Further Advancement in Filtration Criteria through Constriction-Based Techniques

In this technical note, the concept of constriction size in design is highlighted while elucidating some of the limitations of current professional guidelines that are only based on particle size ratios. The implications of the controlling constriction size, $D_{c35}$ , and the self-filtering constriction size, $D_{c95}$ , are elaborated on; $D_{c35}$ =constriction size whereby 35% of the filter constrictions are finer than this, and $D_{c95}$ =constriction size whereby 95% of the filter constrictions are finer than this. Combining the salient findings of two recent papers by Indraratna et al. in 2007 and Indraratna and Raut in 2006, a further refinement for filter design, i.e., $D_{c35}∕d_{85}^{*}⩽1$ , is introduced here based on the self-filtering base fraction and controlling constriction size of the filter, where the specific parameter $d_{85}^{*}$ =value of $d_{85}$ of the base soil grading curve modified by the self-filtering constriction size, $D_{c95}$ . The proposed criterion is verified using several large-scale tests carried out at the University of Wollongong and numerous test data available in the literature.