The polarizability of sand-gravel deposits according to the results of laboratory and field measurements

Abstract

Тhe article describes electrical exploration aimed at studying the polarizability of sand-gravel deposits in the Kaluga region. On the one hand, laboratory tests of the polarizability of sand and sand-gravel mixes (SGM) were carried out, on the other hand, field electrical survey work on the wellknown manifestation of SGM. Samples of SGM were collected from 18 actively operating quarries in the Moscow and Kaluga regions for laboratory petrophysical measurements. Induced polarization (IP) measurements were conducted in time domain. The results showed that sand and gravel mixes are characterized by a rapid process of induced polarization. The minimum values are associated with pure sand samples and the level of polarizability increases with increasing gravel content in the sample. The maximum values of polarizability are achieved when the moisture content of samples is 1,5–2,5%, however SGM samples polarized stronger than pure sand samples all over the moisture range. The field work was performed by the method of vertical electrical soundings with measuring of IP along the well-known sand and gravel deposits in the Kaluga region. The profile step and spacing of the electrical survey installation are selected in such a way as to use the same grounding locations many times. A similar approach is used for multichannel measurements of electrical tomography and allows for further 2D data inversion. The induced polarization was measured in the frequency domain in the frequency range from 0.15 to 19 Hz. The results of the multi-frequency inversion showed the differentiation of the section by the time parameter τ. According to inversion data the geological-geophysical model was constructed. In the section, zones of increased polarizability associated with a gravel-pebble fraction, as well as zones with partial water saturation of sediments were identified. Thus, under the certain favorable conditions, the IP method allows to delineate zones enriched with gravel-pebble fraction within the SGM deposit.