The ultimate shear strength of dry sandy gouges infilling artificial and flat discontinuities in sound and fine grained granite were studied by using a direct shear equipment. The results obtained concluded that the ultimate shear strength of the filled discontinuities was always lower than that of the unfilled discontinuity and they influenced the traditional plots shear strength vs. thickness which in our ease show two branches: an upper one, presenting the decrease of the shear strength with the increase of thickness; and a lower one reproducing the increase of shear strength with thickness (rolling friction may control this behaviour).
Des essais de cisaillement direct en laboratoire ont ete faits pour etudier la resistance de discontinuites remplies de sols sableux sees. La resistance des discontinuites remplies a ete toujours plus basse que celie des discontinuites sans remplissage. En general, on considere que la resistance d'une discontinuite remplie se reduit avec l'augmentation de I'epaisseur. Mais les resultats obtenus montrent qu'il peut avoir 2 branches: une, traditionelle qui montre le decroit de la resistance avec I'augmentation de I'epaisseur, et une autre qui monte à partir d'une valeur plus basse (Ie frottement par roulement doit controler le comportement).
Die Scherspannung von, mit trockenem Sand aufgefuellten Granittrennflaechen, wurde durch direkten Schervesuch studiert. Die erziehlten Ergebnisse zeigen, dass die Scherspannung bei gefuellten Trennflaechen immer geringer war als bei ungefuellten. Diese Ergebnisse beeinflussten die traditionellen graphische Darstellungen von Scherspannungen hinsichtlich ihrer Dicke, welche in unserem Fall zwei Seiten zeigen: die Obere, eine Scherspennungsverminderung mit zunehmender Dicke; und eine Untere, die eine Steigerung der Scherspannung und Dicke verursacht (rollende Reibung kann dieses Verhalten erklaeren).
As filled or unfilled discontinuities represent the weakest surfaces in a fair or good quality rock mass, the behaviour of rock joints in shear has been investigated since the sixties and a number of papers reported these studies. Besides the need to assess correctly the spatial geometry of the single diseontinuities and of the several families of discontinuities in the rock mass, the determination of the ultimate shear strength for each joint appeared as the most important feature to study and laboratory tests were performed in order to evaluate the corresponding shear parameters. After gathering this information, the rock engineers (mainly, geotechnical, civil and mining engineers) were able to define the surfaces Where failure had the highest probability to occur and the potential volumes which could detach from the rock mass and they could design or construct the works or structures involving the rock mass
Thus, in this period, the relevance of the laboratory tests was emphasized. After selecting the weakest or the main representative discontinuities during the field survey; the samples were brought to the laboratory and were submitted to direct shear tests which were the most popular tests to evaluate or to assess the shear parameters of the sliding plains. In comparison with in-situ shear tests of weak plains existing in the rock masses, direct shear tests in laboratory were preferred
