Investigation Into Prediction And Control Of Mining Subsidence Of The Gently Inclined Bedded Ore Body

Abstract:The area of mining subsidence increasing with groudwater overdrafting and mineral resources excessive mining, at present, is serious threats to the human life and property and the surrounding environment. The gypsum is a gently inclined bedded ore body that is characterized by shallow burial, narrow forebody, wide distribution, watered expanding and softening, and mined out the gypsum ore bady is easily to cause the events of mining subsidence. There is little research results on the mechanism of mining subsidence because of the lower price, it is very important to study on the mechanism of mining subsidence. This paper combined use laboratory test, theory anlysis, similar simultion, field test and numerical simulation for analyzing the characters of gypsum ore body, broken mechanism of goaf roof and deformation law of overlying strata, and control measures and prediction method. The main results are as follows:(1) The instantaneous mechanics characteristics of the gypsum standard sample in a natural state and saturated state and the gypsum with six different ratios of height to diameter in a natural state by using RMT-150B rock mechanics testing machine. The laboratory test results show that, the compressive strengths of the gypsum standard sample in a saturated state is79.94%of the gypsum in a natural state, the laboratory test ruesults were used for establishing the theoretical model between strength and dimension effect and its parameters.(2) The rheological mechanics characteristics of the gypsum in a natural state and in a saturated state under step loading by using SAW-2000rock mechanics testing machine. The laboratory test results show that, the stress-strain full curve of the gypsum under step loading is in good agreement with viscoelastic creep curve, the long-term strength of the gypsum in a natural state and in a saturated state is77%and68.8%of its peak strength, and the long-term strength of the gypsum in a saturated state is55%of the peak strength of the gypsum in a natural state.(3) The elastic-viscoelastic correspondence principle was used for establishing the viscoelastic plate mechanics model for analysing critical loading and the formula of the flexural function of the goaf roof, and establishing the brocken criterion of the goaf roof. The suitable room length and interval room span and immediate roof thickness of the mining stope of the gypsum mine are determined. The Burges creep model in FLAC3D programe was used for simulating the creep deformation of the goaf roof and overlying strata, and simulating the bearing capacity of the gypsum pillar at different height to span ratios. The simulate results show that, the subsidence of the goaf roof is slowly grew, gradually separated strata, forming a thin plate bending structure with the time increasing after60days of the ore body mined out, and the goaf roof and overlying strata begin to brocken and the surface appear subsidence at the same time after180days of the ore body mined out, and the goaf roof and the surface begin to collapse as an integrity after360days of the ore body mined out. The gypsum interval pillar begin to brocken and don't support the surrounding rock pressure as the interval pillar span is less than4m.(4) The similar simulation model was estalished based on similarity theory. The simulation results show that, the immediate roof start to produce the vertical fracture and bed separated fissures when the room span is more than10m, the goaf roof and overlying strata begin to separated strata, bent, sunk, brocken and collapsed as an integrity with room span increasing, and the height of the collapse and the height of the transmissive fractured belt of a stope is56m and94.5m, that is18.7times and31.5times of the height of the goaf, and the maximum of the surface subsidence is115cm, and the subsidence coefficient is0.38as the room span is164m.(5) FLAC3D was used for simulating the surface subsidence of the old goaf with different structural parameters and analyzed the factors which is influencing the surface subsidence. The simulating results were used for establishing the ANFIS (adaptive neuro-fuzzy inference system) model for predicting the surface subsidence and the vertical deformation of the roof of the goaf and the fitting and predicting capabilities were analyzed. The ANFIS model was used for predicting the surface subsidence and the vertical deformation of the roof of the goaf of a gypsum mine in Hengshan and the practical surface subsidence and vertical deformation of the roof were measured. The results show that, the accuracies of the fitting results of the surface subsidence and the vertical deformation of the roof by the established ANFIS model amount to96%and98%, and the accuracies of the predicting results of the surface subsidence and the vertical deformation of the roof by the established ANFIS model amount to97%and96%, respectively, and the predicted results of the surface subsidence and the vertical deformation of the roof of the goaf of a gypsum mine by the established ANFIS model and he measured results are in good agreement. The interval pillar span and room span are suitable to4m and10m for the mining stopes of the gypsum mine in Hengshan.(6) The compressive strengths of the backfills of the cemented waste rock with cement and loess with seven different mixture ratios at different solidification durations were measured by using RMT-150B rock mechanics testing machine. In addition, the mechanical parameters for the backfills of the cemented waste rock with cement and loess at the solidification duration of28days were used to simulate the mining and filling processes of test stop by using FLAC3D. Based on the simulation results, the backfills of the cemented waste rock with cement and loess with type C mixture ratio was used to filling in the test stope, and the stress measurements were conducted for the backfills and surrounding rocks. The results show that the compressive strength of the backfill of the cemented waste rock with cement and loess with type C mixture ratio at the solidification duration of28days was larger than2MPa. The stress measurements of the backfills and surrounding rocks in the test stope are in good agreement with the simulation results, which means that the backfills of the cemented waste rock with cement and loess with type C mixture ratio can be used to effectively control the ground pressure in stope mining.(7) FLAC3D was used for simulating the influence of the sufface subsidence and the vertical deformation of the roof with five different backfilling schemes for backfilling the gaof of the gypsum used the cemented waste rock with cement and loess with type C mixture ratio. The simulate results show that, the sufface subsidence and the affected areas and the subsidence coefficient by mining with optimal scheme to backfill the gaof of the gypsum is65.1%and56%and64.6%that the unfilled gaof of the gypsum.