Study on the anchorage mechanism and roof stability control technology of bolts in fractured or weak surrounding rock

The effect of bolt support in mining roadways with fractured or weak surrounding rock is poor, and the roof easily loses stability. Studying the support control technology of bolts on fractured surrounding rock is necessary. Based on the theories of pressure arches and combined arch support, the bolt anchorage and anchorage effect angle are proposed a model is established, and the optimal bolt anchorage is calculated. The influence of related factors on the bolt anchorage and the scope of bolt action are analysed via numerical simulation and experimental methods. The pretightening force of the bolts and the spacing between the rows of bolts are positively correlated and negatively correlated with the bolt anchorage, respectively. The compression zone conforms to the reinforced arch state when the bolt end is anchored. The experimental work shows that the maximum spacing a of the anchor rods and the length L of the anchor rods in the surrounding rock satisfy 4.28a < 2L < 5a. The support of fractured surrounding rock is discussed, and the concept of roof fall prevention and control with an increasing or constant pretightening force, high surface strength and reasonable support density as the core principles is proposed. A field test of the Youzhong Coal Mine shows that the corresponding support effect is good and that this work provides a new method for roof support of fractured surrounding rock.