The effect of particle size towards resistivity and chargeability for groundwater interpretation

Abstract

The most reliable and common method of surveying the groundwater is the electrical resistivity tomography (ERT). ERT is a non-destructive method of groundwater surveying where the current is being injected into the ground and the value of the subsurface resistivity and chargeability are determined. Multiple factors may influence the results of the ERT, especially the mineralogy, soils, rocks and water content. In this study, the effects of particle size and moisture content are assessed towards the resistivity and chargeability value. The materials that are used to conduct the testing are obtained from quarry and river. The gravel size samples from quarry were varied from sample size retained at 37.5 mm, 28mm, 20mm, 11.2mm, 6.7mm, 5mm and 2.36mm. Meanwhile, the sand size samples from the river were varied from sample sieve size passing 2mm and retained at 1.18 mm, 0.85mm, 0.60mm, 0.43mm, 0.30mm, 0.20mm, 0.15mm and 0.063 mm sieve. The gravel and sand-sized particles were tested on a saturated condition. The device used for the experiment is Terrameter LS 2 and the setting used is C1C2P1P2 to conduct the resistivity and induced polarization tests. The resistivity value for the gravel ranges from 162.5 Ωm at its highest to 77.5 Ωm at its lowest. In a fully saturated condition, the resistivity value for the sand ranges from 121 Ωm at its highest to 86.1 Ωm at its lowest. The chargeability value for the gravel in a saturated condition ranges from 5.57 ms to 7.87 ms with decreasing particle size. The highest chargeability value for sand is 12.31 ms and the lowest is 2.04 ms in a fully saturated condition also in a decreasing size of particle size. The resistivity and chargeability for water used in this study are 101.7 Ωm and 0.41 ms, respectively. Keywords: Resistivity, Induced Polarization, Granite, Sand, Chargeability.