Application of Self-Drilling Anchor Bolt in The Underground Tunnel

Time:2023-02-07From:sinorock View:

The prestressed anchor bolt at the underground bottom of the underground tunnel can increase the soil pressure and reduce the floating of the existing subway tunnel caused by soil unloading. Self-drilling anchor bolt makes up for the deficiency of traditional technology and is suitable for construction in narrow places with fast construction speed, good anchoring effect, and low comprehensive cost. The practical application case will be shown in this blog and analyze the construction and economical effect.

The Basic Introduction of Self-drilling Anchor Bolt

Self-drilling anchor bolt technology is a new type of rock-soil anchoring technology developed in recent years, which can adapt to various complex geological conditions and construction site environments. It has the advantages of a simple process, fast construction, and good economic benefits. For now, the self-drilling anchor bolt has been widely applied in construction projects such as deep foundation support, slope stability, and tunnel support

The composition of the self-drilling anchor bolt system

The self-drilling anchor bolt system consists of a drill bit, a hollow anchor bar, a coupling, a centralizer, a plate, and a nut. The drill bit of SDA bolt can be selected according to different geological conditions. After the hollow anchor bar is drilled into the rock mass with a drilling rig, high-pressure grouting, and then install the plate and nut. The self-drilling anchor bolt can complete drilling, grouting, and anchoring at one time, and has a better drilling and anchoring effect.

Application of Self-Drilling Anchor Bolt as Anti-floating Measure in Underground Tunnel

Project Background

During the construction of Xidan Station of Beijing Subway Line 4, it needed to pass through the original section tunnel of Line 1. Due to the early construction of Line 1, there was no reinforcement, and the deformation resistance was poor. There were also longitudinal cracks in the vault and side walls. With the excavation of Line 4, cracks would be increased and deepened, seriously affecting driving safety. Therefore, it is necessary to take control measures such as distributed excavation during the construction of the underground excavation section of Xidan Station of Line 4, and at the same time take reinforcement measures for the soil around the tunnel of Line 1.

Fundamental Design of self-drilling prestressed anti-floating bolt

The prestressed anchorage parameter design and mechanical calculation are based on the failure mechanism and instability mode of the prestressed anchorage system. For prestressed anchorage systems in geotechnical engineering, there are mainly the following four failure modes:

(1) The bond between the anchor rod and the grouting body is damaged;

(2) Destruction of the bonding surface between rock and soil mass and grouting mass;

(3) Shear failure occurs inside the rock and soil mass or slippage along the weak geological plane becomes unstable;

(4) The anchor cable rod is broken or the top of the anchor seat is damaged.

The design basis for the anchorage depth of the anchorage section in the stratum is according to the failure mode of the rock and soil mass. The design of prestressed anchor bolts should not only ensure that the anchorage section has sufficient anchoring force to ensure that the anchor bolts will not be pulled out;

Construction Effect And Benefit Analysis

The station geology of the underground excavation section is mainly gravel soil, and it is difficult to form drill holes. Since the self-drilling anchor bolt is drilled in place, the rod body stays in the hole and does not need to be withdrawn, so the hole will not collapse, saving construction time and reducing construction difficulty. Each process of its construction can be completed in one process, which can greatly save construction time. Since the drilling and grouting are completed at one time, the number of machinery on the construction site is greatly reduced, which is beneficial to the operation.

140 anchor rods are used in this project, with a cumulative extension of 1960m. After calculation, the comprehensive cost of the project is generally 25-35% lower than that of the traditional anchor cable technology, and the working hours can be saved by about 25%.

Summary

According to the actual case of the project, the self-drilling anchor bolt technology makes up for the shortcomings of the traditional technology, with fast construction speed, good anchoring effect, and lower overall cost, which is very suitable for construction in narrow places such as tunnels. As a professional self-drilling anchor bolt manufacturer, Sinorock specializes in SDA bolt manufacturing, and development and has rich practical experiences. If you have any questions or are interested in self-drilling anchor bolts, welcome contact us.

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