| Abstract | A substation grounding system (SGS) is the most critical component in a substation. Its function is to dissipate the electric current that may affect people and equipment in the vicinity to the ground. The backfilled soils used for the SGS required specific electrical resistivity characterization with low soil resistivity (< 80 Ω-m). Moreover, the backfilled soil should perform high plasticity larger than 4, not be sand, silty sand, or silt, complying with EGAT’s criteria. However, soils from different locations proposed to be the backfilled soil also have extremely undesirable properties. That is why the soils need to be treated to obtain excellent performance for their function. In this study, three groups of disturbed soil collected from the different locations consisting of BP soil (CL), LP soil (ML), and PK soil (CL-ML) were mixed with distilled water, salt solution (NaCl) at 2% and 4%, and tested for the Atterberg Limits, the microstructure to observe the changes in soil plasticity and soil structure, respectively. Then the three soils with the salt proportion mentioned above were remolded to perform the UCS test and resistivity measurements to examine how effective salt solution proportion can reduce the soil resistivity and maintain the UCS by observing two phases of releasing time; moreover, the salt mixed with soils' effect on the environment was estimated. As a result, the salt content affects the soils' plasticity insignificantly because all three soils are classified as low plasticity soil. There was no change in mineral components; however, the microstructure observed from SEM presented more aggregation behavior when the salt solution was added from 2% to 4%. Remarkably, an increase in salt content affects the soil resistivity of three soils; soil resistivity is reduced intensely when the salt content increases. Although a decrease in UCS of soil is influenced by salt solution incretion, the salt content maintains moisture in the soil and presents the low UCS, then keeps stable UCS as the time released from 0-day to 28-day, respectively. In conclusion, BP, LP, and PK soils used for the SGS propose that were treated using the salt solution at 2%, and 4% perform the PI higher than 4, and low soil resistivity lower than 80 Ω-m and the treated soils can maintain their UCS as the time was released. In order to correlate the laboratory results to the field condition initially, Archie’s law was applied in this study by using the relationship between the formation factor of soil and soil porosity to obtain Archie’s equation. In the beginning, Archie’s law was developed for clean sandstone, which performed accurate factor values such as the formation factor, including the bulk soil resistivity and pore-fluid resistivity, porosity, a, m. Nevertheless, Archie’s law can be used to estimate an appropriated pore-fluid resistivity for the backfilled soil with fair results, because the porosity measured from the laboratory was rough measurement resulting in inaccurate values of all factors mentioned above. Although the laboratory result need to be more precised and validated with the results from field, this application could be used as an initial guidline, and developed for the future work. It can be concluded that the salt solution at 2% and 4% reflecting in pore-fluid conductivity reveals the enormous value of electrical conductivity larger than the standard of surface water quality (> 3 mS/cm is not permissible for irrigation). It should be noted that the laboratory tests were performed in the controllable condition such as temperature and electrical conductivity of water, which is different from the field that was affected extremely climate, natural water, and rainfall intensity. Therefore, the results should be validated and cautiously considered for the mentioned factors. |