Earthquake Strengthening – Royal NZ Police College

This building upgrade to the Barry Mason building was one of the first of its kind performed in New Zealand.  The Pile Desired Loads had to be achieved with the minimal number possible within testing and adverse conditions.

Project scope

This was a balancing act by the engineers in term of achieving the required Pile Designed Loads verses the minimal number of piles required to successfully achieve the desired results. Piles were designed to achieve loads of –7166kN Compression and 3349kN Tensile, this building upgrade was one of the first in New Zealand to such specifications.

Complicating factors and solutions

There were a number of factors that made this project practically challenging.

For starters, there was drilling 400mm diameter piles up to 8 metres deep inside the building, with only 3.3m of head room. Combine that with harder than expected rock and ground water, along with pile cages containing 8x HD 40 bars that had to be installed in sections. Then to make things even harder, all the work could only be done at night and over the weekends, so the College could remain open and operating as usual during the day.

To overcome the harder than expected rock we needed to use a combination of methods, firstly break up the rock using percussion drilling, then auger within the limited space using our mini rig, this was followed by vacuum excavation to clear the watery paste left behind.

Next came the installation of the steel pile cages which came in 2m – 4m sections hoisted through a small hole in the ceiling by electric wench. They were then lowered into position where they were supported before the next section was lifted and lowered on top and welded together before lowering the completed pile into place. This time intensive process was then repeated on every hole.

The majority of the ground water was pumped out prior to the concrete going in, this was then tremied (pumped to the base of pile) to displace any remaining water which could then be sucked off the surface as the concrete came up to prevent any flooding inside the building.