Home – Home – Jornals – Journal of Mining Sciences 2024 number 2S

The article focuses on formulation and substantiation of a problem of safe subsoil management in view of the more and more difficult geological and climatic conditions, as well as growing depth and scale of mineral mining. It is shown that the current basic and applied research has created prerequisites for a successful solution of this problem. In Russia these prerequisites are connected with finding energy-based mechanisms of origination and growth of high-stress concentration and destruction zones in rock masses and geomaterials which feature a hierarchical block structure and many phases, and show properties of open self-organizing geosystems in the tectonic stress and strain field. Using advances in nonlinear geomechanics and geophysics, and cloud technologies of Big Data, a new methodology, technologies and software systems are developed for shaping a multilayer geoinformation and monitoring system for diagnostics, control and prediction of the industrial and ecological safety of mining regions in Russia.

In order to clarify the relationship between the mechanical properties of coal-rock composite and the loading rate and rock-coal strength ratio, uniaxial compression tests were carried out on coal-rock combinations with three different rock-coal strength ratios at four different loading rates. The rock-coal strength ratio λ is a ratio of the compression strength of rock to the compression strength of coal. The test results indicate that the relationship between the mechanical properties of coal-rock composite and loading rate is influenced by both the strong and weak components in the composite. The peak stress and elastic modulus mainly depend on the weak component, while the peak strain is determined by both the strong and weak components. For peak stress and elastic modulus, when the weak body is the same, the relationship with loading rate is the same, otherwise it is different. The relationship between the mechanical properties of coal-rock combination and λ is not affected by the loading rate. The weak body in the coal-rock combination is the main body of damage, and the greater the value of λ, the more severe the damage. At the same time, the failure mode shows a gradual transition from weak body failure inducing strong body failure to only weak body failure.

This article experimentally investigates the characteristics of P-wave propagation in block rock mass when blocks fracture transversely and longitudinally. The velocity of P-wave, rock block acceleration, kinetic energy, displacement response, and the time-frequency response of rock block were analyzed. The results show that when the rock block fractures, the P-wave velocity decreases, the acceleration response duration time increases, and the maximum acceleration and kinetic energy decrease. However, transverse fractures show a more evident decrease in the acceleration and kinetic energy near the fracture area, and longitudinal fractures show a more evident decrease in the displacement amplitude far from the fracture area. On transverse fractures, the dominant frequency of acceleration and kinetic energy leads to a low value near the fracture area, but the dominant frequency of displacement-to a high value. Longitudinal fracture leads to a dominant frequency of block response occurrence time delayed far from the fracture area.

This article studied the biomechanical properties of salix root sampled from arid and semi-arid regions of China. The damage law of root in the process of stretching was analyzed by acoustic emission technique. The fractal dimension of root failure section was calculated by digital image processing technology. The results show that salix root tensile strength and ultimate elongation decreases with the diameter increasing, while ultimate tensile resistance and diameter are positively correlated. Damage variable characterized by cumulative AE energy can not only help research the rule of root damage quantitatively, but also allows determining the critical elongation when root became inactive. The optimal mining depth values are proposed, which enable reduction of ground surface deformation, elimination of root system damage, protection of planting on ground surface and, thus, decrease of possibility of bench convergence.

Taking working face 8006 of a coal mine in North China as the engineering background, the contact stress of each rock stratum interface is calculated based on the principle of composite beam to predict the development position of the separation layer. The distributed fiber optic sensing technology monitors the horizons where the abscission develops. The test results can accurately reflect the deformation characteristics of the overlying strata in the field, which provides an important theoretical basis and guiding role for the design of the overlying strata grouting scheme in this coal mine. The results show that when the working face is fully mined, the separation layer is mainly developed between the coarse-grained sandstone and the lower sandy mudstone at a distance of 265 m from the coal seam roof. The grouting scheme is effective, which can provide a useful reference for similar grout injection in overburden separation projects.

A large number of cases of tunnel bottom deformation occur in nearly horizontally layered strata. This article analyzes the common characteristics of such tunnel bottom deformation through case studies, and introduces the limitations and requirements for bottom designs for China’s high-speed railway tunnels. The deformation mechanisms of the tunnel bottom were studied through the physical model experiment which revealed the interaction characteristics between the layered surrounding rock and the tunnel bottom structure. Through the numerical simulation study, the effect of different elevated arch curvatures on deformation of the tunnel bottom was investigated, and the effectiveness of elevation arch deepening in deformation control of the tunnel bottom was verified. The classified control countermeasures for deformation at the bottoms of the tunnels in nearly horizontally layered strata are provided.

In response to the engineering problem of severe damage to tunnels caused by coalburst, which leads to support failure and personnel casualties, a method of preventing coalburst through the support and energy-absorbing effects of supports has been proposed. An energy-absorbing hydraulic support is designed for circular or arched tunnels: it is called gantry energy-absorbing hydraulic support. The support mainly consists of three parts: an arched top beam, a micro-arc base, and an energy-absorbing hydraulic column. Through experiments, two types of the energy-absorbing components were compressed and tested. The results show that the average yield strength of a single anti-impact component is 1840 kN, and the energy absorption is 180 kJ when compressed by 100 mm. The average yield strength of the double section anti-impact component is 2460 kN, and the energy absorption is 410kJ when compressed by 100 mm. Both of these energy-absorbing components with a total energy absorption capacity of over 700 kJ are used in actual gantry energy-absorbing hydraulic support.

Ground-penetrating radar is used to study defects in the form of internal layers in concrete structures. It is found that modulus of deflection coefficient of GPR signals changes as function of the layer thickness and electromagnetic properties of the material filling the layer (sand, wet sand or air). The experimental and numerical research used the method of peak-to-peak amplitude ratio, which enabled determining the Fresnel coefficients for the upper and lower boundaries of a layer. The minimal layer thickness recorded by GPR was 2 mm.

Movements and deformations of ground surface at the Almaz-Zhemchuzhina deposit are studied using surveying techniques. The source data in estimation of parameters and patterns of the stress-strain behavior were observations over the modern geodynamic movements using survey markers and GPS / GLONASS technologies. The proposed scientific approach and guidelines on the use of the studies of trend and cycling geodynamic movements made it possible to determine the natural stress-strain parameters and to accomplish zoning of the test area by the intensities of the movements.

The spontaneous high-temperature conditions in deep mining cause significant changes in one of the factors that determine the risk of rock burst in coal mine roadways. Therefore, based on the test method of the bursting proneness of coal, uniaxial loading tests were conducted on coal specimens under different thermal loads to explore the variations in the bursting proneness and energy release of heated coal, analyze the variations and mechanism controlling the coal skeleton, physicochemical properties, quality, fracture mode evolution, and macrocrack quantity with different loading rates, and calculate and discuss the changes in the critical conditions of a coal-rock system during heating. In summаry, the study of the change in bursting energy release caused by the heating of coal can lay the foundation for the engineering-based prevention and control of composite dynamic disasters in deep coal mines.

The energy absorption buffer test system is developed, the impact load compression test of single free face coal sample is carried out, and the digital speckle analysis technology is used to obtain the law of the influence of the hole rate, which is the volume of the borehole divided by the volume of the coal sample, on the energy absorption rate and deformation and failure characteristics of coal sample after drilling. The change of the drill layout of two and three holes in coal samples has little effect on the energy absorption performance. The complete coal sample is easy to form vertical main cracks, and the drilled coal sample first forms stress concentration near the borehole, and a large number of cracks appear. The multihole coal samples are easy to form cracks that make the boreholes connected, which converts more impact energy into surface energy and improves the energy absorption rate of coal samples.

The authors put forward a look-ahead concept of science-based problem solving in deep-level mining. The issues of the problem realization and tooling are also addressed. A borehole charge is designed as a cluster of closed-spaced borehole charges to produce the directed blast effect by varying the cluster charge layout in a wide range. Using alternative technical capabilities of drilling, it is possible to variously redisperse the same equivalent energy in the single large-diameter borehole charge and in the cluster of smaller diameter borehole charges. The blast mechanism of the cluster charge pushes the limits of its application range and offers new approaches to problem solving in deep-level mining. Some technological aspects of geotechnologies are presented through the results of modeling the new approach to blast-induced impact using smooth particle hydrodynamics. Some tentative research findings inspire continuing with the study.

This study proposes a mathematical fracture model including processes of fracture of structural bonds on micro scale (tens microns) and meso scale (millimeters and centimeters), as well as interaction of structural fragments on macro scale (fractures longer then tens centimeters). The model uses two geometrical criteria of fracture growth, connected with the structure of rocks and governing transition between structural scale. The problem on the stress-strain behavior of an elastic medium near a fracture at the change in the fracture length and in the scale of its influence is solved. The limit equilibrium of a fracture is analyzed. For a meso-scale fracture, such condition is unstable, and the fracture, therefore, develops dynamically and up to a macro scale. Sufficiently long macro fractures can grow in the mode of quasi statics due to independent advance of fracture tips.

To reduce intensity of deformation in rocks prone to buckling and plastic deformation, and sensitive to geo- and gas-dynamic phenomena, the authors propose a consolidated backfill technology using salt waste and processing reuse brine at the consumption limits of water-yielding capacity. A set of laboratory tests is carried out to find backfill mixtures adaptable to deep-level potash mining with estimation of deformation characteristics and strength properties of potash salt rocks. New principles and technologies of deep-level sylvinite extraction and backfill material transport by creating such geotechnical structures in stopes which ensure formation of consolidated backfill mass with the mined-out stope space factor close to one. This approach can enhance mine efficiency owing to increased extraction of sylvinite from rib and safety pillars.

This article uses XGBoost algorithm to calculate rock in-situ stress. By using Pearson correlation coefficient method, it is determined that the logging parameters with the best correlation with minimum horizontal principal stress are Depth, GR, LLD, ILD, AC, VCA, with maximum horizontal principal stress are: Depth, GR, SP, CAL, DEN. In order to verify the performance of the model, linear regression, support vector machine, and random forest models are used for comparison. In order to improve the generalization performance, the k-fold cross-validation method is used. The results show that using XGBoost algorithm to predict rock in-situ stress with a small amount of data has a high average accuracy of 94% and good generalization performance. The linear regression model has a faster fitting speed, but the fitting accuracy is the lowest. The random forest and support vector machine models are in-between. The result confirms that the research method in this article has certain universality and can be extended to solve other rock in-situ stress prediction problems.