CNI
The CNI strength model is described by the following equation:
where:
- Ï„ is the shear stress
- σc is the rock mass compressive strength
- a is the strength magnitude coefficient
- σn is the normal stress
- To is the direct tensile strength expressed as a negative value
- n is the curvature coefficient
- The input for tensile strength requires a positive number but is calculated internally as a negative value during computation
- The equivalent Mohr-Coloumb cohesion and phi are calculated as the instantaneous angle and y-intercept at the point on the non-linear shear envelope. The instantaneous phi has been restricted to a maximum of 70 degrees.
References
- Cylwik, S.D., Killian, J.R., Cicchini, P.F., A practical nonlinear strength criterion for rock masses and other geological materials, Rocscience International Conference 2023, April 2023, pp 681-699.