Split sets / friction anchors have been used as a primary roof support in the underground mining environment for many years. The anchor consists of an open seamed high tensile Supraform S420 steel tube with a face plate. One end is tapered for easy insertion into a pre-drilled hole. It is installed by driving the assembly into a marginally smaller hole than the split sets diameter and the welded steel ring then provides the necessary support to hold the washer plate in place. The set then uses friction to anchor itself along the whole length of the bolt by relying on the radial spring force generated through compression of the tube. Split set technology is used worldwide by many mines for an extensive variety of mining applications.
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Key Advantages of using Split Sets
Pull testing on the split set friction anchors proves their superiority in anchoring themselves inside the drilled hole. Once the product has been installed, the spring loading allows the anchor to adapt to minor changes in the ground conditions. This is an important advantage over inelastic bolts that are unable to adapt to changing ground conditions.
The split set is a popular choice due to its easy installation. Once the hole is drilled, the driver tool drives the anchor into the wall. Installation time is typically less than a minute and there is no waiting time for grout to set, no tightening or torqueing and no ongoing maintenance is needed after installation. This saves time, labour and additional grouting or resin expenses.
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Coal mining needs to excavate a large number of tunnels underground. Tunnel support can keep the tunnel smooth and the surrounding rock stable, which is of great significance to the construction and production of coal mines. Split set is one of the main materials for tunnel support, which has the characteristics of simple installation and convenient use. There are many types of rock bolts, and a split set is one of them, which is used in geological engineering and other fields. Because of its simple installation and easy use, it is gradually becoming popular.
Split set is a new type of anchor bar that is full-length anchored and actively reinforces the surrounding rock. It is a high-strength steel pipe with longitudinal slits. When installed in a borehole slightly smaller than the diameter of the pipe, it can immediately exert radial pressure on the hole wall at full length and prevent the surrounding rock from sliding down the friction force. In addition to the supporting strength of the anchor bar pallets, the surrounding rock is in a three-derection stress state and achieves rock stability.
In the case of the anchoring movement of surrounding rock caused by blasting vibration, the anchoring force increases significantly in the later stage. When the surrounding rock is obvious displacement, the bolt does not lose its support resistance.
Install the split set in a borehole smaller than the diameter of the pipe. At this time, three forces are acting on the surrounding rock. One is the radial pressure on the hole wall within the entire length of the split set. One is the friction force to prevent the surrounding rock from sliding down, and the other is the supporting force of the split set pallet. These three forces make the surrounding rock more stable.
Split set includes an anchor rod and tray.
1. The anchor rod is rolled into a tubular shape from a thin plate with a full-length longitudinal seam, it is used as an anchor bar in the field of support, so it is called a split set.
2. The tray is equivalent to the plate. It is square with a bowl-shaped protrusion in the middle and is the component that transmits the tensile force received by the anchor bar to the surrounding rock. The tray used for split sets is usually thin plates.
1. High-strength alloy strip steel is used as raw material. One end is forged with a tapered head for the anchor bar to insert the hole, and the other end is welded with an iron hoop to bear the weight of the plate.
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2. Installation is simple and can be completed only by impact.
3. Anchorage agent is not required.
4. The friction between the anchor bar and the rock mass is high.
5. It has high shear and tensile strength.
6. Equipped with a high-strength tray, the tray is evenly stressed.
7. The drilling depth is greater than the anchor bar depth.
8. It can provide timely support in radial and axial directions. It is unfit for permanent support in soft rock.
After the bolt is installed, with the growth of time, the reasons for the anchoring force not to attenuate but to increase significantly under the conditions of blasting vibration and rock mass displacement are as follows:
1. The split set is full-length force and will not produce stress concentration like other bolts. Generally, creep relaxation will not occur and reduce the anchoring force.
2. The strain displacement or dislocation of different rock formations around the rock bolt, blasting shock, and vibration will cause local deformation of the rock bolt in the axial direction so that the rock mass squeezes the rock bolt more tightly and the anchoring force will increase.
3. In soft rock or expansive rock formation, with the extension of time. The rock hole will gradually shrink, constantly compressing the tube diameter so that the bolt produces greater tension. Its friction between it and the hole wall is increasing, and the anchoring force will increase with the extension of time.
4. Because of the full-length anchoring of the split set, the anchoring force still exists when the bolt is tensioned or moves with the rock mass.
Split set support has the advantages of being timely and effective, cost-saving, and effectively reducing maintenance, and it plays a significant role in various underground projects. With the increased market demand, the appropriate use of split sets can reduce the mining cost and achieve good economic benefits. At the same time, the continuous development of technology also promotes the continuous improvement and innovation of split sets, providing more possibilities for the safety and stability of geological engineering.
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