Concept
Description and Procedure
The thermo-hydro-mechanical oedometer apparatus is similar to oedometer test apparatus with the exception that it allows controlling/measuring the soil suction and temperature. The test is designed to investigate the effect of the temperature and the suction on the mechanical response of the soils. There are three main methods to control suction for unsaturated soil testing :
- Axis translation method
- Osmotic method
- Vapor equilibrium method
Custom-designed thermo-hydro-mechanical oedometer cellls cells use one or a combination of the above methods to control the soil suction. The vapour equilibrium method, however, appears to be an approriate candidate in combination with temperature-controlled condition. In the vapour equilibrium method, total suction is controlled through the control of relative humidity. A salt or acid solution regulates the relative humidity of the atmosphere within a desiccator. A convection circuit forces this regulated atmosphere to circulate through the sample or on its boundaries. Once the equilibrium reached, the soil water potential is equal to that of the vapour phase which itself is in correlation with the relative humidity of the surrounding atmosphere.
The temperature is usually controlled by means of a heating device consisting of a ring-shaped chamber surrounding the soil sample and filled with circulating heated water or oil. The liquid itself is heated to the desired temperate through an electric cryostat. An approriate thermal insulation of the oedometer cell is required in order to avoid the influence of ambient room temperature. This can be done by placing the oedometer cell system in a isulated box or by using thermal isulating covers around the cell.
The mechanical load, or the axial stress can be applied by means of a classical hydaulic jack. Depending on the controlling systems and methods, different ranges of suction, temperature and axial stress can be applied to the sample.
The test is carried out on a cylindrical specimen of saturated or unsaturated soil. As in oedometer test,incrementals of vertical static load are applied to the sample and the vertical displacement of the sample is measured at different loading steps. The difference here is that the loading can be a combination of vertical stress, suction, and temperature variation. The results are then used to characterize the consolidation and the stress-strain behaviour of the soil under the influence of suction and temperature.
Standards
- NA
References - External Links
- François, B. & Laloui, L. (2010), An Oedometer for Studying Combined Effects of Temperature and Suction on Soils, Geotechnical testing journal, vol. 33, num. 2, 2010, p. 112-122
- Richards, B. (1965). Measurement of free energy of soil moisture by the psychrometric technique using thermistors. In Moisture equilibria and moisture changes in soils beneath covered area, pages 39–46, Australia, butterworths.
- Fredlund, D. and Rahardjo, H. (1993). Soil mechanics for unsaturated soil. John Wiley & Sons, Inc.