5:15 PM - 6:30 PM
[HTT17-P01] An Atempt to Estimate the Water Level Change of
Non-confined Groundwater by Earthing Resistance (III)
- Characteristics of the Anniversary Changes -
Keywords:electrical equipment, Musashino district, loam layer, perchied water, flood damage, equivalent earthing resistance
1. Introduction
In order to investigate the relationship between the water level of unconfined groundwater and the earthing resistance of the grounding electrode attached to electrical equipment, measurements of both have been conducted since April 2019. As a result, the relationship was confirmed on both. In addition to the variation of the groundwater level, it is considered that the variation of the ground resistance may be affected by the annual change of the distribution of the ground temperature (Ryoki, 2020). The results, which are measured up to now, are reported and the future measurement plan is described In this paper.
2. Measurement
The earthing resistance is expected to change considering the relationship between the thickness of the first layer and the equivalent earthing resistance in a horizontal two-layer structure (Ryoki, 2019b). Therefore, in order to investigate the relationship between the water level of unconfined groundwater and the earthding resistance, an observation well, WPTU, was installed in the area where the Kanto loam layer is widely distributed. The Specifications of WPTU and measuring instruments are shown in Table 1. At the same time, groundwater temperature and electrical conductivity are measured at 10-minute intervals in WPTU. In the vicinity of the observation wells, the earthing resistance of the grounding electrodes for the safety of electrical equipment was measured repeatedly.
3. Result
Fig. 1 shows groundwater level, water temperature, and electrical conductivity in WPTU from April 23, 2019 to January 25, 2021. It shows that the conductivity increases when the water level rises rapidly. And decreases when the water level decreases relatively slowly, except for the unstable period immediately after the excavation of the observation pit.
Fig. 2 shows the earthing resistance which connected to Class A earthing electrode under a concrete building near the WPTU. It shows the water level observed at the same time, and the air temperature directly above the WPTU, too.
Fig. 2 shows that as the water level rises, the earthing resistance decreases, and as the water level decreases, the ground resistance increases. The relationship with the water level and the earthing resistance is harmonious. On the other hand, when the annual change in the 10-day moving average curve of temperature is compared with the change in water level, the relationship is harmonious, but the phases are not coincident. In general, when the temperature rises, the ground resistance decreases, and when the temperature decreases, the ground resistance increases. The phase lag of the earthing resistance to the air temperature is about two months if we focus on these extreme values.
In areas where marine clay strata are outcropping, it has been reported that when spontaneous potential is formed by the sulphide minerals in marine clay strata, the annual change in spontaneous potential lags behind the temperature (Ryoki, 1990). In response to this, Ryoki (2020) suggested that since the ground resistance is also affected by the underground temperature, the annual variation of the earthing resistance would show a lagging phenomenon with respect to the surface temperature. The measurement results shown in Fig. 2 are in harmony with this suggestion.
References
Ryoki, K. (1990): Annual Variation of Spontaneous Potential -Toward a Teaching Material for Familiar
Geophysical Phenomena-, Sci. Edu. in Osaka, 4, 25-32.
Ryoki, K. (2019a): An Attempt to Estimate the Level of Non-confind Groundwater by Earthing Resistance
(I) -Outline of Theory-, Proc. Jap. Geosci. U. 2019, HTT22-03.
Ryoki, K. (2019b): A Theory of Water Level Estimation to Focus on the Change of Earthing Resistance for
the Prediction of Flood Occurrence, Jour. of Polytech. Sci., 35, 30-35.
Ryoki, K. (2020): A Study on the Relationship between Earthing Resistance and Groundwater Level, Pro. of
Kansai Geo-Sym., 8, 18-21.
In order to investigate the relationship between the water level of unconfined groundwater and the earthing resistance of the grounding electrode attached to electrical equipment, measurements of both have been conducted since April 2019. As a result, the relationship was confirmed on both. In addition to the variation of the groundwater level, it is considered that the variation of the ground resistance may be affected by the annual change of the distribution of the ground temperature (Ryoki, 2020). The results, which are measured up to now, are reported and the future measurement plan is described In this paper.
2. Measurement
The earthing resistance is expected to change considering the relationship between the thickness of the first layer and the equivalent earthing resistance in a horizontal two-layer structure (Ryoki, 2019b). Therefore, in order to investigate the relationship between the water level of unconfined groundwater and the earthding resistance, an observation well, WPTU, was installed in the area where the Kanto loam layer is widely distributed. The Specifications of WPTU and measuring instruments are shown in Table 1. At the same time, groundwater temperature and electrical conductivity are measured at 10-minute intervals in WPTU. In the vicinity of the observation wells, the earthing resistance of the grounding electrodes for the safety of electrical equipment was measured repeatedly.
3. Result
Fig. 1 shows groundwater level, water temperature, and electrical conductivity in WPTU from April 23, 2019 to January 25, 2021. It shows that the conductivity increases when the water level rises rapidly. And decreases when the water level decreases relatively slowly, except for the unstable period immediately after the excavation of the observation pit.
Fig. 2 shows the earthing resistance which connected to Class A earthing electrode under a concrete building near the WPTU. It shows the water level observed at the same time, and the air temperature directly above the WPTU, too.
Fig. 2 shows that as the water level rises, the earthing resistance decreases, and as the water level decreases, the ground resistance increases. The relationship with the water level and the earthing resistance is harmonious. On the other hand, when the annual change in the 10-day moving average curve of temperature is compared with the change in water level, the relationship is harmonious, but the phases are not coincident. In general, when the temperature rises, the ground resistance decreases, and when the temperature decreases, the ground resistance increases. The phase lag of the earthing resistance to the air temperature is about two months if we focus on these extreme values.
In areas where marine clay strata are outcropping, it has been reported that when spontaneous potential is formed by the sulphide minerals in marine clay strata, the annual change in spontaneous potential lags behind the temperature (Ryoki, 1990). In response to this, Ryoki (2020) suggested that since the ground resistance is also affected by the underground temperature, the annual variation of the earthing resistance would show a lagging phenomenon with respect to the surface temperature. The measurement results shown in Fig. 2 are in harmony with this suggestion.
References
Ryoki, K. (1990): Annual Variation of Spontaneous Potential -Toward a Teaching Material for Familiar
Geophysical Phenomena-, Sci. Edu. in Osaka, 4, 25-32.
Ryoki, K. (2019a): An Attempt to Estimate the Level of Non-confind Groundwater by Earthing Resistance
(I) -Outline of Theory-, Proc. Jap. Geosci. U. 2019, HTT22-03.
Ryoki, K. (2019b): A Theory of Water Level Estimation to Focus on the Change of Earthing Resistance for
the Prediction of Flood Occurrence, Jour. of Polytech. Sci., 35, 30-35.
Ryoki, K. (2020): A Study on the Relationship between Earthing Resistance and Groundwater Level, Pro. of
Kansai Geo-Sym., 8, 18-21.