The stability of the clay outcrop when driving transport or sewage tunnels determines the efficiency and safety of mining operations, as the time of the steady state of the clay outcrop depends on the regulated lag of the permanent excavation support, the mechanization method of excavation works, the time of rock mass removal, etc. In addition, clayey strata in recent years are widely used as storage facilities for various wastes (e.g., radioactive), so the steady state time of the outcrop plays an important role here, too.
