Introduction
With the rapid development of highway construction, especially in mountainous areas, tunnel engineering has become an indispensable and vital part. In tunnel construction, rock bolts are essential supporting structures and play a crucial role in the stability of surrounding rock and construction safety. Due to their unique advantages, split sets have gradually emerged in highway tunnel construction and have shown broad application prospects.
Introduction to split set
The split set was first successfully developed by Professor James Scott of the United States and Ingersoll Rand in 1973. This type of rock bolt has the characteristics of a simple manufacturing process, easy use, strong anchoring force, high tensile strength, and excellent corrosion resistance. It has been widely used in many countries, such as the United States, Japan, and Austria. The main part of the split set is a high-strength alloy steel strip pipe (galvanized) with a longitudinal slit, which is installed in a borehole slightly smaller than the pipe diameter, and the surrounding rock is anchored and reinforced through radial pressure and friction.
Technical performance and structural characteristics
The initial anchoring force of the split set can reach 3-7t, the pull-off load of the pipe ring is between 8-10t, and the anti-breaking capacity of the rock bolt is as high as 12-13t. These excellent technical performances allow it to effectively handle various complex geological conditions. In addition, the split set also has the following structural characteristics:
- Excellent raw materials: made of high-strength alloy strip steel, it ensures the strength and durability of the anchor.
- Easy installation: no anchoring agent is required, and the installation process is simple and fast.
- High friction: the friction between the anchor and the rock mass is high, which enhances the anchoring effect.
- High shear and tensile strength: it can withstand high shear and tensile forces.
- Equipped with a high-strength tray: the tray distributes stress evenly, further enhancing the stability of the support structure.
Working principle and force analysis
The working principle of the split set lies in its full-length anchoring and active reinforcement of the surrounding rock. When the rock bolt is installed in the borehole, it exerts radial pressure and friction on the borehole wall. Combined with the support force of the anchor tray, the surrounding rock is in a three-dimensional stress state, thereby achieving the stability of the rock formation. When the surrounding rock is displaced, the anchor can continue to provide support resistance and maintain its support effect.
In terms of force analysis, the split set mainly bears elastic resistance, longitudinal tensile stress, and the bearing capacity of the tray. The elastic resistance of the anchor generates friction through radial pressure, while the longitudinal tensile stress comes from the friction resistance between the surrounding rock and the anchor. The bearing capacity of the tray is used to prevent the surrounding rock from displacing into the tunnel and ensure the stability of the support structure.
Construction method
The construction method of the split set is relatively simple, mainly including the following steps:
- Initial spraying: after excavation, the initial spraying of concrete is carried out to seal the surrounding rock surface.
- Determine the hole position and drill holes: determine the anchor hole position according to the design requirements on the surface of the initial spraying concrete, and use a drill to drill holes.
- Clean the rock powder in the hole: use compressed air to blow away the rock powder in the hole to ensure that the hole is clean.
- Install the rock bolt: install the rod body on the tray and use an impact drill to drive the anchor into the hole, ensuring that the tray compacts the steel mesh and is close to the rock surface.
- Subsequent support: install system anchors on the surface of the initial sprayed concrete support to further enhance the tightness and integrity of the support structure.
Quality inspection and drainage function
The quality inspection of the split set is relatively easy. We can test the length by inserting a small steel ruler, measuring the inter-row spacing and angle on site, and performing pull-out tests. In addition, when applied on the surface of the initial support, the split set can also effectively play the role of drainage, which is especially suitable for the water-rich section of the tunnel. Driving triangular wooden wedges into the rock bolts can also provide fixation for the later hanging of geotextile and waterproof sheets.
Project cost and economic benefits
From the point of view of project cost, the raw material cost of the split set is more economical than that of hollow grouting anchors, and the installation process is simple without the need for grouting, which reduces construction costs and improves work efficiency. Overall, using a split set can effectively reduce project costs, enhance construction quality and safety, and provide significant economic and social benefits.
Conclusion
In summary, split sets have broad application prospects in highway tunnel construction. Its excellent technical performance, simple construction method, and significant economic benefits make it the preferred solution for tunnel support structures. With ongoing advancements in science and technology and the deepening of applications, split sets will play an increasingly crucial role in the construction of highway tunnels.
