Study on the mechanical response and failure behavior of the rock-like material with hole-bolt composite structure

To investigate the influence of bolt pre-tightening force and hole-bolt spacing on the mechanical responses and failure characteristics of rock-like materials with hole-bolt composite structures, a comprehensive set of physical tests was carried out. The findings suggest that enhancing the pre-tightening force improves the peak stress and elastic modulus of the material. However, these properties initially increase and then diminish with widening hole-bolt spacing. An increase in pre-tightening force results in more fractures around the hole, altering the material's failure mode from tensile-shear to purely tensile. Additionally, as the hole-bolt spacing expands, the tensile crack positioned above the hole progressively shifts away from the bolt, leading to a transition in failure mode from tensile to tensile-shear. Field tests confirm that the bolt force proximate to the pressure relief hole remains significantly greater than that at a distance, establishing hole-bolt spacing as a critical factor in anchorage stability.