When first developed in the 1950s, the micropile method was used as one of the underpinning methods to suppress additional subsidence in the foundation of existing structures or to reinforce the bearing capacity. However, in recent years, this method has been used as a foundation method to solve geotechnical problems such as support for the foundation of a new structure, seismic resistance, slope stability, and shear keys of the pier foundation.
Also, since micropile can be constructed evenly in a narrow space, the frequency of use in the field is gradually increasing. In addition, as the use of microfiles gradually increased, various types of microfiles were developed, and a representative microfile developed recently is a triaxial micropile.
The triaxial micropile was developed for the purpose of improving the resistance to horizontal load or the seismic performance of the structure. This pile consists of small-diameter steel pipes tightly filled with grout are installed inclined in the three-axis direction (installation direction = 120 degrees), and the micro piles of each axis are fixed by pile caps made of steel plate. Due to the characteristics of the pile structure, a small steel pipe pile installed in an inclined three-axis structure was developed for more effective resistance to horizontal loads than the existing micro piles.
In order to effectively utilize the horizontal bearing capacity of the triaxial micropile, a study considering the ground conditions related to the horizontal bearing capacity characteristics of the pile, and the installation conditions of the pile (pile length ratio, installation angle, etc.) is required. Currently, the triaxial micropile is in the early stages of development, and research on it is insufficient, and only one type of installation method of the pile is applied when using it in the field.
In this study, in order to solve this problem, field load test and numerical analysis were performed to evaluate the horizontal behavior characteristics of the triaxial micropile comprehensively considering the ground conditions and the installation conditions of the piles. First, the horizontal behavior characteristics of the actual triaxial micropile were evaluated through field horizontal load test, and further study on the actual pile was confirmed by comparing and analyzing the test results and the numerical analysis results simulating the field test process. Then, three-dimensional analysis was performed by changing the ground conditions and the installation conditions (length ratio, installation angle) of the pile, and the horizontal behavior characteristics and horizontal bearing capacity of the triaxial micropile were evaluated by comparing and analyzing the analysis results comprehensively.