Exploring Discontinuity Roughness Measurement Scale Effects


Ms Erin Moss Tressel (Senior Geological Engineer - Clifton Associates), Dr Doug Milne (Associate Professor - University of Saskatchewan)

It is important in rock mechanics design to be able to accurately, and consistently, characterize discontinuity planes with respect to their mechanical behaviour. The characterization of discontinuity roughness using core logging and line mapping methods was studied, focusing on how each data collection method described large and small scale roughness properties. Differences were identified, and the significance of these differences with respect to how the discontinuity would be classified for design was considered. Field data was collected in August 2016. Large and small scale roughness measurements using core log and line map descriptions were collected from the same discontinuities. Trends in characterizing roughness between the two methods were evaluated through comparison plots. The data suggests that core logging has a conservative bias in the assessment of discontinuity waviness, especially on discontinuities with a large wavelength. Core scale roughness and shape do appear to correlate to the 10 cm JRC values. The lack of accuracy in characterizing the discontinuity waviness at the core scale may not significantly impact the overall rock mass classification, although this should be confirmed with more data.