Abstract: To investigate the effects of the water-to-solid ratio, fly ash-soil ratio, and fly-ash replacement level on the performance of flowable backfill materials, dredged sludge was used as the fine aggregate and combined with fly ash and cement as the cementitious components to prepare flowable stabilized soil. Results from flowability and mechanical tests indicate that the water-to-solid ratio directly governs both the flowability and strength of the material: increasing the water-to-solid ratio enhances flowability but reduces strength. An increase in the fly ash-soil ratio leads to varying degrees of improvement in flowability and strength. When the fly ash-soil ratio increases from 0.2 to 0.3, flowability and 28-day compressive strength rise markedly, by 18% and 130.2%, respectively. As the fly-ash replacement level increases, flowability gradually improves, the 7-day compressive strength decreases, and the 28-day strength first declines and then increases.

Key words: Solidified Flowable Backfills, Water-Solid Ratio, Fly-Ash Soil Ratio, Fly Ash, Flowability, Unconfined Compressive Strength