Workers repairing the New Brighton Pier will be inside watertight tubes on the seabed.
Earthquake repairs on the pier began on Monday and are estimated to cost $9.7 million.
General manager of city council services David Adamson said work will focus on damage sustained by the support columns at the seabed-level.
"I'm told it's a bit unnerving when you're standing under all that water, but the caissons create a safe, dry space in which to work."
"Over the first few weeks, the caissons will be driven firmly into the sea-bed, built up around each of the damaged pier columns with a watertight seal, and then all the seawater will be pumped out.
"It's a really interesting process that you don't see too often in Christchurch," he said.
There will also be repairs to cosmetic earthquake damage on the deck and railings.
Mr Adamson said it was the fastest option to get the repairs done.
The pier performed as expected during the earthquakes and remains safe to use.
The impact on visitors to the pier will be minimised - with the exception of the occasional closure to allow contractor vehicles to come and go, it will remain open to the public throughout.
Events based around the pier, including the Treetech Guy Fawkes Fireworks Spectacular, the Kathmandu Coast to Coast and the New Zealand Surf Life Saving Championships, will all go ahead as planned.
The adjacent New Brighton Library is currently closed for repairs, and is set to reopen on February 13.