ABSTRACT:
The prediction of failure conditions has always been a critical issue in rock engineering. One of the factors that makes this a complex problem is the influence of scale (size) on the response of rocks and rock masses. A variety of approaches have been developed and used to estimate the strength of rock media at different scales. These include a scaling function proposed by the authors, which is partly based on the statistical variability of uniaxial compressive strength of intact rock samples. In this paper, this approach is revisited. A simple method is presented for determining the required parameters for predictive applications, using standard laboratory test results. The validity of the proposed approach is evaluated using test results recently obtained by the authors and with some data taken from the literature.
1 INTRODUCTION
The mechanical properties of rocks are known to vary with sample size (e.g. Durelli & Parks 1962, Lundborg 1967, Lo & Roy 1969, Einstein et al. 1970, Brace 1981, Jackson & Lau 1990, Newman & Bennett 1990, Frantziskonis et al. 1991, Cunha 1993a, Andreev 1995, Ghosh et al. 1995, Goodchild & Wade 2002). This behavior is important because most rock engineering projects require the knowledge of the rock media response at a relatively large scale. However, the direct measurement of rock properties at a representative scale is often difficult to conduct due to technical or economical constraints. The influence of scale manifests itself in various ways (e.g. Cunha 1990, 1993b, Bandis 1990, Hudson & Harrison 1997). Figure 1 presents schematically how the uniaxial compressive strength sc of rock media typically varies with size. On Figure 1, the unit bock is defined as the maximum size of intact rock units in situ (between geological discontinuities).
