How does moisture alter rock elasticity and trigger failure during brittle creep?
Water profoundly influences rock deformation and failure, yet the coupled effects of moisture, mechanical stress, and water transport remain poorly understood. In this talk, I will present three interconnected laboratory studies exploring how moisture modifies rock elasticity and ultimately promotes brittle failure.
First, experiments on sandstone under simultaneous control of humidity and cyclic loading reveal a strong interplay between adsorption-induced softening and stress-induced stiffening. Vapor adsorption reduces Young's modulus by up to 40% at low stress, whereas this reduction diminishes to less than 10% under elevated stress. A grain-scale micromechanical model explains this behavior through the competing effects of adsorption and mechanical loading on contact stiffness.
Second, I present how progressive wetting affects rock elasticity through ultrasonic measurements and moisture transport modeling. P-wave velocity initially decreases ahead of the advancing wetting front due to vapor adsorption, followed by stiffening as liquid water infiltrates the rock. These contrasting responses reveal how evolving moisture distributions govern transient elastic behavior and complicate seismic interpretations of wetting processes.
Finally, I examine how moisture-induced weakening interacts with subcritical crack growth to accelerate brittle creep. Experiments on notched rock beams under sustained loading demonstrate that water introduction can destabilize otherwise stable specimens. Rapid elastic weakening and crack opening are followed by delayed microcracking, accelerated deformation, and eventual brittle failure.
Short Bio: Dr. Rui Wu is a Senior Research Scientist and research group leader at the State Key Laboratory of Intelligent Coal Mining and Strata Control in Beijing, China, where he has worked since 2023. He received his Ph.D. in Earth Sciences from ETH Zurich in 2022, with a dissertation entitled 'Laboratory acousto-mechanical studies into moisture-induced changes of elastic properties in fine-grained granite' in 2022.
His research focuses on understanding how environmental factors, particularly water availability and humidity, influence the mechanical and physical behavior of rocks, with implications for climate-driven changes in near-surface geological environments. He has published in journals including Geophysical Research Letters, Physical Review E, International Journal of Rock Mechanics and Mining Sciences, Journal of Nondestructive Evaluation and Sensors and Actuators A: Physical. You can learn more about his work here: https://scholar.google.ch/citations?hl=en&user=iouPIcQAAAAJ&view_op=list_works&sortby=pubdate
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