Recently, due to the unusual weather caused by global warming which is the result of industrialization, natural disasters such as earthquakes, tsunamis, typhoons and localized heavy rains have been occurring frequently and their intensity has also increased so that they spread to secondary disasters such as facility disasters and social disasters, which created direct and indirect social damage and fear factor; therefore, an earthquake resistant design has become a significant social issue.
When designing soil nails, for the most part, they partly adjust the installation interval of soil nails under the condition of static load.
With regard to the installation angle, for the most part, they fix them with a descending angle of about 20 degrees and use the diameter and length of the nails, considering the design variables such as strength parameter of the ground, strength characteristics of the nails, grade of slope and the frictional force of grout material and natural ground. Therefore, there is lack of research into mutual influence concerning the installation angle and installation interval of soil nails and design variables. As the results somewhat vary depending on the proponent, further research is required as to the behavior characteristics of slope regarding the installation angle of soil nails when dynamic load happens.
Therefore, in this study, after changing the installation angle of soil nails to upward 5 degrees, horizontal 0 degree, downward 15 degrees and downward 25 degrees under earthquake load, the model tests were performed on a model vibration table using a long-period wave and a short-period wave and an analysis on numerical value and measured the acceleration and displacement and then compared and contrasted them.
The results of the model tests on a vibration table showed that, in terms of all of the upper part maximum displacement and acceleration amplification, the upper part vertical displacement, the front upper part and lower part on a slope, the more downward the installation angle of soil nails was when they were not reinforced, the larger the acceleration amplification and the upper part vertical and front vertical displacement were shown in the short-period wave rather than in the long-period wave. This means that the effect of the short-period seismic wave on the ground was the biggest, and that, with regard to the horizontal displacement of the front upper part and the lower part of the slope, the horizontal displacement on the lower part of the slope was bigger.
In addition, in both long-and short-period waves, the installation angle of the nails was steep in incline towards the unreinforced place on the basis of downward 15 degrees and was gradual in incline towards downward 25 degrees. This confirmed that, the reinforcement effect is big up to downward 15 degrees of the nails and is gradual in the case of downward 15 degrees and below. when the seismic wave operates.
The results of the numerical analysis are as follows: The more downward the installation angle of the nails was when they were not reinforced, both long- and short-period waves decreased; the acceleration amplification of the short-period wave was rated larger than that of the long-period wave; as in the case with the results of the model tests on a vibration table, the installation angle of the nails was steep in incline towards the unreinforced place on the basis of downward 15 degrees and was gradual in incline towards downward 25 degrees, which confirmed that, when the seismic wave operates, the reinforcement effect is big up to downward 15 degrees of the nails and is gradual in the case of downward 15 degrees and below. These results show a similar tendency as the results of the model tests on a vibration table.
In the case of existing research, there is research indicating that, with regard to the optimum angle based on the installation angle of the nails under static load, the installation angle of the nails has a favorable displacement and safety factor in upward direction, and that it has a favorable displacement and safety factor in downward angle of about 10 to 20 degrees. However, in this study, it was shown that, under dynamic load, the more downward the installation angle of the nails was, the smaller the acceleration and displacement became. Therefore, it was judged that it is favorable to install the nails in downward direction. In particular, considering that the installation angle of the nails noticeably decreased up to downward 15 degrees and gradually decreased from downward 15 degrees to 25 degrees when they were not reinforced, it was found that the displacement decreased at the point of downward 15 degrees.
As mentioned above, after analyzing the characteristics of their dynamic behavior depending on the installation angles of the soil nails through the dynamic tests and numerical analysis, we were able to see that it is favorable to install the nails in downward direction, and that the short-period wave has the biggest influence on the ground. However, it seems necessary the research under a various conditions be performed in order to suggest quantitative design standards according to the behavior characteristics of the soil nails under static load.