Abstract: To prevent structural catastrophic responses induced by the collapse of the roof in goafs, based on field investigations and considering the impact disturbance behavior of roof collapses in goafs on the floor, a structural response model for the impact of goaf collapses on the floor and a dynamic response governing equation are established. The characteristics and attenuation laws of the structural response of the floor in goaf groups are studied, and the effects of factors such as joint density and thickness-to-span ratio on the displacement and stress response of the floor are analyzed, revealing the characteristics of its structural response. The results show that with the increase of the distance, the displacement and stress of the floor attenuation gradually and the attenuation rate decreases under the impact load. The response of floor is affected by the collapse position, distance and surrounding rock. As the collapsed goaf is closer to the center, the displacement and stress attenuation rates of the floor are smaller, and the impact and damage to the surrounding goafs are more extensive. With an increase in joint density, the stiffness, vibration frequency, and energy dissipation rate of the floor decrease, while the peak values of displacement and tensile stress show an increasing trend, leading to a reduction in impact deformation resistance and stability. As the thickness-to-span ratio increases, the peak values of displacement and tensile stress of the floor decrease exponentially. A significant inflection point appears when the thickness-to-span ratio is 0.6, with the attenuation rate differing by more than 10 times. Increasing the thickness-to-span ratio of the floor can shorten the response time, reduce displacement and tensile stress, and improve the stability of the floor. The reliability of the theoretical method is verified by numerical methods. The research results can provide some theoretical support for the safe production and disaster prevention and control in open stope mining method.

Key words: goaf group, collapse roof, multi-level goafs, structural response, impact load