ABSTRACT:

The uniaxial compressive strength of rock materials could be estimated by adopting a simple, quick, and less expensive index - the point load strength. However, no one specific value of the correlation factor (k) exists for all rock types since this factor tends to be sensitive to variations in both the intrinsic rock properties and the external conditions of the test specimens. The extent to which rock anisotropic fabric influences k has been critically examined in the present study following an experimental investigation on a suite of metamorphic rocks. An evaluation of the degree of foliation is useful in the choice of an appropriate k value for a particular metamorphic rock. In view of the advances made during recent times to improve and standardize the point load strength testing method, it is deemed prudent and economical to use this parameter in its own right particularly for rock classification purposes.

RÉSUMÉ:

La force compressive uniaxiale de materiaux rocheux pourrait être estimee en adoptant un index simple, rapide, et moins complique - la charge ponctuelle. Cependant, il n"existe une seule valeur specifique du facteur de correlation (k), ce facteur tendant à être sensitif à la variation des proprietes intrinsèques du roche et aux conditions externes des echantillons d"essai. L"etendue de l"influence anisotropie des roches sur k a ete criticalement examinee dans cette etude. Une evaluation du degre de foliation est important en choisissant une valeur k appropriee d"un rocher metamorphique particulier. Compte tenu des progrès realises recemment à ameliorer et standaliser la methode charge ponctuelle, il est considere prudent et economique d"utilliser ce"paramètre, particulierement pour la classifications de roches.

ZUSAMMENFASSUNG:

Die einachsige kompressive Festigkeit von Gesteinstoffen koenute durch eines einfachen schnellen und preisguenstigen indexes - die Punktlastfestigkelt, geschaetzt werden. Jedoch existiert kein einziger spezifischer Wert des Korrelationsfaktors (k) fuer alle Gesteinarten, da dieser Faktor zu Veraenderungen sowohl in den intrinsischen Gesteineigenschaften als anch in den externen Zustaenden des Proben empfindlich zu sein tendiert. Das Ausmass zu dem die anisotropische Fasern den Faktor k beeinflussen ist in vorliegender Studie, im Auschluss eines,experimentellen Versuchs ueber metamorphische Gesteinzuege, kritisch untersucht worden. Eine Bewertung des Foliationsgrades ist bei der Wahl eines fuer einen gegebenen metamorphischen Gestein augemessenen k- Wertes nuetzlich. Augesichts der Erkenutnissen der letiten Zeiten die Pruefungesmethode fuer die Punktlastfestigkeit zu verbessern und zu standardisieren, wird es fuer zweckmaessig und wirtschafthich gehalten, dieser Parameter selbstaendig anznwenden insbesondere zum Zweck der Klassifizierung von Gesteinen.

1 INTRODUCTION

Strength properties are vital inputs for the engineering design of many structures on or within rock masses or for assessing the potential use of rock materials for construction works. The uniaxial compressive strength (UCS) is perhaps the most widely used rock strength parameter for the purposes of classification and design. This is because the test method seems to be better known and also it offers the opportunity of investigating rock behaviour under more complex stress regimes for linking re- saults to field performance. However, the UCS test requires a rather more sophisticated equipment and the test specimens need to be prepared to strict specifications.

The desire to obtain strength properties more quickly and at a less cost particularly for rock classification purposes has led to the development of the point load strength index test about three decades ago. It is basically an indirect uniaxial tensile strength test but its use to measure tensile strength under polyaxial conditions (see Wijk 1979) is becoming popular. The advantages of the point load test over the UCS test include the relaxation of the tolerances for specimen size and shape as well as the use of a simple portable equipment.

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