Water-saturated zone recognition using integrated 2D electrical resistivity tomography, borehole, and aerial photogrammetry in granite deposit, Malaysia

Weathering in humid, tropical regions generate cracks in the rock mass. The resultant cracks promote the infiltration of water into the rock mass and are the key source of water accumulation in rock pores and joints. This necessitates the regional information of spatially distributed water-saturated zone for a feasibility assessment of the deposit before development in such tropical regions. Traditional techniques such as drilling suffer several limitations such as data coverage, time, and cost. As the cores provide point-based information, therefore, even a large number of boreholes are insufficient for comprehensive subsurface hydrogeological investigations due to unidentified subsurface geology in the gaps between the boreholes. This paper presents an integrated two-dimensional electrical resistivity tomography (2D ERT), borehole, and aerial photogrammetry survey for detailed recognition of water-saturated zone in granite deposits. In line with this, the influence of the water-saturated zone on explosive selection for better extraction of rock aggregate is also discussed in this paper. Based on a successful demonstration of 2D ERT, a water-filled subsurface layer with resistivity values 100–300 Ωm were found in higher concentration in the study area. However, 2D ERT independently may give an ambiguous interpretation due to the overlapping resistivity values of the topsoil (100 to 800 Ωm) and the water-saturated zone (100 to 300 Ωm). 2D ERT was applied alongside the coring technique in this research work to raise the confidence in the obtained subsurface geological model. Meanwhile, to understand the surface topography of the study area, an aerial photogrammetry survey was performed. The integrated 2D ERT, borehole, and aerial photogrammetry approach allows for obtaining a detailed surface topography and continuous subsurface geological model. Thus, based on this research work, it is concluded that 2D ERT in conjunction with borehole survey is a rapid, inexpensive, and reliable technique for recognition of the water-saturated zone in regions with wet tropical climates.