ABSTRACT:

Bonded Block Models (BBMs) have become increasingly used to simulate laboratory rock samples in Unconfined Compressive Strength (UCS) and Triaxial tests. BBMs require input parameters that describe the deformation of the blocks themselves (block properties), as well as the interaction of the blocks with adjacent blocks (contact properties). For rocks with more than one mineral (i.e. block) type, there exists more than one type of contact between blocks, each of which requires a different set of input parameters. Little is known about the effect of heterogeneity of the contact properties on individual aspects of the overall behavior of the BBM. Therefore, this study has conducted a sensitivity analysis on the heterogeneity of contact input parameters. Contact input parameters were tested separately by varying the degree of heterogeneity between contact types, while keeping the weighted average of each given contact property constant for all simulations. Both a UCS and a Triaxial test with 12 MPa of confining pressure were simulated for each case to evaluate the effects of heterogeneity under unconfined and confined conditions. Rock specimen properties were computed from the model results including Young's Modulus, Poisson's Ratio, UCS and Peak Strengths, and Crack Initiation (CI) and Crack Damage (CD) parameters. While several minor influences of heterogeneity on macroscopic properties were noted, the primary influence was that of contact peak cohesion heterogeneity on CD under both unconfined and confined conditions.

1. Introduction

With the advent of high-performance computing, numerical models have become increasingly used to study rock behavior. Numerical models can be used to complement laboratory testing, as they require significantly less time and labor to complete. Unconfined Compressive Strength (UCS) and Triaxial tests are laboratory tests that are commonly used to assess the material properties of intact rock. Such laboratory tests can be simulated using Bonded Block Models (BBMs) (Sinha and Walton, 2020) and can be further applied to field-scale modeling scenarios like excavations, roof stability, underground pillar design, and other scenarios that cannot be tested in a laboratory.

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