Classification and assessment of rock mass parameters in Choghart iron mine using P-wave velocity

Engineering rock mass classification, based on empirical relations between rock mass parameters and engineering applications, is commonly used in rock engineering and forms the basis for designing rock structures. The basic data required may be obtained from visual observation and laboratory or field tests. However, owing to the discontinuous and variable nature of rock masses, it is difficult for rock engineers to directly obtain the specific design parameters needed. As an alternative, the use of geophysical methods in geomechanics such as seismography may largely address this problem. In this study, 25 seismic profiles with the total length of 543 m have been scanned to determine the geomechanical properties of the rock mass in blocks I, III and IV-2 of the Choghart iron mine. Moreover, rock joint measurements and sampling for laboratory tests were conducted. The results show that the rock mass rating (RMR) and Q values have a close relation with P-wave velocity parameters, including P-wave velocity in field (V_PF), P-wave velocity in the laboratory (V_PL) and the ratio of V_PF to V_PL (i.e. K_P = V_PF/V_PL). However, Q value, totally, has greater correlation coefficient and less error than the RMR. In addition, rock mass parameters including rock quality designation (RQD), uniaxial compressive strength (UCS), joint roughness coefficient (JRC) and Schmidt number (RN) show close relationship with P-wave velocity. An equation based on these parameters was obtained to estimate the P-wave velocity in the rock mass with a correlation coefficient of 91%. The velocities in two orthogonal directions and the results of joint study show that the wave velocity anisotropy in rock mass may be used as an efficient tool to assess the strong and weak directions in rock mass.