Study on dynamic mechanical properties of prestressed bolt group under impact load

Abstract

To study the dynamic behaviour of the bolt group system caused by the impact load of a deep roadway, a drop hammer impact test of a single bolt and a bolt group of left-handed screw steel was performed using a self-developed bolt group or single bolt collaborative impact resistance test device. The influences of the mechanical law of the impact force of the bolt and the three parameters of prestress, bolt spacing and drop hammer impact height under an impact load were studied. LS-DYNA numerical simulation software was used to analyse the loading deformation process of a single bolt and bolt group under an impact load. The time–history curve of the impact force was compared with the experimental results, and the two were in good agreement, verifying the correctness of the numerical simulation. Based on this, the strain response law of the rod body when the bolt group was subjected to an impact load was explored. The results show that under the same impact energy and prestress state, the oscillation attenuation time of a single bolt after reaching the peak impact force is significantly longer than that of bolt group The strain peak of a single bolt is greater than those of bolt group. The energy of the bolt group system is dispersed owing to the mutual support of each unit bolt, and this situation becomes increasingly evident with a decrease in bolt spacing. Therefore, the bolt group has better integrity than single bolt, and reducing the bolt spacing can make the effective compressive stress zone formed by prestress more concentrated, enhance the overall stiffness of the bolt group and improve the impact resistance of the bolt group. When the impact energy and bolt spacing are constant, strengthens the influence of bolt spacing on the overall stiffness of the bolt group system and significantly improves the anti-deformation ability of the bolt group system. Therefore, the peak impact force of bolt MG2 increases with the increase of prestress. Under the same spacing, with the increase in impact energy, the bolt MG2 produces greater axial deformation to adapt to the larger impact energy, resulting in a longer impact time, whereas the strain curve of the side bolt MG1 does not change, indicating that the stress field distribution of the bolt group support system does not change with the change in impact energy.