Evolution of Elastic Wave Velocities and Amplitudes During Triaxial Deformation of Aji Granite Under Dry and Water‐Saturated Conditions

Abstract

Elastic wave velocities and amplitudes in fine‐grained Aji granite are measured during a series of deformation experiments under both dry and fluid‐saturated conditions, where compressional and shear waves traveled in a direction normal to the compressional axis, and shear wave was polarized normal to the compressional axis. In the early stages of deformation, both VP and VS increase slightly due to closure of preexisting cracks and then decrease due to nucleation and crack growth as the sample approaches failure. During deformation, the different sensitivities of compressional and shear waves to fluid‐filled cracks mean that the ratio VP/VS tends to increase for wet experiments and decrease for dry experiments prior to failure. The relative changes in elastic wave amplitudes are also related to deformation and fluid saturation: amplitude decreases at high differential stresses due to the opening of cracks oriented subparallel to the axis of maximum compression, whereas a relatively minor change in amplitude was observed under fluid‐saturated conditions. Thus, the changes in velocity and amplitude during the deformation experiments are linked to crack development and geometry. However, this sensitivity differs between dry and fluid‐saturated conditions. The monitoring of fluid injection volumes during fluid‐saturated experiments shows that decreasing elastic wave velocities and amplitudes coincide with increasing fluid injection. These systematic relationships among elastic wave velocity, amplitude, crack development, and fluid saturation suggest that understanding changes in seismic wave properties can offer significant insights into the temporal changes in the structure of fracture zones.

Effect of ultrasonic pretreatment monitored by real‐time online technologies on dried preparation time and yield during extraction process of okra pectin

“…The ultrasonic voltage peak is monitored by the PVDF sensor, as shown in Fig. 2(A), which is a characteristic value of the ultrasonic field in the time domain 41 . It is found that the ultrasonic voltage peak of SFU pretreatment is higher than that of FFU pretreatment in the range 2.25–10.98%, and that of 60 ± 1 kHz/30 min with a value of 0.05387 V is the highest during the ultrasonic pretreatment process.…”

“…It is found that, with the enhancement of ultrasonic pretreatment intensity in time and frequency domains, the pectin extraction yield increases. Some studies have shown that the monitored ultrasonic signal was sensitive to changes in material properties 41 . The extraction yield is 16.70% at the strong monitored ultrasonic intensity of 0.05387 V and −6.62 dBm in the 60 ± 1 kHz/30 min pretreated group, 1.94 times higher than 5.68% at the weak ultrasonic intensity of 0.04533 V and −23.49 dBm in the 40 ± 1 kHz/15 min pretreated group, and 2 times higher than 5.55% of the control without pretreatment.…”

Contrasting dilatant behaviors of mafic and ultramafic rocks based on triaxial deformation experiments

“…Since the formation and growth of axial microcracks are characterized by dilatancy, differences in dilatant behavior between mafic and ultramafic rocks can result in the different evolutions of these physical and transport properties during deformation. In mafic rocks, marked dilation during deformation may cause a large decrease in seismic wave velocity and a large increase in permeability (e.g., Mitchell and Faulkner, 2008;Fortin et al, 2011;Zaima and Katayama, 2018). In contrast, the relatively small dilation of ultramafic rocks means that the physical and transport proper-ties of an ultramafic rock layer is not significantly modified due to the small amounts of opening of axial microcracks until failure occurs.…”

Temporal Change in Seismic Wave Attenuation Using High-stable Vibration Sources.

“…Fracturing, crack opening, and saturation increase of pore fluid cause attenuation, as shown in laboratory experiments (Lockner et al 1977;Toksöz et al 1979;Tao and King 1990;Best et al 2007;Chichinina et al 2009;Amalokwu et al 2014;Zaima and Katayama 2018). These studies measured the changes in attenuation with fluid saturation and confining pressure, and reported an increase in attenuation with crack opening and saturation.…”