Determination of the geometrical REV based on fracture connectivity: a case study of an underground excavation at the Songta dam site, China

Abstract

This paper presents a technique for estimating the geometrical representative elementary volume (REV) of a fractured rock mass based on fracture connectivity. A three-dimensional fracture network model, of dimensions 78 m × 50 m × 50 m, was generated and validated for a granite rock mass using joint data collected from an exploration tunnel at the Songta dam site in southwest China. Two hundred and forty cubic specimens with edge lengths ranging from 1 to 20 m were sampled from the model, and connectivity parameters of each specimen, including the number of intersections per unit volume (C 1) and the intersection length per unit volume (L 1), were calculated. The REV was determined using the connectivity parameters and a series of statistical tests. The results demonstrate that both the C 1- and L 1-based REVs are equal to 11 m × 11 m × 11 m. In this work, the volumetric fracture intensity (P32) was also used to calculate the REV for comparison. The REV obtained by P32 is 9 m × 9 m × 9 m, which is smaller than that calculated by C 1 and L 1. Finally, the geometrical REV for the rock mass by integrating C 1, L 1, and P32 is 11 m × 11 m × 11 m.