There are several supporting theories of anchor bolt:
1. The theory of suspension.
To avoid damage, unstability and collapse of weak stratum, suspending it on stable stratum. The tension bore by anchor bolt is from the weight of suspended stratum.
2. The theory of combination beam.
Squeezing stratum in the range of anchoring tightly to increase friction force, avoid slide, prevent separation layer and enhance self-support ability. The maximum bending strain and stress will decrease largely by compressing several thin stratum into a thicker one.
3. The theory of compound arch.
In weak and broken stratum, pressure stress of anchor bolt distributes in the form of cone. The distance among each anchor bolt is small enough to form an even compression zone (pressure-bearing arch), which can bear load of radial direction. The strength will be improved and supporting capacity will be enlarged.
4. The theory of largest horizontal stress.
The horizontal stress of mine has obvious directivity, it is usually greater than vertical stress. Under the function of largest horizontal stress, stratum is easy to have shear fracture, swell and deformation, anchor bolt has the effect of restraint.
5. The theory of reinforcement.
With the formation of bearing structure by anchor bolt and surrounding rocks, its supporting strength will be increased, ultimate strength and residual strength of surrounding rocks will be improved. To a certain extent, it can control plastic deformation and keep stable of roadway.