February 2008 MONTHLY MEETING
DATE: Wednesday 13th February 2008
VENUE: Rugby Club, Level 1, Rugby Place (near Pitt & Alfred St) Sydney<
TIME: 5.30pm for 6:00pm
Annual General Meeting
This is a reminder that the Annual General Meeting of the
NSW Branch of the ASEG
will be held at 5:30 pm for a 6:00 pm start on Wednesday 13th February 2008 at
The Rugby Club, Rugby Place,
Sydney CBD.
Nominations are openly sought for executive positions.
Please forward any nominations to Guo Bin.
Technical Meeting
Some Recent Australian Engineering & Environmental Geophysical Case
Studies
Bob Whiteley and Simon Stewart (Coffey Geotechnics Pty. Ltd)
Abstract:
Within Australia’s major coastal cities and urban areas geotechnical engineers
are increasingly applying engineering geophysics for improved site
characterisation in civil engineering projects and to assist with specific
problems. Recent case studies from these cities illustrate the application
of a variety of methods to a range of projects. Combining conventional surface
geophysics, innovative borehole and underground geophysics with geotechnical
methods increased innovative engineering opportunities and assisted the solution
of specific design, construction and remediation problems for these projects.
In Darwin, Vertical
Shear Wave Profiling (VSSP), surface-to-borehole seismic tomographic imaging or
Site Uniformity Borehole Seismic (SUBS) Testing combined with
Standard Penetration Testing (SPT) improved the confidence of the designers that
fill materials and construction processes for a new berth construction were
meeting specifications and identified problem areas.
The route of pipelines
for a desalination plant at the Gold Coast, traversed an old landfill whose
margins were identified with electromagnetic (EM31) profiling. Seismic
refraction and Multiple Analysis of Shear Waves (MASW) imaging on this route
showed variable bedrock levels and soft soils at some locations. This led
to the abandonment of shallow tunnel construction in favour of rock tunnelling a
much greater depth.
A heavily
contaminated, former steelworks site in the industrial city of Newcastle was to
be remediated by capping and containment on three sides within a soil-bentonite
groundwater barrier wall. Gravity and Electrical Resistivity Imaging (ERI)
proved very effective in providing sufficient subsurface information on rock
levels thicknesses of the extensive shallow fill materials for initial design
and for the bid process.
Ground subsidence near the Helipad at Sydney
Airport was believed due to groundwater and sand being drawn into leaking
sections of a nearby buried concrete encased sewer. Conventional drilling,
Cone Penetration Testing (CTP) testing and Closed Circuit Television (CCTV)
inspection were combined with innovative seismic imaging from the surface to the
sewer (called SEWREEL) to rapidly define the extent of loosened ground.
Following remediation, SEWREEL was used to evaluate the effectiveness of the
remedial works that involved extensive grouting.
Webb Dock, one of Melbourne’s main container
terminals is sited on reclaimed land underlain by soft to very soft sediments.
As a result, settlements and bearing capacity were key issues in the development
of the site.During initial construction, failures occurred in this
material, resulting in the formation of mud waves. The combination of drilling,
seismic refraction and SUBS imaging provided clear indications of the degree of
sediment displacement due to construction and was used to calculate more
accurate settlement profiles and improve preloading strategies for future
construction.
A major residential development near Adelaide was
proposed adjacent to an old limestone quarry showing open caves and other major
karst features. To better define the subsurface beneath each allotment drilling
near the centre of each proposed house foundation was supplemented by seismic
refraction, SUBS and calibrated with VSP (Vertical Seismic Profiling) and
geotechnical logging. This approach identified areas of weak and
potentially voided limestone and assisted safe development.
To the north of Perth a detailed seismic
refraction survey on dune sands along the alignment of proposed shallow waste
water tunnel showed highly variable geology, coastal limestones and siliceous
calcarenites with karst features and pinnacles.; The area is within
sensitive parkland and aboriginal heritage lands and only limited drilling sites
were available. This information was used to estimate the expected
rock-fraction at the tunnel level and the rock mechanics parameter, QTBM.
Variable tunnelling conditions were predicted from seismic with some sections
having estimated QTBM values of < 0.1 suggesting tunnelling “may be problematic”
beneath many of the limestone pinnacles to “very problematic” with estimated
QTBM values of < 0.01.
Geophysics is continuing to make important
contributions to infrastructure development within Australia with excellent
prospects for geophysicists willing to work in the engineering and environmental
areas.
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