James Sim,32, from Barry, South Wales was a subcontractor working on behalf of Balfour Beatty Utility Solutions Limited.
On the 14 April 2010, Sim was working in a trench, laying ducting for new cable for an offshore windfarm that was being built off the coast by Heysham, Lancashire.
The trench was dug to a depth of 2.4 metres, without any shoring.
Sim was killed when he became trapped in the trench after it collapsed on him.
Balfour Beatty Utility Solutions Limited pleaded guilty at Preston Crown Court today after an investigation by the HSE.
The court heard that Balfour Beatty failed to adequately risk assess the works or control the way in which the excavation took place.
HSE inspector Chris Hatton said after the hearing: “The Health and Safety Executive are very pleased with the judge’s verdict today.
“The level of this fine should serve as a warning to industry not to ignore health and safety matters.
“Balfour Beatty failed to adequately assess, plan and supervise the work being undertaken. Trench collapses are easy to prevent, and it is disappointing that James’ life was lost in such a tragic way.
“The family has shown great patience and support throughout this investigation which is a credit to both them and James’ memory.”
Balfour Beatty said: “Balfour Beatty has offered its deepest sympathies to the family and friends of James Sim who was killed in this tragic incident.
“The safety of the public and our workforce is always our primary concern. We have since taken appropriate corrective action to take the lessons learnt from this tragic incident and share them across our business.”
The fine is one of the largest seen in the construction sector.
It comes after safety sentencing guidelines were changed in February amid warnings from legal professionals that penalties would soar following site accidents.