Acoustic emission and yield in sand
An experimental investigation into the Acoustic Emission (AE)
response of sand has been undertaken, and the use of AE as a
method of yield point identification has been assessed.
Dense, saturated samples of sand were tested in conventional
triaxial apparatus. The measurements of stresses and strains were
carried out according to current research practice. The AE
monitoring system was integrated with the soil mechanics
equipment in such a way that sample disturbance was minimised.
During monotonically loaded, constant cell pressure tests the
total number of events recorded was found to increase at an
increasing rate in a manner which may be approximated by a power
law. The AE response of the sand was found to be both stress
level and stress path dependent. Undrained constant cell pressure
tests showed that, unlike drained tests, the AE event rate
increased at an increasing rate; this was shown to correlate with
the mean effective stress variation. The stress path dependence
was most noticeable in extension tests, where the number of
events recorded was an order of magnitude less than that recorded
in comparable compression tests. This stress path dependence was
shown to be due to the differences in the work done by the
In constant cell pressure tests containing unload/reload cycles
it was found that yield could be identified from a discontinuity
in the event rate/time curve which occurred during reloading.
Further tests involving complex stress paths showed that AE was a
useful method of yield point identification. Some tests involving
large stress reversals were carried out, and AE identified the
inverse yield points more distinctly than conventional methods of
yield point identification.