Mining Science and Technology (China)最新文献

Ground stress is the fundamental cause of deformation and failure during underground structural engineering. Field stress measurements in the main coal bed in the Lüliang mining area were made by the bore hole, stress relief method. From these data the ground stress distribution of the mining area was obtained. The relationship between the horizontal principal stress and the deformation and failure of a roadway is discussed with an engineering example. The results indicate that horizontal stress dominates in the shallow crust in the Lüliang mining area. Roadways at different angles to the maximum principal stress have different levels of stress concentration. This leads to a significant difference in stability of the corresponding roadways. These research results provide an important criterion for determining roadway position and direction, stope layout, and roadway support design.

High temperature affects rocks in a way that changes the physical and mechanical properties of them. The temperature field in rock overlying a high temperature zone has been estimated using experimental research on thermal conductivity of the overlying strata. Numerical analysis software was used to estimate rock thermal conductivity at different temperatures. These estimates were then used with COMSOL Multiphysics to perform a numerical analysis with the heat conduction model. The results show that rock thermal conductivity decreases as the temperature increases and that various lithologies show similar behavior. The thermal conductivity of each rock type differs from the others at a given temperature. Exact values for the temperature distribution in the overlying strata during the process of underground coal gasification are obtained from the numerical simulation. The temperature in the rock changes with the height and direction from the gasifier. Temperature gradients vary for different types of rock. This result provides an important reference for further study of the strength of overlying strata subject to the process of underground coal gasification.

A fully mechanized coal mining with backfilling (FMCMB) provides advantages of safety and efficiency for coal mining under buildings, railways, and water bodies. According to the field geological conditions, we analyzed the controlling effect of strata movement by the waste and fly ash backfilling in FMCMB face. Based on the key strata theory, we established the equivalent mining thickness model, and analyzed the action of the bulk factor of backfilling body to the equivalent mining thickness. In addition, we numerically simulated the controlling function of the strata movement by backfilling bodies with different strength. And the numerical simulation result show that the deformation of stratum and the subsidence of surface can be controlled by FMCMB. The result provides references to the effective execution of fully mechanized coal mining with solid waste backfilling in goaf.

Chemical analysis, methane isothermal adsorption studies, and mercury porosimetry were performed on ten samples taken from the magma intrusion boundary in the Wolonghu coalfield. The physico-chemical properties of coals from the magma intrusion region are compared to those from the normal regions. The results show that the volatile content (V_ad), the limiting adsorption constant (a), and the initial methane diffusion rate of samples from the magma intrusion region are generally smaller than those values from samples from the normal region. The number three coal sample from the magma intrusion region has a large vitrinite reflectance, well developed macropores, a small surface area, and weak methane adsorption capacity. The number ten coal sample from the normal region has a small vitrinite reflectance, well developed micropores, a large surface area, and a strong methane adsorption capacity. The maceral of the coal samples from the magma intrusion region and the normal region are similar. The coal in the area near the magma intrusion boundary is rich in methane and is an area where coal and gas outbursts often occur.

Three drums with different helical angles (15°, 20°, and 25°) were developed to investigate improved loading performance of the shearer drum. Nine trials were performed at different drum rotation speeds (80, 100, and 120 r/min) and different haulage speeds (1.5, 2.0, and 2.5 m/min) in an orthogonal test design. Loaded coal quantity and cutting power of the drum were the responses measured under the different conditions. The effect of the parameters was determined by means of the extreme difference method. The significance of the effects was determined by analysis of variance. The results indicate that the effect from changes in the helical vane on loading performance of the drum is the largest in magnitude. The haulage speed has the least affect on loading performance. The helical angle has the least affect on cutting power of the drum. Haulage speed has the largest affect on the cutting power of the drum.

This study was performed to investigate the effects of the cyclonic separation mechanism on the removal of magnesium from phosphate ore. An analysis of the particle-bubble collision mechanism in a cyclonic force field was used to design two different pulp circulation systems for a cyclonic-static micro-bubble flotation column (FCSMC). Experiments comparing the two conditions were then conducted. Size analysis of the feed and separated products was conducted with a BXF cyclone size analyzer. The results show that about 34.60% of the total MgO content in the feed exists in the −10 μm fraction. This demonstrates that magnesium removal from phosphate ore has the characteristics of a micro-fine particle flotation problem. Under conditions of cyclonic circulation the MgO level of the concentrate is 1.74%, which is lower than that obtained from the column operated in direct-flow circulation by 0.34%. These results indicate that the cyclonic circulation mechanism of the FCSMC can promote removal of micro-fine particles containing magnesium. This is attributed to the function of surface flotation and to the reduction of the lower separation limit under conditions of cyclonic circulation.

The swelling behavior of argillaceous rocks is a complex phenomenon and has been determined using a lot of indexes in the literature. Determining the required modeling indexes that need to be performed requires expensive tests and extensive time in different laboratories. In some of the cases, it is too difficult to find a relation between the effective variables and swelling potential. This paper suggests a method for modeling the time dependent swelling pressure of argillaceous rocks. The trend of short term swelling potential during the first 3 days of the swelling pressure testing is used for modeling the long term swelling pressure of mudstone that is recorded during months. The artificial neural network (ANN) as a power tool is used for modeling this nonlinear and complex behavior. This method enables predicting the swelling potential of argillaceous rocks when the required indexes and also correlation between them is unattainable. This method facilitates the model of all studied samples under a unique formulation.