Study On Acoustic Emission Mutation Characteristics And Prediction Of Rock Unstable Failure Under Triaxial Compression

Adopting MTS815.02 servo-controlled rock mechanical test system and AE21C detection system, Acoustic Emission (AE) tests of coal and rock under axial and triaxial compression are carried out, AE characteristics and prediction of failure unstable of coal and rock under triaxial compression are extraordinarily studied. Besides, AE tests of coal under creep are carried out, AE regulations of coal under creep are analyzed.The results of AE tests under axial compression indicate that the deformation and fracture of coal and rock samples is paroxysmal. The damage evolution process of primary fracture's compression, new fracture's generation, development and transfixion of rock samples is well reflected by AE parameters characteristics.AE experiments of rock under triaxial compression are always carried out by placing AE detector outside cell, so that is difficult to detect all of real acoustic emission signal, and the detected acoustic emission signal to noise ratio is low. A comprehensive and real AE signal is receipted by developing a new type experimental head that can be placed inside of triaxial cell and equipment modification. In the process of loading, AE activity under triaxial compression is less than that under axial compression, most of the AE activity occurs at the moment of failure. The reason is that the micro-cracks and micro-pores of specimen are compressed, and the integrity of the specimen is strengthened. According to tests results, damage evolution modelσ1=1/2σ3+E(1-DU (Cd)/(C0))εunder triaxial compression is derived based on the total ring counts of AE as damage variable D. The damage evolution process is divided as initial damage stage, damage stable evolution and development stage, damage accelerate development stage and damage failure stage according to the curves of damage-strain of coal and rock. From the analysis of transmission mechanized of wave and AE characteristic parameters, AE signals received from triaxial cell interior is more accurate, direct and less interference by external noise. Through wavelet coefficient decomposition, the time when Lipschitz index a of AE parameter firstly becomes negative on different scales can be used as the prediction time of specimen rupture.The three stages of coal creep rupture is fitted through empirical creep equation, and can be well fitted by the Cubic polynomial ofε(t)=ε0+(1.46E-6)t-(3.38E-9)t2+(2.67E-12)t3 (ε0=0.00796),Correlation coefficient of the three coal samples are 0.916,0.893,0.934.the process of damage evolution in creep can be well reflected by AE characteristics of coal.