Research On Long-term Stability Mechanism Of Gypsum Ore Pillar Under Blasting Disturbance

The pillar is an important part that determine the stability of the stope area.The stable pillar is damaged by the rheological and blasting disturbance,which may lead to the safety accident caused by instability.The damage evolution law of gypsum ore pillar is studied by means of laboratory tests,theoretical analysis,field measurement and numerical simulation.The main contents and conclusions are as follows:(1)The mechanical tests of ore rock samples are carried out by laboratory tests,and the basic mechanical parameters of gypsum ore samples are obtained.The stress and the strain are used to divide the stress-strain curve stages,which provides the basis for the subsequent research and numerical simulation.(2)Using the RSM-SY5(T)non-metallic acoustic wave detector to monitor the creep tests,the damage law of gypsum specimen is studied from the aspects of strength,deformation and wave velocity.According to the slope of the specimens’ creep curves under different stress levels,the stress is divided into three intervals.The long-term strength of the gypsum specimen is obtained by viscoplastic strain rate method,as well as the damage strength and velocity of the specimens.On the basis of the creep tests,the disturbance conditions at different time intervals are added to analyze disturbance factors on the damage of the specimens.The contribution of disturbance to the deformation of the specimens is prominent.With each unit load in the low and medium stress leves,the creep increment of stable disturbance in the axial direction is about as 6.2 times as the creep increment without disturbance,and the axial creep increment caused by continuous disturbance is about as 1.5 times as that caused by the stable disturbance.(3)In order to study the effect of different stress levels and different intensity disturbance on the damage of gypsum specimens,the rheological disturbance test is carried out.In the low,medium and high stress levels,the gypsum samples are subjected to disturbance of 0.4,0.6 and 0.8 MPa respectively.Increased damage is gradually reduced with the increase of the number of disturbance.The damage caused by the first 100 disturbance is about half of the first 375 disturbance,The damage law of the specimen is fitted by the one-third function,and the correlation coefficient is 0.982.(4)Using the method of sound wave detection to monitor the stability of the pillar under site blasting.The polynomial is used to fit the velocity of the depth of the surrounding rock,and the correlation coefficients are above 0.93.According to the change rate of wave velocity under blasting disturbance,the main influence range is between 125 cm and 225 cm.Not every blasting cause damage,after three blasting,the law of damage of surrounding rock shows an increasing trend.The pillar is damaged after 30 blasting disturbance but is still in a stable state according to the damage law obtained by laboratory tests.(5)The ANSYS workbench is used to simulate the mechanical response caused by blasting disturbance in three different directions from displacement and stress.The amount of roof sinking and the increasement of stress are small.After 30 blasting disturbance,the stress and strain value of the gypsum ore pillar are below the critical value of failure,while the gypsum ore pillar is still in stable state.