Research on AE waveform characteristics of rock mass under uniaxial
loading based on Hilbert-Huang transform (HHT)
Abstract
Acoustic Emission (AE) waveforms contain information on microscopic
structural features that can be related with damage of coal and rock
masses. In this paper the Hilbert-Huang transform (HHT) method is used
to obtain detailed structural characteristics of coal and rock masses
associated with damage, at different loading stages, from the analyses
of the characteristics of AE waveforms. The results show that the HHT
method can be used to decompose the target waveform into multiple
intrinsic mode function (IMF) components, with the energy mainly
concentrated in the c1-c4 IMF components, and where the c1 component has
the highest frequency and the largest amount of energy. As the loading
continues, the proportion of energy occupied by the low-frequency IMF
component shows an increasing trend. In the initial compaction stage,
the Hilbert marginal spectrum is mainly concentrated in the low
frequencies between 0-40KHz. The plastic deformation stage is associated
to energy accumulation in the 0-25KHz and 200-350KHz frequency ranges,
while the instability damage stage is mainly concentrated in the 0-25KHz
frequency range. At 20KHz, the instability damage reaches its maximum
value. There is a relatively clear instantaneous energy peak at each
stage, albeit being more distinct at the beginning and at the end of the
compaction phase. Since the effective duration of the waveform is short,
its resulting energy is small, and so the relatively high value from the
instantaneous energy peak, at the time of destruction, is relatively
long lasting and is where the waveform reaches its maximum energy value.
The Hilbert three-dimensional energy spectrum is generally zero in the
region where the real energy is zero. In addition, its energy spectrum
is intermittent rather than continuous. It is therefore consistent with
the characteristics of the several dynamic ranges mentioned above, and
it indicates more clearly the low-frequency energy concentration in the
critical stage of instability failure. This study well reflects the
response law of geophysical signals in the process of coal-rock
instability and failure, providing a basis for monitoring coal-rock
dynamic disasters.