A New Method for Correlating Rock Strength to Indentation Tests

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  • In this Paper, UCS of limestone rock was determined by indentation testing on rock fragments. The size of the
    fragments was in the range of 2 to 5 mm, which is within the size range of drill cuttings. Here, scatter of the data
    was investigated by calculating the coefficient of variation that showed the size dependency of the conventional
    indentation parameters; Indentation Modulus (IM) and Critical Transition Force (CTF). Thus, it is recommended
    that the results of indentation tests should be normalized by the fragment size and presented in the form of
    Normalized Indentation Modulus (IMn) and Normalized Critical Transition Force (CTFn). Regression analysis
    was carried out to show the relationship between the IMn or CTFn and the UCS. Linear and exponential
    regression provided reasonable correlation coefficients of higher than 0.74 and 0.85, respectively. The proposed
    empirical equations for estimation of the intact rock UCS from the normalized indentation indices were verified
    using independent data from limestone rocks not used in developing the correlations. The outcome was a strong
    agreement (R~1.00) between the estimated and measured UCS. Based on statistical analysis, minimum number
    of indentation test was determined for random size samples. It is suggested that indentation testing be carried out
    using uniform fragment sizes to reduce the required number of indentation tests.

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    Article (Draft / Submitted)
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    Attribution-NonCommercial 4.0 International