A novel geological classification based grouting strategy in fractured rocks

Highly complex and concealed geological conditions result in grouting parameter design relying mainly on empirical methods. This study proposes a geological classification based grouting strategy (GCGS), integrating a grouting geological classification model and a maximum grouting pressure model, to quantify the grouting parameters in the curtain grouting process. The grouting geological classification model is developed to calculate the critical fracture aperture for a fractal fracture network and guide the selection of grouting materials. The formation permeability obtained from the water pressure test and the fracture density captured through borehole imaging are combined to characterize the grouting geological property based on the proposed geological classification diagram. The maximum grouting pressure model is further proposed to determine the allowable grouting zone, considering the coupling process of the Bingham fluid flow and the mechanical effect based on the Model I center fracture model. Sensitivity analysis is carried out to investigate the influence of fracture geometry and fluid rheological properties on the maximum grouting pressure. The proposed GCGS is applied at field grouting tests at the Dongzhuang hydraulic project. A better grouting effect can be achieved when the grain size of the cement grout is appropriate for the grouting geological model and applied grouting pressure is in the allowable range obtained from the GCGS.