考虑列车间歇循环荷载作用下孔压消散的多尺度PVD地基长期沉降研究

In poorly drained situations the increase in excess pore pressures generated by cyclic loads (e.g. high speed rail) will decrease the effective load capacity of the soil foundation. The dynamic stresses can cause significant, immediate and long term settlement after the railway is put into operation. Furthermore, the stress pulse generated when a train wheels travel across a rail embankment consists of vertical and horizontal components, where an approximate sinusoidal vertical pulse is transferred to the foundation. This cyclic pulse varies with speed or frequency, load magnitude and the vehicle direction, becoming repetitive with the passage of increased axle loads. Under these circumstances combined with the extra rainfall caused by the global warming, slurrying or pumping of clay beneath rail tracks may initiate catastrophic undrained failure, causing unacceptable or uneven settlements and damage the overlying infrastructure. Therefore, in the absence of appropriate ground improvement, excessive settlement and lateral movement adversely increases in the maintenance costs which may also further affects the stability of the railway transport infrastructure built on such soft ground. This study will be the first of its kind aimed at understanding the behaviour of soft soil improved by Prefabricated Vertical Drains (PVDs) under cyclic loadings. A constitutive model of effectiveness of PVDs in dissipating excess pore water pressure induced by cyclic loading on soft soil will be established based on the test results by dynamic large-scale triaxial consolidation tests. The real flow ratio within the void of the soil will be tested by using CT scanner and the flow ratio from Pore-scale to Darcy-scale will be established by using DEM-PFV method. A multiscale 3D finite element analysis with high resolution in the immediate vicinity of the PVD will be developed. The constitutive model considers elasticity-plasticity of the soil and the moving traffic loading caused the cyclic principal stress rotation and complex stress path will be developed based on GDS dynamic hollow cylinder test results in order to verify the multiscale 3D FEM results. And then the numerical predictions will be calibrated by field data. The project outcomes will guarantee a better understanding of soft soil mechanics under cyclic loading and the benefits of PVD consolidation for stabilising soft soil foundations through numerical and experimental processes. The applied research will be most timely and beneficial to transport infrastructure in both urban and regional China.

行车荷载产生的附加动应力会引起交通基础设施土体超静孔压急剧上升，导致土体刚度软化，产生过大附加变形，增加维护成本及安全隐患。针对固结理论在模拟这一问题时的局限性，本项目拟采用室内试验、理论分析、数值计算、现场试验相结合的方法，对间歇循环荷载作用下经塑料排水体（PVD）加固后软基长期变形机理进行系统研究，揭示间歇循环荷载作用下土体渗流微观特性与宏观特性之间的关系，构建考虑主应力旋转情况下土体弹塑性变形模型。研究列循环载作用下土体渗流规律，定量分析排水体周围土体孔压及土体塑性变形的时空发展规律。开发多尺度三维有限元计算方法，实现考虑间歇循环荷载作用及土体主应力轴旋转的PVD地基长期沉降全过程模拟，进行现场工程试验验证，为行车荷载作用下PVD 地基的设计方法提供理论依据。项目的研究方法和成果，可为控制高速铁路，公路甚至机场跑道软基长期沉降提供可靠的理论指导和技术支持，保障行车安全，降低维护成本。

行车荷载产生的附加动应力会引起交通基础设施土体超静孔压急剧上升，导致土体刚度软化，产生过大附加变形，增加维护成本及安全隐患。针对固结理论在模拟这一问题时的局限性，本项目采用了用室内试验、理论分析、数值计算、现场试验相结合的方法，对间歇循环荷载作用下经塑料排水体（PVD）加固后软基长期变形机理进行了系统研究，揭示了间歇循环荷载作用下土体渗流微观特性与宏观特性之间的关系，构建了考虑主应力旋转情况下土体弹塑性变形模型。研究列车循环载作用下土体渗流规律，定量分析了排水体周围土体孔压及土体塑性变形的时空发展规律。利用多尺度三维有限元计算方法，实现了考虑间歇循环荷载作用下PVD地基长期沉降全过程模拟。现场工程试验，为行车荷载作用下PVD 地基的设计方法提供理了论依据。项目的研究方法和成果，可为控制高速铁路，公路甚至机场跑道软基长期沉降提供可靠的理论指导和技术支持，保障行车安全，降低维护成本。