Variability in macrozoobenthic assemblages along a gradient of environmental conditions in the stream water of karst caves (Lower Shakuranskaya Cave, western Caucasus)

The fauna of the stream water in the Lower Shakuranskaya Cave in central Abkhazia, western Caucasus, was studied. This cave has a large inlet and an extended entrance ecotone area of approximately 60 m, which makes it a convenient area for studying macrozoobenthic assemblages across a gradient of environmental factors. The cave has 13 species of stygobionts, 10 species of stygophiles and 18 species of stygoxenes. The number of species and the abundance and biomass of stygobionts per station were the highest near the boundary of the photic zone, at a distance of 50–60 m from the entrance to the cave, and gradually decreased toward both the remote parts of the cavity and the cave exit. The most abundant stygobionts were gastropod mollusks of the Hydrobiidae family, and Xiphocaridinella shrimp comprised the main part of the biomass. It has been shown that the main environmental factors determining the distribution of macrozoobenthos are luminosity and distance from the entrance to a cave. According to the differences in their reactions to these environmental factors, several groups of species were identified. In addition, three main assemblages of macrozoobenthic species were described: (1) an assemblage of epigean species near the cave entrance area; (2) stygobionts in remote parts of the cave outside the photic zone; and (3) a mixed assemblage in the cave ecotone, where a faint light penetrates. The specific details related to the faunal structure in the ecotone of the cave are discussed, as well as active and passive methods by which stygoxenes invade underground cavities.

The behaviour of six electrode arrays used in electrical resistivity imaging to detect underground cavities: a numerical study

The aim of this work is to evaluate the efficiency of six electrode arrays used in electrical resistivity imaging. Pole-Pole (PP), Pole-Dipole (PD), Wenner-Alpha (WA), Wenner-Schlumberger (WS), Dipole-Dipole (DD) and multiple Gradient (MG) electrode arrays have been selected to detect underground cavities at shallow depth. Numerical simulation has been made for three synthetic models that have been generated using Res2dmod program. Each model represents three cavities with 2m diameter, spaced 6m from each other and located at a depth of 1.5m from the surface of the ground: 1) air-filled cavity, 2) half-watered cavity and 3) full-watered cavity. The background resistivity of each model was chosen equal to 10, 50 and 250 Ωm respectively. The resistivity of the air and water were set at 106 Ωm and 1 Ωm respectively. The results show that the PD, MG, PP and WS arrays gave good resolutions and clear images, and are less contaminated by noise. The DD array is very sensitive to noise and for this reason, it gave less accurate results for the first and the second synthetic models. An exception is the third synthetic model, where a good resolution model was obtained. This means, that the DD is more efficient in mapping cavities when the background environment is moderately resistive. The shapes of resistive air-filled cavities were found more clearly than those of conductive watered cavities, for the latter, however, the true resistivity values were better estimated than for the air-filled cavities. From the results of the analysis of the inverted synthetic models, the PD, MG, PP and WS arrays show the best results among the other used electrical arrays.

Physicochemical mechanism of structure formation and strengthening in the backfill massif when filling underground cavities

The strength and microstructural properties of the backfill massif have been studied and assessed when filling underground cavities that pose a threat of mine rocks collapsing in the process of mining mineral deposits. It is suggested that due to a tendency to mechanical destruction by crushing Ca–O ionic bonds rather than Si–О covalent ones, the backfill mixture composition is saturated with a large amount of Ca2+ ions. This leads to the formation of a highly-basic type of hydrated calcium silicates and a decrease in the massif strength properties. To study the mineral composition of the components of the mixture and solidified massif and to investigate the microstructure and chemical composition of new formations in the backfill massif, infrared spectroscopy and scanning electron microscopy were used. Laboratory studies of the strength properties of backfill massif were also conducted. The minerals of the mixture components, melilite and pseudowollastonite, have been revealed that perform the main function of the new formations occurrence. It was found that the strength of the backfill massif is by 16% less than the required standard value of 7.0 MPa at the age of 90 days. It was determined that highly-basic jellylike hydrated silicates of tobermorite type of the group CSH (II) with variable composition and a ratio of CaO/SiO2=2–3 are formed in the studied structure of the backfill massif after 90 days of hardening. There are no strong low-basic hydrated calcium silicate bonds that could have a reinforcing effect. Providing the conditions for occurrence of low-basic hydrated calcium silicates in the structure is one of the ways to create a hard backfill massif.