Model tests on negative skin friction of single pile considering applying sequence of pile load and surcharge loading

Based on the laboratory model tests, the influence of the sequence of pile load and the soil load surrounding the pile on the negative friction of single pile is studied. The results show that under pile-soil load, after the applying of the soil load surrounding the pile, the neutral point is the furthest away from pile top. With the increase of pile load, the position of the neutral point gradually moves up, eventually, 0.5l far from the pile top. The axial force of pile body increases first and then decreases, the exert coefficient of bearing capacity of single pile is 0.69. When the pile load is first applied, the axial force of pile shaft gradually decreases along the depth, there is no neutral point. While the soil load is applied, the axial force increases first and then decreases, and the neutral point appears and gradually moves down, finally it is near 0.41l, and the exert coefficient of bearing capacity of single pile is 0.86. There is the greater exert coefficient of bearing capacity in the pile-soil load sequence, that is, the safety reserve of the bearing capacity of the pile is smaller. The above analysis shows that the bearing layer of the pile tip and the sequence of loading have great influence on the distribution of negative skin friction. It is suggested to select the appropriate loading sequence to reduce the negative skin friction of the pile by analyzing the geological conditions, stress characteristics of the pile foundation and bearing requirements in practical engineering.