Transmission of ultrasonic wave across moisture rocks: Effects of moisture sorption on velocity variation and attenuation

This study focused on investigating the impact of moisture-induced mechanical degradation on three types of rocks. Dynamic moisture sorption experiments were conducted to understand water vapor sorption across different relative humidity (RH) conditions. Ultrasonic tests, performed at various RH levels, revealed the sensitivity of wave velocities and attenuations to changes in moisture content. Subsequent measurements of unconfined compressive strength (UCS) demonstrated how moisture-induced degradation affects the mechanical properties of rocks. This study evaluated the effects of RH on ultrasonic P-/S-wave velocities in three rocks, revealing distinct moisture effects on wave velocity variations. Gray shale and sandstone exhibited similar P-wave behaviors, while black shale differed significantly, showcasing early stiffening effects at lower RH. Saturation heterogeneities at the pore-scale and patchy effects at the large scale highlighted complex interactions between rock, moisture, and wave characteristics. Furthermore, the research assessed the impact of relative humidity on ultrasonic wave attenuations in partially saturated rocks. As RH increased, P-wave attenuation generally rose, influenced by dynamic water saturation and fabric heterogeneity. S-wave attenuation exhibited a similar trend, with noticeable variations among rock types. UCS tests indicated that higher moisture content led to decreased UCS values across various rock specimens. The P- and S-wave velocities during loading further emphasized moisture sensitivity, with S-wave velocity being more responsive to moisture content variations. Dynamic Young's moduli exhibited distinct changes during UCS measurements, highlighting the influence of moisture content on mechanical degradations. These findings underscore the importance of considering moisture effects in understanding and predicting the mechanical behavior of rocks.