Shear‐induced force fluctuations and acoustic emissions in granular material

Abstract

[1] We conducted a series of strain-controlled experiments to study the characteristics of a shear zone forming in dense flow of confined dry granular media. The primary objective was to link force fluctuations due to jamming and force network reformation with episodic release of elastic energy as passively monitored by acoustic emission sensors. Under constant deformation rate, the shear stress exhibits a characteristic sawtooth behavior reflecting the strong influence of micromechanical processes on the macroscopic stress-strain behavior. Measured shear stress jumps were highly correlated with low-frequency (< 20 kHz) acoustic emission events. High-frequency (30 kHz-80 kHz) acoustic signals that were measured with different sensors appear to be directly linked to continual grain-scale interactions (e.g., friction, rolling). A conceptual mechanical fiber bundle model (FBM) was used to represent dynamics at the shear zone of large granular assemblies. The model was capable of reproducing the dynamics of stress jumps and associated elastic energy release events. The combination of acoustic emission (AE) measurements and FBM framework offers new insights into the behavior of shear failure and enhances capabilities for resolving grain-scale mechanical processes and for predicting rapid mass movement such as shallow landslides and debris flows.

Quantification of reactivated landslide behaviour using acoustic emission monitoring

“…Fujiwara et al 1999, Shiotani & Ohtsu 1999, and in Switzerland (e.g. Michlmayr et al 2012 andMichlmayr et al 2013). This body of international research has demonstrated that acoustic emission is generated during soil slope movements and that AE monitoring is capable of detecting pre-failure deformations.…”

Stability monitoring of a rail slope using acoustic emission

“…sliding and rolling friction) and rearrangement of the particle-contact network (e.g. release of contact stress and stress redistribution as interlock is overcome and regained) are mechanisms that generate AE within soil (Lord and Koerner, 1974;Michlmayr et al, 2012aMichlmayr et al, , 2012bMichlmayr et al, , 2013. Research has shown that soil-generated AE is detectable and measurable.…”

“…The characteristics of the AE generated are governed by the properties of the soil (e.g. AE from fine-grained soils is highly influenced by moisture content and plasticity, and AE events of greater magnitude are produced in granular soil with large angular particles), and AE events with greater magnitude are generated by deforming soil with high interparticle contact stresses (Garga and Chichibu, 1990;Koerner et al, 1981;Michlmayr et al, 2013;Mitchell and Romeril, 1984;Shiotani and Ohtsu, 1999).…”

Fiber-bundle model with time-dependent healing mechanisms to simulate progressive failure of snow

“…The stick-slip FBM exhibits a plastic macroscopic deformation behavior despite the brittle constituents. Similar models have been proposed for modeling the acoustic emission response produced by rearrangement of the force chain networks in granular materials [16,17]. Fan et al [18] used a FBM with time-dependent healing of broken fibers to reproduce healing of soil strength and root reinforcement after rainfall events for a landslide model at hillslope scale.…”