Correlation between geo-mechanical and petro-physical properties of the Sekondian Group

Abstract

Instability issues have been a challenge in the Sekondian Group in Sekondi-Takoradi in the Western Region of Ghana, with regards to civil works and underground excarvations over the years. Uniaxial compressive strength, which is essential in stability analysis in engineering projects, requires high quality core samples of appropriate standards for its test, which cannot easily be obtained except at deeper depth strata. However, it could be inferred from physical properties of rocks. This research examined some geomechanical and petrophysical properties of Efia Nkwanta Sandstone, Elmina Sandstone and Takoradi Sandstone by correlation and regression analyses and obtained models for stability inference. The correlation and regression analyses were carried out with t- and F-tests using Minitab programming language. The analyses were based on results obtained from laboratory investigations of uniaxial compressive strength, porosity and particle density of samples. The laboratory investigations were respectively performed by uniaxial compressive test, saturation test and density test. For correlation, results were interpreted based on correlation coefficients and p-values whereas regression analyses were based on R squares, p-values and residual standard deviations. From the results, it was observed that linear association only exists between UCS and porosity in sandstones with well sorted grains and connected pores. Thus, the compressive strength of the sandstones is highly dependent on the degree of pore connectivity. Hence, the prediction of geomechanical and petrophysical properties of the Sekondian Group is only possible for UCS and porosity in the Efia Nkwanta beds.