The characterization and modelling of flow and transport through the vadose zone are receiving increased attention in the last years, particularly as regards the pollutant phenomena. Hence water content estimation and its monitoring, from which strongly depend the hydrological processes that occur within the unsaturated zone, is an important task. A number of methods and devices are available for measuring the water content in soils but, usually, they are not usable with the rocks too and very few are the attempts to verify their applicability. The installation of the probes is the main difficulty in applying the devices for water content estimation in rocks, because the installation procedure has to ensure a good contact between the rock and the sensor in order to reduce the uncertainty due to the gap effects. In this study a non-traditional method, known as electrical impedance spectrometry (EIS), was used. Using the new apparatus Z-meter, developed within the European International Project E!3838 of EUREKA Program, the electrical impedance in complex form and its changes over time were monitored in order to verify the suitability of the device for water content estimation in rocks. Both the real component of impedance (resistance R) and the imaginary component (capacitive reactance X) were independently investigate. One kind of stainless steel probes have been installed into samples of calcarenite, a sedimentary rock coming from a quarry located in Canosa (South of Italy). The relationship between the output device and water content was investigated within a wide frequency range (from 100Hz to 10000Hz), using different water solutions with different electrical conductivity (EC) values. Due to the influence of temperature variation on all indirect moisture measurement methods, the experimentation was performed in a temperature controlled room provided with a ventilation system. Correlating the real component of the impedance with the directly measured water content, determined using a gravimetric method, functions of exponential type, with a good correlation coefficient, were obtained for different water solutions. The independence of the real component of impedance to changing the frequencies is confirmed; any frequency can be used. On the contrary, the sensitivity of resistance to changing the EC value of the solution used for sample saturation is evident. The analysis of reactance data confirms a strong dependence on the applied frequency. The reactance outputs are not continuously recorded for all investigated range of water contents (from saturation to dry) but appear in correspondence of water contents which depend not only on applied frequency but also on the EC of the solution used to saturated the sample. Particularly, higher frequency and lower EC of solution seem to assure reactance values in a wider range of water content. This evidence, together with a lower precision of the device on reactance outputs, makes it more difficult to use reactance to obtain any indirect measurement of water content. Though the experimentation is still ongoing, these preliminary results are encouraging for further studies both on different type of rocks, and in order to better investigate the capacitive reactance, that could provide more information about the physical properties of the investigated rock.
ROCK WATER CONTENT MEASUREMENTS BASED ON ELECTRICAL IMPEDANCE SPECTROMETRY METHOD
CAPUTO MC;DE BENEDICTIS F;MASCIALE R
2010
Abstract
The characterization and modelling of flow and transport through the vadose zone are receiving increased attention in the last years, particularly as regards the pollutant phenomena. Hence water content estimation and its monitoring, from which strongly depend the hydrological processes that occur within the unsaturated zone, is an important task. A number of methods and devices are available for measuring the water content in soils but, usually, they are not usable with the rocks too and very few are the attempts to verify their applicability. The installation of the probes is the main difficulty in applying the devices for water content estimation in rocks, because the installation procedure has to ensure a good contact between the rock and the sensor in order to reduce the uncertainty due to the gap effects. In this study a non-traditional method, known as electrical impedance spectrometry (EIS), was used. Using the new apparatus Z-meter, developed within the European International Project E!3838 of EUREKA Program, the electrical impedance in complex form and its changes over time were monitored in order to verify the suitability of the device for water content estimation in rocks. Both the real component of impedance (resistance R) and the imaginary component (capacitive reactance X) were independently investigate. One kind of stainless steel probes have been installed into samples of calcarenite, a sedimentary rock coming from a quarry located in Canosa (South of Italy). The relationship between the output device and water content was investigated within a wide frequency range (from 100Hz to 10000Hz), using different water solutions with different electrical conductivity (EC) values. Due to the influence of temperature variation on all indirect moisture measurement methods, the experimentation was performed in a temperature controlled room provided with a ventilation system. Correlating the real component of the impedance with the directly measured water content, determined using a gravimetric method, functions of exponential type, with a good correlation coefficient, were obtained for different water solutions. The independence of the real component of impedance to changing the frequencies is confirmed; any frequency can be used. On the contrary, the sensitivity of resistance to changing the EC value of the solution used for sample saturation is evident. The analysis of reactance data confirms a strong dependence on the applied frequency. The reactance outputs are not continuously recorded for all investigated range of water contents (from saturation to dry) but appear in correspondence of water contents which depend not only on applied frequency but also on the EC of the solution used to saturated the sample. Particularly, higher frequency and lower EC of solution seem to assure reactance values in a wider range of water content. This evidence, together with a lower precision of the device on reactance outputs, makes it more difficult to use reactance to obtain any indirect measurement of water content. Though the experimentation is still ongoing, these preliminary results are encouraging for further studies both on different type of rocks, and in order to better investigate the capacitive reactance, that could provide more information about the physical properties of the investigated rock.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
