A practical classification of rocks for engineering purposes

  • Necdet Türk
  • Dearman W. R. 


A new method of classification of rocks is proposed based on rock material properties determined in the laboratory. Uniaxial compressive strength is plotted against the ratio of tangent elastic modulus to Poisson's ratio. For unweathered rocks this gives the horizontal strain of the rock at failure. It is convenient to plot the experimental values on log-log paper in order to assess the mean value.

Weathering not only decreases strength but also the ratio of elastic modulus to Poisson's ratio. If, for example, the experimental results from a granite weathered to different grades is similarly plotted the relationship is linear. From the graph the horizontal strain at failure can be determined for any rock strength in the weathering suite. The slope of the curve for any particular rock is constant, so that for each rock there is a unique linear equation.

Dynamic properties of rocks can be plotted on the same graph, as can field data.

For classification purposes both the strength and elastic modulus to Poisson's ratio scales can be divided into classes.


Elastic Modulus Rock Mass Uniaxial Compressive Strength Triaxial Test Rock Material 

Methode de classification des roches pour les projets de genie civil


Une nouvelle méthode de classification des roches est proposée par les auteurs; elle est fondée sur les propriétés des matériaux rocheux déterminées en laboratoire. On établit un graphique: résistance à la compression simple en fonction du rapport entre le module élastique tangent et le coefficient de Poisson. Pour les roches non altérées, on obtient ainsi la déformation horizontale de la roche à la rupture. Il faut établir les graphiques à partir des valeurs expérimentales sur du papier log-log de façon à estimer la valeur moyenne.

L'altération diminue la résistance ainsi que le rapport entre le module élastique et le coefficient de Poisson. Si, par exemple, l'on dispose de cette façon les reśultats expérimentaux obtenus sur un granite à différents stades d'altération, la relation est linéaire. A partir de ce graphique on peut déterminer la déformation horizontale à la rupture pour n'importe quelle résistance de roches prises dans le cortège d'altération. La pente de la courbe pour une même roche est constante, et il n'existe donc pour chaque roche qu'une seule équation linéaire.

Les propriétés dynamiques des roches peuvent être reportées sur le même schéma, de même que les données de terrain.

Pour les besoins de la classification, les échelles résistance et rapport module élastique—coefficient de Poisson peuvent être subdivisés en classes.


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Copyright information

© International Association of Engineering Geology 1983

Authors and Affiliations

  • Necdet Türk
    • 1
  • Dearman W. R. 
    • 1
  1. 1.Department of Geotechnical EngineeringUniversity of Newcastle upon TyneNewcastleUK

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