THM耦合过程中裂隙岩体冻融劣化机理研究

Freeze-thaw deterioration of rock mass is a key issue that needs to be addressed urgently in the areas of geological disaster prevention and prejudicial to the safety and stability of rock engineering in cold regions. Freeze-thaw deterioration is the result of rupture evolvement in fractured rock mass caused by frost heaving pressure, which is produced by water/ice transition in the coupled thermo-hydro-mechanical process. Combining with the research methods of laboratory tests, theoretical analysis and numerical simulation, this project intends to conduct research on the key scientific problem “Rupture evolvement mechanism of fractured rock mass under freeze-thaw in the coupled thermo-hydro-mechanical process”. Considering the variation of critical coupling parameters under low temperature, the mechanism of water migration in crack will be studied in order to present a coupled thermo-hydro-mechanical model on the condition of water/ice transition. By experimental study on the evolution law of frost heaving pressure and fractured characteristics under freeze-thaw for crack, a calculation equation of this pressure and related crack propagation criterion under freeze-thaw will be built. Then, the evolution mechanism of frost heaving pressure and the rupture mechanism of fractured rock mass under freeze-thaw will be revealed. Based on XFEM, a kind of iterative algorithm for frost heaving pressure and program for crack propagation criterion under freeze-thaw will be developed so as to put forward a simulation method of rupture evolvement process in the coupled thermo-hydro-mechanical process under freeze-thaw eventually. The research results will provide significant theoretical foundation and reference basis for preventing frost damage and conducting stability analysis under freeze-thaw in cold regions.

岩体冻融劣化是寒区地质灾害防治中面临的关键问题，严重威胁寒区岩体工程的安全与稳定。岩体冻融劣化主要是在热-水-力（THM）耦合过程中水冰相变产生的裂隙冻胀力引起岩体破裂演化的结果。项目采用室内试验、理论分析和数值模拟相结合的研究方法，围绕关键科学问题“THM耦合过程中裂隙岩体冻融破裂演化机理”开展研究。考虑关键耦合参数的低温变异性，研究裂隙水冻融迁移机制，建立水冰相变条件下裂隙岩体THM耦合模型；开展裂隙冻胀力测试与裂隙岩体冻融力学试验，研究裂隙冻胀力萌生演化规律和裂隙冻融断裂特征，构建裂隙冻胀力计算模型和裂隙冻融扩展准则，揭示THM耦合过程中裂隙冻胀力的萌生演化机制和裂隙岩体冻融破裂机理；基于扩展有限元方法，开发裂隙冻胀力迭代算法和冻融扩展准则实现程序，提出THM耦合过程中的裂隙岩体冻融破裂演化过程模拟分析方法。研究成果可为寒区冻害防治和冻融稳定性评价提供理论基础与参考依据。

本项目采用了室内试验、理论分析和数值模拟相结合的研究方法，围绕关键科学问题“THM耦合过程中裂隙岩体冻融破裂演化机理”开展了系统研究。首先对岩石孔隙中的未冻水含量进行了研究，基于双孔隙结构分布模型，推导了未冻水含量方程，进而考虑未冻水含量变化提出了关键耦合参数（热传导系数、冻胀力、渗透系数等）的低温表达式；同时考虑孔、裂隙水冻结特征，基于水冰相变理论和多场耦合理论，构建了裂隙岩体低温多场耦合模型，该模型可以较好的应用于裂隙介质冻结过程中的渗流-传热过程计算分析；开展了裂隙冻胀力测试及冻融后的岩体力学强度试验，特别是得到了冻结方式、裂隙形态以及裂隙水迁移对裂隙冻胀力的影响，全面揭示了裂隙冻胀力的萌生演化过程及冻胀裂纹对岩体强度的影响机制，结合裂隙扫描和图像分析，提出了裂隙冻融断裂特征；最后，基于试验研究成果，构建了裂隙冻胀力计算模型及冻融破裂判据，初步实现了裂隙冻融破裂过程模拟。本项目通过上述研究揭示了THM耦合过程中的裂隙岩体冻融破裂演化机理。