Microscale mechanical modeling of deformable geomaterials with dynamic contacts based on the numerical manifold method
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ORIGINAL PAPER
Microscale mechanical modeling of deformable geomaterials with dynamic contacts based on the numerical manifold method Mengsu Hu 1 & Jonny Rutqvist 1 Received: 2 May 2020 / Accepted: 24 July 2020 # The Author(s) 2020
Abstract Micromechanical modeling of geomaterials is challenging because of the complex geometry of discontinuities and potentially large number of deformable material bodies that contact each other dynamically. In this study, we have developed a numerical approach for micromechanical analysis of deformable geomaterials with dynamic contacts. In our approach, we detect contacts among multiple blocks with arbitrary shapes, enforce different contact constraints for three different contact states of separated, bonded, and sliding, and iterate within each time step to ensure convergence of contact states. With these features, we are able to simulate the dynamic contact evolution at the microscale for realistic geomaterials having arbitrary shapes of grains and interfaces. We demonstrate the capability with several examples, including a rough fracture with different geometric surface asperity characteristics, settling of clay aggregates, compaction of a loosely packed sand, and failure of an intact marble sample. With our model, we are able to accurately analyze (1) large displacements and/or deformation, (2) the process of high stress accumulated at contact areas, (3) the failure of a mineral cemented rock samples under high stress, and (4) post-failure fragmentation. The analysis highlights the importance of accurately capturing (1) the sequential evolution of geomaterials responding to stress as motion, deformation, and high stress; (2) large geometric features outside the norms (such as large asperities and sharp corners) as such features can dominate the micromechanical behavior; and (3) different mechanical behavior between loosely packed and tightly packed granular systems. Keywords Dynamic contacts . Bonded and sliding . Cohesion and tensile strength . Fracture asperities . Granular systems . Numerical manifold method
1 Introduction Numerical modeling of microscale mechanical behavior of geomaterials (soils and rocks) is of great importance for understanding and predicting material constitutive and geomechanical behavior at larger scales in subsurface engineering activities such as unconventional hydrocarbon production [22], nuclear waste disposal [23], and CO2 sequestration [21]. Some unique features of geomaterials are that they are naturally stressed and heated to variable degrees, and often
* Mengsu Hu [email protected] Jonny Rutqvist [email protected] 1
Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
fluid filled. The microscale structure of geomaterials contains minerals, pores, and fractures of complex shapes that evolve as a result of coupled fluid, heat, mechanics, and chemical reactions. In order to understand such dynamic multiphysics problems, in the past decade, new technologies have been developed for visualization and cha
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