考虑地下水位影响的现浇混凝土梯形渠道冻胀破坏力学分析

地下水的补给与迁移是高地下水位渠道的冻胀破坏的主要影响因素。该文提出了一种考虑地下水位影响的梯形渠道衬砌冻胀力分布计算方法,推导出地下水位影响的渠道基土冻胀强度和冻结深度分布的计算公式,并得到现浇混凝土衬砌的截面最大弯矩和最易破坏截面位置的解析表达式。从整体与局部2个方面定量分析梯形渠道衬砌冻胀力分布的不均匀性,为渠道的抗冻性能评价和断面优化提供了定量指标,结果表明:渠深越浅,坡板倾角越小,冻胀力分布越均匀,越不易发生破坏,揭示了宽浅式梯形渠道抗冻性能良好的原因。以塔里木灌区某梯形渠道为原型,对不同地下水埋深的渠道冻胀特征和受力进行了分析,并与观测资料进行了对比,其中基土冻深的计算值与观测值之间的最大相对误差为3.5%,估算最大弯矩所在截面的位置为距离坡顶63.9%坡板长处,与灌区实地调查结果基本相符,表明了方法的实用性和合理性。最后,对高地下水位梯形渠道的冻害机理进行了分析,该研究可为高地下水位现浇混凝土梯形渠道衬砌的抗冻设计和相关研究提供参考。

Mechanical analysis on frost heave damage of cast-in-place concrete trapezoidal canal considering influence of groundwater table

Abstract: Groundwater migration and supply is the main influence factor causing frost heave damage of concrete lining trapezoidal canals with high groundwater table. Considering the influence of groundwater table on frost heave of canal foundation soil, the article puts forward a method to calculate the distribution of frost heave force acting on concrete trapezoidal canal lining, presents the design formulas to calculate the distribution of frost heave intensity and frozen depth of canal foundation soil, and then proposes the analytical expression to determine the maximum bending moment of cast-in-place concrete trapezoidal canal lining and the position on canal lining plate which is the easiest to crack. The inhomogeneity of distribution of frost heave force is quantitatively analyzed both locally and integrally, and a new indicator to judge frost heave resistance of canal lining and a method for cross-section pattern optimization are provided. For specific region with fixed groundwater table, the smaller the canal cross-section depth, the more homogeneous the distribution of frost heave force integrally. For specific region with fixed groundwater table from canal top, the smaller the inclination of canal slope plate, the smoother the variation tendency of frost heave force locally. In a word, when the canal cross-section depth is shallower and the inclination of canal slope lining plate is smaller, the distribution of frost heave force is more homogeneous, and the canal lining is harder to be damaged by frost heave force, therefore revealing the reason that the frost heave resistance of trapezoidal canal with wide and shallow cross-section is favorable. By taking a trapezoidal concrete lining canal in Tarim irrigation area as prototype, the frost heave characteristics of canal lining are analyzed, as well as the distribution of frost heave force acting on trapezoidal canal lining with different groundwater table, and the rationality of the method is confirmed by comparing the calculated value with the measured value. The results of comparison show that the maximum relative error of frozen depth of canal foundation soil is 3.5%, and the position of the section undergoing the maximum bending moment estimated is 63.9% of the length of canal slope lining plate from canal top. In addition, the analysis results also show that different groundwater table remarkably influences frost heave characteristics of canal lining and distribution of frost heave force acting on canal lining with high groundwater table. The tendency of variation of frost heave force becomes more linear when groundwater table is higher and the maximum bending moment on canal slope lining plate increases following exponential law. Therefore, the canal with high groundwater table is extraordinarily easy to suffer serious frost heave damage. Eventually, the mechanism of frost heave damage of trapezoidal canal with high groundwater table is analyzed. Because of long and severe winter in North China, in addition to slowly decreasing of air temperature, frozen rate of canal foundation soil is small, and then soil water has sufficient time to migrate and supply. While groundwater table is shallow, groundwater migration and supply is enough to cause serious frost heave damage to canal lining. On account of specific characteristics of canal cross-section, different distances from each position of canal slope plate to groundwater table result in inhomogeneous distribution of the intensity of groundwater supply, and then cause transverse difference of intensity of frost heave and frozen depth of canal foundation soil, and therefore the distribution of frost heave force and the deformation of canal lining can be inhomogeneous. In fact, inhomogeneous distribution of frost heave force acting on canal lining is also a main reason causing serious frost heave damage to canal lining. The research can provide theoretical basis for relevant study and frost heave resistance design of cast-in-place concrete trapezoidal canal with high groundwater table.