![]() RQD described by: The RQD is defined as the percentage of core recovered in intact pieces of 100 mm or more in length in the total length of a borehole. (Goodman R, 1989) In 1964 Deere proposed a quantitative index of rock mass quality based upon core recovery by diamond drilling. in this part, we explain 3 quantitative indexes that are useful: RQD, Total Core Recovery and Discontinuity Frequency. In addition of strength index of rock mass, there are quantitative indexes of rock mass quality that are very important to predict behavior of rock mass. ![]() Table 3 shows Standard diamond drill core sizes. this core barrel Reduces frictional heat that may damage sample. Outer core barrel for initial cut and second barrel to cut and second barrel to cut finer size. for obtaining core sample in fractured rock and highly weathered rocks.
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