Continuous Caving Mechanisation Of Gypsum Ore Goaf Under Thick Layer Limestone

In recent years,many mines have failed to be effectively dealt with because of the gobs left after the mining was completed,and accidents have occurred in the goafs.This paper takes the Yurong gypsum deposit in Shandong Province as the research background,and conducts theoretical analysis,experimental research and numerical simulation on the process of gypsum mine accidents.The mechanism of successive fall of gypsum mine gob down under thick limestone is studied.The results have a certain guiding significance for the safety management of gypsum mines.The gypsum rock specimen finely machined to meet the test conditions was selected at the site.The uniaxial compression test,creep test,and dynamic perturbation creep test were performed.The test characteristics and basic creep theory of the test piece were combined.An improved Burgers body creep constitutive model was established.In order to investigate the influence of axial pressure and the number of disturbances on the creep of gypsum rock,40%,60%,and 80%of the uniaxial compressive strength was applied to the specimens respectively,and low-intensity disturbances with different numbers of disturbances were applied,the FLAC^3D numerical simulation software was used to simulate the stress,displacement and plasticity area of the gypsum rock after dynamic disturbance,and the sequential falling process was concluded.This article mainly draws the following conclusions:?1?Under the same stress,the transverse deformation produced by the specimen is more obvious than the axial deformation.The time for the test piece to enter the stable creep stage is positively related to the stress,and the resulting transverse strain variable is inversely proportional to the axial strain amount.The longer the creep time,the higher the degree of nonlinearity.?2?When the number of disturbances is constant,the greater the axial pressure,the greater the incremental damage,and the greater the cumulative damage of the specimen.With the increase of the number of disturbances,the cumulative growth rate of cumulative damage is reduced logarithmically.The total growth rate also decreased,and the total amount of damage increased exponentially.?3?Seismic waves are transmitted to the stope due to lack of shear strength of the top layer and the upper shale,which makes the protective top layer fall off and the shale on the top plate hangs.The nature of the shale rock mass cannot withstand a large area of suspension,so when the shedding area of the shale layer gradually increases,the shale breaks and the upper shale layer of the pillar is squeezed out due to the lack of tensile strength.Causes the top layer of protection and the shale layer to collapse,leaving only the limestone layer.At this time,the limestone is equivalent to simply supported beam.When the actual span of the limestone is greater than the limit span,the limestone breaks and the generated energy is transferred to the neighboring mine house and circulates until the energy generated by the seismic wave is insufficient to destroy the mine.It reveals the entire sequence of falling off of the fracture of the protection top layer-the shale layer suspension-the shale extrusion-the limestone layer fracture.