Flowable Backfill Materials from Bottom Ash for Underground Pipeline

The purpose of this study was to investigate the relationship between strength and strain in manufacturing controlled low strength materials to recycle incineration bottom ash. Laboratory tests for controlled low strength materials with bottom ash and recycled in-situ soil have been carried out. The optimum mixing ratios were 25%–45% of in-situ soil, 30% of bottom ash, 10%–20% of fly ash, 0%–3% of crumb rubber, 3% of cement, and 22% of water. Each mixture satisfied the standard specifications: a minimum 20 cm of flowability and 127 kPa of unconfined compressive strength. The average secant modulus (E(50)) was (0.07–0.08) q(u). The ranges of the internal friction angle and cohesion for mixtures were 36.5°–46.6° and 49.1–180 kPa, respectively. The pH of all of the mixtures was over 12, which is strongly alkaline. Small-scale chamber tests for controlled low strength materials with bottom ash and recycled in-situ soil have been carried out. Vertical deflection of 0.88–2.41 mm and horizontal deflection of 0.83–3.72 mm were measured during backfilling. The vertical and horizontal deflections of controlled low strength materials were smaller than that of sand backfill.