An employee could have been killed by the collapse of the face of a four-metre-deep excavation that buried him in earth and rubble up to his waist, according to the HSE inspector who investigated the case.
As it was, his right hip and left knee were seriously injured in the incident at Benenden School for Girls on 18 January 2011, and he was unable to return to work for several months.
Maidstone magistrates heard on 8 May that the collapse occurred during work to build a new multi-storey science block at the school in Cranbrook by Kent construction firm BBS Construction.
The injured man, a groundwork foreman then aged 44, was excavating a basement to support the new building. However, concrete to fix the posts for a supporting wall had been over-poured and the excess was being chipped away with a manually-operated hydraulic breaker. It was this work that triggered the collapse.
A quick-thinking excavator driver managed to stem the flow of earth by placing the bucket of his machine into the face of the weakened earth, but his colleague was still caught and trapped. Another worker managed to jump clear.
Earlier in the project a waste-water drain had been installed by BBS less than half a metre from the face of the basement excavation, at a depth of two metres. Magistrates were told that this may have weakened the earth around the basement and made it more susceptible to collapse.
HSE inspector Kevin Golding told SHP that a more sensible way of dealing with the over-poured concrete would have been to remove it mechanically, or to have erected large steel sheets behind the posts to support the face of the excavation. The risks of manually breaking the excess concrete were not properly assessed.
In mitigation, BBS said it had used a recognised design company to design the system, which it had asked for supervision and advice, but it felt let down by this company because it only provided assistance early on in the project.
BBS Construction, of Maidstone, Kent was fined £8000 and ordered to pay £10,536 in full costs after pleading guilty to breaching reg.3(1) of the Construction (Design and Management) Regulations 2007 by failing to ensure that an excavation was safe from collapse.
“This prosecution demonstrates the need to properly plan all aspects of excavation activity, and to reassess systems and methods of work if a problem arises — as happened here, when the concrete for the supporting posts was over-poured,” the inspector said.
He added: “The retaining wall system itself was sound, but the decision to manually chip away the excess was flawed. The injured worker was dangerously exposed, and could have been more seriously hurt, or possibly even killed, but for the instinctive action of his colleague in using the excavator to shield him.
“BBS Construction could and should have done more to prevent workers from needing to work so close to the unsupported vertical face of a four metre-deep excavation.”
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