Large-scale Filter Performance Tests

The Bureau of Reclamation, in partnership with the U.S. Army Corps of Engineers, conducted a large-scale filter testing program over several years. The testing program studied the performance of filters subject to cracking to help designers assess cracking related failure modes and improve design practices. These tests simulated the cracked conditions that occur in the upper portions of embankment dams. Each test focused on three main factors: how well a crack can form within a filter, how well a cracked filter can heal when subjected to a concentrated leak, and how effectively a filter can stop or control a concentrated leak. These factors were assessed by correlating filter performance to material properties such as gradation, density, and moisture content. This paper discusses the testing device, filter materials tested, test procedures, results for 14 tests, and lessons learned. Conclusions include the following: non-plastic, cohesionless filter materials with low fines content can sustain a crack under certain conditions and may eventually become unable to stop a concentrated leak; broadly-graded, cohesionless filters are capable of sustaining a crack; two-stage filters performed appreciably better than single-stage filters; and wide single-stage filters performed appreciably better than narrow single-stage filters.