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Geometrical modelling with finite element method and slope effect of geosynthetic reinforced and pile-supported embankments
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摘要: 桩承式加筋路堤常用的有限元几何建模方法包括单桩模型（含轴对称模型和单桩3D模型）、平面应变模型和3D断面模型，这些模型各具特点且前提假设各不相同，但却缺乏对比研究。使用非线性有限元软件ABAQUS结合现场试验结果进行了几何建模，对比分析了基于大面积堆载假定的模型与带边坡3D断面模型应力分布及变形的差异与原因。计算表明：3D断面模型最能反映桩承式加筋路堤真实工况，而单桩模型及大面积3D断面模型均低估了沉降量。边坡效应引起的水平位移及坡外隆起使得桩土沉降差、平均桩土应力比、桩顶荷载分担系数及土工加筋横向拉应力均在路肩区域达到极大值，且在路面范围内均大于大面积堆载工况。Abstract: The finite element geometric modeling methods commonly used for the geosynthetic reinforced and pile-supported embankments include the single pile model (including axisymmetric model and single pile three-dimensional (3D) model), the plane strain model and the full 3D piled embankments model. These models have different characteristics and assumptions, however, few studies have been carried out to focus on the comparison. The geometric modeling analysis is carried out by using the nonlinear finite element software ABAQUS combined with the field testing results. The differences and causes of stress distribution and deformation between the models with hypothesis of large-area surcharge filling and the full 3D piled embankments model with slope are compared and analyzed. The results of numerical model calculation show that the full 3D piled embankments model can best fit the real performance, while both the single pile model and the large-area surcharged full 3D piled embankments model underestimate the settlement. Due to the horizontal displacement and uplift swelling caused by embankment slope, the settlement difference, average stress ratio between pile and soil, the load sharing coefficient of the pile and lateral tensile stress of the geogrid all reach the maximum values under the shoulder region of the embankment. Meanwhile, under the pavement area, all the four parameters of the full 3D model with slope are larger than those of the full 3D piled embankments model with large-area surcharge filling. The numerical simulation results given by this paper can provide a meaningful reference for the geometrical numerical modelling of composite foundation under embankments and the analysis of the three-dimensional slope effect of embankments.
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图 2 正方形布桩单桩3D模型
Figure 2. Three-dimensional model for single pile with square distributed piles
图 7 路中测点位置桩、土应力分担
Figure 7. Vertical stress distribution of soil and pile at measuring point near center line of embankment
图 8 路中位置桩、土平均应力分担
Figure 8. Average vertical stress distribution of soil and pile at central location of embankment
图 9 路堤堆载结束时刻3D断面模型位移矢量图和水平位移云图
Figure 9. Displacement vector diagram and horizontal displacement contour of full 3D piled embankments model after surcharge filling
图 10 路堤堆载结束时路堤和地基土大主应力云图(单位：kPa)
Figure 10. Principal stress contour of soils and fills after surcharge filling (unit: kPa)
图 11 路堤堆载结束时各桩位处沉降及荷载
Figure 11. Settlement and load distribution between each pile and its surrounding soil after surcharge filling
图 12 路堤堆载结束时土工加筋横向拉应力云图(单位：kPa)
Figure 12. Lateral tensile stress contour of geogrid after surcharge filling (unit: kPa)
表 1 数值模型所用本构模型及单元类型
Table 1. Constitutive models and element type applied in FEM modelling
模型分部 本构模型 单元类型 轴对称模型 3D模型 地下水位之下的地基土 修正剑桥模型 CAX4P C3D8P 路堤填土、碎石垫层、地表填土 摩尔库伦理想弹塑性模型 CAX4 C3D8 PCC桩 线弹性模型 CAX4 C3D8 土工加筋 线弹性模型 MAX1 M3D4 
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