EXPERIMENTAL SUBSTANTIATION OF THE NPEMFE GEOPHYSICAL METHOD TO SOLVE ENGINEERING AND GEOLOGICAL PROBLEMS

109 UDC 631.672.3:627.826 Iryna Viktorivna Chushkina, Senior Lecturer, Department of Civil Engineering, Construction Technologies, and Environmental Protection, Dnipro State Agrarian and Economic University, 25 S. Yefremov St., Dnipro, 49005, Ukraine, e-mail: zalomiy80@gmail.com; https://orcid.org/0000-0003-1251-6664; Dmytro Serhiiovych Pikarenia, Doctor of Sciences (Geology), Professor, Department of Ecology and Environmental Protection, Dniprovsky State Technical University, 2 Dniprobudivska St., Kamianske, 51900, Ukraine, e-mail: nippel@ua.fm; https://orcid.org/0000-0003-1405-7801; Olha Viktorivna Orlinska, Doctor of Sciences (Geology), Professor, Head of the Department of Civil Engineering, Construction Technologies, and Environmental Protection, Dnipro State Agrarian and Economic University, e-mail: egmsitb@gmail.com; https://orcid.org/0000-0002-4670-7787; Nataliia Mykolaivna Maksymova, PhD (Technics), Associate Professor, Department of Ecology, Dnipro State Agrarian and Economic University, e-mail: natalya.maksimova@i.ua; https://orcid.org/0000-0003-1684-7479

Analysis of recent studies and publications. As a rule, generation of electromagnetic radiation was analyzed during deformation of crystalline or consolidated sedimentary rocks as well as artificial building materials. Such issued were considered by Vorobiov, О.А., Salnikov, V.N., Gold, R.М., Bespalko Papers [28][29][30] analyzed qualitative contribution of electromagnetic signal intensity with energy properties of solid bodies. It has been defined that the intensity of electromagnetic signal grows along with the increase in mechanical and electric density of solid bodies [11]. Studies [32] proposed the approach based on the measured minor flows within the loaded rocks to determine their integrity.
Studies by Bespalko, A.A. and Yavorovych, L.V. [11] dealing with EMR during dynamic effect of sandstone samples in terms of their different water-saturation and changes in the solution mineralization ( Fig.1) are of special interest. When sandstone is held in the distilled water that results in considerable decrease in EMR amplitude comparing with the sample in its initial state. Saturation of distilled water with NaCl is accompanied by the increasing EMR amplitude. In this context, EMR of porous sandstone of different water-saturation degree is proportional to the effecting energy.
Singling out previously unsolved parts of the general problem. Problems concerning the nature of EMR occurrence in loose rock, e.g. argillaceous, loamy, and sandy soils, which usually makes up the HES body of CC1 structure category in terms of irrigation systems, reservoirs, and tailing facilities, have not been studied before. Fig. 1. Amplitude-frequency spectra of electromagnetic signals in terms of acoustic excitation of sandstone samples [11]: аin the initial sample state; bwithin the samples held in distilled water during 24 hours; cin NaCl water solution with the concentration of 1%; d -2.5%; e -3.75% Formulation of the paper objective. Objective is to substantiate experimentally application of the NPEMFE method within the man-made ground and evaluate its possibility for determining hidden filtration zones in terms of agricultural HES.
Description of the research methodology (structure, sequence). To analyze interaction between the changes in electromagnetic radiation (EMR) amplitude occurring within the man-made earth dams of retention basins during their fillingemptying, a series of experiments has been carried out involving compression of man-made ground samples on the odometer within simultaneous record of density of EMR pulse flow being generated during the loading.
Physical characteristics of soils (humidity, density and solid phase, porosity and porosity coefficient) were determined according to standard methodologies [33].
During the first series of experiments, loading values of ground samples on the odometer were selected basing upon the real loads in the retention basin filled with water completely up to the level of 4.2 m. According to the calculations, water pressure is 42.2 kPa; taking into consideration pressure of concrete plates, overall loading value is specified as 45.3 kPa.
Second series of experiments meant studies in terms of RB emptying before winter time. When water was discharged from the basin, 0.4-0.5 m layer of water was left in the basin forming pressure of 5.3 kPa along with the plates. Those experiments were carried out to study EMR level during relaxation of natural soils.
The experiments have resulted in the construction of graphs of dependences of EMR pulse flows upon the loading degree of the ground samples. To validate the NPEMFE method application, monitoring studies have been performed in terms of retention basin of Kalynivska irrigation system (IS) in 2013 and 2017. To determine the ground water level (GWL), method of vertical electric sounding was applied along with the NPEMFE method.
Statement of the basic research material. Retention basins and bund walls are built from the native ground represented by loessoid varieties. According to the majority of inter-regional water economy authorities, the dams are constructed using heavy clay loams or sand loams. Ground samples taken from the dams and near basins belong to clay loams and sandy loams. Basing on the proper studies by the picnometer method, average density of sandy loam soil is 2.74 g/cm 3 ; in terms of plasticity and flow values, they belong to plastic varieties (Ip = 1.8-2.5; IL = 0.5); as for granulometric composition, they belong to dusty soils as they are characterized by following granulometric composition (in terms of fraction fineness mass): 0.5-1 mm -0.07 %; 0.25-0.5 mm -0.61 %; 0.1-0.25 mm -61.25 %; >0.1 mm -38.07 %. Average natural moisture is 8.63 %.
Density of the clay soil particles is 2.75 g/cm 3 ; in terms of plasticity and flow value, they belong to light (Ip = 17,51-18,32), solid (IL = -(0.23-0.18)) type; content of sandy particles is 0.02 % which also indicates some varieties [36]. Natural moisture of clays is 19.3 %. Table 1 represents results of compression tests on the odometer.
Along with the compression studies, pulses of electromagnetic radiation were registered according to the scheme represented in Fig. 2.
Let's consider the results of the effect of soil compression upon the changes in pulse electromagnetic radiation. Figures 3-11 show compression curves ε = f (t) combined with the density of EMR pulse flow (pulse/second). Periods of EMR rise and drop during the experimental studies are marked with red straight lines, which coincide conditionally with the results of EMR curve smoothing by means of polynomial approximation. Curves of the trend represented in blue are constructed with the help of Microsoft Excel; they are described by the sextic equation.
Thus, in terms of maximum loads (45.58 kPa) corresponding to the conditions of a water-filled retention basin, wavelike alternation of ranges of EMR pulse numbers with their repeated excitation has been obtained ( Fig. 3-5). That is traced properly beginning from 1320 s since the start of experiment #1 (Fig. 3), from 1380 sfor the experiment #2 (Fig. 4), and in terms of the experiment #3from 1200 s since the third loading stage or from 4680 s since the beginning of the study (Fig. 5).  Probably, first peak of the density of EMR pulse flow is stipulated by the closing of gaps and cavities in the soil sample in terms of loading increase. It is most likely that the drop of EMR curve is determined by the decrease in acoustic emission, which transfers partially into EMR. EMR growth (second maximum) may be connected with the deformation of crystals of argillaceous materials characterized by minor piezo-effect with following reorientation of crystals and their fragments into the plane perpendicular to the pressure (descending branch of graphs after the second maximum).
Further experiments were carried out with the decreased pressure (down to 5.3 kPa); that corresponds to the conditions of a retention basin, which is not completely emptied ( Fig.6-8). Fig. 9 and 10 show EMR generation during artificial additional moistening of sandy loam samples up to 24.7-25.4 % during the experiment in terms of the emptied retention basin; that simulates processes of watering due to filtration. It is clear that EMR curve has one excitation type at the beginning of compression; then, it experiences dramatic fall demonstrating flat lines. In this context, it should be noted that the more moistened the soil is, the more straight the line is (Fig.10). That is very important observation since it demonstrates that in terms of sandy loam watering, there is the absorption of EMR pulses being the basis to specify zones of watering and filtration with the help of the NPEMFE method. Fig. 11 shows the nature of EMR changes during the argillaceous soil loading. In this context, EMR excitation in terms of the compression stabilization of a sample is observed.
Results of compressive studies have shown that the increased EMR values correspond to the maxi-mally stressed state of the man-made ground and vice versatheir drop is peculiar for relaxation of the soil samples. Thus, extremes of the amplitude of EMR oscillation are recorded at the beginning of the compression experiments during the most intensive sample compression. The peak excitation is followed by slight "drop" in the pulse number with its further slow rising. That is stipulated by the decreased intensity in the process of soil compression. In terms of the watered soils, amplitude of EMR oscillation is insignificant owing to the moisture redistribution (experiments #7, 8).  2. For the first time, as a result of analysis of compression of sandy loam and clay samples on the odometer, it has been determined that increasing stress-strain state of the soils provoke gradual rise of the electromagnetic radiation amplitude (it is observed at the beginning of every loading stage).
3. Availability of electromagnetic radiation during the transfer of uniaxial loading on the argilla-ceous soil sample may be explained by the decrease in its porosity and occurrence of acoustic signal during the closing of pores, being characteristic for experiments # 4-10, taking into consideration transferred pressure р = 5.3 kPa onto the argillaceous soil samples, and at the beginning of experiments # 1-3, if р = 45.58 kPa.
4. It is proved experimentally that in terms of man-made ground moistening, EMR amplitude experience its decrease.
Thus, the specified regularities make it possible to substantiate experimentally possible application of the NPEMFE method to detect technical condition of the retention basins and principal channels by localizing zones of loosening and watering of the HES body; those zones are characterized by low Consider the results of detecting hidden filtration zones within the HES body in terms of retention basin РБ-1 of Kalynivska irrigation system located in Sinelnikovo district of Dnipropetrovsk Region.
To validate the data obtained using the NPEMFE method, in spring 2013 and autumn 2017 technical conditions of RB of Kalynivska irrigation system were monitored in terms of its two states: before its filling with water and in when it was water-filled.
According to the data of field studies using Golden Software Surfer 8 computer product, schematic maps of the density of pulse flow of the NIEFF magnetic component have been built (Fig. 12). The maps demonstrated the repeated nature of the results of field studies of 2013 and 2017. Interpretation of the field study results is based on the effect of intense absorption of the NPEMFE pulses by the considerably moistened rock or building materials. Fig. 11. Graph of EMR dependence upon clay loading (Experiment #9) In terms of the schemes, sites of the decreased values of density of pulse flow of the NPEMFE magnetic component (red and yellow colours) correspond to the zones of EMR absorption; they are diagnosed as the sites of watering and filtration. Shape of isolines and general image of the NPEMFE field make it possible to highlight anomalies of low values as well as to determine their dimensions. The NPEMFE method is a "quantitative" one; thus, while interpreting the image, fields lie relative to the valueincreasing or decreasing in the pulse number within certain period of time.
In 2013, according to the results of field studies, certain sites of filtration and watering were singled out within the western side and within the joint zone of western and southern sides. Total length of the sites is 46 m. According to the VES data, ground water level (GWL) right under the sides was at the depth of 7.5 m; at the distance of 20 m, the depth was 13.0 m (Fig.13). According to the formula by V.V. Vedernikov, filtration losses were 86.02 m 3 /day [37]. Thus, singling out of filtration zones in terms of HES earth dams involving the NPEMFE method is rather expedient both practically and economically, which is proved by the corresponding work order by the Regional Office of Water Resources of Dnipropetrovsk Region.
Conclusions. Results of the laboratory com-pression and field monitoring studies have proved the possibility of applying geophysical electric surveying method of natural pulse electromagnetic field of Earth (NPEMFE) to localize the water filtration sites and broken state of earth dams of agricultural HESs.
According to the results of compressive studies, it has been demonstrated that the increase in stressed state of sandy loam and argillaceous soils corresponds to gradual rise of electromagnetic radiation amplitude, and its drop is characteristic for soil relaxation after the loading removal. In terms of retention basins, that may be interpreted as the increasing action of loading on the soil, when the basin is water-filled; as for the loading decrease that occurs in terms of basin emptying.
Possibility to detect the zones of EMR absorption using the NPEMFE method along with the VES technique allows both determining filtration zones and ground water levels and evaluating nonproductive water losses from the earth HESs of the irrigation systems. It should be noted that the first method is a "qualitative" one, i.e. it helps localize the sites of broken technical state of the earth HESs, which are not found visually. Efficiency of the use of quick and low-cost NPEMFE method is proved by high frequency of the results of technical state monitoring of the retention basin in 2013 and 2017.
Within more than 10 years of observations of technical state of the earth HTSs of CC1 structure category, the authors have emphasized following regularity [3][4][5][6]: almost all the retention basins are characterized by sufficient state of the bottom; zones of excessive moistening and filtration within the bottom areas of the basins have not been recorded, which is possible to be explained by colmation of fissures with sludge deposits.