Ground liquefaction is causing great damage to the structure of land during earthquakes. Accordingly, various liquefaction damage reduction methods have been studied and developed. However, most of the ground liquefaction prevention methods have limitations in their application to existing structures. Therefore, in this study, a ground liquefaction damage reduction method, applicable to existing structures, was studied using the grouting method. A 1-G shaking table test was performed, and the ground was created with Jumunjin standard sand. A two-story model structure was manufactured by applying the similarity law, and an input wave applied a sinusoidal motion with an acceleration level of 0.6 g and a frequency of 10 Hz. The grouting chemical was produced by mixing water and cement, and the effect of reducing structural damage was analyzed according to various mixing ratios; in addition, the separation distance between the grouting chemical injection point and the structure was analyzed. As a result of the analysis, when the ground was reinforced by applying the grouting method, the settlement of the structure was about 84% smaller than when the ground was not reinforced, and the mixing ratio with the smallest settlement was 0.45. In addition, when there was no separation distance between the structure and the grouting chemical injection point, it was confirmed that the effect of reducing structural damage was the greatest. These research results will be used as basic data for developing a grouting method applicable to existing structures in the future.

Global warming is becoming worse owing to carbon dioxide emissions around the world, and eco-friendly energy for reducing carbon dioxide emissions is gaining importance. Wind power plants are the most representative of the environmentally friendly energy power plants built in the ocean. The fatigue loading and long-term dynamic behavior of offshore soils are important considerations in the construction of structures such as wind turbines in the ocean as they are subject to long-term loads such as wind and wave loads. A design graph presents the short- and long-term behaviors of soil. Several laboratory tests are typically conducted to create design graphs. In this study, a cyclic simple shear test conducted at various confining pressures and relative densities is presented in design graphs. The authors analyzed the sensitivity of the relative density and the confining pressure, and proposed a drawing technique to easily create two-dimensional design graphs. The authors found that the effect of the relative density on the design failure curve was higher compared with that of the confining pressure. The elliptic equation graph achieved the best match to the design failure curve, and the design failure curve drawing technique was summarized in five stages. In addition, the normalized cyclic stress ratio graph to distinguish safety or failure was presented.