| 講演要旨(和文) | | 2%の塩水で飽和された未固結媒体の凍結過程における超音波波動伝播実験を行い、P波ならびにS波の減衰特性を明らかにした。減衰に用いた周波数はP波では350-600 kHz 、S波では150-250 kHzである。P波の減衰特性は-3°Cで最大となり、その後温度低下に伴い徐々に減衰値が低下する傾向が得られた。S波については、減衰値からは明確な傾向は見られなかったが、振幅スペクトルの傾向からP波と同様の傾向が見ることができることがわかった。 |
|
|
| | 講演要旨(英文) | | Ultrasonic wave transmission measurements were conducted in order to examine the influence of ice-brine coexisting system grown in unconsolidated porous material on ultrasonic P- and S-waves. We observed the variations of a transmitted wave, changing its temperature from 0C to -15C and quantitatively estimated attenuation for unconsolidated porous material during the freezing of brine in porous material by considering different distances between the source and receiver transducers. This paper is concerned with attenuation at ultrasonic frequencies of 350-600 kHz for P-waves and 150-250 kHz for S-waves. The waveform analyses for P-waves indicate that the attenuation curves reach their peak at a temperature of -3C and gradually decrease with decreasing temperature, which is interpreted as the increase of the ice fraction or the increase of the effective bulk modulus of the system. The waveform analyses for S-waves indicate that the attenuation decreases with decreasing temperature, which is interpreted as the increase of the effective shear modulus of the system due to the increase of cementation of ice in the frozen sand. The laboratory experiments of the present study demonstrated that ultrasonic waves with such a frequency range are significantly affected by the existence of a solid-liquid coexistence system in the porous material. In terms of a plausible mechanism for attenuation, we must consider the physical interactions between pore fluid, sands, and ice, that is, the pore microstructure and permeability in such system is important. |
|
|
|
| |
|