For the past six weeks, contractors have been working to remove a rock bluff. A blast on Monday caused large rocks to fall on the line, resulting in its temporary closure.
A KiwiRail spokeswoman said contractors had carried out up to two blasts a day in a safe environment. Roads and the railway line were closed during these periods.
The blasting programme was unlikely to result in further disruption, she said.
The removal of the rock bluff would enable KiwiRail to ease the tightest curve on the line, allowing trains to climb the steep gradient from Sawyers Bay to the Mihiwaka tunnel more easily.
Work to realign and ease the curve, which restricts the speed of trains, would be completed early next year.
The $250,000 earthworks contract is being carried out by Andrew Haulage Ltd, of Balclutha, and is expected to continue for another three weeks.
