深部冻融土-混凝土结构相互作用接触界面力学特性研究

Numbers of shaft lining fracture damage were occurred during or after the melting stage of frozen wall by using freezing method in deep alluvium and it was recognized as a major challenge for the coal industry and geotechnical engineers in China. Mechanism of deep frozen-thawed soil-concrete structure interaction is one of the most important elements which affect the safety and sustainability of a shaft lining. Such frozen-thawed soil-structure interfaces not only exist between shaft linings and their surrounding frozen soils in freezing sinking, but also in the urban underground freezing engineering and construction in cold regions. However, most of the current studies only focused on mechanical behaviors of unfrozen soil-structure interaction under a normal stress level, the characteristics of the frzoen-thawed soil-concrete interface, as well as characteristic variation of thawed soil in deep alluvium are still poorly understood and few researchers pay attention to this issue. For this reason, in this application, we will take the physical and mechanical characteristics of frozen-thawed soil-concrete interface layer under high stress condition as the key scientific issue for clarifying the mechanism of vertical additional stress-induced shaft lining fracture associated with frozen wall thawing. Based on comprehensive research approches including direct shear tests, physical model tests, numerical simulation and theoretical analysis, the primary goals of this study are (1) to clarify the basic and mechanical characteristics of frozen-thawed soil-concrete interface under high normal stresses with circumstances of various soils, different interface roughness, stress state, stress paths and thawing temperatures; (2) to investigate the microstructure and characteristics variation of thawed soil; (3) to explore the mechanism of frozen-thawed soil and shaft lining structure interaction during the frozen wall melting. On the basis of above mentioned, we will then propose a frozen-thaw constitutive model of the interface for analyzing the stability of shaft lining in deep alluvium. The results from this study will provide scientific basis for applying artificial freezing method in consturction of deep shaft as well as other urban underground engineering.

本项目以深厚表土层中新建深立井井壁安全与稳定问题为背景，针对深部冻融土-井壁结构相互作用接触界面变形机理与物理力学特征，计划采用实验室高压冻融土-混凝土结构面剪切试验、井壁-解冻冻结壁相互作用物理模拟试验、数值试验和理论分析相结合的研究手段，考虑土层性质、应力状态、结构接触面特征、冻融作用等多种影响因素，围绕深厚表土冻结壁解冻过程关联的冻融土-混凝土结构接触界面层物理力学特性、冻融后土体微观结构与性状变化、井壁 “融沉附加力”演化规律等方面开展深入研究，揭示深部冻融土-井壁结构相互作用的内在物理机制，建立适用于深部冻融土-混凝土结构接触界面本构关系模型，为我国应用冻结法进行深立井以及其它城市地下工程建设提供科学依据。

项目紧紧围绕深厚表土解冻冻结壁-井壁“双壁”相互作用问题，针对高压冻融土-混凝土结构接触界面层性状、高压冻融土-结构接触面剪切力学特性、深厚表土解冻冻结壁-井壁相互作用机制等开展了系统的研究工作。研制了高压冻融土-结构接触面单调和循环剪切试验系统，建立了高压冻融土-结构接触面剪切试验的标准化流程和方法，创新了考虑原位现浇混凝土外表面随机起伏特征的结构面建模和制作方法，实现了深厚表土立井井筒冻结法凿井施工的全过程模拟，获得了深厚表土冻结壁、井壁的受力变形规律及其与应力状态、冻融过程、土层性质等影响因素的相关关系，掌握了深部高压下冻融粉质黏土、砂砾石土-混凝土规则及随机起伏结构接触界面的剪切变形破坏特性和演化规律，基于PFC等数值手段揭示了冻融土-结构接触界面细观结构演变与宏观剪切变形行为的内在关联，在室内单元试验和模拟试验基础上，建立了冻融土-随机起伏结构接触面剪切负乘幂本构模型，引入Weibull随机分布变量和损伤因子，建立了冻融土-结构接触面循环剪切统计损伤本构模型，以上研究成果对更深入分析和解决深厚表土层中深立井井壁安全稳定问题提供科学依据。