Safety mining in thick loose water-bearing strata also becomes a hindrance.
A series of Chinese studies have been conducted on the safety mining of a thin basement shallow seam in thick loose water-bearing strata. It is widely acknowledged that once mining-induced fractures extend upward into confined aquifers, these fractures can serve as passageways between aquifers and workings, triggering water and sand inrush.
When two key layers exist in a thin basement below the loose water-bearing strata, the calculation formula of the working resistance (P1) of support in Figure 7(a) is as follows :
Moreover, [P.sub.2] involves the additional pressure from the loose water-bearing strata [mu]Q compared with [P.sub.1].