Laboratory investigation on the effect of microsilica additive on mechanical properties of deep soil mixing columns in loose sandy soils

Abstract

The present study is devoted to the laboratory investigation of the effect of microsilica additive on performance of deep soil mixing (DSM) columns in loose sandy soil. In this matter, 163 DSM columns were constructed using laboratory scale DSM apparatus in a poor-graded sand with particle size of. 4–1 mm and 70% relative density. Cement slurry with three different water-to-cement ratios of .8, 1.0 and 1.2 and microsilica with four percentages of 5, 10 15, and 20 by weight of cement replacement was used for treatment. Compressive strength, modulus of elasticity and unit weight of all columns at the ages of 7, 14 and 28 days were evaluated using the uniaxial compression test. For better understanding of the results, SEM images were taken from DSM columns containing 15 and 20% microsilica. The research findings indicate that DSM columns with 15% microsilica and water-to-cement ratio of .8 have the highest compressive strength and modulus of elasticity. In the final part of the research, based on the test results, five regression equations are proposed for prediction of compressive strength, modulus of elasticity and unit weight of the DSM columns.