Anyone near the inner city site will have noticed that the piling work on the outpatient building sounded somewhat different and louder yesterday, after workers changed focus from hammering in 23m steel piles to testing the vibrations from the pile-driving operation, and also the load-bearing capacity of the piles.
"We get a measurement of the capacity of all the piles when we drive them," Scott Sutherland, a chartered geotechnical engineer with environmental and engineering consultancy Tonkin + Taylor, said.
"What we are doing here with PDA testing is giving us a more accurate reading which we then use to calibrate all the rest of the piles ... The gauges measure the compression wave as it goes down the pile and as it is reflected back up."
Sensors were attached to each pile before "Hammeroid" — the pile-driving crane christened by Otago Daily Times readers — was dropped several times from differing heights to see how the steel tube performed.
Two cranes were needed for the job, one to lift the hammer, the other to hoist the driving frame which kept Hammeroid in line.
Of the 78 piles on the site, 10% were being given a PDA, Mr Sutherland said.
"What we are trying to do is get a cross-section of the site so we are testing piles across the whole site so our data is valid for the entire footprint."
The piles are in 12m sections and range in height up to 24m.
Although difficult to see from outside the site, getting access to the other side of the barrier revealed that many were already driven in to their full depth.
"Once they are driven in to their final depth they will be cut off at ground level or just slightly below and pile caps constructed."
Ground beams would then be laid between the piles to form the base of the building.
