Clarification of spatial-temporal change of rock permeability and its application to prediction of long-term groundwater flow

选取日本中部Toki花岗岩体作为试验场地，对岩石渗透率测量、化学分析、微裂纹提取、微裂纹特性表征等进行了综合研究。将现场尺度上的结果与区域三维裂缝分布模拟结果相结合，明确了渗透率的多尺度结构。综合表明，热液蚀变带在几千万年间保持了高渗透率，而富泥断裂带则起到了屏蔽水的作用。因此，可以认为在几千年的时间里，岩体的渗透性结构几乎是相同的。风化引起的地形变化及其伴随的水力边界条件的变化、断层运动引起的裂缝和裂缝的产生以及局部渗透性的增强都可能导致地下水流动模式的时间变化。

Comprehensive studies including permeability measurement, chemical analysis, microcrack extraction, and characterization of microcrack properties of rocks have been implemented by selecting the Toki granitic body, central Japan as a test site. By integrating the results at site scale with a simulation result of regional 3D fracture distribution, a multi-scale structure of permeability was clarified. The integration suggested that the hydrothermally-altered zones had maintained high permeability for the period of several ten million years, while the gouge-rich fault zone had acted as a water shielding structure. Therefore, the permeability structure of rock body can be considered to be almost the same for the period of several thousand years. Topographic change by weathering and its accompanying change of hydraulic boundary conditions, generation of fractures and cracks by fault movements, and local enhancement of permeability may cause the temporal change in groundwater-flow patterns.