A proposal for a Secondary Permeability Index obtained from water pressure tests in dam foundations

The permeability of fissured rock masses is strongly related to joint characteristics; degree of jointing, opening, continuity and presence of weathering in-fill. Inspection of the drill core boxes allows for estimating to the degree of jointing and opening. Nevertheless, continuity and weathering in-fill cannot be detected. In this sense, the rock mass quality is defined by the Secondary Permeability Index (SPI). The rock mass foundation can be zoned regarding different quality classes and each zone treated separately. The proposed method requires the interpretation of the results, from which the water pressure test effect in the test section is confirmed and the rock mass classification criteria are applied. In this sense, the hydrofracturing appearance has a special importance. The rock mass quality of the test section obtained from SPI completed with the degree of jointing of the drill core acts as a useful reference for ground treatment design. Finally, a theoretical approximation to the maximum water injected distance reached into rock mass from the SPI is suggested.