Abstract
Tests were conducted to determine the retention curve using the thermocouple psychrometer and evaporation techniques. The retention curve describes the relationship between the soil suction and the water content. Three soils with varying plasticities were examined. Soil samples were remolded using the modified and standard Proctor efforts. Soil samples were compacted at two different water contents: 2% wet of optimum and 2% dry of optimum. One thermocouple psychrometer per sample was installed during compaction. The water content was determined by periodical weight measurements of the soil sample. The measured data were fit to existing parametric models (e.g. van Genuchten, 1980, and Fredlund and Xing, 1994) using the Solver subroutine provided with Microsoft Excel. Variations in the retention curves based on the soil type, compactive effort, and the compaction water content were observed. The van Genuchten model fit the measured retention curves better than the Fredlund and Xing model. Retention curves were arranged according to their Plasticity Index (PI). The higher the PI, the higher the location of the retention curve on the graph. Samples prepared using the modified compactive effort plotted above samples prepared using the standard compactive effort. The retention curve for samples prepared wet of optimum water content plotted above samples prepared dry of optimum water content. The thermocouple psychrometer provided a simple and efficient tool in the determination of the soil suction. The results of this study are in good agreement with results of previous studies (Tinjum et al., 1997, Miller et al., 1999, and K. Yaldo, 1999).