Dunedin City Council group manager transport Jeanine Benson said contractors had also added extra ballast to four shipping containers positioned to protect houses at Careys Bay, below the site.
Workers would today turn their attention to constructing an earthbund below the boulder, also to hold it in place.
The aim was to finish the bund tomorrow and break down the rock in time to reopen Blueskin Rd on Friday, Ms Benson said.
Contractors would drill into the boulder to split it into fragments small enough to be removed, she said.
Other options, including using explosives to demolish the boulder and a temporary reopening of the road for limited hours in the meantime, were not considered viable or safe.
Staff and contractors were working as quickly as possible, and the inconvenience to motorists and residents from the road closure was regretted, but public safety was paramount, she said.
The boulder was made of a type of rock known as breccia, also known locally as ‘‘Port Chalmers rock’’.
