Characteristics and rippability conditions of near-surface lithologic units (Penang Island, Malaysia) derived from multimethod geotomographic models and geostatistics.

The nature and rippability conditions (rock mass quality [RMQ]) of the near-surface lithologic units of Batu Maung, Penang Island, Malaysia, were investigated to develop sustainable groundwater and infrastructure. This study used a novel approach that combined seismic refraction tomography (SRT), electrical resistivity tomography (ERT), borehole drilling, and simple linear regression (SLR) analysis. The seismic P-wave velocity (Vp) and resistivity models revealed four distinctive units: residual soils (silty sand), very poor-to-good (weathered) granite, and the fresh granitic unit, including the fractured/faulted zones. The thicknesses of the residual and weathered materials ranged from a few centimeters to 15 m and 1.0–16 m, respectively. The developed empirical relationship effectively predicted rock quality designation (RQD) from Vp data through SLR analysis, with a prediction accuracy of 96% and a p -value<0.05. Also, the results from five key regression assumptions: linear relationship, multivariate normality, no multicollinearity, no autocorrelation, and homoscedasticity, suggested an accurate and statistically significant empirical relationship for use in granitic environments. The RMQ statistical model accurately classified the lithologic units beneath the area into Classes I–VI. Due to the low load-bearing of the rippable residual soils, very poor-to-fair weathered granitic rock masses, and fractured/faulted zones based on their Vp and resistivity values, and the steep slopes in the northern section of the study area, all intended infrastructures, particularly high-rise buildings and buildings with continuous footing foundations, should be piled to rest on the non-rippable fresh granitic units, with RQD and Vp values of >90% and >2100 m/s, respectively, in the central to the northcentral section in the study area. Conversely, the deep-weathered/fractured zones of depths >35 m, beneath Line 1, towards the central part of the area, with resistivity and Vp values of 100–900 Ω-m and <1900 m/s, respectively, were identified as potentially water-containing zones for sustainable groundwater abstraction. • This study entails strata rippabilities using SRT, ERT, and geostatistical analyses. • An empirical relationship to estimate RQD from Vp for granitic rocks was developed. • Rock masses within Classes I and II have a good-to-excellent RQD of 75% to 100%. • The excellent rocks certify the soundness criteria for founding engineering structures. • Sustainable groundwater development was envisaged at fractured/weathered zones. [ABSTRACT FROM AUTHOR]