The global situation related to the COVID-19 pandemic has forced employers to find an adequate way to conduct training in order to ensure work safety. The underground mining industry is one of the ...industries which, due to its nature, was not able to switch to remote work. Conducting traditional training risked spreading the virus among workers. For this purpose, it was necessary to start a search for a form of training that would be safe and would not cause additional stress for employees. Research on the development of an active employee training method and testing of the method itself was conducted online. In order to develop a method of active training, one of the most important workstations was selected, which is the operation of the conveyor belt. The training method comprises four training modules. The modules cover questions related to the operation of the conveyor belt, emergencies, its assembly and disassembly, repair and maintenance. The developed issues also take into account questions concerning natural hazards and work safety. The entire training course lasts 10 days. Every day, an employee receives a set of eight questions sent to their email address, which they must answer before starting work. The article describes the methodology and implementation of the training.
The influence of acid solutions was investigated on the mechanical properties of mudstone. Uniaxial compression tests on mudstone samples were conducted to determine the variations of relative mass, ...porosity, deformation, and strength characteristics of mudstone subjected to acidic solutions with different pH values. The change of pH, relative mass, and porosity of mudstone in the process of acid solution immersion was monitored during soaking. The mechanism of hydrochemical corrosion of mudstone samples was preliminarily discussed. The damage parameter was introduced based on the porosity rate. The results show that with increased solution acidity, the peak stress and elastic modulus decreased to different levels, while the peak strain increases in the rock samples. The increased chemical damage parameters reduce the mechanical parameters and increased the deformation parameters. On the basis of the mechanical test, considering the stress-strain relationship of rock in the compaction stage, a segmented damage constitutive model of rock based on chemical damage parameters is established, and the test results are verified. The results show that the correlation coefficient between the theoretical curve and the experimental data is as high as 0.98, and the model is suitable for the analysis of chemically corroded rock under the uniaxial compression test. The results provide a reference for the analysis and design of coal-bed methane wells where the rocks frequently become acidic during the production of methane.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Corrosion of steel roof support systems can cause potential premature failure of the support, thus adversely affecting the excavation stability and rock-related safety. An in-house corrosion test ...system was designed and developed to test fulllength roof bolts for material performance based on tensile load capacity and strength under different corrosive conditions found underground. Initially, ASTM A615 grade 60 steel roof bolts, which are the most commonly used bolt material in the United States, were tested with and without stresses in a simulated underground coal-mining environment for approximately six months. This paper mainly discusses the test system, protocol and system shortcomings, and makes recommendations based on the observations and results.
In underground tunnels, caverns or pillar goaf, the time-dependent deformation or failure of the rock or coal mass is a major safety concern, which affects the mechanical properties and stability of ...the coal and rock in the underground excavations. However, the damage surrounding rock or coal usually occurs from the time mining starts. This initial damage is rarely considered during the current creep tests used for coal. In the present study, an experimental specimen processing method to identify the initial damage to a coal deposit is suggested. The effect of the strain history on the deformation of coal samples with initial damage during multi-level loading triaxial compression creep tests was studied. The laboratory tests showed that the strain versus creep curve of the coal samples experiences three typical creep stages of deceleration creep in the early stage, constant velocity creep in the medium term and catastrophic accelerated creep in the later stage. With the increase in initial damage, it was observed the gradual decrease in total creep time, deviating stress of creep failure, stress threshold of accelerated creep and starting time of the volume expansion. When the initial damage value increased from 0.0 to 0.50, the deviating stress of creep failure, stress threshold of accelerated creep and starting time of the volume expansion of the coal decreased by 42.3%, 48.5% and 51.4%, respectively. The study is of great significance to conduct researches on the deformation, mechanical characteristics and long-term strength of coal pillar with initial damages under long-term pressure, and also provides insight into the underground excavations and the design of supports to the opneings under such disturbance.
Aiming to address the following major engineering issues faced by the Pingdingshan No. 12 mine： （1） difficulty in implementing auxiliary lifting because of its depth （i.e., beyond 1000 m）; （2） highly ...gassy main coal seam with low permeability; （3） unstable overlying coal seam without suitable conditions for imple- menting conventional mining techniques for protective coal seam; and （4） predominant reliance on ＂un- der three＂ coal resources to ensure production output. This study proposes an integrated, closed-cycle mining-dressing-gas draining-backfilling-mining （MDGBM） technique. The proposed approach involves the mining of protective coal seam, underground dressing of coal and gangue （UDCG）, pressure relief and gas drainage before extraction, and backfilling and mining of the protected coal seam. A system for draining gas and mining the protective seam in the rock stratum is designed and implemented based on the geological conditions. This system helps in realizing pressure relief and gas drainage from the pro- tective seam before extraction. Accordingly, another system, which is connected to the existing produc- tion system, is established for the UDCG based on the dense medium-shallow trough process. The mixed mining workface is designed to accommodate both solid backfill and conventional fully mechanized coal mining, thereby facilitating coal mining, USCG, and backfilling. The results show that： The mixed mining workface length for the Ji15-31010 protected seam was 220 m with coal production capacity 1.2 million tons per year, while the backfill capacity of gangue was 0.5 million tons per year. The gas pressure decreased from 1.78 to 0.35 MPa, and the total amount of safely mined coal was 1.34 million tons. The process of simultaneously exploiting coal and draining gas was found to be safe, efficient, and green. This process also yielded significant economic benefits.
•Infrared radiation is used to characterize the strain of rock.•The advantages and disadvantages of normal distribution damage model and Weibull distribution damage model are compared.•A new ...statistical damage model based on infrared radiation is established.
Rock fracture is the root cause of collapses of the overburden and mine water inrush. Monitoring and identifying the precursor information of the mine surrounding rock during the progressive failure process are the foundation for an advancement of mine safety. In this paper, the infrared radiation observation experiments of both dry and water saturated sandstone under uniaxial loading was carried out. The representative dry and water saturated sandstone samples with specific microstructure and composition, mechanical, and infrared radiation characteristics during the fracture process were studied. The results show that water saturation not only weakens the mechanical properties of rock, but also promotes infrared radiation which can be used as a precursor for stresses. The saturated rock uniaxial compressive strength, elastic modulus, compaction stress decreased and the magnitude of Infrared Radiation Variance (IRV) increased: which are 0.55, 0.54, 0.67 and 10.69 times that of the dry rock, respectively. Furthermore, water saturation changes the failure mode of rock from tensile failure to tensile shear composite failure. In addition, an innovative constitutive model of rock under uniaxial loading based on infrared radiation is established. The model considers the compaction stage and integrates the advantages of the lognormal distribution and Weibull distribution. The established piecewise constitutive model gives the coefficient of performance of more than 0.95, therefore, this model can be effectively used for the prediction of stress in both dry and saturated rocks. The research results can lay a theoretical and experimental foundation for monitoring the stability of engineering rock masses using infrared radiation.
Overburden strata movement can create problems in longwall coal mines at shallow depths located in the West of China, due to surface subsidence affecting the surface structures and sensitive land ...features. Solid backfill mining (SBM) has been successfully used in several mines to solve many subsidence related problems, including coal extraction under buildings, water bodies and railways, and protecting the sensitive landscape. Due to the relatively shallow depth of coal seam, however, the solid backfilling materials must have high compactibility (i.e. be stiff). Based on the longwall working face 15 061 in the Dong Ping coal mine, the different size of the backfill gangue and the affects of porosity, stress and strain, strain energy density and strain were obtained in the laboratory. The deformation and energy absorb of the gangue with different particle size during compaction were analyzed. A multi-layer, composite and elastic foundation mechanical model of the key layers in the shallow coal seam was built. The compression modulus of the backfilling samples with different particle size was obtained with which the bending deflection, stress and strain energy density expression of the critical layer under different particle size range were derived. The result shows that when adopting SBM with longwall in the mine coal seam, the gangue backfilling body can effectively reduce the deformation of the key layer and absorb the energy accumulated in the key layer during the bending process. It was determined that when the gangue particle size is less than 31.5 mm (the porosity is less than 32.9%), the key layer will not break and the gangue filling body can effectively absorb 99% of the energy during the key layer bending. Whilst a smaller backfill (gangue) particle size reduces the porosity thus improving the strength, the cost of the backfill increases and this must too be considered when deciding on the material specifications. The roof deformation and fracturing in the key strata were monitored during mining in the Dong Ping coal mine site. The roof was found to be deflected but with no tensile cracking of the key immediate roof strata, showing the successful implementation of SBM.
The paper discusses the results of a study carried out to determine the thermal condition of a conveyor power unit using a thermal imaging camera. The tests covered conveyors in the main haulage ...system carrying coal from a longwall. The measurements were taken with a thermal imaging diagnostic method which measures infrared radiation emitted by an object. This technology provides a means of assessing the imminence and severity of a possible failure or damage. The method is a non-contact measuring technique and offers great advantages in an underground mine. The thermograms were analysed by comparing the temperature distribution. An analysis of the operating time of the conveyors was also carried out and the causes of the thermal condition were determined. The main purpose of the research was to detect changes in thermal state during the operation of a belt conveyor that could indicate failure and permit early maintenance and eliminate the chance of a fire. The article also discusses the construction and principle of operation of a thermal imaging camera. The findings obtained from the research analysis on determining the thermal condition of the conveyor drive unit are a valuable source of information for the mine’s maintenance service.
In this research paper, a new method is developed that can be used as a precursor of violent rock failure. It is based on measuring the characteristics of rock failure using infrared radiation (IR) ...under uniaxial cyclic loading and unloading. The loading–unloading response ratio (LURR) is determined based on IR indexes such as average infrared radiation temperature (AIRT) and infrared radiation temperature rate (IRTR). The results show that the LURR based on AIRT revealed an overall rising trend and mutation that occurred in the last cycle, which can be used as a precursor of the imminent rock failure. By contrast, the LURR based on IRTR has a noticeable ‘mutation‐rapid decrease’ in the middle and later periods of cyclic loading and unloading, which can also be considered as an early precursor of rock failure. Combined with the precursors of the imminent rock failure, the categorized warning of rock failure is recognized.
Mechanical performance of rock bolts under combined load conditions Pinazzi, P.C.; Spearing, A.J.S. (Sam); Jessu, K.V. ...
International Journal of Mining Science and Technology/International journal of mining science and technology,
03/2020, Letnik:
30, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Rock bolts are subjected to different loading conditions along their lengths such as axial, bending, and/or shear forces, which can cause failure at lower loads than those considered for design ...purposes. The common existing methodologies do not consider the actual loading of the rock bolts and assume it is only pure axial or pure shear. This study was conducted to investigate the un-grouted rock bolt performance under combined load conditions. Two loading regimes were evaluated: the effect of initial shear displacement on axial load capacity and displacement, and the effect of axial displacement on the shear load capacity. The first regime was also conducted for shear with a gap, when there is a spacing between the shear interfaces. The results of this study showed that the rock bolt can resist higher axial loads than shear under pure or combined load conditions. Under combined load conditions, the rock bolt capacity decreased significantly for both regimes. However, when applying the shear load with a gap, the rock bolt load capacity was not affected significantly. Also, the total bar deformation was improved for shear and axial. The findings of this study show the need to improve the rock bolt design considering the complex loading conditions in situ with/without a gap.
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