A new empirical formula for evaluating uniaxial compressive strength using the Schmidt hammer test

The uniaxial compressive strength (UCS) of rock is an important geotechnical parameter for engineering applications. However, how to determine the UCS simply and accurately has drawn the attentions of may researchers. To date, different kinds of indirect methods have been invented to determine the UCS of rocks, and among these methods, estimation of the UCS based on the Schmidt hammer rebound value (H-r) was commonly adopted. In this paper, an insightful analysis of the literature related to UCS estimation using the Schmidt hammer test was conducted, and three stages for the development of UCS estimation using H-r were classified. The drawbacks and merits of different kinds of techniques were analyzed in detail. Then, a data set containing the data for different rock types was collected from references, and to obtain an objective empirical formula, the simulated annealing-gene expression programming (SA-GEP) method was employed to establish the correlation between UCS and H-r. Based on the calculation results, the L-type Schmidt hammer was suggested for use in UCS estimation, and the corresponding empirical formula was established. To confirm validity of the empirical formula, the Schmidt hammer tests and uniaxial compressive tests were conducted separately, the experimental results were in a good agreement with the proposed empirical formula, implying that the proposed empirical formula can be applied in engineering practice.