Rock mass classifications RMR, Q and GSI do not suggest decreasing modulus ratio with the decrease in the quality of rock. These have been linked to joint factor, Jf, for better prediction. An engineering classification is suggested based on strength and modulus applicable to both intact and jointed rocks.


Fels Masse Klassifizierungen RMR, schlagt Q und GSI daß das Abnehmen von modulus Verhaltnis mit der Abnahme in der Qualitat des Felsen nicht vor. Diese sind zu gemeinschaftlichem Faktor, Jf, fuer bessere Voraussage verknuepft worden. Eine technische Klassifizierung wird auf der Basis auf Kraft und modulus vorgeschlagen die zutreffend sind zu beiden unversehrten und jointed Felsen.


RMR de classifications de masse de Rocher, Q et GSI ne suggèrent pas la proportion de modulus decroissante avec la diminution dans la qualite de rocher. Ceux-ci ont ete relies au facteur de jointure, Jf, pour mieux la prediction. Une classification construisant est suggeree base sur la force et modulus applicables intacts et les rochers de jointed.


When intact or jointed rocks are classified for geotechnical purposes, they need to be classified on the basis of strength and / or modulus to give an indication of their stability against failure and for deformation analysis. In assessing the strength and modulus only the significant parameters of the rock mass should be considered which will influence the engineering behaviour most; each of the parameters is to be easily measured and they are to be linked in such a way that the quality of the rock mass is reflected in terms of its strength and modulus.

Currently there are four main approached available to estimate the uniaxial compressive strength and the corresponding modulus, namely RMR, Q, Jf and GSI. Each of the approaches gives different values and each one is tested for its reliability by considering the modulus ratio. The approach of Jf is based on vast experimental data and suggests continuous decrease of modulus ratio with the decrease in the quality of rock, unlike other approaches. It also enables to estimate the strength and modulus under any desired confining pressure. A rock, whether intact or jointed, should be classified in its simplest state of existence, i.e. in the unconfined condition. The influence of in situ stress and seepage pressure should be considered suitably in the analysis / design carried out in terms of effective stress.

Classification of Intact Rocks

The classification proposed by Deere and Miller1 for intact rock is based on the combined influence of the uniaxial compressive strength (σ ci) and the tangent modulus (Eti) at 50 per cent of the failure stress (subscript i refers to intact rock). It is a realistic and useful engineering classification which takes into account at a time more than one measurable basic property of the rock. Based on these properties they categorized rocks into a number of classes assigning two lettered combination.

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