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University of North Carolina at Charlotte (2018)

Acoustic emission and environmental monitoring of two natural granite boulders : semi-arid vs. temperate environment

Sadler Ching Suzanne

Titre : Acoustic emission and environmental monitoring of two natural granite boulders : semi-arid vs. temperate environment

Auteur : Sadler Ching Suzanne

Université de soutenance : University of North Carolina at Charlotte

Grade : Master of Science (MS) 2018

Résumé
The role of insolation as an instigator for crack initiation in rock is still a continuously perplexing topic. An immense amount of data has been collected on the influence of insolation on cracking---however, ongoing questions arise regarding the role this process plays in physical weathering. A study conducted by Dr. Martha Cary Eppes (2016) focused on the role of insolation in the initiation of cracking on a granite boulder in a temperate climate (North Carolina, USA), where 11 months of continuously recorded acoustic emissions (AE) data were used as a proxy for cracking. When these data were compared with simultaneously collected climate and rock surface data, it was found that insolation is a preliminary and contributing factor of crack initiation. However, this comprehensive data set was only representative of one climate zone---therefore, it was necessary to evaluate this relationship in other climates to support these conclusions. The following is a comparative study involving a similar granite boulder placed for an unprecedented three-year period in a semi-arid climate (New Mexico, USA). Utilizing the instrumentation of the Eppes 2016 study, acoustic emission sensors, strain gages, thermocouples, moisture sensors, and a site-located scientific weather station were deployed and monitored. During the 3-year study, 303,912 AE events (avg. 101,304 per year) occurred over a total 14,853 individual minutes over 713 days. A total 212,856 events occurred between 12:58 p.m. and 9:04 p.m. accounting for 70% of the overall deployment period. Comparable to the results of the Eppes 2016 study, high-event days (≥ 50 events) accounted for 98% of total events. Both boulders experienced the majority of events in the northern hemisphere and eastern position of the rock and no trends were indicated concerning the timing of events with precipitation. The results of this study 1) support the hypotheses that diurnal insolation contributes to the initiation and continuation of physical rock weathering and cracking whether alone or combined with temperature variations, and 2) suggest that this is characteristic of variable global locations, climates, and rock types.

Présentation (World Cat)

Page publiée le 9 novembre 2018