In order to systematically study the size effect on the shear strength of rock joints, this study used the computer-aided-manufacturing system to reproduce the artificial rock joints for saw-toothed joints, Barton's standard joint profiles of JRC = 4~6 and 18~20, and natural rock joint profiles. We divided, enlarged, reduced, and assembled these joint profiles to obtain joint specimens of various sizes ranging from 75 mm to 300 mm in length. The shear strengths of these joint specimens were tested under different normal stresses using a direct shear test apparatus. The surface conditions of the joints at failure were also examined. The size and geometry effects on the shear strengths of these joints of various sizes and configurations were evaluated based on the test results.

Um die kuenstlichen Trennflachen fuer regulare dreieckige Trennflachen, Bartonsche standardmaßige Querschnitte der Trennflachen von JRC = 4~6 und 18~20 und natuerliche Querschnitte von Trennflachen wiederherzustellen, benutzt diese Forschungsarbeit das Computergestuetzte-Erstellungssystem, damit die Maßstabswirkung auf die Scherfestigkeit von Trennflachen systematisch untersucht werden kann. Die Querschnitte werden geteilt, vergrößert, verkleinert und zusammengesetzt, um Trennflachenproben in Langen variierend von 75 mm bis 300 mm zu erhalten. Die Scherfestigkeit dieser Trennflachenproben wird unter unterschiedlichen Normalspannungen mit einem Direktscherversuchsgerat getestet. Die Querschnittszustande der Trennflachen bei Versagen werden ebenfalls untersucht. Nach den Untersuchungsergebnissen werden die Maßstabs- und Geometriewirkung auf die Scherfestigkeit dieser Trennflachen verschiedener Größen und Konfigurationen ausgewertet.

Pour etudier systematiquement l'effet de la dimension des fractures des roches sur leur resistance au cisaillement un système de creation de fractures artificielles à l'ordinateur a ete employe. Des fractures artificielles triangulaires, profils de fractures de Barton avec JRC = 4~6 et 18~20, et profils de fractures naturelles ont ete reproduits. Les profils des fractures ont ete arranges de manière à obtenir des echantillons de longueur entre 75 et 300 mm. Une boîte de cisaillement a ete utilisee pour etudier la resistance des fractures au cisaillement, sous plusieurs conditions de contraintes normales. Les conditions superficielles des fractures après rupture ont ete etudiees. Les resultats de ces essais, effectues sur plusieurs echantillons de dimensions et configurations variees, ont contribue à etablir l'influence des dimensions et de la geometrie des fractures sur leur resistance au cisaillement.

Introduction

There exists a size effect on the strength of rock materials, including rock masses, intact rocks, fractured rocks and rock joints. The strength of a rock material differs with its specimen size. For the shear strength of rock joints, many researchers divided a larger natural or artificial rock joint specimen into various smaller sizes of rock joints. Direct shear tests under a given normal stress were conducted on these rock joints of various sizes. Average shear strength of each specimen size were obtained from the test results. The size effect on the shear strength was then obtained by comparing the average shear strength of rock joints of different specimen sizes. It was found in some studies that the shear strength of joints decreased with increasing specimen size1, 2, while in other cases, the strength increased with specimen size2, 3.

Previous studies of the size effect on shear strength of rock joints were generally performed based on the statistical reduction from the data of many shear strength tests on various sizes of artificial and natural joints empirically, e.g.4, 5.

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