53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: Ubiquitous joint constitutive models have been available for numerical analysis for a few decades. However, mis-understanding of the true behavior of these models is still quite prevalent among users. The purpose and goal of addressing strength anisotropy through a ubiquitous joint model embedded in a constitutive model has been successful, but the deformations do not follow the intuitive behaviour in many cases. This paper dissects the constitutive formulation of the ubiquitous joint model and compares its behaviour against explicitly modelled joint networks to show the range of applicability of ubiquitous joint models and when they fall short of capturing the correct deformation behaviour. The paper will show that ubiquity does not equate to continuity and that ubiquitous joint models are not able to capture the correct behaviour for discontinuities of large extent, such as bedding or faults. The paper will also show that this behaviour is inherent in the incremental stress/strain formulation of constitutive models and not specific to any finite element or finite difference code.
Ubiquitous joint constitutive models have been available for numerical analysis for a few decades. The motivation for the development of ubiquitous joint models in domain methods (continua) was borne of the necessity to capture the anisotropic strength behaviour of jointed rock masses at a time when the use of explicit joint networks was computationally prohibitive. Although this computational bottleneck has been alleviated with the increase of computer power, it is pragmatically only feasible in two-dimensional modelling, as the computational demands of modelling discrete joints in three dimensions are very large.
Recent experience by the authors in the use of ubiquitous joint models, especially when trying to simulate discontinuities of large extent, such as faults or bedding, has raised some questions regarding its applicability and led to a further investigation of the constitutive model.
2. THE UBIQUITOUS JOINT MODEL
The ubiquitous joint model embeds the behaviour of one (or more) weak plane within a continuum model such as the Mohr-Coulomb or the Hoek-Brown models.
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