Improving mechanical characteristics and minimizing the weight of the backfill material has remained an area of interest for geotechnical practitioners, and it has motivated the authors to investigate the mechanical behavior of light-weighted backfill (LWBS) soil. LWBS is an engineered mixture of cement, fly ash, silt, EPS beads, and water. The effect of cement, EPS beads, and fly ash contents on the shear behavior of LWBS were studied by using unconfined compression and direct shear tests. The test results show that increasing the fly ash and cement content does not affect the internal friction angle, but significantly increases the cohesion. On the other hand, increasing the content of fly ash and cement increases the UCS. However, the unconfined compressive strength, cohesion, and angle of internal friction decrease with increasing EPS bead size. It also improves ductility. The density of LWBS can be efficiently controlled by large-size EPS beads added to make the material.

The study finds that combining silty soil reinforced with EPS beads and 5% cement and 10% fly ash produces a high-strength, low-density material with twice the shear strength of normal silty soil. The results provide potential solutions for increasing the shear strength of simple silty soils by filling them with LWBS. The paper’s findings are useful in the design and construction of infrastructure projects that require backfill material with specific mechanical properties

Keywords: light-weighted backfill soil, strength characteristics, fly ash, EPS bead