Meaningfull block sizes for Rock Fall modelling from Synthetic Rock Mass Models

Abstract

The determination of the so-called design block is one of the central elements of the Austrian Guideline for rock fall protection ONR 24810. It is specified as a certain percentile of a recorded block size distribution (BSD). BSDs may be determined from the detachment area (IBSD) and/or from the deposition area (RBSD). Most measuring methods are subjective, uncertain, not verifiable, or inaccurate. The statistical method seems the most efficient and cost-effective method to determine IBSDs with many blocks within the full range of block sizes. Today, we can model Synthetic Rock Masses (SRM) based on Discrete Fracture Networks (DFN). We asked whether IBSDs derived from SRM models can be described by probability distribution functions (pdfs) and if yes, how well. We show that the generalized exponential pdf best describes IBSDs across various lithologies, when compared to 78 other pdfs. This could allow for more certain, accurate, verifiable, holistic, and objective results.