Masters Theses

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Matthew Mauldon

Committee Members

Eric Drumm, Chris Pionke

Abstract

Analyzing the stability of rock slopes involves predicting the sliding stability of blocks formed by planes of weakness within the rock mass. Plane and wedge sliding analyses, for which there are one and two sliding surfaces, respectively, have been widely used for the last thirty years. For plane and wedge slides, given certain assumptions, the distribution of normal forces on the contact planes is statically determinate. The resisting and driving forces may then be calculated by limiting equilibrium methods and the factor of safety determined directly. Certain geologic environments, however, especially those of folded rocks, produce potential failures which cannot be modeled as either plane or wedge slides. In these slopes the sliding of blocks may occur along non-planar surfaces. Standard rock stability analysis methods presently available are not adequate to treat these folded rock slopes. For this reason, a new energy model has been developed that can analyze the stability of a rock block with any number of contact planes or a curved contact surface. This research extends previous work by Mauldon and Ureta (1995, 1996) and Ureta (1994) and formulates the energy model in terms of stresses.

This model can analyze the stability of a prismatic rock block with any number of sliding surfaces or a cylindrical block with a curved surface. The factor of safety is evaluated as a function of the block geometry, loading conditions, and frictional resistance. The block is acted upon by an active resultant force R which is resolved to components RN and RT, the normal and tangent to the sliding surface, respectively. The tangential component provides the disturbing force on the block that causes movement. The normal component is equilibrated by normal reactions on the sliding surfaces. These normal reactions, multiplied by the coefficient of friction, provide the frictional resistance to movement. The distribution of these normal contact forces, however, is statically indeterminate. The energy based approach described in this thesis finds the distribution of normal contact forces corresponding to the minimum potential energy of the system. Once the contact forces have been determined, the frictional force may be found and the factor of safety calculated.

A computer program, ROCKSLIP, is also presented to implement the model. The program is demonstrated on a case study slope in Carter County, Tennessee. This slope is an area of a past failure in cylindrically folded shale. Results indicate that this failure could have been predicted with the model and computer program. The results also show that treating this failure as a wedge with two sliding surfaces greatly overestimates the factor of safety, possibly leading to an unsafe design.

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