Abstract: In order to explore the reinforcement effect of chemical slurry on fractured coal,the modified urea-formaldehyde
resin slurry was used to carry out grouting test on fractured coal samples. Through macroscopic mechanical test and microscopic
observation,the mechanical properties and microstructure characteristics of coal samples after grouting were analyzed,
and the chemical grouting reinforcement mechanism of fractured coal body was revealed. The results show that the anisotropy of
compressive strength and tensile strength of coal is significant. The compressive strength and tensile strength of the test coal
sample when the compressive surface and the tensile surface are parallel to the bedding are 1. 62 times and 0. 27 times that of
the vertical,respectively,and the failure characteristics are obviously different. The bedding surface is a typical weak surface.
The modified urea-formaldehyde resin has a significant reinforcing effect on the fractured coal body. For the coal sample with
cracks developed along the bedding,when the loading direction is perpendicular to the bedding plane,the compressive strength
of the fractured coal sample after grouting is restored to 94. 1% of the raw coal,and its tensile strength is basically the same as
that of the intact coal sample. When the bedding plane of the loading direction is parallel,the compressive and tensile strength
of the fractured coal sample after grouting is 1. 26 times and 1. 08 times that of the raw coal sample. The slurry realizes multiscale
reinforcement from macro-cracks to micro-voids. The slurry can effectively penetrate into the micro-cracks and micropores
on the surface of the coal body,and form a dense slurry-coal chimeric structure,which can greatly improve the bonding
force of the slurry-coal interface. The slurry not only bears and transmits stress as a skeleton,but also effectively eliminates the
damage of cracks to the coal body and greatly eliminates the stress concentration caused by cracks. In the site of broken coal
reinforcement,the slurry effectively forms a transaction circle,showing its good permeability and diffusion performance and reinforcement
effect.

Key words: fractured coal bodies,grouting reinforcement,bedding plane,modified urea-formaldehyde resin,electron microscopy
scanning