The firm pleaded guilty at Lincoln Crown Court and was fined £200,000 with over £36,000 in costs.
It is understood Scott Dobson, 26, was working on a railway line near Saxilby on 04 December 2012.
However, he strayed out of the correct line position into a gap between the two lines and was struck by a passing train.
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An investigation by the Office of Rail and Road (ORR) found a number of failings on Carillion's part, including planning and management of the work.
Only one of the two railway lines had been blocked while the maintenance was being carried out, whereas both lines should have been closed for safety reasons.
Ian Prosser, HM Chief Inspector of Railways, said: "This accident was wholly avoidable, had Carillion Construction Ltd followed health and safety rules set out for the railways.
"The safety of workers and passengers is a top priority for the regulator, which is why ORR inspectors are out on the railway daily, monitoring to ensure safety isn't compromised.
"Our sympathies are with Mr Dobson's family."
(LM/MH)
