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Porosity; Waxman–Smits equation; normalization; resistivity method

Porosity ($\phi$) of soil/rock is frequently approximated using Archie’s Law where bulk resistivity ($\rho_{\rm{o}}$) is obtained from resistivity method while pore-fluid resistivity ($\rho_{\rm{w}}$) relies on well/borehole availability. This research proposes a new approach in obtaining $\phi$ of unconsolidated soil. The study was conducted at Balik Pulau, Minden and Teluk Kumbar. Clay’s presence was determined via particle size distribution (PSD) analysis. PSD graphs’ curves show that Balik Pulau is composed of elastic silt, while the other two sites consist of sand dominantly. For verification, soil samples’ porosities, $\phi_{\rm{sample}}$, were measured to produce 31.93, 32.95 and 26.47% values for the three sites, respectively. The new approach uses saturated layer’s resistivity values for porosity calculation, $\phi_{\rm{resistivity}}$. The resistivity values generated $F_{\rm{a}}$, $\rho_{\rm{w}}$ and $\rho_{\rm{o}}$ with constraints applied according to published reports for the parameters’ range of values. Conventional and normalized Waxman–Smits models were then employed for $\phi_{\rm{resistivity}}$. Conventional model produced $\phi_{\rm{resistivity}}$ of 12.66, 25.33 and 12.94%, while normalized model produced better $\phi_{\rm{resistivity}}$ values of 30.38, 31.91 and 27.32% for the three sites, respectively. Normalized model significantly outperforms with errors of <5%. Hence, the new approach accurately estimates saturated layer’s $\phi$ with no dependency on physical samplings and is applicable even in clay’s presence.

N ROSLI¹ N A ISMAIL¹ R SAAD¹ N RAHMAN¹

1. School of Physics, Universiti Sains Malaysia, Minden, Pulau Pinang, Malaysia.

Published

1 January 2020

Manuscript received

19 September 2018

Manuscript revised

31 May 2019

Accepted

13 August 2019

Early published

Unedited version published online

Final version published online

19 December 2019