Characteristics of Different Acoustic Emission Sources of Particles in Shearing Process

Debris flows and landslides are composed of granular materials with different grain sizes, shapes and mineral compositions. These geological hazards are complex evolutionary processes of granular structure from stable state to unstable destabilizing deformation, followed by large deformation flow. From the view of particle matter mechanics, the occurrence of these hazards is the process of the development of the particle assemblage comprising the geological body from a blocked state to a rheological state under the constraints of external boundaries. During the deformation process, the mutual collision, friction, fragmentation and structural changes between the particles will release strain energy and disperse it in the form of elastic waves, which is called acoustic emission (AE). Consequently, the characteristics of the acoustic emission signal generated during the deformation of granular materials and the changes of its parameters can be used to reflect the stability state inside the granular structure. We thus utilized three AE sensors to capture the elastic waves and investigated the relationships between characteristics of AE and mechanical behavior of granular deformation during direct shear tests with different normal stress, shear speed and grain sizes. Our results suggested that during the granular shearing process there was a strong correlation between stick-slip events and the distribution of AE characteristics. Some AE features - energy and Root Mean Square (RMS)- showed significant spatial clustering which can represent the different processes of stick-slip event. In particular, some low RMS and medium-high energy AEs represent internal local failure. And, the AE rate and B-value show a regular increase and decrease during the state of granular structure from stabilization to failure. All of them are valuable information for the prediction or early warning of geological hazards.