Slope stability analysis is a major design challenge for safe excavations in civil engineering and mining. In mining, very large open pit operations can exceed depths of 1000m, facing geotechnical challenges of high stress, deformation, complex geology with multiple rock mass domains and movement on major faults. Using SIMULIA Abaqus to perform a Shear Strength Reduction (SSR) test on this virtual twin of the mine, questions that used to take days to solve can now be answered in as little as 10 minutes. Abaqus/Standard's iterative solver allows fast equilibrium analysis in complex in-situ stress settings and Abaqus/Explicit's highly scalable, non-linear, quasi-static analysis capabilities combined with Cavroc 's IUCM material library for anisotropic rock mass provides realistic behaviour and ultimate performance.
I will be presenting a paper on "Current state and limitations of 3D continuum models for slope stability models using Abaqus with octree meshing and IUCM" at the International Slope Stability Symposium 2024 (14th to 19th of April 2024 in Brazil, abstract below). The model discussed in the paper, demonstrating achievable HPC performance, consists of 3.6 million elements with six major faults (4.6M nodes, 14M DoFs).
Abstract
Three-dimensional slope stability models require considerably more effort than simpler tools. Therefore, their use is affected by factors such as cost considerations, availability of geotechnical consultants, previous experiences, and biased views on modelling methods, leading to reduced uptake of 3D models in geotechnical engineering. Very few in-house capabilities exist at site level. This is in stark contrast to the requirements of a safe pit slope design to prevent slope failures of significant consequence as well as for slope risk management transitioning towards a performance-based approach. Importantly, design acceptance criteria for operating mines require consideration of advancing technology.
Abaqus is a general-purpose finite element solver for non-linear problems. Combining this solver with the IUCM continuum constitutive model for the rock mass allows the use of a non-linear Hoek-Brown relationship between shear strength and confining stress, strain softening, brittle to ductile transition and stiffness softening. The most time-consuming parts of 3D models, model creation, geometry preparation and meshing, can be accelerated significantly with octree meshing. By far not a new approach, acceptance of octree discretisation of the domain is still a topic of debate. The inclusion of major faults in such models is possible through mesh refinement and anisotropy in the constitutive model.
Efficient numerical models provide an opportunity to investigate the relationship between Factor of Safety (FoS) and the Probability of Failure (PoF) using statistical methods and tools like Design of Experiments. This paper presents a view of the current state and limitations of 3D continuum models in slope stability problems.
