Theory/Literature

The Stochastic Approach for Discontinuity Shear Strength (StADSS) represents a fundamental shift in how the shear strength of natural rock discontinuities is predicted. Its core principle is to capture roughness information directly at the scale of the project to bypass the well know scale effect; and to apply rigorous statistics and mechanics to predict the discontinuity shear strength. The statistical properties of surveyed traces (referred to as seed trace) are used to reconstruct many 3D synthetic surfaces through rigorous random field modelling. These synthetic surfaces preserve key statistical descriptors of the seed trace, most importantly the standard deviation of gradients, and are produced at engineering scale allowing the method to work directly at field scale without downscaling or empirical scale corrections; bypassing any scale effects. Each reconstructed surface is sheared virtually using a semi‑analytical mechanistic model (called NDSS, developed at the University of Newcastle), which triangulates the synthetic morphology into facets, identifies “active” and estimates peak and residual shear strength from rock strength parameters, without the need for empirical calibration factor. By repeating this over 100+ realisations in a Monte Carlo manner, StADSS yields a probabilistic strength distribution, rather than a single deterministic value. 

The novelty of StADSS lies in several breakthroughs: 

  • It bypasses the scale effect on roughness: one of rock mechanics’ longstanding unresolved problems, through statistical reconstruction at full discontinuity scale.  
  • It is based on rigorous statistical and mechanistic modelling,
  • It does not rely on ill-defined or subjective roughness predictor, but on the full geometrical profile of the seed trace,
  • It can predict peak and residual shear strength of very rough surfaces where traditional tangent-based models are mathematically limited, returning negative values of shear strength, and
  • Its probabilistic formulation efficiently captures uncertainty about discontinuity morphology and variability of material strength (an often-overlooked aspect in rock mechanics) and allows efficient sensitivity analyses.

StADSS has been validated in the laboratory on a 2m per 2m rough surface and tested in the field. StADSS has been developed with the support of PSM, Geotechnical Consultants, Sydney.

Together, these advances establish StADSS as a transformative, scale‑independent methodology capable of delivering shear strength predictions where classical models fail or are inapplicable.

To read more on StADSS please refer to the following articles in literature:


• Casagrande, D., Buzzi, O., Giacomini, A., Lambert, C. and Fenton, G. (2018), ‘A New Stochastic Approach to Predict Peak and Residual Shear Strength of Natural Rock Discontinuities’, Rock Mechanics and Rock Engineering, vol. 51(1), pp. 69–99.

https://link.springer.com/article/10.1007/s00603-017-1302-3

• Buzzi, O. and Casagrande, D. (2018), ‘A step towards the end of the scale effect conundrum when predicting the shear strength of large in situ discontinuities’, International Journal of Rock Mechanics and Mining Sciences, vol. 105, pp. 210–219.

https://www.sciencedirect.com/science/article/abs/pii/S1365160917309383

• Jeffery, M., Huang, J., Fityus, S., Giacomini, A. and Buzzi, O. (2021), ‘A rigorous multiscale random field approach to generate large scale rough rock surfaces’, International Journal of Rock Mechanics and Mining Sciences, vol. 142, art. no. 104716.

https://www.sciencedirect.com/science/article/abs/pii/S1365160921001027

• Jeffery, M., Crumpton, M., Fityus, S.G., Huang, J., Giacomini, A. and Buzzi, O. (2022), ‘A Shear Device with Controlled Boundary Conditions for Very Large Nonplanar Rock Discontinuities’, Geotechnical Testing Journal, vol. 45(4).

https://dl.astm.org/gtj/article/45/4/725/3448/A-Shear-Device-with-Controlled-Boundary-Conditions

• Jeffery, M., Huang, J., Fityus, S., Giacomini, A. and Buzzi, O. (2023), ‘A Large-Scale Application of the Stochastic Approach for Estimating the Shear Strength of Natural Rock Discontinuities’, Rock Mechanics and Rock Engineering, vol. 56(8), pp. 6061–6078.

https://link.springer.com/article/10.1007/s00603-023-03393-1

• Buzzi, O., Jeffery, M., Moscato, P., Grebogi, R.B. and Haque, M.N. (2024), ‘Mathematical Modelling of Peak and Residual Shear Strength of Rough Rock Discontinuities Using Continued Fractions’, Rock Mechanics and Rock Engineering, vol. 57(2), pp. 851–865.

https://link.springer.com/article/10.1007/s00603-023-03548-0

• Butcher, C., Buzzi, O., Giacomini, A., Bertuzzi, R. and Griffiths, D.V. (2025), ‘Influence of Roughness Digitisation Error on Predictions of Discontinuity Shear Strength’, Remote Sensing, vol. 17(4), art. no. 599.

https://www.mdpi.com/2072-4292/17/4/599

• Butcher, C., Buzzi, O., Giacomini, A., Bertuzzi, R., Griffiths, D.V. and Fityus, S. (2025), ‘Shear Strength of a Large Limestone Discontinuity: In Situ Pull Test and Prediction’, Rock Mechanics and Rock Engineering, vol. 58(2), pp. 2203–2222.

https://link.springer.com/article/10.1007/s00603-024-04270-1

• Butcher, C. and Buzzi, O. (2025), ‘Quantifying Rock Strength Variability Under Different Tests and Failure Modes’, Rock Mechanics and Rock Engineering, 59, pp. 1441–1454.

https://link.springer.com/article/10.1007/s00603-025-04952-4