ABSTRACT:

Roughness performs a dominant role in the mechanical and hydraulic behaviour of rock joints, but no method exists to completely describe it. This paper presents the work done for digitisation of 10 joint samples, a statistical study of the asperity heights, a review of the roughness indices and the calculation of some indices and of the fractal dimension of the joints. Correlations with JRC were established and critically analysed.

RESUME:

La rugosite joue un rôle dominant dans Ie comportement mecanique et hydraulique des joints rocheux, mais aucun methode peut la decrire completement. Cette communication presente Ie travail fait pour la digitalisation de 10joints, un etude statistique des asperites, une revision des indices de rugosite et Ie calcul de quelques indices et de la dimension fractale des joints. Des correlations avec JRC ont ete etablies et sont critiquement analisees.

ZUSAMMENFASSUNG:

Rauhigkeit spielt eine beherrschende Rolle im mechanischen und hydaulischen Verhalten von geklueftetern Fels, aber es existiert kein Verfahren um sie vollstandig zu beschreiben. Der vorliegende Bericht stellt die Arbeit der Digitalisierung von 10 Rissen dar, eine statistische Untersuchung der Rauhigkeit, eine Übersicht der Rauhigkeitsindexe, sowie die Berechnung einiger Indexe und der Fraktaldimension der Exemplare. Korrelationen mit JRC wurden hergestellt und kritisch analysiert.

I. INTRODUCTION

In fractured rock masses, the mechanical and the hydraulic properties are influenced to a large extent by the presence of the joints. In order to understand this decisive role of the joints it is important to study the basic properties of the individual joints, which are intimately linked to their geometry. One of the main geometrical properties of individual joints, which is recognized to perform a relevant role in their hydraulic and mechanical behaviour is roughness. Roughness of rock joints is, however, a property difficult to define and to quantify, because there are no measurable quantities that can completely describe it. In the work reported in this paper several methods were used for quantification of roughness, based on the surface topography of natural joints, and the results obtained are presented and analysed. This research is part of a doctoral thesis (Lamas, 1993) concerned with the hydro mechanical behaviour or jointed rock masses. For the geometrical characterization of individual joints, 10 samples (labelled A01 to A10) of granite joints of the Alto Lindoso hydro-electric power scheme, located on the river Lima, in the North of Portugal, were studied in laboratory. The samples were collected in the zone of the powerhouse complex, at a depth of 340 m. They are cylinders with the joint in the axial position, the dimensions of the joint being 102 mm × 51 mm. The grain of the granite in samples A0I to A06 is slightly coarser (2 to 4 mm) than in samples A07 to AI0 (2 to 3 mm). The joint surfaces are little to moderately weathered and show no sign of previous shearing. Previous results of uniaxial compression tests on this rock gave mean values of the Young's modulus. Poisson's ratio and uniaxial compressive strength of E=60GPa, v=0.2 and µ= 140MPa respectively, and the results of joint shear tests in joint samples gave mean values of the friction angle and apparent cohesion of Coulomb's model of ø = 37° and c = 0.08 MPa.

2. JOINT PROFILING

For the study of joint surface topography it is necessary to determine the heights of the asperities with respect to a reference plane. Ideally, the sampling process should be uniform in the whole surface. In the present work, however, it was considered reasonable to obtain several linear profiles along the axial direction of the samples.

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