Estimating rock mechanical properties from microrebound measurements

Understanding rock mechanical properties is essential to many engineering geology applications. Comprehensive rock mechanics testing, however, is often not practical due to limited available sample volume, time constraints, and cost. Therefore, an alternative means for estimating mechanical properties at relatively low cost is desirable. In this investigation, we evaluate microrebound measurement on cut rock surfaces as a substitute for rock mechanical testing. We first explore the influences of rock sample thickness and testing substrate (material upon which samples rest) on microrebound, then perform systematic microrebound analysis of a range of well-characterized rock types with associated rock-mechanics datasets. Our analyses show that microrebound measurements are not sensitive to sample thickness greater than approximately 5 cm. Microrebound appears to be insensitive to the substrate among tested substrates including 2-mm-thick foam rubber, three different thicknesses of polystyrene foam (1.1 cm, 2.2 cm, and 3.6 cm), and standard lab tabletop. Strongest relationships between microrebound and rock properties are for unconfined compressive strength, tensile strength, and cohesion. Moderately strong correlations were found for density, Young's modulus, and porosity. A weak correlation was found for Poisson's ratio, and a very weak correlation was found for friction angle. Microrebound data can be obtained quickly and in a non-destructive manner using cut samples collected from outcrop or core, and at relatively low cost compared to traditional rock mechanics tests. Microrebound measurement can substitute for rock mechanics measurements for a multitude of applications in engineering geology where rock property data are needed, but full rock mechanics testing is not practical.