Discovery and Remediation of Internal Erosion/Piping Voids between Incompatible Materials

摘要

During a May 2015 inspection, several depressions were observed surrounding the transmission line foundations on the Hennepin Island Earth Dam. Investigations of the depressions revealed the presence of fill materials with a wide range of particle sizes, some with minimal sand/fines content. Seepage was noted from a downstream retaining wall, approximately 10 feet lower in elevation and 20 feet horizontally from the depressions. The seepage was correlated to the depressions with tracer dye. The repair consisted of grouting the larger void spaces between the particles in the earth dam. This type of grouting is termed "compaction grouting", but the grouting operations were primarily intended to limit the potential for internal erosion through the coarse zone by filling void spaces. The grouting addressed an issue (i.e., erosion due to incompatible materials) and the Hennepin Island Earth Dam appears to be performing without additional internal erosion or a heightened phreatic surface.