Abstract: In response to the poor cementation condition of loose soft rock roadway and obvious features of layers of granular mechanical behavior, this paper has introduced granular material to study the instability mechanism of loose soft rock roadway. Based on the analysis of static mechanical behavior of granular materials，the research has obtained Coulomb Yield Criterion of granular material; combined with the present specific situations of a certain mine field, the roadway supporting mechanical model has been constructed and surrounding rock plastic zone extension formula under the poor cemented geological conditions has been obtained. By analyzing the results, this paper has shown that the roadway plastic zone radius decreases as the ratio of the strength of initial support and the primitive stress increases; but the plastic zone is still very large. So only by raising the strength of initial support of the roadway can we control the expansion of such roadway plastic zone effectively, and it also needs to improve the physical and mechanical rock properties and increase the carrying capacity of supporting structure. As a result, the “pre-grouting + anchor net shed + bolt-grouting” united supporting scheme has been proposed, which has achieved good efficiency and ensured the smooth construction process.

Key words: granular material, loose soft rock, plastic zone, grouting, united supporting