Slope stability monitoring from microseismic field using polarization methodology
Numerical simulation of seismoacoustic emission (SAE) associated with fracturing in zones of shear stress concentration shows that SAE signals are polarized along the stress direction. The proposed polarization methodology for monitoring of slope stability makes use of three-component recording of the microseismic field on a slope in order to pick the signals of slope processes by filtering and polarization analysis. Slope activity is indicated by rather strong roughly horizontal polarization of the respective portion of the field in the direction of slope dip. The methodology was tested in microseismic observations on a landslide slope in the Northern Tien-Shan (Kyrgyzstan).
Landslide Noise
Acoustical monitoring of real landslides has revealed the existence of subaudible noise activity prior to failure and has enabled prediction of the depth of the seat of sliding when conducted in boreholes beneath the surface. Recordings of noise generated in small slopes of moist sand, tilted to failure in laboratory tests, have been analyzed to determine the foci of discrete subaudible noise events. The noises emitted shortly before failure were plotted close to the true sliding surface observed after failure. The foci of earlier events lay either within the central portion of the sliding mass or in a region behind the failure surface. The head and toe zones were devoid of strong seismic activity.
Acoustic Emission Monitoring of Soil Stability
Seventeen sites monitored for acoustic emission are described, including twelve earth dams, two surcharge fills, two embankments and one man-made reservoir where seepage was detected. The results from all sites lead to the following generalizations. Soil masses can deform and consequently will produce acoustic emissions which exceed background noise levels. Soil masses which generate no acoustic emissions are probably not deforming, and are in a state of equilibrium. Soil masses generating moderate levels of acoustic emissions (10 counts/min to 100 counts/min) are marginally stable and require continued monitoring. Soil masses generating high levels of acoustic emissions (100 counts/min to 500 counts/min) are actively deforming and unstable, requiring immediate remedial action. Soil masses generating very high levels of acoustic emissions (greater than 500 counts/min) are in, or are very near a failure state.