A Study of a Three Phases Structure and the Mechanical Properties of Partly Saturated Soil

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A study of a three phases structure of partly saturated soil is necessary to make clear its mechanical properties. First experimental study is conducted in triaxial compression test using silt specimen, and second the behavior of pore air/water pressure generated by external load or fluid pressure is investigated analytically as well as experimentally. Main results obtained from the present study are as follows.(1) Examination of state variables measurement of partly saturated soil in triaxial apparatus is important to describe its mechanical properties.(2) Negative pore water pressure measured by suction plate method is adequate for all range of degree of saturation.(3) The observed relationship among volume strain, pore air pressure and all round external pressure in triaxial test on silt can be explained by the two phases mixture ( air and soil skelton ) theory if soil sample is below the thirty percent of degree of saturation.(4) Two dimensional particulate model is formulated in the assembly of rod particle with equal diameter and examined to describe the structure and its properties( void ratio, number of contact point, mean diameter of pore space and so on ) in the experiment of uniform sand.(5) Darcy's law can be applied to air flow through partly saturated soil underlow pressure. The coefficient of air flow through soil varies with degree of saturation, and it vanishes to zero about over sixty percent.(6) Pore air/water pressure generated in partly saturated soil is investigatedunder the sample of sand column with different degree of saturation in some conditions of dewatering and/or air intrusion. As a result, it is shown in both analysis and experiment that soil water moves, being caused by air pressure fluctuation.