Study of Seepage Characteristic Testing Method for Unsaturated Soils By Controlling Air Pressure

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In this study, three topics have been examined concerning with the seepage testing method developed as the stationary flow through unsaturated soils. ( 1 ) Accumulation of data in the unsaturated seepage characteristics, ( 2 ) study on the relationship between seepage characteristics and soil properties including grain size characteristics, ( 3 ) development of composite testing apparatus for seepage and compression and its utility.( 1 ) Accumulated data are, 1) moisture holding characteristic curve, 2) coefficient of permeability for unsaturated soils to the degree of saturation, and 3) coefficient of air flow. Ten kinds of soils are following as Toyoura Standard sand, the Nagara sand, coarse sand, silt, roam and so on.( 2 ) The relationship between the grain size distribution ( 50 % diameter, diameter estimating grain size distribution, etc. ) and moisture holding characteristic values ( air entry value, specific moisture holding capacity, etc. ) are examined to establish the proposed formula with good accuracy among many equation like the Haverkanmp method and the van-Genuchuten method. Among these results, it is clear that air entry value is in reverse proportion to the diameter estimating grain size distribution, and that the pore diameter indices and the specific capacity are strongly dependent to the coefficient of uniformity.( 3 ) As a result of the composite testing apparatus for seepage and compression, permeability and strength of silt are depended on the degree of saturation, as was found in former study of tested specimens respectively. A sample of results is that the uni-axial compression strength is in reverse proportion to the logarithm of coefficient of permeability, and that stress-strain relationship varies from brittle to ductile at certain water content.