Finite-frequency effects for imaging underground cavities

<p>We study finite-frequency effects that arise in cavity detection. The task comes along with the Onsite-Inspection part for the Comprehensive Nuclear Test Ban Treaty (CTBT), where the remnants of a potential nuclear test need to be identified. In such nuclear tests, there is preexisting knowledge about the depths at which nuclear tests may take place, and also about sizes that such cavities can attain. The task of cavity detection has consistently been a difficult one in the past, which is surprising, since a cavity represents one of the strongest seismic anomalies one can ever have in the subsurface. A conclusion of this study is that considering finite-frequency effects are rather promising for cavity detection, and that it is worthwhile to take them into account. We utilize an analytical approach for the forward problem of the a seismic wave interacting with a underground cavity in order to develop an inversion routine that finds and detects an underground cavity utilizing the transmitted wave-field.</p><p> </p>

A Method for Determining the Thicknesses of the Reserved Protective Layers in Complex Goafs Using a Joint-Modeling Method of GTS and Flac3D

In this study, a C-ALS underground cavity scanner was used to detect the shapes of mining goafs. In addition, GTS software was adopted to establish a three-dimensional geological model based on the status of the stopes, geological data, and mechanical parameters of each rock mass and to analyze the roof areas of the goafs. In regard to the morphology of the study area, based on a thin plate theory and the obtained field sampling data, a formula was established for the thicknesses of the reserved protective layers in the goafs. In addition, a formula for the thicknesses of the protective layers in the curved gobs was obtained. The thickness formula of the protective layers was then successfully verified. The detection results showed that the roof shapes of the goafs in the Yuanjiacun Iron Mine were mainly arc-shaped, and the spans of the goafs were generally less than 20 m. The stability of the arc-shaped roofs was found to be greater than that of the plate-shaped roofs. Therefore, by reducing the thicknesses of the protective layers in mining goafs, the ore recovery rates can be increased on the basis of safe production conditions. The formula of the thickness of the security layers obtained through the thin plate theory was revised based on the statistical results of the roof shapes of the goafs and then combined using GTS and FLAC3D. The modeling method successfully verified the stability of the mined-out areas. It was found that the verification results were good, and the revised formula was able to improve the recovery rate of the ore under the conditions of meeting safe production standards. Also, it was found that the revised formula could be used in the present situation. At the same time, it was also determined that the complexity of the rock masses obstructed the full identification of the joints and fissures in the present orebodies. Therefore, it is necessary to incorporate C-ALS underground cavity scanners to regularly observe the shapes of the goafs in order to ensure that stability and safety standards are maintained.

Assessment of stratification of the breeds of the underground cavity roof

Authors of the research consider the approach to the assessment of possibility of formation of stratification and shift cracks in the roof of extended horizontal cavity, based on the method of boundary elements. The algorithm implements the iterative procedure of variation of the formed crack length with control of tension in its tip. At the same time, the angle of the crack coasts closing is defined by the tensile strength of the layer material. The crack with smooth closing of coasts is formed in case of equality to zero this durability. The mechanism of failure forming over the developed space with vertical pipe type walls is considered. The results received by the authors, can be useful as the offered approach allows to model the destructions localization in the massif of rocks, location and sizes of the arising cracks of stretching and shift if there are strength defects in the massif

MICROMYCETES IN KARST CAVES

Micromycetes are an integral part of the microbial community of cave ecosystems, they play the role of decomposers or lead a parasitic lifestyle. Microscopic fungi, including yeast, in caves are isolated from soil, air, water, mineral formations, rock surfaces and even troglobionts. By the ratio of fungi of different temperature regimes and the succession of species, one can inference the relationship between the underground cavity and the surface and the intensity of nutrient intake. Representatives of Chrysosporium, Mucor, Mortierella, Peniciliium, Trihoderma, Aspergillus, Geomyces predominate among microscopic fungi in caves. Micromycetes are actively involved in geochemical transformations of the environment, causing corrosion of rocks, which can pose a danger to the preservation of rock paintings in decorated cavities. Anthropogenic load leads to changes in the composition of microscopic fungi due to an increase in the trophic status of cave ecosystems, as well as due to the possible active transboundary transfer of microorganisms by visitors. The use of underground cavities as tourist sites dictates the need to develop criteria for standardizing the content of micromycetes in the air, taking into account the specifics of caves to ensure the safety of people. This review is aimed at summarizing the accumulated data on the diversity and distribution of microscopic fungi in karst caves.