Self-drilling Anchor Bolt

Self-drilling anchor bolt integrates drilling, grouting, and anchoring into one, with a simple construction process, high construction efficiency, and good anchoring effect, which can effectively solve the problems of easy collapse and difficult hole formation during drilling. Therefore, it applies to a wide range of geological conditions, such as siltstone, miscellaneous fill, strongly weathered rock, pebble layer, and conglomerate layer.

Application fields

Self-drilling anchor bolt is a new type of support material, mainly used in tunnel and underground engineering, slope stabilization engineering, ground and foundation engineering, such as various slope support, foundation support, tunnel pipe umbrella support, foundation support of transmission towers or wind power towers, existing buildings and structures repair and reinforcement. It is used for temporary support and permanent support in the pre-project period, which can effectively enhance the own stability of soil and rock, and has become an indispensable material in geotechnical anchorage engineering.

Product advantages

• It is suitable for all kinds of geological conditions.

Especially that are not easy to be constructed by traditional anchor construction techniques, such as geology prone to the collapse.

• There is no limit to the drilling depth of self-drilling anchor bolts.

While conventional anchors have a relatively shallow drilling depth due to limitations in both anchor material and drilling equipment, self-drilling anchor bolts can achieve much greater depths thanks to their low drilling resistance.

• Suitable for construction in narrow spaces.

The self-drilling anchor bolt’s length can be cut or extended as needed, with general specifications of 2m, 3m, 4m, and 6m.

• Simple process.

Self-drilling anchor blots complete drilling, grouting, and anchoring in one drilling, simplifying the process and speeding up the construction.

• It is beneficial to stabilize the hole wall.

The cement grout with a water-cement ratio of 0.4~0.5 is supplied under pressure by a screw grouting machine while drilling so that the grout fills the hole and the fissures of the geotechnical body rapidly and is absorbed and cured by the hole wall to ensure the stability of the hole wall.

Self-drilling anchor bolts are available in two series: R thread and T thread. The R series includes models such as R25, R28, R32, R38, R51, while the T series includes T30, T40, T52, T64, T73, T76, T103, T111, T130 and T150 models. Customers can choose different product types and models according to different engineering needs.

Composition of self-drilling anchor bolt

Self-drilling anchor bolt consists of six major accessories, a hollow anchor bar, a drill bit, a coupler, a plate, a nut, and a centralizer.

Hollow anchor bar

It combines an anchor rod with a drill pipe and has the dual function of drilling and grouting. The hollow anchor bar is made of seamless steel pipe of high tensile alloy steel, and the tensile strength and yield strength can meet various complex geological conditions according to the design requirements. Additionally, it features continuous R thread and T thread along its body for easy cutting and connection during construction.

Drill bit

The drill bit is made of wear-resistant metal, and has flush hole. The selection of the appropriate model according to the rock and soil conditions. Commonly used drill bits include hardened cross-cut drill bits, tungsten carbide cross-cut drill bits, clay bits, hardened button drill bits, and tungsten carbide button drill bits.

Coupler

The coupler is a rod extension part, and it is of equal strength to the hollow anchor bar. Two rods can be connected seamlessly by the coupler, and there will be no grout leakage when grouting.

Plate

The plate is installed at the tail of the anchor bar, between the nut and the rock formation. There are two shapes: domed and flat plates. Domed plates are generally used in soil nail applications, while flat plates are used in micropile applications.

Nut

The nut is a device that has internal threads, which transmit the anchoring force of the hollow anchor bar to the plate and lock it in place. One end of the nut has a rounded surface. When there is a slight angle between the plate and the rod, it can fit with the plate to ensure proper force transmission. If the angle is large, you can choose a domed nut or add a domed washer. Cooperating with the hollow anchor bar, they provide equal strength and the effect of preventing rock mass deformation.

Centralizer

The centralizer is a component used to realize the centering of the hollow anchor bar in the hole, which is installed on the hollow anchor bar in front of the coupler and realize the thickness of the grouting layer not less than 20mm outside the hollow anchor bar, thus ensuring the uniform thickness of the slurry around the rod during the construction of the self-drilling anchor bolt. The anchoring effect is further enhanced.

Construction process of self-drilling anchor bolt

• Material preparation

Before using the self-drilling anchor bolt, check whether the drill bit and anchor bar are damaged. If problems are found, solve them promptly, and construction can start after they are normal. Then, assemble the hollow anchor bar with the drill bit to be used and prepare the coupler and anchor bar.

• Drilling and grouting

The drilling construction of self-drilling anchor bolts generally uses a special drilling rig for self-drilling anchor bolts, which can perform high-frequency impact and high-speed rotation to speed up drilling. During drilling, the rod and grouting hole are flushed with pressurized water or cement slurry prepared according to a certain water-cement ratio through the screw grouting machine to avoid being blocked by debris. Then use a screw grouting machine for grouting to achieve the effect of simultaneous drilling and grouting.

• Lengthening anchor bar

Usually, the length of the self-drilling anchor bolt is 3m, 4m, 6m, etc. If the drilling depth designed in the project is relatively deep, it is necessary to lengthen the rod with a coupler and then drill and grout.

•  Install plates and nuts

The plate and nut are essential accessories for the self-drilling anchor bolt, which installed at the end of the anchor bar. The plate goes between the nut and the rock to transmit the anchoring force of the hollow anchor bar to the plate. By applying preload, it presses against the rock surface to prevent any deformation.