How to Support Tunnels By Self Drilling Rock Bolts？The Advantages of Self Drilling Rock Bolts

Time:2023-03-12From:sinorock View:

With the development of social economy and the advancement of science and technology, we are developing and utilizing underground space more and more, especially tunnel engineering and underground mining engineering. Then, in the process of construction and excavation, if broken surrounding rock with poor self-stabilization ability is encountered, the traditional excavation or support scheme may not be able to meet the requirements of project quality. Self-drilling anchor bolts can integrate the functions of drilling, grouting and anchoring, and realize simultaneous drilling and grouting. Therefore, it is a very effective construction plan for ensuring construction quality, speeding up project progress, and reducing project costs. Next, I will introduce how to use self-drilling anchor bolts to support the broken underground surrounding rock?

1. Characteristics of Broken Surrounding Rock

Broken surrounding rocks are generally high-grade surrounding rocks of Class IV-VI. Such surrounding rocks generally appear on the cave surface and in areas where the overburden is thin, and some are determined by the rock mass itself, such as expansive formations, weak loess formations, water-bearing unconsolidated surrounding rock, faults, quicksand, etc. If the surrounding rock joints are seriously developed, the overall stability is poor, and there are fissure waters, the construction will be extremely harmful, and large-area vaults will often collapse, and the surrounding rocks on the face of the tunnel will slide along the weak interlayer.

rock bolts

2. Why Does It Need to Support the Broken Surrounding Rock?

After the excavation, the self-stabilizing ability of the original rock mass will be destroyed, and the stress will be redistributed to a new self-stabilizing state. Its stress-strain relationship curve is in a nonlinear state. Deformation and damage usually cause stress concentration along some weak structural surfaces or weak interlayers, which changes the structure and stress conditions inside the rock mass, resulting in the stress reaching or exceeding its shear strength, resulting in overall deformation and failure. The stability of weak interlayers in tunnels is particularly important. At the same time, because broken rock mass is often a channel for groundwater and water-rich zones, it has a greater impact on the self-stability of tunnels. Therefore, it is necessary to support the broken surrounding rock.

3. Existing Problems in Excavation of Broken Surrounding Rocks

Under the condition of broken surrounding rock, the lining surface of the tunnel is mostly supported by mesh and sprayed anchors. From the perspective of construction quality and economy, resin capsule anchor bolts are often used in actual construction. However, the traditional esin capsule anchor bolts have the following problems:

（1）Difficult to Drill

Due to the limitation of the surrounding rock type, the circular excavation reserved core soil method is used for operation, and the working space is narrow. After completing a 3m deep hole, the drill bit needs to be replaced 3 times. Not only the work efficiency is low, but also the slag in the hole is dropped. The problem cannot be overcome.

（2）Difficult to Install Resin Bolts

Because the surrounding rock of the tunnel is broken and the hole wall is rough, the strength of resin capsule bolts decreases after absorbing water, and the slag in the hole is dropped, so it is difficult to fill it in place.

（3）Difficult to Install

The surrounding rock of the tunnel is broken, and slag and blocks are easy to drop in the borehole, which makes the installation of the bolt in place or impossible.

Based on the above problems in the construction, self-drilling anchor bolts are the best choice to improve and overcome the problems in the traditional bolt construction.

4. The Advantages of Self Drilling Rock Bolts

(1) The self-drilling anchor bolt has continuous thread alongthe body, and can be cut and connected at any location. It is suitable for construction in narrow work sites and overcomes the difficulty of drilling holes for bolts. At the same time, the continuous thread has stronger bonding resistance than ordinary steel bars.

(2) The self-drilling bolt can efficiently grout, fill cracks, consolidate rock mass and soil layers, control groundwater, and has a good diffusion radius and reliable anchoring quality.

(3) It integrates the functions of drilling, grouting and anchoring. Under the condition of broken surrounding rock, no casing is required, which overcomes the problem of difficult installation of anchor rods, and can also ensure the effect of anchoring and grouting. It is easy to operate, fast and time-saving, and reduces engineering costs.

(4) The end of the self-drilling bolt can be directly installed with a special nut, which overcomes the difficulty of installing the traditional bolt bearing plate.

Summary

The above is the supporting method of the tunnel under the broken surrounding rock. The self-drilling anchor bolt is a kind of grouting anchor that can integrate the functions of drilling, grouting and anchoring, which can ensure the anchoring effect under the condition of broken surrounding rock. It is characterized by reliability, high efficiency and simplicity. Sinorock is a professional manufacturer of self-drilling rock bolts. As a leading expert in the ground support industry, the Sinorock team has many years of experience in providing complete geotechnical engineering services. If you have any needs or questions about self-drilling anchor systems and their applications, please feel free to contact us at sinorock@sinorockco.com.

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