Dynamic Time-Space Law Of Overburden Instability Motion In Fast Advance Longwall Face

In recent years, the high intensity longwall face of western shallow seam is mainly for fast advancing, large mining space characteristics. In such a large space, fast advancing longwall face, the dynamic time-space law of overburden instability motion and its dynamic change and mutation features important significance for reasonable selection of shield, effectively control of strata and prediction and prevention of roof disasters. Advancing rate is one of the important factors affect mine pressure and also an important guarantee for safe and efficient production of longwall face. Therefore, the research of time-space law of overburden instability motion, mine pressure behave law and its relationship with advancing rate when accelerating advancing rate especially when the advancing rate exceeds 10m/d will provide important technical and theoretical support for safe and efficient exploitation of coal in western coal field of China, white it also has important reference for home and abroad safety and efficient mining which has similar geological conditions.In this paper, field research, statistical analysis, theoretical studies, numerical simulation and similarity simulation methods were integrated used for studying and exploring dynamic time-space law of overburden instability motion of fast advanced longwall face in shallow seam in the western coal field. Western shallow seam mining technology status was summed up, mechanics model of time-space instability motion of overburden under fast advanced rate was established and influence law of advancing rate on the motion of overburden.A three-dimensional numerical model under conditions of fast advanced rate was established using 3DEC numerical simulation software. Dynamic time-space law of the main roof and distribution of motion field of overburden at different mining speed were comparatively analyzed. The analysis results showed that under the condition of a fast mining speed, the horizontal displacement of the measured points within the main roof, the rotation amount of the main roof and the displacement of the main roof are smaller. Accelerate the mining speed will lead to a longer weighting step.Dynamic time-space law of the main roof and distribution of motion field of overburden at different mining speed were comparatively analyzed by similar simulation experiment. Impact of mining speed on the caving step and caving law of immediate roof was studied. Impact of mining speed on the first weighting and periodic pressure of the main roof was studied. As the increase of advancing rate, the first weighting step and periodic weighting step increase. The influence characteristics of the advancing rate on the overburden was revealed by analyzing the velocity field of the overburden. The accelerate of the advancing speed will lead to the increasing of the length of the roof overhang which will lead to the occurrence of dynamic pressure of the longwall face. The subsidence curves of the overburden rock stratification shows a "bifurcation" phenomenon from the lower stratum of the key strata. The mining speed promoted a significant impact on the rotation angle of the key layer. Along the face advance direction, the overburden of the face can be divided into a stable area, slow settling zone, accelerate subsidence area and pre-movement zone. Advance rate sensitive area is mainly located in the accelerate subsidence area which is rear the face in the range of 50 m. In the case of advance faster, rotation angle of the overburden decreases which slower the upper strata of bending down and the rock integrity sinking becomes more obvious.A logistic S-curve dynamic settlement model was establishment by theoretical analysis. According to this model, we deduced dynamic time-space impact formula of subsidence movement of the overburden. Combining similar simulation results, the time-space movement model was established of the overburden. Based on the characteristics of the overburden mining speed sensitive area, the mining speed sensitive factor Kv was introduced which revealed the impact mechanism of advancing speed on the longwall face pressure.Field data analysis showed that the weighting step and the weighting range increased with the face advancing speed increases, while the dynamic load coefficient decreases with the increase rate of face advance. The central pressure along the longwall is greater than the pressure at both ends and decreases with the face advance rate increases. In the actual production of coal mining, it should be combined with the influence of the speed of advance on underground pressure, select the appropriate advancement speed to effectively reduce the impact of face pressure to ensure safely and efficiently produce.