engleski

The particle size distribution as a key factor for hydrogeological investigations

In the field of urban hydrogeology, it is often needed to define the permeability, as the most important hydrogeological parameter for interpretation of impact of pollutant on groundwater quality. Calculating permeability from grain size data is fast, relatively simple and cheap, and is often used for stated purpose. Causeless modifications of original methods for determination of hydraulic conductivity or permeability from grain size data have been, in the last three decades, widely disseminated in scientific and expert articles and published in numerous scientific journals. Modification of referential grain size, which is generally integrated in the calculations as square value, is especially a sensitive issue. Such and similar modifications strongly affect the results compromising the valuable utilization of grain size data for the permeability assessment in loose deposits and similar porous materials. This problem was demonstrated in this research though the presentation of original versions of four permeability calculation methods from grain size distribution: Hazen’s, as a representative of extremely experimental method, USBR /USCRO (Urumović et al., 2020) as empirical method, and Slichter’s and Kozeny – Carman (Urumović and Urumović, 2016) method as theoretical methods. Validity and proposal for corrections were demonstrated as their validity ceases to depend on the grading of the analyzed materials. This is especially important for Kozeny – Carman method that integrates formulation of specific surface area, making it widely applicable in soil science disciplines. In this research, samples of loess and loess-like sediments (Pola et al., 2020) were analyzed in laboratory within the ISSAH project (funded by Croatian Science Foundation), and later mathematically processed for hydraulic conductivity calculation. Statistical analyses show high accuracy of mentioned methods when properly used, opposed to recently (mis)used formulae.

hydrogeology, permeability, particle size distribution, specific surface.

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