Application of the UIUC model for predicting ballast settlement to unsaturated ballasts under moving wheel loads

The main objective of this study is to evaluate the practicality of the UIUC model to the Japanese design standard for ballasted tracks of aged lines as well as of new lines by considering some uncertain effects which are not verified and incorporated in the UIUC model, like the effects of ballast fouling, fluctuation in moisture content, and principal stress axis rotation. For this reason, in this study, first the trends in the permanent deformation accumulation of ballasts with various moisture contents and fine fraction contents under moving wheel loads were examined based on the results of advanced laboratory element tests such as triaxial compression tests on unsaturated ballasts and multi-ring shear tests on ballasts under moving wheel loads. Next, the applicability of the UIUC models to the estimation of the permanent deformation accumulation of ballasts were verified by considering the influences of fine fraction content, moisture content, and principal stress axis rotation, and a modification method of the UIUC model necessary for improving the prediction precision and extending the applicability was proposed.