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How to support the tunnel through the cobblestone?

How to support the tunnel through the cobblestone? Self drilling anchor bolt system support method.

The rock formations traversed by the tunnel often encounter complex geological conditions, one of which is the pebble layer. The pebble layer has the characteristics of poor rock crushing and cohesion. The support of the pebble layer needs to adopt a method with strong permeability and strong cohesion. Self drilling anchor bolt system can realize the function of grouting while drilling, which is more conducive to the bonding of broken rock layers and is convenient for construction. The following will introduce to you how to support the tunnel through the pebble layer.

 Reasons for the support of the tunnel passing through the pebble layer

The pebble stratum is loose, the cohesion is small, and the pores are large. Once excavated, it is easy to have a decline in bearing capacity, poor resistance, and then some instability and disintegration.

There are several reasons why the tunnel needs to be supported when crossing the pebble layer in emergencies.

1. Loose structure

The wooden structure of the pebble layer is loose. If the tunnel is in the area near the river or sea water, the fine particles will be eroded by the immersion of dry groundwater, and the rock mass with poor cementation will be in the area.

Under the action of excavation, the mechanical properties will decrease sharply.

2. Sudden deformation

The pebble layer is very sensitive to actions such as opening and control. Once the excavation is disturbed, the stress will be redistributed and the resistance capacity will be reduced.

3. The palm face is cracked

The pebble layer includes pebbles, boulders, large-diameter gravel, etc., and the mud-calcareous filler in the middle will become weak, which will lead to further loosening and cracking of the face. The phenomenon of falling blocks in the part above the arch waist of the face will lead to deformation of the surrounding rock, breaking through the reserved deformation, and squeezing the tunnel structure.

Support method for tunnel crossing pebble layer

The geological structure of the pebble layer tunnel is loose, and the rock mass is seriously broken. It is difficult to form holes by using the general support construction method, resulting in the delay of the construction progress. Self drilling anchor bolt integrates drilling, grouting and anchoring, which can well bond unstable rock formations and make the project achieve the expected anchoring effect.

1. Drilling preparation

The drilling angle, length, slurry mix ratio, and drill bit  selection of the Hollow anchor bar should be determined according to the rock formation. Most tunnel advance supports will use 51, 76 Self drilling anchor bolt. Adjust the drilling angle of the rock drill according to the terrain and geological conditions.

2. Drilling and grouting

When the Self drilling anchor bolt  is too long and needs to be spliced, the drill bit should be put on the front end of the first section of the Hollow anchor bar, and the star end of the rod body should be connected to the grouting machine through the rotary grouting adapter. During drilling, grouting is carried out, and the slurry is pressed into the hole and into the cracks of the rock mass to consolidate the rock mass and stay in the deep stable rock mass, and bond together with the stable layer as the slurry solidifies.

3. Hollow anchor bar connection length

When the remaining 30 cm of the hollow anchor bar in the first section, stop drilling, put a coupler with artificial lubricant on the tail of the hollow anchor bar in the previous section, and then connect the hollow anchor bar in the next section, and so on. Until the designed length is drilled, the hollow anchor bar  is exposed at least 10 cm at the end of the drilling, which is convenient for installing the domed plate and domed nut.

4. Pull test

After the self drilling anchor bolt is constructed, it is necessary to test the pullout force value of the hollow anchor bar to check whether it meets the design value of pullout force. The test needs to randomly check a lot of hollow anchor bars in every 300 hollow anchor bars in the operation area. Carry out a pull-out force test to ensure that the construction effect meets the expected requirements.

The above is the answer to the question of how to support the dry tunnel passing through the pebble layer. The quality of the support affects the safety of the tunnel construction. It is necessary to adopt the support materials that are rich in successful support cases and verified by rich construction cases. The Self drilling anchor bolt system produced by LIAOCHENG JINJUFENG IMPORT AND EXPORT CO., LTD has multiple tunnel application cases and can provide customers with a complete set of solutions. You are welcome to inquire.

Steven Gao

Foreign trade manager

Liaocheng Jinjufeng Import and Export Co., LTD


Whatsapp/Wechat: +8617863522625

Email: gaoshenxu@jinjufenggt.cn


6#1307 International Financial Center, Economic Development Zone, Liaocheng , Shandong Province

Post time: Aug-31-2022