Research On Bearing Behavior Of Pile Foundations In Calcareous Sands

Calcareous sand is a special marine geotechnical medium, which is widely spread throughout the oceans near Nansha Islands. Since its unexpected physical and mechanical properties, pile foundations in calcareous sands have lots of particular behavior. During the past 30 years, the design and construction of offshore oil platforms founded in calcareous sands have been a major technical challenge for the offshore industry. The traditional practice, successfully used for other types of materials, proved to be ineffective when used for pile foundations driven into calcareous sands. In this thesis, based on the existing theory, the bearing behavior of pile foundations in calcareous sands is systematically studied by means of laboratory testing and theoretical analysis.1. The special physical properties and measurement methods of calcareous sands are introduced first, which are taken from the Yongshu coral reefs in Nansha Islands in South China Sea. The physical and mechanical parameters of calcareous sands and silica sands, which are used in model tests, are analysed. Model test equipment is introduced, which includes the design and construction of model chamber and model pile groups. The measurement equipment and test program used in model tests are also explained.2. Model pile and pile groups tests with open or close ended are carried out to investigate the bearing and deformation characteristics in calcareous sands with different relative density. In contrast to the tests with silica sands, the difference in the bearing capacity behavior and load transfer of piles between calcareous sands and silica sands, are emphasized in the analysis. The action laws of pile end resistance and shaft friction are obtained.3. Based on research data and model test result, the bearing behavior of piles in calcareous sands is analyzed, which includes pile end resistance, shaft friction and the effect of pile group.4. Considering the depth effect of shaft friction of pile in calcareous sands, a set of analytical solutions for the axial loading-settlement curve of pile in calcareous sands is established. Three fold-lines model is used in the load transfer functions of pile shaft, and the load transfer functions of pile end uses two fold-lines model.