Experimental investigation of the fracture grouting efficiency with consideration of the viscosity variation under dynamic pressure conditions

摘要

Grouting techniques have been extensively and effectively implemented to prevent water bursts originating from limestone aquifers in underground mining. Using widely employed grout with time-varying viscosity, promoting the effective propagation of slurry in fractures, especially fractures with narrow apertures, and improving the grouting efficiency (GE) are critical issues that remain unsolved. In this study, an experimental investigation of the fracture GE was conducted considering the dynamically changing injection pressure for viscosity--time-dependent grout using a fracture model constructed from acrylic glass. Three grouting pressure adjustment schemes (periodic-increasing pressure, constant pressure and periodic-reducing pressure) and two narrow hydraulic apertures (200 and 250 mu m) were selected for testing. Each trial utilizing the fracture replica was filmed, allowing the advancing slurry to be analyzed versus the propagation distance over time. The measured penetration lengths and fracture GE were then compared with the simulation data. The measured penetration length versus time curves agreed well with the theoretical data. Moreover, the pressure adjustment mode and grout rheology significantly impacted the GE. In general, the periodic increases in pressure reduced the GE, which decreased by 4.16% and 10.19% for the slow- and rapid-growth viscosity grouts (G1 and G2), respectively. However, phase reduction of the pressure considerably enhanced the GE. Relative grouting efficiency (RGE) was increased by 3.18% and 10.08% for G1 and G2, respectively, indicating that a step-by-step reduction in the injection pressure can effectively improve the GE for the remarkable rheological grout during the grouting process. Additionally, the tests suggested that the hydraulic aperture width has an unclear effect on the GE of microfissures.