Experimental Study On The Relationship Between Kaiser Effect Of Acoustic Emission And Characteristic Stress Of Red Sandstone

The accurate measurement of the original rock stress is an important prerequisite for safe and efficient mining.At present,the measurement of the original rock stress by using Kaiser effect is one of the most widely used methods,but there is a certain effective range of Kaiser effect.There is a close relationship between the Kaiser effect and the characteristic stress point of rock,which is the boundary point of each crack evolution stage in rock.In order to explore the relationship between Kaiser effect and characteristic stress of rock,this paper takes red sandstone as the research object,and plans to carry out uniaxial compression test and cyclic loading unloading acoustic emission test of different pre stress.The characteristic stress of red sandstone is determined by crack volume strain method,so as to explore the relationship between characteristic stress and Kaiser effect of rock,and the effective range of Kaiser effect of rock is carried out The specific conclusions are as follows:(1)When the loading stress of red sandstone exceeds the cracking stress,the acoustic emission signal is weak,and the acoustic emission event rate,ringing count rate and energy rate are relatively low;when the loading stress is between the cracking stress and damage stress,the acoustic emission signal is significantly enhanced,at this time,the acoustic emission event rate is stable at a higher level,and the acoustic emission ringing count rate and energy rate are stable for a short time When the loading stress exceeds the damage stress,the number of AE events decreases to a certain level and then tends to be flat,the count rate of AE ring increases slowly,and the AE energy rate increases sharply.(2)When the pre stress of red sandstone is less than the cracking stress,there will be obvious crack growth in the rock after the loading stress exceeds the cracking stress,and a large number of acoustic emission signals will be generated.At this time,if the inflection point of the cumulative acoustic emission characteristic parameter change curve is determined as Kaiser effect point,the measurement result will be far greater than the real value.(3)When the pre stress of red sandstone is greater than the cracking stress,the acoustic emission signal will be generated when the loading stress is close to the cracking stress.At this time,if the points corresponding to a large number of acoustic emission characteristic parameters are determined as Kaiser effect points for the first time,the measurement results will be less than the real value.(4)When the pre stress is between the crack closing stress and the crack initiation stress,Kaiser effect is not fully established.When the pre stress is close to the crack closure stress,Kaiser effect will fail.Kaiser effect is effective when the pre stress is close to the crack initiation stress;when the pre stress is between the crack initiation stress and the damage stress,Kaiser effect is obvious,only when the pre stress is close to the damage stress,Kaiser effect may fail;when the pre stress exceeds the damage stress,Kaiser effect fails,and felicity effect appears.The above research results are of great significance for revealing Kaiser effect mechanism and accurately judging Kaiser effect points.