In this study, based on hydrolysis and condensation via Stöber process of sol-gel method, synthesis of mono-dispersed silica nanoparticles was carried out with hydrophilic solvent. This operation was expected to be a more simplified process than that with organic solvent. Based on the sol-gel method, which involves simply controlling the particle size, the particle size of the synthesized silica specimens were ranged from 30 to 300 nm by controlling the composition of tetraethylorthosilicate (TEOS), DI water and ammonia solution, and by varying the stirring speeds while maintaining a fixed amount of ethanol. Increasing the content of DI water and decreasing the content of ammonia caused the particle size to decrease, while controlling the stirring speed at a high level of RPMs enabled a decrease of the particle size. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were utilized to investigate the success factors for synthesizing process; Field emission scanning electron microscopy (FE-SEM) was used to study the effects of the size and morphology of the synthesized particles. To analyze the dispersion properties, zeta potential and particle size distribution (PSD) analyses were utilized.

In this study, to improve the dispersity of Fe 3 O 4 nanoparticles, dispersion properties were considered with various types of functionalization of Fe 3 O 4 nanoparticles. Due to its high surface area, the electrically neutral state of its surfaces, and its magnetic momentum, Fe 3 O 4 nanoparticles are easily aggregated in solution. In order to prevent aggregation, Fe 3 O 4 nanoparticles were functionalized with carboxyl and amine groups in the form of a polymer compound. Carboxyl and amine groups were attached to the surface of Fe 3 O 4 nanoparticles and the absolute value of the zeta potential was found to be enhanced by nearly 40 eV. Furthermore, the morphology and the magnetic property were analyzed for the application of Fe 3 O 4 nanoparticles as a magnetic fluid.

In case of underground construction affected by groundwater, CIP (Cast-In-Place Pile) method is generally used to solve the geo-hydraulic problem. However, as this method has poor connectivity between piles, an auxiliary method for cut-off is required in many cases. In this study, a newly-developed cut-off wall (H-CIP) with no auxiliary method, by using surfactant grout (Hi-FA), which improves anti-washout and infiltration ability, is introduced, and the field applicability of H-CIP method is evaluated. CIP and H-CIP piles were installed with same ground conditions, and field and laboratory tests were conducted to verify the performance, respectively. As results, newly-contrived H-CIP method shows higher field performance for cut-off and strength than conventional CIP method.