Investigating the scale effect on strength and failure mechanism of roadway surrounding rock

An analysis model for surrounding rock was established, considering excavation-induced damage and failure zones. Meso-mechanical parameters for Particle Flow Code (PFC) were calibrated using sandstone test data from Brazilian splitting, uniaxial, and triaxial tests. The strength variation of multi-scale surrounding rock was investigated: at a fixed width of 50 mm, the strength decreases linearly as height increases from 20 to 80 mm, then increases with height from 80 to 300 mm; at a fixed height of 100 mm, the strength increases linearly with width from 20 to 300 mm. The ratio of damage stress to strength(multi-scale surrounding rock with a width of 50 mm)/the second ratio of damage stress to strength(with a height of 100 mm) does not change with height/width, which is approximately 0.91. The mechanical mechanism of only shallow failure or zonal disintegration characteristics of the surrounding rock were revealed by analyzing the failure characteristics of multi-scale surrounding rock: under shallow burial conditions, a narrow stress concentration zone leads to only shallow failure, whereas under deep burial, a wider stress concentration zone leads to both shallow failure and zonal disintegration. These findings provide a theoretical basis for stability assessment of underground roadway surrounding rock.