ABSTRACT:

This paper describes the program of laboratory testing of soft rock samples that has been carried out at the University of Nottingham to characterize weak materials. This work, which is part of the EU RFCS project “Geosoft”, has been conducted to examine alternative methods of obtaining physical properties of soft rock when conventional rock mechanics testing methods are not appropriate. This is because the weakness of these strata types often results in samples breaking up into pieces when being collected at the working face, during transport to the laboratory or during sample preparation. In this study, tests were conducted on intact, reconstructed and broken samples to obtain the strength and stiffness parameters that could be fed into numerical modeling of underground situations. The Unconfined Compressive Strength (UCS) of intact and reconstituted rock samples was determined in the stiff press. The friction angle and cohesion of reconstituted and broken soil-like samples were determined using conventional soil element testing techniques such as the shear box and triaxial cell. The experimental data obtained from all the tests are compared and analyzed in this paper.

1. INTRODUCTION

Severe roadway floor and side deformations constitute a major impediment to efficient production in European coal mines due to their depth, the ground stresses and, particularly the soft strata around the mine workings. In order to apply realistic numerical modeling and to find the best support solutions to these problems, it is important to understand the behavior of these soft rocks. The strength properties of various soft rocks have been evaluated by means of tests performed with a specially devised triaxial apparatus [1] and [2]. Stiffness of soft rocks has also been investigated [3]. Therefore, laboratory work was carried out in the University of Nottingham to obtain the stress-strain properties for weak materials.

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