Self drilling rock bolts are the basic component of roadway support in coal mines. They are not only used in mines but also in engineering technology. They are mainly used in reinforce slopes, tunnels and dams. In general, the composition of self drilling rock bolts mainly has the following three necessary factors:

1. A rod with higher tensile strength than rock and soil.

2. One end of the rod body can be in close contact with the rock and soil body to form friction (or adhesion) resistance.

3. The other end of the rod body located outside the rock and soil body can form radial resistance to the rock and soil body.

How does the self drilling rock bolt break?
1. The tail of the rock bolt is the part of the entire rod body with complex forces and easy to break. A stress analysis was performed on the threaded section of the anchor rod. It was found that 2-3 times the stress concentration of the threaded portion occurred due to the reduction in diameter; because the spherical rotation center between the tray and the ball cushion was unreasonable, resulting in self-locking between the two spherical surfaces and causing the force of the rod deteriorated sharply and even cracked.

2. When the angle of the anchor device is too large and the tensile stress reaches a certain value, a long period of load will cause the thread section of the tail of the anchor to bend and show cracks or even cracks; when the applied pre-torque is greater than 600 N'm, The composite stress is close to the yield stress of the data. The anchor first cracks from the twists and turns, and the crack expansion causes the anchor to crack when it does not reach the breaking tension.

3. The combination of tension, bending, torsion and tension, bending, shearing and torsion are the common stress states in the process of the underground bolt device. The closer to the fixed end, the greater the stress, so the unfavorable orientation is the fixed end.

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