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Objective The results of laboratory tests on the electrical resistivity of sand are widely used in the interpretation of field electrical resistivity tomography. However, the influences of testing conditions and the field implementations of relationship curves between the electrical resistivity and properties of sand need further research. Methods First, the electrical resistivity test device was developed by using the two-electrode method. Then, the influences of current type, alternating current (AC) frequency, voltage and grain size of sand on the relationship between electrical resistivity and water saturation (ρ-Sr), as well as electrical resistivity and salinity of the pore water (ρ-n), were studied. Results The results showed that an AC current frequency of 10 Hz and an input voltage of 1 V were recommended to reduce the test error of resistance. There was a power function between the electrical resistivity and water saturation (ρ-Sr), as well as electrical resistivity and salinity of pore water (ρ-n), under AC and direct current (DC). As DC might cause an electrolysis reaction of the electrodes of the sand column under the high salinity of pore water, the AC electrical method was suggested. When the water saturation is greater than 50%, the electrical resistivity difference caused by the grain size of sand becomes small. Moreover, the electrical resistivity did not decrease significantly with increasing water saturation, which suggested that a relatively stable interface of the electrical resistivity might exist in the unsaturated zone with 50% saturation rather than in the water table. When the salinity of pore water is greater than 2 g/L, the electrical resistivity of all five types of saturated sands did not decrease obviously with increasing salinity. Conclusion Research results comfirm the electrical resistivity method easily distinguishes fresh water from brackish water but has difficulty further subdividing brackish water, salt water and brine. |
