Theoretical and experimental study on cement grout penetration into fractures with a new magnetic tracking method

<p dir="ltr">Rock fracture grouting is a vital technique for enhancing rock mass stability and controlling groundwater inrush in underground engineering projects. However, its application remains largely empirical due to a limited fundamental understanding of grout flow mechanisms in narrow fractures and the inability to accurately determine the extent of grout penetration within opaque rock masses. This thesis pursues two main objectives: to deepen the fundamental understanding of cement grout flow behaviour within fractures, particularly the mechanisms governing its penetration and stoppage, and to track the grouted area by developing a non-destructive magnetic method.</p><p dir="ltr">The research integrates theoretical modeling, numerical simulation, and physical experimentation. To advance the understanding of grout flow, especially near the stoppage point, a novel virtual bond model was developed to describe grout thixotropy based on interparticle interactions. The motion of cement particles under applied force was simulated using 3D discrete element methods (DEM). Furthermore, a physical model was developed and controlled experiments were conducted to investigate pressure distribution and penetration behaviour in a smooth fracture, considering the effect of critical shear rate and plug width of grout. A novel magnetic tracking method was developed and experimentally validated, showing that incorporating a small amount of magnetite powder makes the grouted area magnetically detectable. Building on this, analytical solutions for magnetic forward modeling were derived, and a magnetic inversion algorithm was developed to localize grouted area geometry from multiple magnetic anomaly observations.</p><p dir="ltr">Key findings demonstrate that the developed virtual bond model effectively captures cement grout thixotropy from a particulate level. Analysis of pressure distribution highlights limitations in traditional models and shows how factors like critical shear rate and plug width, particularly yield stress, significantly control pressure decay during penetration. The magnetic tracking method is validated as a feasible, non-destructive method for visualizing grout extent, and the inversion approach successfully estimates key geometric parameters of the grouted area. This thesis provides valuable fundamental insights into grout behaviour and presents a promising new approach for evaluating grouting performance in the field.</p>