Enhancing the accuracy of rebound test to predict rock UCS: reliability analysis and a novel wave impedance-based approach

The rebound test, which measures the rebound height (R_H) to swiftly assess the uniaxial compressive strength (UCS) of rock, is a potential alternative to address the costly and time-consuming of traditional direct testing methods. However, practical applications have revealed significant predictive inaccuracies with rebound testing, raising doubts about the reliability of current standards and previously empirical equations. This study critically evaluates the reliability of the rebound testing standard and existing empirical equations using the N-type Schmidt hammer. A total of 482 rock samples from Western China was analyzed through a series of laboratory tests, indicating that the N-type Schmidt hammer causes a significant decrease in UCS, even leading to sample damage. Moreover, the choice of rebound testing standard substantially influences the testing results. Cross-validation of reference and laboratory data exposed regional variations in data distribution characteristics, and statistical analysis showed that existing equations, developed from limited data, are not universally applicable. To enhance prediction accuracy, this research proposes the use of wave impedance to characterize initial rock damage, thereby gives a practical physical significance to the predictive equation. This research contributes to the refinement of current rebound testing standards and presents a novel methodology for improving the accuracy of rebound testing in rock mechanics.