Applicability of Novel Pile-Plank Embankment in Seasonally Frozen Regions
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摘要: 针对莫喀（莫斯科—喀山）高速铁路季节性冻土区路基冻胀病害防治问题，提出了铺设保温板垫层的新型桩板结构路基. 通过对聚苯乙烯泡沫塑料板（EPS）、聚氨酯板（PU）和挤塑聚苯乙烯泡沫塑料板（XPS） 3种保温材料性能的对比分析，发现新型桩板结构路基中的保温板可采用在保温隔热、隔水防渗和抗压性能方面表现良好的XPS保温板. 通过建立热弹塑性冻胀计算模型，研究了冻胀力作用下保温板铺设范围、厚度、路基填高和外界温度对新型桩板结构路基受力变形的影响. 结果表明：当保温板铺设范围延伸到线路两端的信号线槽处时，可以更好地阻滞外界负温向下传递（减小冻深），抑制因桩板结构周边土体冻胀对结构物产生的不良影响；随着保温板厚度的增大，冻胀量呈指数形式减小，冻深呈抛物线形减小，保温板上表面处起到抑制外界负温向下传递的作用，下表面处起到控制下部土体温度耗散的作用；增大路基填高，有利于抑制路基冻胀量，减少保温板的使用厚度，当路基填高0.8 m时，保温板垫层厚度需大于0.40 m；当路基填高2.8 m时，保温板垫层厚度需大于0.31 m.Abstract: In order to control the frost heaving damage in the seasonally frozen regions of the Moscow−Kazan high-speed railway, a novel pile-plank subgrades with an insulation board was proposed. Comparing the performance of three kinds of thermal insulation materials, expanded polystyrene (EPS) foam board, polyurethane (PU) board and extruded polystyrene (XPS) foam board shows that the XPS insulation board could be used in the new subgrade for its better performance in heat insulation, waterproof, impervious and compressive properties. The thermo-elasto-plastic model was established to study the influences of laying range, insulation board thickness, filling height, and external temperature on the mechanical deformation of the new type subgrade. The results show that when the laying range of the insulation board is extended to the signal wire slot, it can do better to preventing the downward transfer of negative temperatures (reducing the frozen depth), and diminishing the harmful effect of soil frost heaving surrounding the pile-plank structure. With increasing board thickness, the heaving amount decreases exponentially and frozen depth decreases close to a parabolic curve. The upper surface of the insulation board can prevent the downward transfer of negative temperatures and its lower surface plays a role in controlling the soil temperature dissipating under embankment. Increasing the filling height of embankment is helpful to suppress the subgrade heaving amount and reduce the usage thickness of the insulation board. The insulation board thickness should be greater than 0.4 m when the filling height is 0.8 m; and the board thickness should be greater than 0.31 m when the filling height is 2.8 m.
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图 1 铺设保温板垫层的桩板结构路基横断面及纵断面（单位：m）
Figure 1. Cross-section and longitudinal profiles of pile-plank structure with insulation boards (unit：m)
图 4 M1、M2各埋深处温度分布
Figure 4. Temperature distribution curves of M1 and M2 at different buried depths
图 5 M1、M2各位置不同埋深处温度分布
Figure 5. Temperature distribution curves of M1 and M2 along buried depth at different sites
图 7 保温板位移云图及上、下表面温度分布云图
Figure 7. Nephogram of insulation board displacement and temperature distribution of its upper and lower surface
图 8 冻胀量与冻深随保温板厚度变化
Figure 8. Variations of frost heaving amount and frozen depth with insulation board thickness
图 9 保温板上下表面温度时程曲线
Figure 9. Temperature time-history curves of upper and lower surface of insulation boards
图 10 两种路基填高下冻胀量随保温板厚度变化
Figure 10. Variations of frost heaving amount with insulation board thickness at roadbed filling heights
表 1 保温板物性参数
Table 1. Physical parameters of insulation boards
材料类型 表观密度/（kg•m−3） 导热系数/（W•m−1•K−1） 体积吸水率/% 抗压强度/kPa EPS 30～40 0.030 0～0.044 0 3.60～6.00 300～345 PU 59 0.019 7 1.40 322 XPS 40～45 0.011 0～0.012 0 0.96～0.97 500～650 
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表 2 冻融条件下3种保温板稳定性对比
Table 2. Stability comparison of three kinds of insulation boards under freeze-thaw conditions
材料
类型冻融循
环/次导热系数/
（W•m−1•K−1）体积吸
水率/%抗压强
度/kPaEPS 5 0.025 3 2.60 347 10 0.024 9 2.50 335 20 0.025 3 2.80 352 30 0.024 2 2.50 326 PU 5 0.019 3 0.50 308 10 0.018 4 1.10 306 20 0.018 8 1.00 263 30 0.018 1 0.90 282 XPS 5 0.009 8 0.91 646 10 0.010 2 0.78 637 20 0.009 3 0.84 628 30 0.008 6 0.82 663
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表 3 土层划分及参数
Table 3. Physical parameters by soil division
土层 高度/m 密度/（kg•m−3） 弹性模量/MPa 泊松比 黏聚力/kPa 内摩擦/（°） 路堤 2 000 50.00 0.25 75.4 34 微湿润粉砂 2.5 1 720 25.00 0.25 1.0 31 饱水细砂 9.0 1 940 46.45 0.25 2.0 34 饱水粉砂 6.0 1 980 26.80 0.25 3.0 28 饱水细砂 7.0 1 940 46.45 0.25 2.0 34 湿润及饱水细砂 25.5 2 040 69.65 0.25 4.0 34
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表 4 桩板结构参数选取
Table 4. Parameter selection of pile-plank structure
构件
类型尺寸/m 密度/（kg•m−3） 弹性模量/MPa 泊松比 导热系数/（W•m−1•K−1） 承载板 长 22.48，宽 4.99 × 2（双线），高 0.80 2 500 32 500 0.18 1.58 托梁 长10.40，宽 1.30，高 0.85 2 500 32 500 0.18 1.58 桩基 长 30.00，直径 1.25，纵向桩间距 7.50，横向桩间距 5.00 2 500 30 000 0.20 1.58
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