Subsurface void mapping using geophysical and geotechnical techniques with uncertainties estimation: case study of Kinta Valley, Perak, Malaysia

Abstract

In this study, an assessment of the subsurface conditions was carried out using both the geophysical and geotechnical methods for delineating lithology units and mapping cavities in the subsurface. In light of this, geo-electrical vertical electrical soundings (VES) technique and drilling tests from which in situ standard penetration tests (SPT-N) and particle size distribution (PSD) analysis on some selected samples were carried out. Additionally, accuracy assessment of the field measurements was carried out statistically using coverage factor and uncertainty analysis at 95% confidence level in justification of the relationship between the estimated depth of the cavity and the resistivity values. The results of VES and 2D resistivity imaging show that three layers are delineated. The weathered bedrock with resistivity of about 500 Ωm hosts the cavity which is air-filled at shallow depth and saturated with fluid or clay with low resistivity of about 127 Ωm at deeper depth. The SPT N-values obtained ranges between 0–5 and 10–20 corresponding to weak/unconsolidated zone and consolidated sediments, respectively. The SPT N-values from the boreholes drilled agreed with the inferred lithology units from electrical resistivity survey. The results of the PSD suggest that sand/gravel sediments with grain sizes more than 0.075 mm dominated the study area. A combination of both the geophysical and geotechnical data shows good agreement and their relevance in addressing subsurface problems.