From Transportable Moisture Limit to Flow: Interpreting TML Criteria through Evaporation-Derived Hydraulic Functions for Iron Ore Fines

Abstract Understanding the water retention behavior of unsaturated granular materials is essential for interpreting water redistribution in porous media, particularly when changes in moisture content may affect drainage, saturation and flow-type responses. In iron ore logistics, this issue is relevant both during maritime transport, where internal moisture redistribution within bulk cargoes may generate locally saturated zones, and in stockpiles, where variations in water content influence drainage conditions and mechanical behavior. Although Transportable Moisture Limit (TML) procedures provide operational criteria for safe shipping, they do not explicitly describe the hydraulic state of the material or the transient redistribution processes that may occur after loading. This study investigates the soil water retention curve (SWRC) and the unsaturated hydraulic conductivity function, k(ψ), of a Brazilian iron ore fines material using the HYPROP system, a semi-automated evaporation apparatus based on Wind’s method. Tests were performed on the complete grain-size distribution at different void ratios, and additional tests were conducted on grain-size fractions associated with TML-related procedures, including the Flow Table Test. The results show that changes in packing state produce modest shifts in the SWRC but more pronounced differences in k(ψ), indicating the sensitivity of hydraulic conductivity to void ratio and pore connectivity. The comparison between the MPFT/PFD80 and Flow Table results suggests that the normative TML criteria can be interpreted within a hydraulic state framework defined by moisture content, degree of saturation, suction and hydraulic conductivity. The findings support the interpretation of TML not only as an empirical moisture threshold, but also as an initial hydraulic condition for time-dependent moisture redistribution under restricted drainage conditions.