Edmund Nuttall's specialist geotechnical division Ritchies recently won a contract from ESB International to remove 2,500m3 of rock from the site of a new electricity substation in Greenock, Inverclyde.
As the site was surrounded by a railway line, a main road, a primary school and private housing, the use of normal methods of rock excavation were not possible. Blasting with explosives or hydraulic breaking would have been too disruptive and noisy.
Ritchies instead proposed using the Cardox system which releases high pressure carbon dioxide in the ground to move rock. It is an adaptation of the method used in coal mining and consists of a hollow pressure vessel charged with liquid carbon dioxide. When an electric impulse is passed through an energiser, the liquid CO2 changes to a gas, increasing its volume by 600 times and the resulting pressure increase ruptures a shear disc. The energy release of 267MPa has a heaving effect on the surrounding rock and is much less dramatic than blasting, and is almost silent.
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