NSTU scientists are developing a method for strengthening soil using alternating asymmetric current electroosmosis. The technology will not only effectively remove moisture in porous media, but also reduce the energy consumption of the process itself.
As noted by Evgeny Porsev, Professor of the Department of Electrotechnical Complexes, Doctor of Technical Sciences, in dispersed materials of a dielectric nature (soils), a double electric layer appears at the interface "solid dielectric — water" due to polyunsaturated bonds on the surface of the dielectric with a thickness of no more than 3-5 diameters of a water molecule. When an external electric field is applied, the double electric layer begins to move, dragging the surrounding water with it, and mass transfer of water occurs in the stationary skeleton of the soil. This phenomenon of creating hydraulic pressure under the action of an electric field is called electroosmosis. Using this method, wet soil can be dewatered, which will increase its density, strength and bearing capacity, prevent deformation and subsidence under the weight of structures, and ensure the stability of foundations. Reduced water permeability is especially critical for clay soils prone to swelling. Electroosmotic dewatering technology can be used, for example, in the construction of a subway system to stabilize the soil and lower the groundwater level.
The essence of the method being developed at NSTU-NETI is the use of asymmetric alternating current for electroosmotic soil dewatering. As Evgeny Porsev explains, when the soil is drained by direct current, parasitic processes occur that prevent the movement of water in the soil skeleton. This, for example, creates a moisture gradient between the electrodes, which leads to an increase in electrical resistance in the soil. Uneven moisture distribution creates areas with low conductivity and can lead to process attenuation. A parasitic factor is also the polarization of the electric field — the occurrence of a negative voltage directed counter to the voltage applied to the skeleton of the soil. This creates additional resistance, which takes a significant amount of energy to overcome. As a result, the specific energy consumption for the electroosmotic dehumidification process increases.
"Alternating current uses an electric field with varying polarity and unequal pulse amplitude. The main task is to select the frequency of current pulsation so that it coincides with the natural frequency of mechanical vibrations of soil particles. This allows you to remove the polarization of negative factors affecting overall energy consumption. The asymmetric alternating current creates pulses of different polarities, which ensures more uniform drainage of the soil," the scientist said.
In the course of the research, electroosmotic experiments were conducted with several grades of alumina. The experimental results showed that the energy efficiency of alternating asymmetric current electroosmosis is almost 11 times higher than that of direct current electroosmosis (energy consumption for the dewatering process requires 11 times less).
In continuation of the work, scientists will conduct a series of field experiments to determine the energy resonance in order to find the optimal characteristics of the external electric field to reduce energy consumption for the process of hardening the soil skeleton.