Abstract
Representative elementary volume (REV) is defined as the usual size of a rock mass structure beyond which its mechanical properties are homogenous and isotropic, and its behavior can be modeled using the equivalent continuum approach. Determination of REV is a complex problem in rock engineering due to its definition ambiguity and application area. This study is one of the first attempts to define a REV for jointed rock masses using the equivalent continuum approach. It is aimed to numerically search a ratio between the characteristic size of an engineering structure and pre-existing joint spacing, which are the two most important contributing elements in assessing REV. For this purpose, four hypothetical engineering cases were investigated using the RS2 (Phase2 v. 9.0) finite element (FE) analysis program. An underground circular opening with a constant diameter, an open-pit mine with varying bench heights, a single bench with a constant height, and an underground powerhouse cavern with a known dimension were executed for possible changes in the safety factor and total displacement measurements under several joint spacing values. Different cut-off REVs were calculated for FE models depending on the type of excavation and measurement method. An average REV size of 19.0, ranging between a minimum of 2 for tunnels and a maximum of 48 for slopes, was found in numerical analysis. The calculated sizes of REV were significantly larger than the range of values (5 to 10) commonly reported in the relevant geotechnical literature.
Highlights
The mechanical behavior of rock masses surrounding engineering structures is always a concern in rock engineering studies
It was found that depending on the type of engineering structure and descriptor used, the structures responded differently due to the scale effect
The commonly reported Representative elementary volume (REV) size range (5–10) in the relevant geotechnical literature in Table 1 is significantly smaller than the values found in this study
Summary
The mechanical behavior (strength and stiffness) of rock masses surrounding engineering structures is always a concern in rock engineering studies. Opening underground excavations in deep hard rock mines may lead to two types of failure: (1) structurally controlled gravity-driven failure and (2) stress-induced failure [23]. The former is predominant when both the radial and the tangential stresses are low,the latter is prevalent when tangential stresses are high. Controlled failures are most frequently observed at shallow depths It is always challenging for rock engineering to study the rock masses’ mechanical behavior, displaying a wide array from a simple brittle failure of an intact core sample to a complex mass-controlled failure of the overall pit slope (Fig. 1)
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