Investigating the construction parameters of deep mixing columns in silty soils

Abstract

In the present research, the optimum condition of the grout consisting of cement, fly ash, superplasticizer, and water was determined to produce the most durable and impermeable deep mixing columns (DMC) on silty soils. It is aimed to reduce the grout cost and environmental pollution by using high-rate fly ash in the grout. Superplasticizer additive was used to increase the flow consistency of grout consisting of high-rate fly ash. The design of the experiments was made using the 5-parameter and 4-level L16 orthogonal array table specific to the Taguchi method. Accordingly, the unconfined compression strength (qu) and the permeability coefficient (k) of the soil-binder mixtures at the end of the 7- and 28-days curing time were determined. According to the test results, regression analyzes were performed and models with high reliability were created for qu and k. As a result of optimization studies, to produce DMC having high strength and low permeability, grout content should be consisting of 14% cement, 14% fly ash (ratio of fly ash in the binder is 50%), 2.68% super plasticizer additive, and 0.95 water/binder ratio. The pozzolanic reactions in soil-binder samples with different grout contents were examined by SEM analysis.