Taking gob-side entry retaining with large mining height (GER-LMH) of the 4211 panel in the Liujiazhuang coal mine as the engineering background, a numerical simulation was conducted to study the surrounding rock deformation, stress, and plastic zone distribution of GER-LMH with respect to retained entry width. The concept of critical retained entry width of GER-LMH was proposed. In view of the deformation characteristics of surrounding rock, an innovative approach to determine the critical width of GER-LMH based on the cusp catastrophe theory was proposed. The cusp catastrophe functions were set up by approximate roadside backfill body rib convergence and roof subsidence series with respect to different retained entry widths. The critical retained entry width of GER-LMH was 4.0 m according to bifurcation set equations. Surrounding rock stability control principle and technique of GER-LMH was proposed, including “rib strengthening and roof control”: road-in support with high pre-stress rockbolts and anchor cables, roadside backfill body construction technology with high-water quick consolidated filling materials and counter-pulled rockbolt, road-in reinforced support technology with hydraulic prop support and roof master. Field test and field monitoring results show that GER-LMH with supercritical retained entry width in the 4211 panel could meet the requirements for ventilation when the 4211 panel was retreating.

Based on the analysis of the monitoring data of surface displacement and internal multipoint displacement of coal pillars near three inclined strata roadways, which have similar burial depth and different surrounding rock conditions in a coal mine in the east China, the coal pillars' stress change was combined with discontinuous numerical simulation software to simulate the deformation process of one of the roadways. Field monitoring data and numerical simulation results show that when this working face roadway is dug, the coal pillar enters plastic state after being affected by multiple mining influence, but it can still maintain the basic stability of the roadway and control coal pillar deformation under the current widely used supporting method. With the shortening of the distance between the monitoring area and the working face, the vertical and horizontal stress in the coal pillar increase gradually, but the maximum value of the vertical stress decreases by 1.4 MPa, and deformation amount and velocity of the coal pillar show the characteristics of nonlinear rapid increase. The shape of the vertical stress core area in the coal pillar changed from oval to rectangle, and the width of the core area increased, and it moved 1 m to the goaf side. In the process of coal pillar deformation, there is no zero displacement surface within the monitoring range of 6 m. K E Y W O R D Scoal pillar deformation, ground control, numerical simulation, stress concentration | 545 WU et al.

Taking a deep-mine horizontal roadway in inclined strata as our research object, the true triaxial simulation technique was used to establish a model of the inclined strata and carry out high-stress triaxial loading experiments. The experimental results show that the deformation of surrounding rock in the roadway presents heterogeneous deformation characteristics in time and space: the deformation of the surrounding rock at different positions of the roadway occurs at different times. In the process of deformation of the surrounding rock, deformation and failure occur at the floor of the roadway first, followed by the lower shoulder-angle of the roadway, and finally the rest of the roadway. The deformation amount in the various areas is different. The floor heave deformation of the roadway floor is the greatest and shows obvious left-right asymmetry. The deformation of the higher side is greater than that of the lower side. The model disassembly shows that the development of cracks in the surrounding rock is characterized by more cracks on the higher side and fewer cracks on the lower side but shows larger cracks across the width. The experimental results of high-stress deformation of the surrounding rock are helpful in the design of supports, the reinforcement scheme, and the parameter optimization of roadways in high-stress-inclined rock, and to improve the stability control of deep high-stress roadways.

No abstract

In order to study the influence of burial depth on the roadway deformation, the deformation data of more than 100 roadways were collected and classified. The results have shown that, in the first 5 days of new digging roadways, the surrounding rock deformation is basically not affected by the buried depth. The influence period of roadway deformation with different depths is the same, namely, the severe period (1∼15 days), the mitigation period (15∼35 days), and the stable period (35∼50 days). With the increase in depth, the surrounding rock deformation increment of new digging roadways with a depth of 300∼600 m is much larger than that of 600∼900 m. Within 100 m of the working face from the monitoring point, the deformation of mining roadways can be divided into two stages: severe impact (10∼60 m) and stable impact (60∼100 m). With the increase in depth, the deformation increment of the surrounding rock in the mining roadways with a depth of 600∼900 m is much larger than that of 300∼600 m. The surrounding rock deformation increases with the increase in the width and height of roadways and gradually increases with the decrease in the strength of rock mass.