Site specific geophysical-geotechnical integration: correlating ERT and SPT for subsurface characterisation

Subsurface investigations are critical for infrastructure development in the Lubok Antu region of Sarawak, Malaysia due to its complex geological conditions and seismic risk. Conventional geotechnical site investigation, such as standard penetration test (SPT) is accurate but discrete, costly, and limited in spatial coverage. This study established robust, site-specific correlations between electrical resistivity tomography (ERT) and key geotechnical parameters to enable rapid, cost-effective subsurface characterisation. ERT surveys and SPT boreholes were conducted at nine locations with a maximum depth of 30 m. Soil resistivity (ρ) was correlated with $$\:\text{S}\text{P}\text{T}-\text{N}$$ values, shear wave velocity ($$\:{\text{V}}_{\text{s}}$$) derived from empirical relationships, and laboratory measured moisture content (ѡ) and plasticity index (PI). A strong nonlinear correlation was observed between ρ and ѡ (R2 = 0.74), while moderate linear correlations were found for $$\:{\text{V}}_{\text{s}}$$ (R2 = 0.62) and $$\:\text{S}\text{P}\text{T}-\text{N}$$ (R2 = 0.55). The results demonstrate that ERT can effectively estimate geotechnical properties, offering a practical tool for preliminary site assessment that reduces reliance on extensive and expensive drilling programs. This study offers a novel approach for geotechnical investigation in Lubok Antu, reducing the reliance on extensive drilling programs and improving the efficiency of subsurface investigations. The developed correlations are particular valuable for seismic hazard assessment and foundation designs in this tectonically active region. Subsurface investigation is essential in geotechnical and earthquake engineering.