Strength estimation of evaporitic rocks using different testing methods

Rock strength is defined as the limit of the ability of a rock to resist stress or deformation without breaking. Testing methods recommended by ISRM (International Society of Rock Mechanics) and ASTM (American Standards Testing Material) include unconfined compressive strength (UCS), point load index (PLI), indirect tensile strength (ITS), Schmidt hammer rebound (SHR), sonic velocity (Vp and Vs), and slake durability index 2nd cycle (Id2). This contribution compares the results of these methods and explores the influence of rock composition and texture on Lower Miocene evaporites from Al Ain city, United Arab Emirates (UAE). These sedimentary rocks are common in the Arabian Peninsula as exposures or in the subsurface where they may constitute the foundations of buildings. A large number of UCS, PLI, ITS, SHR, SV, and Id2 tests were carried out on both core samples and rock blocks according to ASTM Standards. Examination of compositional and textural characteristics of representative rock samples was performed using XRD, XRF, polarized-light microscopy, and SEM. The results reveal variable correlations between the rock strength parameters with specific significant values between 0.53 and 0.72. The effect of composition and texture of the evaporitic rocks on their strength behavior is related to impurities such as clay minerals and celestite and grain interlocking textures. Despite the limited compositional variability of the evaporitic rocks (5–10%), the textural variability may present a challenging feature in rock strength testing and should be taken as a primary factor for consideration during applications.