No studies were found that examined the effect of pile geometry on the group pile effect of vertical bearing capacity. This paper discusses the ground behavior near the pile tip based on image analysis results obtained from vertical loading tests of model piles assuming belled piles and straight piles in a pressure chamber. The results showed that diagonal downward ground displacement occurs from the corner of the pile tip face regardless of the pile geometry, and that these interfered with each other in the double pile, and that the effect depended on the pile geometry and pile spacing.
Kumada et al. (Sun,) studied this question.