Research and application on in-situ enhancement mechanism of coal-slurry interface in grouting modification of coal roadway

Grouting modification is an effective means for reinforcing fractured coal roadways, with the regulation of the coal-slurry interface being the core of grouting modification. This article analyzes the current status and existing issues of grouting modification technology in coal roadways and introduces a new method and material for in-situ reaction enhancement of the coal-slurry interface modification, along with its application effects in underground mines. Focusing on the key issue of the in-situ reaction mechanism for enhancing the bonding of the coal-slurry interface, this study develops a novel inorganic grouting material based on the distribution and morphology of coal fractures, as well as the physical topography and chemical structure of the coal surface. A pioneering nanoparticle delivery system is created to achieve compatible delivery of the components of the inorganic grouting material. The nanoparticles exhibit a typical core-shell structure and pH-responsive characteristics, remaining stable in neutral environments during storage and transportation. However, in the alkaline environment of cementitious material hydration, the nanoparticles decompose and release internal active molecules. These molecules enhance the interface by forming hydrogen bonds at the coal-slurry interface. Combined with dynamic interface wetting experiments, the structural evolution mechanism of the in-situ reaction between organic components and chemical groups on the coal surface is elucidated at the molecular level. The active molecules delivered by the nanoparticles use the terminal hydroxyl groups on the coal surface as initiators to undergo in-situ reactions at the coal-slurry interface, generating polymer macromolecules. These macromolecules act as "molecular bridges" at the coal-slurry interface, improving the bonding strength and the effectiveness of grouting modification. During the hydration of the grouting material, the nanoparticles serve as crystal nuclei, promoting the nucleation and growth of cementitious material crystals, resulting in a more regular and denser crystal structure. After grouting, the anchoring force of the coal mass increased from 93.5 kN to 213 kN. Following grouting, the strength of the roadway improved from 26.4 MPa to 33.5 MPa. Additionally, the roadway deformation decreased from 1300 mm to 200 mm. Meso-mechanical and macro-mechanical experiments validate the significant enhancement of the interface strength and mechanical strength of fractured coal through grouting modification. Underground tests demonstrate that grouting modification significantly improves the anchoring performance of bolts in coal, while also enhancing the strength of the roadway roof strata and the coal walls, providing an effective method for reinforcing soft and fractured surrounding roadways.