Abstract
Abstract. Understanding the impact of fracture networks on rock mass properties is an essential part of a wide range of applications in geosciences from understanding permeability of groundwater aquifers and hydrocarbon reservoirs to erodibility properties and slope stability of rock masses for geotechnical engineering. However, gathering high-quality, oriented-fracture datasets in the field can be difficult and time-consuming, for example, due to constraints on field work time or access (e.g. cliffs). Therefore, a method for obtaining accurate, quantitative fracture data from photographs is a significant benefit. In this paper we describe a method for generating a series of digital fracture traces in a geographic information system (GIS) environment, in which spatial analysis of a fracture network can be carried out. The method is not meant to replace the gathering of data in the field but to be used in conjunction with it, and it is well suited when field work time is limited or when the section cannot be accessed directly. The basis of the method is the generation of the vector dataset (shapefile) of a fracture network from a georeferenced photograph of an outcrop in a GIS environment. From that shapefile, key parameters such as fracture density and orientation can be calculated. Furthermore, in the GIS environment more complex spatial calculations and graphical plots can be carried out such as heat maps of fracture density. Advantages and limitations compared to other fracture network capture methods are discussed.
Highlights
Fractures are the main pathways of fluid flow in rocks, and they exert a strong influence on rock mass properties
To illustrate the use of systematic 2-D digital fracture analysis methods for applied geoscience investigation, we present a number of case studies to highlight a range of geoscience applications and illustrate key benefits, including (1) rapid data collection to support regional hydrogeological assessment (India), (2) enabling the quantitative, rather than typical qualitative, assessment of key parameters for engineering rock mass strength evaluation (India), (3) analysing catchment-scale variability in sediment source characteristics for applied geomorphic studies in erosional terrains (Scotland), and (4) fracture network analysis from historical images for sites where modern exposures are unavailable (Sweden)
Commonly used qualitative approaches for estimating key rock mass strength parameters such as the geological strength index (GSI) are subject to variability through interpretation bias and practitioner experience, resulting in increased uncertainty and potentially in higher project risks and costs
Summary
Fractures are the main pathways of fluid flow in rocks, and they exert a strong influence on rock mass properties. The characterization of fracture networks is an essential aspect of various applications in the earth sciences, such as understanding the behaviour of fluid flow in groundwater aquifers (Singhal and Gupta, 2010) and hydrocarbon reservoirs and the erodibility and slope stability of rock masses (Clarke and Burbank, 2010; Krabbendam and Glasser, 2011). Fracture network data are essential for assessing future sites of nuclear waste repositories (Follin et al, 2014), predicting rock slope stability (Selby, 1982; Park et al, 2005) and understanding rock mass strength for the engineering of infrastructure (Hoek and Brown, 1997; Zhan et al, 2017; Ren et al, 2017). Due to the limited distribution of suitable rock exposures in many settings, understanding the spatial variability of fracture network pa-
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