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Joints
A Joint represents an interface along which movement can take place. Joints can represent:
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structural discontinuities in a rock mass
interfaces between support and rock or soil (e.g. liners, sheet pile walls)
any other type of sliding interface which may occur in a geotechnical project
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There are various ways of modeling Joints in a Phase2 analysis: as a Joint boundary, as a Structural Interface boundary, or as part of a Composite Liner.
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Joints: Joint Boundary
A Joint can be explicitly modeled as a Joint boundary in Phase2. A Joint boundary is created with the Add Joint option.
Joint boundary intersecting a rectangular tunnel. The deformed tunnel shape illustrates the effect of joint slip on tunnel behavior. Deformation vectors (red arrows) and displacement contours illustrate the rock mass behavior due to the presence of the joint.
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Joints: Structural Interface
A Structural Interface boundary allows you to model support such as sheet pile walls or geosynthetics, which can have a sliding interface on BOTH sides of the support element. A Joint is automatically created on BOTH sides of the support element, when you define a Structural Interface boundary.
Schematic representation of structural interface boundary
Geogrid modeled as structural interface, joint slip (red) occurs at toe of embankment
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Joints: Composite Liner
With the Composite Liner option, you may include a Joint which will exist between the first layer of the Composite Liner and the rock or soil. This is done through the Define Composite Properties dialog as shown below.
Defining a composite liner with a joint
When you add a composite liner (with slip) to a boundary, a joint will automatically be created between the liner and the rock mass.
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Joints: Properties
Joint properties are defined in the Define Joint Properties dialog, and include:
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Elastic properties (normal and shear stiffness)
Strength properties (Mohr-Coulomb, Barton-Bandis, Geosynthetic
hyberbolic)
Internal pressure (e.g. due to groundwater)
Staging of joint properties (i.e. properties can change with staging)
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Joints can be defined as elastic or inelastic. If a joint is elastic (i.e. Slip Criterion = None) then strength properties are not applicable, and only elastic displacements can occur. If a joint is inelastic (i.e. Slip Criterion = Mohr-Coulomb, Barton-Bandis or Geosynthetic Hyperbolic), then the joint can yield (slip) if the shear stress on a joint element exceeds the shear strength.
Joint properties dialog
Barton-Bandis joint strength properties
Geosynthetic Hyperbolic joint strength properties
The Geosynthetic Hyperbolic slip criterion can be used for modeling the shear strength of the interface between a geosynthetic (e.g. geotextile or geogrid) and soil. This can be used in conjunction with the Structural Interface option described above.
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Joints: Analysis Results
After the Phase2 analysis has been computed, you can examine the stresses and displacements along joints. Joint data can be:
The Show Values option allows you to display joint results directly on the model, in the form of a histogram or line graph, superimposed directly on the joint boundary. The numerical values can be displayed, and the display can be customized.
Joint shear stress plotted with Show Values
Joint normal stress plotted with Graph Joint Data
The Show Yield option highlights yielding (slip) along joints.
Yielded joint elements are highlighted in red
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Joints: Ubiquitous Joints
Joints can also be treated as "ubiquitous" (i.e., they may occur at any location in the rock mass). However, this is strictly a post-analysis feature, and only applies to strength factor calculations in the Phase2 Interpret program. Stresses and displacements are not affected.
For more information see the Ubiquitous Joints help topic.
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