Collapse patterns in porous materials under degradation fields

Abstract

Porous materials consist of a solid skeleton with empty spaces (pores). They are ubiquitous in nature and understanding their behaviour is an interest of various fields, including environmental science, mining, and material processing. Emerging collapse patterns in deforming porous media can significantly alter their properties. Recent findings suggest these patterns can arise from material degradation. This thesis presents an experimental study on collapse patterns in a diverse range of materials and degradation fields. We first investigate the emergence of a novel collapse pattern, consisting of cycles of slow and sudden compaction, as a ubiquitous collapse mechanism in porous media. Three key requirements for these ‘creep-quake cycles’ are identified: a collapsible length scale in the material, sufficient compressive stress, and a non-uniform degradation field. We then develop a theoretical model that recovers the cycles based on these requirements. After asserting the ubiquity of this mechanism, the precise conditions for its emergence in calcareous sands are investigated. This reveals that grain size distribution plays a crucial role in creep-quake collapse, outweighing the influence of grain shape. In addition, we uncover a range of stress and degradation rates in which creep-quake cycles can emerge. Finally, these findings are related to real geological scenarios with an investigation on sand samples under compression and a transversal acid flow. Here, the collapse mechanisms of chemical degradation-induced sinkholes are examined. Remarkably, creep-quake cycles remain relevant even in these different loading conditions and are intertwined with other failure mechanisms associated with sinkhole collapse. The findings of this thesis contribute to the understanding of collapse patterns in degrading porous media. They provide insights for future research on monitoring these patterns to forecast and prevent impending catastrophic collapse events.