APPLICATION OF GEOPHYSICAL METHODS IN ENGINEERING AND ENVIRONMENTAL STUDIES
| Presenter | : | ZURIATI BINTI JUSOH |
| : | - | |
| Date | : | 12 / 3 / 2010 |
| Time | : | 3.00 PM |
| Venue | : | BILIK MESYUARAT (ARAS 3) , PUSAT PENGAJIAN SAINS FIZIK |
| Sypnosis | : | Construction at reclaimed land can pose problem for piling work such as foundation broken and bended when coupling on boulder. Saltwater intrusion can weaken the concrete of the foundation and cause crack to the building while limestone area cause many geotechnical problems such as sinkhole, cavities, collapse and settlement of a building. The geophysical studies were conducted at Tanjung Tokong, Penang and Gunung Keriang, Kedah. The objective of the study at Tanjung Tokong is to obtain subsurface information that include the depth to bedrock, boulders, subsurface structures and saltwater intrusion by using 2-D resistivity and seismic refraction method while at Gunung Keriang, the objective is to detect cavities, pinnacles and fractures that may formed in limestone area by using 2-D resistivity method. ABEM SAS 4000 Terrameter was used for 2-D resistivity survey using Pole-dipole array while ABEM Terraloc MK6 seismograph was used for seismic refraction survey. The 2-D resistivity data were processed using RES2DINV software whereas seismic refraction data were processed using Firstpix and Gremix software. The geophysics result for each method were correlated and supported by 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 zone with thickness 5 to 7 meter from surface and has medium resistivity value (3 - 20 Ωm). Based on borehole record, the reclaimed zone consist of clay, sand and gravel with N value 1 to 8. Boulders in reclaimed zone has high resistivity value (> 20 Ωm) and at depth 0.5 to 8 meter. The velocity of reclaimed zone is non-uniform (500 - 669 m/s) due to boulder. The second layer is saturated zone at depth 7 to 30 meter and has very low resistivity value (<1 Ωm) due to saltwater intrusion. Based on borehole record the granite bedrock was at depth 20 to 36 meter while the result shows at depth 17 to 31 meter with high resistivity value (> 20 Ωm). The higher velocity of second layer (1489 - 1837 m/s) is due to granite bedrock and saltwater intrusion. Gunung Keriang area, the borehole record shows the weathered limestone was detected at depth 7.3 meter with N value 37. There was a fractured zone under the weathered limestone with N value 17 and 10 meter depth. The resistivity image shows the subsurface consist of two layers which is alluvium soils and saturated zone. The alluvium soils which located 5 to 10 meter from surface have medium resistivity value (10 - 1000 Ωm) and mix up with clay, silt and sand. The saturated zone which dominate most of the pseudosection has very low resistivity value (<3 Ωm) due to saltwater intrusion and mixture of chemical substances in the water. The boulder and limestone bedrock have high resistivity value (>1000 Ωm). The limestone bedrock was detected from surface to 70 meter. There are six air-filled cavities with high resistivity value (> 1000 Ωm) and one water-filled cavity with low resistivity value (< 10 Ωm) were detected at depth 5 to 60 meter. The pinnacles were detected at depth 5 to 70 meter with medium resistivity value (> 50 Ωm). As a conclusion, the 2-D resistivity and seismic refraction technique have been successfully used to image the subsurface of Tanjung Tokong, Penang and limestone at Gunung Keriang, Kedah. |
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