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Abstract Calcareous sand is a special marine geomaterial medium，which has unexpected physico-mechanical properties due to its origin and fabric. The traditional practice，successfully used for other types of materials，is proved to be ineffective when used for pile foundations driven into calcareous sands. Model pile tests are carried out in a cylindrical testing chamber to investigate the bearing and deformation characteristics of pile groups in calcareous sands，which are taken from the Yongshu coral reefs 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 due to grain crushing. Relative density has effect on the bearing capacity of pile group in calcareous，and the bearing capacity of close-ended pile group is 17%–20% larger than that of open-ended pile group，but it is less than that in silica sands. The axial force of pile group in calcareous sands has a slow decay rate，and the ultimate shaft friction of pile group in calcareous sands is only 21%–30% of that in silica sands，which is effected by depth，and it is very sensitive to density in silica sands but less in calcareous sands. In addition，when Dr = 46% and 75%，the bearing efficiency of pile group in calcareous sands is less than 1，and it increases with relative density，which is completely different from silica sands. The conclusion drawn from the study can provide valuable references for the practice.
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Received: 09 March 2009
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