高放废物处置库多尺度结构面级联耦合及渗流特征研究

Discontinuities with different scales generally possess certain relationships in terms of genesis and hydraulic properties. These relationships could somewhat influence the regional flow field of groundwater and the migration rule of solute, and further have impact on critical issues involving the radioactive nuclide migration in the surrounding rock mass of a high-level radioactive waste repository. This study primarily aims at improving the intrinsic deficiencies in reconstructing the objective structure of the fracture system and in reproducing discontinuities with deterministic features of the stochastic network model. Based on the data of multi-scale discontinuities via digitalization investigation in Beishan candidate site for the Chinese high-level radioactive waste repository, this study first focuses on developing a method to analyze the internal patterns of multi-scale hierarchical discontinuities on the basis of structural geology. Attempt is made to introduce user-defined module into pure stochastic simulations in order to represent typical internal interconnections in a programmed manner. The user-defined module is then implemented in a program used for updating the information of multi-scale discontinuities as well as for "deterministic-stochastic" coupling realization. This program is applied to investigate generation of the conditioned model which incorporates internal structures. Groundwater flow simulations are conducted based on the conditioned model. Characteristics of hydraulic properties of multi-scale hierarchical discontinuities are studied in detail. Prediction of regional groundwater flow field for Beishan candidate site is obtained using conditioned model. This study will provide sound basis for the evaluation of nuclide migration in terms of practical and innovative methodology as well as of effective techniques.

岩体中不同尺度地质结构面往往具有一定成生关系和水力联系，此联系一定程度上影响区域地下水流动及溶质运移，进而影响硬岩处置库高放废物迁移、扩散等关键问题评估。本研究针对随机网络模型在结构面系统内在联系及确定性特征表达方面的不足，基于我国高放废物处置库甘肃北山预选区多尺度结构面数字化调查数据，从构造地质角度入手研究多尺度结构面内在关联模式解析方法；尝试在随机模拟基础上引入自定义模块，探索典型内在联系模块化表征途径；编制自定义模块耦合算法及多尺度结构面确定性信息修正程序，研究具备内在联系客观表达功能的“确定-随机”耦合模型构建方法。在此基础上开展渗流模拟，考察多尺度结构面系统水力联系，获取北山预选区地下水流动性预测结果，力求为我国高放废物处置库废物迁移评估提供切实可行的创新方法和行之有效的技术手段。

区域地下水流动预测在高放废物处置库场址评价中占据极为重要地位，不同尺度结构面间水力连通程度影响地下水流动规律，进而影响场址评价中核素迁移、扩散的测评精度。针对研究区典型断裂构造，运用地质学原理及实验观测方法识别大尺度结构面导水规律，并与中尺度结构面、小尺度节理裂隙结合构建多尺度结构面级联耦合体系，是数值模型逼近客观实际的有效途径，也是本项目的主要研究内容和关键落脚处。.以我国北山预选区芨芨槽岩块大、中、小尺度结构面为研究对象，运用高精度测量仪器捕捉大样本数据，经数值统计与构造分析提取特征参数、辨别内在关联，构建结构面体系概念模型；进一步借助数值方法解析区域渗流场、追踪渗流路径，定量考察结构面系统渗流规律及其水力联系。主要取得以下成果：.（1）多尺度结构面调查统计结果表明：研究区结构面体系存在“Parent-daughter”和“Step-structure”两类典型裂隙模式；改进的Miller法对岩体结构均质区边界的辨别效果最佳。.（2）基于结构面内在成生关系及水力联系，在纯随机模型关键部位修正特征参数，融入人工辨识的确定结构模式构建多尺度“随机-确定”耦合模型。耦合模型结构面数量更接近客观实际，模型准确度约提升48.8%，结果精度约提升1/3，渗流路径及流量较随机模型更显客观真实。.（3）地下水渗流解析结果表明：十月井断裂带存在3 组裂隙，Ⅰ组裂隙占优时渗透系数高于104 cm/s，导水能力最强；Ⅱ组裂隙占优时渗透系数介于105-104 cm/s，导水能力居中；Ⅲ组裂隙占优时渗透系数普遍低于105 cm/s且介于106-107 cm/s 之间，导水能力最弱。裂隙岩体水流状态表现为层流型、充填型及冲蚀型特征，相应导水性能逐步递减。.（4）基于级联耦合结构面的地下水流动计算结果表明：地下水在多尺度结构面体系间流动时选择优势渗流路径快速运移，粒子首先进入与其直接交切连通的小尺度随机裂隙，运移过程中当遇导水性较强的大尺度断裂或中尺度长大裂隙则会改变运移路径，优先沿断裂带或长大裂隙运移、扩散直至模型边界。