Network Rail (NR) and principal contractor BAM Nuttall will initially focus on earthworks for the new line in the Monktonhall area south of Edinburgh, and the excavation of the site of the new Shawfair station.
NR says the preparatory phase of the project involved significant mining remediation around the site of the former Monktonhall colliery.
Around 90% of the line reuses the alignment of the Waverley Route between Edinburgh and Carlisle, which closed in 1969.
The seven-station non-electrified line is due to open in mid-2015, although Transport Scotland says the line could be handed over by the end of next year.
