Porosity model of the goaf based on overlying strata movement and deformation

摘要

In view of the complexity and concealment of goafs, numerical simulations have become an important means for studying the coupling disasters of spontaneous coal combustion and gas. Porosity is an important parameter in the numerical simulation, but this is difficult to detect directly on site, as the current porosity model does not fully reflect the characteristics of "three horizontal areas" and "three vertical zones" in the goaf. To establish a more accurate porosity model which is based on a theory of overlying strata movement, the Sigmoid function was introduced to reflect the distribution characteristics of the "three horizontal areas" in the goaf, and subsidence models of the main roof and overlying strata were established. A model that measures the porosity of the goaf was formulated, which reflects its O-shaped circle characteristics. The accuracy of the theoretical model was verified by obtaining experimental data. The results showed that the main roof subsidence in the natural accumulation area was approximately zero, there was an exponential decrease in the load-affected area, and the maximum subsidence appeared in the compacted area. The descending displacement was very small around the impacted area along the roadway wall. The movement of overlying strata in the fractured zone was controlled by the main roof, and the subsidence of the strata near the roadway wall and the working face was very small. In the vertical direction, the subsidence of the overlying strata decreased as the distance from the mining coal seam increased. The distribution of porosity in the goaf was shaped like a dustpan. In the horizontal direction, the porosity of the natural accumulation area and the impacted area of the roadway wall was the largest. Deep within the goaf, the porosity gradually decreased. The porosity in the fractured zone decreased in the vertical direction in a logarithmic manner. The porosity model proposed in this paper fully reflects the characteristics of the goaf, and provides a more accurate porosity model for the numerical simulation of spontaneous coal combustion and gas coupling disasters in the goaf.