Abstract

The mechanical behavior of rock under high-temperature was simulated using a grain-based distinct element model. The microstructure of rock was represented as an assembly of deformable polygonal grains, and the micro-parameters characterizing the deformability and strength of each grain and interface were calibrated based on the experimental results of UCS and Brazilian tests at room temperature. For implementation of the mechanical analysis, a commercial code UDEC based on DEM theory was adopted in the present study. With the microstructures and a set of micro-parameters, the specimen was heated up to a maximum of 250 °C prior to being loaded, and then UCS and Brazilian tests on the heated specimens were numerically carried out. The estimated and experimentally measured behavior of rock showed moderately good agreement, which suggests the ability of the grain-based model combined with UDEC to capture the thermo-mechanical behavior of rock at microscopic scale.

1 Introduction

A concern regarding the thermo-mechanical coupled behavior of rock has arisen in many rock engineering projects including thermal energy storage, geothermal energy development and nuclear waste disposal. Spatial and temporal change in temperature can initiate new micro-cracks and propagate pre-existing micro-cracks within rocks, and the micro-cracks can influence substantially the physical properties of the rocks (Homand-Etienne & Houper 1989). Many experimental studies have reported that the mechanical properties characterizing strength and stiffness of rock tend to decrease with increasing temperature at high temperature (Dwivedi et al. 2008). Two mechanisms for thermally induced micro-cracks have been suggested in the literature (Yong & Wang 1980); first, new micro-crack can be generated at the interface between different rock-forming minerals because of a mismatch in the thermo-elastic behavior; and the other is that the thermal stress due to local variations in the temperature gradient in rocks causes the propagation of existing cracks. Thus, the thermo-mechanical behavior of rock, in nature, should be understood be based on the observations at mineral scale.

With the rapid progress of computer technology, many attempts have been made to reproduce the mechanical behavior of rock using numerical techniques, such as finite element method, boundary element method, and discrete element method. In terms of explicit representation of heterogeneous material at microscopic scale, it would appear more desirable to make use of a polygonal grain-based micromechanical model to adopt other numerical models assuming obscure constitutive laws including a large number of assumptions and uncertainties. Lan et al. (2010) simulated the behavior of brittle rock using a grin-based geometry generated by the power Voronoi tessellation and a commercial code UDEC (Universal Distinct Element Code). They named the technique as GBM (Grain Based Model)-UDEC model, and demonstrated the feasibility of GBM-UDEC model for the reproduction of the brittle rock's failure process induced by its microstructure heterogeneity. Shin (2010) also successfully applied this technique to the simulation of the spalling failure that was observed around AECL's Mine-by Test Tunnel in Canada.

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