Research On Strata Movement Rule And Control In Deep Solid Backfilling Mining

Solid backfilling is a coal mining technology with functions of solid waste emission reduction and surface subsidence control,which is highly instrumental in protecting the environment of coal mines.Due to the long term mining,the coal resources exploitation of our country has step into deep mining stage.However,the current strata movement research achievements of backfilling technology are mainly based on the shallow mining engineering,which limit its application in deep coal resources exploitation.In this thesis,the comprehensive methods combined with similarity simulations,numerical simulations and theory analysis are employed to study the strata movement mechanism of and control method in deep backfilling mining.The main research achievements are as follows:(1)The evolution rules of strata movement,stress distribution and strata destruction of deep solid backfilling mining are numerically analyzed,the results show that: 1)Along with working face being advance,the subsidence increase rate of stratum differs with the rock horizon.According to this feature,the strata subsidence process is divided into three stages,named accelerated sinking,gradual fitting and cooperative bending.2)The strata movement boundary in deep backfilling is approximated to a exponential curve,along with working face being advance,the curve's form evolved from steep to moderate and finally being stable in the strata cooperative bending stage.3)With the advance of the working face,the stress distribution of deep solid filling mining has changed from "single stress arch" to "double stress arch".The bearing stress of coal body near to the goaf has experienced a process of rapid increase-slow release,and the bearing stress of the filling body has been increasing,locally close to the original rock stress level.4)The roof destructions of deep solid backfilling performs to be a form of fixed bearing rock beam failure,and the overburden cracks occur at the mining boundary of each advancing stages.Due to the support of backfills,the roof only produces local fractures within a limited height,and there is no obvious separation between the rock layers.In total,the overburden structure of deep filling mining still can be divided into fracture zones and bending zones in the vertical direction.(2)The influence of different factors on deep backfilling surface subsidence control is numerically analyzed,the results show that: In single working face backfilling,the maximum surface subsidence is approximately linear increase with working face width,mining thickness and backfill porosity,while is linear decrease with backfilling ratio.The influence order of each factors is performed with the range moralization method,the result is concluded as follows: working face width>backfilling ratio>backfilling porosity>mining thickness.(3)The strata subsidence control mechanism of deep solid backfilling is concluded with the simulation results.In deep backfilling mining,the backfills provide a good quality supporting for roofs.Under this supporting condition,the strata within a certain height above the goaf tend to form the “composite subsidence reduction control layers”.Within the “composite subsidence reduction control layers,the stratum subsidence range expands rapidly with the increase of vertical distance to the goaf,such that the stratum subsidence value will quickly descend.While the subsidence range of strata above the subsidence reduction control layers” fluctuate within a narrow extent,and their subsidence reduction effect decreased significantly.(4)Taking the elastic foundation plate as the boundary condition,a three-dimensional integrated model for calculating strata movement and surface subsidence is established based on the spatial layered medium theory.Meanwhile,a two-dimensional integrated model for calculating strata movement and surface subsidence of deep backfilling mining is established with the combination of elastic foundation theory and subsidence space conservation principle.These models are useful for analyzing the deformation of strata in deep solid filling mining.(5)The influence of deep-buried super thick hard stratum on strata movement in large-range deep caving mining is studied with a similarity simulation test.By concluding its strata movement and destruction features,a systematic partial backfilling method is proposed to achieve the regional strata movement.The normal procedures are as follow: distinguishing partial control stratum under the thick hard stratum—calculating the breaking distance(determine the design position of filling surface)— simulation analysis and backfilling parameters adjustment(to meet the surface subsidence control requirements).The influence of different partial backfilling design factors on surface subsidence is also numerically analyzed.The results show that: Under the condition of ensuring the thick-hard rock stratum is not broken,the change of backfilling width and backfilling rate has a great impact on surface subsidence.While the interval width between two backflling workface is limited to the breaking distance of super-thick-hard stratum,the change of its value has relatively little impact on surface subsidence.(6)The surface subsidence prediction method,suitable for deep backfilling mining,is established based on laminated plate mechanical analysis.The computing of mining space functions and prediction parameters for the prediction models are introduced in detail.Finally,combined with the geological and mining conditions of Tangkou 830 mining area,a practical engineering application example of the prediction model is given.