Investigation of saturation effect on the relationship between compressive strength and Schmidt hammer rebound

Schmidt rebound values obtained by Schmidt hammer tests have recently been used to predict the uniaxial compressive strengths of both intact rocks and rough joint surfaces. The easy application procedure, short test duration and nondestructive nature of Schmidt hammer testing are the main reasons for which it is preferred by numerous investigators. To date, relationships derived between uniaxial compressive strength and Schmidt rebound values are generally valid only in dry conditions. However, while the adverse effects of saturation upon uniaxial compressive strength are known and emphasized in many studies, there has yet to be a comprehensive investigation dealing with the effects of saturation on Schmidt rebound values. Considering this deficiency, an attempt was made to investigate the effects of saturation on uniaxial compressive strength and Schmidt rebound values and to derive relationships between these two parameters considering the saturation degree. For this purpose, the uniaxial compressive strength and Schmidt rebound values of 14 rock types and one construction material were determined for dry and fully saturated conditions. According to results of laboratory tests, the adverse effects of saturation on both quantities were determined. The results showed that the levels of these adverse effects were dramatically different for the two parameters. Statistical evaluations indicated that relationships between uniaxial compressive strength and Schmidt rebound values are dependent on the degree of the saturation of intact rock material. By considering this, simple and multivariate regression analyses were performed and the resultant simple and multivariate equations were produced. In multivariate regression analysis, the degree of saturation and Schmidt rebound values are used as independent variables. All derived equations have high prediction performance and were determined to be statistically reliable.