| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系專班 === 101 === In this study, we apply the theory of poroelasticity combined with the linear stress-strain relationship for a two-fluid system to determine the phase speed and attenuation coefficient of the shear wave in an elastic porous medium containing two immiscible fluids. This study is divided into two parts; in the first part, we discuss the effect of soil texture on the propagation and attenuation of the shear wave, where eleven different soils [sand, loamy sand, sandy loam , sandy clay loam, sandy clay, loam, clay loam, silt loam, silty clay loam, silty clay and clay] bearing the air-water mixture are examined. The second part investigates the impact of different pore fluid mixtures on the propagation and attenuation of the shear wave, including the air - water mixture (air being the non-wetting fluid, water being the wetting fluid), the oil - water mixture (oil being the non-wetting fluid, water being the wetting fluid), and the air - oil mixture (air being the non-wetting fluid, oil being the wetting fluid). In these cases, Lincoln sand and Colombian fine sandy loam are selected as illustrative examples. Five lower excitation frequencies (50–200 Hz) are carried out for numerical simulation, and the saturation degree of the wetting fluid ranges from 0.01 to 0.99.
Our numerical results show the phase speed of the shear wave behaves more stable in sand, loamy sand, Lincoln sand, and Columbia fine sandy loam, among which the sand has the greatest phase speed of 94 m / s as water saturation is 0.01. Except sand and loamy sand, the phase speed of the shear wave is observed to increase abruptly with water saturation. We find that an important cause behind this phenomenon is the viscous coupling between the fluid and solid phases, i.e. R11, R22. In addition, , it is revealed that the phase speed of the shear wave increases with an decrease in water saturation in Lincoln sand and Columbia fine sandy loam saturated by any pore fluid mixture. Lastly, a conclusion is drawn that the attenuation coefficient of the shear wave appears to be proportional to the cubic of excitation frequency.
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