By Gaylord Pierce - September 17, 2021
Types of Ground Support for Mining
Ground support is a combination of procedures that enables to conserve or mobilize the initial strength of a rock mass. This way, the rock mass will be able to support itself throughout the whole mining duration. This is a very important aspect of safe mining practice as this will help maintain the stability of the excavations occurring underground.
You can find 2 main categories for these techniques. These are support techniques and reinforcement techniques. In support techniques, an external reactive force is applied to the rock surface. This is done when the rock purpose has started to deform or change shape. Reinforcement techniques are used to give support the rock mass internally in order to maintain or improve the properties of rock mass before deformation starts. Experts can get an idea of the condition of the rock mass through Mine Civil Integrity Testing. There are active and passive supports. In active support, a load is forced onto the surface of the rock which will support the broken mass and improve the stability. Examples of active supports are rock bolts, hydraulic jacks as cable bolts. Passive support is more adaptive to the ground movements and the load it develops is directly related to the deformation of the rock. Some examples of passive support are steel arches, meshes, screens, shotcrete and reinforcing bars.
One of the most common methods of ground support you can find are rock bolts and cable bolts. Traditional method for ground support was mechanical rock bolts. These are quite useful for short term support. They are also subjected to blast vibrations and corrosion. You can find different types of bolts such as thread end bolts and forged end bolts. To install a rock bolt, the workers will drill a hole to the diameter that is specified and then insert the bolt into the hole with a plate and nut. The bolt is tensioned afterwards. Cable bolts are commonly used in large span applications. This can be used before or after reinforcement with the use of pre-tensioning or post tensioning. There are several types of cable blots such as bulbed, birdcaged or nutcages and all these types are grouted in cement along the full bolt length. Depending on the wire lay type, the frictional resistance provided will differ. You can get a higher frictional resistance with birdcaged or bulbed lays.
Shotcrete is a passive method to support rock mass. It is a combination of cement, a mix of fine and coarse particles and other additives that include activators, retarders etc. This is used as standard ground support when used in combination with mesh. It can also be used in light rock bursting conditions. Shotcrete can also be used in arches and pillars. The steel mesh will give flexibility for the shotcrete. There are set proportions for the mixing of shotcrete components and there are different techniques used as well. The mix of the components has to be formulated to the requirements of specific situations. Mesh and screens can also provide support as they can trap and keep bulging pieces of rock in piece.