Small Strain Behaviour of a Compacted Subgrade Soil

The small strain behaviour is a key indicator for assessing the performance of compacted fills. The initial compaction conditions i.e. water content and applied energy, govern compaction effectiveness and, thus, the structure and matric suction of compacted subgrade soil. This paper presents an experimental study of the small strain behaviour of a typical compacted subgrade soil, i.e. silty sand, prepared with different compaction conditions. Specimens were prepared for different compaction states to mimic the typical acceptance criteria of end-product specifications. The small strain modulus (G0) was evaluated using Bender elements, while the post-compaction matric suction was measured using the filter paper method and a tensiometer. The experimental data indicates a strong modulus dependency on water content or suction across the compaction plane but suggests G0 is better described as a function of the degree of saturation (Sr). The laboratory results are also examined in light of common end-product specifications, which show that it may be beneficial to compact the soil slightly dry of optimum moisture content from the modulus point of view.