Rock quality determination, rock structure rating

Rock quality determination, rock structure rating

1. Rock Quality Designation Index (RQD)Rock Quality Designation Index (RQD)
(Deere et al. 1967)(Deere et al. 1967)
• Aim : to provide a quantitative estimate of rock mass
quality from drill logs
• Equal to the percentage of intact core pieces longer than
100mm in the total length of core
The rock quality designation (RQD) is a commonly used
index for the description of rock mass fractured state

2. RQDRQD
• Directionally dependant parameter
• Intended to indicate rock mass quality in-situ
• Adapted for surface exposures as number of
discontinuities per unit volume

3. Procedure for Measurement and Calculation of RQDProcedure for Measurement and Calculation of RQD

5. RQD classification index
RQD Rock mass quality
<25% - very poor
25-50 % - Poor
50-75% - Fair
75-90% - Good
90-100% - Excellent
Limitations of the RQD
• RQD gives no information of the core pieces < 10cm
excluded, i.e. it does not matter whether the
discarded pieces are earth-like materials or fresh rock pieces
up to 10cm length
• Gives wrong values where joints contain thin clay fillings or
weathered material
• Does not take direct account of joint orientation

6. Rock Structure Rating (RSR)
It is a quantitative method for describing quality of a rock
mass and appropriate ground support, in particular, for
steel-rib support, developed by Wickham, Tiedemann and
Skinner.
The RSR concept introduced a rating system for rock
masses. It was the sum of weighted values in this
classification system.
There are considered two general categories:
geotechnical parameters:
rock type; joint pattern; joint orientations; type of
discontinuities; major faults; shears and folds; rock
material properties; weathering or alteration. and
construction parameters:
size of tunnel; direction of drive; method of excavation.

7. The RSR value of any tunnel section is obtained by summing the
weighted numerical values determined for each parameter.
The RSR concept is a very useful method for selecting steel rib
support for rock tunnels.
The nature and distribution of structural features within a rock
mass which may have a dominant effect on the response of the
rock.

8. Rock Structure Rating: Parameter A: General area geology

9. Rock Structure Rating: Parameter B: Joint pattern & direction of
drive

10. Rock Structure Rating: Parameter C: Groundwater, joint
condition