A Combined Non-Destructive Prediction Method for Evaluating the Uniaxial Compressive Strength of Rocks Under Freeze–Thaw Cycles

Freeze–thaw degradation of rocks is an unavoidable problem in geotechnical engineering in cold regions, and the uniaxial compressive strength (UCS) of rocks is considered to be one of the most important parameters in rock engineering practices. In this study, we examine the relationships between UCS and porosity, longitudinal wave velocity, and mass of the rock under freeze–thaw cycling conditions using three non-destructive testing methods (nuclear magnetic resonance, wave velocity, and weight) and uniaxial compression test. Our experimental results show that: (1) the freeze–thaw damage of the rock is mainly due to the increase in the number of micro-pores and meso-pores, which is also the main reason for the decrease in the uniaxial compressive strength of the rock; (2) the rock damage exhibits three forms under freeze–thaw cycles: splitting damage, cone damage, and multi-crack damage. The freeze–thaw cycles induce internal cracks in the rock; (3) all three of these indexes show some correlations with the UCS, but none of the individual indexes can reflect it well enough alone. Among the three indexes, porosity is the best to reflect the changes of UCS with freeze–thaw cycles, with a correlation coefficient of 0.8. Based on these results, we propose a combined non-destructive prediction model. The comparison results show that the proposed model is more accurate than any of the single-index prediction models, with a correlation coefficient up to 0.943.