Investigation of behavior of deep mixing column with zeolite additive manufactured in layered soil environment with model experiments

The aim of conducting this study is to investigate the behavior of deep mixing columns (DMC) created by using zeolite, which is a natural pozzolanic material in a layered soil environment consisting of clay and sand soil. Small- and large-scale test samples were applied in this study to gain reliable results. In preparing small-scale DMC samples, an experimental design table including seventeen designs was created using the Response Surface Method for the cement, zeolite, and plasticizer additive amounts and water/binder ratio, the four parameters that make up the injection mixture. The applied structural design in this study consists of 9-30% for cement, 0-40% for zeolite, 0.5-4% for plasticizer additive and 0.9-2.5 for water/binder ratio. For each design, Marsh Funnel Viscosity Tests were performed on the injection mixtures, and the fluidity of the injections were checked. Unconfined Compressive Strength and Permeability Tests were carried out on small scale samples prepared using both clay and sand soil for all designs after twenty-eight- and fifty-six-days experiment. Scanning electron microscope (SEM) images of seven samples that can represent the designs were taken. For optimum designs obtained by optimizing experimental results, large-scale DMC was employed within model tanks, taking into account the layered soil layout. After twenty-eight days of experiment period, the prepared columns were subjected to staged pile loading tests, and core samples were taken from the formed columns. For optimum designs in small scale DMC, the estimated results at the end of the twenty-six days of experimenting were 92% on clayey soil and 83% on sandy soil in Unconfined Compressive Strength Tests, and 71% and 57% in Permeability Tests, respectively. The results of replacing the zeolite with cement indicate a slight decrease in the strength value; as these results are considered within the acceptable limits, they are considered satisfactory DMC values. The results revealed that increasing the amount of zeolite leads to a slight increase in the permeability coefficient, and even if the zeolite is used in the maximum possible replacement, the permeability coefficient will remain within the required limit values. Furthermore, the SEM analysis results indicated that the possibility of utilizing zeolite up to a certain amount as a replacement with cement. However, the small amount of cement leads to a decrease in C-H and C-S-H gels. The load test results of large-scale DMC have shown the DMC's sufficiency formed in the layered soil environment in terms of bearing capacity and settlement criteria, and the unconfined compressive strength of the core samples taken from the columns was 90% of the strength of the small-scale DMC.