This paper describes the time-dependent de formations of a jointed coal. Cylindrical samples of jointed coal were tested under constant triaxial load condition. Based on the results and interpretation of 9 (nine) single-stage creep tests, an empirical stress-strain-time relationship is put for ward. Qualitative remarks about the time-de pendent response of a jointed rock-like material are made as well.


The phenomenon of time-dependent behavior of rocks is a source of many problems in designing structures in rock. Foremost amongst them is the need for methods of predicting the performance of underground structures in creeping rocks. In order to address this problem it is necessary to have data on the stress-strain-time response of rock.

An extensive literature on time-dependent behavior is available covering both a wide range of materials (such as metals, plastics, rubber, ice, soils and rocks) and applications (such as mechanical, civil and mining engineering, metallurgy, geological and geophysical studies). The developments with respect to the time-dependent behavior of rocks have been summarized by state-of-the-art reports given by Robertson (1964), Cruden (1969), Wawersik (1973) and da Fontoura (1980). Most of the existent data are based on creep tests performed on relatively intact rock. Exceptions are Lama (1974) and Kaiser and Morgenstern (1979) who present qualitative information on the time dependent behavior of jointed rock-like material.

The present paper investigates the general features of the time-dependent behavior of a jointed rock mass and the parameters describing this process at the laboratory sea le. In order to better represent rock mass properties experiments have been conducted on a natural rock-like material that possesses a well defined set of discontinuities and yet, where the effects of these discontinuities can be represented adequately in a sample of a reasonable size.


The coal samples used in the present study were obtained from the coal seams exploited at the Highvale Mine which is situated on the south shore of Wabamun Lake, Alberta, Canada. This coal has been classified as a subbituminous coal B according to the Canadian Classification. The major geological features as well as topography and drainage of the area in the proximity of the sampling site have been described by Pearson (1959) and Noonan (1972).

Table I presents a summary of some index properties for the Wabamun coal. Additional mechanical properties for this coal have been presented by Noonan (1972), Guenot (1979) and Kaiser and Morgenstern (1979).


Cylindrical cores of about 6,90 cm in diameter and different lengths were drilled from large blocks of coal collected in the field. All the samples were drilled with their long axis parallel to the bedding planes and at an angle of 309 with the joints. This configuration would correspond to a horizontal sample in the field.

A simple double-lever arm rig capable of applying a constant axial load was designed and built for the series of creep test reported herein.

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