静压沉桩引起的土体应力与孔压分布特征

Distribution Characteristics of Stress and Pore Pressure Induced by Pile Jacking

通过开展一系列离心模型试验,对饱和粉质黏土中沉桩挤土应力和孔隙水压力分布特征进行研究.利用微型传感器监测沉桩过程中土体的应力和孔压变化,并根据试验结果对已有的圆孔扩张模型进行修正,提出考虑地表隆起的沉桩挤土模型,对其可靠性进行验证.研究结果表明,桩周土体总应力和超孔压变化特征主要由距桩的水平距离和埋深控制,对于确定埋深处的土体,当桩尖接近并经过其埋深位置时,应力和孔压先增大后减小;当水平距离相同时,埋深越大,沉桩引起的应力和孔压增量越大,分析认为是地表自由边界的存在影响了浅埋土体中应力变化;当沉桩深度达到7～7.5倍的桩径时,地表边界效应的影响不再明显.

A series of centrifuge model tests were conducted on the spatial distribution characteristics of stress and pore pressure due to pile installation.According to test data,the existing cavity expansion theory was modified,and a pile installation model,which took ground surface heave into account,was proposed.The reliability of this model was validated by the centrifuge test data.The results showed that variation characteristics of total radial stress and the pore-water pressure were controlled by the distance from the pile axis and depth of the soil element.For a certain depth,the stress and pore-water pressure of soil increased as the pile tip reached and decreased as the tip passed.For the same distance from pile,the increases of stress and pore-water pressure caused by deep penetration were larger than those induced by shallow penetration.The reason was that the free ground surface influenced the stress conditions.If the pile penetration depth in the silty clay reaches 7~7.5times pile diameter,the influences can be ignored.The studies of this paper will provide the basis for time-dependent prediction of pile foundation capacity.