Degree Name

Doctor of Philosophy


University of Wollongong. Dept. of Civil and Mining Engineering


This study highlights an analytical model simulating the filtration phenomenon applicable to any base soil-filter system. Prior to development of such a model, different approaches in filter design criteria are reviewed, and their advantages and disadvantages are critically discussed. The mechanics of filtration are investigated both analytically and experimentally to achieve a better understanding of the behaviour of particle migration within the filter medium, and highlight the influencing parameters affecting the filtration process. The evaluation of pore size and coefficient of permeability of the filter are studied, and a new relationship is established to determine the coefficient of permeability based on finer fraction of particle size distribution curve (D5 and D10). Considering the theoretical concepts of filtration phenomenon, the proposed model include the actual hydraulic conditions and the relevant material properties such as: coefficient of permeability, porosity, friction angle, and the shape and distribution of particles. The model is founded on the concept of critical hydraulic gradient derived from limit equilibrium considerations, where the migration of particles is assumed to occur under applied hydraulic gradients exceeding this critical value. The rate of particle erosion, and hence, the filter effectiveness is quantified on the basis of mass and momentum conservation theories. By dividing the base soil and the filter domains into discrete elements, the model is capable of predicting the time-dependent particle gradation and permeability of each element, thereby the amount of material eroded from or retained within a given soil-filter system. Laboratory tests conducted on a fine base material verified the validity of the model. A design procedure for efficient filter using the proposed model is presented in a separate chapter for two dimensional flow in a simplified earth structure. The model predictions are also compared with the commonly used empirical recommendations, including the conventional grading ratios. The response of the model in relation to the self-filtration phenomenon is also discussed. Finally, recommendations for further research are given in the context of the findings of this study.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.