砂土中单桩抗拔极限承载力的计算

桩侧极限摩阻力是砂土中单桩抗拔极限承载力的主要组成部分，作为计算桩侧极限摩阻力的关键参数--土侧压力系数K的取值合理与否直接影响到单桩抗拔极限承载力计算的准确度。首先，基于密砂和松砂中的桩在上拔破坏时桩侧土压力分别呈被动和主动状态，同时考虑桩侧摩阻力和桩身表面粗糙度的影响，分别推导了不同相对密实度砂土中的土侧压力系数。然后，利用所得到的土侧压力系数并考虑桩侧单位摩阻力发挥的临界深度，按沿桩-土界面发生圆柱状剪切破坏模式建立了砂土中单桩抗拔极限承载力的计算方法。最后，利用该方法对已有的抗拔桩试验结果进行分析和比较，结果表明计算值与实测值吻合较好。

Calculation of the ultimate uplift capacity of single piles in sand

As an important parameter of calculating the limit skin friction which is a main part of the ultimate uplift capacity of single piles in sand, the rationality of the coefficient of lateral earth pressure K will affect the accuracy of the ultimate uplift capacity of single piles. Firstly, based on the passive stress state of dense sand around uplift piles and the active stress state of loose sand around uplift piles, the coefficients of lateral earth pressure of different relative densities sand are derived considering the effects of the skin friction and the surface roughness of piles. Afterwards according to cylindrical shear failure mode, a method for predicting the ultimate uplift capacity of single piles in sand is obtained considering the development critical depth of unit skin friction. Lastly, the test results of uplift piles are analyzed by the present method and the predicted ultimate uplift capacity of single piles agree well with those measured values.