Using Grain‐Size Distribution Methods for Estimation of Air Permeability

Abstract

Knowledge of air permeability (ka ) at dry conditions is critical for the use of air flow models in porous media; however, it is usually difficult and time consuming to measure ka at dry conditions. It is thus desirable to estimate ka at dry conditions from other readily obtainable properties. In this study, the feasibility of using information derived from grain-size distributions (GSDs) for estimating ka at dry conditions was examined. Fourteen GSD-based equations originally developed for estimating saturated hydraulic conductivity were tested using ka measured at dry conditions in both undisturbed and disturbed river sediment samples. On average, the estimated ka from all the equations, except for the method of Slichter, differed by less than ± 4 times from the measured ka for both undisturbed and disturbed groups. In particular, for the two sediment groups, the results given by the methods of Terzaghi and Hazen-modified were comparable to the measured ka . In addition, two methods (e.g., Barr and Beyer) for the undisturbed samples and one method (e.g., Hazen-original) for the undisturbed samples were also able to produce comparable ka estimates. Moreover, after adjusting the values of the coefficient C in the GSD-based equations, the estimation of ka was significantly improved with the differences between the measured and estimated ka less than ±4% on average (except for the method of Barr). As demonstrated by this study, GSD-based equations may provide a promising and efficient way to estimate ka at dry conditions.

Localized Sulfide Oxidation Limited by Oxygen Supply in a Full‐Scale Waste‐Rock Pile

“…4). Similar to the approach used to estimate D eff , values for K air can be predicted using physico-empirical relationships (see equations in Supplemental Table S2; Wang et al, 2015). In addition, the in situ air permeability (i.e., k air K air ) of the waste rock can be calculated by considering the pore-gas pressure dissipation with depth in a borehole as a natural slug test, i.e., as an alternative to a controlled injection test or laboratory analysis, which are highly challenging for coarse waste rock.…”

Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management

“…Both diffusive and advective gas transfer are strongly controlled by the properties of the waste rock, including its permeability, degree of porewater saturation, and spatial heterogeneity therein [194,266]. Various empirical and semi-empirical formulae to estimate diffusivity and permeability from particle size distributions or porosity ranges exist [267][268][269] but these often invoke tortuosity or constrictivity parameters that are poorly defined [266]. Typical effective permeability and gas-diffusivity ranges for waste rock have been reviewed [16] and vary orders of magnitude between and within sites [194].…”