Analysis Of Time-dependent Process Of Phosphate Rock Mass Based On Microseismic Activity Characteristics

In order to improve the efficiency of phosphate resource utilization,the scale and depth of underground phosphate mining are gradually increasing,and the geological hazards caused by rock excavation are becoming increasingly prominent in the development of deep phosphate mineral resources.In the process of mining phosphate rock resources,the mining of phosphate rock breaks the original stress balance,causing unloading damage to the surrounding rock.The failure of rock masses at different locations in phosphate mines usually exhibits different time dependent failure characteristics,which directly affects the design of support schemes for the mined area and the construction safety of adjacent areas to be mined.Therefore,conducting research on the characteristics and evolution process of time dependent failure and microseismic activity of phosphate rock masses has important engineering significance for mine safety production and risk management.This article relies on the Shanshuya Underground Phosphate Mine Project to conduct indoor samples in the 303Q1 mining area,including uniaxial compression and shear samples,and analyze the brittle damage characteristics of the rock mass;Drilling camera testing and acoustic testing were conducted in the mining area to analyze the characteristics of rock damage and evolution in the area.Feasibility analysis was conducted for using microseismic monitoring technology to obtain rock fracture signals;A microseismic monitoring system was constructed in the 303Q1 mining area,and real-time microseismic monitoring was carried out for 365 days.Firstly,extracting and identifying rock mass fracture information,analyzing monitoring results,and summarizing the distribution patterns of time,space,and intensity of microseismic activities induced by blasting mining;Based on the statistical analysis of on-site damage and the time characteristics of phosphate rock mass damage,the phosphate rock mass damage was classified and summarized,and the microseismic activity patterns of rock mass damage under different failure modes were analyzed;Based on the on-site rock mass fracture characteristics and microseismic activity information,the evolution process of different rock mass failure modes was analyzed.The main conclusions obtained are as follows:(1)The results of borehole imaging tests on the pillar and roof indicate that the fracture of the roof is most obvious near the hole opening,with rich development of penetrating fractures within 1 meter.The surface of the pillar is severely exfoliated,and there are local blocks and microcracks in the roof.Several months after mining,the internal damage evolution process of the rock mass near the horizontal hole 3 # borehole(Area I)is slow.There are microcracks formed near the hole mouth,and the existing cracks in the hole gradually extend and expand over time.The rock mass in Area IV is damaged in a short time after mining,and the aging failure characteristics of the rock mass in different mining areas are different;(2)The microseismic monitoring system of Shanshuya underground phosphate rock mass was successfully constructed.Using the spatial distribution design of sensors,a spatial gradient from south to north was formed in the mining area.The spatial array of sensors surrounded the mining area.Combined with the field mining information and similar engineering experience,various microseismic signals were extracted during the mining of Shanshuya underground phosphate rock.On the basis of Time–frequency analysis,Accurately identify rock mass fracture signals.The results show that the blasting signal has the characteristic of multi peak superposition,and the rock drilling signal is an intermittent signal with a longer overall duration.However,the duration of a single signal is shorter,and the amplitude of the electrical interference waveform is lower.The composition of the rock fracture waveform is single,with an amplitude ranging from tens to hundreds of millivolts.During the attenuation process,the tail wave is more developed.Accurately identifying different types of microseismic signals can provide data support for subsequent analysis of rock mass fracture characteristics;(3)Extract a total of 2750 microseismic events from May 1,2021 to May 1,2022,and analyze the distribution characteristics of microseismic events in time,space,and intensity.The results show that there are significant differences in the number and energy distribution of microseismic events at different times.The microseismic activity of some rock masses above the mining layer is greater than that of the lower layer,and the upper layer of rock mass is relatively more prone to damage,but microseismic events are mainly small energy events,With a small number of high-energy events,the possibility of strong Rock burst is not high as a whole.After 10 hours of blasting construction,there are still a certain number of microseismic events at different positions in the rock mass,and the timeliness of rock mass fracture is obvious;(4)According to the characteristics of on-site failure timeliness,the failure of phosphate rock mass is mainly divided into three types: intermittent failure,time-delay failure,and immediate failure.Intermittent failure refers to multiple intermittent failures of the rock mass in the same area,where the failure areas intersect in space and mainly occur in layered rock bodies with large goaf areas and roadway spans.Under the action of self weight and blasting vibration,the rock mass undergoes layer by layer failure;Delayed damage refers to the formation of many disturbed cracks during mining in the area,but no obvious damage phenomenon occurs.After a period of time after the mining activity ends,the rock mass cracks gradually connect and cause damage,mostly occurring in the pillar rock mass;Instant failure refers to the occurrence of rock mass failure immediately with mining activities,without obvious time lag characteristics,and often occurs in the thin layer of phosphate rock roof.