考虑施工特性的浅埋软弱洞口段管棚变形量预测及工程应用

Deformation prediction of pipe roof in shallow soft portal section of tunnels considering construction feature

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。

The characteristics of pipe roof are affected by the excavation process, such as the delay of initial support, the time difference of stress release in surrounding soil and the uneven coefficient of formation and slope. Having considered these factors, a model for deformation prediction of pipe roof according to Pasternak theory of elastic foundation beam was established. The theoretical deformation prediction was derived with the finite element method and longitudinal shear transfer theory of beam section and the method was applied to Huapilin tunnel. The Pasternak model bases on a more realistic hypothesis in elastic soil than Winkler model, and therefore agrees better with the result of field test. The maximum deviation is 11.8% less than that of Winkler model. The deformation of pipe roof decreases with the increase of elastic modulus, shear modulus and diameter, but increases with the increase of circumferential spacing. The effect of controlling pipe roof deformation is very poor by adjusting the grouting to improve reaction coefficient and diameter when exceeding a certain value. The economic and reasonable construction parameters are determined under a given deformation control criteria considering different longitudinal slopes and different surrounding rock grades.