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In order to study the deformation and failure mechanism of the roof in end slope mining, a mechanical model of the two-end fixed beam was established, combined with the theory of elasticity to derive the calculation equations for the stress and displacement of the roof, and to consider the effect of the extrusion of the overlying weak rock layer of the rib pillar on the deformation of the roof, and finally, the analysis obtained the stress distribution and deformation law of the roof. The research shows that the distribution of normal stresses in the roof is parabolic with a secondary axisymmetric distribution at the center of the roadway, and the maximum tensile stress is at the center of the bottom of the roadway. The maximum tensile stress and the maximum shear stress on the roof increase continuously with the increase of mining progress. The location of the middle of the bottom surface of the roof first shows tensile failure, and then gradually changes to shear failure at the contact location with the coal pillars. The value of u at the bottom of the roof rock beam shows a trend of first decreasing, then increasing, and finally decreasing as x increases, but lateral extrusion has little effect on the horizontal displacement of the roof. The displacement component ν of the roof shows a parabolic variation law with x opening upward. The absolute value of displacement |ν| considering the simultaneous action of vertical compression and lateral extrusion is the most obvious.

In-situ experiments were conducted to investigate the mechanical properties of the soil-rock mixture in the internal dump of the Shengli #1 Surface Coal Mine, China. Based on the experimental results, this study used comparative analysis and found that the shear strength of the soil-rock mixture in the dump was greater than the residual shear strength of the original rock. The results showed that the material presented in the dump as large blocks was the main factor affecting the strength of the soil-rock mixture. Numerical simulation was carried out for the analyses of three factors: different combinations of shear failure, rolling failure along with different large-block radius ratios, and mixture densities. The results illustrated that the cohesion and angle of internal friction of the soil-rock mixture are 12 kPa and 32.26°. However, in some cases the bench angle in the dump was controlled by a coupling relationship of rocks in the material. Finally, the stability of a soil slope showed a linear relationship with the large-block radius ratio and the bulk density. Keywords: Surface coal mine, Soil-rock mixture, Residual strength, In-situ experiment, Mechanical model

The non-uniformly distributed calcareous concretion among the oil shale in the Junggar basin of China has led to the difficulty in achieving the slope stability. This paper presents the numerical simulation of the behavior of oil shale with calcareous concretion via the Particle Flow Code (PFC2D) program based on the trial experimental test results. The critical parameters investigated in this research covered the size, distribution, strength, and number of the calcareous concretion. The following conclusions can be drawn based on the discussions and analysis: (1) the hard concretion always results in the high compressive strength of the specimen compared with that without concretion; (2) when the radius of the concretion size raised from 2.5 mm to 20 mm, the peak strength of tested specimens is approximately 50 MPa, whereas, the specimen with large concretion is much more ductile under compression; (3) the compressive behavior of tested specimens is similar even when the position of the concretion is variable; and (4) different from the specimens with only one concretion, these specimens contained two concretions featured with the double "X" failure mode. Meanwhile, the peak strength of the specimens with two hard concretions is about 2.5 times that of its counterparts with two soft concretions. The numerical simulation results are meaningful in guiding the design and analysis of the oil shale slope with the concretion. [ABSTRACT FROM AUTHOR]

In order to study the stability difference of dump slope under different pore water pressure redistribution and evaluate the stability, according to the actual groundwater level distribution of a mine dump from August to September, the influence mechanism of water pressure redistribution on slope stability is analyzed. SLOPE/W module is used to simulate the slope stability difference and safety factor variation under different pore water pressure distribution. The results show that the redistribution of pore water pressure will change the pore space in the slope, accelerate the infiltration, and weaken the slope of waste dump in different degrees. With the decrease and expansion of the negative pore water pressure distribution range, the matrix suction of the slope changes and the safety factor first decreases and then increases. When the slope safety factor increases to 1.421, the groundwater level decreases by 30 m. It is close to the basement as a whole and will no longer affect the slope stability of waste dump.