As an economical and efficient reinforced method, Anchor bolt has been applied largely in civil construction, tunnel, hydroelectric station and coal mine, etc., which can save plenty of materials and cost in actual projects.
Anchor bolt combines drilling, grouting and anchoring together. Drilling machine pushes rock bolt into stratum, injection pump helps slurry full of drill holes and have good anchoring effect.
Anchor bolt is a main supporting method in geotechnical project, which combines functions of drilling, grouting and anchoring together. It shows that there are three stages during the loading process of anchor bolt:
1. At the beginning of anchor bolt’s installation, grouting is finished, while the bonding force between grouting materials and soil layer is not formed. At this time, soil nail bears a little force.
2. Grouting materials bond anchor bolt to stratum. Rock bolt produces tension gradually with the increase of excavation depth and then it concentrates tension on the position of bonding stratum. Closing to the stratum, the tension is maximum and it decreases gradually.
3. When anchor bolt digging enough depth, most parts of anchor bolt are in slip crack range. Internal force has decreased from middle part to both sides.
When anchor bolt has got ultimate load, there are grip force of anchor bolt body, friction force between soil and anchor bolt and shearing strength, etc.
The grip force and shearing strength are smaller in soil than rock conditions. When anchor bolt is in soil condition, it will be damaged by shearing strength, while in rock condition, it will be damaged by grip force.
Also, the friction force needs to be considered when confirming bearing capacity in soil conditions. It demands that the standard compressive strength of mortar stone body should not less than 20MPa in soil condition and 30MPa in rock condition.