Geotechnical Applications of the Self-Potential Method. Report 3. Development of Self-Potential Interpretation Techniques for Seepage Detection

摘要

This report consists of four distinct but complementary parts: a laboratory/field study of environmental effects on self-potential (SP) electrodes and long-term stability of the electrodes; field investigations at Beaver Dam, Arkansas; development of a computer program for interpreting seepage-related SP field survey data; and development of an extensive bibliography and database for acquisition and interpretation of seepage-related SP data. The geotechnical problem at the Beaver Dam, AR, site was anomalous underseepage in the foundation of a large embankment dike. SP data were effectively used to map the seepage paths. Three electrodes were investigated: non-polarizing copper-copper sulfate (CS), copper-clad steel (CCS), and lead. Of the three, the commercial-grade lead electrodes are least suitable for long-term monitoring of SP. CS electrodes with gelled electrolyte appear capable of surviving at least a few years without maintenance or significant deterioration of physical properties or performance. For SP measurements, CCS electrodes have a lower signal to noise ratio than do CS electrodes. Field and laboratory measurements indicate that responses of CCS electrodes to environmental disturbances are an order of magnitude or greater than CS electrodes. The higher noise level is due both to the direct exposure of the metal to the soil as well as the exposure of the unburied portion of the electrodes to solar heating and rainfall. Thus, the considerably higher initial cost and extra effort involved in installation of the CS electrodes are justified, and CS electrodes are recommended for geotechnical applications of the SP method. (EDC)