Computer controlled volumetric strain measurements in metadolerite

Abstract

A new volumetric strainmeter system has been developed for the measurement of true volumetric strains occurring in selected fresh and decomposed rock samples tested under computer controlled triaxial loading conditions. The system is capable of resolving volume adjustments of the confining medium to within ±2.8 mm3 and maintain confining pressure deviations to ± 6.9 kPa. The results of the investigation have shown the inadequacy of the commonly used strain gauge method to represent the volumetric strains occurring in the whole of the test specimen and they have provided further experimental evidence for the continuity concept in the fracture mechanism of rocks. Even in the most decomposed samples tested, crack initiation and propagation starts at lower stress levels than previously recognised, in contrast to the generally accepted concept of critical stress levels which characterise and define the process of brittle fracture propagation in rocks.