Filter performance test for dams containing cracks

A new test procedure has been developed to evaluate filter performance when both the filter and the core (base) material have been cracked. This procedure allows the orientation of the crack to be horizontal or vertical, and accommodates flow in the horizontal and vertical directions as well. The applied hydraulic gradient and the thickness of the crack can also be varied. Two apparatuses have been constructed and tested. The smaller apparatus allows testing of truncated cylindrical test specimens that are 4" (10 cm) in diameter by 8" (20 cm) long. The larger apparatus allows testing of specimens that are approximately 12" x 12" x 12" (30 cm x 30 cm x 30 cm). An automated data acquisition system was developed to measure the pressures and flow rates through the test specimens as well as obtaining a video record of the filter performance. Initial tests have shown that the current filter criteria used by the U.S. Bureau of Reclamation, U.S. Army Corps of Engineers, and the National Resource Conservation Service provide filters that perform reliably even when cracked at the start of flow.