A lightweight fill was produced by blending expanded polystyrene (EPS) beads and sands in proportions. Such formed granular geomaterials, known as sand-EPS lightweight fills, have potentials of being lightweight compared to traditional fills, thus are suitable for many infrastructure works where less overburdens are expected, e.g., utilities trench backfills. Consolidated drained triaxial compression (TC) tests were conducted on the lightweight fills to observe materials' stress-strain relationships, specifically, the stress-strain variations associated with the mixing ratios of EPS beads. EPS beads were incorporated into the mixtures based on their mass ratios over sands, I.e., 0.5%, 1.5% and 2.5%. It was found that confining pressures and mixing proportions played important roles in affecting the stress-strain behaviors of lightweight fills. The materials underwent shear contraction, which is related to the inclusion of EPS beads. The constitutive law of the lightweight fills was derived based on Cam-clay model and modified Cam-clay model, and verified by the test results.
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