Abstract:Under the action of the ground surcharges,field measurements for time effects of negative skin friction behaviors of three piles with different vertical loads on the pile top are adopted. Test results show that negative skin friction behaviors change with the extension of time under the action of surcharges. Ground surcharges will cause the soil settlement surrounding the piles;and the soil settlement surrounding the piles can induce negative skin friction in piles. At the initial stage of surcharges,the additional settlement rate of piles caused by negative skin friction gets rapidly;and the final additional settlement in piles increases with the increase of load on the pile top. Drag forces caused by negative skin frictions in piles increase gradually with the extension of surcharges loading time;and final drag forces in piles decrease gradually with the increase of load on the pile top in both vertically loaded and unloaded piles. Under the action of surcharges,the load on the pile top postpones the arrival of negative skin friction in piles. The larger of the load on the pile top is,the later the appearance of the neutral point in pile is,and the smaller the length between the neutral point and the pile top is. The time of the neutral point in piles is delayed with the increase of the load on the pile top. Increase of load acted on pile top would promote above-mentioned phenomena. It may be useful for the research of negative skin friction behaviors of piles.