Novel protocol of engineering geophysics in urban environments
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Date
2009
Authors
Saad, Rosli
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Abstract
This research was carried out in an urban area and it was focused on detecting and
mapping fractures, voids, filled cavities, collapsed cavities, pinnacles, cliff subsurface
and overhangs that often occur in limestone areas. Prior to the field survey, the
geophysical method, 2-D resistivity imaging was used and the research was to develop
new resistivity acquisition techniques (protocols) that can provide better image; deeper
penetration and less noise. The arrays used are Wenner, Wenner-Schlumberger and
Pole-dipole. The new protocols (RSWenner, RSWenner-Schlumberger and RSPoledipole)
were tested for their ability to map the underground features. Three models were
designed to study the suitability of the new protocols; a theoretical model using
RES2DMOD software, a laboratory model and a field model (miniature) with original
medium. The study shows that the RSPole-dipole protocol with proper electrode
spacing is the best protocol used to detect and map cavities, fractures and rock head.
The study area was at the Stormwater Management and Road Tunnel (SMART) project
along Jalan Chan Sow Lin (Tunnel alignment), Kuala Lumpur. The study was divided
into two parts, which was pre-tunnel and post-tunnel survey. In the pre-tunnel study,
detail information of the subsurface was needed to avoid problems which can
compromise safety. Due to constraint of the study area being traffic congested, limited
spacing and time, not all data acquisition was done using RSPole-dipole protocol. Some
of the survey lines were replaced by RSWenner 32SX (L and S) protocol. All the data
were correlated with each other and with borehole data provided by the developer. The
pre-tunnel survey results show the presence of many weak zones (fractures, voids, filled
cavities and collapsed cavities) along the tunnel alignment and the depth of the rock
head was 1.25 – 10 meter. The post-tunnel survey was conducted in order to see and
map the effect of grouting and tunnelling using the Tunnel Boring Machine (TBM). To
assist the mapping of utilities and very shallow subsurface features the Ground
Penetrating Radar (GPR) was used. The GPR result shows the presence of many
utilities in the subsurface.
Description
PhD
Keywords
Science Physic , Engineering geophysics , Urban environments