The assessment of overall modulus (or stiffness) of a fractured weak to moderately strong rock mass is a key parameter in the design of civil engineering works in these materials. It also provides the highest level of uncertainty due to scale effects, anisotropy and the influence of joint frequency and joint stiffness. Using the example of the Melbourne Mudstone, this paper compares approaches using empirical rules based on intact rock strength, laboratory testing, insitu field testing, semi-quantitative assessment techniques based on rock mass classification and back analyses.
L'evaluation du module (ou rigidite) global d'une masse rocheuse faible et fissuree a moderement forte est un paramètre principal dans la conception des travaux du genie civil dans ces types de materiaux. Elle fournit egalement le niveau le plus eleve d'incertitude due aux effets d'echelle, à l'anisotropie et à l'influence de la frequence et de la rigidite des joints rocheux. En utilisant l'exemple du schiste de Melbourne, cet article compare des approches empiriques basees sur la force intacte de La roche, les essais experimentaux au laboratoire, les essais sur site, les techniques semi-quantitatives d'evaluation basees sur la classification de la masse rocheuse et les analyses en retour.
Die Schaetzung des allgemeinen Steifigkeit-Moduls des gebrochenen schwachen bis zu maessig starken Felsmassen ist eine Haupt- Annahme in dem Entwurf von Tiefbau-Projekten in diesen Materialien. Es verursacht den hoechsten Grad der Ungewissheit in Folge der Groessenordnung, Spaltorientierung und dem Einfluss der Haeufigkeit der Risse und Bruch-Steife. Unter Verwendung des Beispiels des Melbourner Tonsteine, vergleicht diese Darlegung die Anwendung der empirischen Regeln, die sich auf die Staerke des ungestoerten Fels Basieren mit Versuchen in der Material Pruefungsanstalt, Untersuchungen auf der Baustelle und halb-quantitative Schaetzungsverfahren, die sich auf die Felsmassen Klassifikation und fruehere Analysen stuetzen.
The assessment of overall modulus (or stiffness) of a fractured weak to moderately strong rock mass is a key parameter in the design of civil engineering works in these materials. It also provides the highest level of uncertainty due to scale effects, anisotropy and the influence of joint frequency and joint stiffness. Rock mass properties are difficult to measure directly and their estimation has historically relied on subjective assessments of rock mass quality and measurements of intact values. Using the example of the Melbourne Mudstone, this paper compares approaches using empirical rules based on intact rock strength, laboratory testing, insitu field testing, semi-quantitative assessment techniques based on rock mass classification and back analyses.
‘Melbourne Mudstone’ is a generic name used to describe the open folded and faulted sedimentary deposits comprising predominantly siltstones with some fine grained sandstones and rare mudstones of Silurian and early Devonian age that underlie the Melbourne area. The weathering state, varying from extremely weathered to fresh, was first classified for engineering purposes by Bamford (1969) and Nielson (1970).
The saturated water content of the siltstone provides a useful quantitative indicator of the engineering properties of the intact rock varying from around 20% (void ratio ≈ 0.54).