Study On Acousitic Emission Characteristics Of Creep Destruction Of Sandstone Under Staged Cyclic Loading And Unloading

In this paper,the normal uniaxial compression creep test of fine sandstone is carried out,and the acoustic emission characteristics of creep failure of small wave and bottom fine sandstone under cyclic loading and unloading conditions are studied.On the basis of the test,the variation of acoustic emission parameters with time,the variation of acoustic emission b value with time and stress level,and the creep changes of the sample in different loading and unloading conditions,stress level and creep stage,the relationship between the creep characteristics of the fine sandstone and the acoustic emission parameters,and the construction of fine sandstone are established.The creep model is proposed,and the acoustic emission prediction method for creep failure of fine sandstone is put for ward.The main conclusions are as follows:(1)Compared with the average compressive strength of the specimen conventional uniaxial compression,the creep failure strength of the fine sandstone samples decreased and the strength decreased to the average uniaxial compressive strength(82.72%-94.16%)under the classified cyclic loading and unloading conditions.(2)Under low stress level,compaction is the main factor in the rock,and this stage has little effect on rock stability.Under high stress level,the internal damage evolution of rock is mainly caused by crack propagation.The amplitude of acoustic emission,the variation of the peak frequency with time and the macroscopic damage of the sample coincide closely with the change of time.The change characteristics of the acoustic emission signal can be used as the basis for predicting the instability of rock fracture.(3)The b value curve of acoustic emission at the initial stage of loading has no obvious change.With the increase of load,the b value of acoustic emission has a obvious decreasing trend.With the further increase of load,the b value of acoustic emission decreases sharply when the sample enters the unstable stage.The rapid decline of B value before acoustic emission can be regarded as a precursor of specimen destruction.(4)The creep strain increment of the specimen increases with the load,and the load instantaneous strain and the unloading recovery strain increase linearly with the increase of load.(5)The generalized Kelvin creep model with 3 parameters is constructed.The minimum fitting value of the specimen is 0.95 under different stress levels.The creep model curves and experimental creep curves of specimens under different stresses show that the model can better describe the creep characteristics of fine sandstone samples.(6)At the loading stage,the constant load stage and the unloading stage,the amplitude of acoustic emission,the peak frequency of acoustic emission,the number of acoustic emission events,the number of aco ustic emission ringing and the acoustic emissio n energy all show the change law of "increase-decrease-rise".The acoustic emission signal in the stage of creep has low frequency and high intensity relative to the loading and unloading stage.Features?(7)The amplitude of acoustic emission increases with the "cluster" shape,and the peak frequency of acoustic emission,the number of acoustic emission events,the number of acoustic emission ringing and the acoustic emission energy increase greatly,which can be used to predict the creep failure of fine sandstone under the condition of classification and unloading.