The determination of soil water retention curves requires the volume to be measured in order to calculate the void ratio and degree of saturation. The volume change of sample during drying and wetting cycles in soil water retention test is obvious and non-ignorable, especially for soils with deformability. The soil water retention curve is generally superimposed with the volume change of soil specimens. However, in general, many apparatus that are used for soil water retention testing cannot measure the volume change during the test process. In this study, a modified experimental system, which can measure and record volume change during test, and also can control the entire testing process via computer, is proposed to determine the soil water retention curve. The new system has several advantages over existing apparatus. Notable amongst them is that it can automatically determine both the wetting and the drying characteristics with high accuracy, and can measure volume change during test, using only one sample. This technical note presents the design detail and algorithm for control software. Water retention curves considering volume change are determined for four types of soil, ranging from sandy to silty. Then the effect of volume change on soil water retention curve is briefly discussed.
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