A steep rocky slope is no place for a little digger – unless it's got a bigger digger to hang onto.

On the slopes above the earthquake damaged Sumner Rd crews from Button Logging have been using a 3- tonne excavator tethered by a cable to a winch on a second 35-tonne excavator to safely scale the steep slopes of loose rock.

Operating an excavator on a 35 to 45 degree slope with a cliff below is not for the ill-prepared or faint-hearted, but it has not fazed experienced operator Shane Anderson.

"I really enjoy it – I actually like getting up in the morning to do this job,'' Anderson said.

He is looking forward to the day when Sumner Rd is re-opened and he can drive along it and show his kids the work he did.

"I will be able to look up and say I did a bit of that – I had a hand in helping,'' Anderson said.

While winch-assisted excavators are used for harvesting in the forestry industry on slopes of up to 50 degrees, this is believed to be the first time it has been used for rock scaling on the Port Hills.

"The area where they have been working is between Sumner Rd and the catch bench that has been constructed above the road to catch rockfall from the Crater Rim Bluffs,'' said city council senior project manager Peter Bawden.

"We need to clear the slope of loose rock so that work can then begin on repairing the retaining walls and road below.''

About 100,000 cubic metres of rock has been excavated from the slope above Sumner Rd to create the catch bench, which stretches for a length of about 400 metres and is 15 metres wide and 18 metres high.

It is one of a number of rockfall protection features that are being built to mitigate the rockfall risk as part of stage one of the multimillion-dollar project to get Sumner Rd re-opened.

McConnell Dowell is the principal contractor on the project, which is being jointly funded by the Council and the NZ Transport Agency.

Stage one of the project, focused on rock fall mitigation, has been running for more than a year. The second stage of the project involves repairing the damaged retaining walls and reinstating the road itself.

Initial work to open up access from Lyttelton, with a cutback at Windy Point and a couple of key retaining walls, is nearly complete, allowing repair work to ramp up through the summer construction season.

It is expected Sumner Rd will reopen early to mid 2019.