Improvement of organic soils by deep mixing method

The deep soil mixing method is a technique used for soil improvement. In this method, the soil is mixed with special equipment to a certain depth. This process increases the bearing capacity of the soil and enables the structures to be built on more solid foundations. Improvements made by deep soil mixing method depend on many factors such as soil type and properties, type and amount of additive, curing conditions, loading conditions, mixing conditions and construction process. When the soils have organic content, the improvement works performed by this method become more complex. In this thesis, the improvement of organic soils by soil deep mixing method was investigated. For this purpose, in the first stage, an organic soil with 12.4% organic content obtained from the Haliç (Golden Horn) region of Istanbul was studied. Three different cement types, three different binder dosages and three different w/c ratios were used in the experiments. In order to determine the soil behavior after remediation, unconfined compression tests were performed on specimens with curing times of 7, 14, 28, 90 days and one year, and measurements were made with an ultrasound device. XRF and TGA experiments were performed on the 28-day cured samples at METU Central Laboratory to determine the chemical properties. In the second stage, in order to investigate the effect of deep mixing method on the soil with high organic content and low pH value, an artificial soil with a pH value of 5.1, which was obtained in a mixture of 50% Kaolin clay + 50% Leonardite, was formed. The same experiments were carried out on this soil. Within the scope of this thesis, a total of 540 samples were prepared in 54 sets. As a result, the increase in the amount of binder used and the increase in the curing time caused an increase in the strength values. The strength values decreased with increasing water binder ratio. The results of 28-day XRF experiments on the specimens showed that the increase in SAC ratio caused a decrease in strength values. In the TGA analysis results, it is seen that the increase in weight loss between 115°C and 400°C causes an increase in strength values and the increase in mass loss between 400°C and 600°C causes a decrease in strength values. As the original results of this thesis, as a result of the evaluation of the effect of curing time, it was observed that the strength gain rate increased with the increase in w/c values in cures longer than 28 days and values up to four times the 28-day strength values were obtained in the long term. This evaluation was based on the "curing time effect index, (fc)". In terms of total water-cement ratio (wt/c), the R2 value of the curve presented by FHWA (2013) for deep mix design is 0.66, while this value is 0.88, 0.91 and 0.85 for estuary clay, artificial soil and all soil data, respectively. As a result of this study, it is seen that the Haliç clay, which has an organic content of around 12%, can be successfully improved by DSM method. The artificial soil, which has a higher organic content and lower pH value, could be improved more effectively at higher cement dosages and lower wt/c ratios.