NATURE OF PROJECT: RESISTIVITY SURVEY
DURATION: 8 MONTHS
LOCATION: AMPANG JAYA, SELANGOR
INTRODUCTION
Geomapping Technology Sdn. Bhd. has conducted geophysical survey of Electrical Resistivity Tomography (ERT) on the study area. This survey works was conducted to identify subsurface information related to potential geohazards of the area. The study also including geological aspect in terms of subsoil/ geomaterial descriptions, surface and groundwater hydrology (water table regime) and subsurface location of existing boulders along the profiles. Fieldworks were carried out between 27th December 2017 to 9th
February 2018.
METHODOLOGY
Six (6) lines of Electrical Resistivity Tomography (ERT) survey labelled as L1 to L6 were conducted along the slope area near to ongoing highway
construction project and residential area. Pole-dipole arrays was selected for this survey with 200 m spread length and 5 m spacing of electrode and connected to ABEM Terrameter LUND Imaging System. The
data captured by electrical imaging was a raw data and was transferred to the software program called RED2DINV software.
Figure 1: Six (6) lines of Electrical Resistivity Tomography (ERT) survey conducted within the study
RESULT AND DISCUSSION
Based on the 2D image of resistivity survey for L1, L4 and L5, this survey lines were conducted parallel to the slope and all the subsurface profile shows similar results. The subsurface materials consists of debris material which are granite boulders (high resistivity value 3993.0 Ωm), medium dense to dense layers of soil (medium resistivity value 721.0 Ωm – 2603.0 Ωm) and loose to medium dense soil with perched of water (medium low resistivity value 200 Ωm-721 Ωm). The results revealed that the slope is made up of saturated soil that become weak plane.
While L6 were carried out perpendicular to L1, L4 and L5 and are located at the foot of slope. The result shows that the area is dominantly covered by loose to dense layers of soil and water containing zone which can be related to the result of L1, L4 and L5.
Furthermore, a trend of fault dipping to Northwest are also interpreted by from line L1, L4 and L5. This fault/fractured increases groundwater flow and thus increases the rate of subsurface weathering as observed with the case of the granite bedrock.
Geological cross section was produced from resistivity image result and being used to describe in detail the subsurface lithology and structures.
Figure 2: 2D image of electrical resistivity tomography result for Line 1
Figure 3: 2D image of electrical resistivity tomography result for Line 4
Figure 4: 2D image of electrical resistivity tomography result for Line 6
Figure 5: Geological interpretation based on resistivity image result of Line 1
Figure 6: Geological interpretation based on resistivity image result of Line 4
Figure 7: Geological interpretation based on resistivity image result of Line 6
