RUI: Engineering Characterization of Rock-Like Materials with Large Voids Project Abstract: While the effects of porosity on rock strength and elastic properties have been widely investigated both experimentally and analytically, the effects of macroporosity (large voids) on strength and elastic properties are poorly understood and are poorly addressed in the scientific literature. Besides the basic lack of scientific understanding of these materials, the results are of importance to a number of entities. One of the most important aspects of this study is its applicability to the analysis and design of the U.S. high level radioactive nuclear waste repository; portions of the repository will be constructed in tuff units that contain large cavities. The research will also be relevant to engineering applications involving weakly cemented aggregates, which are currently employed as backfill for mine openings and stabilization of sinkholes, and may possibly have military or homeland security uses as potential impact-resistant materials. The primary aim of this research is to investigate the engineering behavior of materials displaying macroporosity, by quantifying the variation in behavior as a function of macroporosity characteristics. A three stage approach will be employed, corresponding to master's thesis work of four graduate students. In the first and second stages of the research, the effects of cavity size and cavity shape, on the strength (unconfined compressive strength, friction angle, cohesion), deformability (Young's modulus), and failure behavior (stress-strain response and failure mode) will be quantified. The third stage will focus on studying the effects of multiple sizes of cavities, since real macroporous materials tend to contain a wide range of cavity sizes. All stages of the proposed project will be accomplished through a combination of laboratory testing and numerical modeling, utilizing Montana Tech's state-of-the-art rock triaxial testing apparatus and PFC3D distinct element numerical modeling software. Real rock (tuff) and cemented rockfill specimens as well as synthetic samples composed of plaster of Paris with Styrofoam inclusions will be tested. After performing validation using the experimental data, numerical models will be used to supplement the laboratory experimental data, facilitating analysis of a larger number of samples under a wider range of conditions. The proposed project team is both interdisciplinary and inter-institutional, involving faculty from three different departments (Civil, Geological, and Mining Engineering) on two campuses (Montana Tech of The University of Montana and the University of North Florida, both primarily undergraduate institutions). Funding for a 3-day short-course on Itasca's PFC software will allow project participants, as well as other interested members of the engineering community who will be invited to attend, to gain a more thorough understanding of this powerful numerical tool. The research results will be disseminated via journal publications and presentation at rock mechanics symposia, and will be incorporated into several courses at Montana Tech. The extensive opportunity for collaboration, which will allow sharing of tools, ideas, and expertise, is one of the most exciting and beneficial aspects of the project. The work will promote diversity within the engineering workforce by providing support for a female PI and several female graduate students. Undergraduate and high school students will be involved in various aspects of the work; interaction between these students and the graduate student researchers is expected to encourage the younger students to continue their education to the next level.
