Effect of Pore Fluid Properties and the Increase of Temperature on Geotechnical and Geo-Environmental Parameters of Smectite

Researchers use smectite in different geotechnical and geo-environmental projects, such as industrial/municipal waste disposal sites and cut-off walls due to its specific properties. On the other hand, previous researches show that the load conditions, and pore fluid properties may significantly affect the behaviour of clayey soils. In spite of several researches that have been conducted on the engineering behaviour of smectite clays, there has been little attention to the influence of pore fluid changes and temperature increase on the geotechnical and geo-environmental properties of smectite. In this research, the influence of pore fluid properties changes and temperature on thephysico-mechanical behaviour of smectite has been Experimentally investigated. This study has been performed from micro-and macro-structural points of view. Due to the vast applications of smectite in geotechnical and geo-environmental engineering projects, this study focuses on a smectitic soil sample behaviour. The geotechnical properties of soil were determined based on the ASTM Standard [1]. The geo-environmental engineering properties of soil were measured by the method presented by Yong et al. [2]. The pore fluid analysis was performed by GBC 932 Plus atomic absorption spectrophotometer. Tables 1 and 2 show the geotechnical and geo-environmental engineering parameters of smectite sample. To investigate the possibility of changes of smectite behaviour due to the changes of pore fluid properties, the influence of calcium and sodium ions upon smectite behaviour was studied. These two cations are the most common cations that might be found in different sites. For this purpose, calcium sulfate and sodium sulfate in concentration of 0 to 1 normal was used. In addition, due to the importance of swelling and water retention properties of smectitein its application as barrier in geotechnical and geo-environmental projects, a part of experiments has focused upon swelling properties change of smectite sample. Finally, by performing a series of experiments related to the interaction process of soil-water including suction and swelling, the change in smectite behaviour due to thetemperature effect was investigated. For this purpose, saturated smectite samples were kept in four different. The achieved results indicate that due to the interaction of smectite with different electrolytes and with increasing the electrolyte concentration, the density of samples increase while the external load kept constant. This increase in density is attributed to the smectite-electrolyte interaction. A reduction in repulsive forces among clay particles was responsible for such a decrease in soil void ratio at constant external loading. Furthermore, the achieved XRD results indicate that after the interaction of clay particles with electrolyte, with increasing the electrolyte concentration, the position of basal spacing of smectite remains constant while theintensity of major smectite's peak decreases. This is attributed to the flocculated fabric due to the change in electrostatic forces among clay particles [3]. On the other hand, since hydraulic conductivity in clayey soils is a function of such a force among particles, the permeability of different smectite sample at different electrolyte concentration was evaluated. According to the results of Figure 1, the permeability may increase as much as 100 times after exposure of sample to different electrolyte concentration. In the last section of this research, the free swelling of smectite samples was measured after different levels of heat treatment from 25 to 200 oC. The results show a 16% reduction in swelling percentage of smectite after heat treatment. The achieved results of this study show that due to the interaction of different electrolytes and due to the temperature change, the water retention of smectite and its mechanical behaviour will be changed. This change in some cases was more than 50%. The results of micro-structural experiments show that the main reason for these changes in smectite behaviour after the interaction with electrolyte and temperature rise, was due to the change in morphology and new soil structure of smectite particles. In fact, the micro-structural change has affected the macrobehaviour of smectite.