Grouting pressure distribution in a parallel fracture

Rock grouting is crucial for improving rock tightness in engineering projects. Grout, as a typical yield stress fluid, exhibits a complex flow behaviour characterized by a transition from liquid-like to solid-like regions. This critical transition between yielded stable flow and unyielded local flow complicates the accurate prediction of pressure decay but has received limited attention in grouting design. This study investigates the influence of the critical shear rate and the yield surface on pressure distribution during grout injection into a narrow, smooth fracture. A novel physical model was developed to simulate grout propagation and experimentally assess the limitations of the traditional Bingham model. The experimental results reveal a logarithmic pressure decay along the radial direction of penetration, which gradually approaches a linear trend as the grout nears full stoppage. Comparisons between experimental and analytical results indicate that the Bingham model tends to overestimate pressure distribution. By expanding the plug width to 1.01–1.3 times that predicted at zero shear rate, or by increasing the critical shear rate to approximately 4–8 s⁻¹, the modified analytical model aligns closely with experimental observations. These findings advance the understanding of grout rheology and its impact on pressure distribution, offering practical insights for minimizing hydraulic jacking risks and optimizing grouting strategies in fractured rock masses.