多年冻土隧道洞口段融化圈回冻冻胀机理及冻胀预报研究

Many freezing patterns and water resources are the characteristics of the surrounding rock near the permafrost tunnel portal. Its frost heaving mechanism is more complex than the other parts. There are many serious frost damages near permafrost tunnel portal. It shows that frost heaving mechanism of surrounding rock near the portal is not completely clear. One of the main contents is the conditions of emerging segregated ice when the water supplied to surrounding rock and different freezing patterns act on surrounding rock. The frost heaving prediction model based on segregated ice is the other main content. The conditions of emerging segregated ice in the complex water and thermal environment are studied by the numerical simulation, physical model experiment and theoretical analysis. And its formation mechanism is revealed. Furthermore, THM coupled numerical model based on segregated ice is established according to the conditions. On this basis, the refreezing processes of thaw circle near the permafrost tunnel portal are reappeared, the frost heave prediction model is established and the accuracy of the frost heave prediction is improved. The research results can contribute to understand the frost heaving mechanism of surrounding rock in the complex water and thermal environment, and provide theoretical and technical support for the prevention and cure of permafrost tunnel in China.

多年冻土隧道洞口段具有丰富水源、多回冻模式的特点，洞口段围岩冻胀机理比洞身段更加复杂。大量多年冻土隧道洞口段冻害严重，由此表明洞口段围岩冻胀机理还不完全清楚。本项目以不同补水条件、多向冻结模式的分凝冰形成条件和基于分凝冰的隧道冻胀预报模型为核心，通过数值模拟、物理模型实验和理论分析，系统研究复杂水、热环境下分凝冰的形成条件，揭示其形成机制；其次，结合形成条件，构建基于分凝冰的水、热、力（THM）三场耦合数值模型。在此基础之上，再现多年冻土隧道洞口段融化圈回冻过程，揭示多年冻土隧道洞口段融化圈回冻冻胀机理，建立冻胀预报模型，提高冻胀力预报的准确性。研究成果有助于理解复杂水、热环境中隧道围岩的冻胀机理，为我国多年冻土隧道冻害防治提供理论和技术支持。

多年冻土隧道洞口段具有丰富水源、多回冻模式的特点，洞口段围岩冻胀机理比洞身段更加复杂。大量多年冻土隧道洞口段冻害严重，由此表明洞口段围岩冻胀机理还不完全清楚。通过现场调查、资料收集、模型试验、理论分析和数值模拟等手段，完成了多向冻结模式下分凝冰的形成机制和基于分凝冰的隧道冻胀预报模型等研究内容，主要获得了以下重要结果。(1) 获得了分凝冰的形成条件，厘清了分凝冰的重要影响因素。导水率、降温速率、年平均温度、年较差对分凝冰的厚度、下限影响巨大；外荷载对分凝冰的形成、厚度影响较小。(2) 建立了基于分凝冰的冻胀模型。基于隧道围岩冻融圈边界存在分凝冰的结果，将隧道结构附近围岩分为二衬、冻融区和冻结区，建立了三区冻胀弹性力学模型，运用弹性力学理论，假定分凝冰形成的厚度 作为冻融区和冻结区的共同变形，将总变形 按照 、 的大小按比例分担（弹性模量大着变形小，弹性模量小者变形大）在此基础上推导了考虑分凝冰的冻胀力计算公式。(3) 获得了不同分凝冰厚度对冻胀力大小的影响规律。分凝冰的存在使衬砌的受力大于无分凝冰情况，衬砌受力随分凝冰的厚度增加而增加；当分凝冰厚度为10cm时，衬砌受力大小为无分凝冰的12倍；即或分凝冰仅有1cm，衬砌受力都为无分凝冰的2.1倍。因此，在具备分凝冰形成条件的洞口浅埋段，尤其是地下水丰富的地方，应该重视层状分凝冰的影响。研究成果有助于理解多年冻土隧道洞口段冻害产生的根源，深层次揭示多年冻土隧道洞口段融化圈回冻冻胀机理，同时提升多年冻土隧道洞口段冻胀预报模型的完备性，对完善多年冻土隧道设计理论具有重要的科学意义。