Award Date

5-1-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Committee Member

Moses Karakouzian

Second Committee Member

Samaan Ladkany

Third Committee Member

Douglas Rigby

Fourth Committee Member

Mohamed Kaseko

Fifth Committee Member

Vernon Hodge

Number of Pages

340

Abstract

The host rock of portion of the first proposed high-level nuclear waste repository in the United States of America (Yucca Mountain, Nevada) is tuff rock that contains voids (lithophysae) with different shapes, sizes, and distributions. The existence of these voids can cause a dramatic change in the rock's mechanical properties such as uniaxial compressive strength, UCS, and Young's modulus, E. Accordingly, in an experimental program, the effects of void existence on the engineering properties of the tuff rocks was explored in a work of US Department of Energy conducted in the Department of Civil and Environmental Engineering and Construction of the University of Nevada at Las Vegas (UNLV); Project Activity Task ORD-FY04-013. Since it was difficult to test actual rock specimens, due to heterogeneity, break down during coring and sampling, and impossibility of controlling shape, size and distribution of voids in actual specimens of tuff rock, rock-like material (Hydro-StoneTB®), instead, was used in the experimental program. The experimental works consisted of laboratory testing on rock-like material (Hydro-StoneTB®) cubes under uniaxial compression. To obtain porous cubes with different void geometries, cubes with open ended longitudinal openings having different cross sections (circular, square, and diamond), different sizes (uniform large, medium, and small, and mixed voids), and different distributions (patterns A, B, and C) were made and tested under uniaxial compression. Fifty two porous specimens were made. Each porous specimen, porous cube, was produced in triplicate. Ten solid cubes were also cast to represent analog material with zero void porosity. The total number of experiments, including the ten solid cubes, was one hundred sixty six, 166, cubes.

This study attempted to characterize the effects of void porosity on compressive strength and elastic modulus more definitively through considering the other factors in data analysis and sought for more effective relationships between them using the experimental results of Project Activity Task ORD-FY04-013. In addition, the experimental results were used to validate a numerical analysis carried out using a discontinuous computer program; Universal Distinct Element Codes - UDEC. Furthermore, another numerical analysis was performed to study the effect of void geometry on mechanical properties more systematically.

The results showed that not-only the porosity but also the void geometry can affect the strength and deformability of rock-like materials. Void shape, void orientation, and void spatial distribution are partially responsible for the scattering in the mechanical property values as a function of void porosity. In addition, the results of the numerical simulations using UDEC software displayed consistent trends in Hydro-StoneTB® uniaxial strength and deformation as a function of void porosity. Furthermore, the two-dimensional numerical results can be transferred to three-dimensional experimental results through a power correlation.

Keywords

Failure Modes; Rock-like Materials; Stiffness; Strength; Tuff Rock; Void Geometry

Disciplines

Civil Engineering

Language

English


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