Types of Rock Bolts

Rock bolts are used to support underground excavations.

Mechanically-anchored Rock Bolts

Rock bolts are used in mining installations.Rock bolts are used in mining installations.
They consist of a long metal shaft that is sunk into the rock and secured through various means. Usually the inner end of the shaft is connected to the rock, and the outer end is attached by means of some sort of faceplate. Many different types of rock bolts exist, each with its own strengths and weaknesses.

Mechanically anchored rock bolts use expansion shells on the end of the shaft to connect the bolt to the rock. The holes are drilled in advance, and the expansion shell is placed into the hole. Make the hole about 100 mm longer than the bolt. Once the bolt is inserted, pull on it sharply so that it will expand and dig into the rock. Dig the bolt deeper into the rock by turning the nut on the bolt. This kind of bolt is best for moderately hard to hard rocks. One of this system's pitfalls is that it is prone to slipping in very hard rock.

Resin-anchored Rock Bolts

Resin anchored rock bolts, also called grouted rock bolts, are sealed using a resin and a catalyst. A cartridge full of the resin is placed at the end of the hole, and the bolt is stuck in the hole after it. The rebar is then "drilled" through the hole, puncturing the cartridge and causing the resin to dry and seal the bolt in the hole. The resin is then released into the hole, and it slowly hardens and keeps the bolt in place. This type of rock bolt is very common because it is very simple to install.

Split-set Friction Rock Bolts

Split-set friction rock bolts are placed inside predrilled holes. They are made of collapsed steel tubing, which is placed within the hole and twisted. This twisting causes the tubing to expand, which secures the bolt to the hole's wall. These bolts are simple to install, but they lack tension and the bolts can't be anymore than 3 meters long.

Swellex Friction Bolts

Swellex friction rock bolts are similar to split-set friction bolts. They are also made of collapsed tubes except they expand through the use of water pressure. They are extremely simple to install. The main problem with them is their lack of durability.

About the Author

Justin Mitchell has been a writer since 2009. In 2002, he received a B.A. in theater and writing from the University of Northern Colorado. Mitchell worked as an ESL teacher in Europe and Asia before earning a master's degree in journalism from the City University of New York. He has written for the "New York Daily News" and WNYC.org, among other outlets.