刚性桩复合地基负摩阻区深度的一种计算方法

A Calculation Method for Depth of Negative Friction Zone of Rigid Pile Composite Foundation

根据刚性桩复合地基桩身的受力特性,从其变形模式出发,利用Bjerrum公式,推导了考虑桩-土-垫层相互作用时负摩阻区深度l0的计算方法.与实测数据对比,验证了该算法的可行性.参数分析表明,当桩身的弹性模量Ep大于某一数值时,桩土应力比n与l0曲线变化已趋稳定,此时提高桩体强度对复合地基承载力的影响不显著;而置换率的合理确定对于复合地基承载力的整体发挥有着重要影响;桩侧土模量增加时负摩阻区深度会减小,随着荷载的增加,减小趋势将变弱;从参数分析结果对比可以得出,桩侧土模量变化对负摩阻区深度的变化影响最大,尤其是在等沉面上部土体模量较小时,l0的变化幅度可达23.6%.因此,在软土地区采用刚性桩复合地基处理方法时要充分考虑土体模量对负摩阻区深度的影响.

Based on the load-bearing characteristic and the deformation model of rigid pile composite foundation, the calculation formula of the negative friction area on piles considering the interaction of pile-soil-cushion is deduced and confirmed through a tested example. Parametric analysis shows that when the pile elastic modulu is over a certain value, the curve of n-10 tends to be stabilized. Thus, it is not necessary to make a high value of pile strength in compositefoundation design. Rationally determination of the replacement rate has an important impact on developing the whole bearing capacity of composite foundation. The depth of negative friction zone will reduce when the soil modulus on the side of pile increasing and the reduction trend will become weak with the increasing of load. A comparison of the results of parametric analysis shows that the change of soil modulus on the side of pile has the greatest impact on the depth of negative friction zone, especially when the soil modulus is small, the depth changes up to 23.6%. Thus, in soft soil area where the rigid pile composite foundation treatment methods are adopted, full consideration should be taken that the soil modulu has great impact on the depth of the negative friction zone.