Investigation of amorphous silica-added deep mixing column behaviours produced in layered ground by model experiments

In this thesis study, the factors affecting the performance of amorphous silica-added deep mixing columns (DMC) in the layered ground were investigated by experimental laboratory studies. Experimental studies were carried out in three stages. In the first stage, the limits of material usage percentages were determined with preliminary design experiments. In the second stage, two different 18-level designs were made for sand and clay soils by using the Design Expert program in view of the data obtained from the first stage. Soil-injection mixes (small-scale DMC) were created with a laboratory mixer for design experiments. Both sand and clay soils were used for all design levels, and unconfined compressive strengths (qu) and permeability coefficients (k) were determined by performing free pressure tests on the prepared samples and permeability tests on a triaxial test device for 28 and 56 days curing periods. Experiment results were analyzed using the Response Surface Method in the Design Expert program. Chemical, mineralogical and petrographic analyzes were performed on the samples taken from the small-scale experiments, the results were evaluated and optimization studies were carried out. In the third stage, with the optimum design determined after the optimization studies, large-scale deep mixing columns were manufactured with laboratory-type deep mixing machine setup in model tanks. The deep mixing columns formed in the model tanks were subjected to loading tests and their bearing capacities and settling-load behaviors were determined. The unconfined compressive strengths (qu) of small scale DMCs manufactured on clayey soils were found to be between 810 kPa and 6729 kPa for the 28-day curing period, and between 886 kPa and 7125 kPa for the 56-day curing period. The permeability coefficients (k) of small scale DMCs manufactured on clayey soils were found to be in the range of 4.32-341x10-11 for the 28-day curing period and 3.65-283x10-11 for the 56-day curing period. The unconfined compressive strengths of small scale DMCs manufactured on sandy soils were found to be between 4026 kPa and 19776 kPa for the 28-day curing period, and between 886 kPa and 7125 kPa for the 56-day curing period. The permeability coefficients of small scale DMCs manufactured on sandy soil were found to be in the range of 4.32-341x10-11 for the 28-day curing period and 3.65-283x10-11 for the 56-day curing period. In the ANOVA analyzes, the effect of amorphous silica on the unconfined compressive strength in clayey soils were found to have a positive effect when the water/binder (w/b) ratio was selected in the range of 1-1.5, the amorphous silica in the range of 25%-35%, and the superplasticizer additive of 2.5-3.5%. It has a positive contribution to the unconfined compressive strength in sandy soils where the w/b ratio is selected as 0.9-1.0 and other parameters are selected as in clayey soils. In ANOVA analysis, it was found that the contribution of amorphous silica to permeability was more dominant. In the appropriate selection of parameters, amorphous silica decreased the permeability coefficient by 60% for clayey soils and 70% for sandy soils. For optimum design in small-scale DMCs, the accuracy of 81% for the 28-day curing time and 79% for 56-day curing time were reached between the results obtained from the unconfined pressure tests and the predicted results in clayey soil. For optimum design in small-scale DMCs, the accuracy of 89% for the 28-day curing time and 86% for 56-day curing time were reached between the results obtained from the unconfined pressure tests and the predicted results in sandy soil. For optimum design in small-scale DMCs, the accuracy of 83% for the 28-day curing time and 78% for 56-day curing time were reached between the results obtained from the permeability tests and the predicted results in clayey soil. For optimum design in small-scale DMCs, the accuracy of 77% for the 28-day curing time and 93% for 56-day curing time were reached between the results obtained from the permeability tests and the predicted results in sandy soil. Micro-scale void states, C-S-H gels, C-H plates and ettringite formations were examined in samples taken from small-scale DKKs in SEM images, EDS, XRD and XRF analyzes and correlated with DMC performance. Loading tests of large-scale DKK columns were carried out, bearing capacities were determined by different methods and the results were evaluated.