What are split set bolts for?

[Sandra]

Hello,

I have come across a bolting technique called split set but I do not know whether I could use this as permanent support to substitute standard rockbolts in tunnelling.

I could not find any answer to this question in the specialised literature and I hope someone could help me out here?

Sandra

[webmaster]

Hello Sandra,

Thanks for giving me the chance to grab again into my tunnelling memories...

As you probably read from specialised literature, split set bolts are typically friction bolts. They are inserted in a bore hole and compressed water is blown through the bolt head nozzle to deform (expand) the bolt body, to finally compress the surrounding rock in the bore hole.

This technique is less expensive and quicker than standard rockbolting because no grouting of the bolts are required for installation.

The only problem with this system is that the split set full deformation and efficiency to provide the needed friction can practically not be guaranteed. This is why you should only use split set bolts for temporary support and not for the tunnel permanent support!

For permanent support, you need to have a reliable support technique based on known resistances of common materials (bolts/anchors/shotcrete/ribs/etc.) and not based on a somehow unpredictable bolt final deformation, where the efficiency of the bolt friction remains unknown after installation and over time.

Manufacturers of split set generally avoid this subject by not indicating whether their bolts are to be used for temporary or permanent support.

If you require more information on split set bolting, please let me know.

[Sandra]

Thank you for your advice not to use split set for permanent support.

This seems to be very logical indeed, but I am still missing some references from the literature in order to be able to technically support this statement.

Thanks anyhow,

Sandra

[webmaster]

I would suggest you to read the following book, which may give you enough academic material to substantiate my previous advice:

Underground Excavations in Rock, E.Hoeck & E.T.Brown.

This book is the 'underground bible' for tunnel designers.

[Sandra]

Many thanks for your great support.

I shall buy you some wine for this.

Greetings
Sandra