V. N. Zakharov, V. A. Trofimov, Yu. A. Filippov
Academician Melnikov Research Institute of Comprehensive Exploitation of Mineral Resources, Russian Academy of Sciences, Moscow, Russia
Keywords: rock mass, rheological behavior in deformation, rock bolt support, numerical modeling, stress, tunnel
The article presents a geomechanical model of a tunnel with rock bolt support. The numerical modeling is performed in ANSYS. The effect of the rock bolt support on the tunnel stability is analyzed with regard to the rheological properties of rocks. The loading and functioning of rock bolts are actualized owing to joint deformation of the rock bolts and enclosing rock mass during their interaction with each other and with the anchoring grouting. The authors discuss feasibility of loss of the load-bearing capacity by the rock bolts because of their fracture. The algorithm of timing of a rock bolt to keep functioning and damage localization is described.
V. M. Seryakov
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: mineral deposits, rock, stress state, great depths, mined-out void, backfill, mining sequence, nonlinear deformation
The article discusses application of the deep-level stress determination method developed for modeling stress redistribution in rocks and in backfill as mining operations are advanced. It is suggested to take into account elastoplastic properties of rocks and backfill using the stiffness matrix of intact rock mass. The illustrative calculations are presented.
M. Z. Emad1, M. U. Khan1, S. A. Saki1, M. A. Raza1, M. U. Tahir2 1University of Engineering and Technology (UET) Lahore, Pakistan 2NESPAK, National Engineering Services, Pakistan
Keywords: porosity, UCS, rock properties, correlation, Salt Range, sonic velocity
A study was conducted to uncover the possible correlations among mechanical and index properties of sandstones from formations of Salt Range area, Punjab, Pakistan. For this purpose, sandstone block samples were collected from seven formations of the Salt Range. The samples were prepared for rock testing according to the guidelines set by International Society of Rock Mechanics (ISRM). Defective samples were discarded and those meeting the ISRM specifications were tested for sonic velocities, dry density, porosity, uniaxial compressive strength, tensile strength and elastic constants. Results obtained were then statistically analyzed to find the predictive relationships. The analysis revealed that correlations exist between two groups of tested rocks. The predictive relationships were determined between porosity and static mechanical properties of rocks and between porosity and dynamic mechanical properties.
P. Litwa, G. Merta
Central Mining Institute, Katowice, Poland
Keywords: natural hazards, occupational safety, rock burst, rock burst assessment methods
The paper concerns an analysis of the causes of the rock burst that occurred in 2019 in one of the underground hard coal mines in the Upper Silesian Coal Basin (Poland). This incident occurred in the area of an active longwall with complex mining and geological conditions. The operation was linked to natural hazards, with seismic (rock burst) and methane hazards predominating. The recorded seismic activity in the course of the operation was at a high level. Commonly used methods of assessing the state of the rock burst hazard are characterised by the difficulty in predicting the occurrence of tremors which may result in dangerous incidents (rock bursts or relaxation). There is therefore a need to constantly improve methods of forecasting the state of such hazards. The paper presents selected results of the applied analytical and empirical methods, which made it possible to determine the causes of the rock burst and to determine the principles of further exploitation in the area covered by the study.
V. P. Efimov
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: rocks, tensile strength, Brazilian test, structural parameter
The paper discusses the direct and Brazilian tensile strength testing data in terms of the mechanical properties of rocks. The statistical correlation factors by categories of rocks only offer rough estimates of the direct strength in tension using the Brazilian tensile strength test data. It is suggested to compare the two methods using models which include the structure of a material. It is shown that when the analysis includes the biaxial stress field, which leads to a decrease in the strength by the Brazilian test as compared with the strength value from the direct tension, as well as when the analysis includes the nonuniformity of the tensile stresses, which brings an opposite effect, the tensile strength values of the two methods are correlated more accurately.
A. V. Azarov, S. V. Serdyukov
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: hydraulic fracturing, fracture initiator, fracture growth trajectory, hole, hole bottom, strength and elasticity, fracturing pressure, mathematical modeling, extended finite element method
The authors describe the numerical studies into hydraulic fracturing in an isotropic elastic medium with a fracture initiator set at the hole bottom. The influence of individual factors, including the setting depth of the fracture initiator, its distance from the hole bottom, the bottom shape, the strength and elasticity of the medium, on the shape of the created fractures and on the fracturing pressure is determined. The application of the revealed dependences in optimization of the technology and equipment of the directional hydraulic fracturing is illustrated.
S. V. Serdyukov, A. V. Azarov, L. A. Rybalkin, A. V. Patutin
Chinakal Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: rock mass, underground opening, stress state, hydraulic fracturing, fracture shape, fracturing fluid pressure, numerical modeling, extended finite element method, physical simulation and full-scale experiment
The article presents the theoretical and experimental results on propagation of hydraulic fractures in the neighborhood of an extended cylindrical cavity in an isotropic elastic medium under the hydrostatic stress and in the triaxial stress field composed of unequal components. The influence exerted on the curvature and volume of the created fractures by the fracture initiator and cavity spacing, as well as by the strength and compression of the medium is illustrated. The main types and conditions of the created fractures are described. The physical simulation and the full-scale experiment prove the numerical research reliability and the applicability of the program and method solutions in design of hydraulic fracturing at short distances from underground openings and structures.
S.Sh. Mehdi, M. Miandad, M.M. Anwar, G. Rahman, H. Ashraf
University of Gujrat, Penjab, Pakistan
Keywords: urban landscape, spatio-temporal changes, controlled classification, land use, land cover, growth
The fundamental changes in the land use and condition of the land in Gujrat (Punjab province, Pakistan), which have occurred over the past several decades, have been studied. They have a long history and represent an important factor in global changes in urban landscape. An attempt is made to determine the spatio-temporal changes in land use and land areas caused by anthropogenic activities. The study was carried out on the basis of multi-time satellite images (for 1985, 1995, 2005 and 2015) of the US Geological Survey, obtained from various Landsat satellites. Satellite image processing was carried out in the ERDAS Imagine 2014 and ArcGIS 10.3.1 programs. As a result, four maps were compiled that reflect the spatial and temporal dynamics of land. They are divided into five types: vegetation cover, bare soil, sand, water bodies and built-up areas. The results of the study indicate a significant decrease in the area of vegetation cover: from 85.1 % in 1985 to 79.6 % by 2015. There was also a significant increase in the built-up area, from 0.7 to 4.0 % over a 30-year period. It is established that unplanned changes in land use have an extremely negative impact on the ecological situation as well as on the human habitat. It is concluded that it is necessary to conduct a reasonable policy aimed at correcting unplanned urbanization and the demographic situation in the province under consideration.
P.S. Belyanin
Pacific Geographical Institute, Vladivostok, Russia
Keywords: Java Island, equatorial landscapes, Pacific Ring of Fire, Sunda Islands, altitudinal zonation
The structure of Gede-Pangrango Stratovolcano, the highest volcano in Java Island, has been analyzed. Based on landscape mapping and the field observations, geographical data reflecting the spatial structure, relationships, interaction, and distribution characteristics of different-ranked ecosystems have been obtained. The influence of equatorial climate, volcanism, altitudinal zonation and anthropogenic impact on the formation of the structure of the volcanic landscape are shown. It was established that an increase in the altitude on the slopes of Gede-Pangrango Volcano resulted in an increase in the areas of subclasses of the steep and vertical slopes as well as in an increase in the slopes of moderate steepness. At the same time, the share of subclasses of plume slopes, gentle slopes and valley bottoms decreases. They are almost absent in the summit belt of the volcano. In this case, the composition of vegetation formations becomes simpler and floristic elements of higher latitudes appear, due to a decrease in average daily temperatures. At present, the anthropogenic factor has a significant impact on the landscapes of the volcano. As a result of the plowing of land and the construction of roads and settlements, the natural complexes of gentle slopes and their aprons have been strongly transformed. The slopes of moderate steepness are less affected by the anthropogenic impact. The subclasses of the steep and sheer slopes as well as of valley bottoms have mostly preserved their natural features. The anthropogenic disturbance of ecosystems decreases with an increase in altitude, which is due to a decrease in heat supply as well as to an increase in volcanic influence and intensification of erosion processes. This makes agricultural activity, the construction of roads and location of settlements difficult, and on steep slopes, even impossible. The reserve status of the territories in the middle and upper altitudinal belts of the volcano is favorable for the preservation of natural landscapes.
