Aiming at 8~12m hard and Extra-thick Coal seam, the fully mechanized top-coal caving mining with super-large mining height，with the cutting height increased, is adopted to enhance the caving performance of top-coal, the paper optimizes the matching parameters of working face equipment, develops a complete set of equipment for fully mechanized top-coal caving mining with super-large mining height of hard coal, researches a strong disturbance and high-efficiency caving mechanism, develops a large volume coal flow transportation system, allocates a Four-level crushing system and memory + remote intervention caving system, etc., have created a safe and efficient intelligent fully mechanized caving face with active perception, automatic analysis, system coordination, which could provide a basic to achieve an annual output of 1.5 Mt thick seam fully mechanized caving mining.

In order to solve the problem of high gas working face with multi-entry layout and the upper corner gas overrun under large mining heightand the improvement of the underground extraction system in the well, the invention can ensure the reliability of the non-wind and the gas discharge behind the working surface, The method of combining the theoretical analysis, the numerical simulation and the on-site practice is adopted to solve the problem that the gas over-limit of the upper corner of the upper corner is solved in a way that the partial Y-type ventilation of the working surface 5 and the two times of the working surface is realized by the stage-type gob-side entry way, However, the key to the realization of the stage-type gob-side entry is to determine the reasonable stage length and the support width of the filling body. The research shows that the movement of the surrounding rock of the Dayin coal mine along the gob-side retaining tunnel has experienced the influence of the mining and moving, the two stages of the retaining-lane stability stage,0-40m behind the working face, obvious deformation of the surrounding rock along the air-retaining tunnel, the stability of the 40-60m trend, and the requirements for the use of the gob-side entry; and at the same time, The ventilation system of the working surface is improved, and the ventilation problem of the goaf behind the working surface is solved.

The hoisting well tower undertakes all the lifting work of human-beings, equipment and mineral resources. Consequently, it is an essential structure during the mining production. In China, the reinforced concrete structure was the most common structural type used for the well towers. According to the technical and functional requirements of the well tower, as well as the stress characteristics of the steel structure, the structural analysis of the steel hoisting tower was performed based on several aspects (the plane and vertical layout , the lateral force resistance, etc.). This study maintains the calculations and analyses of several structural systems, including the braced steel frame system, the large scale steel frame system, and the trussed tube system. Among these structural systems, the braced steel frame system is emphasized , which provides a reference for the further design.

The paper expatiates concisely the characteristics of coal mine industrial yard and the classification of grounding systems of low-voltage distributing system, and as well as the Applicable situations of each type of grounding system. Then the advantages and disadvantages of TN and TT grounding systems for road lighting are analyzed. Furthermore, the setting principle & method of the operating current of the RCD(Residual Current Operated Protective Device) in TT grounding system is expounded and the suggestion about how to select the reasonable grounding system for the road lighting is displayed.

Ningdong energy and chemical industry base is developing rapidly relying on coal-based energy economy. However, due to excessive water use on the Yellow River and restricted by the red line of water use, the base is facing with severe economic development water resource constraints. Based on the analysis of the industrial status and water supply and consumption status of Ningdong base, this paper points out the major water problems existing in the base at present. Combined with the industrial development plan, a series of water-saving schemes are proposed for the coal, coal power and coal chemical industry to reduce the contradiction between water resources and economic development. We took 16 coal enterprises,14 coal power enterprises and 10 coal chemical enterprises in the base as samples. And calculated the water saving potential of each industry. The results show that: the water consumption of Ningdong base is close to the control index; the mine water has great development potential, and the recyclable water consumption is 30.41 million m3 by improving the utilization rate; the water-saving potential of coal development, coal power generation and coal chemical industry is 7.88 million m3,6.86 million m3 and 25.22 million m3 respectively, with a total water-saving potential of 39.96 million m3.

In order to solve the problem that the surrounding rock in the deep high stress area is broken and the initial support means can not effectively control the surrounding rock, the research on the surrounding rock control technology of the cutting top and retaining roadway is carried out under the actual engineering background of a deep mining face in chensi floor. According to the geological conditions of the working face, the deformation mechanism of the remaining roadway is analyzed, and the blasting parameters and the supporting scheme of the initial roadway are designed. In view of the large deformation of the roadway and the broken surrounding rock in the process of advancing the working face, this paper designs a scheme of reinforcing the roadway by cutting the roof and retaining the roadway: a new type of quick setting and early strength inorganic double liquid grouting material is used to reinforce the broken surrounding rock of the cutting roof and retaining the roadway, so as to control the deformation of the roadway quickly and effectively; at the same time, the measures of retaining the gangue by the side of the roadway with the flexible gangue retaining wall are designed to realize the combination of active and passive roof cutting and retaining the gangue Roadway reinforcement support mode. The results show that the roadway reinforcement technology is adopted in a working face of Chensilou Mine. Under the action of secondary mining stress, the maximum roof subsidence is 147 mm, the maximum displacement of two sides is 335 mm, and the maximum floor floor heave is 402 mm. The surrounding rock of the retained roadway is effectively controlled.

In view of the difficulty to leave the roadway under complex stress disturbance for 3 # coal mining height working face in Sihe mine, and the serious deformation of surrounding rock of roadway multiplexing at the airport side, Hydraulic fracturing technology is adopted to conduct directional pre-cracking on key strata of roadway roof, and the cantilever beam above the coal pillar on the face side of the roadway is cut off, so as to reduce the overhanging load of the cantilever beam and the rotary deformation force, so as to cut off or greatly weaken the load transferred from the rock beam to the coal pillar protecting the roadway and the remaining roadway, and fundamentally improve the mechanical environment of the roadway. The results show that the application of hydraulic fracturing in cutting off the top of the roadway can effectively improve the stress state of the surrounding rock, control the deformation of the surrounding rock, avoid the secondary or multiple repair of the roadway, and reduce the support difficulty and cost of the roadway.

For the bottom pumping road of close-distance coal seam, it is in a high stress state after the upper working face mining and it is difficult to maintain. The hydraulic fracturing technology is studied. It is concluded that the hard roof of the hard surface is easy to form a long time span. The overhanging effect is the key to the pressure of the bottom coal roadway. Hydraulic fracturing eliminates or weakens the formation of hard roof and improves the overburden of the goaf. The proportion of stress distribution in the coal pillar is changed and the stress state of the bottom pumping road is improved; The multi-stage retracting hydraulic fracturing technology combined with the straddle drilling packer forms obvious artificial cracks in the hard rock strata of the roof, which reduces the stress concentration of the surrounding rock of the bottom pumping roadway and reduces the maintenance difficulty of the bottom pumping roadway.

In order to find out water abundance and development distribution situation of water conducted structure within the scope of the+10 roadway ahead 80 meters, based on the analysis of geophysics premise such as elasticity and the electric magnetic differences, combined with the actual production data of roadway, designed optimal observation system, the seismic probing MSP and transient electromagnetic method are used to advanced detection of +10 roadway. The results show that there is no obvious water conducted structure within the detection area, no significant water abundance abnormal phenomenon, it tallies with the actual mining data, the effect is better, prove that the selected detection technology is more reasonable.

In order to solve the problem about rockburst monitoring and early warning of an approximately vertical seam, the evolution law of the energy and frequency of acoustic emission events before and after rockburst was studied and precursor information of rockburst was recognized based on previous rockburst events of Wu Dong coal mine B3+6 working face in +450 level. The results show that before the occurrence of rockburst, the activity of acoustic emission events experienced a transition from a calm period to a strong period. The phenomenon of sudden changes in acoustic emission activity from calm to intense abruptness can be used as the precursor information of rockbrust.

In view of the problems of roof and coal wall slabs encountered when the working face passes through the fault, the 14207 fully mechanized mining face of Majialiang Mine is taken as the background. By establishing the mechanical model of the elastic deep beam of the roof in the fault zone of the working face, the stress distribution law of the roof is analyzed, and the surrounding rock control technology of the rigid-flexible coupling with the rigid-flexible coupling is proposed. Flac3d is used to calculate and analyze the proposed control scheme, and combined with on-site monitoring data for comparison and determination. The research shows that the top plate breakage of the working face is mainly caused by the effective ultimate shear stress; the plastic zone range and the roof subsidence of the surrounding rock are obviously reduced in the simulation; the measured displacement of the roof is reduced from 38 cm to 7 cm, and the subsidence is reduced 81.6% small. The shallow and shallow zone rigid-flexible coupling grouting surrounding rock control technology can effectively solve the problem of roofing and chipping.

Before the S206 fully mechanized caving face in S2 mining area of changcun coal mine, the roof is weakened by direct charge pre-splitting blasting, and the initial pressure step distance of the basic roof is 17.6m. It is known from the analysis of the crushing radius that the roof pre-splitting effect is not good. In order to further shorten the first compressing step distance of fully mechanized caving face, taking the adjacent S208 fully mechanized caving face as the engineering background, according to the analysis of seam forming mechanism of cumulative blasting, a kind of cumulative charging structure was studied, and the characteristics of cumulative blasting were used to improve the effect of roof precracking. Then ANSYS/ ls-dyna numerical simulation was carried out to analyze the pre-splitting effect of direct charging and shaped charge blasting from the stress cloud diagram, crack radius and pressure-time history. It was concluded that shaped charge blasting has shaped charge effect, and the pre-splitting effect is better, which can weaken the roof and guarantee the safety of the initial mining period. In the end, S208 fully mechanized caving face has the first compressing step distance of 15.2m, which reduces 2.4m and improves the primary recovery rate. It has good economic value and application value.

In order to effectively control the roof water inrush of 16020 working face in Xin'an Coal Mine, the paper discusses the technical problems of the roof water inrush under the condition of the old empty water supply by using the knowledge of hydrogeology, coal geology, mining, grouting and so on. The results show that: first of all, through analysis of the water level, water quality, water temperature and other factors to accurately and quickly identify the water inrush source and water diversion channel, and then use curtain grouting to cut off the roof water supply channel in this roof water inrush treatment is effective. It took three months to successfully block the supply channel, and the water blocking was successful. For the roof water inrush with old air water supply, curtain grouting is an effective way to cut off the supply channel, the technology can be used for reference for similar roof water inrush.

Aiming at the evaluation of grouting reinforcement effect and water inrush danger after grouting on floor in 14030 working face, the "27381 Grouting and Water Control System" was used to evaluate it. Results showed that the L2 aquifer and its guiding zone has less dangerous to water inrush risk because they are farther from the working face and its water-rich medium. The L8 aquifer has medium dangerous to water inrush risk because it is close to the working face and its water-rich strong. There is no unimpeded hydraulic connection between L2 and L8. Severely dangerous zones are affected by faults. The types of water-rich in the severe danger zones of I, II and V are J-type, the risk of water inrush is low; and severe danger zones of the III, IV and VI are U-type, the risk of water inrush is medium. The results of the three-parameter evaluation of the grouting effect in the severely dangerous zones are good. The grouting process of the working face has experienced the initial increase—smooth grouting—interacting—the final stage of the final pressure stabilization. The normal zone grouting amount is 0.012t/m3, the fault zone is 0.220t/m3, and the grouting coefficient is 18.3. The working face grouting effect comprehensive evaluation is good, and the water inrush is lower.

Exploration and drainage drilling has been widely applied in underground coal mine, which provides technical guarantee for coal mine safety production. In order to solve the water hazard problem of floor limestone aquifer in the mining of "Group A Coal" in Zhangji Coal Mine, the directional drilling technology was introduced into the floor water exploration and drainage drilling, and the success was achieved. The directional drilling project in -600 hydrophobic roadway was constructed to control the water hazard of floor limestone in 1612A and 1613A working faces. At present, 15 boreholes have been constructed in the water hazard control projects of drainage roadway in these two working faces. With a total footage of 5480 m and two important water outlets identified, the problem of water hazard detection of working face floor limestone can be effectively solved. The technology of water exploration and drainage of working face floor limestone based on directional drilling in Zhangji Coal Mine has been formed, which can be widely applied in similar mines.

With the depletion of shallow resources and the development of coal mining, the disaster of soft rock engineering is prominent. Based on the engineering background of II66 auxiliary descending of Liuqiao No.1 mine, according to its deformation and instability characteristics, the mechanism of auxiliary descending asymmetric deformation and failure is analyzed by means of field measurement, laboratory experiment, theoretical analysis, numerical simulation and industrial test, and the optimal control measures are proposed. The research shows that :(1) the auxiliary downhill floor is weak and broken, and the roadway has significant asymmetric deformation. The surrounding rocks are of low strength, and the fine sandstones are rich in hydrophilic minerals such as illite, feldspar and chlorite. (2) according to the in-situ stress measurement, it is found that the auxiliary down-hill is in the stress zone of the plateau rock. The maximum main stress is horizontal stress and has obvious direction, and the included Angle with the roadway axis is large, which is not conducive to the stability of the surrounding rock. (3) the original support scheme did not adopt bottom control measures, ignoring the stability of u-shaped steel bearing structure, and the failure of bottom plate drives the instability of wall; (4) the numerical analysis results are close to the field observation, and the auxiliary down-slope is greatly affected by the adjacent excavation engineering disturbance, which is the main reason for its asymmetric failure. (5) based on field observation and analysis of deformation and instability mechanism, multi-level combined control measures of grouting bolt and grouting anchor cable are adopted, and structural reinforcement of u-type support is carried out at the same time, which results in good industrial test results and meets the field requirements.

Based on the geological conditions in shallow-buried, weak-cemented soft rock in the west of China, the failure mechanism of mine roadway is revealed by the X-ray diffraction, electron microscopy, test of rock mechanics and on-site monitoring; FLAC3D numerical simulation mode is established to simulate the stress distribution, surrounding rock displacement and range of plastic zone in mine roadway by the large deformation theory of mine roadway. The results show that the maximum principal stress of the surrounding rock of weak cemented soft rock roadway determines the failure depth of the surrounding rock, which is approximately distributed with the depth of the surrounding rock in the shape of “へ”. The relationship between the deep deformation “s” in different directions of the surrounding rock and the surface distance “h” of the roadway is negative exponential decay. The accord of plastic zone range in mine roadway proved true by the comparative analysis of the FLAC3D simulation and GPR exploration, giving a scientific guideline for the stability analysis, design of supporting and reinforcement scheme of the roadway surrounding rock in slight contact cement rock conditions. Finally, targeting the range of the plastic zone in slight contact cement rock roadway, the technology of combining support of anchor net spray active support +36U steel support + full section anchor injection is proposed to determine the plastic zone range of mine roadway in slight contact cement rock conditions, which can control the deformation of the surrounding rock and the expansion of the plastic zone effectively, having been showed by on-site monitoring results.

In this paper, the difficulty of slag discharge and the low porosity of the high-gas soft coal in the underground coal mine are studied. The numerical simulation of the deformation and slag production of deep high gas soft coal under the combined stress is carried out by FLAC3D numerical simulation technology. The law of slag generation and deformation of deep high gas soft coal in the bedding layer is revealed, and the deformation characteristics and stress variation of the coal around the long hole in the bedding layer are analyzed. The numerical simulation study shows that the large-volume sudden collapse will occur after the critical condition of the stress balance of the coal body in the deep high gas soft coal bedding hole; the maximum deformation displacement of the drilling level is 1.22mm, and the maximum deformation displacement in the vertical direction is 10.7mm; along the radial distribution of the borehole, the vertical deformation of the coal around the hole shows a decreasing trend, and the vertical deformation is significantly larger than the horizontal deformation of the borehole. In the horizontal direction, the stress distribution of the coal body around the borehole increases first and then gradually decreases. The influence of the radial distance on the horizontal stress distribution gradually decreases. With the increase of the radial distance, the borehole The stress distribution of the coal body gradually decreases, the stress of the coal body at the wall of the borehole appears the maximum, and the stress value in the vertical direction is the largest.

Abstract: The 3# coal seam of Sangshuping Coal Mine in Hancheng Mining Area is a soft and thick coal seam. The coal and gas outburst is mainly caused by the ground stress. Based on the theory and field observation, the pore shape and stress distribution of the soft coal after different types of failure are analyzed. When the coal cutting rate is 3% by numerical simulation, the radius of the plastic failure zone around the borehole is about 2.2m, and the width of the plastic failure zone between the reaming boreholes is 1.6m;The width of the pressure relief area of a single reaming borehole is about 3.2m; the pressure relief effect of the hydraulic reaming technology is investigated on site, and the attenuation coefficient of the borehole gas flow is reduced by 3~4 times. The amount of gushing increased by 2~3 times; the evaluation of the effect of mine area measures was carried out by using the method of expanding the coal chip rate combined with the residual gas content. When the coal expansion rate is above 3%~5%, the geostress-oriented type of the Sangshuping coal mine can be effectively solved. The anti-burst problem of coal roadway excavation in soft and thick thick coal seam.

In order to explore the influence of buried depth and particle size on the minimum ignition temperature of coal dust layer, coal samples from Jibei mining area were selected. Based on the study of physicochemical properties of deep coal seams, the minimum ignition temperature of coal with different depths and particle sizes was measured by hot plate experiments. The results show that in the experimental temperature range, the thickness of the coal dust layer is 5mm, the buried depth increases, the volatile content increases from 33.65% to 38.9%, and the minimum ignition temperature of the coal dust layer decreases from 330°C to 270°C. The phenomenon of layer fire can be observed with the naked eye. As the particle size of the coal sample decreases continuously, the minimum ignition temperature of the coal dust layer of different buried coal samples is significantly reduced. When the coal dust layer is 5 mm, ith the coal sample particle size decreasing from 180μm to 75μm, the minimum ignition temperature of the coal dust layer of three different buried depths decreased by 16%, 19% and 25%, respectively, and the difference was significant.

In view of the impact of mining on the Ma-jia-shi-pan-gou Bridge, the two aspects of surface movement deformation and foundation stability are analyzed. According to the observation data of the bridge's moving deformation, combined with the bridge structure and the geological mining conditions of the mining area, the law of surface movement and deformation of the goaf is analyzed. On this basis, combined with the analysis of the damage status of the bridge, the probability integral prediction simulation method is applied to simulate the expected impact of the residual movement deformation of the mining surface on the bridge, and the influence degree of the mining on the bridge is determined to be within the I-level range. Aiming at the stability of the foundation of the bridge, using the combination of traditional analysis and FLAC 3D, it is determined that the undercut goaf of the bridge is in a basically stable state. and the research results can be used as the basis for the later repair of the bridge.

Fault is one of the common abnormal structures in coal measure strata. The study of fault geometry is an effective method to improve the accuracy of fault detection. Based on the elastic wave theory, a 3D coal-bearing strata model is established, and the finite element numerical simulation method is used to analyze the influence of fault throw and dip on the channel wave. From the record of channel waves and the time-frequency spectrum, it can be seen that the blocking effect of fault on channel wave increases with the increase of fault distance and inclination. For channel waves after fault, when there is a fault less than coal thickness, with the increase of fault distance, the frequency of the peak energy is higher, and the occurrence time is advanced. When there is a fault larger than the coal thickness, the frequency of the peak energy is lower, and the occurrence time is delayed. With the increase of the fault inclination, the main frequency is lower, and the occurrence time is delayed. It is not easy to judge the fault location for faults less than 1/2 coal thickness. The results can provide theoretical support for the detection of fault geometry, and are of great significance for the precise detection and signal interpretation of channel wave.

Coalbed methane development in China is generally faced with the problems of low pressure, low permeability, low saturation and other natural attributes of coal reservoirs, aiming at this problem, the technology of hydraulic fracturing assisted by liquid gas injection is put forward. The mechanism of improving the critical desorption pressure by liquid nitrogen injection and the mechanism of CO2 displacing coal seam methane are described respectively, combined with the ground coalbed methane industrial test of Luling Coal Mine, the test results of liquid nitrogen and liquid CO2 displacement with hydraulic fracturing were analyzed. The results show that, (1) after injecting liquid nitrogen, nitrogen molecules will occupy the space of methane molecules in the coal seam and provide external energy for methane gas, at the same time, it can reduce the molecular pressure of methane, improve the critical desorption pressure, promote its faster desorption of methane gas in coal seam, and promote gas production, it only took 190 days to reach the peak gas production of 3145.2m3/d in NO.2 well, and the average gas production during the stable production period was 1400m3/d. (2)The strong adsorption of CO2 can replace the methane with the adsorbed CH4, which promotes the rapid change of coalbed methane from the adsorption state to the free state, and achieves the effect of massive desorption of coalbed methane,CO2 can also effectively reduce the partial pressure of free methane and promote gas production under the condition of constant pressure, the theoretical critical desorption pressure ratio was 3.29, and it only took 124 days to reach the peak gas production of 3351.9m3/d in NO.3 well, and the average gas production during the stable production period was 800m3/d. Comparative analysis shows that the advantages of liquid nitrogen injection technology are obvious, and there is no CO2 outburst risk in the subsequent coal mining process.

To solve the problem of subjectivity and inaccurate result in the risk assessment, this paper presents a method which is applied in Yu Liao Tunnel based on Fault Tree Analysis(FTA) and Bayesian Network（BN. This risk probability assessment method includes three methods, such as the probability intervals, the weight and confidence index and confidence interval. First, FTA was used to construct the BN, and the dependent relationships between the factors in the cases were used to calculate the Conditional Probability Table (CPT) of every node. Second, the professor’s investigations were carried out to get the survey data which is based on the small probability interval hierarchies and the weight and confidence index method. The survey data gained from professor j about factor will be presented by . All the survey data will be used to estate the sample space and the statistic, introducing the confidence interval to get the probable range of factor . After finished all the data processing, the probable range and CPT will be used to calculate the risk, it also can be used to diagnosis the accident.

In order to further study the movement characteristics of vibration flip-flow screen, the paper consider the rotation of the screen frame around the centroid, establish a linear six-degree-of-freedom dynamic model of vibration flip-flow screen and solved the steady solution of the differential equation of motion. Analysis the Motion Trajectory of flip-flow screen by using State Space and Calculus Module. Combined with the design example, calculate the centroid displacement and rotation angle of the active screen frame and the floating screen frame of the vibration flip-flow screen. And according to the motion equations of any point on the screen frame, simulated the motion track of the special point on the sieve frame. The results shows that the rotation of the screen frame around the centroid has a great influence on the amplitude of the input and the outlet, so the influence of the rotation should be considered in the modeling. The paper provides theoretical basis for further research and product design.

In order to study the influence of different impact energy per mass on the size distribution of ore and rock, a theoretical model of fractal dimension of particle size and impact energy per mass was established based on fractal theory. The crushing tests of anthracite and gangue under different impact energy per mass were carried out with the drop weight impact tester. The results show that the impact energy per mass has little influence on the particle size distribution of anthracite and gangue, and the G-S distribution can well characterize the cumulative distribution of anthracite and gangue under different impact energy per mass. The fractal dimension of particle size increases logarithmically with the increase of impact energy per mass. The experimental results and published data verify the correctness of the theoretical model.

Abstract:In order to separate kaolinite and quartz, the effect of calcium ion on flotation of kaolinite and quartz at different pH values in sodium oleate (NaOL) system was investigated according to the test results of Zeta potential and adsorption quantity.The results show that Kaolinite has good flotation characteristics in pH range of 6~8,and the recovery rate is above 70.00% ;quartz has good flotation characteristics at pH of 12, and the recovery rate reaches 70.43%.In 0.8mmol/L sodium oleate with 1.0mmol/L Ca2+ system, A 1:1 ratio of artificially mixed minerals can be separated by flotation at pH of 6 and 12,The concentrate yields were 47.83% and 47.83%, respectively, and the grades were 73.23% and 17.45%, respectively.Zeta potential and adsorption quantity show that in the sodium oleate system,Ca2+ has little effect on the floatability of kaolinite,and inhibits the floatability of quartz in the acid andneutral condition,and promotes its adsorption in strong alkaline conditions .

Oxidation results in an increase in the amount of oxygen-containing functional groups on the surface of coal particles, a decrease in hydrophobicity, and a decrease in the recovery effect of flotation. But oxidized coal reserves are huge, the study on its separation and utilization has important significance. The oxidation layer obstructs the effective contact of collector molecules and bubbles with the hydrophobic part of coal slime, which is the main reason for the decrease of floatability of fine oxidized coal. The hydrophobic pretreatment of fine oxidized coal surface before flotation has become one of the main methods and the research focus to improve the floatability of fine oxidized coal. In this paper, the identification and quantitative characterization techniques and methods of oxygen-containing functional groups on the surface of oxidized coal were summarized, and the methods of surface hydrophobic pretreatment were reviewed. The analysis results show that, some materials surface analysis techniques, such as infrared spectrum, Raman spectrum, and X-ray electron spectroscopy effectively supply the information about the functional groups properties at different levels of fine oxidized coal, and have been used widely by researchers. Suitable pretreatment, such as grinding, high strength and high concentration conditioning, and ultrasonic treatment can achieve the surface hydrophobic modification of fine oxidized coal. However, different measurement and pretreatment methods have their own limitations, so researchers and engineers need to choose and comprehensively apply them according to the properties of materials, research purposes, feasibility and other aspects. This paper provides some references for improving the floatability of fine oxidized coal.

Aiming at the problems of single monitoring direction and poor coupling of borehole stressmeter, a new type of flexible stressmeter is designed, and its working principle is analyzed through mechanical modeling. The linearity, sensitivity, durability and temperature characteristics of the new stressmeter are tested in laboratory. The experimental data show that:① the flexible borehole stressmeter has good linearity, and the sensitivity of the stress gauge is about 0.29;② the long-term stability of the stressmeter is high, and the initial pressure stability period is about 2.5d-3d; ③ the flexible borehole stressmeter is significantly affected by the temperature change, and is more suitable for the stress monitoring of deep coal body with little temperature change, if carried out. Temperature effect should be considered in shallow coal or geotechnical engineering monitoring. Through field practice, the monitoring accuracy of the flexible borehole stressmeter is improved compared with the ordinary borehole stressmeter.

With the advancement of wireless sensor network technology, wireless monitoring systems for equipment status have received more and more attention. Aiming at the existing mining wireless sensor terminals with high power consumption, short communication distance, and poor anti-interference ability of RF signals, a design scheme of mining wireless composite sensors based on LoRa technology is proposed. Selection and design of hardware modules such as control unit and radio frequency unit, as well as software modules such as vibration data acquisition, temperature data acquisition and data transmission Performance test of power consumption, wireless transmission distance and data validity of composite sensors. The test results show that the designed wireless composite sensor has low power consumption, and the wireless transmission distance is better than 600 meters when the packet loss rate is less than 10%. The collected data is truly valid and achieves the design expectations. The research results provide technical support for the wireless monitoring system of mining equipment status.

In order to study the effect of three intake types on the internal unsteady flow field of the fan, the SST k-ω turbulence model combined with the automatic near-wall treatment method is used to simulate the three-dimensional flow in the whole flow passage, including the intake air duct, of a mining contra-rotating main fan for forced type ventilation. The FFT technique is used to analyze the transient pressure change in the two impellers of the fan, and the pressure fluctuation spectrum of flow field in the impellers is obtained. The results show that, compared with the undistorted intake type, both the elbow distortion and the complex distortion intake types seriously deteriorate the flow field in the intake air passage upstream the first stage impeller, thereby significantly reduce the fan performance. Furthermore, the maximum pressure fluctuation amplitude appears in the internal flow field of the second stage impeller, and the non-uniformity of the air flow increases in the circumferential direction.