Support mechanism and numerical analysis of full-length prestressed self-drilling bolts in fractured roadway surrounding rock

Conventional resin-anchored bolts rely on stable boreholes and reliable end anchorage in fractured roadway surrounding rock, whereas conventional self-drilling bolts have good construction adaptability but limited active pretensioning capacity. To improve bolt installation reliability, pretension retention, and grouting reinforcement in fractured surrounding rock, this study proposes a full-length prestressed self-drilling bolt that integrates self-drilling installation, end grouting bearing, active pretensioning, and full-length grouting reinforcement. A theoretical model for bolt pretension transfer was established, and a single-bolt pretension-transfer model and a roadway-support numerical model were developed in FLAC3D. The mechanical responses of threaded steel bolts, conventional self-drilling bolts, and full-length prestressed self-drilling bolts under different pretension levels were compared. The results show that, during initial pretensioning, the proposed bolt can maintain a high axial force over most of the bolt length and transfer pretension to the deeper rock mass through the end anchorage section, forming a more continuous axial compressive-stress influence zone. Under the adopted numerical-model conditions, the proposed bolt reduced roof subsidence, rib deformation, and plastic-zone development relative to conventional support schemes. The results indicate that the synergistic action of end grouting bearing, active pretensioning, and full-length grouting reinforcement can improve pretension transfer and surrounding-rock control in fractured rock masses, thereby providing a new bolt-grouting collaborative support method for active support of fractured coal-rock roadways.