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# Joints Overview

A Joint represents an interface along which movement can take place. A Joint is assigned strength and stiffness properties. Relative movement of the two sides of a joint may be elastic, or inelastic (if the shear strength of the joint is exceeded by the shear stress).

Joints can represent:

• Structural discontinuities in a rock mass
• Interfaces between support (e.g. liners, piles, geosynthetics) and rock or soil
• Any other type of sliding interface which may occur in a geotechnical project

There are various ways of modeling Joints in a RS2 analysis:

1. Joint Boundary - a Joint can be explicitly modeled as a Joint boundary in RS2. A Joint boundary is created with the Add Joint option.
2. Structural Interface Boundary - a Structural Interface boundary allows you to model support such as piles or geosynthetics, which can have a sliding interface on BOTH sides of the support element. A Joint will automatically be created on BOTH sides of the support element, when you define a Structural Interface boundary. See the Structural Interface Overview topic for more information.
3. Composite Liner with Joint - with the Composite Liner option, you may include a Joint between layers of the composite liner. See the Composite Liner Overview topic.
4. Joint Network - a network of joint boundaries can be created with the Joint Network option.

In all of the above modeling scenarios, the Joint properties (e.g. strength, stiffness) are defined with the Define Joint Properties option.

## Ubiquitous Joints

There are two additional methods of modeling the effect of joints in RS2, using a ubiquitous joints approach (i.e. assuming joints may occur at any location in the rock mass).

1. Jointed Material option (RS2 Model program) - the Jointed Material option allows you to define strength properties for 1, 2 or 3 ubiquitous joint sets, for any material in the Define Material Properties dialog. During the stress analysis, the program checks for failure in the rock mass AND the ubiquitous joint planes. If failure occurs on the joint planes, this will affect stresses and displacements in the rock mass.
2. Ubiquitous Joints (RS2 Interpret program) - Ubiquitous Joints can be included in Strength Factor calculations of a rock mass. However, this is strictly a post-analysis feature available in the RS2 Interpret program, and is independent of the Jointed Material option in the RS2 Model program.

Note: for ubiquitous joints only the joint strength is considered; joint stiffness is not considered.

Sign convention

If you right-click on the joint you’ve defined in the Interpret, you should be able to select slip directions. This will display paired couple forces along your joint. Couple forces causing an anti-clockwise rotation are responsible for positive shear displacement while couple forces causing a clockwise rotation are responsible for negative shear displacement.