Lecture 2_ Rockmass Characterisation_2.pptx

Rockmass characterisation

1. Presenter: WB Motlhabane Geotechnical Engineering 3A (GEMIN 3A) Lecture 2 ROCKMASS CHARACTERISATION AND CLASSIFICATION

2. Agenda Geotechnical/Rock Engineering Definition and Objectives Safety Hazards (+ visuals) Rockmass Characterisation and Classification Data Collection (and RQD) Q-System by Barton et al (1974) Geomachanics Classification System by Bieniawski (1989). Mining Rock Mass Rating by Laubscher and Taylor (1976) and refined by Laubscher (1994 ). Design Rockmass Strength (DRMS) Applications Classification Systems for Mine excavation design Worked Examples

3. Rockmass Classification – Mining Rock Mass Classification ( M RMR) MRMR Parameters: RMR PARAMTERS

4. MRMR - Classification

5. MRMR – Classification_ Joint Spacing Rating Adjustment

6. MRMR – Classification_ Joint Condition and Groundwater R ating Adjustment

7. Rockmass Classification – MRMR adjustments MRMR Adjusting For: Weathering Joint Orientation Stress Environment Blasting

8. Rockmass Classification – MRMR adjustments MRMR Adjusting For Weathering

9. Rockmass Classification – MRMR adjustments MRMR Adjusting For Joint Orientation

10. Rockmass Classification – MRMR adjustments MRMR Adjusting For Shear Zone

11. Rockmass Classification – MRMR adjustments MRMR Adjusting For Stress Environment Based on good judgement Good confining stress – 120% Poor confinement, closely spaced, etc – 60%

12. Rockmass Classification – MRMR adjustments MRMR Adjusting For Blasting Effects

13. Rockmass Classification – MRMR adjustment ADJUSTED MRMR

14. Rockmass Classification – Design Rockmass Strength (DRMS) RMS = UCS x (MRMR – R UCS )/100 Where R UCS is the corresponding UCS rating value in MRMR table. DRMS = RMS (adjustment parameters)

15. Rockmass Classification – Systems Applications

16. Rockmass Classification – Systems Applications

17. Rockmass Classification – Systems Applications

18. Rockmass Classification – Systems Applications

19. Rockmass Characterisation and Classification Worked Problems Problem 5 An excavation is to be developed in a Rockmass along strike direction and against dip of joints . Determine the competence of this rock mass to host this excavation by using geomachanics classification system. Also Determine the design rock mass strength for this conditions. Given the following pertaining to the Rockmass: Intact rock strength of 60 Mpa RQD = 67% Average Joint spacing = 1m and the joints are slicken sided. Damp environment Joints dip angle = 30 degrees

20. RMR – Classification Problem solution

21. RMR – Classification Problem solution RMR = 7 + 13 + 15 + 10 + 10 – 5 = 50

22. Rockmass Characterisation and Classification Worked Problems Problem 6 An excavation is to be developed along strike direction and against dip of another joint set in a rock a mass described below. Determine the competence of this rock mass to host this excavation by using Mining Rock Mass Rating system (MRMR). Also determine the rock mass strength (RMS) and Design rock mass strength and comment on your results. Intact rock strength of 60 Mpa RQD = 67% 2 joint sets and average j oint spacing = 1m and the joints are slicken sided. Damp/moist environment Average joints dip angle = 30 degrees, J oints are curved, smooth, unaltered and have finely sheared infill material Rockmass is slightly weathered and the excavation expected lifespan is 9 yrs. The excavation will be developed by conventional blasting methods Good confining stress is known to be prevalent in this environment.

23. MRMR – Classification Problem Solution 25 x 0.88 = 22 40 x 0.85 x 0.6 x 1.0 x 0.55 = 11.22

24. MRMR – Classification Problem Solution 0.88

25. MRMR – Classification Problem Solution

26. MRMR – Classification Problem Solution 25 x 0.88 = 22 40 x 0.85 x 0.6 x 1.0 x 0.55 = 11.22 Therefore MRMR = 10 + 6 + 22 + 11.22 = 49

27. MRMR – Classification Problem Solution MRMR Adjusting For Weathering

28. MRMR – Classification Problem Solution MRMR Adjusting For Joint Orientation

29. MRMR – Classification Problem Solution MRMR Adjusting For Shear Zone No mention of any shear zones, thus no rating or rating of 100%

30. Rockmass Classification – MRMR adjustments MRMR Adjusting For Stress Environment Based on good judgement Good confining stress – 120% Poor confinement, closely spaced, etc – 60%

31. Rockmass Classification – MRMR adjustments MRMR Adjusting For Blasting Effects ADJUSTED MRMR = 49 X 0.96 X 0.80 X 1 X 1.2 X 0.94 = 42 RMS = UCS x (49 – RUCS)/ 100 = 60 x (49 – 6)/100 = 25 Mpa D RMS = 25 Mpa X 0.96 X 0.80 X 1 X 1.2 X 0.94 = 22 Mpa