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Geotechnical go-ahead for huge cube cutout in Canary Islands mountainside

WORK TO carve out an enormous cube in a mountain on the Canary Island of Fuerteventura is ready to start, says Arup Geotechnics.

The huge artwork on Mount Tindaya, a vision of the late Spanish artist Eduardo Chillida, will cost E70M (£47.5M).

Arup and its fellow members of the feasibility study team, structural engineer Scott Wilson Piesold and architecture practice Estudio Guadinana, said the cube will be stable despite fractures in the rock.

The project to create one of the world's largest underground caverns - 50m x 65m and 45m high - is expected to start next year.

The fissured rock surface of the cube walls will be covered by a roof that will be the largest span of its kind in the world.

Arup Geotechnics said the preferred option of an unsupported at roof, as opposed to an arched roof, would be possible.

Arup associate Steve Macklin said it should be possible to cut rock out of the mountain and leave the fractured surface exposed, as envisaged by Chillida.

Macklin said detailed ground investigation, which included drilling 14 bore holes up to 170m deep, had shown up master joints and weathered basalt dykes and trachyte - igneous light coloured rock.

'There is a design weakness in the rocks but at the same time there is a policy of exposing them as the finished surface of the cavern, ' he said.

'There are master joints that have persistent fractures right through the rock and this is something we were concerned about.'

Measures that would mar Chillida's original concept, such as surfacing the cavern with a shotcrete lining, should not be necessary.

Instead the cube would be secured with rock bolts that would be recessed and covered with rock.

'There are three to four thousand individual joints but the rock quality designation (RQD) in the cores is well in excess of 95%, ' Macklin added.

The solution was found after numerical modelling firm Itasca developed a bespoke programme known as 3DEC to model the behaviour of the master joints and dykes in three dimensions.

Meanwhile, Spanish contractor Nesco has been appointed as concessionaire to lead a design and build contract to create the cube.

This autumn the firm is expected to start work on a trial tunnel to test ground conditions further.

The trial tunnel would later form part of the main excavation of an access tunnel.

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