多年冻土区块石路基结构层劣化机理及其热力过程的研究

Porous crushed-rock layers have been widely used in cooling embankments in permafrost regions. However, this rock pile can be damaged and deformed by load, freezing-thawing, wetting-drying, radiation and other environmental factors, altering the porosity of the layer and subsequently the convective heat transfer process inside the layer. Since the convective cooling is crucial to the long-term thermal stability of crushed-rock embankment, it is imperative to systematically study the deterioration mechanism of crushed-rock layer and to reveal how the deterioration influences the thermo-mechanical stability of crushed-rock embankments. In this project, we conduct laboratory study to ascertain the damage mechanism of commonly-used crushed rock on the Qinghai-Tibet Plateau. We then numerically analyze the effects of environmental factors, rock types and weathered degree on damage features of the layers to sieve the controlling factors that lead to the deterioration of the crushed rock. We sequently conduct model experiments and field tests to observe the crushed-rock-layer deterioration process and its effect on heat transfer and deformation of embankment. Finally, based on the thermo-mechanical interaction in the foundation soil, the influence of the structural deterioration on the deformation process is evaluated. The results will improve the stability theory of the crushed-rock embankments, and supply scientific proofs for the design and long-term stability evaluation of crushed-rock embankments in permafrost regions.

块石层作为多孔介质层得以在冻土区冷却路基中广泛采用，但是，荷载、冻融、干湿交替及强辐射风化等环境因素综合作用将引起块石结构层内颗粒损伤碎化和结构层变形，尤其影响到对于对流换热起决定性的块石层孔隙度，进而影响块石层的降温效能和路基的整体变形。目前，如何评价块石路基换热强度及预测路基长期稳定性，都需要深入开展有关块石结构层劣化机理及其对路基热力稳定性影响的研究。本项目拟通过室内试验，研究青藏高原常用块石料损伤机理，基于数值仿真试验明确各种环境因素、岩石类型和等级对损伤的影响，阐明主导影响因素；再结合室内模型试验和野外监测，揭示块石结构层劣化冻土块石路基传热性能和变形的影响，探明结构层劣化对路基变形发育的贡献，完善多年冻土区块石路基工程稳定性理论。研究成果可为多年冻土区块石路基的设计和长期稳定性评估提供科学依据。

块石层作为多孔介质层得以在冻土区冷却路基中广泛采用，但是，荷载、冻融、干湿交替等环境因素综合作用将引起块石结构层内颗粒损伤碎化和结构层变形，尤其影响到对于对流换热起决定性的块石层孔隙度，进而影响块石层的降温效能和路基的整体变形。目前，如何评价块石路基换热强度及预测路基长期稳定性，都需要深入开展有关块石结构层劣化机理及其对路基热力稳定性影响的研究。本项目以青藏高原首条高等级公路（共和至玉树高速公路）块石路基为调研对象，对青藏高原常用块石料的耐久性进行了评价。并选取3类代表性块石，对其矿物成分等进行了室内测试。针对具体块石，综合扫描电镜、低场核磁、CT扫描、超声以及单轴压缩等细-微-宏观多尺度测试技术，揭示了块石劣化特征，查明了岩石内可溶性矿物成分和岩石初始致密性是决定岩石劣化程度的主要因素。基于室内测试和理论推导，建立了考虑劣化效应的岩石本构关系，并利用试验结果对模型进行了验证；考虑块石结构层表面块石劣化后填堵块石层表面孔隙，项目还针对不同厚度块石层，开展了边界开放和堵塞条件下块石层的降温特征模型试验，评估了不同厚度、不同边界下块石层的降温性能。最后，在青藏高原多年冻土区建立了3个块石路基现场监测场地，通过长期监测，进一步揭示了冻土块石路基传热性能和变形随时间的变化特征，探明结构层劣化对路基变形发育的贡献，完善了多年冻土区块石路基工程稳定性理论。研究成果可为多年冻土区块石路基的设计和长期稳定性评估提供科学依据。