where: k(x) is permeability coefficient of gob ([m.sup.2]), [[mu].sub.g] is the coefficient of dynamic viscosity ([Nsm.sup.-2]), l is the total length of the longitudinal longwalls (m), [r.sub.0], a are empirical factor depending on the mining-geological conditions gobs.
Normally, the coal pillar is in biaxial loading state at the side closer to the gob in which case plastic deformation or local damage is likely to occur and the load-carrying capacity is relatively low; the stress in the coal body transfers to the inner side of the coal pillar from the edge of coal pillar to the inside, the uniaxial stress state of the coal body shifts gradually to tri-axial stress state and the load-carrying capacity is improved; In the elastic core region of the coal pillar, the boundary effect of the coal pillar is relatively small and the load-carrying capacity of coal body in that region is stable.
This makes it a hugely rich copper + gold field, but GoB was offered only 25% of the sales value of the ore not the finished product - copper and gold.
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