Application of 2-D Resistivity Imaging and Seismic Refraction Methods for Engineering Geological Studies
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Date
2011-06
Authors
Ismail, Nur Azwin
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Abstract
Detailed knowledge of subsurface and structural geologY is essential for
engineers before commencement of any construction projects. The effectiveness of
2-D resistivity imaging and seismic refraction in determining the amount of
overburden, bedrock mapping, characterizing subsurface and investigation on karstic
features were tested at five different locations in Malaysia. Interpretation of results
obtained is supported by borehole records. Generally, Damansara is underlain by non
rippable granite bedrock encountered at depth 10-30 m with velocity and RQD of
>3000 ms-1 and 37-85% respectively. First and second layers are generally rippable
with velocity 400-600 rns-1 and 1600-2000 rns-1 respectively which predominantly
consists of gravelly soil and weathered layer. For Chendering, results indicate that
the whole area are fractured metasediment shale bedrock with resistivity value,
velocity and RQD of >5000 Om, 2155-3165 rns·1 and <8 % respectively, covered
with <5 rn thick colluviurns with resistivity value of 1500-3000 (lm. Saturated zones
with resistivity value <100 Om were found. Velocity of frrst layer is 340-740 rns·•
while second layer have velocity 943-2040 rns·1 predominantly consist of gravelly
soil and very poor shale or hard gravelly silt and silty gravel. These two layers are
formed overburden with SPT -N value of 40-50 which is generally rippable while
third layer is non rippable. As for Gopeng, the rock head of limestone bedrock
encounter at depth 8-12 m with resistivity value of 70 Om. competent limestone
bedrock with RQD of 40-50% and weak/fractured limestone with resistivity value
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> 100 Om and 20-100 Om respectively are also obtained. In correlation with borehole
records, alluviums with thickness 6-10 m were identified. Other karstic features such
as pinnacle and cavity with resistivity, value 20-50 Om are also detected. Lenggong
results indicate that the study area generally made up with weathered granite grade
IV and V, having resistivity value of 800-3000 Om. Granite bedrock is encounter at
depth 8-47 m with resistivity value >3000 Om and velocity of>2000 ms-1
• First and
second layer is rippable with velocity 312-583 ms-1 and 814-8550 ms-1 respectively
while third layer is non rippable. Granite boulders with resistivity value 1500-3000
Om and saturated zones with resistivity value 0-100 Om are also identified. The
results are correlated well with borehole records provided. For Limbang, it consists
of highly fractured or weathered sandstone/mudstone with resistivity value > 300
Om. The saturated zones with resistivity value <1 0 Om were identified. Slightly
weathered sandstone/mudstone bedrock is encountered at depth 15-30 m with
velocity and resistivity value of >3000 ms-1 and 800-3000 Om which generally non
· rippable. First and second layer with velocity 270-630 ms-1 and 790-2500 ms-1 are
generally rippable which predominantly consist of gravelly soil and highly weathered
and fresh sandstone/mudstone. Saturated zone with resistivity value <1 0 Om is also
detected.
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Description
Keywords
APPLICATION OF 2-D RESISTIVITY IMAGING AND SEISMIC REFRACTION METHODS