Investigation Of Analogous Hyperbola Model Of Overburden Movement Induced By Mining

Underground mining will result in overburden movement,stress redistribution,groundwater and gas flowing along the fissures,surface subsidence,etc.The probability integration method has been widely used to predict mining induced surface subsidence.However,the probability integration method is a mathematical method,which cannot explain the mechanism of fundamental rock strata movement,and does not connect the surface subsidence with the roof fracture.In this paper,in order to reveal the mechanism of rock strata movement,some means including similar material simulation experiments,mechanical analysis,numerical simulation and field measurement,were used to investigate the mining induced movement of overburden.The different mechanisms are revealed that the movement boundary of bedrock is similar to an inverted funnel and a funnel shaped subsidence zone for topsoil.Based on the key stratum theory,a new analytical solution,the Analogous Hyperbola Model(AHM),was proposed to describe the movement and damage of overburden.The Analogous Hyperbola Model(AHM)has a revolution of "AHM-H?AHM-S?AFM",as the bedrock weakens.The Distinct Element Method(UDEC)and MDDA(Mining Discontinuous Deformation Analysis)were used to assess the performance of the theoretical model and the Analogous Hyperbola Model(AHM)is verified by field measurement data.The above research can provide some scientific basis for strata control,gas extraction,ground water flowing and mining design.The main research contents and results of the thesis are as follows:(1)Some similar material simulation experiments show that the movement boundary of bedrock is similar to an inverted funnel and a funnel shaped subsidence zone for topsoil.There is a thick and stiff layer in overburden damaged least.(2)Similar material experiments was used to investigate the fracture type of bedrock with different uniaxial compression strength.Uniform loading was used to similate an increase of load on the roof as mining face advancing.The fractured traces of the beams are similar to an inverted funnel.Additionally,the uniaxial compressive strength almost has no influence on the dips of fractured traces.(3)The movement and damage zone of bedrock is similar to an inverted funnel,which may be caused by two main reasons.On one hand,the fractured trace between strata is discontinuous,namely that short cantilever beams occur in bedrock strata.On the other hand,the shape of fractured trace of each layer is similar to an inverted funnel.(4)Fracture mechanics and elastic mechanics are used to analyze the movement of overburden caused by mining.It is revealed that the movement boundary of bedrock is similar to an inverted funnel and a funnel shaped subsidence zone for topsoil.(5)The critical dip angle ?Cr of movement boundary above primary key stratum was obtained.Additionally,the variation of ?Cr was analyzed with an increase of cohesion c,internal friction angle ?,the span of layers above primary key stratum Ls and the thickness of layers above primary key stratum H1.(6)Based on the key stratum theory,the Analogous Hyperbola Model(AHM)was proposed to describe the movement and damage of overburden.The inflection points of Analogous Hyperbola Model is located at level of primary key stratum,namely that the damaged width of primary key stratum is the smallest of overlying strata.The Analogous Hyperbola Model is the further development and application of the key stratum theory.(7)As the thickness and stiffness of primary key stratum decrease,the Analogous Hyperbola Model(AHM)evolves and has three different forms,namely AHM-H,AHM-S and AFM.The requirements of overburden and theoretical prediction of overburden movement for each evolution model were given.(8)The Distinct Element Method(UDEC)was used to assess the performance of the theoretical model.Three subsidence parameters(Smax/T,Sgoaf/Smax,D/H),used to describe surface subsidence trough,agree with statistical field measurements of the South Coalfield in Australia.The surface subsidence and the movement boundary in the overburden are very close to the theoretical predictions.The good match indicates that the Analogous Hyperbola Model is reasonable to some extent.The UDEC was also used to simulate the evolution of Analogous Hyperbola Model(AHM)as the parameters of bedrock weakening.(9)The bulking factor Kp of caved rock masses between the primary key stratum and the coal seam plays an important role on subsidence prediction.As the excavation width increases,the bulking factor Kp experiences three stages:keeping constant,approximate linear reduction and almost keeping constant.This may be because the primary key stratum has not yet fractured at the first stage.As the excavation width increases,the primary key stratum fractures and compresses the caved rock mass.Finally,the caved rock masses cannot be any further compacted.(10)The Mining Discontinuous Deformation Analysis(MDDA)method was developed based on the existing DDA.The developed MDDA can be used to simulate the continuous excavation of mining process and display the realtime stress field and fracture field of overburden.The MDDA was used to simulate the mining induced movement of overlying strata with a thick loosen layer,and the movement boundary of overburden is similar to a hyperbola.(11)The field measurement data of Yanzhou coalfield and Shanbei coalfield were used to verify the Analogous Hyperbola Model(AHM).The theoretical prediction errors are very small,which indicates that the Analogous Hyperbola Model(AHM)is reasonable.