Study On Acoustic Emission And Infrared Radiation Characteristics Of Sandstone Failure Under Dry-wet Cycle

Due to the influence of the groundwater level fluctuation,part of rock mass is always in the periodic humid environment with the alternate cycle of dry and wet.The mechanical properties and failure deformation mechanism of rock under the action of dry-wet cycle are different from those under the normal condition.The dry-wet cycle has a specific "fatigue effect" on the rock mass,and the accumulation of fatigue damage will accelerate the deterioration rate of the rock mass.Finally,it can cause geological disasters.Given the above engineering background,this paper takes sandstone as the research object to study the change of mechanical properties and fracture mechanism of sandstone under dry-wet cycle.In this paper,0,1,2,4,6,8,and 10 dry-wet cycles were carried out firstly,and then acoustic emission(AE)and infrared radiation observation experiments uniaxial compression were carried out.Comparing and analyzing the AE time domain parameters(event rate,energy rate,RA-AF value),frequency domain waveform(original waveform signal,two-dimensional spectrum diagram and dominant frequency)and infrared radiation indicators(frequency histogram,partial degrees and infrared thermal image).The influence of dry-wet cycle on sandstone fracture mechanism is revealed by multi-parameter and multi-angle,and further enrich the critical precursory characteristics of rock failure.The main research results are as follows:(1)By analyzing the physical and mechanical properties of sandstone under different drywet cycles,the results show that dry-wet cycles increase the water absorption of sandstone and deteriorate the uniaxial compressive strength and elastic modulus.With the increase of the number of dry-wet cycles the failure of sandstone gradually changes from obvious brittleness to ductility.(2)The change law of AE time-domain parameters shows that the apparent vacancy in the AE event rate curve near failure can be used as AE precursor information of sandstone fracture.The dry-wet cycles cause AE activity to reach a vigorous level earlier.The dry-wet cycle has an inhibitory effect on the shear crack development of sandstone,and sandstone under different drywet cycle times mainly develop tensile crack,which is consistent with the macroscopic failure pattern of sandstone.(3)The spectrum characteristics of the AE frequency domain show that the dry-wet cycle changes the original waveform signal characteristics and the main existing forms of the spectrum characteristics in the process of sandstone loading.The evolution law of the dominate frequency components of AE after several times dry-wet cycle is more complex.After 6 cycles,the proportion of the characteristic frequency band in each stage change significantly.(4)The dry-wet cycle enhances the sensitivity of infrared radiation in the initial stage of rock loading and changes the response time of crack propagation effect.With the increase of drywet cycle times,the characteristics of anomalous areas on the sandstone surface change.The differential infrared thermal image can observe the spatial distribution of primary pores and sandstone fractures propagation.The quiet period of the partial degrees curve before sandstone failure and the differentiation phenomenon of the differential infrared thermal image can be used as the infrared precursor characteristics of rock failure.(5)With the increase of dry-wet cycles,the AE activity of sandstone in the loading process is gradually intense,while the change of infrared radiation temperature field is gradually slowed down.The latter is more sensitive to the effect of dry-wet cycles.