The stress state at the boundary of any underground mine opening is that of plane stress. This planar state of stress can be simulated in laboratory by subjecting a cubic rock specimen to a biaxial loading condition. Thus, research on the behaviour of biaxially loaded rock is important for better understanding of the stability of mining fronts such as crown pillar skin, drift face or shaft floor. / The objective of this research is to study the geomechanical behaviour of biaxially loaded rock. Three rock types were selected, namely limestone, granite and sandstone. / The laboratory work was conducted using a newly developed, 500-tonne biaxial loading frame, that is equipped with a servo-controlled load and displacement system. Recently patented in China, the new biaxial loading frame is spatially symmetric and equally rigid in both directions. Steel brush platens and solid platens with and without MoS2 were developed to help examine the end friction effect on biaxial strength. It is found that the biaxial strength can decrease up to 26.7% with the increase of cubic specimen size from 75 mm to 150 mm. The biaxial strength increases by 29.3% with the increase of loading rate from 1 MPa/s to 10 MPa/s, for granite. The biaxial strength of granite specimen decreases by nearly 6% when either solid platens with MoS 2 lubricant or brush platens are used. A comparison of the sigma 1-sigma2 failure envelopes reveals that the shape of the envelope and the location of the peak biaxial strength are dependent on the rock type. / Varying intensities of rock spalling generally initiate at the free faces of the specimen when sigma1 and sigma2 exceed sigma c/2. Ultimate failure occurs in the form of an out-of-plane shear failure, which splits the rock specimen into two or more wedges. / It is shown that both Mohr-Coulomb and Hoek-Brown criteria underestimate the biaxial strength of the rock. The Drucker-Prager failure criterion appears to provide poor correlation with experimental results. A new empirical biaxial rock failure criterion for intact rock is derived and another, accounting for rock mass characteristics through the Geological Strength Index (GSI), is then proposed.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 102-103). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 119-121). Also available via the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 25, 2006) Vita. Includes bibliographical references.

No description available.

Deep foundations are commonly recommended when large displacements are expected. Typically, though, their design involves only checking and providing for sufficient capacity to carry the applied loads. Load-displacement behavior of piles is considered secondary to the axial capacity; displacements are ordinarily overlooked or not calculated if and when the estimated pile capacity is two to three times the design or expected loading. However, in cases, such as long piles or piles in dense cohesionless soils, displacements can be the critical factor in design or it could be a structural requirement to limit the displacements. In this dissertation, the displacements of axially loaded single piles are investigated by conducting analyses with the aid of an approach based on elasticity. The original solution predicting displacements due to a vertical load within a semi-infinite soil mass has been modified for varying soil conditions and layering, and assumptions of stresses and displacements acting on the soil-pile interface. Aside from the available/known factors of the pile (length, diameter, cross-sectional area, etc.) and the layering of the surrounding soil, Young's modulus and Poisson's ratio of the soil encompassing a pile are the unknowns required as input to obtain predictions based on the elastic method. In this study, attention is directed towards determining Young's modulus because the range and variability of Poisson's ratio is not significant in displacement calculations. Axial pile load testing data were provided by the California Department of Transportation as part of a project to improve its general approach to pile design. All of the tested piles were driven into the ground. Measurements of displacements and loads were made only at the top of the pile. Supplementary in-situ testing involving cone penetration (CPT) and standard penetration (SPT), drilling, and sample collection, were conducted in addition to laboratory testing to enhance the available information. In this research, predicted displacements are compared with those deduced from pile load tests. Two sets of predictions based on elastic method are conducted for comparing displacements. First, various correlations for Young's modulus are employed to determine how accurately each predicts the actual measured displacement. The chosen correlations utilize laboratory triaxial undrained shear strength and standard penetration test blowcount for cohesive and cohesionless soils, respectively. Secondly, the same data are also utilized to obtain back-calculated values of Young's moduli for analyses involving the elastic method. The measured displacements at loads of a third, a half, twothirds, and equal to the failure load were matched iteratively. Results from this research are deemed to have an impact on engineering practice by improving the determination of Young's modulus for displacement analyses involving the elastic method. A unique approach that has potential is the reconciliation of load ratios (percentage of failure load) with displacement calculations to provide a better overview of the range of load ratios for which these newly formulated correlations may be employed. Through this research, it is anticipated that better determination of soil parameters for elastic analysis of axial pile displacements can be made by researchers and engineers alike.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Vita. Includes bibliographical references (leaves 275-293). Also available in an electronic version.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: John L. Tassoulas. Vita. Includes bibliographical references. Also available from UMI.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy