Incorporating scale effect into a multiaxial failure criterion for intact rock

• Development of a modified multiaxial failure criterion with scale effect parameters.
• Incorporating scale effect into the failure criterion under different stress paths.
• Assessment of the scale dependency of the proposed parameters for the modified multiaxial failure criterion.

The design of structures on or within a rock mass requires an estimation of the strength of the intact rock blocks. These blocks can be many orders of magnitude greater in scale than the core samples typically tested. Thus, including the scale effect into a failure criterion is required for a more realistic estimation of rock strength with various scales. In this paper, a modified multiaxial failure criterion with scale effect parameters was developed based on the model proposed by Christensen. The modification process was carried out according to the proposed scale effect equations for different stress paths, such as uniaxial compression, point loading, uniaxial tension and pure shearing. Furthermore, the scale dependency of the proposed parameters for the modified failure criterion was assessed using the results from the uniaxial compressive and point load tests. Finally, it was confirmed that one of the modified failure criterion parameters is scale independent when the results from uniaxial compressive and point load tests are included.