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Organic-rich soil is a typical special soil often encountered in foundation treatment. Previous research has revealed that Portland cement (PC) not only pollutes the environment but is significantly affected by organic matter during its hydration and cementation. Although quicklime (CaO)-GGBS binder (CG) is an effective alternative to PC, its efficiency in treating organic-rich soils has not been studied. In this study, organic-rich soil was treated with two binders of CG and PC. The physical, mechanical, and chemical characteristics of the stabilized soils were tested at various organic contents, binder contents, and curing ages. The results show that the cracks in two treated soils increase with the increase in organic content and the reduction in binder content. CG-treated soils are more likely to shed big lumps after damage than PC-treated soils. The unconfined compressive strength (qu) and deformation modulus (E50) of stabilized soils increase with the increasing curing age and binder content but the decreasing organic content. The E50 of PC-treated soil is about 22~73 times qu, and the E50 of CG-treated soil shows an excellent linear relationship with qu. The moisture content of two treated soils increases as the organic content grows, but it falls as the curing age and binder content increase. The soil pH rises with the increasing organic content and binder content, but it declines with increased curing age. The strength development of organic-rich soils treated by the CG binder has an evident attenuation with the organic content. Given its possible environmental benefit, alkali (especially low calcium)-activated binder is appropriate for practical engineering with modest strength needs.

The unconfined compressive strength (UCS) of sludge with different consistency limits solidified by cement was investigated. The results showed that under the condition of constant initial water content, a higher liquid index of soil resulted in higher UCS. A novel strength-evaluation model based on the ratio of the liquid index to the cement content was developed, and the prediction deviation of the model was within 30%. The influence mechanism of the consistency limit of sludge on the cement solidification was revealed by scanning electron microscopy, mercury intrusion porosimetry, X-ray diffractometer and thermogravimetric analysis. For the cement-solidified dredged sludge (CDS) with a lower liquid index, a large amount of hydrate was interlaced with each other and wrapped soil particles, promoting the formation of a dense structure. For the CDS with a higher liquid index, hydrates such as C-S-H and ettringite challenged each other to play the role of “cementing particles” and “filling pores”, resulting in the formation of the porous structure. The mineralogical analyses confirmed that more C-S-H gels and ettringites were generated in the CDS with a lower liquid index, but less calcite was formed due to its denser structure. In engineering applications, reducing the liquid index by adjusting the consistency limit can improve the strength performance of CDS.