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针对洞口管棚受开挖过程影响的特点,考虑初期支护延滞性、围岩应力释放差异性、地层反力系数不均匀性和仰坡坡度等因素,将管棚划分为初支闭合段、初支未闭合段、开挖未支护段、掌子面前方塑性扰动段、弹性扰动段和无扰动段,建立基于Pasternak弹性地基梁理论并考虑施工特性的洞口管棚变形量预测模型。利用有限单元法思想和梁段纵向剪力传递理论,获得管棚变形预测理论值,并应用于桦皮岭隧道工程。结果表明:(1)Pasternak力学模型摈弃了Winkler弹性地基梁不能传递纵向剪力的缺陷,其预测值与现场试验结果吻合度较高,最大偏差较Winkler模型减小11.8%,更适合洞口管棚变形预测。(2)管棚变形量随地层反力系数和管棚直径增大而减小,但非线性关系;管棚环向间距与变形呈正比例关系;当地层反力系数和管棚直径超过某一数值,通过调整注浆改善地层反力系数或直径方法来控制管棚变形效果甚微。(3)在给定变形控制基准下,确定IV,V和VI级围岩不同纵坡条件下经济合理的管棚直径和环向间距,并制定了管棚设计施工参数选择一览表。其研究成果为完善管棚计算方法、设计施工体系提供参考和借鉴。
In view of the characteristics of tunnel shed affected by the excavation process, considering the factors of initial support delay, difference of stress release of surrounding rock, formation reaction coefficient inhomogeneity and slope gradient, The initial branch unclosed section, the unsupported section of excavation, the plastic perturbation section, the elastic perturbation section and the undisturbed section in front of the face of the excavator, a prediction model of the deformation of the tunnel shed based on the Pasternak elastic foundation beam theory and considering the construction characteristics is established. By using the theory of finite element method and longitudinal shear transfer theory of beam section, theoretical predictions of pipe shed deformation are obtained and applied to the Birch Ridge tunnel project. The results show that: (1) Pasternak mechanics model discards the defect that Winkler elastic foundation can not transfer longitudinal shear force. The predicted value is in good agreement with the field test results. The maximum deviation is 11.8% less than Winkler model, Deformation prediction. (2) The deformation of pipe shed decreases with the increase of formation reaction coefficient and pipe shedding diameter, but it is non-linear; the distance between pipe shed ring and the deformation is in a positive relationship; when the reaction coefficient of the formation and the pipe shed exceed a certain diameter Numerical, by adjusting the grouting to improve the strata reaction coefficient or diameter method to control the shed effect is very small. (3) Based on the given deformation control criterion, the reasonable and reasonable pipe shedding and annular spacing under different longitudinal conditions of IV, V and VI surrounding rock are determined, and a list of the design parameters of pipe shed design is established. The research results provide a reference and reference for perfecting the calculation method of pipe shed and design and construction system.