Application of electrical resistivity

Application of electrical resistivity Introduction Electrical resistivity imaging is a widely used tool in near surface geophysical surveys for investigation of various geological, environmental and engineering problems including landslide. In addition, a 2-D synthetic resistivity modelling study was carried out to understand the response of the resistivity method to a landslide problem before the field surveys (Drahor,MahmutG et al, 2006). The relevance of electrical surveys is to identify the subsurface resistivity distribution by making measurements on the ground surface. The true resistivity of the subsurface can be quantified from these measurements (Singh et al 2006). The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity and degree of water saturation in the rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining and geotechnical investigations. More recently, it has been used for environmental surveys. The resisti vity measurements are normally made by injecting current into the ground through two current electrodes (C1 and C2), and measuring the resulting voltage difference at two potential electrodes (P1 and P2). From the current (I) and voltage (V) values, an apparent resistivity (pa) value is calculated. pa = k V / I where k is the geometric factor which depends on the arrangement of the four electrodes. Resistivity meters normally give a resistance value, R = V/I, so in practice the apparent resistivity value is calculated by pa = k R The calculated resistivity value is not the true resistivity of the subsurface, but an â€Å"apparent† value which is the resistivity of a homogeneous ground which will give the same resistance value for the same electrode arrangement. The relationship between the â€Å"apparent† resistivity and the â€Å"true† resistivity is a complex relationship. An according to Singh et al (2006), an inversion of the measured apparent resistivity va lues using a computer program must be carried out to determine the true subsurface resistivity. Problem statement Landslide – Jalan Baru Gap ,Fraser Hill A recent problem faced in Malaysia is landslides on hill slopes. This harmful situation always occurred in highland area during wet season. One landslide occurred in km 90,FT055,Kuala Lumpur/Kuala Lipis (Gap Road/Tranum),Fraser Hill starting December 16 2007 until almost recently. This road is the only one that is connecting Kuala Kubu Baru or Fraser Hill to Raub. In recent tragedy on April 5 2008 at 9 pm,sliding of some boulders onto one old bridge in km 38.4,FT055,Kuala Kubu Road-Raub ,Fraser Hill ,Raub district, Pahang had occurred. The landslides are often triggered by water accumulation within part of the slope which leads to weakening of a section of the slope. Thus, it is important to accurately map the zone of ground water accumulation. Landslide is one of natural hazards that are often occur all over the world. In t ropical climate such as Malaysia, the phenomenon is common especially in hilly areas during monsoon season. According to the report by Jamaludin et al, 2006, serious natural landslides in this country normally occur in monsoon seasons where intense precipitation is the main triggering factor. Early indication of the slope stability prone area such as the landslide hazard maps may help planners and developers to choose favorable locations for locating development schemes. Careful engineering and geologic study could then follow before such specific project could be implemented.