Fractured rock mass characterization parameters and seismic properties: Analytical studies

Abstract

Analytical studies have been carried out based on a modified displacement discontinuity fracture model to characterize the relations between seismic properties and fractured rock mass parameters. Models of a fractured medium are developed to represent vertically aligned fractures embedded in an intact rock material. Seismic properties, including velocities and quality factors ( Q), are computed from seismic waves transmitted through the medium. The geometrical properties of the fractures, that is, the fracture length, spacing, and aperture, are assumed to exhibit fractal or Weibull behavior. The discontinuity index I d, fracture density parameter C, and the RQD, which provide a descriptive measure of either the hydraulic properties or the strength of the fractured medium, are computed for simulated distributions of the geometric fracture properties. These parameters are analyzed and then related to the seismic properties. The investigations suggest that consistent low seismic velocity and Q values associated with a fracture zone are indicative of a permeable or hydraulically transmissive zone. Lower rock strengths are also associated with lower seismic velocity and Q values. The results show that reasonable inferences characterizing the hydraulic and strength properties of fractured rock mass may be derived from measured seismic properties.