Microscale mechanical modeling of deformable geomaterials with dynamic contacts based on the numerical manifold method

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.

Multi-scale Coupled Processes Modeling of Fractures as Porous, Interfacial and Granular Systems from Rock Images with the Numerical Manifold Method

“…This example confirms a conclusion in the earlier paper by the authors (Hu and Rutqvist 2020b): the sequential evolution of geomaterials as responses to stress is motion, deformation and accumulation of high stress at local contacting areas (especially at sharp corners). In addition, through this example, we find the fact that the damage zone with softer material can accommodate larger deformations, and therefore, dominate contact evolution and redistribution of stress of a granular system toward a system with minimized porosity.…”

“…However, a significant difference between these two types of calculations is that contact pairs and contact states can change more rapidly and significantly when the contact pairs are no longer straight lines as in discrete fracture networks. A recently published paper by the authors (Hu and Rutqvist 2020b) explained the challenges of capturing these features in detail and developed a rigorous model with multi-step contact calculations that tackled these challenges.…”

“…The numerical manifold method (NMM, Shi 1992, 1996, based on the theory of mathematical manifolds is a promising method for analyzing both continuous and discontinuous media. In the past two decades, NMM has been successfully applied to analyze mechanical processes in geologic media (Ma et al 2010) involving higher order interpolation (Chen et al 1998), fracture propagation (Zheng and Xu 2014), wave propagation across fractured media (Fan et al 2013), slope stability (Ning et al 2011;He et al 2013), fracturing of sandstone (Wu et al 2017) and microscale mechanics of deformable geomaterials with dynamic contacts (Hu & Rutqvist, 2020b). For fluid flow analysis, NMM also has been successfully applied for analyzing moving interface problems such as free surface flow (Wang et al 2014(Wang et al , 2016Zheng et al 2015).…”

Microscale Mechanical‐Chemical Modeling of Granular Salt: Insights for Creep

“…Based on this dual‐mesh concept and global approximation, both continuous and discontinuous processes can be rigorously solved by flexibly defining functions of the physical covers. Benefited from these groundbreaking fundamentals, the authors have developed a number of models for analyzing flow and fully coupled hydro‐mechanical processes of fractured, granular, and porous media at different scales (Hu et al., 2016, Hu & Rutqvist, 2020b, 2020c; Hu, Rutqvist, & Wang, 2017; Hu, Wang, & Rutqvist, 2017).…”

Guest Editorial to the CouFrac 2018 Special Issue Coupled Thermal-Hydro-Mechanical-Chemical Processes in Fractured Media: Microscale to Macroscale Numerical Modeling

“…For the first time, Hu and Rutqvist [3] developed a microscale mechanical model that can simulate dynamic contacts of deformable geomaterials. In their approach, separation, bonding, and slip between microscale material bodies can be simulated as well as tensile and/or shear failure at the grain boundaries.…”