Abstract:

According to the current situation of pile foundation engineering, a model test equipment is designed to study the bearing and deformation characteristics of steel pipe piles in calcareous sands, which are taken from Yongshu reef in Nansha Islands in South China Sea. In contrast to the tests with silica sands, it is shown that calcareous sands behave in a completely different manner than silica sands. For sands having the same relative density, the ultimate bearing capacity in calcareous sands is only 66-70% of that in silica sands, the axial force has a slow decay rate, and the ultimate shaft friction of open-ended piles is less than that of close-ended piles in calcareous sands, nonetheless, it is only 20-27% of that in silica sands. In addition, shaft friction is very sensitive to density in silica sands but less so in calcareous sands. It is found that the reduction in lateral pressures on the pile shaft, which is caused by grain crushing under the high stress levels produced during pile driving, is the main reason for low shaft friction of steel pipe piles in calcareous sands.

Key words: calcareous sands, model test, steel pipe pile, shaft friction, grain crushing