Influence of Precipitation on the Determination of Proper Time for Soil Resistivity Measurement

In order to obtain reliable and effective upland soil resistivity measurements, it is necessary to know how much time after the rain stops is required before making soil resistivity observations so that the influence of precipitation on the measurements can be eliminated. Based on the soil resistivity monitoring data at different depths obtained from the soil conductance automatic monitoring system using the triple-electrode method, and the precipitation data from the synchronous and automatic observing system in Hechuan County of Chongqing, this paper analyzed the effect of rain on the determination of upland soil resistivity measurement time.The results showed that the required interval time between the measurement and the termination of rain should be as follows: if the rainfall was less than 0.1 mm , the interval time was zero;the interval time was 24 h if the precipitation time was less than 1 h or the rainfall was 0.1-2.0 mm; the interval time was 72 h if the precipitation time was 2-10 h or the rainfall was within 2.1-5.0 mm; and the interval time of 72-232 h was observed when the precipitation time was 10-25 h or longer or the rainfall was 5.0-10.1 mm or larger. Relevant observations showed that the above conclusions were on the whole valid for different soil depths. On the other hand, the results indicated that the maximum variance ratio for the influence of precipitation on resistivity measurement was about 28.9%, and the average variance was about 3.9%. Moreover, a preliminary analysis also showed that the precipitation process time might play a more crucial role in the resistivity recovery time than the precipitation amount. It is also found that it is practically better to use the rank correlation method than the numerical correlation analysis method to determine the time break between the stop of rain and the time to carry out the soil resistivity measurement.