Abstract

It is well known that rocks behave in a viscoelastic manner. Therefore, the theory of elasticity does not provide valid answers to problems of rock behavior. Various rheological models have been developed conforming to rock deformation. Most important of these is the Kelvin solid model. The model involves a coefficient of solid viscosity, which appears to have the makings of a future criterion for rock fracture.

The paper describes the evaluation of the Kelvin model and presents a few analytical developments concerning rock's viscosity from measurement in the mine stopes and the structural volume flow of rocks. Some experiments, results obtained in the laboratory are presented. These results indicate the advisability of using a Kelvin model and give an idea of the types of failure mechanisms operating in the rocks.

In light of these and other development's, the directional properties of rocks are discussed. The possibilities of exploitation of these properties in drilling in preferential directions, reorientation of mine workings, and oil well fracturing are briefly mentioned.

Introduction

It is well known that rocks behave in a viscoelastic manner. Among rheological models applicable to rock behavior, the most import is that of the Kelvin solid, although the Maxwell and Burger models are also applicable to some extent. One of the two constituents of a Kelvin solid deals with time-dependent behavior of rocks and involves the coefficient of structural viscosity. This solid-viscous parameter appears to be a future potential criterion for structural design involving rocks and rock-like materials. The parameter has been experimentally determined in the laboratory, using a number of independent techniques. This paper is a step further in this direction and consists of theoretical development for determination of structural viscosity from mine stope measurements. Some data obtained in the laboratory are used to calculate some values of the coefficient of solid structural viscosity. The above are then used in formulating the comments concerning exploitation of the directional properties of rocks in drilling reorientation of mine workings and oil well fracturing.

ANALYTICAL CONSIDERATIONS

In analytical development presented here, it is assumed that the rocks behave like a Kelvin solid, represented by the equation:

........................................(1)

The solution of Eq. 1 is given by:

........................................(2)

If is constant, Eq. 2 reduces to:

........................................(3)

P. 121^

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