Triaxial compressive strength tests on sandstone and limestone specimens. Description of the triaxial test equipment and procedure, analysis of the test data by using a computer. Straight-line relations found between the principal stresses at failure and between strains and radial stresses as well. An approximate relation determined for the variation of strains in time. An increase of the rock types to be tested as well as the automation of the test equipment and the strain measurements aimed at in the near future.

1 — Introduction

The continuous straining of the surrounding rock at relatively low stress levels acting for a certain time without causing the failure of the rock is a phenomenon often to be observed. These deformations (creeps) occur slowly under constant stresses, and their knowledge is just important for the practising engineer as the ascertainment of rock fractures and rock movements.

The state of stress resulting from the own weight of the rock shell, that is, a certain state of compressibility can — according to our present knowledge — be produced under laboratory test conditions best of all in a s.c. triaxial load cell; a secondary and, possibly, also a tertiary state of stress of the rock shell can, with some further simplifications, be simulated in a test model by arbitrarily varying the stress components applied by multi-directional stressing.

At relatively low confining pressures, the triaxial compressive strength tests resulted in brittle fractures, while in case of high confining pressures an increase of the range of plastic deformations could be observed. According to experience, the range of elastic deformations does not solely depend on the type of the rock but also on the magnitude of the confining pressure. There is, of course, no marked transition between elastic deformations and yield (creep) and the determination of an accurate boundary line would require the knowledge of the strain-time relation characteristic for the respective rock, including the variation of the stress components in time as well. Now-a-days it can be taken for granted that the transition between elastic and plastic deformations will be different for the various rock types (minerals). The adopted load cell (Fig. 1) is suitable for the application of vertical stresses up to 4000 kp/cm2 in value and horizontal stresses of up to 600 kp/cm2. Vertical stresses are applied by the pressure of a piston acting on the end faces of the specimen, while horizontal stresses are produced by hydraulic pressure. The vertical pressure is produced by a hydraulic jack built together with the pressure cell. The fluid pressures needed are produced by hydraulic pumps.


Description du dispositif d’essai triaxial et de la méthode d’essai des roches et le traitement des données mesurées sur ordinateur. Il est possible de poser des relations linéaires entre les tensions principales de rupture ainsi qu’entre la pression latérale et les déformations. On pouvait déterminer une relation d’approche pour les déformations dans le temps. Il est projeté d’étendre le nombre des roches examinées et d’automatiser le dispositif et la mesure des déformations.


Triaxiale Druckfestigkeitsmessungen an Formstücken von Sandstein und Kalkstein. Beschreibung der Triaxialgeräte und des Verfahrens. Analyse der Messwerte mit Hilfe eines Digitalrechners. Lineare Beziehungen konnten sowohl zwischen den Hauptspannungen beim Bruch als auch zwischen Dehnungen und radialen Spannungen gefunden werden. Eine Annäherungsformel wurde auch ermittelt für die Veränderung der Dehnungen in der Zeit. Eine Erhöhung der Zahl der zu untersuchenden Gesteinsarten und die Automatisierung der Prüfgeräte und der Dehnungsmessungen wurde erzielt.

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