Kevin Richards, 46, of Weymouth, was checking preparatory work for a basement retaining wall at a property in Lilliput in June 2012 when the unsupported sides of a three metre excavation collapsed.
He was struck from behind and was rapidly engulfed by the sheer volume of the soil.
A colleague who heard the noise used his hands to remove the material and create and airway for Richards.
He suffered a collapsed lung, a fractured left shoulder blade, a double break to his right leg, and two fractured ribs. He was in hospital for more than four weeks.
An HSE investigation found that the excavation at the site, managed by principal contractor Bluebay Properties Ltd, was not supported or suitably battered back.
Bournemouth Magistrates’ Court was told that the site in Blake Hill Crescent was also the home of the firm’s proprietor.
Richards was working for a firm sub-contracted for the basement part of extension works.
The excavation was 150 square metres and three metres in height.
Richards was undertaking final checks on formwork constructed to form a retaining wall as part of the basement. He was in a narrow space between the formwork and the face of the excavation when the collapse happened without warning.
Bluebay Properties Ltd, of Lilliput, Poole, pleaded guilty to a safety breach and was fined £ 6,000, ordered to pay £4,000 in costs and a victim surcharge of £120.
After the hearing, HSE Inspector James Powell said: “This incident should never have happened. It was only a matter of good fortune that Mr Richards was not killed. Other workers were also put at risk.
“There is a risk of collapse or partial collapse causing serious injury or death if an excavation is not supported or suitably battered back. Any collapse has the potential to bury or injure people working in an excavation.
“Whilst Bluebay Properties Ltd had identified collapse as a hazard, they failed to implement control measures to reduce the risk, instead relying on a visual inspection. No ground can be relied upon to stand unsupported in any circumstances.”