Finite element modelling types for rigid pile composite foundation under geosynthetic-reinforced embankment
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摘要: 基于加筋路堤下CFG桩复合地基现场试验段分别建立单桩、群桩及全断面有限元模型,探讨几何模型、桩土接触等条件对系统变形、应力分布及荷载传递的影响。结果表明：受路堤边界效应影响,全断面模型的沉降及荷载分配完成较快,应力比n、桩的荷载分担效率系数E均在路肩内侧附近达到最大值,且分别高于路中位置15.7%和5.2%。坡脚位置桩顶位移矢量角、桩的水平荷载及弯矩显著。单桩与群桩模型规律较为相近,沉降发展相对迟缓且略低于全断面模型。各有限元模型预测的最终状态的n,E及等沉面高度均正比于其桩土沉降差。统计表明单桩加固范围内实测与理论荷载误差可达-35.1%～58.5%,桩土竖向应力分布并不均匀。设置允许桩土发生相对位移的接触条件将增大沉降量及等沉面高度,并影响浅层桩身受力。桩承式加筋路堤有限元数值计算应优先选择考虑桩土接触条件的全断面模型。Abstract: Based on the in-situ test section of CFG pile composite foundation under geosynthetic-reinforced embankment, the finite element models for a single pile, group piles and full section are established, respectively, and the influences of the geometric model, pile-soil contact and other conditions on system deformation, stress distribution and load transfer are discussed. Mostly due to the influences of embankment boundary effect, the settlement and load distribution of the full-section model are both developed in time as the in-situ test results. The stress ratio (n) and the load-sharing efficiency of pile (E) both reach the maximum near the inner side of the embankment shoulder and are 15.7% and 5.2% higher than those in the center of the embankment, respectively. At the toe of the slope, the displacement vector angle of the pile top, the horizontal load and bending moment of the pile are quite significant. Under the surcharge with the same equal thickness, the single-pile model has similar performance with the group-pile model, and the settlement development of both is relatively slow and slightly lower than that of the full-section model. In each model, the predicted results show that n, E and the equal settlement surface height are all directly proportional to the differential settlement of soil-pile on the subsurface at the final computing time. The distribution of non-uniform vertical stress on the subsurface is shown according to the numerical results. According to the statistic results, the deviation between the test load and the theoretical load can be -35.1% to 58.5% within single-pile reinforced area. Setting the contact interaction to enable the relative displacement of pile and soil will increase both the settlement and the height of the equal settlement surface, and also affect the stress of the shallow pile shaft. The full-section finite element model with pile-soil interaction is recommended to investigate the composite foundation under reinforced embankment.
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图 1 加筋路堤下CFG桩复合地基剖面图
Figure 1. Profile of CFG pile composite foundation under reinforced embankment
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图 5 路中位置桩土应力
Figure 5. Stresses on pile and soil on subsurface in center of embankment
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图 6 全断面模型路中位置桩土应力等值线
Figure 6. Contour map of stress of pile and soil on subsurface in center of embankment in full-section model
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图 7 单桩加固范围荷载统计对比
Figure 7. Comparison of statistic loads within single-pile reinforced area
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图 8 路中位置单桩加固范围最终应力
Figure 8. Ultimate stresses within single-pile reinforced area in center of embankment
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图 9 填筑结束时刻路中位置桩和桩间土中心之上路堤中沉降差及竖向应力分布
Figure 9. Difference of settlement and distribution of vertical stress in embankment above pile and soil center in center of embankment at end of filling
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图 10 填筑过程路中位置各模型桩土应力调整分析
Figure 10. Analysis of stress adjustment of pile-soil of numerical models during embankment construction
表 2 有限元计算材料参数
Table 2 Parameters of materials for finite element analysis
土层 厚度/m w/% γ/(kN·m-3) e— K0— IP— E/MPa — c/kPa φ/(°) ψ/(°) k/(10-3m·d-1) 面层 0.186 — 22.0 — — — 1200.00 0.22 — — — — 基层 0.575 — 21.0 — — — 100.00 0.30 — — — — 填土 4.060 — 19.2 — 0.59 — 30.00 0.37 6.0 24.0 0 — 碎石垫层 0.500 — 21.0 — 0.36 — 60.00 0.26 0 40.0 10 — ①粉质黏土 2.500 31.0 19.1 0.872 0.69 14.0 2.74 0.41 20.0 18.0 0 5.2 ②淤泥质土 6.400 34.1 18.6 0.951 0.74 8.3 2.85 0.43 11.3 15.0 0 5.4 ③淤泥质土 22.100 42.1 18.1 1.160 0.85 13.2 2.00 0.46 12.6 8.9 0 0.8 ④细砂 12.000 29.5 19.1 0.834 0.58 — 5.79 0.37 0 25.0 0 617.8 CFG桩 33.000 — 24.0 — 0.25 — 12000.00 0.20 — — — — 加筋 0.005 — — — — — 2000.00 0.20 — — — — 
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表 3 路中位置单桩加固范围荷载
Table 3 Loads on subsurface within single-pile reinforced area in center of embankment
文献 桩顶压强/kPa 桩间土压强/kPa Fsingle/kN γHeA/kN 误差/% 本文 672 37 253 362 -30.2 Liu et al[8] 649 47 896 932 -4.0 姜彦彬等[2] 352 30 472 425 11.1 Chen et al[11] 375 19 720 788 -8.5 Briançon et al-2R[12] 595 88 411 370 11.1 Briançon et al-3R[12] 2957 55 547 378 44.8 Briançon et al-4R[12] 2483 44 452 397 13.7 Liu et al[13] 596 70 931 588 58.5 Zhou et al[14] 127 27 259 399 -35.1 Cheng et al[15] 210 12 580 812 -28.6 Cao et al[16] 179 116 320 233 37.1 郑俊杰等[17] 521 54 1132 1164 -2.7 夏唐代等[18] 553 11 1333 1079 23.5
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