TITLE:
Hydraulic Conductivity Estimation for Non-Plastic Tailings-Derived Silty Sands
AUTHORS:
Hans Rönnqvist
KEYWORDS:
Hydraulic Conductivity, Tailings, Silty Sand, Empirical Equations, Calibration, Permeability
JOURNAL NAME:
Geomaterials,
Vol.16 No.4,
September
3,
2026
ABSTRACT: Classical empirical hydraulic-conductivity equations were developed mainly for cleaner granular soils than the fines-influenced materials often encountered in tailings settings. This study evaluates such equations for non-plastic tailings-derived silty sands. Two dataset levels are distinguished: an expanded dataset comprising all 14 tested materials from 6 source groups, and a restricted subset comprising 8 materials from 4 source groups that define the main low- to medium-fines recommendation domain. In this restricted subset, where fines contents are below about 30%, the particle-size distributions resemble ordinary non-plastic silty sands in engineering terms, suggesting broader synergistic effects than merely restricted to the tailings-derived origin. In the expanded dataset, Sherard emerged as the strongest gradation-based method. Within the restricted subset, Slichter emerged as the strongest porosity-dependent method in both original and calibrated form. This distinction is consistent with the underlying formulation of the methods: gradation-based equations implicitly represent a typical medium-dense to dense packing state, whereas porosity-dependent equations explicitly account for densification. Coefficient-only calibration improved both methods at the standard interpreted conductivity target,
k
std
, but Sherard calibration proved more domain-bounded, whereas Slichter transferred more favourably under boundary checking. The results support a domain-bounded recommendation: Sherard as the preferred gradation-based method and Slichter as the preferred porosity-dependent method for low- to medium-fines non-plastic tailings-derived silty sands.