柱状节理玄武岩卸荷劣化的钻孔波速变异机制与时效松弛力学模型研究

Columnar joints are native rupture structures which are ordered columnar forms in basaltic lava. The cracks and joints inside them are well-developed which lead to the weak self-supporting ability after excavation. Moreover, the characters of anisotropy and time-dependent relaxation are remarkable. In the Baihetan hydropower station under construction, the large tunnel diameter and high in-situ stress with concentration of columnar joints exist in the diversion tunnel and underground powerhouse. Therefore, the unloading relaxation of surrounding rocks exerts great impact on the stability of underground tunnels. Aiming at the evaluation methods and time-dependent relaxation of columnar joints rock mass based on the borehole sound wave methods, this project proposed an evaluation method of unloading relaxation with the borehole sound wave and the evolution law of the fissures to reveal variability character and mechanism and laws of the borehole wave velocity in strongly unloading basalt according to the laboratory physical model test, synchronization testing technique of acoustic emission and creep tests with true triaxial apparatus as well as field test. Then, this project construct a typical time-dependent degradation element based on the principle of Boltzmann superposition and minimum strength. Finally, this theoretical method and mechanical model is applied and proved in the Bai-he Tan hydro-power station. The solution to this problem is of great significance for both theory and practice to evaluate and analysis unloading relaxation mechanism after excavation in columnar basalt.

柱状节理是火山熔岩中呈规则柱状形态的原生破裂构造，其内部节理裂隙异常发育，自稳能力差，各向异性和时效松弛特征显著。在建的白鹤滩水电站地下洞室洞径大、地应力较高，柱状节理玄武岩集中发育，围岩卸荷松弛效应对洞室稳定性影响十分突出。项目针对基于钻孔声波的柱状节理岩体卸荷过程松弛效应评价方法及其时效松弛力学特性，通过室内模型试验、同步声发射测试、真三轴蠕变试验和现场试验，揭示不同钻孔孔径、方向和应力水平下强卸荷玄武岩钻孔波速的变异特征、规律和机制，建立基于钻孔声波和裂隙演化的岩体卸荷松弛评价方法，构建基于Boltzmann 叠加原理和最小强度原则的柱状节理围岩时效劣化典型单元体，提出柱状节理玄武岩的时效松弛劣化力学本构模型，结合白鹤滩水电站地下工程，对提出的理论方法和力学模型进行应用和验证。研究成果对于柱状节理岩体开挖工程的围岩卸荷松弛机制、评价及时效松弛分析具有重要的理论意义和工程应用价值。

本项目执行过程中，严格按照既定的任务要求，系统开展了室内真三轴试验和柱状节理特性现场原位试验，揭示了不同钻孔孔径、方向和应力水平条件下柱状节理玄武岩卸荷劣化的钻孔波速变异机制，建立了基于钻孔声波和岩体裂隙演化的柱状节理玄武岩松弛界限的判据及卸荷松弛评价方法，提出了考虑多节理及其粗糙度、各向异性、时效损伤的柱状节理岩体本构模型，结合白鹤滩水电站地下工程，对项目提出的松弛评价方法和力学模型进行了应用和验证，为柱状节理岩体力学特性和地下工程稳定性评价提供了理论支撑。研究成果产出方面，在国内外核心期刊和国际会议发表论文16篇，其中SCI论文5篇，EI论文9篇，申请发明专利5项，授权2项，研究成果参与申报获得省部级自然科学一等奖1项（排名5），项目申请人还获得包括国家百千万人才工程、中国青年科技奖等荣誉5项，此外还培养博士生3名，硕士生4名。圆满完成了项目预期的各项研究任务和目标。