Features of the thermal regime formation in the downcast shafts in the cold period of the year

In the cold period of the year, to ensure the required thermal regime in underground mine workings, the air supplied to the mine is heated using air handling systems. In future, the thermodynamic state of the prepared air flow when it is lowered along the mine shaft changes due to the influence of a number of factors. At the same time, the processes of heat and mass exchange between the incoming air and its environment are of particular interest. These processes directly depend on the initial parameters of the heated air, the downcast shaft depth and the presence of water flows into the mine shaft. Based on the obtained experimental data and theoretical studies, the analysis of the influence of various heat and mass transfer factors on the formation of microclimatic parameters of air in the downcast shafts of the Norilsk industrial district mines is carried out. It is shown that in the presence of external water flows from the flooded rocks behind the shaft lining, the microclimatic parameters of the air in the shaft are determined by the heat transfer from the incoming air flow to the underground water flowing down the downcast shaft lining. The research results made it possible to describe and explain the effect of lowering the air temperature entering the underground workings of deep mines

Experimental Study on Mechanical Properties of High Performance Hybrid Fiber Concrete for Shaft Lining

In order to solve the problem of highly brittle shaft lining under dynamic loading, a combination of hybrid fiber concrete mixed with steel and polypropylene fiber is proposed to make shaft lining. C60, the concrete commonly used in shaft lining, was selected as the reference group. The static mechanical properties, dynamic mechanical properties, and crack failure characteristics of the hybrid fiber concrete were experimentally studied. The test results showed that compared to the reference group concrete, the compressive strength of the hybrid fiber-reinforced concrete did not significantly increase, but the splitting tensile strength increased by 60.4%. The split Hopkinson compression bar results showed that the optimal group peak stress and peak strain of the hybrid fiber concrete increased by 58.2% and 79.2%, respectively, and the dynamic toughness increased by 68.1%. The strain distribution before visible cracks was analyzed by the DIC technology. The results showed that the strain dispersion phenomenon of the fiber-reinforced concrete specimen was stronger than that of the reference group concrete. By comparing the crack failure forms of the specimens, it was found that compared to the reference group concrete, the fiber-reinforced concrete specimens showed the characteristics of continuous and slow ductile failure. The above results suggest that HFRC has significantly high dynamic splitting tensile strength and compressive deformation capacity, as well as a certain anti-disturbance effect. It is an excellent construction material for deep mines under complex working conditions.

COMPREHENSIVE ANALYSIS OF THE SHAFT STRUCTURE OF THE DNIPRO METRO

Purpose. The construction of the Dnipro Metro, which today is characterized by high efficiency and widespread introduction of new technologies, has proved the need for predesign, design and construction work. The purpose of the scientific article is to identify during the complex analysis of the structure of the mine shaft its stress-strain state, which was obtained during the numerical analysis and geodetic monitoring. Methodology. During the complex analysis of the shaft № 16-bis of the Dnipro Metro, prognostic calculations of the stress-strain state were performed. To do this, a finite-element model is built, in which fully reflects the geometric features of the shaft, the load on it and boundary conditions. Part of the comprehensive analysis is geodetic monitoring, which is carried out during the construction of the shaft and during its operation. The works included the measurement of deformations both in the lining of the shafts and in the sections of the mine workings, as well as on the surface near the houses along the route in the area of influence of the working workings. Findings. During the numerical analysis of the structure of the shaft № 16-bis of the Dnipro Metro, displacement and force factors (normal forces and bending moments) were determined. Based on these results, the reinforcement of the elements of the shaft lining (bored pile, cap beam, reinforced concrete ring beam) was selected. The value of the deformed state obtained from the prognostic analysis indicates on the insignificant displacements of the designed structure. During the geodetic monitoring, horizontal and vertical deformations of the № 16-bis shaft lining were recorded, which were caused by the influence of public transport and heavy vehicles. But the values of these deformations reached 1 … 2 mm, which for their effect on buildings and structures is within normal limits. Originality. A comparison of the deformed state obtained during numerical analysis and geodetic monitoring, which proved the high accuracy of the prognostic calculation. Practical value. The results of a comprehensive analysis of the mine shaft of the Dnipro Metro made it possible to carry out a test the design solution and ensure high strength and stability of the lining made of bored piles.

Experimental Study on Durability of Hybrid Fiber-Reinforced Concrete in Deep Alluvium Frozen Shaft Lining

This article proposes hybrid fiber-reinforced concrete (HFRC) mixed with polyvinyl alcohol fiber (PVA) and polypropylene steel fiber (FST) as a wall construction material to improve the bearing capacity and durability of frozen shaft lining structures in deep alluvium. According to the stress characteristics and engineering environment of the frozen shaft lining, the strength, impermeability, freeze–thaw damage, and corrosion resistance are taken as the evaluation and control indexes. The C60 concrete commonly used in freezing shaft lining is selected as the reference group. Compared to the reference group, the test results show that the compressive strength of HFRC is similar to that of the reference concrete, but its splitting tensile strength and flexural strength are higher; according to the strength test, the optimum mixed content of 1.092 kg/m3 PVA and 5 kg/m3 FST are obtained. According to the impermeability test results, the mixing of PVA and FST can improve the impermeability resistance of concrete. For the freeze–thaw cycle test results, the mixing of PVA and FST can improve the frost resistance of concrete; based on the 120 days sulfate corrosion test, the mixing of PVA and FST will improve the corrosion resistance of concrete.

Experimental Study on High Performance Concrete of Ultra-Deep Mines on the Coast of Eastern China

To solve the problem of ultra-deep mines on the coast of eastern China under the complex external environment of "high in-situ stress, high osmotic pressure, and strong corrosion", the high-performance concrete shaft wall structure with “high strength and low impact liability” was proposed. The field test study of the high-performance concrete shaft lining was carried out in-1120m ingate and-1114m to-1124m shaft in Sha-ling Gold Mine, and its stress and deformation were monitored and analyzed. Finally, according to the Von-Mises strength criterion and the thick-walled cylinder theory, the calculation formula of bearing capacity of HPC shaft wall was deduced. The results showed that: (1) On the 5th day after in-situ casting, the stress of high-performance concrete tends to be stable. Compared with ordinary concrete, high-performance concrete showed good early strength (2) The high-performance concrete shaft lining strain changes smoothly, and concrete strain can be divided into three stages: rapid growth stage, slow growth stage, and stable stage. (3) Under the external environment of "high in-situ stress, high osmotic pressure, and strong corrosion", the − 1120m ingate and − 1114m~-1124m shaft lining of Sha-ling Gold Mine supported by high-performance concrete had uniform stress and good mechanical properties, which can provide a reference for similar engineering support design.

Microgravity Survey to Detect Voids and Loosening Zones in the Vicinity of the Mine Shaft

In mining and post-mining areas, the assessment of the risks to the surface and its infrastructure from the opening or closed mine is of the utmost importance; particular attention should be paid to mine shafts. The risks include the occurrence of undetected voids or loosening zones in the rock mass. Their detection makes it possible to prevent their impact on a mine shaft and surface infrastructure. Geophysical methods, and in particular, a microgravity method lend themselves for the detection of changes in the distribution of masses (i.e., the density) due to voids and loosening zones. The paper presents the results of surface microgravity surveys in the vicinity of three mine shafts: under construction, working, and a liquidated one. Based on the gravity anomalies, the density distribution of the rock mass for all three cases was recognized. The properties of the anomalies allowed to determine which of the identified decreased density zones may pose a threat to the surface infrastructure or a mine shaft. The microgravity survey made inside the working mining shaft provided information on the density of rocks outside the shaft lining, regardless of the type of lining. No significant decrease of density was found, which means that there are no larger voids outside the shaft lining. Nevertheless, at a depth of 42 m in running sands layer, the decreasing density zone was located, which should be controlled. Additionally, measurements in two vertical profiles gave the possibility of directional tracking of density changes outside shaft lining. Such changes were observed on three boundaries of geological layers, with two of them being on the boundary of gypsum and other rocks.