Use of Hydraulic Test Data to Recognize Fracture Network Pattern of Rock Mass in Taiwan Mountainous Areas

Abstract

Featured Application The proposed approach provides the interpretation of fracture network properties of rock mass around a borehole, to establish a hydrogeological site descriptive model which facilitates the design and planning of groundwater-related engineering systems. Comprehensive information on fracture network properties around a borehole is indispensable for developing a hydrogeological site descriptive model. However, such information usually relies on various cross-hole field tests at a high cost. This study presents a cost-effective option regarding the identification of fracture network density around a borehole. Based on packer-test and drilling-core data from 104 boreholes in Taiwan mountainous areas, Barker's generalized transient radial flow model and the concept of fractal flow dimension were used to reanalyze the existing hydraulic test data for obtaining the n value related to the geometry of groundwater flow for each test section. The analyzed n value was utilized to explain the characteristics of the fracture network in the adjacent area of each packer inspection section. The interpretation results were verified, using five hydrogeological indicators, namely rock-quality designation, fracture aperture, fracture density, hydraulic conductivity, and fracture/matrix permeability ratio. All hydrogeological indices have high correlations with flow dimension n values. Based on the verification results from using these indices, the proposed method in exploring such information was proven to be feasible. Finally, three practical relations were established, to provide additional information for designing and planning groundwater-related engineering systems in Taiwan mountainous areas.