Award Date

2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering

Department

Civil and Environmental Engineering

Advisor 1

Moses Karakouzian, Committee Chair

First Committee Member

Nadar Ghafoori

Second Committee Member

Samaan Ladkany

Third Committee Member

Douglas Rigby

Graduate Faculty Representative

Samir Moujaes

Number of Pages

128

Abstract

This project determines the tensile strength of lithophysal analog rock and presents failure criteria that can be used by geotechnical engineers to evaluate underground structures in rock. The physical and mechanical properties that are related to the failure criterion, such as porosity, compressive strength and modulus of elasticity, are also discussed. Experimental tensile tests were made using direct uniaxial and indirect Brazilian tests. Three 4-inch specimens were fabricated and tested in direct uniaxial tensile tests using Hydro-Stone TB. The results showed that the elastic tensile modulus of elasticity was within two percent of existing data for the compressive modulus of elasticity. The direct tests were not successful in determining the ultimate tensile strength, as failure occurred at the connections. Twenty 4-inch diameter by 2-inch long specimens were fabricated and tested using the indirect Brazilian tensile test method. Hydro-Stone TB was also used as the analog material in the Brazilian indirect tests. The Brazilian tests were successful in determining the splitting tensile strength and the effect of porosity on the ultimate tensile strength of the Hydro-Stone TB specimens. Results showed that the tensile strength of the specimens was approximately 10 percent of the compressive strength. New test data were obtained for 0 (solid), 6.2, 12.5 and 18.7 percent porosities. Photographs, figures and graphs are shown for the test setups and results. Computer simulations of both direct and indirect tensile testing were made using Itasca's UDEC 2D, 3.1 computer program. The computer results were then compared with the experimental data. The results showed that the UDEC computer models can successfully predict the cracking patterns of the experimental test specimens. Results of the experimental tensile tests were combined with existing compressive test data and the Mohr-Coulomb, Mohr-Coulomb in s-t Space, Griffith and Power Failure Criteria were then formulated from these test data. Also, the four criteria were used to show the effect of porosity on the failure strength of the analog rock material for porosities between 0 and 18.7 percent.

Keywords

Compressive strength; Dog bone type tests; Failure; Lithophysae; Lithophysal analog rock; Lithophysal Topopah Tuff; Nevada Test Site; Porosity; Rock mechanics; Tensile strength; Underground rock structures; Yucca mountain

Disciplines

Civil and Environmental Engineering | Geotechnical Engineering | Materials Science and Engineering

Language

English


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