Ballasted tracks fouled with sand particles are a widespread phenomenon in many countries, significantly affecting the hydraulic behavior of these tracks during both saturation and unsaturation stages. In this study, the Kozeny-Carman equation has been applied to predict the hydraulic conductivity during the saturation stage. This approach has been used after gathering data on various sandy fouled ballast materials and those with closed characteristics, due to the limited publications on sandy fouled ballast. However, it has been found that the Kozeny-Carman equation cannot be used directly for sandy fouled ballast without modifying its parameters. Subsequently, the validation of the modified equation has shown a high degree of agreement with the measured hydraulic conductivity. Moreover, theoretical equations have been derived to express the relationship between porosity of fouled ballast and its fouling index with setting up a new constant. This constant has been determined through an empirical equation and validated with seven different sandy fouled ballast materials. The validation results have indicated a strong correlation between the predicted and measured data on sandy fouled ballast porosity. Hence, based on the material characteristics and the modified Kozeny-Carman equation, the hydraulic conductivity of sandy fouled ballast can be determined in the saturation stage.