STRATA CONTROL
		General

STRATA CONTROL

General

The term "strata control" generally refers to controlling the strata to maintain stability around the mine openings underground where operations are or will be taking place. It does not cover such subjects as subsidence or strata remote from the workings.

Strata control is the science (some would suggest art) of utilizing various techniques to prevent or control failure of the strata around mine openings at least for the period where access is required. For different locations in the mine this period may be for the life of the mine (which can be considered as permanent), such as the main mine accesses from the surface, or for a matter of less than an hour, such as a lift off a coal pillar with a continuous miner.

The need for strata control may extend into a goaf area for a short distance, essentially to the goaf edge, however strata control within the goaf is generally of no interest.

In order to analyse strata reactions, properties such as strength (tensile and compressive), modulus of elasticity, Poisson's ratio, etc are required, as well as details of the likely stress fields to which they will be subjected. If these are not known or cannot be measured it will be necessary to assume values with excessively conservative designs likely to result.

A reasonably detailed knowledge of any geological structures is also required as these can affect both strata properties and stress fields locally.

Strata control techniques which are used include:

• Mine design relating to dimensions and shape
• Mine design relating to mining direction
• Sacrificial support external to strata
• Reusable support external to strata
• Strata reinforcement
• Retention of failed strata