<p>This study examined the change in the permeability of clean sand during soil liquefaction under dynamic loading. Several studies proposed empirical expressions for estimating the permeability variation during liquefaction as a function of the excess pore pressure ratio. These formulations remained limited because no comprehensive expression existed for predicting the excess pore pressure ratio while considering influencing parameters such as acceleration, frequency, relative density, depth, layer thickness, and time. A detailed parametric analysis was carried out using a numerical finite-difference model to evaluate the evolution of the excess pore pressure ratio with respect to these variables. The analysis results supported the development of a generalized expression for the excess pore pressure ratio, providing a more accurate estimation of the permeability coefficient of homogeneous sandy soils during liquefaction. The validity of the proposed function was assessed through comparison with centrifuge test data available in the literature, and the predicted values showed good agreement with the measured results.</p>