Svitlana Sakhno

In the case of pillarless coal mining, the floor uplift reaches 60–80% of the total vertical convergence in gob-side entry, while total convergence often exceeds 1.0 m. This is one of the key factors impedimental to pillarless mining in deep coal mines. Traditional methods of floor heave control in gob-side entry are not effective enough, so they need to be improved. This paper is devoted to the improvement of the anti-shear pile method in gob-side entry retaining. Finite element analysis was used as the main study method. The influence of pile diameter and its design on the stress–strain distribution in the surrounding rock and on the floor uplift magnitude was determined. It was found that the filled piles are the most efficient in reducing floor heave magnitude, asymmetry of floor uplift, and size of post-peak strain in the immediate floor. In filled piles, the steel tube prevents the concrete core from fracturing, while the concrete core prevents the steel tube from plastic yielding. Therefore, with the same diameter and elastic modulus, filled piles are 1.06–1.7 times more effective in floor heave control than comparable analogs.

The uncontrolled floor heave in gob-side entry retaining is the serious problem of underground coal mining. This phenomenon has gravely restricted the application of pillarless mining that has been increasingly used in coal mines in recent years. This study proposes rock bolts-steel piles coupling support method to control severe floor heaves in gob-side entry retaining. This study employs finite element method to analyze stress-strain state in surrounding rocks around gob-side entry retaining. It was found that essential floor heave was caused by high horizontal stresses, which were transmitted from the sides of the entry, and vertical delamination of floor strata in the post-peak strains zone under the entry span. These processes complement each other and aggravate the floor heave. This paper proposes four floor reinforcement schemes. As a result of the study, the most effective floor reinforcement scheme was determined, which consists of 3 elements: steel piles installed in the corners of the entry, rock bolts installed between the piles and a steel belt that coupled the bolts in entry floor. The combination of the advantages of floor reinforcement with bolts and steel piles was the basis for the design of rock bolts-steel piles coupling technology. As a result, the post-peak strain and stress areas are the smallest, and floor heave reduces by 80%. Compared with other reinforcement methods, the advantages of rock bolts-steel piles coupling technology were successfully defined in controlling effect.

The protection of underground infrastructure from modern missiles has become a critical engineering challenge for countries involved in military conflicts. This study presents a numerical investigation of the stress–strain response and blast resistance of underground tunnel structures subjected to a ballistic missile impact. The analysis was conducted for typical soil conditions of the Kyiv region (Ukraine), where sandy soils prevail at shallow depths. ANSYS Explicit Dynamics, combining Eulerian and Lagrangian solvers, was used. The propagation of blast waves in the soil mass, the formation of a blast crater, and the resulting stress distribution were analyzed for cases without protection and with reinforced concrete protective slabs of varying thicknesses. The results demonstrate that surface protection significantly alters blast wave characteristics and reduces peak stress in the near‐surface zone, although excessive slab thickness may shift stress concentrations to a deeper zone. An express assessment method was proposed, based on the ratio between peak stresses in the soil and tensile stresses in the tunnel’s support, enabling rapid estimation of safe depth and required protective slab thicknesses. The proposed approach can contribute to rapid decision‐making for the protection and design of underground infrastructure.

The process of fully mechanized coal seam mining under aquifers and surface water bodies has been a challenge in recent years for different countries. During the evolution of subsidence and the overburdening of rock mass movement above the longwall goaf, there is always a potential risk of connecting the water-conducting fracture zone with aquifers. The water inflows in the coal mine’s roadways have a negative impact on the productivity of the working faces and pose significant hazards to miners in the event of water inrush. Therefore, the assessment of the height of the water-flowing fractured zone has an important scientific and practical significance. The background of this study is the Xinhu Coal Mine in Anhui Province, China. In the number 81 mining area of the Xinhu Coal Mine during the mining of the number 815 longwall, a water inflow occurred due to fractures in the sandstone in the overburden rock. The experience of the successful implementation of the water inrush control method by horizontal regional grouting through multiple directional wells is described in this paper. This study proposes an algorithm for the assessment of the risk of water inrush from aquifers, based on an ANSYS 17.2 simulation in the complex anticline coal seam bedding. It was found that the safety factors based on the stress and strain parameters can be used as criteria for the risk of rock failure in the aquifer zone. For the number 817 longwall panel of the Xinhu Coal Mine, the probability of rock mass failure indicates a low risk of the occurrence of a water-flowing fractured zone.

Underground coal gasification (UCG) is a clean and automated coal technological process that has great potential. Environmental hazards such as the risk of ground surface subsidence, flooding, and water pollution are among the problems that restrict the application of UCG. Overburden rock stability above UCG cavities plays a key role in the prevention of the mentioned environmental hazards. It is necessary to optimize the safety pillar width to maintain rock stability and ensure minimal coal losses. This study focused on the investigation of the influence of pillar parameters on surface subsidence, taking into account the non-rectangular shape of the pillar and the presence of voids above the UCG reactor in the immediate roof. The main research was carried out using the finite element method in ANSYS 17.2 software. The results of the first simulation stage demonstrated that during underground gasification of a thin coal seam using the Controlled Retraction Injection Points method, with reactor cavities measuring 30 m in length and pillars ranging from 3.75 to 15 m in width, the surface subsidence and rock movement above gasification cavities remain within the pre-peak limits, provided the safety pillar’s bearing capacity is maintained. The probability of crack initiation in the rock mass and subsequent environmental hazards is low. However, in the case of the safety pillars’ destruction, there is a high risk of crack evolution in the overburden rock. In the case of crack formation above the gasification panel, the destruction of aquiferous sandstones and water breakthroughs into the gasification cavities become possible. The surface infrastructure is therefore at risk of destruction. The assessment of the pillars’ stability was carried out at the second stage using numerical simulation. The study of the stress–strain state and temperature distribution in the surrounding rocks near a UCG reactor shows that the size of the heat-affected zone of the UCG reactor is less than the thickness of the coal seam. This shows that there is no significant direct influence of the gasification process on the stability of the surrounding rocks around previously excavated cavities. The coal seam failure in the side walls of the UCG reactor, which occurs during gasification, leads to a reduction in the useful width of the safety pillar. The algorithm applied in this study enables the optimization of pillar width under any mining and geological conditions. This makes it possible to increase the safety and reliability of the UCG process. For the conditions of this research, the failure of coal at the stage of gasification led to a decrease in the useful width of the safety pillar by 0.5 m. The optimal width of the pillar was 15 m.

Purpose. Determination of the operating temperature regime of a non-explosive destructive mixture based on calcium oxide in different temperature fields from the range of the spring-summer period, typical for Ukraine. Methodology. The work used following methods: laboratory modeling, field tests, engineering analysis, synthesis, statistical processing. Findings. The developed mining industry is an attractive industry for the implementation of SCDA in Ukraine. The main reasons for restraining the widespread implementation of SCDA are their high sensitivity to ambient temperature and a long destruction time, which is due to the long hydration hardening of the mixture. The results of the studies indicate that the time of the onset of hydration and the growth of the volume of structural neoplasms exponentially depend on the temperature of the material containing SCDA. At an ambient temperature of 50°C and more, the SCDA does not operate in the set mode, a sudden increase in temperature and a corresponding increase in the volume of the mixture with uncontrolled expansion are observed. Thus, the upper limit of the operating temperature range of the mixture is 50°C. The critical temperature of granitoids in the field experiment was 39°C. Field experiments confirmed that an increase in temperature leads to an acceleration of the hydration rate of non-explosive destructive mixtures and can reduce the destruction time by half. Originality consists in establishing the laws of changes in the hydration rate of non-explosive destructive mixtures based on calcium oxide in different temperature fields and environments with different thermal conductivity. Practical implication. The results of the research can be used in the development of improved mixtures for non-explosive destruction, improving the technology of non-explosive destruction at ambient temperatures above 30°C. Keywords: soundless chemical demolition agents, rock destruction, quasi-static destruction, borehole, temperature field of rocks.

The severe floor heave in gob-side entry retaining is the major restriction factor of the wide application of pillarless mining thin coal seams. Reinforcement and stress-relief floor heave control methods are the most promising. However, in practice, floor restoration is widely used. Therefore, floor heave control technology in gob-side entry retaining needs to be improved. This study proposes anti-shear pile technology to control floor heave in gob-side entry retaining. The research was mainly carried out by numerical simulation. It was found that the transformation of high vertical stresses in the entry floor underneath the filling wall and coal seam body into horizontal stresses starts the floor heave process. The vertical dilatancy of rocks under the roadway span and their subsequent unloading lead to the delamination of the floor strata and uplift of the entry contour. In this paper, the best pile installation scheme was found. It is a 2pile 5+2 scheme with the installation of two piles, each 2 m long. After that, it was shown that filling piles are more than 3.3 times cheaper than comparable analogs, and pile installation is less labor-intensive. The implementation of the proposed floor heave control method leads to a reduction in heaving by 2.47 times.

The floor heave is one of the key factors that can restrict high-efficiency and safety mining, especially in the deep roadways with soft rock. Considering the influences of rock fracturing over time on rock mass properties, a case study of the floor heave evolution and rock bolts reinforcement technology was performed in this paper. A numerical simulation was used to study the stress-strain state and displacement of surrounding rocks. It was found that significant floor heave caused by nonlinear deformation of laminated immediate floor under an increase in rock fracturing. The post-peak strain regions appear in the bottom corners of the roadway, after which strata in the immediate floor are destroyed one by one. The joint spacing of 0.45 m on the immediate floor is critical. At this step, post-peak strain regions merge in the central part of the roadway floor, which is the cause of uncontrolled floor heave. Rock bolts reinforcement was proposed to control the floor heave. Three floor support schemes with two types of support elements, different bolt orientations, and lengths of reinforcement were studied. The numerical simulation demonstrated that after reinforcement, post-peak plastic strain in the floor strata was reduced effectively. The optimal floor support scheme and depth of reinforcement were determined by the allowable floor heave. Ideally, the floor heaves could be reduced by rock bolts with a steel belt installed according to the support scheme III and reinforcement length of 2.0 m for outer bolts and 3.0 m for central bolts.