Characterization of fractured rock for grouting design using hydrogeological methods

This paper aims at briefly presenting a methodology for characterization of fractured rock for grouting design using hydrogeological methods. The conceptual model is based on a grouting fan and is built up by fractures inferred from hydraulic tests and geological mapping. Instead of the commonly used Lugeon value, the specific capacity (Q/dh i.e., flow divided by difference in hydraulic head) is central since it has shown to be a robust parameter, which can be related to transmissivity and fracture aperture. Fracture aperture is important for grouting design due to its influence on both penetration length and grout take. The methodology described for estimation of transmissivity and aperture distributions has potential for further development for computer use, which would enable a fast analysis of data from hydraulic tests and geological mapping at a working site. Based on aperture distribution and expressions describing the spreading of grout, the choice of input parameters such as grout properties, pressure and borehole distance could be improved. Furthermore, the transmissivity and aperture distributions for probe holes give a general description of rock, which is used for the interpretation of data from individual grouting boreholes. This description of fractured rock for grouting should be a good basis for further discussions and development as well as facilitating the choice of strategy.