Data Requirements
What is needed to engage StADSS to characterise the peak and residual shear strength of a discontinuity?
StADSS model has several key inputs:
– Hoek-Brown intact material strength parameters σci and mi,
– Basic friction angle 
b,
– Effective normal stress σ’n,
– High resolution image of seed trace, and
– Seed trace scale survey data.
Comments on obtaining this data and their individual requirements are tabulated below:
| Data Type/Parameter | Comment/Description |
| σci and mi | The Hoek-Brown intact material compressive strength and intact material parameter is typically obtained via a series of triaxial tests conducted on material representative of the discontinuity. The parameters are obtained by fitting the failure criterion to the data. Please note the intact material compressive strength is not simply equal to the uniaxial compressive strength (UCS). Where specimens are not obtainable, similar data may be used from literature as substitute. If test data cannot be obtained, please contact us so we can give guidance in obtaining this data or other possible solutions. |
| b | The basic friction angle can be obtained via multiple suggested methods in literature. Perhaps the simplest method is the ISRM Suggested Method for obtaining the basic friction angle where 3 core specimens of specific dimensions are set up in a tilt test apparatus. The basic friction angle is taken as the median of 5 tests after a mathematical correction is applied to the raw data. Values of the basic friction angle can be inferred from literature where specimens cannot be obtained. |
| σ’n | The effective normal stress is commonly estimated from density calculations and site measurements. The presence of pore pressure in the joint must be carefully considered and measured wherever possible if present. |
| Image of seed trace | The image of the seed trace is the most essential input to StADSS. The image must be captured with a high resolution image (minimum 20 megapixel), suitable lighting conditions (no shadowing or harsh lighting), the trace must be clean and visible, the camera must be perpendicular to the rock face/parallel with the likely shear direction, and a prime lens should be adopted. Corrections for lens distortion should be applied prior to submitting to StADSS for analysis. The image of the seed trace should capture the entire trace with a ground sampling distance (GSD) equal to or better/less than 1.4 mm/pixel. |
| Seed trace scale survey data | Clear datapoints must be visible in the image of the seed trace with corresponding survey data so that the image can be scaled during post-processing. A minimum of 3 control points are required and hand measurements on site are recommended where possible for sanity checks. |
| Angle of rock face relative to camera orientation | When capturing an image of the daylighting seed trace with a camera it may not be possible to orient the camera perpendicular to the rock face. In this scenario, roughness data is distorted within the image and a geometrical correction must be applied. Wherever possible, this angle should be reported as 90 degrees. |
| Dip of the discontinuity relative to the rock face | As above, if the rock face is not perpendicular to the camera orientation and the average discontinuity plane, roughness data is distorted in an image. The angle between the average discontinuity plane and the average rockface plane must be reported to make geometrical corrections. |
Frequently asked questions:
“We don’t have access to a lab or 3rd party provider for sample testing.”
Please contact us to discuss an option moving forward. Whilst it is not a service we typically provide, we have experience with labs in our region who can facilitate this testing.
“What camera should be use to capture the seed trace?”
Many modern cameras are suitable for use. The key requirements are a minimum of a 20 megapixel camera sensor should be used, and a prime (i.e. fixed focal length) lens should be adopted where possible. Any attempt to reduce lens distortion (i.e. fisheye) will greatly improve results.
“We cannot achieve an adequate GSD and contain the trace in a single image.”
Please contact us to discuss an approach to move forward. A stitching process can be adopted using multiple images, but this is more intensive and requires careful survey techniques.
“We would like more in depth analysis including sensitivity analysis, what data is required?
For any analysis outside of the typical StADSS workflow, please contact us for a specific requirements package tailored to you.