CENTRIFUGAL MODEL TESTS ON SELF-WEIGHT COLLAPSIBLE LOESS AND NEGATIVE SKIN FRICTION OF PILE FOUNDATIONS

Collapse settlement,collapsibility of self-weight collapsible loess and negative skin friction of pile foundation are crucial issues in the basic research of collapsible loess ground.The centrifugal model test is used to simulate the immersion test with undisturbed and remolded collapsible loess foundations,to research and analyze the collapsibility of loess and negative skin friction of pile foundations.The research results show that the processing of undisturbed and remolded loess collapsibilities can mainly be divided into three stages,which are the stages of significant of collapsible deformation,stabilization stage of collapsible deformation and soil consolidation deformation stage after the dropping of water level.The method of centrifugal model test which uses remolded collapsible loess instead of undisturbed collapsible loess to research the self-weight loess collapsibility is practicable for the purpose of settlement study by analyzing the test data.Then the changing laws of negative skin friction and the position of neutral point are concluded.The movement of negative skin friction and the position of neutral point are a continuous changing process.The ratio of the neutral point position to length of pile is in the ranges of 0.68-0.82.