Ground support

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This article is about the application of ground support strategies and techniques to "underground mining projects". For the article on general geotechnical design see Geotechnical Design.

Ground support is a set of techniques, elements and methods that enable the conservation or mobilization of a rockmass' initial strength. The rockmass is given the ability to self-support throughout the course of mining. The ultimate goal of this practice is to allow for mining to occur safely while maintaining the stability of created underground excavations.These techniques can be divided into two main categories [1].

Support techniques refer to the action of applying an external reactive force to a rock surface in the process of deformation, i.e. submitted to strain causing changes in the shape, size and volume of the rock [2]. Reinforcement techniques refer to the action of adding internal support, e.g. rockbolts, to maintain or improve the rockmass' properties prior to deformation. Of course, the selection of ground support is an integral part of the underground mine design process. See Main Article: The information required for the mine design

Significant Properties of Support Elements

Uses of Ground Support

Historically, the installation of ground support was confined to temporary or permanent excavations.
Miner in Lynch, Kentucky, U.S. Steel (1950)[3]
Temporary excavations such as small and narrow shrinkage mining stopes, see article on Mining Methods would have been supported with long timber members to prevent ground failures in these workings. These workings would typically have remained opened for short periods of time (1-2 weeks). As for permanent excavations such as shaft stations which can remain opened for years, permanent support and reinforcement was installed. Often times, the temporary support previously put in place was removed and replaced with more permanent forms. This is contrary to modern practice where the rock-support interactions are an important design consideration.
Active vs. Passive

Unlike the distinction between temporary and permanent support, the distinction between active and passive support refers to the load existing in the chosen support prior to its installation. For example, active support forces a load onto the rock surface in order to support broken rockmass and ensure its stability. Examples of active support types are: tensioned rockbolts, cablebolts, hydraulic jacks and powered supports for longwall mining. Passive support on the other hand is reactive to the ground's movements. It develops its load as the rock deforms. Examples of passive support types are: untensioned rockbolts, meshes and screens, reinforcing bars, shotcrete, timbered sets and steel arches. A combination of active and passive supports is typically optimal for most mining situations. 

Primary vs. Secondary

A more modern way of relating ground support techniques and systems is to define a primary and secondary support strategy. The primary support is installed in conjunction with excavation and serves supporting and reinforcing functions. This enables simultaneous control of boundary displacements. Any support applied at a later stage will be defined as secondary support.

Types of Support

Empirical Support Design

The appropriate ground support strategies are selected through various engineering design techniques. In Ontario, this design selection is governed by legal requirements defined in the Ontario Occupational Health and Safety Act.

Historical Methods of Support

1879 development of rock mass classfication for ground support requirements in tunelling applications reference

Design Parameters

Installation Methods

Equipment

References

  1. Brady, B. H.G. and E. T. Brown. "Rock Support and Reinforcement." Brady, B. H.G. and E. T. Brown. Rock Mechanics. Springer Science, 2005. p. 312 - 346.
  2. Nelson, Stephen A. "Physical Geology - EENS 111." 2007. Tulane University. http://www.tulane.edu/~sanelson/geol111/deform.htm
  3. http://www.miningusa.com/old_photo/2002.asp

Further Reading

External Sources

http://en.wikipedia.org/wiki/Wikipedia:Citing_sources