Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The most commonly used method for assessing the hydraulic erodibility of rock is Annandale’s method. This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten’s index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to the intact rock and the rock mass, such as the compressive strength of intact rock, the rock block size, the discontinuity shear strength and the relative block structure. To quantify the relative block structure, Kirsten developed a mathematical expression that accounted for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonal fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint set is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonal fractured system has a significant effect on Kirsten’s index and, as a consequence, on the assessment of the hydraulic erodibility of rock.