“管幕-冻土”复合结构隧道预支护的力学机理

Freeze-sealing Pipe Roof Method employed in the construction of Gongbei tunnel in Hong Kong-Zhuhai-Macau Bridge Project is national initiative. The "Pipe roof - frozen soil" composite structure is innovative in structure as pre-support system in tunnel construction by mining method. Research on the mechanical mechanism of this composite structure is necessary before the construction. The strength, deformation and failure modes of the "Pipe roof - frozen soil" composite structure is extremely complex because there are significant stiffness difference between solid steel pipe and hollow steel pipe and high-gradient anisotropy in frozen soil between pipes. The temperature field distribution of the Freeze-sealing Pipe Roof Method is obtained by numerical simulation considering phase change; the mechanical numerical model of anisotropic frozen soil is obtained by theoretical analysis; the nonlinear elasto-perfectly plastic model for contact surface of composite structure is developed through shear tests at the contact surface; deformation and failure modes of the composite structure are studied through laboratory model tests; possible failure modes of the composite structure under different conditions are analysed based on numerical simulation for anisotropic frozen soil. The subject is expected to light on the basic mechanical mechanisms of the "Pipe roof - frozen soil" composite structure and develop corresponding numerical models and calculating methods, providing scientific basis for design and construction of the Freeze-sealing Pipe Roof Method in the future.

港珠澳大桥连接线拱北隧道施工所采用的管幕冻结法为国内首创，作为隧道矿山法施工的预支护体系的"管幕-冻土"复合结构，形式新颖、构造特殊。在项目建设之际，迫切需要对其力学机理开展研究。"管幕-冻土"复合结构具有实心钢管与空心钢管的显著刚度差异性和管间冻土帷幕的高梯度非均质性，其强度、变形和破坏的力学机理极为复杂。课题借助非稳态共轭传热计算理论，通过数值模拟求解伴有相变的管幕冻结温度场分布规律，并通过理论分析得到非均质冻土帷幕数值计算模型；借助"钢管-冻土"接触面剪切试验，建立"管幕-冻土"复合结构接触面的非线性弹性-理想塑性模型；再借助"管幕-冻土"复合结构室内模型试验，研究其变形和破坏规律，并进行基于非均质冻土帷幕的数值模拟，分析不同条件下复合结构可能出现的破坏模式。研究期待探明"管幕-冻土"复合结构的基本力学机理，建立相应的力学模型和计算方法，为今后管幕冻结法的设计与施工提供科学依据。

港珠澳大桥连接线拱北隧道施工所采用的管幕冻结法为国内首创，作为隧道矿山法施工的预支护体系的"管幕-冻土"复合结构，形式新颖、构造特殊。本项目主要完成了三方面的工作，一是结合提出的“冻起来、抗弱化、控冻胀”理念，通过原型试验研究验证管幕冻结法的可行性与可操作性。二是基于保角变换将单圈冻结管不等距模型转化为特殊的单排冻结管模型，结合Laplace方程边界可分离特性，推导了该特殊排管的温度场解析解，进而求出单圈冻结管不等距布置的温度场解析解，考虑到现场实际布管中圆形冻结管和异形冻结管存在一定的径向错位距离，在单圈冻结管不等距基础模型上进行改进，推导了考虑错位的双圈冻结管温度场解析解。三是通过复合结构试验探明"管幕-冻土"复合结构的基本力学机理，建立相应的力学模型和计算方法，为今后管幕冻结法的设计与施工提供科学依据。