The Experimental Research On The Damage Evolution And Radon Exhalation Rule Of Sandstone-type Uranium Ore Rock Under Uniaxial Cyclic Loading And Unloading

China's sandstone type uranium ore resources are relatively rich,but in the development and utilization of low hardness of ore,large depth of burial and low permeability of geological conditions,usually take conventional underground mining or mining after infiltration.This kind of underground engineering activity often changes the stress environment of fractured rock mass by repeated loading and unloading.It is of great theoretical and engineering significance to study the damage evolution and radon exhalation of sandstone-type uranium ore rocks under cyclic loading.In this paper,the basic physical and mechanical parameters of sandstone-type uranium ore rocks samples were measured by laboratory test method,and then cyclic loading and unloading experiments were carried out on the samples by different cyclic loading and unloading methods.The strength and deformation characteristics,energy evolution and acoustic emission characteristics of sandstone typeuranium ore rocks were analyzed.Finally,the relationship between the damage degree and the radon exhalation rate of sandstone-type uranium ore rocks under uniaxial cyclic unloading was explored with the accumulated radon concentration measurement experiment.The main research contents are as follows:(1)On the basis of previous studies,sandstone-type uranium ore samples were prepared,and the physical and mechanical parameters of the samples were tested.The results show that it was similar to the relevant mechanical parameters of sandstone and basically meets the test requirements,which provides a basis for subsequent cyclic loading and unloading experiments.(2)The changing trend of dissipative energy of the sample under each cycle was studied,in which the increasing trend is the graded cyclic loading and unloading,while the other two cyclic loading and unloading shows a downward trend.After each cycle loading and unloading,the sudden change of ring count will be a period of time away from the previous one,and continue loading after each mutation will not cause another mutation.This kind of performance appears in the energy parameters at the same time,so the cumulative energy curves basically show a step-by-step rise,showing the Kaiser effect of rocks.(3)For the original sample,the radon exhalation rate was obviously lower than that of the loaded and unloaded sample,mainly because themicrofissure pores of the latter have been expanded in varying degrees due to loading.the calculation results show that the radon exhalation rate of the loaded sample was about 1.5 times of that of the original sample,while the diffusion length and diffusion coefficient decrease.(4)Taking dissipative energy as damage variable,the relationship between sample damage value and radon exhalation rate was analyzed,and it was found that there was a linear relationship between radon exhalation rate and radon exhalation rate,that is,radon exhalation rate increases with the increase of damage value,and the rate of increase remains constant.It was found that the curve of radon exhalation rate on single and double sides with damage value was an inverted S-shaped.There are two mutation points in the change of radon exhalation rate,between which is the "steady period" of radon exhalation rate.(5)The prediction index k was used to redefine the damage degree,and it was preliminarily determined that when the radon exhalation rate of one side was taken as the prediction variable,the internal fracture of the rock mass occurs when the prediction index was greater than 8.9%.