梯形渠道衬砌冻胀破坏弹性地基板模型

    Elastic foundation plate model for the frost heave damage of trapezoidal canal lining

    • 摘要: 为探讨开放系统中梯形混凝土衬砌渠道的冻胀问题,根据衬砌板与冻土地基的相互关系,该研究采用 Winkler弹性地基板理论建立考虑冻胀力和冻结力作用的衬砌板冻胀破坏力学模型,使用解析法得到了衬砌板变形和内力解,对不同地下水埋深、衬砌板几何参数的影响规律进行了分析。通过与已有现场观测值和计算值进行对比,验证了弹性地基板理论计算结果的正确性。研究结果表明:坡板在非均匀分布的冻胀力作用下,挠度、弯矩和剪力也表现为非均匀分布,挠度最大值在坡顶距坡脚2/3处,弯矩最大值靠近底板位置,拉应力分布与内力分布规律一致。与梁理论相比,板理论计算结果表明衬砌板的挠度和内力沿板宽方向为非均匀分布,挠度和弯矩在自由边界(纵向伸缩缝)处增大,扭矩主要分布在衬砌板的拐角处。切向冻结力对渠道冻胀影响较小,在原渠道工况下,不考虑切向冻结力与考虑最大切向冻结力之间,最大挠度相差0.7 mm。针对不同地下水位的渠道,给出了衬砌板的安全厚度,可为现浇混凝土梯形渠道的抗冻胀设计提供参考和理论依据。

       

      Abstract: Frost heave can seriously damage the trapezoidal concrete-lined canal with an open system in cold regions. In this study, the frost heave failure model of canal lining was established to consider the frost heave force and adfreeze force. The Winkler elastic foundation plate theory was also used to describe the relationship between the canal lining and frozen soil foundation. Specifically, the top of the canal slope and the soil of the channel foundation were frozen together, and the foot of the slope and the bottom plate were set as the mutual hinge constraints. The two ends of the plate at the depth direction were assumed to be simply supported boundaries. The adjacent canal lining joints were mostly filled with soft elastic waterproof materials, particularly for the relatively large deformation. The adjacent canal lining board joints were then assumed to be free boundaries. The analytical solution of the model was obtained to clarify the influence of groundwater depth and geometric parameters of canal lining. A comparison was finally made to verify the field observation and calculation. The results show that the bottom plate was subjected to the uniform force of frost heaving. There was an uneven distribution of the internal force and stress along the height direction of the plate. The stress at the free boundary was also slightly larger than that at other positions. The bending moment and shear force of the slope plate were unevenly distributed, where the maximum deflection was 2/3 from the top to the foot of the slope, and the maximum bending moment was close to the bottom plate. A similar distribution of the stress and internal force was also better consistent with the existing research. The maximum stress occurred at the maximum deflection position. The torque was distributed symmetrically along the center of the canal lining, where the maximum was at four corners. It infers that it was easy to produce a stress concentration at the corners. Compared with the beam theory, the plate theory showed that the deflection and internal force of the lining plate were not uniformly distributed along the plate width direction, where the deflection and bending moment were greater at the free boundary (longitudinal expansion joint), and the torque was distributed at the corner of the canal lining. The tangential force posed little influence on the frost heaving of the canal. The maximum deflection of the canal only increased by 0.7 mm, when adding the tangential force. But the adfreeze force produced an eccentric bending moment on the canal lining, indicating a great increase in the overall bending moment of the canal lining. Therefore, the adfreeze force should be considered in the antifreeze design of the canal lining. The relationship between groundwater and frost heave was dominant in the prevention of frost damage to the canal. Different thicknesses of lining plate should be selected for the working conditions of different groundwater depths. The frost heave displacement of the slope plate gradually decreased with the increase of groundwater depth. There was no variation in the position of the maximum frost heave displacement section. Therefore, the increasing thickness of the canal lining can also effectively prevent frost heave damage to the canal. The thick canal lining or high concrete strength can also be expected to prevent freezing damage, particularly for the high water table. As such, the safe range of canal lining thickness can be obtained, according to the canals with different groundwater levels. The finding can provide a strong referent and theoretical basis for the frost-heave-resistant design of cast-in-place concrete trapezoidal canals.

       

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