基于声波与声发射试验的盐岩蠕变损伤表征方法研究

It is the important part of cavern stability analysis to evaluate the damage of surrounding rock for salt cavern gas storage. This project focuses on an important scientific problem closely to study, which is called the generation and evolution mechanisms of creep damage in salt rock. In order to monitor the process of rock creep damage, this project mainly studies at salt rock creep testing technique and develops an integrated synchronous testing platform including creep mechanics testing system, acoustic wave testing system and acoustic emission testing system. By using this platform, the characteristics of salt rock deformation, acoustic wave and acoustic emission activity in the creep testing are studied under different confining pressure and axial stress. Not only the law between ultrasonic wave velocity and macro-mechanical properties, but also the law between AE events and microscopic defects evolution are obtained, which are helpful to reveal the creep damage mechanism of salt rock combined with moment tensor analysis. According to acoustic emission characteristics of energy release rate, and analyzing coupling relationships among creep damage, acoustic wave and acoustic emission activity quantitatively, the occurrence condition and damage variable of salt rock can be determined. Based on the irreversible thermodynamics and internal variable theory, the mathematical model of creep damage for salt rock would be established. According to the field monitoring data of demonstration project of salt cavern gas storage in Jin Tan, the initial model is tested and modified, and the damage characterizing method and accelerating creep criterion of salt rock can be obtained. Research results will provide important reference value for guiding the design and operating safely of salt cavern gas storage groups.

盐穴地下能源储备库围岩损伤评价是储库稳定性评价中十分重要的研究内容。本项目紧紧围绕盐岩蠕变损伤孕育及演化机理这一关键科学问题开展研究工作。主要研究盐岩蠕变损伤测试关键技术，开发盐岩蠕变力学、超声波波速、声发射活动一体化同步测试平台。利用该平台，开展不同围压、不同偏应力状态下的盐岩蠕变特征与声波、声发射活动规律研究，建立超声波波速与宏观力学性能、声发射活动与细观缺陷演化的特征关系。结合声发射震源定位与矩张量反演分析，揭示盐岩蠕变损伤机理。量化盐岩蠕变损伤与声波、声发射参数耦合关系，依据声发射能量释放率特征，判别盐岩损伤发生条件，确定盐岩蠕变损伤变量。基于不可逆热力学和内变量理论，建立盐岩蠕变损伤演化数学模型。结合金坛储气库示范工程的现场监测数据，对所建立的模型进行检验与修正，提出盐岩蠕变损伤的表征方法及加速蠕变的相关判据。研究成果对指导大型盐穴储气库群的设计与长期安全运行具有重要的参考价值。

利用地下深部盐穴腔体进行能源储备已经得到了各国政府的广泛认可，中国盐穴能源储备库正处于大规模的修建过程中。盐穴腔体的蠕变损伤直接影响工程运营安全，建立适用于我国盐矿的盐岩蠕变损伤理论与技术系统具有重要意义。项目针对盐岩蠕变力学—超声波—声发射活动一体化同步测试技术、岩石蠕变与声波—声发射特征试验、盐岩蠕变损伤模型等方面开展科学研究，分析盐岩超声波波速与宏观力学性能、声发射活动与细观缺陷演化的特征关系，分析盐岩横波波速、纵波波速、声发射事件率、声发射能量率、裂隙密度等参数与岩体蠕变损伤的内在联系，寻找岩体损伤的内在表征指标，最终确定盐岩的蠕变损伤演化模型。通过与中国科学院武汉岩土力学研究所联合技术攻关，项目组研发了一套具有自有知识产权的岩石三轴声波—声发射一体化同步测试装置（V2.0），设计了一种岩石力学试验机底座、一种用于高温岩石力学试验的加热装置，相关产品已取得国家发明专利授权，并实现了产业化。研究发现，三轴蠕变状态下的盐岩损伤劣化过程与超声波、声发射活动具有映射关系。利用监测得到盐岩轴向与环向应变规变形信息，发现初始蠕变阶段中盐岩的应变速率逐渐由大变小，稳态蠕变阶段中的盐岩应变速率保持稳定。分析盐岩力学性能与岩石横波波速VP、纵波波速VS特征，可以看出初始蠕变和稳态蠕变过程中，盐岩的超声波波速变化不显著，VP、VS指标不适宜表征盐岩的蠕变损伤程度。总结了AE参数（RA值、AF值）、声发射事件数量与震源位置的响应规律，在每一级应力（升高）加载初期，盐岩的声发射活动表现剧烈，当岩石进入稳态蠕变阶段中，声发射活动进入“平静期”。对比盐岩AE震源定位与岩体破损状态发现，盐岩破裂点主要发生在盐岩中间部分，呈现“鼓”形破坏，声发射事件定位图能够清晰地表达出盐岩的损伤区域分布及严重程度。研究结论对揭示盐岩蠕变损伤机理，保障储气库设计与安全运行具有重要指导意义。