Elastic wave propagation and attenuation across cemented rock fractures under tension

Abstract

Tensile loading plays a critical role in geological processes like landslides and earthquakes, as well as engineering applications such as hydraulic fracturing and tunnel excavation. We investigate elastic wave behavior across cemented rock fractures under tensile stress conditions. Ultrasonic measurements and uniaxial direct tension tests were performed concurrently on quartz diorite and diabase specimens with and without individual cemented fractures to determine the influence of tensile stress on the characteristics of elastic waves. Results show that increasing tensile stress leads to enhanced wave attenuation and reduced velocity, amplitudes, and dominant frequency of transmitted waves. These changes are primarily driven by the formation and growth of microcracks near cemented rock fractures under tensile stress. The jointed quartz diorite samples experienced progressive reductions in static and dynamic fracture stiffness. In contrast, jointed diabase samples maintained nearly constant static fracture stiffness and only saw decreases in dynamic fracture stiffness. The reduction in dynamic fracture stiffness is attributed to microscopic damage that modifies elastic wave velocity and dissipation but is not captured by static stress-strain measurements. The gradual decrease in dynamic fracture stiffness reflects stable crack growth, while sudden reductions indicate crack coalescence at the interface. We propose that dynamic fracture stiffness, assessable with seismic wave measurement, is a more reliable indicator of tensile damage than static fracture stiffness due to its sensitivity to low strains and ability to capture microstructural changes. These findings provide valuable insights into seismic methods applied to assess stress conditions on rock discontinuities in the field.