Nottinghamshire firm Phil Watson Civil Engineering Limited has been fined for the incident which saw 36-year-old Zak Davis, of Billinghay, Lincolnshire fracture his hip and shattered his pelvis.
Davis was working on a small housing development in Bardney, Lincolnshire when the incident happened on August 4 last year.
He was laying drain pipes in a trench being dug by an excavator. It had been raining heavily during the day.
While he was in the trench the digger operator noticed the walls beginning to crack and shouted a warning, but before Davis could escape he was hit by the falling material, including a large lump of concrete, and was pinned down by his legs.
He dislocated and fractured his hip socket and shattered his pelvis. He needed 10 hours of surgery and is still off work.
An investigation by the Health and Safety Executive found Phil Watson Civil Engineering had failed to assess the ground conditions and the effect that the rain would have, and failed to install measures to prevent a trench collapse.
The company, of Mansfield, Nottinghamshire, pleaded guilty to safety breaches and was fined £10,000 and ordered to pay costs of £2,141.
After the hearing HSE Inspector Tony Mitchell said: “Excavation work is a high risk activity, but the risks are foreseeable and preventable.
“The site had previously been a farm. It had been demolished and the rubble spread on site as top fill. The subsoil beneath it was predominantly compacted sandy soil, so the ground conditions were poor.
“However, this was not properly identified as high risk before work started, the rain made the soil structure more unstable and the trench collapsed because it was not sufficiently supported.
“This incident could have been prevented by the use of mechanical trench supports or by sloping the trench sides further. Instead, a man has been left with life-changing injuries.”