Ultrasonic techniques are a simple, cost-effective, portable and non-destructive approach for evaluating the uniaxial compressive strength (UCS) of rocks. However, there are a number of factors affecting the ultrasonic pulse velocity (Vp) values. The main factors controlling the reliability of the method are surface irregularities of rock, micro-cracks and discontinuities, moisture content and porosity. To provide high prediction performances, data obtained from simple test methods are considered in combination to predict the mechanical properties of intact rocks. In this context, the use of both the Vp and Schmidt hammer rebound provides a better estimate of the UCS and minimizes the influence of the factors affecting the two techniques when they are used separately. The scope of this study is to assess the reliability and accuracy of the combined method in rock mechanics applications requiring the in situ determination of the UCS. The study material consists of various rock blocks of different strengths. The empirical relationships relating the Vp and rebound number (RN) were investigated using simple and multiple regression analysis. It was found that the combined method provides better estimates for UCS than Vp and RN separately. This method is proposed to indirectly determine the UCS of intact rocks.

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