How to Support the Water-bearing Rock mass with Self Drilling Hollow Bolt?

In the construction of tunnels, some complex geological conditions, such as water-bearing rock masses, are sometimes encountered. If the water content of this rock mass is relatively large, the whole construction process cannot be carried out at all unless a self-drilling hollow bolt is used. Why is the support construction of water-bearing rock mass so difficult? How to construct self-drilling hollow bolts? How to support the water-bearing rock mass? Today, Sinorock will take a specific application case to explain in detail.

In a certain engineering tunnel, the stratum is dominated by water-bearing rock mass with developed fissures, and the rock mass is severely weathered and has strong water permeability. When the excavation passes through the rock mass karst cave, the broken cave section or the fault fracture zone, because the surrounding rock is under the fault, the daily water inflow is more than 2000m3 in the working face. The problem of stuck drilling and hole collapse, the construction process can no longer be carried out normally.

Self-drilling hollow bolt is composed of six parts: drill bit, hollow bolt body, connecting sleeve, backing plate, nut and centering device. Two problems arise.

The project adopts alloy drill bit, which has strong penetrating power. Under the action of the rock drill, all kinds of rock mass can be easily drilled. The drill bit has a number of slurry holes, which can be cleaned in the initial stage, and can be used to exhaust slurry during grouting.

The self-drilling hollow bolt body has continuous wave thread or trapezoidal thread, which can be connected with the drill bit to complete the drilling construction. At the same time, the rod body can be cut at any position, or it can be lengthened by connecting sleeves, which is very suitable for construction in relatively narrow space conditions such as tunnels.

The hollow design of the self-drilling hollow bolt body makes it have a grouting function. When the bolt body completes the drilling, it does not need to be pulled out, which avoids the problem of slurry loss caused by the traditional process of grouting and anchor pulling. When grouting the self-drilling hollow bolt, the hole is closed and the bottom of the hole is circulated. During grouting, several holes can be grouted at the same time according to the amount of grouting and the situation of grouting.

After the self-drilling hollow bolt is connected with the screw grouting machine, pressure grouting can be realized, which can make the grout more fully fill the rock mass cracks and drilling holes, increase the diameter of the anchor body, and improve the anchoring effect. In addition, the high-strength backing plate and nut can evenly transmit the stress of the deep surrounding rock to the hole wall, and achieve the purpose of mutual support with the rock mass.

The centralizer ensures that the self-drilling hollow bolt is always in the center of the borehole during the drilling and grouting process. The grout can completely and evenly wrap the rod body to avoid corrosion due to contact with the external environment, and the support time is longer.

The results show that when the self-drilling hollow bolt supports the water-bearing rock mass, it has a satisfactory performance in improving the stability of the rock mass and reducing the water seepage of the rock mass.

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Created on Jun 4th 2022 20:57. Viewed 141 times.

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