閉塞湛水浸透における砂層境界の効果について

Abstract

In order to clarify the mechanism of confined ponding infiltration into composite sand col-umns, penetrating phenomena in a 2-layered column where coarse-grained sand lies above fine-grained sand are analyzed theoretically. Results of our previously published experimental researchwith such a sand column reveal interesting stages of infiltration: (1) the short duration just after thewetting front has reached the junction or boundary between two sand layers, (2) the duration asthe wetting front has deeply penetrated into the lower layer. This paper describes the resultsobtained by analyzing basic equations with respect to the movements of water and air in sand-pores in these two stages of infiltration.In stage (1), in the case of relatively little difference in grain sizes between the two layers, calculated results of approximations of infiltration rate and pore-air pressure, deriving from basicequations, interestingly change with time in a manner concident to our experimental results.In stage (2), except in the case of nearly equal grain-size in both layers, the so-called "quasi-saturated zone" developes from junction to some finite depth in a lower layer. The thicknessof the "quasi-saturated zone" in the lower layer increases according as permeability and thicknessin the upper layer increase, and is greater than in the case of corresponding zone following pondinginfiltration into a homogeneous field of the same grain as lower layer. It is, however, foundout in comparison between theoretical and experimental results that patterns of moisture profilein columns, the infiltratin rate, the celertiy and the moisture profile of wetting front, and the rateof change of pore-air pressure are same for the homogeneous field and for the 2-loyered field.