s Rhizotron and Xstrata Tree Top Walkway

The most challenging aspect of the project was to place 12-18m long concrete piles into the ground to provide support for the structure without damaging the tree roots. “We surveyed the root positions to minimise any damage,” says Barfield. “Normally you would have a concrete pile cap but this would have been massive and hideous, so we constructed a steel grillage and steel plate for each pile cap, making them all bespoke.”

The walkway is the main feature of Kew Garden’s summer festival events celebrating the importance of trees.

images James Morley

www.kew.org

www.marksbarfield.com

Marks Barfield’s Rhizotron and Xstrata Tree Top Walkway

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