Rock quality determination, rock structure rating
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Rock Quality Designation Index Rock Quality Designation Index (RQD) (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
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Transcript of Rock quality determination, rock structure rating
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
RQDRQD
• Directionally dependant parameter• Intended to indicate rock mass quality in-situ• Adapted for surface exposures as number of discontinuities per unit volume
Procedure for Measurement and Calculation of RQDProcedure for Measurement and Calculation of RQD
RQD classification indexRQD Rock mass quality<25% - very poor25-50 % - Poor50-75% - Fair75-90% - Good90-100% - Excellent
Limitations of the RQD• RQD gives no information of the core pieces < 10cm excluded, i.e. it does not matter whether thediscarded 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
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. andconstruction parameters:size of tunnel; direction of drive; method of excavation.
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.
Rock Structure Rating: Parameter A: General area geology
Rock Structure Rating: Parameter B: Joint pattern & direction of drive
Rock Structure Rating: Parameter C: Groundwater, joint condition
