Cal Stadium Renovation - Trimble

Surveying Sunken Suburbs in
Christchurch’s “Orange Zone”
After the June earthquake, engineers divided Christchurch
into four zones representing whether repair
and rebuilding were viable: green—yes; red—no;
orange—need more data; and white—not yet mapped.
Approximately 9,000 properties comprising the orange zone
needed to be quickly surveyed to better determine whether
they were “red” or “green.” For many of these properties, the
main problem was land sinkage resulting from liquefaction—
some land had sunk by up to 1.5 m (4.9 ft), making it less
able to support construction. Engineers required survey
data to understand what would be needed to bring land
back above the flood level—and to determine whether it
was worthwhile economically to do so.
Tonkin & Taylor, Ltd, geotechnical consultants working for
the Canterbury Earthquake Recovery Authority (CERA),
awarded the Orange-zone survey contract to Paterson
Pitts, providers of land survey and resource management
services to New Zealand’s Otago region. GeoSystems
New Zealand, Ltd, provided nine additional surveying
systems comprising Trimble R8 GNSS Rovers and Trimble
TSC3 Controllers running Trimble Access Field Software.
The company’s iBASE Network, based on Trimble VRS
technology, has reference stations installed inside and
outside the quake zone and provided control; access to
the network was free for all surveyors during the initial
recovery period.
Due to the large surveying area, time constraints and number
of surveyors from different companies, the project’s
success relied on all data being consistent. “We couldn’t
afford to have any mistakes,” said Paterson Pitts Project
Manager Mike Botting. “People’s livelihoods and properties
were at stake.” To ensure that consistency, GNSS surveying
expert Reece Gardner of 3D World in Christchurch defined
all surveying procedures for the project. Gardner was also
responsible for processing, quality checking and ensuring
data completeness.
Up to 20 surveying teams were on the ground each day;
at peak demand, the iBASE network reached a record
number of concurrent users. Surveyors focused on the
Technology&more; 2012-1
Earthquake Recovery in
-8-
In the pre-dawn quiet on September 4, 2010, New
Zealand’s second largest city, Christchurch, was
struck by a magnitude 7.1 earthquake—with thousands
of aftershocks following the quake since then.
In particular, a magnitude 6.3 quake on February
22, 2011 resulted in 181 fatalities and wreaked havoc
on buildings, city infrastructure and land already
vertical movement of each property, taking measurements
every 10 m (32.8 ft), or 8 to 10 measurements per property.
They also measured from the berm and, if possible, the
centerline of the street, which typically didn’t move as
much as the surrounding land. Most points gathered were
GNSS measurements, with GLONASS satellites proving
especially valuable in areas of tree canopy. The internal
modem on the TSC3 controller also made data capture
easier because no external call phone was required to
access the network.
The project was completed in just two weeks due to the
streamlined project processes and team efficiency. “It was
just basic survey work, but at such a large scale—over
860 ha (2,125 acres)—that the VRS network and the speed
at which we could operate made a significant difference,”
said Botting. “Teams could go straight to a site and start
surveying in a couple of minutes thanks to the network.”