Study On Creep Characteristics Of Granite Under The Action Of In-Situ Leaching Of Ion-Absorbed Rare Earth

Creep characteristics are an important basis for predicting the long-term failure properties of rocks.In the process of in-situ leaching of ionic rare earths,the floor bedrock is leaching by the mother liquor for a long time,which will inevitably lead to complex changes in its related engineering properties,especially including a series of creep mechanical properties represented by long-term strength.These unknown changes may bury potential safety hazards for the follow-up rare earth mine geological environment management and comprehensive land utilization projects.This paper is based on the National Natural Science Foundation of China's "Research on the Macro and Mesoscopic Deterioration Mechanism of Ionic Rare Earth Deposits Bedrock under the Action of Leaching Erosion"(No.51764014),taking granite(base rock of ionic rare earth ore)as the research object,through indoor bedrock leaching erosion simulation test,uniaxial compression and creep test,nuclear magnetic resonance and electron microscope scanning,etc.The basic physical and mechanical properties and meso-structure evolution law of the rock samples with different leaching durations are systematically analyzed,and then the related creep characteristics of the rock samples with different leaching durations are discussed.Attempt to establish an improved Nishihara model model of the bedrock of ion-type rare earth deposits under the action of leaching,and use uniaxial and creep acoustic emission characteristics to verify.The main research conclusions are as follows:(1)The wave speed and quality of the rock samples showed a downward trend in the early stage of leaching,and then began to rise after reaching the lowest value in about 15 days.After leaching for about 30 days until the later stage of leaching,the recovery phenomenon basically tends to be flat.The porosity exhibits the opposite change pattern throughout the leaching period.The change rule of uniaxial compressive strength is more consistent with the change rule of wave speed and mass,but the change rule of elastic modulus shows a certain hysteresis.The lowest value appeared after leaching for about 30 days,and then began to rise,and gradually leveled off until about 45 days.Under the action of leaching erosion,the continuous stress of the rock sample in the stable development stage and the unsteady development stage accounts for an obvious proportion.The failure form generally shows a trend of gradual transformation from brittleness to plasticity,and the meso-structure morphology also simultaneously shows a more consistent dissolution change law.(2)In terms of creep characteristics,the steady creep rate of the rock sample increases significantly with the leaching duration,and the time required to enter the constant-velocity creep stage decreases with the leaching duration.The transient creep method,isochronous stress-strain method and improved steady-state creep rate method were used to obtain the long-term strength of the rock sample under the action of leaching.The results show that the long-term strength obtained by the improved steady-state creep rate method and the isochronous stress-strain curve method are relatively consistent,and the evolution law is basically consistent with the previous research results.The form of creep failure of the rock sample under the action of leaching erosion is mainly shear failure,and the meso-structure morphology characteristics are intensified compared with the uniaxial compression test.(3)Based on the creep test results of rock samples with different leaching durations,an attempt was made to establish an improved Nishihara creep model for the bedrock of ion-type rare earth deposits under the action of leaching erosion.Among them,the elastic element E1 in the Kelvin model is more eroded by leaching,and the fitting coefficient M value related to the leaching time shows a trend of first decreasing,then increasing,and then gentle.It is more consistent with the long-term strength change rule obtained by the creep test.This model can basically reflect the creep characteristics of ionic rare earth bedrock samples with different leaching durations.(4)Based on uniaxial and creep acoustic emission test,the acoustic emission characteristics of the failure process of rock samples with different leaching durations are analyzed.Under the action of leaching erosion,the uniaxial acoustic emission ringing count and energy of the rock sample increased significantly,and the corresponding stress percentage gradually increased when entering a relatively quiet period,and the duration was reduced;Under the action of leaching erosion,the creep acoustic emission ringing count,event number,and energy of the rock sample showed a development trend of falling first,then rising,and then gradually developing.The fractal theory is introduced to calculate the energy fractal dimension D value of the rock samples with different leaching duration during the accelerated creep stage.The overall change law is that it first drops and then fluctuates repeatedly.And it dropped to the minimum when it was about to destroy,after which the order of energy began to continue to increase.The above characteristics can provide a reference for further probing the precursors of creep failure of ionic rare earth ore bedrock under the action of leaching.