Study On Roof Stability Of Goaf With Hard Surrounding Rock

The stability of goaf roof in hard surrounding rock is a comprehensive reflection of its integrity,deformation characteristics,strength and stress state.Its influencing factors are various and its influencing mechanism is complex,which makes the goaf roof have the characteristics of structural discontinuity,mechanical property dispersion and stress load uncertainty.Therefore,the stability of goaf roof in hard surrounding rock is a very complex study,and many conditions must be considered.Taking Xinpu Phosphate Mine as an example,this paper studies the influencing factors,failure mode and failure mechanism of the roof stability of the goaf with hard surrounding rock,analyzes the calculation method of the safe thickness and limit span of the roof with hard surrounding rock and the stability evaluation of the roof.The research results of this paper have reference significance for the study of goaf roof of the same type of hard surrounding rock.The main research results are as follows:(1)Based on the influencing factors of the stability of the goaf roof and the failure mechanism of the roof failure mode,the hard surrounding rock roof of Xinpu Phosphate Mine is analyzed and studied.The main influencing factors of the hard surrounding rock roof of Xinpu Phosphate Mine are the roof span and thickness in the geometric parameters of the goaf,the main failure mode is brittle failure,and the failure mode is barrel failure mode.(2)The physical and mechanical parameters of the roof rock are measured through the indoor test.Four calculation methods are adopted: structural mechanics beam plate theory method,thickness span ratio method,load transfer line intersection method and Proctor arch theory method.The relationship between the safe thickness and span of the hard surrounding rock roof in Xinpu Phosphate Mine is analyzed and studied,and the relationship between the safe thickness and span of the roof is plotted.Based on the analysis of the actual mining situation in the goaf of Xinpu Phosphate Mine,the safe thickness and limit span of the roof in each middle section of the goaf are obtained.(3)According to the actual mining situation of Xinpu Phosphate Mine,the geological model of goaf roof is established,and the geological model is transformed into numerical model.The stress distribution of roof after mining is inversed by software simulation,and the obvious tensile stress concentration phenomenon in the middle of roof is obtained.After analyzing the simulation results,it is found that with the increase of roof span in goaf,the tensile stress in the middle of roof gradually increases;with the increase of roof thickness,the limit span of roof also increases.Based on the analysis of theoretical calculation and numerical simulation results,it is considered that the theoretical calculation method of structural mechanics beam plate is more suitable for the calculation of safe thickness and limit span of roof in goaf of hard surrounding rock in Xinpu Phosphate Mine.(4)The stability of roof depends on its span.When the roof is in the current span,the span of roof meets the safety requirements,and the roof is stable.The roof of-120 m middle section and-200 M middle section collapsed locally,forming collapse pit on the surface of the study area.Based on the analysis and study of the actual mining situation and roof stability of the two middle sections,it is inferred that the ground collapse is caused by the influence of underground mining,blasting activities and surrounding construction activities.Some adjacent pillars are damaged and lose their supporting capacity,resulting in the roof reaching the limit span and local collapse,forming a funnel-shaped collapse pit on the surface.