基于薄环层元法的层状地基中摩擦桩竖向受荷计算

基于薄环层元法和虚土桩假设,提出了层状地基中竖向受荷摩擦桩计算模型。将桩身正下方至基岩间的土层视为虚土桩,并将桩土体系划分为多个薄层单元;随后利用虚位移原理求得薄环单元和桩单元的单元矩阵方程,并根据单元间平衡关系建立整体矩阵方程;最后通过桩与桩周土的协调关系,计算出层状地基中桩土体系位移。计算结果与已有方法结果吻合良好,验证了本文的正确性与可靠性。参数分析表明,计算单元厚度越小,精度越高;三层地基中的摩擦桩,中间夹层模量越大,其分担的荷载越多。桩端下卧土层厚度越小,桩端刚度越大。当桩端土厚度小于0.3倍地基厚度时,桩端刚度显著增大。当桩端以下土体分层时,桩端刚度与持力层厚度和强度密切相关。

Vertically-loaded single floating pile in layered soils by thin annulus element method

Based on the thin annulus element method and the hypothesis of fictitious soil pile, a model for the settlement of an axially-loaded single floating pile in the layered soils is proposed. The soil column beneath the floating pile is regarded as the fictitious pile shaft. The soil-pile system is then divided into the separate thin-layer elements. The stiffness matrices for the soil element and pile element are deduced using the principle of virtual displacements. The global matrices are constructed by considering the continuity and equilibrium conditions between the elements. The vertical displacement of the soil-pile system can be obtained by solving the matrix equation. The comparisons of the results between the proposed model and the available solutions indicate the accuracy of the proposed model. Parametric study shows that the accuracy of the proposed solution depends greatly on the thickness of the thin annulus element and the choice of the displacement function. For the floating pile in the three-layer soil, the bearing capacity of the middle layer around the shaft increases with the increase of its elastic modulus. The tip stiffness of the floating pile increases with the decrease of the layer thickness between the pile tip and bedrock. When this thickness is less than 0.3 times the soil thickness, the pile tip stiffness will increase significantly. The pile tip stiffness is also dependent greatly on the properties of the underlying soil below the tip of the floating pile.