Joint geometry parameter effects on deformability and strength of jointed rock masses at the two dimensional level.

Abstract

In this study, the pre-failure behavior of a jointed rock block is modeled by an incrementally linear elastic anisotropic constitutive model (using an orthotropic model in 2D). In order to estimate the parameters in the constitutive model, a new technique was used in this dissertation. A 2D joint geometry generation code was used to generate finite size actual joint networks in 2D rock blocks. A 2D distinct element code (UDEC) was chosen as the stress analysis tool in this study. Fictitious joints were introduced into the rock blocks which contain finite size actual joints to discretize the problem domain into polygons. A number of stress analyses of rock blocks which contain only persistent joints were performed to estimate representative values for mechanical properties of fictitious joints to simulate the intact rock behavior. Finally, the rock blocks having different deterministic actual joint configurations with fictitious joints were subjected to 2D stress analysis under various stress paths using UDEC. Results of these stress analyses were used to estimate the deformational and strength properties of these rock blocks. Influence of joint geometry parameters on the mechanical properties of jointed rock blocks were found to be very significant. Plots are given to show how mechanical properties of rock blocks vary with joint intensity and joint size/block size for different joint orientations. These plots can also be used to estimate REV (Representative Elementary Volume) size and REV properties for rock masses. It is important to note that these REV property values depend on the chosen constitutive models for intact rock and joints. The concept of fracture tensor is reviewed at the 2D level. Relationships between the mechanical properties of jointed rock blocks and the fracture tensor parameters (its first invariant and components) are established. These relationships can be used to estimate the parameters of the chosen constitutive model for the rock block. This constitutive model has captured both scale dependent and anisotropic behaviors of rock masses. The possibility of obtaining the equivalent continuum properties (REV properties) of jointed rock blocks is explored by using the aforementioned relationships. (Abstract shortened by UMI.)