A Unified Alteration Index (UAI) for Mafic Rocks

The geomechanical properties of diabase in the ophiolitic melange and basalt in the Lower and Middle Eocene volcanics of Ankara, Turkey, were determined as part of an investigation of potential dam sites. A classification is proposed based on a concept called the “unified alteration index (UAI),” which expresses a percentage decrease in uniaxial strength and compressional wave velocity of the mafic rocks determined in the laboratory. The UAI classification consists of five groups—unaltered, slightly, moderately, highly, and extremely altered—for this proposed modified classification system. A statistical analysis was used in examining the relationships between the UAI and geomechanical properties of the mafic rocks, and revealed that the UAI = exp (−0.0495 – 0.001σ_c) (r² = 0.64) and UAI = 1.0058 – 7.663e-5C_p - 8.227e-9C_p² (r² = 0.93).