Abstract:
A major simplification to the flow characterization of cement-based grouts has been the Bingham rheological model. It’ s use has aided in the development of several analytical tools for estimating grout propagation in rock fractures; however, from a practical standpoint the simplifications entail several shortcomings that need to be systematically addressed. For example, cementitious suspensions are known to be thixotropic yield stress fluids that display some characteristic rheological behaviour, i.e. wall-slip, substantial shear rate and time dependency. These prominent flow features that mostly affect the grout propagation, especially at low shear rates are not considered when the Bingham model is used. As such, the consequences of overlooking such crucial phenomena whilst aiming for simplicity in design remains relatively unknown. Within this work, we show how the Bingham model can be better used for cement grouting design, whilst considering the shear rate aspects and appropriate stop criteria within the framework of the Real Time Grouting Control (RTGC) method. Our design suggestions are based on fundamental analysis of Bingham fluid radial flow and current knowledge on cement grout rheology, as evidenced by rheological experiments. In addition, we contribute to the existing design procedure by presenting a shear rate-based nomogram that can readily be used for practical rock grouting design. Keywords: Rock grouting, radial flow, cement grouts, Bingham model, critical shear rate, wall-slip