Self-drilling hollow anchor bolt is widely used in the world, and its reaming effect makes the anchoring effect better. Reaming is to use a smaller drill bit for drilling, forming a large hole diameter, resulting in a larger grout body. The reaming effect is more obvious in soil nails and micropile.

Why can self-drilling hollow anchor bolt expand the hole? When drilling in slope or foundation with soil or broken rock, the inner wall of the borehole usually loosens by disturbance. Self-drilling anchor bolt has the function of grouting while drilling. The cement slurry can be ejected from drill bit’s holes under pressure, making the loose gravel washed and discharged out of the hole with the cement slurry. Thus, a firm and irregular hole wall formed. When grouting is completed, the cement slurry will solidify into a grout body larger than the drill bit diameter and with an irregular surface shape. This makes the grout body more compact and produces a good anchoring effect. According to relevant data, the grout body diameter is at least 20mm larger than drill bit. In rock and soil layers such as sandy soil and gravel soil, it is increased by 50 to 70mm compared with drill bit.

Based on the reaming principle of self-drilling hollow anchor bolt, it can replace conventional reinforced soil nail in construction. Conventional soil nail often uses reinforced anchor bar to drill holes with down-the-hole drill or auger drill first and then insert the steel. To ensure the anchorage effect and avoid difficulty inserting anchor bolt due to hole wall shrinkage or deformation, the actual hole diameter will be larger. For example, φ25mm steel bars usually need to drill holes with more than φ100mm. When using self-drilling anchor bolts for construction, φ32mm anchor bolts only need to be matched with φ76mm drill bits. It can form grout body larger than 100mm through smaller hole diameter and has a better anchoring effect under high-pressure grouting.