Characterization of rock discontinuity openings using acoustic wave amplitude — Application to a metamorphic rock mass

• Published in: Engineering geology 2015-07, Vol.193, p.402-411
• Main Authors: Peyras, Laurent, Rivard, Patrice, Breul, Pierre, Millet, Adrien, Ballivy, Gérard
• Format: Article
• Language: English
• Subjects: Acoustic imaging; Acoustics; Amplitudes; Borehole logging; Discontinuity; Drilling; Environmental Sciences; Manuals; Metamorphic rocks; Quantitative analysis; Rock; Rock discontinuities; Rock mass classification
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2015.05.014

Determining discontinuities is a key step in studying rock mass stability, as they represent potentially weak planes. The determination and description of discontinuity openings currently rely on qualitative analysis based on visual inspections of drill cores or drilling logs by engineers. The purpose of this research work is to improve the characterization of discontinuities to ensure easier classification and aid classical manual and visual processing. Quantity-based approaches are suggested using acoustic imaging log data. This method will facilitate sorting the discontinuities in a rock mass according to their openings, by quantitative analysis of drilling log data. Here, a method is proposed to determine discontinuity openings by analyzing acoustic wave amplitudes. The method is based on determining two statistical parameters for each discontinuity: the resulting discontinuity amplitude, which provides the average amplitude value as measured on the discontinuity, and the discontinuity amplitude standard deviation, which determines the extent of scattering of the amplitude values on the discontinuity. The method was applied to a metamorphic rock mass of a Canadian dam foundation at each stage of the study. •Discontinuities are characterized automatically using acoustic image log data.•Our method characterizes the different fractures and their openings.•Our method determines discontinuity opening by analyzing acoustic wave amplitude.•Our method provides a streamlined, opening-based classification process for discontinuities.•Our method provides an additional tool to the engineers in their classical manual and visual processing.