Masters Theses

Date of Award

12-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Matthew Mauldon

Committee Members

Eric C. Drumm, Don W. Byerly

Abstract

The shear strength of rock joints is an important concept in civil engineering and in the geosciences. Shear strength of rock joints is developed by the sliding of two planes of a rock mass over one another. The peak shear strength for any given normal stress has been shown to be related to the base friction angle, the unconfined compressive strength, and the magnitude of roughness of a rock discontinuity. To help reduce the costs associated with testing, models have been developed to predict the peak shear strength of rock joints. Some of these models have been accepted for use by the International Society for Rock Mechanics for use by practicing engineers. While the models have been used successfully, questions have arisen over the procedure for estimating rock joint roughness. The procedure which has been used to estimate rock joint roughness required the visual matching of standard roughness profiles with those for which shear strength is to be determined. The relatively new science of fractal geometry has been used to quantify rock joint roughness. The research in this area has been primarily conducted along purely academic lines merely for the purpose of classifying variations of roughness. In this study an attempt was made to correlate various fractal parameters to rock joint shear strength. Several fractal methods were used to analyze roughness profiles for rock joints taken from the Foothills Parkway project and the US Highway 19E project, both located in Eastern Tennessee. Included in these fractal methods was a new procedure termed the Window Average Microangle method (WAM) developed for this study. All fractal methods were then verified using computer generated fractional Brownian motion profiles. A series of laboratory tests have been performed so that Joint Roughness Coefficients could be determined for the rock discontinuities. These tests included, shear tests, point load tests, and base friction angle tests. Two fractal parameters, the normalized fractal dimension, Dnand the normalized fractal intercept, bn were then correlated with the Joint Roughness Coefficients. The results of this study showed the normalized fractal intercepts, bn obtained from the variogram and WAM methods were positively correlated with the Joint Roughness Coefficients from laboratory tested samples and the standard profiles. Equations relating the variogram intercepts to the Joint Roughness Coefficients were developed which showed a logarithmic trend. The equations relating WAM intercepts and Joint Roughness Coefficients were of linear form. These equations can be used to quantify the JRC value used in the prediction of peak shear strength. The equations and procedures developed within are thought to provide a foundation for further study.

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