Huainan Mining Area Research Articles

Thermokinetic Behavior and Microcharacterization during the Spontaneous Combustion of 1/3 Coking Coal

ABSTRACTThermal analysis was used to investigate the oxidation and heat-release characteristics of four coal samples from the Huainan mining area in China. Temperature and the evolution of heat and gaseous products were studied to identify each sample’s ignition temperature and inform fire-prevention advice to avoid the spontaneous combustion of the coals studied. Thermogravimetry–differential scanning calorimetry (TG–DSC) tests demonstrated lower heating rates resulted in lower characteristic temperatures, corresponding to a greater propensity for spontaneous combustion. Using the Flynn–Wall–Ozawa method, spontaneous combustion was predicted from approximately 300°C, which agreed well with the TG–DSC analysis. The apparent activation energies for combustion were also obtained and gas products that were released throughout the entire oxidation process were monitored. Simultaneous thermal analysis–Fourier transform infrared spectroscopy was used to explain the changes in the evolution of CO and CO2, the results of which agreed well with those of TG.

Mechanism of Zonal Disintegration Phenomenon (ZDP) Around Deep Roadway Under Dynamic Excavation

Due to the exhaustion of shallow resources, the underground roadway used for coal mining has reached the depth of 1000 m. The zonal disintegration phenomenon (ZDP) in deep rock mass will appear with the increase of depth which is widely different from shallow failure mode.In order to reveal the formation mechanism of ZDP, a new theoretical model is proposed. Based on the strain gradient theory and the deformation theory of plasticity, an elastoplastic damage softening model considering of dynamic excavation is put forward. The dynamic equations and boundary equations are expressed through the Runge–Kutta method. The numerical analysis of rock mass failure induced by blast loading and transient release of in-situ stress after blasting excavation is compiled by Matlab program. Taking the deep tunnel of Dingji coal mine in Huainan mine area as engineering background, the theoretical solutions of radial displacement and stresses present an oscillating mode. The theoretical values are in good agreement with the field measured results in terms of magnitude and change law. The applicability of the elastoplastic damage softening model for ZDP is confirmed and the model can be used to provide theoretical support for the deformation and failure of surrounding rock in deep underground engineering.

Analysis of the characteristics of lymphocyte subsets in peripheral blood among coal worker's pneumoconiosis patients

Objective: To preliminary analysis of the characteristics of lymphocyte subsets in peripheral blood among 135 cases of coal worker's pneumoconiosis patients in Huainan mining area. Methods: The peripheral bloods of 135 cases of coal worker's pneumoconiosis patients and 112 cases of health examiners were collected. Flow cytometry was used to detect peripheral blood lymphocytes, T cell subsets and CD4(+)CD25(+) regulatory T cells. Results: Compared with the control group, CD64 index of granulocytes and lymphocytes was slightly higher. The total T cells (CD3(+)) increased in peripheral blood, CD4(+) expression was reduced and CD8(+) expression was increased in infection group, CD4(+)/CD8(+) ratio was inverted, the differences between the infection group and the control group were statistically significant (P<0.05) . There were significantly fewer NK (nature killer) and B cells, significantly more double negative T cells (DNT, CD3(+)CD4(-)CD8(-)) than the control group (P<0.05) . There was no statistically significant difference of CD4(+)CD25(+)CD127(+low)、CD4(+)CD25(+)CD127(+hi) and the ration of Treg/CD4(+)CD25(+)CD127(+hi) protein expression in peripheral blood in two groups (P>0.05) . Conclusion: The analysis of peripheral blood lymphocyte and subgroup is an ideal index to monitor the immune status of coal worker's pneumoconiosis patients. It has theoretical significance for studying the immune mechanism of pneumoconiosis and guiding clinical treatment.

A Voronoi element based-numerical manifold method (VE-NMM) for investigating micro/macro-mechanical properties of intact rocks

In this study, a two-dimensional Voronoi element based-numerical manifold method (VE-NMM) was developed as a new approach to investigate the micro- and macro- mechanical properties of intact rocks. The Voronoi technique was used to generate a polygonal grain assemblage to approximate the microstructure of sandstone samples from Gubei colliery of Huainan mining area in China. A modified contact model incorporating cohesion and tensile strength was adopted to interpret the interactions between rock grains. A series of laboratory tests, i.e. scanning electron microscope tests, uniaxial compression and Brazilian tests were carried out to obtain the microstructural information and macro-mechanical properties of the sandstone samples. To verify the proposed VE-NMM, simulations of Brazilian tensile splitting and uniaxial compressive tests were carried out and the results, in terms of strength, elastic constant and crack distribution, were compared to those of the laboratory tests. To investigate the effects of grain size on the micro-mechanical parameters and the representative elementary volume (REV) size, numerical uniaxial compression tests with different grain sizes (2mm, 3 mm and 4 mm) were conducted using the developed VE-NMM approach. Simulation results indicate that both the micro-mechanical parameters and the representative elementary volume size are heavily dependent on grain size.

Improved compound support system for coal mine tunnels in densely faulted zones: A case study of China's Huainan coal field

When tunnelling in densely faulted zones of coal mines, serious deformation often occurs due to adverse geological conditions such as extremely broken and weak rock mass, high tectonic stress, fissure water. To investigate a more efficient support strategy for tunnels passing through densely faulted zones, a tunnel in China's Huainan mining area is taken as an experimental site to study an improved support method. Some key factors associated with the stability of tunnels in the densely faulted zone are analysed. Based on the analysis of failure characteristics of a previously excavated tunnel, a detailed procedure for the improved support method is proposed in which a long pipe pre-grouting method together with a new kind of grouting cable are applied. Finally, the improved support strategy is implemented in the experimental tunnel. The monitoring results suggest that serious deformation is avoided, and the improved compound support method is feasible for tunnels in densely faulted zones.

Research on Formation Process of Zonal Disintegration in Deep Rock Mass Based on Field Monitoring and Geomechanical Model Test

The zonal disintegration phenomena in deep rock mass will appear with the increase of underground engineering depth which is widely different from shallow cavern. In order to reveal the formation process and production mechanism of zonal disintegration, the field monitoring is carried out in the deep tunnel of China’s Huainan mining area. With the help of borehole television, the zonal disintegration is observed which is alternation phenomenon of the rupture zone and non-rupture zone. At the same time, using the multi-point displacement meter, the whole process change law of the deep displacement in surrounding rock is tested. Taking the field monitoring deep tunnel as engineering background, the 3D geomechanical model test is carried out based on the high stress 3D loading test system. The typical zonal disintegration phenomenon is observed, and the whole process change law of displacement and strain is measured. Based on comprehensive analysis of the whole process test data of the model test and the field monitoring data, the following conclusions are obtained. Under certain stress conditions, zonal disintegration will appear in the surrounding rock of deep tunnel. The zonal disintegration will not occur at the moment of tunnel excavation, but it will be gradually formed after the excavation completion for a period of time.

Spatial and Temporal Distribution Law and Influencing Factors of the Mining‐Induced Deformation and Failure of Gas Boreholes

Because gas boreholes are easy to damage by integrated coal mining and gas exploration, based on the practice of relieving pressure in deep thin coal seams in the Huainan mining area, a multidimensional coupling numerical simulation method was used to reveal the space‐time evolution characteristics and influence factors of fracture deformation of gob‐side gas boreholes. Results indicate that the danger zone for borehole fractures is primarily between 5 and 12 m above the roof of the roadway. The final‐hole position has little effect on the stability of boreholes, and migrating the open‐hole position to the entity coal side and roadway roof side can improve the stability of the borehole. The initial failure of the borehole occurs at a distance of 10 m behind the coal face. The failure of the borehole is largely stable at a distance of 100 to 120 m behind the coal face. With the increase in mining height, which leads to an increase in the movement of strata and an increase in pressure relief range, the shear stability of the borehole is reduced, and the extrusion stability of the borehole is improved. A hard roof condition promotes borehole shear stability, while a weak roof condition promotes borehole extrusion stability. This change can decrease the maintenance difficulty associated with “minor supports” in boreholes to a certain extent by reinforcing the support strength of “primary supports” in roadway retaining walls. The simulation results are consistent with observed results for the 11 test boreholes, and the accuracy of the numerical simulation is verified.

Investigation of the Rock Fragmentation Process by a Single TBM Cutter Using a Voronoi Element-Based Numerical Manifold Method

In this study, a two-dimensional Voronoi element-based numerical manifold method (VE-NMM) is developed to analyze the granite fragmentation process by a single tunnel boring machine (TBM) cutter under different confining stresses. A Voronoi tessellation technique is adopted to generate the polygonal grain assemblage to approximate the microstructure of granite sample from the Gubei colliery of Huainan mining area in China. A modified interface contact model with cohesion and tensile strength is embedded into the numerical manifold method (NMM) to interpret the interactions between the rock grains. Numerical uniaxial compression and Brazilian splitting tests are first conducted to calibrate and validate the VE-NMM models based on the laboratory experiment results using a trial-and-error method. On this basis, numerical simulations of rock fragmentation by a single TBM cutter are conducted. The simulated crack initiation and propagation process as well as the indentation load-penetration depth behaviors in the numerical models accurately predict the laboratory indentation test results. The influence of confining stress on rock fragmentation is also investigated. Simulation results show that radial tensile cracks are more likely to be generated under a low confining stress, eventually coalescing into a major fracture along the loading axis. However, with the increase in confining stress, more side cracks initiate and coalesce, resulting in the formation of rock chips at the upper surface of the model. In addition, the peak indentation load also increases with the increasing confining stress, indicating that a higher thrust force is usually needed during the TBM boring process in deep tunnels.

Predictive models for thermal diffusivity and specific heat capacity of coals in Huainan mining area, China

Thermal properties of coal govern the thermal transfer in coal mass. Taking coal samples from Huainan mining area as the objects, thermophysical parameters (thermal diffusivity, specific heat capacity, and thermal conductivity) were measured from 30 to 300°C by LFA457 laser-flash apparatus. Predictive models for thermal diffusivity and specific heat capacity were then established. The results indicate that the thermal diffusivity of coal samples in Huainan mining area decreases with increased temperature, whereas specific heat capacity and thermal conductivity rise. The predictive models could accurately forecast the values and variations of thermophysical parameters for coal samples in Huainan mining area below 300°C. Furthermore, the modeling method is suitable for the establishment of models for coal samples in other areas. These will be beneficial for the understanding of thermal transfer in coal mass and shorten the testing time in the laboratory.

Identification methods for anomalous stress region in coal roadways based on microseismic information and numerical simulation

It is believed that the microseismicity induced by mining effect and gas gradient disturbance stress is a precursor to the essential characteristics of roadway unstability. In order to effectively identify and evaluate the stability of coal roadways in the process of mine development and extraction, a microseismic monitoring system was deployed for the study of the stress evolution process, damage degree and distribution characteristics in the tailgate and headgate. The mine under study is the 62113 outburst working face of Xin Zhuangzi coalmine in Huainan mining area. The whole process of microfractures initiation, extension, interaction and coalescence mechanisms during the progressive failure processes of the coal rock within the delineated and typical event clusters were investigated by means of a two dimensional realistic failure process analysis code (RFPA2D-Flow). The results show that the microseismic events gradually create different-sized event clusters. The microseismicity of the tailgate is significantly higher than that of the headgate. The study indicates that the greater anomalous stress region matches the area where microfractures continuously develop and finally connect to each other and form a fissure zone. Due to the mine layout and stress concentration, the ruptured area is mainly located on the left shoulder of the tailgate roof. The potential anomalous stress region of the coal roadway obtained by numerical simulation is relatively in good agreement with the trend of spatial macro evolution of coal rock microfractures captured by the microseismic monitoring system. The research results can provide important basis for understanding instability failure mechanism of deep roadway and microseismic activity law in complex geologic conditions, and it ultimately can be used to guide the selection and optimization of reinforcement and protection scheme.

Research and application on the horizontal tectonic stress influence on the stability of deep roadway

According to the test result of ground stress of -817.0m Horizontal shaft station in Huainan mine area, the stress field distribution characteristic of mainly with horizontal tectonic stress was analyzed, the deep roadway surrounding rock deformation and failure regularity under the situation of the maximum horizontal stress and roadway axis in the different angle were studied by using the FLAC3D simulation software, and then specific way of supporting and its parameters were designed combined with the shaft station layout conditions. The result shows that: the roadway stability is relatively good when its tunnel axis the maximum horizontal stress direction within 30° angle, surrounding rock deformation and the plastic zone at the top and bottom are significantly increasing along with the angle increased from 30° to 90°, the major form of deep soft rock deformation and failure is the floor heave. According to the simulation results, the conditions under the layout condition of the shaft station roadway, support methods and support parameters have been designed and determined. The supporting method can be referenced by the similar mines.

A prediction model and numerical simulation of the location of the longwall face during the highest possible failure period of gob gas ventholes

The failure of gob gas ventholes (GGVs) is the main cause of shortening the highly efficient drainage period of GGVs. Therefore, in order to improve the stability of GGVs, it is of great significance to investigate the location of a longwall face when a GGV is in the highest possible failure period. Based on the probability integral method, this paper obtained a modified equation for calculating the amount of horizontal movement of an overlying stratum during longwall mining, and in this equation, the influence of the distance between the overlying stratum and the coal seam on the subsidence coefficient of the stratum was taken into account. In addition, this paper established a prediction model of the location of the working face during the highest possible failure period of GGVs. Furthermore, taking Zhangbei coal mine as an example, this paper investigated the distribution of the maximal amount of relative horizontal movement (RHM) of the contiguous strata along a venthole and explored the changing characteristics of the maximal amount of RHM of the overlying contiguous strata as the distance of the working face passing GGV increases. In addition, this paper also researched the distribution of shear stress exerted on casing along a venthole during coal mining and the changing characteristics of shear stress as working face advances using numerical simulations. The results showed that when the longwall face passed the venthole by approximately 30–70 m, GGVs were in the highest possible failure period, which is the early stage of longwall face passing GGV. Zhangbei and Xieqiao coal mines in Huainan mining area of China carried out the engineering application of extracting depresssurized gas with GGVs. The measured failure data of ventholes 11418-1, 11418-2, 1242(1)-2 and 1242(1)-3 validated the prediction.

Experimental study of axial stress distribution and transfer along the bolt rods in an underground coal mine

Based on the data of experimental tests, underground pullout tests, and real-time monitoring of active anchor-bolt stress in the Dingji Coal Mine in the Huainan mining area, China, the axial stress distribution along the bolt rods in a coal mine roadway was obtained. The results show that the axial stress in bolts increases initially then decreases along the anchoring direction under a perfect anchoring state. As the pre-tension is increased, the stress variation displays nonlinear behavior. The external section of the anchoring bolt rod plays a primary role in restricting the deformation of the surrounding rock before failure occurs. The results also indicate that the bending moment in the bolt rod has a significant effect on the axial stress distribution and transfer, and the bearing and supporting effects of the bolt increase as the pre-tension increases to a certain extent. The axial stress and its transfer features in a working bolt along the embedded direction are nonuniformly distributed and fluctuate.

Experimental investigation on behaviors of bolt-supported rock strata surrounding an entry in large dip coal seam

In order to investigate the behaviors and stability of rock strata surrounding an entry with bolt supporting in large dip coal seams (LDCSs) dipping from 25° to 45°, a self-developed rotatable experimental frame for similar material simulation test was used to build the model with the dip of 30°, based on analyses of geological and technological conditions in Huainan mine area, Anhui, China. The strata behaviors, such as extracting- and mining-induced stresses development, deformation and failure modes, were synthetically integrated during working face advancing. Results show that the development characteristics of mining-induced stress and deformation are asymmetrical in the roadway. The strata behaviors are totally different in different sections of the roadway. Because of asymmetrically geometrical structure influenced by increasing dip, strata dislocating, rock falling and breaking occur in roof. Then, squeezing, collapsing and caving of coal happen in upper- and lower-rib due to shearing action caused by asymmetrical roof bending and dislocating. Owing to the absence of supporting, floor heaving is very violent and usually the zone of floor heaving develops from the lower-rib to upper-rib. Engineering practices show that, due to the asymmetrical characteristics of rock pressure and roadway configuration, it is more difficult to implement bolt supporting system to control rock stability of roadways in LDCSs. The upper-rib and roof of entries are the key sections. Consequently, it is reliable to use asymmetrical bolt-mesh-cable supporting system to control rock stability of roadways based on the asymmetrical characteristics of roadway configuration and strata behaviors.

Mechanical model for controlling floor heave in deep roadways with U-shaped steel closed support

Open U-shaped steel arch supports are commonly used in large-section static-pressure roadways in coal mines that are more than 900m deep; however, it is very difficult to control floor heave of roadways. In this paper, a U-shaped steel closed support with an inverted U-shaped steel arch in the floor is proposed as a method for improving the support effect of the surrounding rock during the process of floor heaving. This research established a mechanical model for the U-shaped steel closed support, and determined the reaction forces at the connection of a camber angle. Using the limit load method calculated the critical buckling load of the inverted U-shaped steel arch, and use of a strength check method tested the strength of the U-shaped steel material. A numerical simulation was conducted using the finite difference software FLAC3D. The simulation results show that the U-shaped steel closed support is able to control the floor heave of roadways, which is successfully used in the West 11-2 development roadway of the Zhuji Mine in the Huainan mining area in China. The cumulative floor heave over two years was less than 50mm.

Position-optimization on retained entry and backfilling wall in gob-side entry retaining techniques

This study investigates the stability problem of gob-side entry retaining (GER) and backfilling wall which located under the key block B. Based on the combined research of elastic–plastic mechanics, structure mechanics and modern theory of mining-induced pressure, the caving characteristic and roof structure over the GER were analyzed, and the vertical force and the torque on retained entry roof were also derived as the position for the retained entry varies. On the basis of the specific geology in Huainan mining area, the results indicate that a relatively more stable position for retained entry neighbors the hinge point of block A and B, and it also located at a scope ranging from this point to the one-third length of block B in horizontal direction. As to appropriate position for backfilling wall, this study recommends partial-road-in backfilling method for GER. Field trial conducted at panel face 12418 of Xieqiao Mine demonstrates that the recommended width for original entry is 3.6 m and the preferred width proportion between original retained entry and original entry is 75 % or so whereas the avoidable one is 88 % or so. These findings provide qualitative references to the mines which share similar geology as what Huainan mining area characterized.

Study and Application of Hydraulic Fracturing Technology to Increase Permeability in Soft and Low Permeability Coal Seam

In order to improve gas drainage of soft and outstanding coal seam in Huainan mine area, for eliminating outburst hazard, hydraulic fracturing is applied at west one (13-1) rock cross-cut coal uncovering face. By analysising antireflection mechanism of hydraulic fracturing, hydraulic fracturing is designed and construct at rock cross-cut coal uncovering face, and then investigate the effect of hydraulic fracturing, at last it get a hydraulic fracturing complete set of technical system.

Gas Distribution and Geological Controlling Factors of Huainan Mining

The aim of the study is to find out gas composition and distribution characteristic and analyze geological controlling factors of high gas content in Huainan mining, which is vital to the development and comprehensive management of mining area gas. Research on the law of gas distribution in the Huainan mining area shows that, the CH4 content extend in N-W direction and NE higher than SW. CO 2 content in this mining performances that south is higher north, while the N 2 content shows a feature that south is lower than north. CO 2 content is high in the turn end of PanJi anticline and low in the wings of anticline. N2 content is on the contrary. Main factors of controlling gas content in this mining are coal quality, buried depth, coal thickness, geological structure and groundwater activity. In addition, gas content were positively correlated with coal quality, buried depth and coal thickness. Sealing fracture structure is beneficial to gas accumulation, while the open fracture structure will reduce gas content. Gas content decreases with the lithologic particle coarsening. Retention groundwater will make for methane's accumulation.

Gas Distribution and Geological Controlling Factors of Huainan Mining

The aim of the study is to find out gas composition and distribution characteristic and analyze geological controlling factors of high gas content in Huainan mining, which is vital to the development and comprehensive management of mining area gas. Research on the law of gas distribution in the Huainan mining area shows that, the CH4 content extend in N-W direction and NE higher than SW. CO 2 content in this mining performances that south is higher north, while the N 2 content shows a feature that south is lower than north. CO 2 content is high in the turn end of PanJi anticline and low in the wings of anticline. N2 content is on the contrary. Main factors of controlling gas content in this mining are coal quality, buried depth, coal thickness, geological structure and groundwater activity. In addition, gas content were positively correlated with coal quality, buried depth and coal thickness. Sealing fracture structure is beneficial to gas accumulation, while the open fracture structure will reduce gas content. Gas content decreases with the lithologic particle coarsening. Retention groundwater will make for methane's accumulation.

Strata Pressure Behavior Study on Isolated Island Face in Huainan Mine Area

In order to effectively solve strata pressure control of isolated island face and roadway support difficulty, field observation was carried out in Gubei mine 1232(1) face in Huainan mine area. Through the activity regularity of roof and floor in face and pressure mechanism analysis, the contents and method of the mine strata pressure observation were set up. Based on these works, the rule of strata pressure behavior and first weight and periodical weight step were educed. Finally, the technical advantage and theoretical support are provided reference for high yield, high efficiency, and safety production in other isolated island face which had the similar geological conditions.