Rockburst-Specific Flexible Protection Net (RFPN) for Tunnels: Creation, Characteristics, and Preliminary Application

In this study, the principle of the protection net used for rocks falling from a slope was adapted to develop a prototype of a flexible protection net system, which includes a wire-rope net, support cables, and expansion-type anchor bolts for preventing and controlling rockbursts in tunnels. First, a physical test was performed to obtain the ejection velocity of bursting rocks under diverse initial stress conditions. Then, the dynamic process of rocks impacting the protection net was numerically calculated to obtain the nonlinear dynamic response. The capacity of the protection net to intercept rockbursts was verified in a physical experiment. Finally, the effectiveness of the protection net in a tunnel was evaluated through a case study. The results indicated the following: (1) the ejected rock velocity increases with the initial stress, and the maximum velocities of the ejected rocks for different rockburst grades were 2.67, 3.07, and 5.63 m/s in the rockburst ejection test of a tunnel equipped with a rockburst-specific flexible protection net (RFPN). (2) The wire-rope net is the main energy-absorbing component of the protective net. (3) The wire-rope net and bolts are the main bearing capacity components of the protective net. (4) The flexible protective net system can effectively prevent small or moderate rockbursts, and increases the construction speed significantly by 23.8% when compared with the original design.