Influence and Mechanisms of Suspending Agents on the Injectability of Cement Grouts in Fractures

ABSTRACT

Grouting serves as a primary method for seepage prevention and reinforcement in mining and underground engineering, where cement grouts are most widely used. However, as a solid–liquid two-phase system, the grout is prone to cement particle settlement attributed to flow velocity attenuation during diffusion, significantly degrading its seepage characteristics. Enhancing the suspension stability of grouts to improve injectability and effectiveness is currently a key direction in grout modification. This study systematically investigates the controlling influence and mechanisms of suspending agents on the fracture injectability of cement grouts through fundamental property tests, visual fracture grouting experiments, and mechanistic analysis of cement grouts with suspending agent dosages of 0.5 %–9 %. The results indicate that: (1) The viscosity of cement-suspending agent (C-SA) grouts increases exponentially with the dosage of the suspending agent; the bleeding rate decreases significantly with increasing dosage, achieving zero bleeding when the dosage exceeds 5 %. (2) The C-SA grout spreads within fractures following a pattern of “initial triangular accumulation–segmented cyclic transport;” the rate of grouting pressure increase initially decreases and then increases with higher suspending agent dosage, with an appropriate dosage enhancing injectability. Under the same grouting volume, the effective diffusion distance increases with dosage and eventually stabilizes. (3) Microscopic observation reveals that the suspending agent facilitates a transition of the grout from a “particle-dispersed” state to a “densified network framework,” where the compactness of the framework positively correlates with the dosage. This structural evolution reduces the bleeding rate and extends the effective diffusion distance. (4) The seepage of cement grout in fractures exhibits significant stratification, with a lower static particle deposition layer and an upper stable flow channel. The suspending agent inhibits particle settlement and widens the flow channel by constructing a network structure, balancing the resistance issue caused by increased viscosity thus enhancing injectability. This research can provide a reference for the modification and refined application of ordinary cement grouts.