An enhanced multi-stage energy-absorbing cablebolt for rockburst control in deep underground excavation

Deep underground excavations trigger repeated energy releases that often fracture conventional rock support systems. To address this issue, an enhanced multi-stage energy-absorbing cablebolt (MSCB) is proposed. The energy-absorbing system consists of an expandible octagonal tube (EOT), a contractable circular tube (CCT), and a constraining sleeve. Energy is absorbed sequentially through expansion and frictional deformation of the octagonal tube, plastic contraction of the circular tube, and tensile plastic deformation of the cablebolt. By controlling the yield thresholds and deformation paths of these components, the anchoring force increases stepwise to accommodate rock mass deformation. Based on frictional and plastic mechanics, mechanical models were established for each energy-absorption stage. Laboratory pull-out tests and numerical simulations show that the proposed cablebolt achieves a peak load capacity of 320.48 kN, a deformation capacity of 693.65 mm, and a total energy absorption of 166.37 kJ. The first stage provides an anchoring force of 153.42 kN with 73.32 mm deformation and 14.02 kJ energy absorption. The second stage maintains a stable load of 262.18 kN while accommodating 484.89 mm deformation and absorbing 140.57 kJ. In the third stage, the load increases to 320.48 kN before failure, with 43.88 mm deformation and 13.62 kJ energy absorption. Dynamic impact tests show that the cablebolt can withstand multiple consecutive 40 kJ impacts, producing an axial displacement of 744.01 mm and absorbing 147.67 kJ of energy. Good agreement among theoretical, numerical, and experimental results confirms the effectiveness of the proposed cablebolt for mitigating rockburst hazards in deep underground engineering under repeated energy-release conditions.