为研究不同控制措施下基坑开挖对下卧隧道拱顶竖向位移的影响,依托郑州市二七广场隧道工程,在验证数值计算可靠性的基础上,利用有限差分软件MIDAS GTS对地层加固与反压两种措施下隧道拱顶竖向位移的变形规律进行分析,并采用正交试验方法研究加固宽度、加固深度、反压宽度和反压荷载对隧道拱顶竖向位移的影响。结果表明:在类似工程中,随着上跨基坑坑底加固宽度和深度的增加,下卧地铁盾构隧道拱顶竖向位移随之非线性递减,且其纵向变形曲线拟合函数的宽度系数i呈非线性增大;随着反压荷载和反压范围的增加,下卧地铁盾构隧道拱顶竖向位移随之线性递减;坑底加固深度对下卧地铁盾构隧道的影响程度要依次大于反压荷载、加固宽度及反压宽度;坑底加固设计时,建议加固宽度和加固深度易设为基坑开挖深度的0.3倍和0.4倍;坑底加固与反压堆载综合设计时,从变形控制效果、施工流程、施工成本3个方面考虑,正交试验的16组方案中,方案4和方案15控制效果最佳,其中方案4施工成本低于方案15,方案15的变形控制效果优于方案4。本文成果可为粉质黏土或粉土地层条件下类似工程提供设计依据。

In order to study the influence of foundation pit excavation on the vertical displacement of the vault of the underlying tunnel under different control measures, based on the Erqi Square Tunnel Project in Zhengzhou City, on the basis of verifying the reliability of numerical calculation, the finite difference software MIDAS GTS was used to analyze the deformation law of the vertical displacement of the tunnel vault under the two measures of stratum reinforcement and back pressure. The orthogonal test method was used to study the influence of reinforcement width, reinforcement depth, back pressure width and back pressure load on the vertical displacement of the tunnel vault. The results show that in similar projects, with the increase of the width and depth of the bottom reinforcement of the upper foundation pit, the vertical displacement of the vault of the underlying subway shield tunnel decreases nonlinearly, and the width coefficient i of the longitudinal deformation curve fitting function increases nonlinearly. With the increase of back pressure load and back pressure range, the vertical displacement of the vault of the underlying subway shield tunnel decreases linearly. The influence of the reinforcement depth of the pit bottom on the underlying subway shield tunnel is in turn greater than the back pressure load, the reinforcement width and the back pressure width. In the design of pit bottom reinforcement, it is recommended that the reinforcement width and reinforcement depth are easily set to 0.3 times and 0.4 times of the excavation depth of the foundation pit. In the comprehensive design of bottom reinforcement and back pressure surcharge, considering the deformation control effect, construction process and construction cost, among the 16 schemes of orthogonal test, scheme 4 and scheme 15 have the best control effect. The construction cost of scheme 4 is lower than that of scheme 15, and the deformation control effect of scheme 15 is better than that of scheme 4. The above suggestions can provide design basis for similar projects under silty clay or silty soil layer conditions.