Flowability and Strength of Flowable Filling Materials Made from Cement-Stabilized Sand and Soft Clay: Conflicting Effects of Sand Addition

Soft clay with high water content and low strength is largely generated during excavation and dredging activities worldwide. Cement stabilization can effectively increase the strength of soft clay. However, with a high water content, the stabilized clay usually has a high compressibility, which can be solved by adding a proper amount of sand. In this study, sand and cement were mixed with excavated soft clay to produce a flowable filling material, and the flowability of the fresh mixture and the strength of the hardened specimen were investigated. Contrary to expectations, the results showed that the influences of sand addition on the flowability and strength varied depending on the sand content. For the clay used in this study, a sand content lower than 0.08 by volume slightly increased the flowability and posed a risk of reducing the strength of stabilized soils. However, with higher added sand content, the flowability decreased and the strength increased with the increasing sand content. It was found that the ratio of water content to liquid limit (w/wL ratio) increased initially and then decreased with rising sand content, causing the variable influences of different sand addition dosages. Through mathematical analysis, the nonlinear correlation between liquid limit and sand content of a clay–sand mixture can result in the nonmonotonic variation trend of w/wL ratio. A graphical method is proposed to evaluate the effect of sand content on the w/wL ratio of target soils, which can be used as a reference for the mixing design of flowable stabilized clay-based filling material with sand addition.