Using Acoustic Emission Testing in Seepage Investigations

Acoustic emission is the name of both a physical phenomena and a technology. An acoustic emission is the generation of a transient elastic wave by a rapid release of energy. Each different type of acoustic emission source generates a stress wave that has distinctive properties. At the point where seepage is entering or exiting an earth or concrete dam, a resulting stress wave usually is generated. Measuring this stress wave or measuring the flow “noise” with acoustic emission monitoring equipment can help locate seepage sources and exit locations. Laboratory testing was performed to obtain baseline data for various flow conditions. Acoustic emission monitoring was conducted for clear flowing water and for flowing water which was transporting soil particles. Calibration studies were made in the field at the locations where seepage could be measured and at locations where boils were present. Seepage was either known to exist or suspected at three projects. Acoustic emission testing was performed along the upstream sides of the dam and spillways so that suspected seepage locations could be further investigated using salt tracing studies or other electrical methods. Acoustic emission testing was done at two different times so that areas of high counts could be verified. Background noise was reduced by filtering, After the field work was completed, the number of counts was plotted. Locations where high counts were recorded indicated likely seepage areas which were investigated using other techniques. These other techniques verified that the high acoustic emission counts indicated seepage was present. 7 pp., 4 references.