Electrical Breakdown Properties of Soil

The electrical breakdown characteristics of small-scale soil samples subjected to voltage pulses have been measured. The threshold breakdown field for these samples with a water content of 4.5 percent by volume is about 2.7 to 3.0 MV/m. The delay time from application of the voltage to breakdown varied from about 30 ns at the highest available voltages to milliseconds close to the threshold field. The postbreakdown I-V characteristics of the samples are strong functions of the amount of current that can be supplied by the pulser/circuit combination. The breakdown process in the test soils appears to be due to air ionization in the voids between the soil particles. A semiempirical mathematical model for the postbreakdown I-V characteristics, based on a competition between air ionization and a recombination (quenching) process, gives good correlation with the experimental results.