越江海泥水盾构隧道合理覆土厚度研究

Rational depth of earth cover of slurry shield tunnel under river or sea is proposed from view of slurry fracturing, stability of excavation face and security of anti-buoyancy. And research methods conclude theoretical analysis, laboratory experiments, numerical calculation and in-situ tests. Research contents: (1) slurry fracturing mechanical properties of soils; (2) supporting properties of excavation face in soils; (3) fluctuation of slurry pressure during shield excavation; (4) rational depth of earth cover of slurry shield tunnel consider of controllability of slurry shield; (5) rational earth cover of slurry shield tunnel consider of security of anti-buoyancy; (6) determination of rational depth earth cover of slurry shield tunnel under river or sea from overall analysis. Based on the research of slurry fracturing mechanical properties of soils, supporting properties of excavation face in soils and fluctuation of slurry pressure during shield excavation, the mechanics model of initial slurry fracturing, the mechanics model of slurry fracturing propagation and theory of stability of excavation face would be obtained. Thus, the upper and lower limit value of slurry pressure set would be given. The decision method of rational depth of earth cover consider of controllability of slurry shield could be obtained refer to fluctuation of slurry pressure. At last, analytical methods and criterion of rational depth of earth cover of slurry shield tunnel under river or sea could be obtained, while considering of security of tunnel anti-buoyancy.

采用理论分析、室内试验、数值计算和现场试验相结合的研究方法，从泥水劈裂、掘进面稳定和抗浮安全角度提出越江海泥水盾构隧道的合理覆土厚度命题。研究内容包括：(1)软土地层的泥水劈裂力学特性；(2)软土地层盾构掘进面支护力学特性；(3)盾构掘进过程中泥水压力的波动规律；(4)盾构掘进可控下的合理覆土厚度研究；(5)基于抗浮稳定的盾构隧道合理覆土厚度研究；(6)综合分析确定越江海隧道合理覆土厚度。研究从泥水劈裂力学性能、构掘进面支护力学特性和盾构掘进过程中泥水压力的波动规律出发，建立泥水劈裂力学模型、泥水伸展力学模型和掘进面稳定理论，从而给出泥水压力设定的上限值和下限值，参考泥水压力波动范围，给出盾构掘进可控下的合理覆土厚度判断方法。在同时考虑隧道施工运营抗浮稳定的条件下，给出越江海隧道合理覆土厚度的分析方法和判断标准。

过江越海软土隧道往往采用泥水平衡盾构进行施工。小覆土区间由于覆土浅，泥水压力和切削面稳定很难控制，稍有不慎，易引发掘进面泥水喷发。因此，单从工程技术角度也迫切需要研究不同覆土厚度下盾构掘进安全性能，提出隧道合理覆土厚度的计算模型。本研从盾构掘进安全和隧道抗浮安全的角度研究盾构隧道合理覆土厚度问题，并得出了以下结论：.（1）在越江海泥水盾构隧道的纵断面设计中考虑盾构掘进安全和隧道抗浮稳定是必要的。考虑泥水压力可设定的盾构掘进安全是泥水盾构施工的重要影响因素，在隧道覆土厚度设定中要考虑该因素的影响。.（2）泥水劈裂压力与泥水粘度、开孔直径等关系不大，而与土体的应力状态、自身强度有关；在劈裂伸展过程中，劈裂压力分量只与土体强度性能有关，如侧压力系数、摩擦角、粘聚力和容重；劈裂发生后出现的泥水压力降低现象将有利于阻止泥水劈裂进一步伸展。.（3）研制了掘进面稳定试验装置。试验装置运用相似原理同时展示了掘进面前方滑裂面纵剖面和横剖面形状，对描绘滑裂面三维形状起到很好的引导作用。采用升降机对挡板微型位移（精度可达0.01mm）控制，可以得到掘进面土压力随挡板位移的连续变化趋势，弥补了以往试验位移跳跃的不足。.（4）在假定滑裂面纵剖面为对数螺线，滑裂体为对数螺线绕z轴旋转而成的条件下，严格按照摩擦性材料的位移相容和一般滑裂角给出了三维最小支护力的解析解，并给出了其使用条件。.（5）隧道抗浮稳定需要克服不同工况下浆液浮力、水浮力和河床冲刷的影响。工程案例表明：基于极限平衡法的隧道抗浮稳定最小覆土计算公式可以应用于实际工程的最小覆土厚度估算，为隧道纵断面设计提供参考。