Keywords: unsaturated soil, cyclic loading, accumulated axial strain, initial suction.

A good quality coarse-grained soil with minimum fines is the most important requirement for the railway embankment to exhibit minimum deformation during its design life. The soil in the railway embankment undergoes long-term cyclic loading and changes in the water content during its lifetime. To understand the performance of the embankment, this study investigates the mechanical behaviour of coarse-grained soils in terms of accumulated axial strain and volumetric changes during cyclic loading in unsaturated conditions. Suction-controlled unsaturated drained cyclic loading tests were carried out for the soils compacted at different degrees of saturation. The initial suction is measured immediately after the compaction and is deeply investigated with the changes in the degree of saturation. The results show that the decrease in the degree of saturation decreases the accumulated axial strain substantially, at the same degree of compaction. The initial suction is the parameter that resists the particle rearrangement during the cyclic loading. The larger the initial suction, the accumulated axial strain is lower. In addition to that, the larger the initial suction, the volumetric strain shows a more contractive behaviour. This result shows that minimal changes in the initial suction and the degree of saturation could affect the deformation behaviour of soils during cyclic loading.

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