Experimental determination of fractures and conduits and the applicability of Cubic law in closed fractures

A laboratory experimental method has been developed to obtain the hydraulic head loss of either the closed fractures or conduits based on balance of energy. It was found that the linearity between hydraulic head loss and flow velocity decreases as the aperture increases, based on which a possible division of fractures and conduits is proposed. The results of the division show that a closed flow structure with less than 1.4635 mm aperture can be defined as a fracture whilst a closed flow structure with more than 1.8375 mm aperture can be defined as a conduit. The flow structure with an aperture of 1.6000 mm is in the transitional area of fractures and conduits. In addition, the Cubic law could not exactly describe the relationship between hydraulic head loss and velocity when applied to closed fractures in these investigations. The effects of deviations from ideal conditions when applying the Cubic law caused an apparent reduction in hydraulic head loss and may be incorporated into the Cubic law by adding the effects of both the width of the fracture and the ratio of the width to the aperture. The coefficient n was introduced to indicate the influence of the ratio of the width to the aperture on hydraulic head loss.