Penggunaan kaedah pengimejan resistmti 2-d dan seismik biasan dalam kajian subpermukaan untuk kejuruteraan awam
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Date
2010
Authors
Jusoh, Zuriati
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Abstract
Construction at reclaimed land can pose problem such as broken and bended to
the steel piles during piling in foundation works. Saltwater intrusion can weaken the
concrete structure and cause crack to the building while limestone area cause many
geotechnical problems such as collapse and settlement of a building. The geophysical
studies were conducted at Tanjung Tokong, Penang and Gunung Keriang, Kedah. The
study at Tanjung Tokong is aimed to obtain subsurface information which include the
depth of bedrock, boulders, subsurface structures and saltwater intrusion by using 2·D
resistivity and seismi~ refraction method. Whereas the objective of study at Gunung
Keriang is to detect cavities, pim'l.acles and fractures in limestone area by using 2-D
resistivity method. The result from each geophysics method were correlated each other
together with borehole record. At Tanjung Tokong area, the 2-D resistivity and seismic
refraction result shows the subsurface is consist of two layers. The first layer is
reclaimed soils with thickness 5 to 7 meter from surface and has velocity between 500 -
669 mls. The reclaimed soils are generally made up of greyish brown sandy clay and
gravel with medium resistivity value (3 • 20 Qm) and mix up with scattered boulders of
various sizes with high resistivity value {> 20 Om). The content of reclaimed soils is
based on nearby borehole profile up to I 0 meter depth. The second layer is saturated
zone at depth over 7 meter and has velocity between 1489 - 1837 m/s. The saturated
zone has low resistivity value (<3 Om) and the higher velocity is due to saltwater
intrusion. Granite bedrock with high resistivity value(> 20Om) was detected beneath
I 7 to 39 meter depth. The depth was correlated with granite bedrock in borehole record
beneath 21 to 39 meter depth. Gunung Keriang area, 2-D resistivity result shows the
subsurface is consist of two layers. The first layer is alluvium soils with thickness 5 to
10 meter from surface. The alluvium soils consist of dark grey silty clay and gravel with
medium resistivity (1 0 - 800 Om) and mix up with boulder with high resistivity (> 1000 ·
Om). The content is referring to borehole profile near resistivity line 09 and at up to 7
meter depth. The second layer is saturated zone at depth over I 0 mt?ter with low
resistivity(< 10Om) due to mixture of chemical substances in the water and saltwater
intruJion. The limestone bedrock was detected from surface (outcrop) to 70 meter. The
bedrock form cavities and pinnacle at depth 5 to 70 meter with resistivity-over 50 Om.
As a conclusion, the 2-D resistivity and seismic refraction are suitable technique to
determine subsurface profile for civil engineering and supported by borehole
information.
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Keywords
Pengimejan resistiviti 2-D , Seismik biasan , Subpermukaan