Contractors have discovered a large hole underneath part of
the Caversham highway development, where they planned to
put piles for the Riselaw Rd overbridge. Photo by Linda
A hole the size of a double garage has been found
underneath part of the Caversham highway development.
The cavity is about 250cu m in volume, and about 5m under the
It was discovered by contractors drilling proof bores at the
planned location for the new Riselaw Rd bridge piles.
Supplementary drilling exposed the extent and size of the
New Zealand Transport Agency projects team manager Simon
Underwood said the hole would increase project costs and
delay the overbridge construction.
Added costs would not be known until further design work
relating to revised foundations had been done, he said.
''We had planned on completing the bridge works this year,
but this is now likely to be closer to April next year.''
Mr Underwood said the cavity did not extend underneath the
highway and there were no houses or buildings ''anywhere near
it'', so it was not a matter of public risk.
''It is an engineering challenge.''
The cavity was part of a wider, complex geological picture of
the underlying ground conditions at the bridge, and the
design of the bridge and embankment foundations had to be
''managed'' to suit, he said.
The cavity is within a layer of sandstone, which is 5m-7m
below the original ground level.
Contractors had previously excavated down to the sandstone
layer and placed 2m of imported rock fill on top, and planned
to add another 2m-3m of fill.
Mr Underwood said the hole was about 3m below the top of the
''We would have preferred the sandstone layer to be `feature'
free, but we are far better off knowing about this now,'' he