Study On Technological System Of Reducing Surface Subsidence By Injecting Grouts Into Separated Strata In Overburden Under Strip Mining

This thesis is supported by the key science and technology planning project of Hunan province: studying on the green and safe mining technology system in south collieries. On the basis of strip mining and the technology of reducing subsidence by injecting grouts into separate strata, the technology system which couples injecting grouts into separate strata in the overburden and strip mining to improve recovery ratio and the reducing subsidence effect is studied by methods of theory analysis, numerical simulation and engineering examples.Based on the structural characteristic of coal-bearing sequences and the movement characteristic roof overburden, the whole overburden structure is regarded as a composite medium beam with two fixed ends. Considerating differences of physical and mechanical properties among rock strata, the discriminant of key strata in the overburden is educed with elastic beam theory and key strata theory. The discriminant conquers the errors and inconvenience of the original discriminant.The dynamic movement law of overlying strata, the dynamic change laws of stress fileds distribution, the generation process and expanding rule of separated strata, and the instability process of strip pillar are studied with numerical simulation. The production mechanism and conditions of separated strata, the influence factors of separated stratum, the calculation of separated stratum position, the stability of strip pillar and its discriminance and the designing methods of strip sizes are also studied according to the results of numerical simulation and the previous research achievements. Based on the impact of mining on separated stratum, separated stratum before beginning to colse is described as the separated stratum uder non-full extraction, the separated stratum under full extraction and the separated stratum under superfull extraction. Dialectical relationships among separated strata, surface subsidence basin and vacant area are disclosed, which plays an important role in injecting grouts into separated strata to control strata movement.The overburden is abbreviated as a composite slab structure, and each rock stratum is regarded as a rectangular slab with four simply supported edges under homogeneous load. The calculation formulas of the load of rock slab and characteristic values of separated strata are educed by using the elastic slab theory, which has much significance in calculating grouting quantity and estimating grouting effect.The dynamic model of injecting grouts into separated strata to reduce subsidence is proposed, and at the same time, a new consideration on reducing subsidence mechanism is obtained. It is considered that injecting grouts into separated strata reduces partial space of separate strata and latent subsidence range.A new method of controlling surface subsidence, i.e. the technology of reducing surface subsidence by injecting grouts into separated strata in overburden under strip mining is proposed according to the respective mechanism and propertities of partial mining method and mining method with backfill.