Project Hobson involves the replacement of an existing 90-year-old
above-ground sewer that crosses Hobson Bay in Auckland, New Zealand, and which
is nearing the end of its economic life, with a 3 km long, 3.7 m internal
diameter segmentally-lined bored tunnel.
The $118 M project will
offer several benefits to the owner, Watercare Services Ltd, and the local
- provide capacity to meet projected growth in the
- virtually eliminate wastewater overflows into Hobson Bay and the
Waitemata Harbour, and
- remove an obtrusive visual feature and
open up the bay for recreational purposes.
The geology in the region is a sedimentary formation, which has been
significantly influenced by volcanic activity; 49 volcanoes are present within
20 km of the nearby city centre. The geology along the alignment is dominated by
two palaeovalleys which have been infilled with a combination of marine alluvium
and volcanic deposits.
Watercare Services Limited has elected to manage and share tunnelling risk
through, among other key measures, the implementation of a geotechnical baseline
report (GBR); one of the first uses of this type of document in Australasia.
This paper describes the general principles behind the use of a GBR, the
development of the GBR used in Project Hobson and some lessons