黄土塬区隧底黄土干湿循环条件下二次衬砌力学性状演化机理

The tunnel bottom loess is always in the state of dry-wet circulation in loess tableland. The process of dry-wet cyclic deterioration of loess is more complex than immersion softening. The degree of the deterioration is more serious, and its influence on the stress and deformation of secondary lining is more significant. The evolution of mechanical properties of secondary lining is closely related to the occurrence of lining diseases. The dry-wet cyclic deterioration law and model of Q2 undisturbed loess, and the evolution mechanism of mechanical properties of secondary lining under the dry-wet cycle of tunnel bottom loess are researched in this study. Firstly, the deterioration law of shear strength index and elastic modulus of Q2 undisturbed loess is revealed by dry-wet cyclic triaxial compression test and the deterioration degree function is constructed, and then the corresponding deterioration model is established by combining the dry-wet cyclic parameters. Secondly, the dry-wet cyclic deterioration model is secondary developed by finite element method and the numerical simulation of dry-wet cycling of tunnel bottom loess is carried out. Combined with the centrifugal model test results, the stress and deformation of surrounding rock of loess and lining structure under different dry-wet cyclic conditions are analyzed. Finally, the evolution law of surrounding rock pressure under the dry-wet cycling of tunnel bottom loess is revealed, and the evolution mechanism of mechanical properties of secondary lining is expounded from the dry-wet cyclic deterioration of tunnel bottom loess. The outcome of this research will contribute to explain the causes of the secondary lining diseases in loess tableland, and provide theoretical support for the maintenance and reinforcement of the secondary lining.

黄土塬区隧底黄土常态化处于干湿循环状态，黄土干湿循环劣化过程较浸水软化更为复杂，劣化程度更为严重，对隧道二次衬砌受力变形的影响也更为显著，二次衬砌力学性状的演化与衬砌病害的产生密切相关。本项目拟进行Q2原状黄土干湿循环劣化规律和模型，以及隧底黄土干湿循环条件下二次衬砌力学性状的演化机理研究，首先，通过干湿循环三轴压缩试验，揭示Q2原状黄土抗剪强度指标和弹性模量的劣化规律，构建劣化度函数，结合干湿循环参数建立相应的劣化模型；其次，对劣化模型进行有限元二次开发，并开展隧底黄土干湿循环数值模拟，结合离心模型试验结果，分析不同干湿循环条件下黄土围岩和衬砌结构的受力变形情况；最后，揭示隧底黄土干湿循环条件下隧道围岩压力的演化规律，并从隧底黄土干湿循环劣化出发，阐明二次衬砌力学性状的演化机理。该项目的研究有助于分析塬区黄土隧道二次衬砌的病害成因，为二次衬砌的维修加固提供理论支撑。

黄土干湿循环劣化过程较浸水软化更为复杂，劣化程度更为严重，对隧道二次衬砌受力变形的影响也更为显著，二次衬砌力学性状的演化与衬砌病害的产生密切相关。本项目拟进行Q2原状黄土干湿循环劣化规律和模型，以及隧周黄土干湿循环条件下二次衬砌力学性状的演化机理研究，首先，通过干湿循环三轴压缩试验，揭示Q2原状黄土抗剪强度指标和弹性模量的劣化规律，构建劣化度函数，结合干湿循环参数建立相应的劣化模型；其次，在微观层面和宏微观关系方面利用饱和渗透系数测试、核磁共振测试、扫描电镜试验和X射线衍射试验对原状黄土的干湿劣化效应进一步解释劣化机理；最后，揭示隧周黄土干湿循环条件下隧道围岩压力的演化规律，并从黄土干湿循环劣化出发，阐明二次衬砌力学性状的演化机理。该项目的研究有助于分析黄土隧道二次衬砌的病害成因，为二次衬砌的维修加固提供理论支撑。