Меліорація і водне господарство (Nov 2018)
GENERATION OF ELECTROMAGNETIC IMPULSES IN CLAYS DURING THEIR LOADING IN A LABORATORY ENVIRONMENT
Abstract
The relevance of the research. Currently, filtration losses from water-bearing systems and controlling constructions are more than 30% which can be predominantly explained by unsatisfactory technical state of hydraulic engineering structures (HESs). Diagnostics of technical state of HESs of agricultural assignment, relating to a failure effect (responsibility) class CC-1 (i.e. minor effects), is performed usually with the help of visual inspection during inter-vegetation period when irrigation system (IS) is waterless. Searching for low-cost techniques to estimate state of soil HESs as well as determination of areas within them requiring for priority repair is a topical theoretical and practical task. Methods of the research. Geophysical method of natural impulse electromagnetic Earth’s field (NIEEF) may become such a technique; however, a problem of electromagnetic impulses (EMI) generation within soil masses is understudied despite the fact that they are the basic studied environment in the process of diagnostics of soil HESs of irrigation systems using the technique. To make theoretical and experimental substantiation of the NIEEF method to identify zones of filtration as well as zones of raised watering within the body of small soil geotechnical structures, nature of EMI amplitude changes while transferring uniaxial static load to clay samples in laboratory environment has been analyzed. Similar experiments using idealized model validate opportunity to apply the NIEEF technique for estimation of engineering state of HESs. Research results. The experiments were carried out using clay samples with natural moisture and those experienced additional watering. Soil porosity and soil porosity coefficient, being auxiliary characteristics to plot compression curves, were determined before compression tests and after them; standard calculation techniques were applied. The studies involved usual odometer; electromagnetic impulses were recorded with the help of МІЕМП-14/4 device (SIMEIZ series). The clay samples were loaded in accordance with actual pressure from plates and 4.2 m water layer within filled regulating pool (RP) which dimension was 4.789 kN/m2. Analysis of results of the compression tests has verified the following: increased EMI values correspond to maximum stress state of loose soil, and vice versa – their decrease is typical for relaxations of soil samples as well as for their additional watering. Hence, extreme values of EMI oscillation amplitudes are registered at the beginning of the compression tests when the sample experiences the most intensive compression. Peak excitation results insignificant “fall” of EMI number; then it’s slow increase is observed depending upon the decreased intensity of soil compression. Conclusions. The regularity makes it possible to substantiate theoretically the opportunity to apply rapid and low time-consuming as well as low-cost NIEEF method for diagnostics of engineering state of soil HESs. Previously, such experiments, concerning EMI generation, were carried out using crystalline rocks; loose rocks were involved for the first time.
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