The Use of a Geosynthetic Composite as a Chimney Filter-Drain in an Earth Dam

The precedent of using filter and drainage systems in earth and earth-rock dams to control internal erosion, piping, and seepage has been well documented in the literature (References 1, 2). Such systems are almost always constructed of coarse grained materials. These clean, natural sands and gravels or crushed rock are placed in zones with each becoming coarser in the downstream direction. This paper describes a new approach in providing this important defensive design element for an earth dam in Oklahoma. The laboratory testing, design, installation, and monitoring of a geosynthetic composite used as a substitute for sand and gravel is discussed. The use of geosynthetics is not new to the Soil Conservation Service. We have used geotextiles successfully over the last 15 years as bedding layers or separation beneath rock riprap, rock blankets, chutes, and gabion structures. They have also been used as filters and drains in or under small grade control structures. In all cases, however, the geotextiles were used in a setting where their performance could easily be monitored. 7 pp., 12 references.