Mr Hebert is a geotechnical engineer with experience in both the mining and civil industries. He has provided consulting on many projects including underground mining (e.g. block cave mining, pillar stability), open pit mining, underground excavations (e.g. tunnels, caverns, nuclear waste storage) and dams.
This webinar is for people who have used 3DEC before and are interested in the latest developments.
This hands-on, virtual training course is 16 hours total, spread over four days in a 1.5-week period, and covers the analysis of embankment dams using FLAC.
David is a principal geotechnical engineer with more than 20 years of operations and consulting experience in the mining and civil industries. Since joining Itasca in 2007, David has performed numerical back analyses and forward analyses for numerous open pit and underground mining operations around the world using Itasca software. David has also performed numerical analyses for several surface and underground civil infrastructure projects.
Six different joint constitutive models are included with 3DEC to provide a range of behaviors. The most basic is the Elastic joint model which is primarily used for model construction joints. The other joint models are intended to represent geological joints or artificial interfaces: the standard being the Mohr-Coulomb model and a more advanced Continuously Yielding model. With the C++ UDM (User-Defined constitutive Models) option, you may create your own joint (and zone) constitutive models to represent new model behavior.
Joint models and properties can be assigned separately to individual, or sets of, discontinuities in a 3DEC model. Note that the geometric roughness of a joint is represented via the joint material model, even though plotted discontinuities are represented as a planar segment.
The Elastic joint model can be used to simulate construction joints that are required to build model geometries, but do not correspond to real slipping joints or faults. The behavior is governed by the joint normal and shear stiffness; no yielding can occur.
The basic joint constitutive model incorporated in 3DEC is the generalization of the Mohr-Coulomb strength criterion. This law works in a similar fashion both for sub-contacts between rigid blocks and for sub-contacts between deformable blocks. Both shear and tensile failure are considered, and joint dilation is included.
In the elastic range, the behavior is governed by the joint normal and shear stiffnesses. Once the onset of failure is identified at the sub-contact, in either tension or shear, the tensile strength and cohesion are taken as zero, which approximates the “displacement-weakening” behavior of a joint. Dilation takes place only when the joint is at slip. Actual joints display a reduction in the dilation angle as the residual friction state is approached. In 3DEC, the joints can be prevented from dilating indefinitely by prescribing a limiting shear displacement; when the magnitude of the shear displacement exceeds this limit, the dilation angle is set to zero. Since dilation is a function of the direction of shearing, dilation increases if the shear displacement increment is in the same direction as the total shear displacement and it decreases if the shear increment is in the opposite direction.
The continuously yielding model is intended to simulate, in a simple fashion, the internal mechanism of progressive damage of joints under shear. The model also provides continuous hysteretic damping for dynamic simulations by using a “bounding surface” concept. It is considered more “realistic” than the standard Mohr-Coulomb joint model in that the continuously yielding model attempts to account for some nonlinear behavior observed in physical tests (such as joint shearing damage, normal stiffness dependence on normal stress, and decrease in dilation angle with plastic shear displacement). The essential features of the continuously yielding model include the following:
As a consequence of these assumptions, the model exhibits, automatically, the commonly observed peak/residual behavior of rock joints. Also, hysteresis is displayed for unloading and reloading cycles of all strain levels, no matter how small.
The Softening Healing Mohr-Coulomb model is based on the standard Mohr-Coulomb model with two additions to improve modeling seismicity:
Two formulations, linear and non-linear, for the evolution of shear strength are available. For the non-linear formulation, an exponent (α > 1) dictates the severity of the strength drop.
The Bilinear Mohr-Coulomb joint model has two different shear strength envelopes. The failure envelope changes when a critical level of normal stress is exceeded. By default, the normal stress threshold is automatically calculated at the intersection of the two failure envelopes, but the user may override this default and specify any value. Both the peak and residual shear strengths can have bilinear envelopes and there may be different normal stress thresholds for the peak and the residual.
The creep behavior in a discontinuity is of a different nature depending on the joint surface (planar or rough) and on the filling material (gauge).
To simulate the creep due to the filling material, Itasca has adapted Norton's law, which is commonly used to model the creep behavior of soft rocks subjected to a shear load, for the joint elements. The Power-Law-Creep joint model in 3DEC is characterized by a visco-elasto-plastic behavior in the shear direction and an elasto-plastic behavior in the normal direction. The visco-elastic and plastic elements are assumed to act in series; the visco-elastic behavior corresponds to a Norton’s law; and the plastic behavior corresponds to a Mohr-Coulomb joint model.
This optional feature allows the use of joint constitutive models that are developed and compiled outside of the executable code, written in C++ (using Microsoft Visual Studio 2010) and compiled as a DLL (dynamic link library) file that can be loaded as needed. The main function of the model is to return new forces, given displacement increments. However, the model must also provide other information (such as names) and perform operations such as writing and reading save files.
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