1. Open Portal Slope and Support Design:
Dilokong Chrome Mine
ASA Metals (Pty) Ltd
Pieter Groenewald
Yolanda Bester
18 September 2009

2. Contents Introduction Location Data Collection Data Processing
Input Parameters
Numerical Modeling
Results
Recommendations

3. Introduction Geotechnical data acquisition
The use of empirical and numerical methods to transform data
Input parameters for FLAC/SLOPE modelling
Probabilistic assessments and kinematic failure analyses.
The portal geometry and support derived

4. Location
The Dilokong Chrome Mine situated on the eastern limb of the Bushveld Igneous Complex (BIC) is planning to exploit the LG6A and LG6 Chromitite seams.

5. Data Collection Field Work Laboratory Work Core Logging
Joint Orientation
Sample Collection
Laboratory Work
Young’s Modulus
Poisson’s Ratio
UCS

6. Data Processing Rock Mass Rating (Bieniawski ‘89) Q Rating
Statistical Analysis
Kinematic Analysis (DIPS and ROCLAB from Rocscience Inc)
Plane Failure
Wedge Failure
Toppling Failure

7. Input Parameters Laboratory Results Geotechnical Domains Water Table
Soil
Highly Weathered Saprolites
Weathered Pyroxenites
Fresh Pyroxenites
Water Table
Taken at 0.5m below surface
Rock Mass Ratings
Uniaxial compressive strength of rock material
Rock quality designation (RQD)
Spacing of discontinuities
Condition of discontinuities
Groundwater conditions
Orientation of discontinuities

8. Input Parameters Joint Orientations (DIPS) Support Circular failure
Plane failure
Wedge failure
Toppling
Support

9. Numerical modelling
ROCLAB
DIPS
Flac – Slope 5.0

10. Results
Factor of Safety (FOS)

11. Results
Factor of Safety (FOS)
ROCLAB

12. Results Factor of Safety (FOS) ROCLAB
Bench Face Angle (BFA) from Flac / Slope
Soil
Weathered Saprolite
Weathered Pyroxenite
Fresh Pyroxenite

13. Results – BFA Soil

14. Results – BFA Saprolite

15. Results – BFA Weathered Pyroxenite

16. Results – BFA Fresh Pyroxenite

17. Results – Fresh Rock CFA Method
The CFA analysis indicates the following:
A BFA of 74º for the Highwall based on plane failure
A BFA of 75º for the Sidewall based on plane failure
A BFA of 64º for the Sidewall based on wedge failure

18. Results Factor of Safety (FOS) ROCLAB
Bench Face Angle (BFA) from Flac / Slope
Soil
Weathered Saprolite
Weathered Pyroxenite
Fresh Pyroxenite
Support

19. Support

20. Recommendations

21. Suggested Configurations
Highwall
Sidewalls

22. Actual Configuration

23. Questions ?