Straight and true

01 May 2008

Recent rock excavations for realignment road close to buildings and traffic in the centre of Stockholm called for accurately drilled blast holes and well chosen explosives.

The city's busy Nynäsvägen road needed to be lowered by 6 m as part of Stockholm's Southern Link orbital motorway project to enable it to be connected to the scheme's tunnels. Drill and blast contractor AB Schakt och Sprängning was given the task of blasting out the 110000 m3 of granite and gneiss.

The company used four Atlas Copco ROC 542 drill rigs to carry out the blast hole and rock bolt drilling at the site. But the close proximity of buildings meant that the drill tools had to be carefully chosen to maximise the accuracy of the blasting. Sandvik worked with AB Schakt och Sprängning to develop one of its tools for the scheme.

“Regulations in Stockholm limit blast holes to a maximum of 51 mm in order to minimise the size of explosives used,” said AB Schakt och Sprängning owner Kjell-Arne Fredin. “Existing tools could not create the straight bores needed for accurate blasting.”

Sandvik's T35 uses the same rod dimensions as the T38 larger tools for accuracy but can drill 54 mm diameter holes. “On site testing showed that the T35 could drill very straight small diameter holes which makes blasting safer and creates less vibration,” said Mr Fredin.

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