| Summary: | 碩士 === 國立臺灣大學 === 農業工程學研究所 === 89 === Experimental Analysis of Fingering during Infiltration into Layered Soils:
Former experiments showed either stable flow or unstable flow may happen in two layered soil during infiltration. Especially when the fine soil overlayed the coarse sand, unstable flow easily occurred. In other words, fingering happened.
This study used two dimensional acrylic glass as experimental apparatus. The soil was silt clay from Shijou Shiang, Changhua, and the subsoil was 2mm glass bead. Three replicates were taken with 5 cm of water depth and 1000,10000 mg/l concentration of sodium chloride solution and 1000 mg/l concentration of cadmium chloride in 5 cm soil column. Because of the difference of the soil texture, fingering can happen during each experiment. Observing infiltration condition and comparing velocity with theoretical value, the results show that observed velocity is slower than theoretical velocity.
Study of Suitability of Miscible Displacement Theory During Fingering:
The miscible displacement has been applied in many fields of study and often uses to describe solutes dynamic transport in soils. To understand the suitability of miscible displacement during fingering, one-dimension of convection-dispersion-diffusion-adsorption equation and diffusion-dominanted equation were employed as basis of the theory. The experimental parameters from miscible displacement were put into equation and then compared theoretical values with experimental values.
The results show that the experimental values of chlorine conforms with theory, but the simulations for sodium and cadmium don’t fit in with experiments. However the simulated results showed that the main transport behavior of cadmium was adsorption and the effect of diffusion on chlorine and sodium is greater than adsorption. Our results indicated that the solute transport during fingering didn’t fit traditional miscible displacement theory.
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