Study on Compressive Strength Degradation of Hard Rocks Induced by Water Saturation Using Acoustic Emission

Water–rock interaction in rock mass practice can lead to significant deterioration of rock strength, posing a substantial threat to the stability and safety of rock engineering projects. By now, the understanding of water weakening properties of hard rocks is still limited, and it remains challenging to accurately quantify and describe the extent of various water weakening effects. In this study, we focused on four representative hard rocks, namely Baoxin marble, Jinping marble, Mahu limestone, and Changtai granite, which posses unique mineral compositions and microstructures. To assess the different water weakening effects, we conducted a series of uniaxial compression tests accompanied by acoustic emission (AE) monitoring. We analyzed certain parameters of both dry and saturated hard rocks, including compressive strength and the dominant frequency of the AE waveform, to evaluate the extent of various water weakening effects. Our findings show that, when the hard rocks are saturated, they exhibited varying degree of compressive strength reductions, e.g., 26% for Baoxin marble, 6% for Jinping marble, 24% for Mahu limestone, and 9% for Changtai granite. A twin-peak feature is observed in the dominant frequency of AE waveforms, regardless of rock types and soaking states. Moreover, water saturation leads to a decrease in the micro shear failures and an increase in micro tensile failures. The degradation of rock strength in hard rocks devoid of clay and siliceous minerals is primarily attributed to the effect of pore water pressure, with the intensity depending on the mineral composition and microstructural characteristics. Stress corrosion may be considered the primary reason for the strength reduction observed in saturated granite.