Rocscience International Conference 2025 is going to take place in Sydney, Australia Read more

Search Results

Shear Strength

In UnWedge, three different strength models are available for defining the shear strength of the joints used in the analysis:

  • Mohr-Coulomb
  • Barton-Bandis
  • Power Curve
For any of these strength models, a waviness angle can also be defined, which will have the effect of increasing the shear strength. See the Waviness Angle topic for details. If the water pressure is included, then all parameters should be considered effective stress parameters. See the Water Pressure topic for details about including water pressure in the analysis.


The Mohr-Coulomb model relates shear strength, equation, and normal stress equation, according to Eqn.1:

MohrCoulomb Shear Strength Equation Eqn.1

Where is the friction angle of the joint plane and c is the cohesion.


For the Mohr-Coulomb model, you may also define tensile strength. If defined, the tensile strength will be applied to wedge faces which are in tension (for example: all planes of a falling wedge, or the non-sliding plane(s) of a sliding wedge). The tensile strength will apply a passive resisting force normal to the wedge plane, equal to the area of the wedge plane multiplied by the tensile strength.


The original Barton equation for the shear strength of a rock joint is given by Eqn.2a:

Barton Shear Strength Equation Eqn.2a

Where Icon is the basic friction angle of the failure surface, JRC is the joint roughness coefficient, and JCS is the joint wall compressive strength [Barton, 1973, 1976]. On the basis of direct shear test results for 130 samples of variably weathered rock joints, Barton and Choubey revised this to Eqn.2b:

Barton Shear Strength Equation Eqn.2b

Where Icon is the residual friction angle of the failure surface [Barton and Choubey, 1977]. Barton and Choubey suggest that Icon can be estimated from Eqn.2c:

Residual Friction Angle Equation Eqn.2c

Where r is the Schmidt hammer rebound number on wet and weathered fracture surfaces and R is the Schmidt rebound number on dry unweathered sawn surfaces. Equations 2b and 2c have become part of the Barton-Bandis criterion for rock joint strength and deformability [Barton and Bandis, 1990].

For further information on the shear strength of discontinuities, including a discussion of the Barton-Bandis failure criterion parameters, see Practical Rock Engineering: Shear Strength of Discontinuities) on the Rocscience website.

Power Curve

The Power Curve model for shear-strength [Miller, 1988], can be expressed as:

Power Curve Shear Strength Equation Eqn.3

Where a, b, and c are parameters typically obtained from a least-squares regression fit of data obtained from small-scale shear tests. The d parameter represents the tensile strength. If included, it must be entered as a positive value.

Rocscience logo, click here to return to the homepage Portal Account Portal Account Log In Log Out Home Shopping Cart icon Click here to search our site Click here to close Learning Tech Support Documentation Info Chevron Delete Back to Top View More" Previous Next PDF File Calendar Location Language Fees Video Click here to visit Rocscience's LinkedIn page Click here to visit Rocscience's YouTube page Click here to visit Rocscience's X page Click here to visit Rocscience's Facebook page Click here to visit Rocscience's Instagram page Click here to visit Rocscience's Reddit page Bookmark Network Scroll down for more Checkmark Download Print Back to top Single User Multiple Users RSLog RocFall3 CPillar Dips EX3 RocFall RocPlane RocSlope3 RocSupport RocTopple RS2 RS3 RSData RSPile Settle3 Slide2 Slide3 SWedge UnWedge RocTunnel RocSlope2 Commercial License Education License Trial License Shop safe & secure Money-back guarantee