Study On Strata Movement Mechanism In Backfill-strip Mining

Backfill-Strip Mining is a kind of partial backfilling mining method which combines strip mining and filling mining to control the strata movement, recycling underground coal resources in high limit at the same time, it can both meet the demand of the surface deformation control, and save materials, reduce the cost of filling mining materials to meet the needs of a wide range of filling mining to protect the environment. Under the background of resource depletion, a large number of strip pillar stranded, high cost of backfilling, environmental constraints increase with the coal resources mining, the backfill-strip mining has a broad prospect. Based on the research method combining the similar material simulation and numerical simulation and the research theory, the bearing mechanism of the composite support pillar, the strata movement and deformation law of the overlaying strata in the backfill-strip mining, the deformation prediction of the strata and surface movement were studied systematically, the main results achieved are as follows:(1) Monitoring methods of similar material model and numerical simulation method have been improved. the optical image method which can be used for dynamic monitoring was put forward combining Bulb lens, close shot photogrammetry with image recognition technology, huge amounts of high precision backfill-strip mining strata movement and deformation data were obtained. At the same time, the surface contact rules between discrete particles and continuous unit, PFC and FLAC force and displacement of data transmission were established and the coupling analysis of discrete and continuous were achieved by simulating rock fracture and fracture characteristics in the caving zone with PFC and the continuity of the strata movement deformation process with FLAC, which was provided as a powerful research tool for the research of the movement and deformation characteristics of the backfill-strip mining.(2) The movement and deformation characteristics, stress migration regularity and failure forms were studied by particle flow numerical simulation in the process of bearing, the composite support pillar can be divided into 3 groups according to the stability of the isolated coal pillar and support features of the strip pillar in the process of mining. The coupling mechanism of the isolated coal pillar and filling body was revealed from the isolation effect of the coal pillar, lateral restrict with each other, the collaborative support effect of the overlying load. The calculation formulas of different types of the composite support pillar broken zone, the plastic zone and elastic zone width were established based on the limit equilibrium theory, the methods of different kinds of pseudo coal pillar width of safety design were put forward, the theory basis was provided for the pseudo coal pillar stability analysis.(3) According to the similar material simulation, movement and deformation characteristics, failure process and the characteristics of gap analysis were analyzed in two stages of strata movement of the backfill-strip mining, which shows that in the backfill-strip mining, strata sinks like waves when it is closed to the coal seam, while it becomes smooth ladle-shaped until a certain level. According to the structure characteristics of the overburden strata, overburden strata can be divided into little tunnel type caving zone, the wave bending belt and synchronous bending belt, and the strata movement characteristics and space distribution characteristics of the different sagging zone was analyzed. At the same time, dynamic subsidence and subsidence velocity characteristics was analyzed of the overburden strata in the backfill-strip mining, which shows that the unburdened strata exists obvious volatility in the process of dynamic deformation, and the subsidence velocity characteristics of the strata exist time scale effect. On this basis, through the coupling analysis method of the discrete and continuous, the influence degree of the main controlling factors of mining subsidence to the subsidence control is analyzed on the backfill-strip mining.(4) In backfill-strip mining, the composite support pillar and structure strata synergistically control the subsidence of the overlying strata, the main structure strata blocks the breakage of the underlying strata, greatly reducing the space spreading upward, synchronization structure strata cuts off the spread of multiple undulating sinking, making its overlying strata sink as a smooth basin. In view of mining degree, backfill-strip mining divides mined-out area into several extremely incompletely mining area so as to achieve the goal of controlling the surface subsidence.(5) According to the control mechanism of the structure strata, combined with plate model based on elastic foundation and mechanical model of the space layer, strata movement coupling prediction model on the back-filling strip mining is established. At the same time, in order to predict the movement and deformation of the back-filling strip mining on the surface more accurately, equivalent superposition model which is suitable for the characteristics of surface movement and subsidence of the backfill-strip mining is established on the basis of the traditional probability integral method prediction model. Considering the stability of the composite support pillar, the value of the surface movement and deformation and economic benefits of coal pillar mining, the subsidence control design method of the backfill-strip mining is put forward in order to provide a theoretical basis for obtaining accurate strata and surface movement prediction and disaster assessment of the backfill-strip mining.