Rock Anchor and Rock Bolt
The material of rock bolt body mainly includes high-strength steel wire, steel strand, hot rolled rebar and other high-strength steel. It can stretch freely under tensile load. When this part of elongation is permanently fixed or “frozen”, a certain pre-compression stress is generated on rock mass or various structures.
Therefore, rock bolt body is the main part to realize medium anchoring by tension. At present, main materials used in prestressed rock bolts in mining are fine-rolled threaded steel bars.
Friction Between Rock Bolt Rebar
The connection of high-strength precision-rolled threaded steel rebar is to prevent mutual sliding of connecting parts by friction between contact surfaces. To make contact surface with sufficient friction, it is necessary to increase clamping force and increase the friction of contact surface. Clamping force between components is achieved by applying a pre-tension to rock bolts, so the connectors (finished rolled rebar, bolts, etc.) must be made of high-strength steel.
Precision-rolled threaded steel bar is a rigid prestressed anchor. It is a steel bar made of 40Si2MnV or 45SiMnV, which belongs to high-strength steel, and has a complete external thread on. At any cross-section, it can be connected or anchored with a connector or anchor with an internal precision rolled screw anchor. The use of this type of rock bolt body is convenient for construction and safe and reliable for anchoring.
European Standard of High Strength Steel Rock Bolt
|S 355 J2+AR||315 – 335||EN 10025||EN 10060||EN 10204|
|42 CrMo4||650||EN 10083||EN 10060||EN 10204|
|34 CrNiMo6||800||EN 10083||EN 10060||EN 10204|
As it is designed, rock bolts must be installed one meter into bedrock and one meter along sheet pile. Usually the length of rock bolts is therefore at least 3 meters or longer.
Typical rock bolt diameters vary between Ø 50 and Ø 90 mm. Contractors tend to prefer small diameters of rock bolts with high steel grades (42CrMo4 is most common), which reduces the weight, and consequently simplifies its handling which is normally done by hand.
These standards are most commonly used in Norway, however, other steel grades may be utilised. The differences in quality of rock bolts defined in different standards should normly be of little importance for this specific type of application.