Analysis of coal face stability of lower coal seam under repeated mining in close coal seams group

Aiming at the problem of coal face failure of lower coal seam under the influence of repeated mining in close coal seams, with the working face 17,101 as a background, the coal samples mechanics test clarified the strength characteristics of the coal face under repeated mining, through similar simulation experiments, the development of stable roof structure and surrounding rock cracks under repeated mining of close coal seams are further explored. And based on this, establish a coal face failure mechanics model to comprehensively analyze the influence of multiple roof structural instabilities on the stability of the coal face. Finally, numerical simulation is used to further supplement and verify the completeness and rationality of similar simulation experiment and theoretical analysis results. The results show that: affected by repeated mining disturbances, the cracks in the coal face are relatively developed, the strength of the coal body is reduced, and the coal face is more prone to failure under the same roof pressure; During the mining of coal seam 17#, the roofs of different layers above the stope form two kinds of "arch" structures and one kind of “voussoir beam” structure, and there are three different degrees of frequent roof pressure phenomenon, which is easy to cause coal face failure; Under repeated mining of close coal seams, the roof pressure acting on the coal face is not large. The main controlling factor of coal face failure is the strength of the coal body, and the form of coal face failure is mostly the shear failure of soft coal. The research results can provide a theoretical basis for coal face failure under similar conditions.

Study and Application of Similar Material Ratio in Collapsible Loess

The similar material of collapsible loess is the basis and premise of the experimental study on the surface movement and deformation law of coal seam mining in collapsible loess-covered areas. The orthogonal experiment is used to make up similar material with different proportions using river sand and barite powder as aggregate, clay and gypsum as cementing material, and diatomite as adjusting material. The reasonable proportion of similar material in collapsible loess is studied by using range analysis, similar simulation, and field measurement. The results show that the content of diatomite plays a leading role in the collapsibility coefficient of similar material, and the collapsibility coefficient is positively correlated with the content of diatomite; moisture content is the main control of the cohesion of the material, and cohesion is negatively correlated with the moisture content; the ratio of bone-to-glue has the most significant effect on the internal friction angle, and the internal friction angle is positively correlated with the ratio of bone-to-glue. The reasonable ratio of the similar material in collapsible loess is 8 : 2 of the ratio of bone-to-glue, the ratio of clay-to-gypsum is 9 : 1, the barite powder content is 6%, the diatomite content is 23%, and the moisture content is 13%, and the mechanical parameters of the collapsible loess are 5.3%–6.3% different from the target value of similar material through laboratory tests, which can meet the experimental requirements. It is verified by a similar simulation experiment that the maximum surface subsidence value and the surface fracture width in the simulation results are 6.9% and 7.8% different from the field measured results, indicating a high degree of agreement. The results of the study have important references and guiding significance for the preparation of similar material with similar models.

Experimental Study of Gangue Layer Weakening with Deep-Hole Presplitting Blasting

Advances in coal mining technology and an increase in coal output are resulting in increasingly challenging conditions being encountered at coal seams. This is particularly so at thin coal seams, where a large number of hard rock layers known as gangue are often present, which seriously affect the normal operation of the shearer and reduce coal output. Therefore, the effective weakening of hard gangue layers in a coal seam is crucial to ensure that the shearer operates effectively and that coal output is maximized. In this paper, the weakening effect of deep-hole presplitting blasting technology on the hard gangue layer in a coal seam is studied via a similar simulation. Four test schemes are designed: (1) A blasting hole spacing of 200 mm with the holes offset vertically. (2) A blast hole spacing of 300 mm with the holes offset vertically. (3) A blast hole spacing of 200 mm with the holes parallel to the gangue layer. (4) A blasting hole spacing of 200 mm with the holes offset vertically and initiation of interval blasting. The effect of the different blasting hole spacings and arrangements and different detonation methods on the weakening of coal seam clamping by gangue is studied, and the best configuration is identified. This improves the effect of weakening the coal gangue layer by deep-hole presplitting blasting.

Dynamic Plus-Delta: an agile debriefing approach centred around variable participant, faculty and contextual factors

The current coronavirus pandemic has necessitated rapid intensive care infrastructure expansion with corresponding demand for training healthcare staff. At the NHS Nightingale Hospital, London, the staff underwent a training programme prior to entering the clinical environment with simulation being a core component. This paper describes the rationale for choosing an initial debriefing model which evolved overtime to consider multiple contextual factors: demands of the clinical environment, the diverse participants and their learning needs, the variable experience of faculty, and the dynamic nature of available debriefing time. The new approach, termed here as the Dynamic Plus-Delta model, blends the traditional Plus-Delta approach with specific dynamic elements which considers the unique demands of rapidly training large number of staff. We outline the core features of this model and detail specific considerations around psychological safety. This debriefing approach can be used in similar simulation intervention settings where rapid training of participants is required with multiple and varying contextual factors.

SEIMR/R-S. General Epidemic Simulation Model Multi-Infected States - Multi Sociodemographic Segments - Multi-Region Mobility. Theory

SEIMR/R-S corresponds to a generalized mathematical model of pandemics that enhances traditional, aggregated simulation models when considering inter-regional impacts in a macro region (conurbed); SEIMR/R-S also considers the impact of modeling the population divided into sociodemographic segments based on age and economic stratum (it is possible to include other dimensions, for example: ethnics, gender, … ). SEIMR/R-S is the core of the SEIMR/R-S/OPT epidemic management optimization model that determines optimal policies (mitigation and confinement) considering the spatial distribution of the population, segmented sociodemographically and multiple type of vaccines. The formulation of SEIMR/R-S/OPT is presented by Velasquez-Bermudez (2021a) that includes the modeling of the vaccination process. SEIMR/R-S can be understood and used by any epidemiologist, and/or physician, working with SIR, SEIR or similar simulation models, and by professionals working on the issue of public policies for epidemic control. Following the theory presented in this document, ITCM (Instituto Tecnologico de Ciudad Madero, México) implemented the SEIMR/R-S epidemic model in a JAVA program (Velasquez-Bermudez et. al, 2021). This program may be used by the organizations that considers the SEIMR/R-S will be useful for management the COVID-19 pandemic, it is presented by VelasquezBermudez et al. (2021).

Study on Evolution Characteristics of Regenerated Roof Structure in Downward Mining of Bifurcated Coal Seam

In recent years, the structural evolution characteristics of the regenerated roof of the lower coal seam have become a research hotspot when the bifurcation coal seam is mined downward. In this paper, taking the bifurcation coal seam of Xutuan Coal Mine in China as an example, the structural evolution characteristics of regenerated roof under the influence of mining in bifurcation coal seam are comprehensively studied by theoretical analysis, field measurement, and indoor similar simulation experiment. The stress transfer law in the floor after mining in the upper coal seam is also analyzed. The results show the overburden structure and stress field change caused by upper coal seam mining. The caving and fracture zones are formed in the roof, the average height of the caving zone is 8.28 m, and the one of the fracture zone is 34.91 m. The results of the field test verify the accuracy of theoretical analysis and similar simulation test results. According to the relative size of the depth of the strong failure zone of the coal seam floor and the coal seam spacing, the rock mass structure of the regenerated roof of lower coal seam is divided into three types: fractured rock mass + scattered rock mass (I), fractured rock mass + scattered rock mass + fractured rock mass (II), and fractured rock mass + bulk rock mass + fractured rock mass + layered rock mass (III), and the stability of the three types of regenerated roof structure is evaluated: III > II > I. The research in this paper can provide a theoretical basis for determining the target area of broken roof control under the mining conditions of bifurcation coal seam and provide guidance for the selection of the location and parameters of the grouting borehole for roof reinforcement.

INVESTIGATION OF THE RANDOM VALUE STATISTICAL DISTRIBUTIONS MODELS CHOICE INFLUENCE ON THE MINING OPERATIONS MODELING RESULTS

The importance of production planning for improving the performance indicators of a mining enterprise is indicated. The possibility of simulation modeling using for this aim is shown. It is shown that the created model has a large number of stochastic parameters. It is investigated that there is a problem of research lack about the choice influence of the mining modeling results with different statistical distributions. It is known that with an increase in stochastic deviations from the initial parameters, the productivity of queuing systems decreases. Purpose of work is to study this influence with four statistical distributions of a random quantity (uniform, normal, negative bi-nomial and Poisson distribution) for individual operations and their combinations. In addition, it is necessary to determine how much a change in one particular parameter will affect the overall result of the modeling. Materials and methods. In the previously created simulation model, a stochastic delay is added to the time of individual operations. The addition of such a delay with different sta-tistical distributions and with the same mathematical expectation is investigated. The simulation re-sults are compared with each other, for each individual operation the absolute and relative devia-tion of the results is shown. Further, a similar simulation is performed when all the simultaneously selected parameters changing. Result. It is shown that the magnitude of the deviation significantly differs among all deviations. It is shown that for various single changes in operations, the largest and smal-lest deviations can be given by different statistical distributions. To study the joint change with all parameters, 3 modeling scenarios are implemented: all uniform distributions (this case is used now), the scenario with the smallest deviation and the scenario with the largest deviation. It is shown that switching to another scenario leads to a significant change in the simulation. Conclusion. It is con-cluded that the used significant influence of statistical distributions choice to the accuracy of model-ing the operation of the mining machine is shown, especially when they are taken into account to-gether. The results can be used to clarify the influence of individual factors in the simulation model and improve the planning of potash mining operations, for individual mining machines too.

Behaviors and Overlying Strata Failure Law for Underground Filling of a Gently Inclined Medium-Thick Phosphate Deposit

In this study, the No. 6 pit in the eastern mining area of the Jinning phosphate mine in China was taken as the research background. In order to reduce the cost of filling, an improved pillarless sublevel caving method is proposed. This method greatly improves the ore recovery rate by adding a recovery route. In addition, the combination of similar material simulation experiments and numerical simulations (discrete element and universal distinct element code) revealed the deformation and failure laws of the surrounding roof rock and the characteristics of the surface subsidence. The results indicate the following. (1) The similar simulation experimental results indicate that the deformation of the overlying rock layer originated from the direct roof of the goaf and gradually developed into the deep part of the rock layer. An irregular stepped caving zone formed in the goaf. The maximum surface subsidence was located above the phosphorus orebody, and it gradually decreased toward both sides. As the stope approached propulsion, the location of the maximum subsidence gradually moved toward the propulsion direction. (2) The numerical results revealed that the displacement of the overlying strata was nonlinear, and it decreased with increasing roof height. A support pressure concentration area was formed within a certain range of the stope roof. The numerical simulation results are basically consistent with the similar simulation experimental results.