Effect Of Loading Rate On Rock Mechanics Interval Intensity And Acoustic Emission Effect

In the actual projects,the rock is often disturbed by dynamic loads such as earthquakes,rockbursts and blasting vibrations.The these dynamic disturbances is complex and variable which will deeply influence the mechanical properties and the damage process of the rock.Theoretical and experimental studies have shown that the uniaxial compressive strength and damage rupture process of different rocks will exhibit different change laws under different disturbances with different loading rates.Therefore,the change of uniaxial compressive strength and damage rupture characteristics of various rock under different loading rates are studied.It can not only provide theoretical basis for the study about the change rule of rocks' mechanical strength characteristics under different loading rate in engineering,but also play an important guiding role in making a new and exact loading rate standard of various rock in rock mechanics strength test.Based on the RMT-150 B rock mechanics test system and acoustic emission signal acquisition system,the uniaxial compression and acoustic emission test of rock under five levels loading rate are carried out for the reasearch on the selection of suitable loading rate and the laws of acoustic emission characteristics under multi-stage loading rate.After the experiment,some conclusions are obtained and shown as follow:(1)The loading rate doesn't make much effect on the elastic modulus.The higher the uniaxial compressive strength of the rock is,the larger the elastic modulus will be.There exists an extreme point of the loading rate for rock materials such as strength granite,limestone and marble with strength ranging from 110 to 200 MPa.Before reaching the velocity point,the strength is positively correlated with the velocity.After reaching the velocity point,they are negatively correlated.At this rate extreme point,the uniaxial compressive strength of the rock is maximum.For the sandstones with strengths ranging from 80 to 100 MPa,the loading rate increases,the compressive strength decreases.(2)In the uniaxial compression experiment,the reasonable loading rate of the limestone rock material of 150~200MPa is 0.002~0.006mm/s or 0.019~0.020mm/s,and the error is within 5%.The reasonable loading rate of the marble rock material of 130 ~150MPa is 0.002~0.005mm/s or 0.019~0.020mm/s and the error is within 2.5%.The granite rock material of 110~130MPa should use the loading rate of 0.003~0.008mm/s,which the error is also within 2.5%.For the sandstone rock materials of 80~100MPa,the reasonable range of loading rate is 0.003~0.009mm/s and 0.015~0.017mm/s,and the error value is about 2.5%.For the four rock materials,the maximum uniaxial compressive strength can be obtained when the loading respectively are 0.013mm/s,0.013mm/s,0.015mm/ s and 0.001mm/s.(3)Under the same loading rate,the higher the rock strength is,the more characteristic of low frequency and high amplitude that the ringing count and energy release will have.The lower the rock strength is,the higher frequency of the ringing count and energy release will be.As for the granite,limestone and marble of 110~200MPa,the larger loading rate is,the later cracking will be.For the sandstone of 80~100MPa,the bigger loading rate is,the earlier cracking will be.(4)During the uniaxial compression process of rock,the ringing count can be divided into four stages with different characteristics,namely the rock coMPaction section of the basic silent emission event activity,and the elastic deformation section which starts the cracking to generate the acoustic emission activity.The launching activity is intensified,the damage phase with more internal rupture events in the rock,and the calming period before the peak.