The influence of advance speed on overburden movement characteristics in longwall coal mining: insight from theoretical analysis and physical simulation

The advance speed of a longwall face is an essential factor affecting the mining pressure and overburden movement, and an effective approach for choosing a reasonable advance speed to realise coal mine safety and efficient production is needed. To clarify the influence of advance speed on the overburden movement law of a fully mechanised longwall face, a time-space subsidence model of overburden movement is established by the continuous medium analysis method. The movement law of overburden in terms of the advance speed is obtained, and mining stress characteristics at different advance speeds are reasonably explained. The theoretical results of this model are further verified by a physical simulation experiment. The results support the following conclusions. (i) With increasing advance speed of the longwall face, the first (periodic) rupture interval of the main roof and the key stratum increase, while the subsidence of the roof, the fracture angle and the rotation angle of the roof decrease. (ii) With increasing advance speed, the roof displacement range decreases gradually, and the influence range of the advance speed on the roof subsidence is 75 m behind the longwall face. (iii) An increase in the advance speed of the longwall face from 4.89 to 15.23 m/d (daily advancing of the longwall face) results in a 3.28% increase in the impact load caused by the sliding instability of the fractured rock of the main roof and a 5.79% decrease in the additional load caused by the rotation of the main roof, ultimately resulting in a 9.63% increase in the average dynamic load coefficient of the support. The roof subsidence model based on advance speed is proposed to provide theoretical support for rational mining design and mining-pressure-control early warning for a fully mechanised longwall face.

Automated summary

As the advance speed of the longwall face increases, the first (periodic) rupture interval of the main roof and key stratum increases, while roof subsidence, fracture angle, and rotation angle decrease. Additionally, with increasing advance speed, the range of roof displacement gradually decreases, and the impact range of the advance speed on roof subsidence is 75 meters behind the longwall face. Increasing the advance speed of the longwall face results in a 3.28% increase in impact load from sliding instability of fractured rock in the main roof, while causing a 5.79% decrease in additional load from roof rotation, ultimately leading to a 9.63% increase in the average dynamic load coefficient of support.