考虑非达西流固结土体中桩基承载时间效应研究

Research on bearing time effect of pile foundation in consolidation soil considering non-Darcy flow

为揭示堆载作用下软土固结沉降过程中桩土相互作用机理,首先,基于非达西流动定律推导土体非达西一维固结非线性方程,考虑土体固结过程中孔隙比和渗透系数等参数变化导致土体的非线性特性,通过有限差分法获得超孔隙水压力的数值解答,建立桩侧土体固结沉降计算模型;其次,基于桩土荷载传递模型,考虑土体有效应力增加对桩土界面强度的影响,提出固结土体中桩基长期承载时间效应计算理论;第三,采用Python语言编制迭代求解计算程序,获得桩身下拉荷载、桩侧负摩阻力以及中性面随时间变化的分布规律;最后,对比本文计算结果与现有试验,并进一步研究排水条件对摩擦桩与端承桩下拉荷载分布及中性面位置变化的影响。研究结果表明:与非达西流动相比,按照达西流动定律计算结果高估了土体的有效应力和桩土界面强度;排水条件对桩基础中性面位置有很大影响,双面排水时摩擦桩中性面位置随结时间向上移动,端承桩则稳定在桩尖附近,单面排水时中性面位置随固结均向下移动;本文计算结果与离心机模型试验结果总体变化规律相似,误差可以接受,提出的桩身下拉荷载及中性面位置计算方法可以高效、准确地预测桩周土体在堆载作用下非达西流动固结过程中桩基长期承载响应。

To reveal the mechanism of pile-soil interaction in the process of consolidation and settlement of soft soil under surcharge,firstly,the nonlinear equation of non-darcy one-dimensional consolidation of soil was derived based on non-darcy flow law.The nonlinear characteristics of the soil was taken into account that was caused by the change of the pore ratio and permeability coefficient of soil and other physical parameters in consolidation process.The numerical solution of excess pore water pressure was obtained by finite difference method.The calculation model of consolidation settlement of soil surrounding the pile was established.Secondly,based on the pile-soil load transfer model,the influence of the effective soil stress on the shear strength of the pilesoil interface was considered.The calculation theory of long-term bearing time effect of pile foundation in consolidated soil was proposed.Thirdly,the iterative solution calculation program was written by Python language.The time-dependent distribution of dragload,negative skin friction and the neutral surface were obtained.Finally,the calculation results were compared with the existing tests,and the effects of drainage conditions on the dragload distribution and neutral surface position change of friction piles and end-bearing piles were further studied.The results show that compared with the non-Darcy flow,effective stress of soil and strength of pile-soil interface are overestimated according to the calculation results of Darcy's flow law.The drainage conditions have a great influence on the neutral plane position of the pile foundation.For double drainage,the neutral surface of the floating pile moves upward with time,while the end bearing pile is stable near the pile tip.The neutral plane moves down with consolidation for single drainage.The calculation results are similar to the overall variation rule of the centrifuge model test results,and the error is acceptable.The proposed method which calculates the dragload and neutral plane position in this paper can efficiently and accurately predict the long-term bearing response of the pile foundation during the non-Darcy flow consolidation process of the soil around the pile.