Analysis of local mechanical properties of rocks using instrumented indentation under cyclic freezing–and-thawing conditions

Abstract

Rock masses in high-altitude or cold regions are subjected to the combined effects of the freeze–and-thaw cycles and mixed-mode dynamic loading, which pose a serious threat to the safety and stability of geotechnical structures. Changes in the physical and mechanical properties of rocks and accumulation of fractures increase the risks of geotechnical accidents. Therefore, it is necessary to analyze rock deformation under cyclic stresses in order to mitigate the geo-hazardous phenomena. A series of tests were carried out as part of this investigation using the instrumented indentation method under cyclic freezing–and-thawing conditions. The impact of the freeze–thaw cycles and brine concentration on the failure characteristics of granite was investigated including its hardness and elastic wave velocity. The experimental results show that the data obtained by instrumented indentation correlate with the conventional methods, such as ultrasonic testing and surface roughness control. Moreover, it is shown that micro-damages in dense granites accumulate during the first 50 cycles, which at this stage does not result in macro-damages. In turn, an increase in the pore brine concentration does not intensify the failure processes at the early stage of cyclic freezing–and-thawing.