No abstract

In order to determine the rational width of coal pillars and study the surrounding rock control technology of gob side entry driving with a narrow coal pillar, this paper first calculates the width of narrow coal pillar according to limit equilibrium theory; after that, the lateral support pressure and plastic zone development of the goaf is analyzed by numerical simulation to determine the rational width of reserved coal pillar; finally, through the ring breaking deformation regulation of surrounding rock of the gob side entry, the deformation and failure characteristics of the gob-side roadway during excavation and the influence of mining on the deformation and failure of the gob-side roadway are analyzed. The research results show that, combined with theoretical analysis and numerical simulation, the width of narrow coal pillar is decided to be 10 m; the deformation of the coal pillar side of the gob side roadway is much bigger than the roof subsidence, the deformation of the solid coal wall and the floor deformation; after the bolt support design of the gob side roadway, the deformation and damage of the gob side roadway during the driving period is small; during mining, the deformation of the narrow coal pillar wall is the key factor to determine the stability of the gob roadway; under the bolt support scheme, the overall deformation and failure of surrounding rock of the goaf roadway is small, and the control effect of the surrounding rock of the goaf roadway is good.

a b s t r a c tIdentifying mine water bursting sources accurately and quickly is the important condition of controlling mine water disasters. In the paper, seven hydrochemistry indexes: Mg 2+ , Ca 2+ , Na + + K + , HCO 3 -, SO 4 2-, Cland TDS were regarded as the evaluation indexes for identifying mine water bursting sources, combined with the importance of hydrochemistry index to water source's identification. Then, ternary mixture model was established based on 28 groups of water sample data collected in the Xinzhuangzi Coal Mine. Furthermore, to test the model's reliability, the model was used to identify the water bursting sources of six groups of water samples in Xuchang Coal Mine under the similar hydrogeological conditions in Xinzhuangzi Coal Mine. The results show that multivariate matrix model for identifying mine water-gushing sources is reliable and practical. Moreover, it can be applied to the actual engineering as well.

In this paper, through a similar simulation experiment, the roof rock breaking situation of horizontal sublevel caving method in extremely thick and steep inclined coal seam is studied, and the response characteristics of coal and rock mass under different dynamic load strength are analyzed. The mechanical response mechanisms of different mining positions under the influence of dynamic load and the law characteristics of the surrounding rock from elastic deformation to impact failure are revealed. The study shows that with the increase in the horizontal sublevel mining depth, the roof is gradually broken from the suspended state, and the broken block fills the goaf. The thin rock strata form a granular structure, and the thick rock strata form a block splicing and occlusion structure. On the same side of the coal seam floor, the concentrated stress gradually increases, and the closer the distance from the goaf is, the more obvious the stress change in the coal body below is. With the increase in dynamic load energy, the dynamic instability and failure of the dynamic load side of the roadway occur, and the stress of the bottom coal in the intake roadway of the working face increases due to the influence of the lateral abutment pressure of the goaf, while the stress of the bottom coal in the middle of the working face and the return airway decreases due to the mining of the upper section, which reveals that the dynamic load-induced dynamic behavior requires the critical energy. Due to vibration waves, the dynamic load effect is short, and the reflective stretching is generated on the surface of the roadway, resulting in the failure of the roadway. The peak acceleration increases linearly with the increase in source energy, indicating that the stronger the dynamic load energy is, the higher the impact risk is. When the dynamic load intensity is constant, the peak acceleration decreases with the increase in propagation distance, indicating that the vibration wave has the dominant propagation direction, and there are certain directional differences in the effect of coal and rock. When the dynamic load is applied, the impact failure of the coal body has a critical displacement. When the displacement of the roadway surface is less than this critical displacement, the impact failure will not occur.

Bolt support is an economic method of roadway support. However, due to the influence of mining disturbance, the stress of roadway-surrounding rock changes, thus resulting in varying degrees of confining pressure in the radial direction of bolt. In this manuscript, a numerical solution was proposed to determine the largest confining stress in longitudinal tests of cable tendons. FLAC3D was selected to simulate the longitudinal process of cable tendons. The structural pile element was selected to simulate the cable tendon. The loading behavior of the cable was controlled by the cohesive and the frictional behavior of the cable/grout surface. To confirm the credibility of this numerical solution, the loading behavior of a normal cable and an improved cable was simulated. Experimental longitudinal tests were selected to validate the numerical results, showing that there was a satisfactory agreement between numerical and experimental results. The loading behavior of normal cables and improved cables was numerically simulated. Under the same test conditions, when the improved cable was used, the confining medium can generate much higher confining stress compared with normal cable tendons. Consequently, higher confining stress can result in a larger loading capacity of cable tendons.