Predictive Permeability Model of Faults in Crystalline Rocks; Verification by Grouting in Seyahoo Dam

This paper deals with quantitative fault zone descriptions, qualitative fracture and fault rock properties, and engineering data in the study of the permeability structure of fault zones. Datasets include scan-lines, drill cores and cement grouting from Seyahoo dam in andesite and basalt rocks, from which systematic grouting volumes can be used to analyze the in-site relative permeability both in host rocks and fault zones. Dam-scale injection of cement reveals patterns that can be ascribed to the impact of faulting; there is an increase in cement injection in fault zones compared to areas with background fracturing away from faults. In detail, there is an innate division of the rock volume into subzones characterized by distinct structural style and permeability, with a background level and three fault related subzones (fault core, inner damage zone, and outer damage zone). Injection data shows that the background sub-zone commonly can be injected with less than 0.05 m³ cement per meter dam (commonly not injected), whereas the fault core has permeability characteristics nearly as low as the outer damage zone, represented by 0.1 m³ cement per meter dam, with occasional peaks towards 0.2 m³. The maximum of cement injection lies in the inner damage zone, the marginal to the fault core, with 0.3-0.5 m³ cement per meter dam, locally exceeding 0.7 m³. This gives a relative relationship for cement injection of approximately 1:3:1 between fault core, inner damage zone, and outer damage zone of extensional fault zones in crystalline rocks.