Abstract: Numerical models of frictional arch, end bearing arch and united arch of anti-slide pile structures are established with FLAC3D. Differences and similarities between three arches about formation, development and law of effect factors are researched comparatively, as well as the combination mechanism of each single one. The results show that the united arch’s development starts with the frictional arch’s forming and ends with the end bearing arch’s breaking. And during all the progresses, each single arch exists and occupies some dominant areas severally. The united arch’s distribution, limit capacity and plasticity zone are almost made up of the two single arches’. Different factors have different influences on both quality and quantity of the same arch, while the same factor has different influences on different arches only quantitatively. So a new method which can help us come to understand it much better is put forward by separating the united arch and combining the two single ones.

Key words: single arch, united arch, formation, distribution, limit state, effect factors