عنوان مقاله [English]
Nowadays, the use of different materials in combination with the soil has been grown in geotechnical applications. One of these materials is expanded polystyrene beads (EPS) that used to reduce the density and to provide lightweight fill. To investigate the possibility of strength enhancement of soil-EPS beads mixture, number of 34 standard triaxial compression tests with diameter of 100 mm and height of 200 mm have been conducted on the soil alone, unreinforced and geotextile reinforced soil-EPS beads mixture with and without sandy lens layers. 0.5%, 1% and 2% of EPS beads by weight to mix with sand, four layers of geotextiles and four layers of sand lens with thickness of 20 mm were used to prepare the samples. The tests were carried out at three different confining pressures of 100, 200 and 300 kPa, up to 15% of axial strain. Test results show that, although EPS beads produces lightweight material but their low rigidity and large volume strain caused loss of mixture strength. It can be seen that ultimate strength of mixure (at strain of 15%) decreases 42%, 65% and 78% for 0.5%, 1% and 2% of EPS beads, respectively as compared with soil alone. To balance between weight loss and loss of strength, the use of 0.5% of EPS beads to mix with sand seems appropriate. To increase the strength of sand-EPS beads mixture, geotextile layers and sandy lens layers were used. The results show that the geotextile layers encapsulated with sandy lens layers have an influential impact in increasing the strength of mixture. For example, the use of four geotextile layers encapsulated with four sand lens layers gives 123% increase in the strength compared with the unreinforced sand-EPS beads mixture. Thus the combination of these two methods significantly increases the resistance of the mixture. On the basis of the study, the concept of sand-EPS beads mixture reinforced by geotextile layers encapsulated with soil lens layers could be used to improve the performance of backfill over soft soil.