黏土心墙弱面水力劈裂演化机理与判别准则

Hydraulic fracturing will cause the damage of clay core in earth-rock fill dam which will result in disastrous consequences. Because of the complexity of the problems of hydraulic fracturing, the hydraulic fracturing evolution process and mechanism is still not distinct, till now there are no relevant experiments reports about completely simulating hydraulic fracturing process. On the basis of previous research results, this project plans to introduce the CT scanning technology, which can analyze the formation and development of crack by using three axes hydraulic fracturing test visually and quantitatively; reveals the hydraulic fracturing crack evolution mechanism with potential weak links from the microscopic aspect; carries out the big scale hydraulic fracturing model tests to obtain the stress distribution and change law of soil around the crack, assisted by the analysis and explanation of mechanics theory, which evalue further the mechanism of hydraulic fracturing from the macro and micro aspect; quantitatively analyzes the physics and mechnics influence factors during the whole process of hydraulic fracturing such as saturation, density of core, consolidation ratio, confining pressure, slot width, slot length, slot depth, hydraulic loading ratio and so on; combined with multi-scale and visualization of test results and theoretical analysis such as expansion theory and fracture failure model, establishes criterion of hydraulic fracturing of clay core in earth-rock fill dam with the potential weak links, and provides mathematical description of mechanical behavior for the material after hydraulic fracturing; provides the analysis method of solving the hydraulic fracturing problem of clay core in earth-rock fill dam. The research results have important theoretical significance and great value of engineering application.

水力劈裂会导致大坝黏土心墙的破坏从而造成灾难性后果。由于该问题的复杂性，其演化过程和作用机理也不明确，至今还未见完全模拟出水力劈裂全过程的相关试验报道。本项目在总结前人研究成果的基础上，引入CT扫描技术，对三轴水力劈裂试验实现裂缝形态及发展的可视化，对裂缝发展程度进行定量描述，从细观上揭示心墙弱面水力劈裂的演化机理；进行大尺寸物理模型试验，获得裂缝周边土体的应力分布及变化规律，辅以力学理论分析诠释，从宏观、微观上进一步论证水力劈裂的演化机理；建立水力劈裂发生发展全过程的劈裂压力与心墙料饱和度、密实度、固结比、围压、缝长、缝宽、缝深、水压加荷速率等物理、力学影响因素的量化关系；综合多尺度、可视化的试验成果，与扩孔理论、断裂模型等理论研究，建立黏土心墙弱面水力劈裂判别准则，并提出劈裂后材料力学行为的数学描述，为土石坝心墙水力劈裂问题提供分析方法。研究成果具有重要的理论意义和广阔的工程应用价值。

水力劈裂是土石坝工程中最为关注，也是土质心墙坝中热点研究问题之一，水力劈裂会导致大坝防渗体的破坏从而造成灾难性的后果。本项目采用理论分析、可视化单元试验、数值模拟、模型试验等方法，对心墙水力劈裂问题进行了宏观与细观机理研究，主要工作内容如下：.（1）引入CT试验技术，对三轴水力劈裂裂缝形态实现可视化及量化描述，从细观上进一步论证水力劈裂的发生机理。.（2）水力劈裂归根结底还是变形问题，由于土的压缩变形引起初始裂缝在二维空间呈椭圆形，从而对裂缝尖端产生楔劈效应。.（3）基于三轴抗拉强度与Jawoski经验公式，可建立较可靠的水力劈裂发生的上限条件。.（4）结合物理模型试验成果、理论分析等对水力劈裂的量化关系进行验证与修正。定义裂缝张开度与等效裂缝长度之比为水力劈裂的判别因子，比较该因子与临界值之间的关系，可对水力劈裂是否发生进行过程判断。