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Joints

Model Creation

How do I define a jointed rock mass in RS2?

In RS2 you can model a jointed rock mass in two ways, as a continuum and as a discontinuum.

When modeling a jointed rock mass as a continuum, you require the intact strength and the scaling relationships to account for the joints. This is commonly done with the Generalized Hoek-Brown strength criterion.

When modeling a rock mass as a discontinuum, we use Goodman joint elements. This method is described in "The Practical Modelling of Discontinuous Rock Masses with Finite Element Analysis".

There are also numerous other papers on the modeling of jointed rock masses using RS2.

How can stacked concrete blocks be modeled?

Blocks can be modeled using joint elements or material boundaries. How the blocks are treated by RS2 depends on the method used.

In order for the blocks to be considered separately, they must be separated with joint elements. The RS2 Joint Network Verification document provides examples of how to create distinct blocks. Note that youâ€™ll also need to define the strength properties for the joints in order to model slip between the blocks. If only material boundaries are used to separate the blocks, they will behave as a continuum.

In terms of modeling the interface, either material blocks or liners can be used. If you are interested in flexural failure and moments, the liner elements are preferable. Note that if you are interested in modeling distinct blocks then material blocks will have to be used. If the wall is acting as a unit, without slip between the blocks, a liner may be preferable.

Material Properties

How does unchecking joint shear affect joint-bolt interaction?

Whether joint shear is considered or not affects the type of failure mechanisms that can occur in the bolt.

If shear is on, it is possible for the bolt to fail in shear.

If shear is off, then failure can occur only through bond failure or tensile failure.

Is it possible to specify different joint properties for tension and compression?

Yes, different stiffness values for tension and compression can be assigned to a joint in RS2.

In the Stress Analysis tab of the Project Settings dialog, there is an option to specify a reduction factor for joint stiffness for tension. This option can also be coupled with zero tensile strength for the joint.

Specifying different joint stiffness for tension and compression

How do I estimate joint stiffness for RS2 analyses?

Joint stiffness is extremely hard to judge, and getting these parameters is difficult. Because of the lack of reliable data, a good place to start could be to set the joint stiffness to be approximately 10 times the minimum modulus of the two materials on each side of the joint. The shear stiffness can be set to be approximately the same as the minimum modulus. This generally gives results that are fairly insensitive to the stiffness values.

A sensitivity analysis can then be performed for these parameters. In all cases where you are initially estimating properties, it is good practice to run sensitivity analyses on these parameters. To look at this topic in more detail, see the following references:

• Kulhawy, F. H. 1975. Stress Deformation Properties of Rock and Rock Discontinuities. Engineering Geology, Vol 9, pp. 327-350.
• Bandis, S. C., Lumsden, A. C. and Barton, N. 1983. Fundamentals of Rock Joint Deformation. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr., Vol 20, No 6, pp. 249-268
• Barton, N, Bandis, S and Bakhtar, K. 1985. Strength, Deformation and Conductivity Coupling of Rock Joints. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr., Vol 22, No 3, pp. 121-140.
• Barton, N.: "A model study of rock joint deformation", IJRM, #9 pp 579-602, (1972).
• chapter 12 of the recently published 4th edition of Fundamentals of Rock Mechanics by J. C. Jaeger, N. G. W. Cook and R. W. Zimmerman

See the Estimating Joint Stiffness help topic for a discussion on how to estimate stiffness from rock mass properties and joint infill properties.