In order to solve the difficult problem of coal wall spalling of soft seam in deep mining, the occurrence mechanism of coal wall spalling in deep mining is studied based on the limit equilibrium theory of D‐P criterion. Through the analysis of the formula of plastic zone, it can be concluded that the coal wall spalling of soft coal seam is related to mining depth, mining height, stress concentration factor, internal friction angle of coal, cohesion, and the compressive strength of coal body. Also, the change of uniaxial compressive strength of soft coal with different moisture content is studied through laboratory experiments. The experimental results show that the uniaxial compressive strength of soft coal reaches the maximum value when the moisture content is about 3.3%. The comprehensive research shows that the cohesion and strength of coal mass can be improved by increasing the working resistance of support, water injection in advanced deep‐hole coal seam of two roadways, and pre‐grouting in shallow hole of coal wall. The control measures can effectively control the coal wall spalling of soft coal seam. The research results have important guiding significance for safe and efficient mining of soft coal seam.

The deformation and instability of roadway surrounding rock reflect the processes of energy accumulation and release. To reveal the instability of roadway surrounding rock, based on the engineering geological conditions of a certain mine, this paper established a nonuniform superimposed stress model of a coal pillar, starting from the energy accumulation and release of the surrounding rock of the floor roadway after coal pillar failure. The essence of the deformation of the lower roadway was revealed, and the following conclusions were drawn: (1) The elastic strain energy accumulated in the lower roadway roof and upper coal pillar is related to not only the physical properties of the coal seam but also the distance between the coal pillar and surrounding rock, the caving height and shape, the burial depth, and the retained pillar width. (2) The elastic strain energy accumulated in the lower roadway roof and the upper coal pillar induced large displacements of the roadway due to the energy release during excavation. (3) It is proposed that the “stress relief degree” and failure morphology are used to identify zones in the rock and coal, and the two zoning modes have a high consistency. (4) The stress distribution in a narrow coal pillar should be calculated in segments. (5) Based on the zoning and energy release characteristics, the following control factors are suggested regarding the coal pillar width and roadway layout: (a) for the coal pillar, avoid the overlap or intersection of the peak values in the limit equilibrium zone and ensure a sufficient elastic zone; (b) arrange the roadway in shear slip Zone B‐2 or the moderate pressure relief Zone B‐2 to reduce the accumulation of elastic strain energy in the surrounding rock.

This paper presents an integrated approach for mathematical statistics, theoretical analysis, and a field test to investigate the distribution law of in-situ stress and its engineering practice of rock burst control. The test site is located in the Juye mining area, Shandong Province, China. The main conclusions included: (1) There are two types of in-situ stress states in the Juye mining area, σ_H > σ_V > σ_h (42.42%) and σ_H > σ_h > σ_V (57.57%), which are mainly caused by the tectonic stress of the Heze and Fushan faults (The σ_H, σ_V, and σ_h is the maximum principal stress, vertical principal stress or intermediate principal stress and minimum principal stress respectively). (2) The lateral pressure coefficients K_H, K_h, and K_av show a non-linear distribution with increased depth, approaching 1.32, 0.96, and 1.41, respectively. The variation range of the horizontal difference stress μ_d is 0.09–0.58. (3) The average value of the stress gradient is 3.05 MPa/100 m, and the main directions of the maximum horizontal principal stress are northeast–southwest, and northwest–southeast. (4) A new combined supporting strategy, incorporating optimization of roadway layout, anti-impact support system design, and local reasonable pressure relief, was proposed for the rock burst control, and its validity was verified via field monitoring. All these design principles and support strategies for the rock burst control presented in this study can potentially be applied to other similar projects.

Coal samples having the same diameter (50 mm) and different length-diameter ratios (l/d), i.e., 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 were tested under dynamic uniaxial impact compression using the Split Hopkinson Pressure Bar (SHPB) experimental system. This study evaluates: (a) The effects of l/d on the energy consumption law and fractal characteristics of coal crushing; (b) The effects of l/d and stress balance on energy dissipation; (c) The effects of l/d and energy consumption density on the fractal characteristics of coal crushing. The findings under different l/d are as follows: (1) The coal samples show similar stress–strain curve shapes in stages including elastic, plastic, and failure stage, which is an “open” shape, the proportion of plastic stage increases, and strain-softening occurs; (2) The dynamic compression dissipation energy and energy consumption ratio of coal shows the same trend, showing two stages with the increase of length-diameter ratio, which increases linearly in the first stage and overall decreases step-by-step; (3) The average particle size increases while fractal dimension of fragmentation decreases linearly, which endorses the decreasing trend of fragmentation degree; (4) It is determined that there is a power relationship between fractal dimension and energy dissipation density; (5) A new index Crushing Density Energy Efficiency (CDEE) is proposed, which can be used to characterize the rock-breaking efficiency of crushing energy consumption under different conditions. This index is inversely proportional to l/d. The research results can provide a basis for the design of top coal caving mining, and the determination of blasting parameters.

In this study, a uniaxial impact compression test was performed on coal samples with length‐to‐diameter (L/D) ratios of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 using a Φ 50 mm split Hopkinson pressure bar (SHPB) test system. This study researched the stress uniformity and deformation behavior of coal samples with different (L/D) ratios during dynamic compression, defined the stress equilibrium coefficient ξ, proposed a new method for determining whether a sample meets the stress uniformity hypothesis, and obtained the critical (L/D) ratio of 0.6 and the optimal (L/D) ratio of 0.3 or 0.4 for coal samples to obtain the stress equilibrium. The experimental results showed that the dynamic stress‐strain curve of coal had an elastic stage, a plastic stage, and a failure stage. As the (L/D) ratio increased, the proportion of the elastic stage to the prepeak curve of the samples declined progressively; with an increase in the (L/D) ratio, the peak part of the curve also changed from “sharp” to “stagnated,” while an increase in the plasticity led to strain softening. As the (L/D) ratio of the samples increased, the average strain rate decreased approximately as a power function, and the decreasing trend was gradually reduced from 296.49 s⁻¹ (L/D=0.3) to 102.85 s⁻¹ (L/D=1), with a reduction of approximately 65.31%. With an increase in the L/D ratio, the peak strain gradually decreased exponentially. This study concluded that the SHPB test protocol design is of a certain reference value for low‐density, low‐strength, heterogeneous brittle materials, such as coal.