Experimental study on bearing characteristics of bolt-grouting support in shallow fractured surrounding rock of roadway

To clarify the bearing characteristics of bolt-grouting support in shallow fractured surrounding rock of roadway, comparative bolt-grouting bearing capacity test was carried out with different rock particle sizes, lithologies, and number of bolts. The results show that: 1) the bearing capacity of the bolt-grouting increases first and then decreases with increasing the particle size. Compared with the non-anchored specimens under the same conditions, the peak stress of the anchored specimens increases by 53.38% on average, and the peak strain decreases by 46.43% on average. 2) Under anchored condition, the free surface opposite to the supporting surface and its vicinity are the preferred area for macro-fracture development. The failure of supporting surface generally lags behind the free surface, and the specimens gradually transit from mainly tensile failure to tensile-shear mixed failure; tensile failure is the main failure mode of specimens under the condition of no anchor. 3) With the increase of bolt number, the bearing capacity of bolt-grouting increases gradually, but the growth rate slows down gradually. The peak strain slows down, which is consistent with the inflection point of peak stress growth. 4) The specimens have three characteristics of progressive destruction: firstly, the cracks generated before peak stress continue to propagate after peak stress; secondly, the surface material of support surface spalls with the crack stretching; thirdly, the cracks gradually develop from surface to inside of the specimens, the rock fragments fall off first, and then the macro-damage develops to the anchor area, resulting in the loss of overall specimen bearing capacity.