Sources and characteristics of acoustic emissions from mechanically stressed geologic granular media — A review

This paper introduces the concept of using active waveguides as part of an acoustic emission monitoring system for assessing the stability of soil slopes. In soil, acoustic emissions are generated by inter-particle friction, and hence the detection of acoustic emission is an indication of straining. The components of a field monitoring system are introduced, and the factors controlling design and performance of waveguides are discussed. It is proposed that active waveguides (i.e. those that generate acoustic emission when deformed by the host soil) can be used as an efficient method of obtaining signals from depth within a deforming soil body. The results of laboratory tests conducted to validate the active waveguide model are presented. The role played by the soil surrounding the steel tube waveguide is highlighted. Results from two full-scale field trials that involved monitoring unstable slopes provide evidence for the relationship between detected acoustic emission and slope deformation rate. It is shown that active waveguides in conjunction with relevant signal processing methods can be used to provide an early indication of slope instability.

/pdf/acoustic-emission-monitoring-of-slope-instability-3b48zqxna2.pdf

Acoustic emission monitoring of slope instability: development of an active waveguide system

Evaluation of damage level for rock slopes using acoustic emission technique with waveguides

[1] Sudden and rapid mass movements associated with landslides and snow avalanches present a hazard to life and infrastructure, yet their predictions and triggering mechanisms remain poorly understood. Statistical methods and correlative studies have been used to produce landslide or avalanche susceptibility maps, often with limited physical basis. Mechanistic approaches based on factor-of-safety computation seldom represent the progressive transition from local failure events to a landslide and, in general, do not include heterogeneities associated with land cover or with subsurface material properties and hydrologic pathways. Focusing on rainfall-induced shallow landslides, we propose the use of the fiber bundle model (FBM), a generic yet powerful and adaptable model used in modeling fatigue and fracture of complex and disordered materials. The primary strength of the FBM is its ability to represent the progressive failure of cracks and shear zones and the ruptures of highly heterogeneous bonding elements that are present in soils at all scales. The model also provides a natural framework for interpretation of acoustic emission signatures from failing slopes, which may form the basis of a monitoring and warning system.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009WR007889

Fiber bundle model for multiscale modeling of hydromechanical triggering of shallow landslides

Acoustic emission (AE) has become an established approach to monitor the stability of soil slopes. However, the challenge has been to develop strategies to interpret and quantify deformation behaviour from the measured AE. This paper presents the first comparison of continuous AE (measured using an active waveguide) and continuous subsurface deformation measurements. The active waveguide is installed in a borehole through a slope and comprises a metal waveguide rod or tube with a granular backfill surround. When the host slope deforms, the column of granular backfill also deforms, generating AE that can propagate along the waveguide. This paper presents results from a field trial at a reactivated soil slope in North Yorkshire, UK. The measurements confirm that AE rates generated are directly proportional to the velocity of slope movement (e.g. the AE rate versus velocity relationship determined for a series of slope movement events produced an R 2 value of 0?8) and demonstrate the performance of AE monitoring of active waveguides to provide continuous information on slope displacements and displacement rates with high temporal resolution.

/pdf/acoustic-emission-monitoring-of-a-soil-slope-comparisons-4jzyhuu3da.pdf

Acoustic emission monitoring of a soil slope: Comparisons with continuous deformation measurements

An ambankment and an unstable natural slope were monitored by using AE monitoring and traditional field techniques. AE characteristics of the two slopes were different. Results from the embankment showed that the period of AE occurrence approximately coincides with the movement of the embankment. In the natural slope, significant increases in levels of AE count rate were recorded at least two months before the observation of detectable ground movement. In the prediction of slope failure, it is important to take the differences of earth structures into consideration

M. Nakamura

Papers

Acoustic emission characteristics of unstable slopes