Acoustic emission tracing and evaluation of stato dynamic instabilities evolving within a snowpack

Abstract

This thesis deals with the investigation of evolution of stato-dynamic instability development within a snowpack using Acoustic Emission (AE) technique. An appropriate detection platform i.e., piezo-composite AE sensors and data acquisition system was used to study the thermal or mechanical instability within snow. Different AE waveguides and arrestors were used for efficient detection of the AE activities in snow. The thermal instability was investigated in context of phase transformations in ice and water and partial melting of snow. The progressive crack growth in snow beam, subjected to three-point bending, was monitored in terms of AEs for entire course of bending, crack initiation and propagation until the failure of beams. To investigate mechanical instability within snow, remotely operated avalanche simulator was used to understand the avalanche formation and release at lab-scale in terms of AE. In this thesis, the field investigations for natural avalanche and snowpack fracturing events, detected in terms of acoustic emissions, are presented. The analysis of AE data was conducted for different static and dynamic phases of instability development and failure. For quantitative assessment of stato-dynamic instability development, (i)hit based (and#946;in), (ii)waveform based (Iw) instability indices and (iii) Shannon s entropy (Hs) were estimated. This study will be helpful towards development of an autonomous early warning system for avalanche, landslide and structural health monitoring. newline