Purpose. The paper addresses the rock mass state estimation while excavating a cross-heading through the area of regional fault "Bohdanivskyi" based on probabilistic approach to assessing the rock strength.Methods. The boundaries and fault zone extension are specified based on geological service database. This hazardous fault area has been confirmed, and the expected water inflow and methane emission have been identified based on the probe holes drilled ahead of the advancing face. To assess the strength of rocks, the statistical strength theory is used. Numerical simulation is performed using finite element method that is well-tested in geomechanical problems. Findings.The technique of rock mass strength estimation using structural factor based on statistical strength theory has been implemented to improve the adequacy of mathematical modeling. Numerical simulation of geomechanical processes based on finite element method and Hoek-Brown failure criterion is carried out. The changes of rock stress-strain state while excavating the cross-heading through various sites of the fault zone are determined depending on the level of rock disintegration.Originality. New regularities of rock mass behavior within the fault area are determined based on developed technique of rock strength assessment considering the rock mass disintegration and watering.Practical implications. Estimation of rock failure has resulted in designing the combination of support systems comprising metal sets, rockbolts and shotcrete.
Purpose. To carry out comparative analysis of results concerning determination of stressstrain state (SSS) of shal low mine workings using calculation models for problems in elastic approach. Methodology. Rock mechanics methods; methods of analysis of the results of theoretical calculations and nu merical experiments using FEM. findings. Algorithm to calculate SSS of rock mass, involving extended mine working, has been substantiated. Nu merical experiment has demonstrated that to determine displacements within a mine working boundary it is required to consider plane strain state. It has been identified that the use of a plane stress state results in misinterpreted values of mine working boundary displacements to compare with accurate ones. The following basic conclusion has been made: it is possible to use adequate threedimensional (i.e. spatial) problem while arranging relations according to certain rules to solve the considered problem with a calculation model of limited length as for the research subject. originality. Divergence has been determined between extended mine working boundary displacements calculated using calculation models of a plane stress state (approximate analytical model), and those of a plane strain (accurate calculation model). It has been demonstrated that calculation of extended mine workings should involve analytical model of a plane deformation reflecting SSS of rock mass-mine working system adequately; otherwise, calculation er rors may be more than 100 % for horizontal displacements, and 25 % for vertical ones. Practical value. The obtained results make it possible to select reasonably calculation models for extended mine workings where support stiffness properties vary periodically. For instance, such mine workings are meant whose stability and deformability are provided by frame, anchor, combined frameanchor, complete reinforcedconcrete, reinforced equally distanced sequences of anchors, and similar support structures.
The strength criteria substantiation of water-saturated soils and mine rocks, which make it possible to obtain the analytical solutions necessary for determining the stability of water-flooded soil slopes and side-hills. Methods. The methods are applied of analysis and generalization of the theoretical and numerical experimental studies results. The rocks and soils characteristics are taken into account: specific cohesion c, internal friction angle φ, compressive strength R c and tensile strength R p of the rock, as well as the bulk density. The load q was imposed to the water-saturated seam roof from the overlying mine rock or soil seams, the weight of equipment or structures located on the surface. It was accepted that the seam is saturated with water (gas) with the excess pressure Р. A point on the mine working surface (or vertical slope surface), located at a depth z is considered. It is determined at which ratio of q, P and z parameters the soil or rock seam will be destroyed. The problem solution is based on the Mohr-Coulomb strength criterion. Findings. The strengths of water-saturated rock and water-free rock are compared. The ratios have been obtained that make possible to determine the critical load on the daylight surface of water-saturated and water-free vertical slopes, side-hills, trenches and foundation pits, as well as various mine workings in soil bases and mine rocks. The analytical solution has been obtained, which makes it possible to determine a value of the critical pressure on the water-flooded vertical surfaces and soil slopes. The generalization has been made of a certain one-dimensional Mohr-Coulomb strength condition for a water-saturated base characterized by the strength characteristics с and φ for the dimensional case. Originality. It has been theoretically proved that for any pore pressure value in the water-saturated mine rock (or soil) their strength will be less than in their water-free state. New solutions have been formulated for determining the critical height of a water-saturated vertical soil slope or the wall in the vertical mine working. Practical implications. The obtained results make it possible to solve the practical engineering problems on determining the stability of water-saturated slopes and side-hills with a load-free daylight surface, therewith, taking into account the weight of the equipment, stored material and the stability of vertical walls of water-saturated seams of open-cut mine workings.
Purpose. Justification of the gas collectors formation physical model on the basis of research of conformity of permeability of rock mass to the full diagram of rock sample deformation. Methodology consists in sequential analysis of the stages of the complete deformation diagram of the rock specimen under “hard” loading, comparing them with the stages of formation of the high stress zone in front of the lava bottom and statistical analysis of laboratory test results. Results. Based on the rock’s deformation properties analysis and their comparison with the rock sample full deformation diagram, the physical model of formation of gas reservoirs during the development of gas-saturated coal seam is substantiated. Within the solved problem framework, four stages of the complete deformation process are analyzed, namely: elastic, at the limit of strength, out-of-bounds stage and equivoluminal flow zone. The gas collector boundaries, which are the characteristic points of the rock sample deformation diagram in specified deformations mode (the limit of elastic strength and the limit of final strength) are determined. It is proved that the structural and textural features of the coal mass in connection with the course of gas-dynamic processes are manifested in the change in the pores and cracks volume contained in it, which together make the filtration space. Knowledge regarding the transfer of the permeability changes established regularities and free methane accumulation zones formation to the real rock mass, if the process of its forgery is considered as a consistent change of geomechanical states of rocks, is obtained. Scientific novelty lies in the first substantiated possibility of modeling the stress state before the longwall face by equivalent stages of the rock sample destruction in the given deformations mode. Gradual comparative analysis of the internal mechanism of rock samples deformation along the complete deformation diagram allowed establishing causal relationships between geomechanical and gas-dynamic processes in coal mass, and qualitatively characterizing general trends in permeability and volumetric expansion in changes of these samples. Practical value of the work lies in the justification of the principle of construction of a digital geomechanical model for the detection of man-made gas collectors in a mined coal mass.
Purpose. carrying out field researches of the conveyor excavation`s state and establishing geomechanical patterns based on the data, that were obtained in the mining and geological conditions of the Krasnolymanska coal mine. Methodology. Mine field researches of the conveyor excavation deformed state, which is under the influence of the longwall face, and moves in time and space, were carried out. The observation was performed by using a measuring station, which included five measuring points. The results of measurements were generalized and the excavation contour deformation features at various stages of mining coal seam were revealed. Results. Dependencies, that characterize the process of coal mass deformation around the mine at various stages of its exploitation. are obtained. During exploitation processes of the conveyor excavation relative to the longwall face, that gradually pass through four geomechanical situations in mining and geological conditions of the Krasnolymanska coal mine, are established – outside influence zone, in the influence zone, within the longwall face, outside the longwall face. These situations differ in the nature of roof and floor deformation, the vertical convergence of which at each stage changes linearly in time and goes to zero at a distance of 23 meters outside the longwall face. These indicators give reason to consider the roof rocks in the longwall as that sink without breaking the continuity, and also to perform the calibration of geomechanical models based on this. Scientific novelty of the research is new patterns establishment of the coal mass deformation, which contain the conveyor excavation, in the process of the coal seam mining in specific mining and geological conditions. Practical value of the research planned to be carried out on the basis of data obtained after field research is allowed to develop a geomechanical model of active methane accumulation zones searching. The model is applied for further industrial use purposes and to improve the safety of coal mining.
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