An untrained worker was crushed when a six-ton dumper truck toppled over and landed on him as he tried to jump clear.
Daniel Robbins was trapped under the dumper and suffered broken backbones and a broken leg and hip, Brighton Magistrates’ Court was told.
The building contractor in charge of the job, Chalmers and Co (Sussex) Limited, of Church Street, Brighton, pleaded guilty to breaking health and safety law.
The firm, formerly of Edburton Avenue, at Fiveways, was fined £26,667 by District Judge Tessa Szagun.
She ordered Chalmers to pay £3,659 towards the cost of the prosecution and a £170 victim surcharge, making £30,496 in total.
Mr Robbins was operating the dumper at Great Bainden Farm, in Piccadilly Lane, Mayfield, in June last year.
He was tipping material from excavation work alongside a barn at the top of an embankment in the East Sussex village.
The Health and Safety Executive said: “As the operator came around the corner of the barn to tip a load, the dumper became stuck.
“When he backed up slightly to gain traction, the dumper tipped over the edge of the embankment.
“Daniel Robbins tried to jump clear but the dumper landed upside down on top of him at the bottom of the embankment, trapping him and causing fractures to his right thigh, hip socket and vertebrae.
“An investigation by the Health and Safety Executive (HSE) found the company had failed to provide the operator with appropriate training for operating a dumper.
“The investigation also found the site manager had not been provided with suitable training for managing a site and to ensure that those operating under him, were doing so safely.
“Furthermore, no measures had been put into place to prevent dumpers from approaching or overrunning the edge of the embankment.”
The judge said that the level of the fine reflected the guilty plea by Chalmers, which operates from Prospect Farm, in Brickhurst Lane, Laughton, near Ringmer.
The company is run by founder and managing director James Chalmers, 51, and 45-year-old Eleanor Cave, of Prospect Farm.
It has previously won awards for its work, including an eco-house in Dyke Road, Hove.
Speaking after the hearing, HSE inspector Stephen Green said: “Those in control of work have a responsibility to devise safe methods of working and to provide the necessary information, instruction and training to their workers in the safe system of working.”