基于黏弹性理论的沉桩再固结问题分析

假设桩周土体为饱和黏弹性介质,采用Burgers流变模型进行描述,同时考虑竖向和径向固结,建立了固结控制方程。根据不排水和自由排水情况,将边界条件分为3类并分别得到超孔隙水压力消散的级数解答,该解答能够为孔压静力触探反求固结系数提供一定的理论依据。在此基础上编制了应用程序,对Burgers流变模型中主要参数进行了分析。结果表明,地基表面自由排水、桩端地基不排水条件下,在一定深度以内的桩周土体的固结速度随深度降低,但超过某一范围后固结速度趋于稳定;上、下边界均自由排水条件下,固结速度随深度增加呈现下降、稳定、升高;上、下边界均不排水条件时,孔压消散速度不随深度变化,可简化为本解答仅考虑径向固结的特例。同时土体的流变特性对超孔隙水压力消散的影响比较显著,流变参数G1/1的变化使超孔隙水压力趋于某不为0的定值,且该值随G1/1比值的增大而增加;其他参数不变时,土体剪切刚度比G1/G2的增大会引起孔压消散速度的下降。

Analysis of consolidation around a driven pile based on viscoelasticity theory

Burgers rheological model is used to establish the consolidation equations with the consideration of vertical and radial consolidations, while soil around pile is assumed to be saturated viscoelastic media. According to free-draining or undrained condition, the boundary condition is divided into three categories. Series solutions for dissipation of excess pore water pressure are obtained. The series solutions can provide theoretical basis for inverse calculation of consolidation coefficient from static cone penetration test. On this basis, application program is compiled to analyze the main parameters of Burgers rheological model. The result shows that the consolidation rate reduces with depth within a certain depth under the conditions of ground surface free-draining and pile tip foundation undrained. But beyond a threshold, consolidation rate tends to stabilize. When both of upper and lower boundaries are under free-draining condition, the consolidation rate with depth will decrease at first, followed by stabilizing, and increase again at the end. When both of upper and lower boundaries are under undrained condition, the dissipation rate of pore pressure no longer changes with the variation of depth, which can be considered as a special circumstance only considering vertical consolidation. Also, the rheological property has great influence on the dissipation rate of excess pore water pressure. The excess pore water pressure tends to a non-zero value with the variation of G1/η1, and the value increases with the increasing of G1/η1. When other parameters are invariant, the dissipation rate of pore pressure decreases with the increasing of G1/G2.