No Erosion Criterion for Granular Filters Based on Constriction Size – An Experimental Study

Filters are provided in embankments in order to arrest the eroded soil particles that are carried by the seepage water .Current design method of graded filters was developed by Terzaghi which is based on the particle size distribution of the filter material and the base material. This paper presents an attempt to develop filter design criteria in relation to constriction size in gravel filters. It is an alternative approach from the conventional filter design criteria of Terzaghi, which is based on the particle size distribution of the filter media and base material. In his study a criterion for filter to prevent erosion is proposed based on the constriction size distribution of the filter media. The proposed constriction size-based criterion, C10/d95 2 directly compares the controlling constriction size (C10) with the specific representative base size (d95) defines the effectiveness of filters, hence it is a more effective method compared to the Terzaghi criterion (D15 /d85<5) which is based purely on particle size. This ratio explains the behavior of filters more clearly and is proved by a number of tests on various base-filter combinations. When compared to Terzaghi criteria, constriction size distribution criterion proves to be more effective.