Introduction

In spite of the increased research on the behavior of geologic materials which has been undertaken in recent years, many of the most important mechanical properties have not been investigated in detail. In particular the effect of time has received very little attention from the experimental point of view, although its importance has been suggested by many workers. Many workers have reported that test results appeared to be influenced by the rate and duration of loading, although few have been willing to accept the fact that such behavior is indicative of an inelastic material.

A general study of the Mechanical properties of geologic materials was initiated in 1951 in The Mining Research Section of the Fuels and Mining Practice Division, Mines Branch, Canadian Dept. of Energy, Mines and Resources, as part of a fundamental study of ground stress in Canadian Coal Mines. initial work was restricted to short-period tests on typical mine rock under uniaxial compressive stress, but as the importance of the "time factor" became more obvious, studies were undertaken to investigate time-dependent behavior. These studies, which were initiated in 1957, consisted mainly of a comprehensive literature search on the subject, and the initial development of experimental facilities. This research project was inactive during the period 1959–1961 due in part to the relocation of laboratory facilities.

In the fall of 1961 the project was reactivated with the proposed research program being broadly outlined as follows:

"To study experimentally the mechanical behavior of selected geologic materials and to analyze these experimental data using the concept of Technical models and the analytical methods of viscoelasticity. In particular to develop governing equations for these materials based on suitable laboratory experiments and valid at least within a range of stress, confining pressure, duration of loading, and temperature consistent with practical applications."

The first phase of this research program included the experimental investigation of the inelastic behavior of a number of "simple" geologic materials using incremental creep experiments, and the associated development of the necessary experimental facilities and analytical methods. This paper outlines briefly the experimental and analytical techniques developed, and presents experimental results for the initial deformation studies carried out on Wombeyan marble.

THEORY

Papers dealing with the behavior of geologic materials are found to be widely dispersed throughout the literature. However, extensive bibliographies dealing with the general mechanical properties of these materials have been published recently by Griggs and Handin and Mitra and Willson. In the more specific field of time-dependent behavior of geologic materials extensive bibliographies have been given in papers by Hardy, Murrell and Misra, and Robertson.

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