Variables Governing Strength of Compacted Soil–Fly Ash

Variables Governing Strength of Compacted Soil–Fly Ash–Lime Mixtures

Consoli, Nilo Cesar / Rosa, Amanda Dalla / Saldanha, Rodrigo Beck

The practice of treating soil with fly ash and lime is an attractive technique when the project requires improvement of the local soil for the construction of stabilized bases under pavements, as a support layer for shallow foundations, to strengthen slopes in slope stability problems, and to prevent sand liquefaction. Currently, efforts are being made to develop dosage methodologies for improved soils based on a rational criterion as it exists in concrete technology, in which the water-cement ratio plays a fundamental role in the assessment of the target strength. This study evaluates the strength controlling parameters of a sandy soil treated with fly ash and lime and shows that the voids-lime (η/Lv) ratio (corresponding to porosity divided by the volumetric lime content) plays a fundamental role in the assessment of the target strength. The controlling parameters evaluated were the amount of fly ash, quantity of lime, porosity, and voids-lime ratio. A number of unconfined compression tests and suction measurements were carried out in the present work. The results show that the unconfined compressive strength (UCS) increased linearly with the amount of lime for soil–fly ash–lime mixtures. A power function adapts better to the relation UCS-porosity (η) for soil–fly ash–lime mixtures. The ratio η/Lv, in which Lv is adjusted by an exponent (in this case 0.12 for all soil–fly ash–lime mixtures studied), is shown to be a good parameter in the evaluation of the UCS of the soil studied (UCS varies nonlinearly with η/Lv in the case of fly ash–lime addition). Finally, it was found that a unique correlation controls the strength of the compacted soil–fly ash–lime mixtures studied; consequently, using this relationship an engineer (considering the specifics of each case such as price, availability, and cost of transportation of each material, among others) can choose the amount of lime, the quantity of fly ash, and the compaction effort appropriate to provide a mixture that meets the strength required by a project at the optimum cost.