Factorial experimental approach for effective dosage rate of stabilizer: Application for fine-grained soil treated with bottom ash

In developing designs for engineered mixtures to improve soil with stabilizers, it is always required that the effective rate of the stabilizer be determined in the stabilization. However, there seems to be an insufficient amount of effort in the decision-making related to the accuracy and the reliability of the effective rate. This paper presents an application of a factorial experimental analysis, together with an effect size estimation, to investigate the effective dosage rates of bottom ash to improve a fine-grained soil. Unconfined compression tests have been conducted to measure the strength parameters considered in the mixtures of soil+bottom ash for which the bottom ash dosages were 0, 5, 10, 15, 20, 25, and 30% by dry weight of the mixture. The effective dosage rates, based on the strength parameters, have been evaluated primarily by multiple comparisons and Cohen׳s d. The results indicate that while there is a significant strength development with “moderate” to “strong” sizes on the untreated soil, due to the 30% bottom ash (p<0.05, Cohen׳s d>1.15), the strength is insignificantly changed (increased or decreased) below the 30% dosage (p>0.05, Cohen׳s d≤0.41). It is found from the experimental analysis that a factorial approach and an effect size estimation compare well in the decision-making. It is suggested from the results that bottom ash can be adequately added to soil in the stabilization for both improvement (i.e., at 30% dosage) and replacement (i.e., below 30% dosage). The proposed use of bottom ash would also be beneficial for recycling and the sustainable development of the environment.