Application of Expansion Shell Prestressed Hollow Anchors in Tunnels

by Anna S. Optimization Specialist

A prestressed expansion shell hollow anchor bar is a kind of anchor bar that can be used for both permanent and temporary support. Especially in hard rocks, horizontal laminae of rock layers, or groundwater occurrence, it can form support force quickly by expansion shell anchor bar, and control the deformation of surrounding rock by applying enough prestress to keep it stable. It is also suitable for preventing and managing rock bursts, slope management and engineering disease management. And in these application scenarios, ordinary anchor bars cannot meet the demand for safe and rapid construction.

Prestressed Expansion Shell Hollow Anchor Bar Components

Expansion Shell, hollow anchor bar, plug, plate, and nut.

Advantages of Prestressed Expansion Shell Hollow Anchor Bar

In the tunnel, the displacement of the surrounding rock is an important indicator to measure the tunnel deformation and determine whether it is stable or not. Generally, after support, the settlement of the cave roof has been reduced to a certain extent, which can increase the stability of the tunnel. If the support is timely, the cavity top displacement can be reduced by about 30%-50% after using a prestressed expansion shell hollow anchor bar to support.

Prestressed Expansion Shell Hollow Anchor Bar V.S. Other Anchor Bolts

Compared with other anchoring products, ordinary mortar bolts can reduce the displacement of the cave roof by about 10%. However, the common mortar bolt is slow to take effect to apply pre-stress, which is passive support and not effective for hard rock. The Swellex-anchor and split set use the friction between the rod and the hole wall to form the support force, which can produce instant anchoring force. But they are non-grouted anchor rods with limited system anchoring force, and are generally only suitable for temporary support.

Construction Process

1、Install the expansion shell onto the anchor bar for spare.

2、Drilling with a drilling rig in the predetermined position to form a borehole and thoroughly remove rock debris from the hole.

3、Insert the anchor bar with the expansion shell installed directly into the bottom of the borehole.

4、Rotate the rod body with an air wrench or drilling rig to open the expansion shell and fix it in the hole.

5、Install slurry plug, plate, and nut in turn.

6、Apply prestressing force to the specified value by tensioning tool according to the design requirement.

7、Finish grouting in the borehole through the hollow bar or grouting pipe according to the design.

Summary

In summary, expansion shell hollow anchor bars are very suitable for underground support projects such as tunning. When the tunnel is excavated, this anchorage method quickly changes the stress state of the cavity wall due to the excavation of the cavity and partially restores its radial stress constraint by the timely application of prestressing, which provides timely support resistance, increases the radial enclosing pressure and improves the physical and mechanical properties of the rock mass. Through grouting, the deformation of the tunnel is effectively suppressed on the basis of further prevention of prestress loss and anchor rod corrosion.

The above is the analysis of the application of rising shell prestressed hollow anchor in tunnel, for different geological conditions also need to use different support materials. Sinorock has experience in the field of multi-difficult geotechnical anchorage, and is a professional self-drilling anchor bolts manufacturer, if you are interested in self-drilling anchor bolts or have other questions, welcome contact: sinorock@sinorockco.com.

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