First you need to confirm drilling depth, and it shall not be less than effective length of rock bolt bar, extra length of rock bolt is usually less than 100mm. Drilling direction should be perpendicular to excavation surface. If excavation surface is not parallel to anchor surface, vertical deviation from excavation surface should not be greater than 20°; self drilling rock bolt arrangement is relatively concentrated, so waterproof work of external under basement floor is more convenient.
The drilling depth of self drilling rock bolt should not be less than the effective length of the anchor rod body, overlength of rod body should not be greater than 100mm. The drilling should be straight, and drilling direction of the system should be perpendicular to the excavation surface.
Advantages and Disadvantages of Self Drilling Rock Bolt
For the case where self-drilling rock bolt have insufficient bearing capacity, due to the fact that with more self-propelled anchors sharing, the stronger resistance forms. Let’s look at the advantages and disadvantages of 3 self-propelled anchor arrangements.
- Self drilling rock bolts installed in points around columns; Advantages: the vertical force transmitted from upper structure can be fully used to balance out some of water buoyancy; due to the concentrated arrangement of rock bolts, basement floor waterproof construction is also more easy, there is more resistance due to more anchor rod sharing in case bearing capacity of rock bolt at certain point is not enough.
- Self-drilling rock bolts are installed in concentrated line, The vertical force transmitted by the superstructure cannot be fully used to balance out some of the water buoyancy (personally, it is considered unsafe if considered, for floor beams with a span-to-height ratio less than 6, the vertical force transmitted by the superstructure can be properly considered To balance out some of the water buoyancy), it is required to be anchored in hard rock, not suitable for soft rock and soil; the basement floor plate is relatively reinforced.
- Self-drilling rock bolts are uniformly arranged in the surface, evenly under the basement floor; advantages: applicable to all soil and rock masses; basement floor beams and slabs have less reinforcement. Disadvantages: The vertical force from upper structure cannot be fully used to balance out some of water buoyancy self-drilling rock bolt.