The suitability of the osmotic technique for the long-term testing of partly saturated soils

The understanding of partly saturated soil behavior can be enhanced with the help of additional specialist testing in the laboratory. From the various techniques available to do so at present, the osmotic technique is probably the simplest one. However, there are concerns with the response of this system over time, and in particular its ability to sustain suctions for long periods of time. In this study, the response of a synthetic semi-permeable membrane in conjunction with a solution of high molecular weight has been investigated. The behavior of the osmotic system has been studied both in isolation and in full scale tests, by incorporating it into a purposely built oedometer. Not only was it possible to establish a calibration curve of osmotic potential versus concentration of solution but, additionally, it was possible to perform tests which extended for up to five months. The results suggest that with the correct choice of semi-permeable membrane and solution, it should be possible to use the osmotic technique in a satisfactory manner to perform any desired test on partly saturated soils, regardless of its duration.