Removal of mass concrete
 Foundations
for a new high rise building were being dug at a down
town Auckland site. It was discovered that the foundations
for the building next door had encroached over the boundary
by up to 1200mm.
Attempts were made to break the concrete off using hydraulic
breakers. This was noisy and there was also a risk of
structural damage to the building so we were asked if
we had a solution. The scale of the job was that there
was a triangular shaped section of concrete, 50 metres
long by 3 metres high that at the bottom of the triangle
had encroached over the boundary by 1.2 metres. In all
about 200 tonnes of concrete had to be cut free.
There were some obvious difficulties such as ensuring
that the slabs of concrete did not fall onto on site
personnel when they were cut free. We solved that by
"pinning" the slabs back to the remaining
concrete. As the existing building was occupied 24hours
per day, 7 days per week, we could not cause a noise
or a vibration nuisance. The job had to be completed
reasonably speedily because it would soon be holding
up progress on the new building.
There was only one way to successfully complete this
job and that was to wire saw it. 32mm. diameter holes
were drilled from underneath vertically upwards on the
cut line. These holes were drilled at 1.5 metre intervals,
and reached a depth of between 2.4 metres and 3.0metres.
Our wire was then threaded through the holes and wire
sawing commenced. After 60 per cent of the slab had
been cut, we drilled two 35mm. diameter holes through
the cut concrete and 400mm. into the remaining foundation.
We then installed 32mm. diameter steel rods to hold
the slab in place while the cut was completed. After
the concrete had been cut free, an hydraulic digger
was used to pull the slab free.
The job took 3 weeks to complete. It was another example
of mass concrete being removed by concrete cutting and
drilling techniques.
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