The point-load test is frequently used to complete "in situ" the boring logs, to test the strength of rockfill and/or to characterise the strength of rock for classification purposes. Commonly a fixed correlation is proposed between point-load and uniaxial compressive strength. The concept of a unique relationship has not been validated by actual testing. Many authors complained about a "lack of accuracy" of the point-load test. The paper considers the theoretical relationships between uniaxial compressive strength and point-load index. A great number of data about the point-load test results are retrieved from the technical literature. Finally different relationships between uniaxial compressive strength and point-load index are proposed for the different classes of rocks, based both on theoretical considerations and on testing results.


L'essaie de compression ponctuelle est utilise d'habitude pour completer les registres de sondages "in situ", pour essaier la resistance de les roches et aussi pour la classifier. Normalment on propose une relation fixe entre las resistances la compression simple et l'indice "point-load". L' idee de une relation fixe entre les resistances en compression et en traction simple n'a pas ete validee pour les essaies. Beacoup d'auteurs signalent une "faute de precision" de I'essaie FRANKLIN. Cete communication etudie les relations theoriques entre la compression uniaxiales et le "point-load" indice. On a resume un grand nombre de donnees de la literature technique. Finalement on propose des differents relations pour les differentes classes de roches, qui s ' acordent mieux avec les considerations theoriques et les donnees reeles.


Der Punktbelastungsfestigkeitstest wird öffsentlich benuzt um den Bohrverzeichnis verzuvallstandigen, um die Festifgkeit des Bergeversatzes zu testen und um die Gesteinsfestigkeit zu klessifizieren, Üblicherweise wurd eine feste korrelation zwischen Punktbelastunsfestigkeit und Druckfestigkeit vorgestellt. Der Begriff einer festen Beziehurg zwischen Druckund zuffestigkeit wurde durch wirckliche Testen nicht beweist und ist nicht standhaft. Viele Autoren beschweren ueber Genanifkeitumangel des Punktbelastungstests. Die Mitteilung berueckuchtift die theoretische Beziechungen zwischen Druckfestigkeit und der Punkbelastungsfestigkeitindex. Eine große zahl der Daten ueber Punktbelastungfestigkeit aus der technischen literatur wird einfeschloßen. Endlich, werden verschiebere Beziehungen zwischen Druckfestigkeit un der punktbelastung, festigkeitsindex fuer verschieve gesteinsarten vorgestellt.


The point load test (also known as FRANKLIN test) is extremely easy to do in the field or in any laboratory and does not require sample preparation. Therefore it is very often used to complete "in situ" the boring logs, to test the strength of rockfill, to characterise the strength of rock for recognition purposes and/or for geomechanical classifications.

The point-load test was defined by REICHMUTH (1968). BROCH and FRANKLIN (1972) proposed the formula for the point-load strength index (Is). The International Society for Rock Mechanics normalised the test (1972. 1985). The most recent complete reference for operative methods is BROOK (1993).


Most of the books mention the correlations between point-load strength. for NX cores (I50) and uniaxial compressive strength (Co).

(Equation in full paper)

which is the form suggested by ISRM (1985). BIENIAWSKI proposes the correlation Co = 25. I50 in all the versions of his well-known RMR geomechanical classification system.

The size effect was pointed to by HOEK and BRAY (1974) which suggested factors of 17.5 for 20 mm cores, 19 for 30 mm, 21 for 40 mm, 23 for 50 mm and 24,5 for 60 mm.

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