The employee of Essex-based Forefront Utilities was connecting gas pipes in a trench on 23 May 2014, Maidstone Crown Court was told.
New pipes had been rested on packing timber across the trench. The weight of the pipes caused the tarmac under the timber at the edges of the trench to give way. One of the pipes fell into the pit and struck the worker, fracturing his spine. He is paralysed and has no feeling in his bowel.
The method the victim used for jointing new sections of pipe to existing ones was unsafe, the Health and Safety Executive (HSE) said after the accident.
Forefront Utilities, which says it "continually aims to be the safest service provider in the utilities sector", was found guilty of breaching s 2(1) of the Health and Safety at Work Act. It was fined £200,000 and ordered to pay cots of £56,686.
HSE inspector Andrew Cousins said: "If a suitable safe system of work had been in place prior to incident, the life-changing injuries sustained by the employee could have been prevented."