Combined ERT and borehole logs for mapping the soil-rock interface in a granitic environment

This study used the efficiency of electrical resistivity tomography (ERT) and borehole logs to map the soil-rock interface beneath four traverses (RS1, RS2, RS3, and RS4) in the granitic terrain of Perak, Peninsular Malaysia. The study aimed to evaluate the impacts of the soil-rock characteristic features and interfaces on groundwater and infrastructure development to meet the needs of the increasing inhabitants yearly. The borehole- and ERT-derived lithologic units are strongly correlated. The delineated lithologic units include the topsoil, weathered granitic units (medium stiff to hard silty clay or clayey silt with <800 Ωm), thin to wide-sized weathered/fractured units, and fresh granitic bedrock. These soil-rock profiles and weathered/fractured apertures support sustainable groundwater developments with drill depths above 45 m. In contrast, the delineated clay/silt alternating with stiffer soils, low load-bearing deep-weathered/fractured zones, and bedrock boulders in most places, except beneath traverse RS3, have high affinities for water retention and differential stresses. These features can adversely impact poorly reinforced foundations. Hence, structural elements of the foundations, such as footings or piles, should be placed on stable bedrock, particularly in the central to western parts of the study area. This study has reduced the paucity of information on using ERT and borehole logs for soil-rock interface studies in the study area.