Tailgate support design rethought

AN alternative to statistically based approaches in the design of tailgate support was presented at the Coal 2003 conference, held in Wollongong in February.

Staff Reporter

Greg Tarrant, of consulting company Strata Control Technology, outlined the approach which combines empirical and analytical methods for roadway layout and detailed gateroad support design.

According to Tarrant there are currently no methods that provide mine operators with reliable tailgate support design.

“The reliance on experience, or at worst, trial and error for tailgate support design is a major contributing factor responsible for longwall downtime and has potentially catastrophic consequences,” he said.

Major gateroad falls can result in the longwall being abandoned, an inability to recover longwall equipment, disruption to ventilation, and others.

Tailgate behaviour is an interaction between the loading environment, geological controls and the interaction with the support elements of primary and secondary tendons, standing support and longwall supports.

An important mechanism controlling roadway behaviour is shear displacement along interfaces.

“If one considers the tailgate within the context of stress change and movement about an approaching longwall, the roadway would experience an environment where the displacements are imposed upon it. In a sense the roadway is a passenger (or is slaved) to the movements associated with the approaching longwall. In this respect the roadway deformation may become displacement controlled, rather than load controlled.”

Thus Tarrant suggests that to better control the tailgate environment, the location and mechanical properties of interfaces must be determined to assess potential behaviour under partially displacement controlled conditions. He said 3D numerical modelling with verification through field measurement was an an appropriate approach for more reliable support design.