Dual stabilizer to improve excavated soil wastes

Cement, lime and fly ash are often used alone to improve the engineering properties of marginal soils. To a lesser extent, these traditional stabilizers have been used in combinations of two – that is, cement and lime, cement and fly ash, and lime and fly ash. However, the choice of dual stabilizer appears to be coincidental. This chapter investigates the effectiveness of dual stabilizer for excavated soil wastes (spoils) to improve the strength of spoils and, hence, to rationalize the selection of a dual stabilizer. The study evaluates the unconfined compressive strength (UCS) of two types of excavated soil wastes and kaolin treated with both single (cement, lime, fly ash) and dual (cement and lime, cement and fly ash, lime and fly ash) stabilizer at a constant stabilizer content of 20% of the soil’s dry mass. A previous framework based on grain size distribution (GSD) and plasticity charts for the selection of single stabilizer is extended. Subsequently, charts are proposed to guide the selection of dual stabilizer. Once a soil falls into the ‘not improved’ zone, the dual stabilizer is less effective than when the primary stabilizer is used alone as a single stabilizer. When both charts show the soil in the ‘improved’ zone, the dual stabilizer works better than the single stabilizer at the same stabilizer content. The extended framework for dual stabilizer selection is validated with data from the literature and shows high accuracy and reliability. However, the proposed charts may not be applicable to organic soils because of lack of data and, hence, factors unique to organic soils that significantly impact the effectiveness of the stabilizer are not fully considered.