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The correlation of Mining Rock Mass Rating with In-situ Rock Mass Rating of some
selected rock types in Edo State, Nigeria was carried out in this research work. The strength
parameters and the discontinuities parameters of the selected rock types were determined on the
field and in laboratory in accordance with American Society for Testing and Monitoring (ASTM) D
2166 standard and the methods suggested by International Society for Rock Mechanics (ISRM).
The results show that, the uniaxial compressive strength of the different calcite, dolomite, marble,
granite and kaolin rock samples at the selected locations are 13.979 MPa, 27.9 MPa, 67.287 MPa,
72.092 MPa and 12.139 MPa respectively. The uniaxial compressive strength of marble and granite
is higher than that of calcite and dolomite at the different locations. The spacing of discontinuities
of the various locations was carried out and the mean values were calculated from locations A, B, C,
D, and E as 100.05 mm, 98.72 mm, 110.14 mm, 109.53 mm and 109.10 mm respectively. The
results were used to correlate the Mining Rock Mass Rating (MRMR) with In-situ Rock Mass
Rating (IRMR). The results of the research shows that the values of MRMR and IRMR were 52.60
and 53.21 respectively, which indicates that there is a good relationship between the rock mass
rating values derived from MRMR and IRMR classification systems. Also from the results of the
various correlations, the correlation coefficient (R2) of MRMR for calcite, dolomite, marble, granite
and kaolin are 0.512, 0.937, 0.880, 0.956, and 0.914, respectively while the correlation coefficient
(R2) of IRMR for the same rock types are 0.755, 0.557, 0.688, 0.936, and 0.908 respectively, which
implies that a very strong positive correlations exist between them and MRMR. This relationship
should not be made redundant but utilize as a mine design tool.
Keywords: Correlation, Rock Mass Rating, In-situ Rock Mass Rating, Uniaxial Compressive Strength,
Orientation, RQD